Modeling Local Hygrothermal Interaction: Local surface transfer coefficients
Steskens, Paul Wilhelmus Maria Hermanus; Janssen, Hans; Rode, Carsten
2009-01-01
Current models to predict heat, air and moisture (HAM) conditions in building components assume uniform boundary conditions, both for the temperature and relative humidity of the air in an indoor space as well as for the heat and moisture surface transfer coefficients. In order to obtain a reliable...... prediction of the HAM conditions in a building component, an accurate description of the indoor boundary conditions is required. This paper presents the modelling of the local indoor environmental conditions, using a (sub)zonal airflow model, focussing on the prediction of the local interior surface heat...
Steskens, Paul Wilhelmus Maria Hermanus; Janssen, Hans; Rode, Carsten
2009-01-01
HAM conditions. The paper focuses on the influence of the interior surface heat and moisture transfer coefficients, and investigates its effect on the hygrothermal performance. The parameter study showed that the magnitude of the convective surface transfer coefficients have a relatively large......Current models to predict heat, air and moisture (HAM) conditions in buildings assume constant boundary conditions for the temperature and relative humidity of the neighbouring air and for the surface heat and moisture transfer coefficients. These assumptions may introduce errors in the predicted...... influence on the predicted hygrothermal conditions at the surface of a building component and on the heat and vapour exchange with the indoor environment....
Piasecka Magdalena
2016-01-01
Full Text Available The aim of the paper is to estimate effect of the heating surface enhancement on FC-72 flow boiling heat transfer for a vertical minichannel 1.7 mm deep, 24 mm wide and 360 mm long. Two types of enhanced heating surfaces were used: one with minicavities distributed unevenly, and the other with capillary metal fibrous structure. It was to measure temperature field on the plain side of the heating surface by means of the infrared thermography and to observe the two-phase flow patterns on the enhanced foil side. The paper analyses mainly the impact of the microstructured heating surface on the heat transfer coefficient. The results are presented as heat transfer coefficient dependences on the distance along the minichannel length. The data obtained using two types of enhanced heating surfaces in experiments was compared with the data when smooth foil as the heating surface was used. The highest local values of heat transfer coefficient were obtained using enhanced foil with minicavities - in comparison to other cases. Local values of heat transfer coefficient received for capillary fibrous structure were the lowest, even compared with data obtained for smooth foil. Probably this porous structure caused local flow disturbances.
Determination of local heat transfer coefficient on the surface of longitudinally finned tubes
Sobota, T.; Taler, J. [Cracow Univ. of Technology (Poland). Inst. of Process and Power Engineering
2008-06-15
The distribution of the heat transfer coefficient is calculated from temperature measurements at interior points of the solid, and the measured fluid temperature. The unknown parameters associated with the solution were selected to achieve the closest least squares agreement between the computed and measured temperatures using the Levenberg-Marquardt method. The nonlinear least - squares problem is parameterised by assuming the stair-case changes of the heat transfer coefficient on the boundary, or by expressing the space variations of the heat transfer coefficient in its functional form. The determination of the circumferential heat transfer coefficient distribution on the heated tube with two longitudinal fins in cross flow demonstrates the accuracy of the developed method. The actual experimental data were used. Experiments were performed with an array of vertical tubes arranged in staggered pattern. (orig.)
Sivaraja Subramania Pillai
2013-06-01
Full Text Available This study investigates the effect of flow velocity and building surface temperature effects on Convective Heat Transfer Coefficient (CHTC from urban building surfaces by numerical simulation. The thermal effects produced by geometrical and physical properties of urban areas generate a relatively differential heating and uncomfortable environment compared to rural regions called as Urban Heat Island (UHI phenomena. The urban thermal comfort is directly related to the CHTC from the urban canopy surfaces. This CHTC from urban canopy surfaces expected to depend upon the wind velocity flowing over the urban canopy surfaces, urban canopy configurations, building surface temperature etc. But the most influential parameter on CHTC has not been clarified yet. Urban canopy type experiments in thermally stratified wind tunnel have normally been used to study the heat transfer issues. But, it is not an easy task in wind tunnel experiments to evaluate local CHTC, which vary on individual canyon surfaces such as building roof, walls and ground. Numerical simulation validated by wind tunnel experiments can be an alternative for the prediction of CHTC from building surfaces in an urban area. In our study, wind tunnel experiments were conducted to validate the low-Reynolds-number k-ε model which was used for the evaluation of CHTC from surfaces. The calculated CFD results showed good agreement with experimental results. After this validation, the effects of flow velocity and building surface temperature effects on CHTC from urban building surfaces were investigated. It has been found that the change in velocity remarkably affects the CHTC from urban canopy surfaces and change in surface temperature has almost no effect over the CHTC from urban canopy surfaces.
Sivaraja Subramania Pillai
2013-01-01
Full Text Available This study investigates the effect of flow velocity and building surface temperature effects on Convective Heat Transfer Coefficient (CHTC from urban building surfaces by numerical simulation. The thermal effects produced by geometrical and physical properties of urban areas generate a relatively differential heating and uncomfortable environment compared to rural regions called as Urban Heat Island (UHI phenomena. The urban thermal comfort is directly related to the CHTC from the urban canopy surfaces. This CHTC from urban canopy surfaces expected to depend upon the wind velocity flowing over the urban canopy surfaces, urban canopy configurations, building surface temperature etc. But the most influential parameter on CHTC has not been clarified yet. Urban canopy type experiments in thermally stratified wind tunnel have normally been used to study the heat transfer issues. But, it is not an easy task in wind tunnel experiments to evaluate local CHTC, which vary on individual canyon surfaces such as building roof, walls and ground. Numerical simulation validated by wind tunnel experiments can be an alternative for the prediction of CHTC from building surfaces in an urban area. In our study, wind tunnel experiments were conducted to validate the low-Reynolds-number k- ε model which was used for the evaluation of CHTC from surfaces. The calculated CFD results showed good agreement with experimental results. After this validation, the effects of flow velocity and building surface temperature effects on CHTC from urban building surfaces were investigated. It has been found that the change in velocity remarkably affects the CHTC from urban canopy surfaces and change in surface temperature has almost no effect over the CHTC from urban canopy surfaces.
Kumar, Varun; Kumar, Manoj; Shakher, Chandra
2014-09-20
In this paper, the local convective heat transfer coefficient (h) is measured along the surface of an electrically heated vertical wire using digital holographic interferometry (DHI). Experiments are conducted on wires of different diameters. The experimentally measured values are within the range as given in the literature. DHI is expected to provide a more accurate local convective heat transfer coefficient (h) as the value of the temperature gradient required for the calculation of "h" can be obtained more accurately than by other existing optical interferometric techniques without the use of a phase shifting technique. This is because in digital holography phase measurement accuracy is expected to be higher.
Shao, Y. F.; Song, F.; Jiang, C. P.; Xu, X. H.; Wei, J. C.; Zhou, Z. L.
2016-02-01
We study the difference in the maximum stress on a cylinder surface σmax using the measured surface heat transfer coefficient hm instead of its average value ha during quenching. In the quenching temperatures of 200, 300, 400, 500, 600 and 800°C, the maximum surface stress σmmax calculated by hm is always smaller than σamax calculated by ha, except in the case of 800°C; while the time to reach σmax calculated by hm (fmmax) is always earlier than that by ha (famax). It is inconsistent with the traditional view that σmax increases with increasing Biot number and the time to reach σmax decreases with increasing Biot number. Other temperature-dependent properties also have a small effect on the trend of their mutual ratios with quenching temperatures. Such a difference between the two maximum surface stresses is caused by the dramatic variation of hm with temperature, which needs to be considered in engineering analysis.
Measuring of heat transfer coefficient
Henningsen, Poul; Lindegren, Maria
Subtask 3.4 Measuring of heat transfer coefficient Subtask 3.4.1 Design and setting up of tests to measure heat transfer coefficient Objective: Complementary testing methods together with the relevant experimental equipment are to be designed by the two partners involved in order to measure...... the heat transfer coefficient for a wide range of interface conditions in hot and warm forging processes. Subtask 3.4.2 Measurement of heat transfer coefficient The objective of subtask 3.4.2 is to determine heat transfer values for different interface conditions reflecting those typically operating in hot...
Costea, M. [Polytechnic University of Bucharest (Romania). Dept. of Applied Thermodynamics; Feidt, M. [University H. Poincare of Nancy (France)
1998-12-31
This study aims to assess for a Stirling engine the influence of the overall heat transfer coefficient variation on the optimum state and on the optimum distribution of the heat transfer surface conductance or area among the machine heat exchangers. The analysis is based on a Stirling machine optimization method, previously elaborated, which is now applied to a cycle with total heat regeneration. The method was conceived for an irreversible cycle with heat transfer across temperature differences at the source and the sink, and heat losses between the hot-end and the cold-end of the engine. Source and sink of finite thermal capacity as well as thermostats are considered. The new approach considers a linear variation of the overall heat transfer coefficient of the machine heat exchangers with respect to the local temperature difference. A comparison of the optimum state and the optimum distribution of the heat transfer surface conductance or area among the heater and the cooler is made for several cases. (author)
Mass transfer coefficients in metallurgical reactors
无
2003-01-01
An overview on the application and achievements of physico-mathematical modeling of metallurgical processes in Chinais briefly declared. The important role of coefficients in model formulation is shown from our experience. The mass transfer coeffi-cients of the slag-metal reactions and the gas-metal reactions are discussed referring to the flow conditions near the interface. Theinfluence of the surface-active species on the mass transfer and the inteffacial reaction is also discussed briefly.
Determination of the convective heat transfer coefficient
Spierings, D.; Bosman, F.; Peters, T.; Plasschaert, F.
1987-01-01
The value of the convective heat transfer coefficient (htc) is determined under different loading conditions by using a computer aided method. The thermal load has been applied mathematically as well as experimentally to the coronal surface of an axisymmetric tooth model. To verify the assumptions m
Durbha, Krishna Sandilya; Aravamudan, Kannan
2012-05-01
The efficacy of power ultrasound of 20 kHz in enhancing the volumetric mass transfer coefficient was investigated in this study. Breakage and dissolution of sparingly soluble benzoic acid dispersed in either water or 24% aqueous glycerol was monitored as a function of time and ultrasound power input. Particle size measurements were carried out at intermediate times during the experiment to estimate the mean particle size and surface area. Linear combination of lognormal distributions was found to fit the experimental particle size distribution data. The De Brouckere mean diameters (d(43)) obtained from the particle size distributions decreased with increase in the ultrasonic power level. Empirical correlations were developed for the evolution of surface area as a function of ultrasonic energy input per unit mass. The effect of ultrasound on the intrinsic mass transfer coefficient (k(c)) could be decoupled from the volumetric mass transfer coefficient (k(c)a) as the surface area was also estimated. Different approaches involving either constant or variable intrinsic mass transfer coefficients were employed when carrying out the delineation. Mass transfer rates were enhanced due to both higher ultrasound induced intrinsic convective mass transfer coefficient and additional surface area created from particle breakage. To delineate the effects of particle breakage from solid dissolution, experiments were also carried out under non-mass transfer conditions by pre-saturating the solvents with benzoic acid. Both the solid-liquid systems examined in the present study attained saturation concentration when the ultrasonic energy input per unit mass was approximately 60 kJ/kg, irrespective of the ultrasonic power level setting.
Heat transfer coefficient for boiling carbon dioxide
Knudsen, Hans Jørgen Høgaard; Jensen, Per Henrik
1998-01-01
Heat transfer coefficient and pressure drop for boiling carbon dioxide (R744) flowing in a horizontal pipe has been measured. The calculated heat transfer coeeficient has been compared with the Chart correlation of Shah. The Chart Correlation predits too low heat transfer coefficient but the ratio...
The Influence of Carburizing Parameters on Carbon Transfer Coefficient
Tadeusz Sobusiak
2004-01-01
Definition of coefficient of carbon transfer in European Standard (EN 10052) is presented as: "Mass of carbon transferred from carburizing medium into the steel, per unit surface area per second for a unit difference between the carbon potential, and actual surface carbon content".In this paper, a model is presented of carbon transfer from endothermic atmospheres to carbon steel. The carbon transfer coefficient values were determined experimentally by the foil technique and on specimens, taking into account the following parameters: chemical composition of atmospheres, carbon potential, temperature and time of the carburizing process. Some examples of the variation of the carbon transfer coefficient for two steps of the carburizing process,including soaking before quenching, are given, based on results obtained. The effect of carbon transfer coefficient on carbon content at the steel surface is given.
Local Transfer Coefficient, Smooth Channel
R. T. Kukreja
1998-01-01
Full Text Available Naphthalene sublimation technique and the heat/mass transfer analogy are used to determine the detailed local heat/mass transfer distributions on the leading and trailing walls of a twopass square channel with smooth walls that rotates about a perpendicular axis. Since the variation of density is small in the flow through the channel, buoyancy effect is negligible. Results show that, in both the stationary and rotating channel cases, very large spanwise variations of the mass transfer exist in he turn and in the region immediately downstream of the turn in the second straight pass. In the first straight pass, the rotation-induced Coriolis forces reduce the mass transfer on the leading wall and increase the mass transfer on the trailing wall. In the turn, rotation significantly increases the mass transfer on the leading wall, especially in the upstream half of the turn. Rotation also increases the mass transfer on the trailing wall, more in the downstream half of the turn than in the upstream half of the turn. Immediately downstream of the turn, rotation causes the mass transfer to be much higher on the trailing wall near the downstream corner of the tip of the inner wall than on the opposite leading wall. The mass transfer in the second pass is higher on the leading wall than on the trailing wall. A slower flow causes higher mass transfer enhancement in the turn on both the leading and trailing walls.
Laser Measurement Of Convective-Heat-Transfer Coefficient
Porro, A. Robert; Hingst, Warren R.; Chriss, Randall M.; Seablom, Kirk D.; Keith, Theo G., Jr.
1994-01-01
Coefficient of convective transfer of heat at spot on surface of wind-tunnel model computed from measurements acquired by developmental laser-induced-heat-flux technique. Enables non-intrusive measurements of convective-heat-transfer coefficients at many points across surfaces of models in complicated, three-dimensional, high-speed flows. Measurement spot scanned across surface of model. Apparatus includes argon-ion laser, attenuator/beam splitter electronic shutter infrared camera, and subsystem.
Condensation heat transfer coefficient versus wettability
Roudgar, M.; De Coninck, J.
2015-05-01
In this paper we show how condensation on substrates can induce wetting behavior that is quite different from that of deposited or impinging drops. We describe surfaces with the same wettability in ambient conditions presenting different wetting behavior and growth of droplets in condensation. The experimental results show a rapid spread of droplets and formation of the film on the copper surface, while droplets on SU-8 surface remains on the regular shape while they grow within the time, without coalescence, as observed for Cu. Although the heat conductivity of SU-8 is much lower, due to a difference in wetting behavior, the heat transfer coefficient (h) is higher for dropwise condensation on Cu with a thin layer of SU-8 than filmwise on the bare copper.
Heat transfer coefficient of cryotop during freezing.
Li, W J; Zhou, X L; Wang, H S; Liu, B L; Dai, J J
2013-01-01
Cryotop is an efficient vitrification method for cryopreservation of oocytes. It has been widely used owing to its simple operation and high freezing rate. Recently, the heat transfer performance of cryotop was studied by numerical simulation in several studies. However, the range of heat transfer coefficient in the simulation is uncertain. In this study, the heat transfer coefficient for cryotop during freezing process was analyzed. The cooling rates of 40 percent ethylene glycol (EG) droplet in cryotop during freezing were measured by ultra-fast measurement system and calculated by numerical simulation at different value of heat transfer coefficient. Compared with the results obtained by two methods, the range of the heat transfer coefficient necessary for the numerical simulation of cryotop was determined, which is between 9000 W/(m(2)·K) and 10000 W/(m (2)·K).
Effect of Rare Earths on Diffusion Coefficient and Transfer Coefficient of Carbon during Carburizing
无
2001-01-01
The diffusion coefficient of carbon in surface layer of steel-20 rare earth carburized at 880 ℃ and 900 ℃ for 8 h was calculated by substituting the measured layer depths into the diffusion equation. The mathematical model of the transfer coefficient of carbon was deduced based on the kinetics of weight gain during gas carburizing. The calculated results show that the main reason why the gas carburizing process is accelerated is due to the obvious increase in the diffusion coefficient and transfer coefficient of carbon resulted from the addition of RE.
E C Monahan
2002-09-01
Stage A whitecaps (spilling wave crests) have a microwave emissivity of close to 1. Thus if even a small fraction of the sea surface is covered by these features there will be a detectable enhancement in the apparent microwave brightness temperature of that surface as determined by satellite-borne microwave radiometers. This increase in the apparent microwave brightness temperature can as a consequence be routinely used to estimate the fraction of the sea surface covered by stage A whitecaps. For all but the very lowest wind speeds it has been shown in a series of controlled experiments that the air-sea gas transfer coeffcient for each of a wide range of gases, including carbon dioxide and oxygen, is directly proportional to the fraction of the sea surface covered by these stage A whitecaps.
Determination of the surface drag coefficient
Mahrt, L.; Vickers, D.; Sun, J.L.;
2001-01-01
This study examines the dependence of the surface drag coefficient on stability, wind speed, mesoscale modulation of the turbulent flux and method of calculation of the drag coefficient. Data sets over grassland, sparse grass, heather and two forest sites are analyzed. For significantly unstable ...
任晓光; 李铁凤; 赵起
2006-01-01
This paper reports the influence of heat transfer surface treatment on the formation of calcium sulphate deposit during flow boiling heat transfer. The surface of several test heaters was treated by surface modification techniques,such as dynamic mixing magnetron sputtering [DLC (diamond-like carbon), DLC-F (diamond-like carbon-fluorine) and AC (amorphous carbon)] and polishing to reduce surface energy. The results showed that heat transfer surface with low surface energy experienced significant reduction of formation of CaSO4 deposit. (1) Magnetron sputtering stainless steel heat transfer surface with DLC, DLC-F and plasma arc sputtering with AC did not change the surface roughness, but they reduced surface energy and improved heat transfer coefficient, so hindered CaSO4 deposit formation significantly. The DLC-F surface performed better than the DLC surface. (2) Surface energy played an important pole in improving heat transfer coefficient. The less the surface energy the more significant the heat transfer coefficient improved with other experimental conditions identical. (3) The polished surface improved the roughness of the heater, but owing to the high surface energy it was not better than the DLC-F surface for a long-term consideration on improving the heat transfer coefficient.
Experimental evaluation of heat transfer coefficients between radiant ceiling and room
Causone, Francesco; Corgnati, Stefano P.; Filippi, Marco
2009-01-01
The heat transfer coefficients between radiant surfaces and room are influenced by several parameters: surfaces temperature distributions, internal gains, air movements. The aim of this paper is to evaluate the heat transfer coefficients between radiant ceiling and room in typical conditions...... of occupancy of an office or residential building. Internal gains were therefore simulated using heated cylinders and heat losses using cooled surfaces. Evaluations were developed by means of experimental tests in an environmental chamber. Heat transfer coefficient may be expressed separately for radiation...
Mass transfer coefficients in cross-flow ultrafiltration
Berg, van den G.B.; Rácz, I.G.; Smolders, C.A.
1989-01-01
Usually, in concentration polarization models, the mass transfer coefficient is an unknown parameter. Also, its variation with changing experimental circumstances is in question. In the literature, many relationships can be found to describe the mass transfer coefficient under various conditions, as
Heat transfer coefficient of wheel rim of large capacity steam turbines
Jinyuan SHI; Zhicheng DENG; Yu YANG; Ganwen JUN
2008-01-01
A way of calculating the overall equivalent heat transfer coefficient of wheel rims of large capacity steam turbines is presented. The method and formula to calculate the mean forced convection heat-transfer coefficient of the surface of the blade and for the bottom wall of the blade passage, are introduced. The heat transmission from the blade to the rim was simplified by analogy to heat transmission in the fins. A fin heat transfer model was then used to calculate the equivalent heat transfer coefficient of the blade passage. The overall equivalent heat transfer coefficient of the wheel rim was then calculated using a cylindrical surface model. A practical calculation example was presented. The pro-posed method helps determine the heat transfer bound-ary conditions in finite element analyses of temperature and thermal stress fields of steam turbine rotors.
Method to estimate surface heat transfer coefficient of solid-state laser%评估固体激光器对流换热系数的方法
王明哲; 郑建刚; 张永亮; 李明中; 严雄伟; 单小童; 蒋新颖; 景峰
2011-01-01
This article proposes a simple method using a false crystal (316L steel) to estimate the surface heat transfer coefficient of solid-state laser. First we set a low cooling water temperature, measure the temperature evolution of outlet water and the false crystal with two thermal couples, and then we calculate temporal evolution of temperature with arbitrary heat transfer coefficient using finite element analysis. By searching the lowest least square difference between measurement and simulation, heat transfer coefficient is estimated finally. The impact of heat transfer coefficient in rep-rated and high-energy laser design is also presented.%为提高固体激光器的热管理效果,提出了一种使用316L不锈钢片代替激光晶体评估固体激光器表面对流换热系数的方法.在低冷却水温的条件下,使用快响应热电偶对替代片和出口水流的动态温度进行测量,应用有限元方法计算不同对流换热系数下替代片的动态温度,讨论了对流换热系数对重频大能量激光器热效应的影响.通过寻找测量值和计算值的最小方差,得到该冷却结构下的激光器表面对流换热系数为3 500 W· m-2·K-1.
Thermal Conductivity and Heat Transfer Coefficient of Concrete
GUO Lixia; GUO Lei; ZHONG Ling; ZHU Yueming
2011-01-01
A very simple model for predicting thermal conductivity based on its definiensis was presented.The thermal conductivity obtained using the model provided a good coincidence to the investigations performed by other authors.The heat transfer coefficient was determined by inverse analysis using the temperature measurements.From experimental results,it is noted that heat transfer coefficient increases with the increase of wind velocity and relative humidity,a prediction equation on heat transfer coefficient about wind velocity and relative humidity is given.
苏梅; 林志敏; 王良璧
2012-01-01
本文以空气和水为流动介质，在空气进口流速um=1—6m／s的范围内，在适体坐标系下，采用耦合数值计算的方法，对圆管管翅式换热器肋侧换热系数进行数值求解，并与实验值相比较。结果表明本文提出的采用换热器总传热系数K1求解得到的肋侧换热系数与实验值最为接近，从而验证了本文提出的数值方法的准确性和可靠性。%The heat transfer coefficient on the fin side surface in circular tube bank fin heat exchanger was studied by using the conjugated simulation method in body-fitted coordinate system with the inlet air flow rate ranging from 1 m/s to 6 m/s in this paper. The numerical results were compared with the experimental results, and the discrepancies were presented in this paper. The results reveal that heat transfer coefficient on the fin side surface obtained by using the overall heat transfer coefficient K1 agrees well with the experimental results, so the accuracy and reliability of this numerical method proposed in this paper can be verified.
Basketball Surfaces and Coefficient of Restitution
Kristyn Peacock; Faith Pearson
2015-01-01
A basketball was released from varying drop heights to simulate the impact speeds of a typical soft, medium, and hard dribble. This was repeated across four different surfaces that students typically play on–exposed aggregate concrete, maple wood flooring, EPI Outdoor Sport flooring, and playground rubber mesh. From the measured drop and bounce heights, the coefficient of restitution(COR)was calculated. It was concluded that only playground rubber mesh had COR’s below the regula...
Measurement of heat transfer coefficient using termoanemometry methods
Dančová P.
2014-03-01
Full Text Available This work deals with a measurement of heat transfer from a heated flat plate on which a synthetic jet impacts perpendicularly. Measurement of a heat transfer coefficient (HTC is carried out using the hot wire anemometry method with glue film probe Dantec 55M47. The paper brings also results of velocity profiles measurements and turbulence intensity calculations.
Overall mass-transfer coefficients in non-linear chromatography
Mollerup, Jørgen; Hansen, Ernst
1998-01-01
In case of mass transfer where concentration differences in both phases must be taken into account, one may define an over-all mass-transfer coefficient basd on the apparent over-all concentration difference. If the equilibrium relationship is linear, i.e. in cases where a Henry´s law relationshi...
Basketball Surfaces and Coefficient of Restitution
Kristyn Peacock
2015-01-01
Full Text Available A basketball was released from varying drop heights to simulate the impact speeds of a typical soft, medium, and hard dribble. This was repeated across four different surfaces that students typically play on–exposed aggregate concrete, maple wood flooring, EPI Outdoor Sport flooring, and playground rubber mesh. From the measured drop and bounce heights, the coefficient of restitution(CORwas calculated. It was concluded that only playground rubber mesh had COR’s below the regulation range, with the other three surfaces having COR’s within regulation.
Prediction of film boiling heat transfer coefficients for binary mixtures
Liu, Ming-Huei; Yang, Yu-Min; Maa, Jer-Ru
Film boiling of binary liquid mixtures may be significantly different from that of single-component liquids due to the mass diffusion effect. A theoretical analysis is performed to outline the effects of mass diffusion phenomena on film boiling heat transfer process from a horizontal cylinder heating surface to the binary liquid mixtures of ethylene oxide/water and ethanol/benzene over whole range of compositions. These two binary systems are chosen for illustrating the strong and weak mass diffusion effects, respectively, on film boiling. Furthermore, a simple correlation for predicting heat transfer coefficient is proposed to demonstrate the idea that the dimensionless F factor can satisfactorily account for the mass diffusion effect on film boiling heat transfer of binary mixtures. Zusammenfassung Infolge des Stoffdiffusionseffektes kann sich das Filmsiedeverhalten binärer Flüssigkeitsgemische ganz wesentlich von dem der Einzelkomponentenfluide unterscheiden. In einer theoretischen Studie sollen die Einflüsse der Stoffdiffusionsphänomene auf den Wärmeübergang beim Filmsieden untersucht werden, und zwar bezüglich einer horizontalen zylindrischen Heizfläche, die Wärme an die Binärgemische Ethylenoxid/Wasser und Ethanol/Benzol bei beliebigen Konzentrationsverhältnissen abgibt. Die beiden Binärsysteme wurden ausgewählt, um einmal starken und dann schwachen Einfluß des Stoffdiffusionseffektes auf das Filmsieden zu zeigen. Schließlich wird eine einfache Korrelationsbeziehung zur Berechnung von Wärmeübergangskoeffizienten vorgeschlagen, die darlegen soll, daß der dimensionslose F-Faktor geeignet ist, den Einfluß des Stoffdiffusionseffektes auf das Filmsieden binärer Gemische befriedigend zu berücksichtigen.
Mass transfer coefficients determination from linear gradient elution experiments.
Pfister, David; Morbidelli, Massimo
2015-01-02
A procedure to estimate mass transfer coefficients in linear gradient elution chromatography is presented and validated by comparison with experimental data. Mass transfer coefficients are traditionally estimated experimentally through the van Deemter plot, which represents the HETP as a function of the fluid velocity. Up to now, the HETP was obtained under isocratic elution conditions. Unfortunately, isocratic elution experiments are often not suitable for large biomolecules which suffer from severe mass transfer hindrances. Yamamoto et al. were the first to propose a semi-empirical equation to relate HETPs measured from linear gradient elution experiments to those obtained under isocratic conditions [7]. Based on his pioneering work, the approach presented in this work aims at providing an experimental procedure supported by simple equations to estimate reliable mass transfer parameters from linear gradient elution chromatographic experiments. From the resolution of the transport model, we derived a rigorous analytical expression for the HETP in linear gradient elution chromatography.
Change of heat transfer- and mass transfer-coefficients with simultaneous heat- and mass transfer
Kast, W.
1981-01-01
The values of sensible and latent heat and of the resulting energy flow through laminar boundary layer have been developed for the four possible combinations of the directions of heat- and mass flows. When the values of heat- and mass flows are used with the correct sign according to the definitions of Fourier's law and Fick's law, the changes of heat transfer- and mass transfer coefficients can be described by one equation alone for all cases. The equations extended in that way are valid for arbitrary cases of countercurrent diffusing mass flows - not only for the well known case of Stefan diffusion.
Evaluation of complex heat transfer coefficients for passive heating concepts
Bansal, N.K.; Sodha, M.S.; Singh, S.P.; Ram, S.
1987-01-01
Passive heating concepts namely Trombe wall, Water wall and Trans wall have been analysed to obtain overall heat transfer coefficients for average values and for time-dependent variations. The numerical values have been obtained and tabulated for various wall thicknesses.
Dissociation and Mass Transfer Coefficients for Ammonia Volatilization Models
Process-based models are being used to predict ammonia emissions from manure sources, but their accuracy has not been fully evaluated for cattle manure. Laboratory trials were conducted to measure the dissociation and mass transfer coefficients for ammonia volatilization from media of buffered ammon...
Gas-Liquid Mass Transfer Coefficient in Stirred Tank Reactors
Yawalkar, Archis A.; Heesink, Albertus B.M.; Versteeg, Geert F.; Pangarkar, Vishwas G.
2002-01-01
Volumetric gas—liquid mass transfer coefficient (kLa) data available in the literature for larger tanks (T = 0.39 m to 2.7 m) have been analyzed on the basis of relative dispersion parameter, N/Ncd. It was observed that at a given superficial gas velocity (VG), kLa values were approximately the same
Gas–Liquid Mass Transfer Coefficient in Stirred Tank Reactors
Yawalkar, Archis A.; Heesink, Albertus B.M.; Versteeg, Geert F.; Pangarkar, Vishwas G.
2002-01-01
Volumetric gas–liquid mass transfer coefficient (kLa) data available in the literature for larger tanks (T = 0.39 m to 2.7 m) have been analyzed on the basis of relative dispersion parameter, N/Ncd. It was observed that at a given superficial gas velocity (VG), kLa values were approximately the same
A correlation for heat transfer coefficients in food extruders.
Levine, L; Rockwood, J
1986-06-01
A dimensionless correlation of heat transfer coefficient for heat flow between the extruder barrel wall and extrudate is presented. The standard error of estimate of the correlation is 12.4%. The correlation is useful for the design and scale-up of food extruders and the design of associated temperature control systems.
Measurement of the convective heat-transfer coefficient
Conti, Rosaria; Fiordilino, Emilio
2014-01-01
We propose an experiment for investigating how objects cool down toward the thermal equilibrium with its surrounding through convection. We describe the time dependence of the temperature difference of the cooling object and the environment with an exponential decay function. By measuring the thermal constant tau, we determine the convective heat-transfer coefficient, which is a characteristic constant of the convection system.
CFD Extraction of Heat Transfer Coefficient in Cryogenic Propellant Tanks
Yang, H. Q.; West, Jeff
2015-01-01
Current reduced-order thermal model for cryogenic propellant tanks is based on correlations built for flat plates collected in the 1950's. The use of these correlations suffers from inaccurate geometry representation; inaccurate gravity orientation; ambiguous length scale; and lack of detailed validation. This study uses first-principles based CFD methodology to compute heat transfer from the tank wall to the cryogenic fluids and extracts and correlates the equivalent heat transfer coefficient to support reduced-order thermal model. The CFD tool was first validated against available experimental data and commonly used correlations for natural convection along a vertically heated wall. Good agreements between the present prediction and experimental data have been found for flows in laminar as well turbulent regimes. The convective heat transfer between the tank wall and cryogenic propellant, and that between the tank wall and ullage gas were then simulated. The results showed that the commonly used heat transfer correlations for either vertical or horizontal plate over-predict heat transfer rate for the cryogenic tank, in some cases by as much as one order of magnitude. A characteristic length scale has been defined that can correlate all heat transfer coefficients for different fill levels into a single curve. This curve can be used for the reduced-order heat transfer model analysis.
Radiative Transfer Model for Contaminated Rough Surfaces
2013-02-01
plot of Figure 8 shows three sharp spectral features (in the LWIR region) that were used for calibration . 1000 1500 2000 2500 3000 3500 0 0.1 0.2...transfer, reflectance, rough surface, BRDF, Kramers-Kronig, penetration depth, fill factor, infrared, LWIR , MWIR, absorption coefficient, scattering...and the calibrated α are plotted in red, and green, respectively
Analysis of the Coupling Coefficient in Inductive Energy Transfer Systems
Rafael Mendes Duarte
2014-01-01
Full Text Available In wireless energy transfer systems, the energy is transferred from a power source to an electrical load without the need of physical connections. In this scope, inductive links have been widely studied as a way of implementing these systems. Although high efficiency can be achieved when the system is operating in a static state, it can drastically decrease if changes in the relative position and in the coupling coefficient between the coils occur. In this paper, we analyze the coupling coefficient as a function of the distance between two planar and coaxial coils in wireless energy transfer systems. A simple equation is derived from Neumann’s equation for mutual inductance, which is then used to calculate the coupling coefficient. The coupling coefficient is computed using CST Microwave Studio and compared to calculation and experimental results for two coils with an excitation signal of up to 10 MHz. The results showed that the equation presents good accuracy for geometric parameters that do not lead the solution of the elliptic integral of the first kind to infinity.
Pool Boiling Heat Transfer on structured Surfaces
Addy, J.; Olbricht, M.; Müller, B.; Luke, A.
2016-09-01
The development in the process and energy sector shows the importance of efficient utilization of available resources to improve thermal devices. To achieve this goal, all thermal components have to be optimized continuously. Various applications of multi-phase heat and mass transfer have to be improved. Therefore, the heat transfer and the influence of surface roughness in nucleate boiling with the working fluid propane is experimentally investigated on structured mild steel tubes, because only few data are available in the literature. The mild steel tube is sandblasted to obtain different surface roughness. The measurements are carried out over wide ranges of heat flux and pressure. The experimental results are compared with correlations from literature and the effect of surface roughness on the heat transfer is discussed. It is shown that the heat transfer coefficient increases with increasing surface roughness, heat flux and reduced pressure at nucleate pool boiling.
Experimental Investigation on the Heat Transfer Coefficient of the Thermosyphon Cross Section Shape
Mohammed M. I. Hammad,
2015-03-01
Full Text Available Two phase closed thermosyphon is a good heat transfer device. A large heat is transferred from evaporator to condenser with relatively a small temperature difference. In the present work, the heat transfer performance of two phase closed thermosyphon is analyzed experimentally with different cross section shape for the thermosyphon tube. A copper thermosyphon has been constructed with three different cross section shape (circular, square and rectangular having the same hydraulic diameter and length. Methanol is used as the working fluid. The temperature distribution across the thermosyphon outer surface was measured and recorded using thermocouples. The results showed that the heat transfer coefficient increases with the increase of input power, thermal resistance is indirectly proportional to the input power. The maximum heat transfer coefficient (1815 W/m2C for square cross section at the input power (500 W.
Microscale surface modifications for heat transfer enhancement.
Bostanci, Huseyin; Singh, Virendra; Kizito, John P; Rini, Daniel P; Seal, Sudipta; Chow, Louis C
2013-10-09
In this experimental study, two surface modification techniques were investigated for their effect on heat transfer enhancement. One of the methods employed the particle (grit) blasting to create microscale indentations, while the other used plasma spray coating to create microscale protrusions on Al 6061 (aluminum alloy 6061) samples. The test surfaces were characterized using scanning electron microscopy (SEM) and confocal scanning laser microscopy. Because of the surface modifications, the actual surface area was increased up to 2.8× compared to the projected base area, and the arithmetic mean roughness value (Ra) was determined to vary from 0.3 μm for the reference smooth surface to 19.5 μm for the modified surfaces. Selected samples with modified surfaces along with the reference smooth surface were then evaluated for their heat transfer performance in spray cooling tests. The cooling system had vapor-atomizing nozzles and used anhydrous ammonia as the coolant in order to achieve heat fluxes up to 500 W/cm(2) representing a thermal management setting for high power systems. Experimental results showed that the microscale surface modifications enhanced heat transfer coefficients up to 76% at 500 W/cm(2) compared to the smooth surface and demonstrated the benefits of these practical surface modification techniques to enhance two-phase heat transfer process.
Saponification reaction system: a detailed mass transfer coefficient determination.
Pečar, Darja; Goršek, Andreja
2015-01-01
The saponification of an aromatic ester with an aqueous sodium hydroxide was studied within a heterogeneous reaction medium in order to determine the overall kinetics of the selected system. The extended thermo-kinetic model was developed compared to the previously used simple one. The reaction rate within a heterogeneous liquid-liquid system incorporates a chemical kinetics term as well as mass transfer between both phases. Chemical rate constant was obtained from experiments within a homogeneous medium, whilst the mass-transfer coefficient was determined separately. The measured thermal profiles were then the bases for determining the overall reaction-rate. This study presents the development of an extended kinetic model for considering mass transfer regarding the saponification of ethyl benzoate with sodium hydroxide within a heterogeneous reaction medium. The time-dependences are presented for the mass transfer coefficient and the interfacial areas at different heterogeneous stages and temperatures. The results indicated an important role of reliable kinetic model, as significant difference in k(L)a product was obtained with extended and simple approach.
Convective Heat Transfer Coefficients of the Human Body under Forced Convection from Ceiling
Kurazumi, Yoshihito; Rezgals, Lauris; Melikov, Arsen Krikor
2014-01-01
The average convective heat transfer coefficient for a seated human body exposed to downward flow from above was determined. Thermal manikin with complex body shape and size of an average Scandinavian female was used. The surface temperature distribution of the manikin’s body was as the skin...... of the convective heat transfer coefficient of the whole body (hc [W/(m2•K)]) was proposed: hc=4.088+6.592V1.715 for a seated naked body at 20ºC and hc=2.874+7.427V1.345 for a seated naked body at 26ºC. Differences in the convective heat transfer coefficient of the whole body in low air velocity range, V
In vivo measurement of swine endocardial convective heat transfer coefficient.
Tangwongsan, Chanchana; Will, James A; Webster, John G; Meredith, Kenneth L; Mahvi, David M
2004-08-01
We measured the endocardial convective heat transfer coefficient h at 22 locations in the cardiac chambers of 15 pigs in vivo. A thin-film Pt catheter tip sensor in a Wheatstone-bridge circuit, similar to a hot wire/film anemometer, measured h. Using fluoroscopy, we could precisely locate the steerable catheter sensor tip and sensor orientation in pigs' cardiac chambers. With flows, h varies from 2500 to 9500 W/m2 x K. With zero flow, h is approximately 2400 W/m2 x K. These values of h can be used for the finite element method modeling of radiofrequency cardiac catheter ablation.
Dag, Yusuf
Forced convection over traditional surfaces such as flat plate, cylinder and sphere have been well researched and documented. Data on forced convection over airfoil surfaces, however, remain very scanty in literature. High altitude vehicles that employ airfoils as lifting surfaces often suffer leading edge ice accretions which have tremendous negative consequences on the lifting capabilities and stability of the vehicle. One of the ways of mitigating the effect of ice accretion involves judicious leading edge convective cooling technique which in turn depends on the accuracy of convective heat transfer coefficient used in the analysis. In this study empirical investigation of convective heat transfer measurements on asymmetric airfoil is presented at different angle of attacks ranging from 0° to 20° under subsonic flow regime. The top and bottom surface temperatures are measured at given points using Senflex hot film sensors (Tao System Inc.) and used to determine heat transfer characteristics of the airfoils. The model surfaces are subjected to constant heat fluxes using KP Kapton flexible heating pads. The monitored temperature data are then utilized to determine the heat convection coefficients modelled empirically as the Nusselt Number on the surface of the airfoil. The experimental work is conducted in an open circuit-Eiffel type wind tunnel, powered by a 37 kW electrical motor that is able to generate subsonic air velocities up to around 41 m/s in the 24 square-inch test section. The heat transfer experiments have been carried out under constant heat flux supply to the asymmetric airfoil. The convective heat transfer coefficients are determined from measured surface temperature and free stream temperature and investigated in the form of Nusselt number. The variation of Nusselt number is shown with Reynolds number at various angles of attacks. It is concluded that Nusselt number increases with increasing Reynolds number and increase in angle of attack from 0
Improved transfer matrix methods for calculating quantum transmission coefficient.
Biswas, Debabrata; Kumar, Vishal
2014-07-01
Methods for calculating the transmission coefficient are proposed, all of which arise from improved nonreflecting WKB boundary conditions at the edge of the computational domain in one-dimensional geometries. In the first, the Schrödinger equation is solved numerically, while the second is a transfer matrix (TM) algorithm where the potential is approximated by steps, but with the first and last matrix modified to reflect the new boundary condition. Both methods give excellent results with first-order WKB boundary conditions. The third uses the transfer matrix method with third-order WKB boundary conditions. For the parabolic potential, the average error for the modified third-order TM method reduces by factor of 4100 over the unmodified TM method.
Castell, Albert; Sole, Cristian; Medrano, Marc; Roca, Joan; Cabeza, Luisa F. [Departament d' Informatica i Enginyeria Industrial, Universitat de Lleida, Pere de Cabrera s/n, 25001 Lleida (Spain); Garcia, Daniel [Departament Projectes d' Enginyeria, Universitat Politecnica de Catalunya, Colom 11, 08222 Terrassa (Spain)
2008-09-15
To determine the heat transfer coefficient by natural convection for specific geometries, experimental correlations are used. No correlations were found in the literature for the geometries studied in this work. These geometries consisted of a cylindrical module of 88 mm of diameter and 315 mm height with external vertical fins of 310 mm height and 20 and 40 mm length. To determine the heat transfer coefficient by natural convection, experimental work was done. This module, containing PCM (sodium acetate trihydrate), was situated in the middle upper part of a cylindrical water tank of 440 mm of diameter and 450 mm height. The calculated heat transfer coefficient changed by using external fins, as the heat transfer surface was increased. The temperature variation of the PCM and the water are presented as a function of time, and the heat transfer coefficient for different fins is presented as a function of the temperature difference. Experimental correlations were obtained, presenting the Nusselt number as a function of different dimensionless numbers. Different correlations were analysed to find which one fit better to the experimental data. (author)
NORMATIVE HEAT-TRANSFER COEFFICIENT OF THE RESIDENTIAL BUILDING
A. E. Piir
2015-01-01
Full Text Available The paper offers a simple but sufficiently accurate technique of the mid-normative heattransfer coefficient for any dwelling house applying the known dimensions, required thermalprotection level and specified facade-glazing portion. The authors present the ascertainment technique of the mid-normative heat-transfer coefficient for a dwelling house with the number of stories from 1 to 16 and the required level of thermal protection. They establish the theoretical dependence and parameters affecting the rate of heat-losses through the external building borders. The article considers the thermal-protection level effect on the heating load and the heating-season fuel consumption rate and finds the correlation between the regulatory requirements to the thermal resistance of certain elements of the building.The authors note the effect of the building geometrical characteristics on the heat-losses rate of the wall portion in the total area of the external borders and its relative quantity as compared with the floor-space of the heated accommodations. The comparison of the specific heat-losses computation results for buildings of 1-, 2-, 4-, 8and 16-storeys with the SNiP 23-02–2003 maximum permissible values show the computational results being less than the maximum values on average by 12 %. This permits recommending the normative heat-transfer coefficient of dwelling houses for evaluating heat-loses at the concept-design stage with the building external-borders engineering constructions being indeterminate or yet under development.
Taler, Dawid
2012-09-01
This paper presents a numerical method for determining heat transfer coefficients in cross-flow heat exchangers with extended heat exchange surfaces. Coefficients in the correlations defining heat transfer on the liquid- and air-side were determined using a nonlinear regression method. Correlation coefficients were determined from the condition that the sum of squared liquid and air temperature differences at the heat exchanger outlet, obtained by measurements and those calculated, achieved minimum. Minimum of the sum of the squares was found using the Levenberg-Marquardt method. The uncertainty in estimated parameters was determined using the error propagation rule by Gauss. The outlet temperature of the liquid and air leaving the heat exchanger was calculated using the analytical model of the heat exchanger.
Rong, Li; Nielsen, Peter V; Zhang, Guoqiang
2010-04-01
This paper reports the results of an investigation, based on fundamental fluid dynamics and mass transfer theory, carried out to obtain a general understanding of ammonia mass transfer from an emission surface. The effects of airflow and aqueous ammonium solution temperature on ammonia mass transfer are investigated by using computational fluid dynamics (CFD) modeling and by a mechanism modeling using dissociation constant and Henry's constant models based on the parameters measured in the experiments performed in a wind tunnel. The validated CFD model by experimental data is used to investigate the surface concentration distribution and mass transfer coefficient at different temperatures and velocities for which the Reynolds number is from 1.36 x 10(4) to 5.43 x 10(4) (based on wind tunnel length). The surface concentration increases as velocity decreases and varies greatly along the airflow direction on the emission surface. The average mass transfer coefficient increases with higher velocity and turbulence intensity. However, the mass transfer coefficient estimated by CFD simulation is consistently larger than the calculated one by the method using dissociation constant and Henry's constant models. In addition, the results show that the liquid-air temperature difference has little impact on the simulated mass transfer coefficient by CFD modeling, whereas the mass transfer coefficient increases with higher liquid temperature using the other method under the conditions that the liquid temperature is lower than the air temperature. Although there are differences of mass transfer coefficients between these two methods, the mass transfer coefficients determined by these two methods are significantly related.
Resonant charge transfer at dielectric surfaces
Marbach, Johannes; Fehske, Holger
2012-01-01
We report on the theoretical description of secondary electron emission due to resonant charge transfer occurring during the collision of metastable nitrogen molecules with dielectric surfaces. The emission is described as a two step process consisting of electron capture to form an intermediate shape resonance and subsequent electron emission by decay of this ion, either due to its natural life time or its interaction with the surface. The electron capture is modeled using the Keldysh Green's function technique and the negative ion decay is described by a combination of the Keldysh technique and a rate equation approach. We find the resonant capture of electrons to be very efficient and the natural decay to be clearly dominating over the surface-induced decay. Secondary electron emission coefficients are calculated for aluminum oxide, magnesium oxide, silicon oxide, and diamond at several kinetic energies of the projectile. With the exception of magnesium oxide the coefficients turn out to be of the order of...
Determining convective heat transfer coefficient using phoenics software package
Kostikov, A.; Matsevity, Y. [Institute of Mechanical Engineering Problems of National Academy of Sciences of Ukraine, Kharkov (Ukraine)
1997-12-31
The two methods of determination of such important quantity of heat exchange on a body surface using PHOENICS are suggested in the presentation. The first method consists in a post-processing of results of conjugate heat transfer problem solved by PHOENICS. The second one is solving an inverse heat conduction problem for solid body using PHOENICS. Comparative characteristic of these two methods is represented. (author) 4 refs.
Numerical prediction of nucleate pool boiling heat transfer coefficient under high heat fluxes
Pezo Milada L.
2016-01-01
Full Text Available This paper presents CFD (Computational Fluid Dynamics approach to prediction of the heat transfer coefficient for nucleate pool boiling under high heat fluxes. Three-dimensional numerical simulations of the atmospheric saturated pool boiling are performed. Mathematical modelling of pool boiling requires a treatment of vapor-liquid two-phase mixture on the macro level, as well as on the micro level, such as bubble growth and departure from the heating surface. Two-phase flow is modelled by the two-fluid model, which consists of the mass, momentum and energy conservation equations for each phase. Interface transfer processes are calculated by the closure laws. Micro level phenomena on the heating surface are modelled with the bubble nucleation site density, the bubble resistance time on the heating wall and with the certain level of randomness in the location of bubble nucleation sites. The developed model was used to determine the heat transfer coefficient and results of numerical simulations are compared with available experimental results and several empirical correlations. A considerable scattering of the predictions of the pool boiling heat transfer coefficient by experimental correlations is observed, while the numerically predicted values are within the range of results calculated by well-known Kutateladze, Mostinski, Kruzhilin and Rohsenow correlations. The presented numerical modeling approach is original regarding both the application of the two-fluid two-phase model for the determination of heat transfer coefficient in pool boiling and the defined boundary conditions at the heated wall surface. [Projekat Ministarstva nauke Republike Srbije, br. 174014
Masiulaniec, K. Cyril; Vanfossen, G. James, Jr.; Dewitt, Kenneth J.; Dukhan, Nihad
1995-01-01
A technique was developed to cast frozen ice shapes that had been grown on a metal surface. This technique was applied to a series of ice shapes that were grown in the NASA Lewis Icing Research Tunnel on flat plates. Nine flat plates, 18 inches square, were obtained from which aluminum castings were made that gave good ice shape characterizations. Test strips taken from these plates were outfitted with heat flux gages, such that when placed in a dry wind tunnel, can be used to experimentally map out the convective heat transfer coefficient in the direction of flow from the roughened surfaces. The effects on the heat transfer coefficient for both parallel and accelerating flow will be studied. The smooth plate model verification baseline data as well as one ice roughened test case are presented.
Henningsen, Poul; Hattel, Jesper Henri; Wanheim, Tarras
1998-01-01
Temperature is measured during backward can extrusion of steel. The process is characterised by large deformations and very high surface pressure. In the experiments, a can in low carbon steel with a lubrication layer of phosphate soap is formed. The temperature is measured by thermocouples in th...... and the workpiece are compared with a number of FEM simulations computed with different heat transfer coefficients. The current heat transfer coefficient is determined from the simulations....
Henningsen, Poul; Hattel, Jesper Henri; Wanheim, Tarras
1998-01-01
from the surface. The thermocouples are welded to the end of grooves milled in a small plug, Which is pressed into a hold in the punch nose. All the temperature measurements in the tool and the workpiece are compared with a number of FEM simulations computed with different heat transfer coefficients....... The current heat transfer coefficient is determined as the one resulting in the best agreement between measurements and the simulations....
Heat transfer coefficient determination for flow boiling in vertical and horizontal minichannels
Piasecka Magdalena
2014-03-01
Full Text Available The paper presents the results of boiling heat transfer research during FC-72 laminar flow along a minichannel of 1 mm depth, positioned vertically and horizontally, with an enhanced heating surface. One glass pane allows to determine the temperature of the heating wall by liquid crystal thermography. Calculations are aimed at the evaluation of one- and two-dimensional heat transfer approaches to determine the local heat transfer coefficient. In the one-dimensional approach only the direction of the flow in the channel is considered. In the two-dimensional approach the inverse problem in the heating wall and the direct problem in the glass barrier were solved by the finite element method with Trefftz functions as shape functions (FEMT. The developed flow boiling area was studied. Heat transfer coefficient values obtained for the horizontal minichannel were higher than those obtained for the vertical one. When the heat flux supplied to heating wall grows, the share of gas-phase increases leading to the heat transfer coefficient decreases. The same courses of the experiment were observed for the two applied methods, but the results obtained in the one-dimensional approach are considerably higher than in the two-dimensional one. One-dimensional approach seems to be less sensitive to measurement errors.
The Heat Transfer Coefficient of Recycled Concrete Bricks Combination with EPS Insulation Board Wall
Jianhua Li
2015-01-01
Full Text Available Four tectonic forms samples were conducted to test their heat transfer coefficients. By analyzing and comparing the test values and theoretical values of the heat transfer coefficient, a corrected-value calculation method for determining the heat transfer coefficient was proposed; the proposed method was proved to be reasonably correct. The results indicated that the recycled concrete brick wall heat transfer coefficient is higher than that of the clay brick wall, the heat transfer coefficient of recycled concrete brick wall could be effectively reduced when combined with the EPS insulation board, and the sandwich insulation type was better than that of external thermal insulation type.
Huerst, C.; Schulz, A.; Wittig, S. [Univ. Karlsruhe (Germany). Lehrstuhl und Inst. fuer Thermische Stroemungsmaschinen
1995-04-01
The present study compares measured and computed heat transfer coefficients for high-speed boundary layer nozzle flows under engine Reynolds number conditions (U{sub {infinity}} = 230 {divided_by} 880 m/s, Re* = 0.37 {divided_by} 1.07 {times} 10{sup 6}). Experimental data have been obtained by heat transfer measurements in a two-dimensional, nonsymmetric, convergent-divergent nozzle. The nozzle wall is convectively cooled using water passages. The coolant heat transfer data and nozzle surface temperatures are used as boundary conditions for a three-dimensional finite-element code, which is employed to calculate the temperature distribution inside the nozzle wall. Heat transfer coefficients along the hot gas nozzle wall are derived from the temperature gradients normal to the surface. The results are compared with numerical heat transfer predictions using the low-Reynolds-number {kappa}-{epsilon} turbulence model by Lam and Bremhorst. Influence of compressibility in the transport equations for the turbulence properties is taken into account by using the local averaged density. The results confirm that this simplification leads to good results for transonic and low supersonic flows.
Determining heat transfer coefficients in radial flow through a polyethylene packed
Luís Patiño
2010-07-01
Full Text Available A numerical-experimental methodology was used for determining interstitial heat transfer coefficients in water flowing through po-rous media where it was not in heat balance with the solid phase. Heat transfer coefficients were obtained through the single blow transient test method, combining experimental test equipment results with a mathematical model’s numerical solution. The partial differential equation system produced by the mathematical model was resolved by a numerical finite volume method-ba-sed methodology. Experimental tests and numerical solutions were satisfactorily carried out for different values from the fluid’s surface speed from the entrance to the bed and for different porosity values, finding that Nusselt numbers increased when Reynolds numbers also increased and that Nusselt numbers increased when porosity decreased. A 650 Reynolds number and 0.375 porosity gave a Nusselt number of up to 2.8.
DMS gas transfer coefficients from algal blooms in the Southern Ocean
T. G. Bell
2014-11-01
Full Text Available Air/sea dimethylsulfide (DMS fluxes and bulk air/sea gradients were measured over the Southern Ocean in February/March 2012 during the Surface Ocean Aerosol Production (SOAP study. The cruise encountered three distinct phytoplankton bloom regions, consisting of two blooms with moderate DMS levels, and a high biomass, dinoflagellate-dominated bloom with high seawater DMS levels (>15 nM. Gas transfer coefficients were considerably scattered at wind speeds above 5 m s−1. Bin averaging the data resulted in a linear relationship between wind speed and mean gas transfer velocity consistent with that previously observed. However, the wind speed-binned gas transfer data distribution at all wind speeds is positively skewed. The flux and seawater DMS distributions were also positively skewed, which suggests that eddy covariance-derived gas transfer velocities are consistently influenced by additional, log-normal noise. A~flux footprint analysis was conducted during a transect into the prevailing wind and through elevated DMS levels in the dinoflagellate bloom. Accounting for the temporal/spatial separation between flux and seawater concentration significantly reduces the scatter in computed transfer velocity. The SOAP gas transfer velocity data shows no obvious modification of the gas transfer-wind speed relationship by biological activity or waves. This study highlights the challenges associated with eddy covariance gas transfer measurements in biologically active and heterogeneous bloom environments.
Measurements of local convective heat transfer coefficients on ice accretion shapes
Arimilli, R. V.; Keshock, E. G.; Smith, M. E.
1984-01-01
The thin-skin heat rate technique was used to determine local convective heat transfer coefficients for four representative ice accretion shapes. The shapes represented three stages of glaze ice formation and one rime ice formation; the ice models had varying degrees of surface roughness. In general, convective heat transfer was higher in regions where the model's surfaces were convex and lower in regions where the surfaces were concave. The effect of roughness was different for the glaze and rime ice shapes. On the glaze ice shapes, roughness increased the maximum Nu by 80 percent, but the other Nu values were virtually unchanged. On the rime ice shape, the Nu numbers near the stagnation point were unchanged. The maximum Nu value increased by 45 percent, and the Nu number downstream of the peak increased by approximately 150 percent.
Experimentally Determined Heat Transfer Coefficients for Spacesuit Liquid Cooled Garments
Bue, Grant; Watts, Carly; Rhodes, Richard; Anchondo, Ian; Westheimer, David; Campbell, Colin; Vonau, Walt; Vogel, Matt; Conger, Bruce
2015-01-01
A Human-In-The-Loop (HITL) Portable Life Support System 2.0 (PLSS 2.0) test has been conducted at NASA Johnson Space Center in the PLSS Development Laboratory from October 27, 2014 to December 19, 2014. These closed-loop tests of the PLSS 2.0 system integrated with human subjects in the Mark III Suit at 3.7 psi to 4.3 psi above ambient pressure performing treadmill exercise at various metabolic rates from standing rest to 3000 BTU/hr (880 W). The bulk of the PLSS 2.0 was at ambient pressure but effluent water vapor from the Spacesuit Water Membrane Evaporator (SWME) and the Auxiliary Membrane Evaporator (Mini-ME), and effluent carbon dioxide from the Rapid Cycle Amine (RCA) were ported to vacuum to test performance of these components in flight-like conditions. One of the objectives of this test was to determine the heat transfer coefficient (UA) of the Liquid Cooling Garment (LCG). The UA, an important factor for modeling the heat rejection of an LCG, was determined in a variety of conditions by varying inlet water temperature, flowrate, and metabolic rate. Three LCG configurations were tested: the Extravehicular Mobility Unit (EMU) LCG, the Oceaneering Space Systems (OSS) LCG, and the OSS auxiliary LCG. Other factors influencing accurate UA determination, such as overall heat balance, LCG fit, and the skin temperature measurement, will also be discussed.
Experimental investigation of drag coefficients of gobi surfaces
董治宝; 屈建军; 刘小平; 张伟民; 王训明
2002-01-01
The response of gobi surfaces to the near-surface air flow can be characterized quantitatively by drag coefficients. By using wind tunnel tests, an attempt is made to define the relationship between the drag coefficients of gobi surfaces and gravel size and coverage. It is concluded that the drag coefficients of gobi surfaces tend to be constants when gravel coverage is over 40%-50%. Consequently, we think that the gobi deflation planes expanding vastly in the arid Northwestern China are aerodynamically stable, at least not the supplying sources of current dust storms, and therefore the emphasis on dust storm control should be paid on the so-called "earth gobi" that has low gravel coverage. The prediction model for drag coefficients of gobi surfaces has been developed by regressing drag coefficients on gravel size and coverage, the predicted results are in reasonably good agreement with wind tunnel results (R 2 = 0.94). The change of drag coefficients with gravel friction Reynolds number implies that the development extent of drag effect increases with gravel size and coverage.
Mass transfer coefficients in a hanson mixer-settler extraction column
M. Torab-Mostaedi
2008-09-01
Full Text Available The volumetric overall mass transfer coefficients in a pilot plant Hanson mixer-settler extraction column of seven stages have been measured using toluene-acetone-water system. The effects of agitation speed and dispersed and continuous phases flow rates on volumetric overall mass transfer coefficients have been investigated. The results show that the volumetric overall mass transfer coefficient increases with increase in agitation speed and reaches a maximum. After having reached its maximum, it falls with further increase in agitation speed. It was found that the volumetric overall mass transfer coefficient increases with increase in dispersed phase flow rate, while it decreases with increase in continuous phase flow rate. By using interfacial area, the overall mass transfer coefficients for continuous and dispersed phases are determined from volumetric coefficients. An empirical correlation for prediction of the continuous phase overall mass transfer coefficient is proposed in terms of Sherwood and Reynolds numbers. Also the experimental data of the column investigated are compared with data for various extraction columns. Comparison between theoretical models and experimental results for the dispersed phase mass transfer coefficient shows that these models do not have enough accuracy for column design. Using effective diffusivity in the Gröber equation results in more accurate prediction of overall mass transfer coefficient. The prediction of overall mass transfer coefficients from the presented equations is in good agreement with experimental results.
Benelmir, R.; Khalfi, M.; Feidt, M. [Nancy-1 Univ. Henri-Poincare, 54 - Vandoeuvre-les-Nancy (France). Lab. d`energetique et de mecanique theorique et appliquee
1997-04-01
The following, which is rather oriented towards experimentation, shows the influence of the humidity content of air on heat transfer. This first article concerns heat transfer between, the external fluid (moist air) and the internal fluid (water containing glycol, whose thermal behavior inside circular tubes is well-known) in a heat exchanger of the same type as those used in automotive air conditioning (horizontal copper tubes and plane aluminium fins), in the absence of condensation. The most difficult part of this experimental work is the measurement and control of the air humidity, since one has to make sure that the measurement in certainties are not significant compared to the precision of the calculation of the heat transfer coefficient. The conclusion is that, for this type of exchanger, the heat transfer coefficient decreases with air humidity in the absence of condensation (dry wall). Some correlations have been developed with respect to the relative air humidity. An analog experimental investigation, but this time carried out in the presence of condensation (partially or completely wetted wall), is about to be completed; the obtained results will be communicated later on. (authors) 15 refs.
Adiabatic Effectiveness and Heat Transfer Coefficient on a Film-Cooled Rotating Blade
Garg, Vijay K.
1997-01-01
three-dimensional Navier-Stokes code has been used to compute the adiabatic effectiveness and heat transfer coefficient on a rotating film-cooled turbine blade. The blade chosen is the United Technologies Research Center(UTRC) rotor with five film-cooling rows containing 83 holes, including three rows on the shower head with 49 holes, covering about 86% of the blade span. The mainstream is akin to that under real engine conditions with stagnation temperature 1900 K and stagnation pressure 3 MPa. The blade speed is taken to be 5200 rpm. The adiabatic effectiveness is higher for a rotating blade as compared to that for a stationary blade. Also, the direction of coolant injection from the shower-head holes considerably affects the effectiveness and heat transfer coefficient values on both the pressure and suction surfaces. In all cases the heat transfer coefficient and adiabatic effectiveness are highly three-dimensional in the vicinity of holes but tend to become two-dimensional far downstream.
Effect of surface etching on condensing heat transfer
Seok, Sung Chul; Park, Jae Won; Jung, Jiyeon; Choi, Chonggun; Choi, Gyu Hong; Hwang, Seung Sik; Chung, Tae Yong; Shin, Donghoon [Kookmin University, Seoul (Korea, Republic of); Kim, Jin Jun [Hoseo University, Asan (Korea, Republic of)
2016-02-15
This study conducted experiments on humid air condensation during heat transfer in an air preheating exchanger attached to a home condensing boiler to improve thermal efficiency. An etchant composed of sulfuric acid and sodium nitrate was used to create roughness on the heat exchanger surface made from STS430J1L. A counter flow heat exchanger was fabricated to test the performance of heat transfer. Results showed that the overall heat transfer coefficients of all specimens treated with etchant improved with respect to the original specimens (not treated with etchant), and the overall heat transfer coefficient of the 60 s etching specimen increased by up to 15%. However, the increasing rate of the heat transfer coefficient was disproportional to the etching time. When the etching time specifically increased above 60 s, the heat transfer coefficient decreased. This effect was assumed to be caused by surface characteristics such as contact angle. Furthermore, a smaller contact angle or higher hydrophilicity leads to higher heat transfer coefficient.
Malinowski, Z.; Telejko, T.; Cebo-Rudnicka, A.; Szajding, A.; Rywotycki, M.; Hadała, B.
2016-09-01
The industrial rolling mills are equipped with systems for controlled water cooling of hot steel products. A cooling rate affects the final mechanical properties of steel which are strongly dependent on microstructure evolution processes. In case of water jets cooling the heat transfer boundary condition can be defined by the heat transfer coefficient. In the present study one and three dimensional heat conduction models have been employed in the inverse solution to heat transfer coefficient. The inconel plate has been heated to about 900oC and then cooled by one, two and six water jets. The plate temperature has been measured by 30 thermocouples. The heat transfer coefficient distributions at plate surface have been determined in time of cooling.
Adhesion coefficient of automobile tire and road surface
刘长生
2008-01-01
The adhesion coefficient of automobile tire and road surface was analyzed and the formula about it was derived.Some suggestions about highway construction,driving safety of the drivers and the judgment of the traffic accidents were presented.The results show that the adhesion coefficient is a function with the extreme value.If there is atmospheric pressure in the tire,the load of the vehicle and the degree of the coarse on the road surface is not selected properly,it will reach the least and affect the safety of the running automobile.
Kaul, Neerej; Agrawal, Himani; Paradkar, A R; Mahadik, K R
2005-08-31
A multifactor optimization technique is successfully applied to study the effect of simultaneously varying the system variables on feasibility of nevirapine analysis by packed column supercritical fluid chromatography (PC-SFC). The optimal conditions were determined with the aid of the response surface methodology using 3(3) factorial designs. The method is based on methanol-modified carbon dioxide as the mobile phase at flow rate of 3.0 ml/min with elution through a JASCO Finepak SIL-5, [C18 (5-micron, 25 cm x 4.6 mm, i.d.)] column using photodiode array detection. The method has been successfully used to analyze commercial solid dosage form to assess the chromatographic performance of SFC system. The present work briefs the thermodynamic applications of PC-SFC with an emphasis on the results of nevirapine. The foremost of such applications is the determination of solute diffusion coefficient in supercritical mobile phase by Taylor-Aris peak broadening technique.
Banerjee, S.; Hassan, Y.A. [Texas A& M Univ., College Station, TX (United States)
1995-09-01
Condensation in the presence of noncondensible gases plays an important role in the nuclear industry. The RELAP5/MOD3 thermal hydraulic code was used to study the ability of the code to predict this phenomenon. Two separate effects experiments were simulated using this code. These were the Massachusetts Institute of Technology`s (MIT) Pressurizer Experiment, the MIT Single Tube Experiment. A new iterative approach to calculate the interface temperature and the degraded heat transfer coefficient was developed and implemented in the RELAP5/MOD3 thermal hydraulic code. This model employs the heat transfer simultaneously. This model was found to perform much better than the reduction factor approach. The calculations using the new model were found to be in much better agreement with the experimental values.
Heat transfer coefficient for flow boiling in an annular mini gap
Hożejowska Sylwia
2016-01-01
Full Text Available The aim of this paper was to present the concept of mathematical models of heat transfer in flow boiling in an annular mini gap between the metal pipe with enhanced exterior surface and the external glass pipe. The one- and two-dimensional mathematical models were proposed to describe stationary heat transfer in the gap. A set of experimental data governed both the form of energy equations in cylindrical coordinates and the boundary conditions. The models were formulated to minimize the number of experimentally determined constants. Known temperature distributions in the enhanced surface and in the fluid helped to determine, from the Robin condition, the local heat transfer coefficients at the enhanced surface – fluid contact. The Trefftz method was used to find two-dimensional temperature distributions for the thermal conductive filler layer, enhanced surface and flowing fluid. The method of temperature calculation depended on whether the area of single-phase convection ended with boiling incipience in the gap or the two-phase flow region prevailed, with either fully developed bubbly flow or bubbly-slug flow. In the two–phase flow, the fluid temperature was calculated by Trefftz method. Trefftz functions for the Laplace equation and for the energy equation were used in the calculations.
Heat transfer coefficient for flow boiling in an annular mini gap
Hożejowska, Sylwia; Musiał, Tomasz; Piasecka, Magdalena
2016-03-01
The aim of this paper was to present the concept of mathematical models of heat transfer in flow boiling in an annular mini gap between the metal pipe with enhanced exterior surface and the external glass pipe. The one- and two-dimensional mathematical models were proposed to describe stationary heat transfer in the gap. A set of experimental data governed both the form of energy equations in cylindrical coordinates and the boundary conditions. The models were formulated to minimize the number of experimentally determined constants. Known temperature distributions in the enhanced surface and in the fluid helped to determine, from the Robin condition, the local heat transfer coefficients at the enhanced surface - fluid contact. The Trefftz method was used to find two-dimensional temperature distributions for the thermal conductive filler layer, enhanced surface and flowing fluid. The method of temperature calculation depended on whether the area of single-phase convection ended with boiling incipience in the gap or the two-phase flow region prevailed, with either fully developed bubbly flow or bubbly-slug flow. In the two-phase flow, the fluid temperature was calculated by Trefftz method. Trefftz functions for the Laplace equation and for the energy equation were used in the calculations.
Turbulent transfer coefficient and roughness length in a high-altitude lake, Tibetan Plateau
Li, Zhaoguo; Lyu, Shihua; Zhao, Lin; Wen, Lijuan; Ao, Yinhuan; Wang, Shaoying
2016-05-01
A persistent unstable atmospheric boundary layer was observed over Lake Ngoring, caused by higher temperature on the water surface compared with the overlying air. Against this background, the eddy covariance flux data collected from Lake Ngoring were used to analyse the variation of transfer coefficients and roughness lengths for momentum, heat and moisture. Results are discussed and compared with parameterization schemes in a lake model. The drag coefficient and momentum roughness length rapidly decreased with increasing wind velocity, reached a minimum value in the moderate wind velocity and then increased slowly as wind velocity increased further. Under weak wind conditions, the surface tension or small scale capillary wave becomes more important and increases the surface roughness. The scalar roughness length ratio was much larger than unity under weak wind conditions, and it decreased to values near unity as wind velocity exceeded 4.0 m s-1. The lake model could not reproduce well the variation of drag coefficient, or momentum roughness length, versus wind velocity in Lake Ngoring, but it did simulate well the sensible heat and latent heat fluxes, as a result of complementary opposite errors.
Nahon, D.F.; Harrison, M.; Roozen, J.P.
2000-01-01
The penetration theory of interfacial mass transfer was used to model flavor release from aqueous solutions containing different concentrations of sucrose. The mass transfer coefficient and the gas/solution partition coefficient are the main factors of the model influencing the release in time. Para
Determination of the gas-to-membrane mass transfer coefficient in a catalytic membrane reactor
Veldsink, J.W.; Versteeg, G.F.; Swaaij, W.P.M. van
1995-01-01
A novel method to determine the external mass transfer coefficient in catalytic membrane reactors (Sloot et al., 1992a, b) was presented in this study. In a catalytically active membrane reactor, in which a very fast reaction occurs, the external transfer coefficient can conveniently be measured by
Identification of Heat Transfer Coefficients by Use Conditions of Quenching Oil
Katsumi Ichitani
2004-01-01
Heat transfer coefficients of the quench medium are necessary for heat-treatment simulation. Cooling characteristics of quenching oil vary with kinds and usage greatly. Users are selecting oil solutions that come up to their desired hardness and quenching distortion requirements. In particular cooling performance rises by agitation and decompression. Therefore we identified a heat transfer coefficient by usage and kinds of quenching oil. Cooling characteristics are different greatly by a kind of quenching oil. A difference of a cooling characteristic by a kind of oil depends on a temperature range of a boiling stage and the maximum heat transfer coefficient mainly. On the other hand, in a convection stage, there are few changes in a boiling stage. Even if quenching oil temperature is changed, heat transfer coefficients do not change greatly. When quenching oil stirred, heat transfer coefficients of vapor blanket stage and a convection stage rise, but there are a few changes in a boiling stage. When quenching oil is decompressed a temperature range of a high heat transfer coefficient moves to the low temperature side. In addition, a heat transfer coefficient in a vapor blanket stage comes down. For precision improvement of heat-treatment simulation, it is important that the heat transfer coefficient is calculated in conformity to the on-site use reality.
张强; 卫国安; 黄荣辉; 曹晓彦
2002-01-01
By utilizing the data of the intensive observation period (May-June, 2000) of Dunhuang land-surface process field experiment that belongs to "Land-atmosphere Interactive Field Experiment over Arid Region of Northwest China", the bulk momentum transfer coefficient Cd and bulk sensible heat transfer coefficient Ch between surface and atmosphere over desert and Gobi in the arid region are determined according to three different methods. The result shows that, though these bulk transfer coefficients are different, they are in the same order. Especially, the means of Cd and Ch are close. Moreover, through analyzing the wind direction, the interference of the building near the observational station with the data is eliminated. From this, the relation between the bulk transfer coefficients and the bulk Richardson number and the range of the typical values of the bulk transfer coefficients over desert and Gobi in the typical arid region are obtained.
Forsyth, Peter; McGilvray, Matthew; Gillespie, David R. H.
2017-01-01
This paper reports an experimental and numerical study of the development and coupling of aerodynamic flows and heat transfer within a model ribbed internal cooling passage to provide insight into the development of secondary flows. Static instrumentation was installed at the end of a long smooth passage and used to measure local flow features in a series of experiments where ribs were incrementally added upstream. This improves test turnaround time and allows higher-resolution heat transfer coefficient distributions to be captured, using a hybrid transient liquid crystal technique. A composite heat transfer coefficient distribution for a 12-rib-pitch passage is reported: notably the behaviour is dominated by the development of the secondary flow in the passage throughout. Both the aerodynamic and heat transfer test data were compared to numerical simulations developed using a commercial computational fluid dynamics solver. By conducting a number of simulations it was possible to interrogate the validity of the underlying assumptions of the experimental strategy; their validity is discussed. The results capture the developing size and strength of the vortical structures in secondary flow. The local flow field was shown to be strongly coupled to the enhancement of heat transfer coefficient. Comparison of the experimental and numerical data generally shows excellent agreement in the level of heat transfer coefficient predicted, though the numerical simulations fail to capture some local enhancement on both the ribbed and smooth surfaces. Where this was the case, the coupled flow and heat transfer measurements were able to identify missing velocity field characteristics.
Investigation of two-phase heat transfer coefficients of argon-freon cryogenic mixed refrigerants
Baek, Seungwhan; Lee, Cheonkyu; Jeong, Sangkwon
2014-11-01
Mixed refrigerant Joule Thomson refrigerators are widely used in various kinds of cryogenic systems these days. Although heat transfer coefficient estimation for a multi-phase and multi-component fluid in the cryogenic temperature range is necessarily required in the heat exchanger design of mixed refrigerant Joule Thomson refrigerators, it has been rarely discussed so far. In this paper, condensation and evaporation heat transfer coefficients of argon-freon mixed refrigerant are measured in a microchannel heat exchanger. A Printed Circuit Heat Exchanger (PCHE) with 340 μm hydraulic diameter has been developed as a compact microchannel heat exchanger and utilized in the experiment. Several two-phase heat transfer coefficient correlations are examined to discuss the experimental measurement results. The result of this paper shows that cryogenic two-phase mixed refrigerant heat transfer coefficients can be estimated by conventional two-phase heat transfer coefficient correlations.
Transfer entropy coefficient: Quantifying level of information flow between financial time series
Teng, Yue; Shang, Pengjian
2017-03-01
In this paper, a new coefficient is proposed with the objective of quantifying the level of information flow between financial time series. This transfer entropy coefficient, which provides an assessment on the multiscale information flow between measurements, is defined in terms of the transfer entropy method and the multiscale method. The implementation of this transfer entropy coefficient is illustrated with simulated time series and financial time series. Examples taken from simulated and financial data demonstrate that the dynamic mechanism of a complex system cannot be detected solely on the basis of transfer entropy of single scale.
Banan, Mohsen; Gray, Ross T.; Wilcox, William R.
1992-01-01
The heat transfer coefficient between a molten charge and its surroundings in a Bridgman furnace was experimentally determined using in-situ temperature measurement. The ampoule containing an isothermal melt was suddenly moved from a higher temperature zone to a lower temperature zone. The temperature-time history was used in a lumped-capacity cooling model to evaluate the heat transfer coefficient between the charge and the furnace. The experimentally determined heat transfer coefficient was of the same order of magnitude as the theoretical value estimated by standard heat transfer calculations.
Porro, A. Robert; Keith, Theo G., Jr.; Hingst, Warren R.; Chriss, Randall M.; Seablom, Kirk D.
1991-01-01
A technique is developed to measure the local convective heat transfer coefficient on a model surface in a supersonic flow field. The technique uses a laser to apply a discrete local heat flux at the model test surface, and an infrared camera system determines the local temperature distribution due to heating. From this temperature distribution and an analysis of the heating process, a local convective heat transfer coefficient is determined. The technique was used to measure the load surface convective heat transfer coefficient distribution on a flat plate at nominal Mach numbers of 2.5, 3.0, 3.5, and 4.0. The flat plate boundary layer initially was laminar and became transitional in the measurement region. The experimental results agreed reasonably well with theoretical predictions of convective heat transfer of flat plate laminar boundary layers. The results indicate that this non-intrusive optical measurement technique has the potential to obtain high quality surface convective heat transfer measurements in high speed flowfields.
Tanaka, Hiroyoshi; Aoyama, Shigeo; Koma, Hachirou; Adachi, Masaaki
In order to enhance the heat transfer coefficient of the fin used in the finned tube heat exchanger, newly designed fin surfaces, especially, with small diameter (≅4mm) pipes are developed. The experiments are made by the transient testing technique, and used the plastic fins scaling up 4 times of the actual metal fin size. The data of the heat transfer coefficient and the pressure drop are transformed to the actual metal fin data. The fin with the anomalous staggered pipe arrangement and the bridge-like cutting-out with inclined leg portion from stream line is found to have very high overall heat transfer coefficient which is about 1.8-fold increase in comparison with the conventional Louvered fin. In this paper the reason why such enhancement is caused is clarified by mean of the calculation based on the rectangular duct flow. The calculated values are coincident with the data of the experiment well.
Surface Roughness Effects on Discharge Coefficient of Broad Crested Weir
Shaker A. Jalil
2014-06-01
Full Text Available The aim of this study is to investigate the effects of surface roughness sizes on the discharge coefficient for a broad crested weirs. For this purpose, three models having different lengths of broad crested weirs were tested in a horizontal flume. In each model, the surface was roughed four times. Experimental results of all models showed that the logical negative effect of roughness increased on the discharge (Q for different values of length. The performance of broad crested weir improved with decrease ratio of roughness to the weir height (Ks/P and with the increase of the total Head to the Length (H/L. An empirical equation was obtained to estimate the variation of discharge coefficient Cd in terms total head to length ratio, with total head to roughness ratio.
Stricker, M.; Steinbichler, G.
2014-05-01
Appropriate modeling of heat transfer from the polymer material to the injection mold is essential to achieve accurate simulation results. The heat transfer is commonly modeled using convective heat transfer and applying heat transfer coefficients (HTC) to the polymer-mold-interface. The set HTC has an influence on the results for filling pressure, cooling performance and shrinkage, among others. The current paper, presents a new strategy to measure HTC in injection molding experiments using Newtons law of cooling. The heat flux is calculated out of demolding heat (measured by means of calorimetry), injection heat (measured by means of an IR-sensor), cooling time and part mass. Cavity surface area, average mold surface temperature and average part surface temperature lead to the HTC.
Experimental study of convective coefficient of mass transfer of avocado (Persia americana Mill.)
Alves, Suerda Bezerra; Luiz, Marcia Ramos; Amorim, Joselma Araujo de; Gusmao, Rennam Pereira de; Gurgel, Jose Mauricio [Universidade Federal da Paraiba (LES/UFPB), Joao Pessoa, PB (Brazil). Lab. de Energia Solar
2010-07-01
Most of all energy consumed worldwide comes from fossil fuels derived from petroleum. With the petroleum crisis in the 70 were sought new energy sources, among them renewable. One such source is biodiesel energy, organic matter originated from animal and/or vegetable. Among the various plant species is the avocado (Persia americana Mill.) showing great potential in the production of petroleum extracted from the pulp and the alcohol removed from the seed. The main obstacle for obtaining the petroleum is the high humidity found in the pulp, being necessary to the drying process, which involves the transfer of heat and mass. The aim of this study was to use the mathematical model represented by Newton's Law of Cooling to simulate the mass transfer on the surface of the avocado pulp during the drying process. The equation of the mathematical model was solved numerically and the method of least squares was identified convective coefficient of Mass Transfer. The dryer used in the experimental process was operated with air flow in the vertical, air flow average fixed 3m/s and temperatures of 50, 60 and 70 deg C. The scheme of the dryer used in the research is composed of the following equipment: centrifugal fan, which drives the air-drying; valve, which allows control of airflow; electrical resistance, used for heating air; the drying chamber, where enables measurement of temperature and relative humidity; support for smaller trays; trays smaller, where the samples of the pulp of the avocado are placed; exit of the air of drying for the environment. The result presented shows the ratio of moisture content as a function of temperature over time, where it is possible to also observe that how much bigger the temperature of drying, greater will be the convective coefficient of mass transfer of the avocado. (author)
EXPERIMENTAL INVESTIGATION OF HEAT TRANSFER ENHANCEMENT OVER THE DIMPLED SURFACE
Dr. Sachin L. Borse
2012-08-01
Full Text Available Over the past couple of years the focus on using concavities or dimples provides enhanced heat transfer has been documented by a number of researchers. Dimples are used on the surface of internal flow passages because they produce substantial heat transfer augmentation. This project work is concerned with experimentalinvestigation of the forced convection heat transfer over the dimpled surface. The objective of the experiment is to find out the heat transfer and air flow distribution on dimpled surfaces and all the results obtained are compared with those from a flat surface. The varying parameters were i Dimple arrangement on the plate i.e.staggered and inline arrangement and ii Heat input iiiDimple density on the plate. Heat transfer coefficients and Nusselt number were measured in a channel with one side dimpled surface. Thespherical type dimples were fabricated, and the diameter and the depth of dimple were 6 mm and 3 mm, respectively. Channel height is 25.4mm, two dimple configurations were tested. The Reynolds number based on the channel hydraulic diameter was varied from 5000 to 15000.Study shown that thermal performance is increasing with Reynolds number. With the inline and staggered dimple arrangement, the heat transfer coefficients, Nusselt number and the thermal performance factors were higher for the staggered arrangement.
Vacca, Santiago; Martorano, Marcelo A.; Heringer, Romulo; Boccalini, Mário
2015-05-01
The heat transfer coefficient at the metal-mold interface ( h MM) has been determined for the first time during the centrifugal casting of a Fe-C alloy tube using the inverse solution method. To apply this method, a centrifugal casting experiment was carried out to measure cooling curves within the tube wall under a mold rotation speed of 900 rpm, imposing a centrifugal force 106 times as large as the gravity force (106 G). As part of the solution method, a comprehensive heat transfer model of the centrifugal casting was also developed and coupled to an optimization algorithm. Finally, the evolution of h MM with time that gives the minimum squared error between measured and calculated cooling curves was obtained. The determined h MM is approximately 870 W m-2 K-1 immediately after melt pouring, decreasing to about 50 W m-2 K-1 when the average temperature of the tube is ~973 K (700 °C), after the end of solidification. Despite the existence of a centrifugal force that could enhance the metal-mold contact, these values are lower than those generally reported for static molds with or without an insulating coating at the mold inner surface. The implemented model shows that the heat loss by radiation is dominant over that by convection at the tube inner surface, causing the formation of a solidification front that meets another front coming from the outer surface of the tube.
B. Stojanovic
2009-06-01
Full Text Available The paper presents experimental research of thermal conductivity coefficients of the siliceous sand bed fluidized by air and an experimental investigation of the particle size influence on the heat transfer coefficient between fluidized bed and inclined exchange surfaces. The measurements were performed for the specific fluidization velocity and sand particle diameters d p=0.3, 0.5, 0.9 mm. The industrial use of fluidized beds has been increasing rapidly in the past 20 years owing to their useful characteristics. One of the outstanding characteristics of a fluidized bed is that it tends to maintain a uniform temperature even with nonuniform heat release. On the basis of experimental research, the influence of the process's operational parameters on the obtained values of the bed's thermal conductivity has been analyzed. The results show direct dependence of thermal conductivity on the intensity of mixing, the degree of fluidization, and the size of particles. In the axial direction, the coefficients that have been treated have values a whole order higher than in the radial direction. Comparison of experimental research results with experimental results of other authors shows good agreement and the same tendency of thermal conductivity change. It is well known in the literature that the value of the heat transfer coefficient is the highest in the horizontal and the smallest in the vertical position of the heat exchange surface. Variation of heat transfer, depending on inclination angle is not examined in detail. The difference between the values of the relative heat transfer coefficient between vertical and horizontal heater position for all particle sizes reduces by approximately 15% with the increase of fluidization rate.
COMPUTATION OF MOMENTUM TRANSFER COEFFICIENT AND CONVEYANCE CAPACITY IN COMPOUND CHANNELS
WANG Hua; YANG Ke-jun; CAO Shu-you; LIU Xing-nian
2007-01-01
The momentum transfer coefficient is an important parameter for determining the apparent shear stress at the vertical interface between the main channel and its associated flood plains, the cross-sectional mean velocity and the discharge capacity in compound channels. In this article, under the Boussinesq assumption and through analyzing the characteristics of velocity distribution in the interacting region between the main channel and its associated flood plain, the expression of momentum transfer coefficient was theoretically derived. On the basis of force balance, the expression of vertical apparent shear stress was obtained. By applying the experimental data from the British Engineering Research Council Flood Channel Facility (SERC-FCF), the relationship between the momentum transfer coefficient with the relative depth and the ratio of the flood plain width to the main channel width, was established, And hence the conveyance capacity in compound channels was calculated with Liu and Dong's method. The computed results show that the momentum transfer coefficient relationship obtained is viable.
Establishment and Application of UFC-ACC Heat Transfer Coefficient Model
Tian-Liang Fu; Zhao-Dong Wang; Yong Li; Jia-Dong Li; Guo-Dong Wang
2014-01-01
Based on medium plate runout table ultra-fast cooling ( UFC)-accelerated cooling equipment ( ACC) system, a heat transfer coefficient model was constructed. Firstly, according to the measured data, heat transfer coefficients under different roll speed and water volume were calculated by using an inverse heat conduction method. Secondly, a monofactorial heat transfer coefficient calculation formula was obtained. Finally, the heat transfer coefficient model based on medium plate runout table UFC-ACC system was constructed by intercept function, slope function, interaction influence function and linear or nonlinear influencing factors. The precision of these models was validated by comparing model prediction value with measured data, and the results were in good agreement with practical needs, and the average deviation was less than 5%.
Herranz, J.; Bloxom, S.R.; Keeler, J.B.; Roth, S.R.
1975-12-17
In the proposed Molten Salt Breeder Reactor flowsheet, a fraction of the rare earth fission products is removed from the fuel salt in mass transfer cells. To obtain design parameters for this extraction, the effect of cell size, blade diameter, phase volume, and agitation rate on the mass transfer for a high density ratio system (mercury/water) in nondispersing square cross section contactors was determined. Aqueous side mass transfer coefficients were measured by polarography over a wide range of operating conditions. Correlations for the experimental mass transfer coefficients as functions of the operating parameters are presented. Several techniques for measuring mercury-side mass transfer coefficients were evaluated and a new one is recommended. (auth)
Heat Transfer Coefficient between Ice Cover and Water in the Bohai Sea
季顺迎; 岳前进; 毕祥军
2001-01-01
The calculative method of heat transfer coefficient between ice cover and water is analyzed considering the heat balance at ice cover bottom firstly. The heat transfer coefficient is calculated with the meteorological, oceanographic data and sea ice conditions measured on the JZ20-2 Oil/Gas Platform in the Bohai Sea during the winter of 1997/1998. From the results, it is shown that the heat transfer coefficient is smaller in the freezing and melting periods, which is about 0.16× 10-3 and 0.04× 10-3 respectively. In the middle of ice season, the heat transfer coefficient has a larger value, which is about 0.5 × 10-3. Lastly, the influences of ice thickness and ice type on the heat transfer coefficient are discussed. With the heat transfer coefficient determined above, the oceanic heat flux in the winter of 1997～1998 is calculated, and its trend in the winter is analyzed. This study can be referenced in the sea ice numerical simulation and prediction in the Bohai Sea.
Tao JIN; Jian-ping HONG; Hao ZHENG; Ke TANG; Zhi-hua GAN
2009-01-01
Inverse heat conduction method (IHCM)is one of the most effective approaches to obtaining the boiling heat transfer coefficient from measured results.This paper focuses on its application in cryogenic boiling heat transfer.Experiments were conducted on the heattransfer of a stainless steel block in a liquid nitrogen bath.with the assumption of a ID conduction condition to realize fast acquisition of the temperature of the test points inside the block.With the inverse-heat conduction theory and the explicit finite difference model,a solving program was developed to calculate the heat flux and the boiling heat transfer coefficient of a stainless steel block in liquid nitrogen bath based on the temperature acquisition data.Considering the oscillating data and some unsmooth transition points in the inverse-heat-conduction calculation result of the heat-transfer coefficient,a two-step data-fitting procedure was proposed to obtain the expression for the boiling heat transfer coefficients.The coefficient was then verified for accuracy by a comparison between the simulation results using this expression and the verifying experimental results of a stainless steel block.The maximum error with a revised segment fitting iS around 6%.which verifies the feasibility of using IHCM to measure the boiling heat transfer coefficient in liquid nitrogen bath.
Estimation of bulk transfer coefficient for latent heat flux (Ce)
Sadhuram, Y.
specific humidity at sea surface tempera- ture, qn is the specific humidity at deck level, and U is the wind speed at the height of anemometer. All the available data in each area and along the boundaries are used to compute E. NFD and Ce. 3. Results...
Mass transfer coefficient of slug flow for organic solvent-aqueous system in a microreactor
Tuek, Ana Jurinjak; Anic, Iva; Kurtanjek, Zelimir; Zelic, Bruno [University of Zagreb, Zagreb (Croatia)
2015-06-15
Application of microreactor systems could be the next break-through in the intensification of chemical and biochemical processes. The common flow regime for organic solvent-aqueous phase two-phase systems is a segmented flow. Internal circulations in segments cause high mass transfer and conversion. We analyzed slug flow in seven systems of organic solvents and aqueous phase. To analyze how slug lengths in tested systems depend on linear velocity and physical and chemical properties of used organic solvents, regression models were proposed. It was shown that models based on linearization of approximation by potentials give low correlation for slug length prediction; however, application of an essential nonlinear model of multiple layer perception (MLP) neural network gives high correlation with R{sup 2}=0.9. General sensitivity analysis was applied for the MLP neural network model, which showed that 80% of variance in slug length for the both phases is accounted for the viscosity and density of the organic phases; 10% is accounted by surface tension of the organic phase, while molecular masses and flow rates each account for 5%. For defined geometry of microreactor, mass transfer has been determined by carrying out the neutralization experiment with NaOH where acetic acid diffuses from organic phase (hexane) into aqueous phase. Estimated mass transfer coefficients were in the range k{sub L}a=4,652-1,9807 h{sup -1}.
Mikielewicz Dariusz
2016-06-01
Full Text Available In the paper presented are the results of calculations using authors own model to predict heat transfer coefficient during flow boiling of carbon dioxide. The experimental data from various researches were collected. Calculations were conducted for a full range of quality variation and a wide range of mass velocity. The aim of the study was to test the sensitivity of the in-house model. The results show the importance of taking into account the surface tension as the parameter exhibiting its importance in case of the flow in minichannels as well as the influence of reduced pressure. The calculations were accomplished to test the sensitivity of the heat transfer model with respect to selection of the appropriate two-phase flow multiplier, which is one of the elements of the heat transfer model. For that purpose correlations due to Müller-Steinhagen and Heck as well as the one due to Friedel were considered. Obtained results show a good consistency with experimental results, however the selection of two-phase flow multiplier does not significantly influence the consistency of calculations.
Determining the surface roughness coefficient by 3D Scanner
Karmen Fifer Bizjak
2010-12-01
Full Text Available Currently, several test methods can be used in the laboratory to determine the roughness of rock joint surfaces.However, true roughness can be distorted and underestimated by the differences in the sampling interval of themeasurement methods. Thus, these measurement methods produce a dead zone and distorted roughness profiles.In this paper a new rock joint surface roughness measurement method is presented, with the use of a camera-typethree-dimensional (3D scanner as an alternative to current methods. For this study, the surfaces of ten samples oftuff were digitized by means of a 3D scanner, and the results were compared with the corresponding Rock JointCoefficient (JRC values. Up until now such 3D scanner have been mostly used in the automotive industry, whereastheir use for comparison with obtained JRC coefficient values in rock mechanics is presented here for the first time.The proposed new method is a faster, more precise and more accurate than other existing test methods, and is apromising technique for use in this area of study in the future.
姚玉换; 王良璧
2012-01-01
为了获得换热器肋侧换热系数定义用比较普适的特征温度,采用分区求解、边界耦合方法与非耦合方法对扁管翅片式换热器三雏模型的流动与传热性能进行了数值模拟,得到了换热器在不同肋片材料和不同雷诺数下用不同特征温度定义肋侧换热系数的区别,并将数值结果与实验结果进行比较.结果表明:当特征温度不同时,肋侧换热系数数值结果不同；当Re小于1000和用非耦合计算时,与实验值吻合最好的是以流动进出口平均温度为特征温度的数值结果；而Re大于1000后,耦合计算时以流动进出口平均温度为特征温度数值结果与实验值更靠近.%To obtain an appropriate characteristic temperature in the definition of the fin side surface heat transfer coefficient, flow and heat transfer characteristics of a flat tube bank fin heat exchanger are simulated by coupled and non-coupled numerical methods. Heat transfer coefficient of the fin side surface under different materials and Reynolds numbers is obtained. The numerical results obtained by two algorithms are compared with experimental data. It shows that the fin side surface heat transfer coefficient is different if the characteristic temperature is selected differently. The numerical result using the average temperature of the fin side fluid as the characteristic temperature agrees well with the experimental results when Re is less than 1 000 and the non-coupled method is adopted. The results are the same when Re is larger than 1 000 and the coupled method is used.
Karaś, Marcin; Zając, Daniel; Ulbrich, Roman
2014-03-01
This paper presents the results of studies in two phase gasliquid flow around tube bundle in the model of shell tube heat exchanger. Experimental investigations of heat transfer coefficient on the tubes surface were performed with the aid of electrochemical technique. Chilton-Colburn analogy between heat and mass transfer was used. Twelve nickel cathodes were mounted on the outside surface of one of the tubes. Measurement of limiting currents in the cathodic reduction of ferricyanide ions on nickel electrodes in aqueous solution of equimolar quantities of K3Fe(CN)6 and K4Fe(CN)6 in the presence of NaOH basic solution were applied to determine the mass transfer coefficient. Controlled diffusion from ions at the electrode was observed and limiting current plateau was measured. Measurements were performed with data acquisition equipment controlled by software created for this experiment. Mass transfer coefficient was calculated on the basis of the limiting current measurements. Results of mass transfer experiments (mass transfer coefficient) were recalculated to heat transfer coefficient. During the experiments, simultaneously conducted was the the investigation of two-phase flow structures around tubes with the use of digital particle image velocimetry. Average velocity fields around tubes were created with the use of a number of flow images and compared with the results of heat transfer coefficient calculations.
Karaś Marcin
2014-03-01
Full Text Available This paper presents the results of studies in two phase gasliquid flow around tube bundle in the model of shell tube heat exchanger. Experimental investigations of heat transfer coefficient on the tubes surface were performed with the aid of electrochemical technique. Chilton-Colburn analogy between heat and mass transfer was used. Twelve nickel cathodes were mounted on the outside surface of one of the tubes. Measurement of limiting currents in the cathodic reduction of ferricyanide ions on nickel electrodes in aqueous solution of equimolar quantities of K3Fe(CN6 and K4Fe(CN6 in the presence of NaOH basic solution were applied to determine the mass transfer coefficient. Controlled diffusion from ions at the electrode was observed and limiting current plateau was measured. Measurements were performed with data acquisition equipment controlled by software created for this experiment. Mass transfer coefficient was calculated on the basis of the limiting current measurements. Results of mass transfer experiments (mass transfer coefficient were recalculated to heat transfer coefficient. During the experiments, simultaneously conducted was the the investigation of two-phase flow structures around tubes with the use of digital particle image velocimetry. Average velocity fields around tubes were created with the use of a number of flow images and compared with the results of heat transfer coefficient calculations.
Estimating the workpiece-backingplate heat transfer coefficient in friction stirwelding
Larsen, Anders; Stolpe, Mathias; Hattel, Jesper Henri
2012-01-01
of the spatial distribution of the heat transfer coefficient are analysed and a simple, two parameter distribution is found to give good results. Originality/value - The heat transfer from workpiece to backingplate is important for the temperature field in the workpiece, and in turn the mechanical properties...
Toward Transfer Functions for Land Surface Phenologies
Henebry, G. M.
2010-12-01
A key problem in projecting future landscapes is simulating the associated land surface phenologies (or LSPs). A recent study of land surface models concluded that the representations of crop phenologies among the models diverged sufficiently to impede a useful intercomparison of simulation results from their associated climate models. Grassland phenologies are far more complicated than cropland phenologies due to multiple forcing factors, photosynthetic pathways (C3 vs C4), and spatial heterogeneities in both resource availabilities and land management practices. Furthermore, many tallgrass species (such as switchgrass) are widely distributed across temperature, but not moisture, gradients, resulting in significant ecotypic variation across the species' geographic range. Thus, how feasible is "transplanting" tallgrass LSPs across isotherms—but along isohyets—to simulate a shift in cultivation from maize-soy to switchgrass? Prior work has shown a quadratic model can provide a parsimonious link between a Normalized Difference Vegetation Index (or NDVI) time series and thermal time, measured in terms of accumulated growing degree-days (or AGDD). Moreover, the thermal time to peak NDVI (or TTP) is a simple function of the parameter coefficients of fitted model. I fitted quadratic models to MODIS NDVI and weather station data at multiple sites across the Northern Great Plains over ten growing seasons, 2000-2009. There is a strong latitudinal gradient in TTP that results in part from a quasi-linear gradient in accumulated daylight hours (or ADH) between 30 and 50 degrees north. However, AGDD improves upon ADH by providing sensitivity to the variability of growing season weather. In the quadratic parameter coefficients there is a geographic pattern apparent as a function of TTP, although it is more variable at shorter TTPs. Using these patterns, an LSP transfer function was implemented along a latitudinal transect to simulate switchgrass cultivation in areas now
Study on heat transfer coefficients during cooling of PET bottles for food beverages
Liga, Antonio; Montesanto, Salvatore; Mannella, Gianluca A.; La Carrubba, Vincenzo; Brucato, Valerio; Cammalleri, Marco
2016-08-01
The heat transfer properties of different cooling systems dealing with Poly-Ethylene-Terephthalate (PET) bottles were investigated. The heat transfer coefficient (Ug) was measured in various fluid dynamic conditions. Cooling media were either air or water. It was shown that heat transfer coefficients are strongly affected by fluid dynamics conditions, and range from 10 W/m2 K to nearly 400 W/m2 K. PET bottle thickness effect on Ug was shown to become relevant under faster fluid dynamics regimes.
VOLUMETRIC MASS TRANSFER COEFFICIENT BETWEEN SLAG AND METAL IN COMBINED BLOWING CONVERTER
Z.H. Wu; Z.S. Zou; W. Wu
2005-01-01
The effects of operation parameters of combined blowing converter on the volumetric mass transfer coefficient between slag and steel are studied with a cold model with water simulating steel, oil simulating slag and benzoic acid as the transferred substance between water and oil. The results show that, with lance level of 2.Im and the top blowing rate of 25000Nm3/h, the volumetric mass transfer coefficient changes most significantly when the bottom blowing rate ranges from 384 to 540Nm3/h. The volumetric mass transfer coefficient reaches its maximum when the lance level is 2. lm, the top blowing rates is 30000Nm3/h, and the bottom blowing rate is 384Nrr3/h with tuyeres located symmetrically at 0.66D of the converter bottom.
Indirect Measurement of Local Condensing Heat-Transfer Coefficient Around Horizontal Finned Tubes
1987-09-01
5.9 Effect of Tube Insulation on Sieder -Tate-Type Coefficient (C ) and Modified Coefficient (C.) for All Tubes •t Atmospheric Pressure...specific tube C Sleder-Tate-type coefficient in eqn. (4.2) C Modified Sieder -Tate-type coefficient in eqn. (5.2) D Tube diameter (m) D Equivalent diameter...an outside diameter equal to the fin root diameter). The Inside heat-transfer coefficent is given by a Sieder -Tate-type equation (4.2) and is
Condensation heat transfer on two-tier superhydrophobic surfaces
Cheng, Jiangtao; Vandadi, Aref; Chen, Chung-Lung
2012-09-01
We investigated water vapor condensation on a two-tier superhydrophobic surface in an environmental scanning electron microscope (ESEM) and in a customer-designed vapor chamber. We have observed continuous dropwise condensation (DWC) on the textured surface in ESEM. However, a film layer of condensate was formed on the multiscale texture in the vapor chamber. Due to the filmwise condensation, the condensation heat transfer coefficient of the superhydrophobic surface is lower than that of a flat hydrophobic surface especially under high heat flux situations. Our studies indicate that adaptive and prompt condensate droplet purging is the dominant factor for sustaining long-term DWC.
Experimental Investigation of Heat Transfer Coefficient in Vertical Tube Rising Film Evaporator
Syed Naveed Ul Hasan
2011-10-01
Full Text Available This paper reports the experimental evaluation of the heat transfer coefficient (U in a VRF (Vertical Tube Rising Film Evaporator. The aim is to describe the variation of U against different process parameters. Experiments were carried out for laminar flow conditions. The experimental unit is a floor standing tubular framework for a rising film evaporation system. There are many parameters affecting heat transfer coefficient in evaporators, but it was not possible to consider all of them, so parameters including, Reynolds Number (NRe, Temperature Difference (DT, Feed Temperature (Tf and Re-circulation Ratio (R were investigated while other factors were kept constant. The experimental results obtained showed that heat transfer coefficient increased with the increase in Reynolds number, feed temperature and temperature difference. The increase in re-circulation ratio also increased the heat transfer coefficient but up to the value of 0.85 and after this the heat transfer coefficient started decreasing slowly and then remained almost constant. An experimental correlation has been developed to relate the Nusselt number and the parameters investigated during the research work.
Purge and trap method to determine alpha factors of VOC liquid-phase mass transfer coefficients
无
2000-01-01
A theoretical approach and laboratory practice of determining the alpha factors of volatile organic compound (VOC) liquid-phase mass transfer coefficients are present in this study.Using Purge Trap Concentrator, VOC spiked water samples are purged by high-purity nitrogen in the laboratory, the VOC liquid-phase mass transfer rate constants under the laboratory conditions are then obtained by observing the variation of VOCs purged out of the water with the purge time.The alpha factors of VOC liquid-phase mass transfer coefficients are calculated as the ratios of the liquid-phase mass transfer rate constants in real water samples to their counterparts in pure water under the same experimental conditions. This direct and fast approach is easy to control in the laboratory, and would benefit mutual comparison among researchers, so might be useful for thestudy of VOC mass transfer across the liquid-gas interface.
Determination of heat transfer coefficients in plastic French straws plunged in liquid nitrogen.
Santos, M Victoria; Sansinena, M; Chirife, J; Zaritzky, N
2014-12-01
The knowledge of the thermodynamic process during the cooling of reproductive biological systems is important to assess and optimize the cryopreservation procedures. The time-temperature curve of a sample immersed in liquid nitrogen enables the calculation of cooling rates and helps to determine whether it is vitrified or undergoes phase change transition. When dealing with cryogenic liquids, the temperature difference between the solid and the sample is high enough to cause boiling of the liquid, and the sample can undergo different regimes such as film and/or nucleate pool boiling. In the present work, the surface heat transfer coefficients (h) for plastic French straws plunged in liquid nitrogen were determined using the measurement of time-temperature curves. When straws filled with ice were used the cooling curve showed an abrupt slope change which was attributed to the transition of film into nucleate pool boiling regime. The h value that fitted each stage of the cooling process was calculated using a numerical finite element program that solves the heat transfer partial differential equation under transient conditions. In the cooling process corresponding to film boiling regime, the h that best fitted experimental results was h=148.12±5.4 W/m(2) K and for nucleate-boiling h=1355±51 W/m(2) K. These values were further validated by predicting the time-temperature curve for French straws filled with a biological fluid system (bovine semen-extender) which undergoes freezing. Good agreement was obtained between the experimental and predicted temperature profiles, further confirming the accuracy of the h values previously determined for the ice-filled straw. These coefficients were corroborated using literature correlations. The determination of the boiling regimes that govern the cooling process when plunging straws in liquid nitrogen constitutes an important issue when trying to optimize cryopreservation procedures. Furthermore, this information can lead to
Bunyakan, C.
2002-04-01
Full Text Available Volatile organic compounds (VOCs have been found in wastewater of many chemical industries. Evaporation of VOCs from open water basin in waste treatment facilities causes air-pollution and has been regulated in many countries. Reduction or prevention of VOCs evaporation from open water basin is then necessary. The aim of this research was to investigate the influence of surface film generated by an insoluble surfactant on the mass transfer coefficient of VOCs evaporating from water. Hexadecanol and octadecanol were used as surfactant in this investigation with the amount in the range of 0 to 35 μg/cm2 and 0 to 25 μg/cm2, respectively. The VOCs used in this study were methanol, acetone, methyl ethyl ketone and toluene. The experimental results showed that the surfactant film can reduce the gas film and liquid coefficients by 56 and 80 %, respectively. The suitable amounts of the surfactant were 25 μg/cm2 for hexadecanol and 15 μg/cm2 for octadecanol. From this investigation we can conclude that covering the water surface with a film of hexadecanol or octadecanol could significantly reduce the VOCs evaporation rate.Finally, the empirical equations correlating gas film and liquid film coefficient to amount of surfactants were developed and verified against the experimental data. The predicted values of the overall mass transfer coefficients, obtained by using these empirical equations, were in good agreement with the measured values. Thus the empirical equations of mass transfer coefficients developed in this work can be used to predict the evaporation rates of VOCs from water surface covered by hexadecanol or octadecanol film.
Balla Hyder H.
2015-01-01
Full Text Available Cu and Zn-water nanofluid is a suspension of the Cu and Zn nanoparticles with the size 50 nm in the water base fluid for different volume fractions to enhance its Thermophysical properties. The determination and measuring the enhancement of Thermophysical properties depends on many limitations. Nanoparticles were suspended in a base fluid to prepare a nanofluid. A coated transient hot wire apparatus was calibrated after the building of the all systems. The vibro-viscometer was used to measure the dynamic viscosity. The measured dynamic viscosity and thermal conductivity with all parameters affected on the measurements such as base fluids thermal conductivity, volume factions, and the temperatures of the base fluid were used as input to the Artificial Neural Fuzzy inference system to modeling both dynamic viscosity and thermal conductivity of the nanofluids. Then, the ANFIS modeling equations were used to calculate the enhancement in heat transfer coefficient using CFD software. The heat transfer coefficient was determined for flowing flow in a circular pipe at constant heat flux. It was found that the thermal conductivity of the nanofluid was highly affected by the volume fraction of nanoparticles. A comparison of the thermal conductivity ratio for different volume fractions was undertaken. The heat transfer coefficient of nanofluid was found to be higher than its base fluid. Comparisons of convective heat transfer coefficients for Cu and Zn nanofluids with the other correlation for the nanofluids heat transfer enhancement are presented. Moreover, the flow demonstrates anomalous enhancement in heat transfer nanofluids.
Laser flash method for measurement of liquid metals heat transfer coefficients
Stankus, S. V.; Savchenko, I. V.
2009-12-01
New laser flash technique for the measurement of heat transfer coefficients of liquid metals is presented. The thermal diffusivity of the liquid mercury has been studied experimentally over the room temperature range. The thermal conductivity coefficient has been calculated with the use of the reference data on density and heat capacity. Analysis of systematic errors of the measurements has shown that the data error is about 3%. Comparison of the obtained results with data available in publications has proved their reliability.
Feyissa, Aberham Hailu; Christensen, Martin Gram; Pedersen, Søren Juhl
2015-01-01
This paper presents and demonstrates a novel idea of using spherical potatoes as a dispensable, cheap device for determining the fluid-to-particle heat transfer coefficient, hfp in vessel cooking processes. The transmission of heat through the potato can be traced by measuring the distance from...... the surface to the gelatinization front, which is easy to identify visually. Knowing this distance, the gelatinization temperature, the period of immersion, and the average radius of the potato, the heat transfer coefficient can be calculated. Either a numerical model based on the Finite Element Method (FEM......) or an analytical solution of the Fourier equation can be applied for the calculation. The gelatinization temperature of the potatoes used was determined to be 67°C by a direct temperature measurement and by visual inspection of the progression of the gelatinization front. A sensitivity analysis demonstrates...
Donne, M.D.; Piazza, G. [Forschungszentrum Karlsruhe GmbH Technik und Umwelt (Germany). Inst. fuer Neutronenphysik und Reaktortechnik; Goraieb, A.; Sordon, G.
1998-01-01
The four ITER partners propose to use binary beryllium pebble bed as neutron multiplier. Recently this solution has been adopted for the ITER blanket as well. In order to study the heat transfer in the blanket the effective thermal conductivity and the wall heat transfer coefficient of the bed have to be known. Therefore at Forschungszentrum Karlsruhe heat transfer experiments have been performed with a binary bed of beryllium pebbles and the results have been correlated expressing thermal conductivity and wall heat transfer coefficients as a function of temperature in the bed and of the difference between the thermal expansion of the bed and of that of the confinement walls. The comparison of the obtained correlations with the data available from the literature show a quite good agreement. (author)
Effect of Heat Transfer Coefficient on the Temperature Gradient for Hollow Fiber
王华平; 余晓蔚; 杨崇倡; 胡学超; 庄毅
2001-01-01
The heat transfer coefficient h caused by blowing affects the heat transfer of fiber greatly. Especially,unsymmetrical blowing forms the unsymmetrical temperature gradient on the fiber cross.section. Based on the results of spinning simulation by computer, the changes of heat transfer coefficient on the cross-section along the spinning line and the effects on distributions of temperature gradients were discussedl It is showed that for the spinning simulation of hollow fiber under strong blowing condition, the heat transfer coetticient should bemodified as: h=0.437×10-4[ G/Vρ ( R2/ R2-n2 ) ] -o.333(V2+ 64( VYsin (θ))2)0.167
Mihailovic, D. T.; Alapaty, K.; Lalic, B.; Arsenic, I.; Rajkovic, B.; Malinovic, S.
2004-10-01
A method for estimating profiles of turbulent transfer coefficients inside a vegetation canopy and their use in calculating the air temperature inside tall grass canopies in land surface schemes for environmental modeling is presented. The proposed method, based on K theory, is assessed using data measured in a maize canopy. The air temperature inside the canopy is determined diagnostically by a method based on detailed consideration of 1) calculations of turbulent fluxes, 2) the shape of the wind and turbulent transfer coefficient profiles, and 3) calculation of the aerodynamic resistances inside tall grass canopies. An expression for calculating the turbulent transfer coefficient inside sparse tall grass canopies is also suggested, including modification of the corresponding equation for the wind profile inside the canopy. The proposed calculations of K-theory parameters are tested using the Land Air Parameterization Scheme (LAPS). Model outputs of air temperature inside the canopy for 8 17 July 2002 are compared with micrometeorological measurements inside a sunflower field at the Rimski Sancevi experimental site (Serbia). To demonstrate how changes in the specification of canopy density affect the simulation of air temperature inside tall grass canopies and, thus, alter the growth of PBL height, numerical experiments are performed with LAPS coupled with a one-dimensional PBL model over a sunflower field. To examine how the turbulent transfer coefficient inside tall grass canopies over a large domain represents the influence of the underlying surface on the air layer above, sensitivity tests are performed using a coupled system consisting of the NCEP Nonhydrostatic Mesoscale Model and LAPS.
Drexel, Rober E; Mcadams, William H
1945-01-01
Report reviews published data and presents some new data on heat transfer to air flowing in round tubes, in rectangular ducts, and around finned cylinders. The available data for heat transfer to air in straight ducts of rectangular and circular cross section have been correlated in plots of Stanton number versus Reynolds number to provide a background for the study of the data for finned cylinders. Equations are recommended for both the streamlined and turbulent regions, and data are presented for the transition region between turbulent and laminar flow. Use of hexagonal ends on round tubes causes the characteristics of laminar flow to extend to high Reynolds numbers. Average coefficients for the entire finned cylinder have been calculated from the average temperature at the base of the fins and an equation which was derived to allow for the effectiveness of the fins. The available results for each finned cylinder are correlated herein in terms of graphs of Stanton number versus Reynolds number. In general, for a given Reynolds number, the Stanton number increases with increases in both spacing and width of the fins, and is apparently independent of cylinder diameter and temperature difference. For a given coefficient of heat transfer improved baffles and rough or wavy surfaces give a substantial reduction in pumping power per unit of heat transfer surface and a somewhat smaller decrease in pressure drop. (author)
Pecha, M. Brennan; Garcia-Perez, Manuel; Foust, Thomas D.; Ciesielski, Peter N.
2017-01-03
Direct numerical simulation of convective heat transfer from hot gas to isolated biomass particle models with realistic morphology and explicit microstructure was performed over a range of conditions with laminar flow of hot gas (500 degrees C). Steady-state results demonstrated that convective interfacial heat transfer is dependent on the wood species. The computed heat transfer coefficients were shown to vary between the pine and aspen models by nearly 20%. These differences are attributed to the species-specific variations in the exterior surface morphology of the biomass particles. We also quantify variations in heat transfer experienced by the particle when positioned in different orientations with respect to the direction of fluid flow. These results are compared to previously reported heat transfer coefficient correlations in the range of 0.1 < Pr < 1.5 and 10 < Re < 500. Comparison of these simulation results to correlations commonly used in the literature (Gunn, Ranz-Marshall, and Bird-Stewart-Lightfoot) shows that the Ranz-Marshall (sphere) correlation gave the closest h values to our steady-state simulations for both wood species, though no existing correlation was within 20% of both species at all conditions studied. In general, this work exemplifies the fact that all biomass feedstocks are not created equal, and that their species-specific characteristics must be appreciated in order to facilitate accurate simulations of conversion processes.
2008-01-01
Based on several hypotheses about the process of supercritical carbon dioxide extraction, the onflow around the solute granule is figured out by the Navier-Stocks equation. In combination with the Higbie’s solute infiltration model, the link be-tween the mass-transfer coefficient and the velocity of flow is found. The mass-transfer coefficient with the ultrasonical effect is compared with that without the ultrasonical effect, and then a new parameter named the ultrasonic-enhanced fac-tor of mass-transfer coefficient is brought forward, which describes the mathe-matical model of the supercritical carbon dioxide extraction process enhanced by ultrasonic. The model gives out the relationships among the ultrasonical power, the ultrasonical frequency, the radius of solute granule and the ultrasonic-enhanced factor of mass-transfer coefficient. The results calculated by this model fit well with the experimental data, including the extraction of Coix Lacryma-jobi Seed Oil (CLSO) and Coix Lacryma-jobi Seed Ester (CLSE) from coix seeds and the extrac-tion of Eicosapentaenoic Acid (EPA) and Docosahexaenoic Acid (DHA) from the alga by means of the ultrasonic-enhanced supercritical carbon dioxide extraction (USFE) and the supercritical carbon dioxide extraction (SFE) respectively. This proves the rationality of the ultrasonic-enhanced factor model. The model provides a theoretical basis for the application of ultrasonic-enhanced supercritical fluid extraction technique.
An empirical correlation of volumetric mass transfer coefficient was developed for a pilot scale internal-loop rectangular airlift bioreactor that was designed for biotechnology. The empirical correlation combines classic turbulence theory, Kolmogorov’s isotropic turbulence theory with Higbie’s pen...
Evaluation of convective heat transfer coefficient of various crops in cyclone type dryer
Akpinar, E. Kavak [Mechanical Engineering Department, Firat University, 23279 Elazig (Turkey)]. E-mail: eakpinar@firat.edu.tr
2005-09-15
In this paper, an attempt was made to evaluate the convective heat transfer coefficient during drying of various crops and to investigate the influences of drying air velocity and temperature on the convective heat transfer coefficient. Drying was conducted in a convective cyclone type dryer at drying air temperatures of 60, 70 and 80 deg. C and velocities of 1 and 1.5 m/s using rectangle shaped potato and apple slices (12.5 x 12.5 x 25 mm) and cylindrical shaped pumpkin slices (35 x 5 mm). The temperature changes of the dried crops and the temperature of the drying air were measured during the drying process. It was found that the values of convective heat transfer coefficient varied from crop to crop with a range 30.21406 and 20.65470 W/m{sup 2} C for the crops studied, and it was observed that the convective heat transfer coefficient increased in large amounts with the increase of the drying air velocity but increased in small amounts with the rise of the drying air temperature.
Y.K.Sklifus
2012-12-01
Full Text Available The article presents the calculation of heat transfer coefficient during condensation of steam, the mathematical model of temperature distribution in the gas and liquid phases of the coolant and the model of the formation of the condensate film on the walls of the tubes.
Modelling water evaporation during frying with an evaporation dependent heat transfer coefficient
Koerten, van K.N.; Somsen, D.; Boom, R.M.; Schutyser, M.A.I.
2017-01-01
In this study a cylindrical crust-core frying model was developed including an evaporation rate dependent heat transfer coefficient. For this, we applied a Nusselt relation for cylindrical bodies and view the release of vapour bubbles during the frying process as a reversed fluidised bed. The cha
Development of a model to determine mass transfer coefficient and oxygen solubility in bioreactors
Johnny Lee
2017-02-01
where T is in degree Kelvin, and the subscripts refer to degree Celsius; E, ρ, σ are properties of water. Furthermore, using data from published data on oxygen solubility in water, it was found that solubility bears a linear and inverse relationship with the mass transfer coefficient.
SUI Da-shan; CUI Zhen-shan
2008-01-01
The interfacial heat transfer coefficient(IHTC) between the casting and the mould is essential to the numerical simulation as one of boundary conditions. A new inverse method was presented according to the Tikhonov regularization theory. A regularized functional was established and the regularization parameter was deduced. The functional was solved to determine the interfacial heat transfer coefficient by using the sensitivity coefficient and Newton-Raphson iteration method. The temperature measurement experiment was done to ZL102 sand mold casting, and the appropriate mathematical model of the IHTC was established. Moreover, the regularization method was used to determinate the IHTC. The results indicate that the regularization method is very efficient in overcoming the ill-posedness of the inverse heat conduction problem(IHCP), and ensuring the accuracy and stability of the solutions.
Yang, H. Q.; West, Jeff
2015-01-01
Current reduced-order thermal model for cryogenic propellant tanks is based on correlations built for flat plates collected in the 1950's. The use of these correlations suffers from: inaccurate geometry representation; inaccurate gravity orientation; ambiguous length scale; and lack of detailed validation. The work presented under this task uses the first-principles based Computational Fluid Dynamics (CFD) technique to compute heat transfer from tank wall to the cryogenic fluids, and extracts and correlates the equivalent heat transfer coefficient to support reduced-order thermal model. The CFD tool was first validated against available experimental data and commonly used correlations for natural convection along a vertically heated wall. Good agreements between the present prediction and experimental data have been found for flows in laminar as well turbulent regimes. The convective heat transfer between tank wall and cryogenic propellant, and that between tank wall and ullage gas were then simulated. The results showed that commonly used heat transfer correlations for either vertical or horizontal plate over predict heat transfer rate for the cryogenic tank, in some cases by as much as one order of magnitude. A characteristic length scale has been defined that can correlate all heat transfer coefficients for different fill levels into a single curve. This curve can be used for the reduced-order heat transfer model analysis.
Opitz, Armin W; Czymmek, Kirk J; Wickstrom, Eric; Wagner, Norman J
2013-02-01
Targeted delivery of imaging agents to cells can be optimized with the understanding of uptake and efflux rates. Cellular uptake of macromolecules is studied frequently with fluorescent probes. We hypothesized that the internalization and efflux of fluorescently labeled macromolecules into and out of mammalian cells could be quantified by confocal microscopy to determine the rate of uptake and efflux, from which the mass transfer coefficient is calculated. The cellular influx and efflux of a third generation poly(amido amine) (PAMAM) dendrimer labeled with an Alexa Fluor 555 dye was measured in Capan-1 pancreatic cancer cells using confocal fluorescence microscopy. The Capan-1 cells were also labeled with 5-chloromethylfluorescein diacetate (CMFDA) green cell tracker dye to delineate cellular boundaries. A dilution curve of the fluorescently labeled PAMAM dendrimer enabled quantification of the concentration of dendrimer in the cell. A simple mass transfer model described the uptake and efflux behavior of the PAMAM dendrimer. The effective mass transfer coefficient was found to be 0.054±0.043μm/min, which corresponds to a rate constant of 0.035±0.023min(-1) for uptake of the PAMAM dendrimer into the Capan-1 cells. The effective mass transfer coefficient was shown to predict the efflux behavior of the PAMAM dendrimer from the cell if the fraction of labeled dendrimer undergoing non-specific binding is accounted for. This work introduces a novel method to quantify the mass transfer behavior of fluorescently labeled macromolecules into mammalian cells.
Calculating the heat transfer coefficient of frame profiles with internal cavities
Noyé, Peter Anders; Laustsen, Jacob Birck; Svendsen, Svend
2004-01-01
or by measurements in accordance to European or international standards. Comparing measured and calculated heat transfer coefficients for two typical frame profiles with cavities shows considerable differences. This investigation considers two typical frame profiles in aluminium and PVC with internal cavities....... The heat transfer coefficient is determined by two-dimensional numerical calculations and by measurements. Calculations are performed in Therm (LBNL (2001)), which is developed at Lawrence Berkeley National Laboratory, USA. The calculations are performed in accordance with the future European standards...... and measurements have been performed at two German research institutes. The internal cavities have a large influence on the overall thermal performance of the frame profiles and the investigation shows that the applied method for modelling the heat transfer by radiation exchange in the internal cavities...
Selgas, R; Carmona, A R; Martinez, M E; Perez-Fontan, M; Salinas, M; Conesa, J; Martinez Ara, J; Sicilia, L S
1985-07-01
The transport of solutes across the peritoneum may be increased by the topical administration of nitroprusside; the effects of the drug seem to be due to an increase in the number of perfused capillaries and/or in their permeability. We have compared the peritoneal mass transfer coefficients (MTC) for urea, creatinine and parathormone (PTH) under basal conditions and after administration of nitroprusside (4.5 mg/l dialysate) in 15 patients under CAPD therapy. The mean increments of the MTC were 48.8% for urea, 77.5% for creatinine and 323% for PTH. The relative MTC increments for the three molecules (taken in pairs) were: MTCPTH/urea' 2.53 times (mean), MTCPTH/creatinine' 1.7 times, and MTCcreatinine/urea' 0.73-times, with very variable ranges. The overall mean increment (OMI) for all three ratios ranged from -1.25 and +6 times. In six patients, some of the relative increments (and in three of them the OMI) were negative but the epidemiological features of these patients revealed no clear data. The OMI shows a direct correlation with the body surface area and an inverse correlation with the the duration of CAPD and ESRD and with the number of peritonitis episodes, albeit without statistical significance. We conclude that the peritoneal vascular reserve has individual characteristics, and that perhaps the OMI or some other similar index might serve to quantify and characterise it, if our findings are confirmed.
Determination of drying kinetics and convective heat transfer coefficients of ginger slices
Akpinar, Ebru Kavak; Toraman, Seda
2016-10-01
In the present work, the effects of some parametric values on convective heat transfer coefficients and the thin layer drying process of ginger slices were investigated. Drying was done in the laboratory by using cyclone type convective dryer. The drying air temperature was varied as 40, 50, 60 and 70 °C and the air velocity is 0.8, 1.5 and 3 m/s. All drying experiments had only falling rate period. The drying data were fitted to the twelve mathematical models and performance of these models was investigated by comparing the determination of coefficient ( R 2), reduced Chi-square ( χ 2) and root mean square error between the observed and predicted moisture ratios. The effective moisture diffusivity and activation energy were calculated using an infinite series solution of Fick's diffusion equation. The average effective moisture diffusivity values and activation energy values varied from 2.807 × 10-10 to 6.977 × 10-10 m2/s and 19.313-22.722 kJ/mol over the drying air temperature and velocity range, respectively. Experimental data was used to evaluate the values of constants in Nusselt number expression by using linear regression analysis and consequently, convective heat transfer coefficients were determined in forced convection mode. Convective heat transfer coefficient of ginger slices showed changes in ranges 0.33-2.11 W/m2 °C.
Determination of the heat transfer coefficient from IRT measurement data using the Trefftz method
Maciejewska Beata
2016-01-01
Full Text Available The paper presents the method of heat transfer coefficient determination for boiling research during FC-72 flow in the minichannels, each 1.7 mm deep, 24 mm wide and 360 mm long. The heating element was the thin foil, enhanced on the side which comes into contact with fluid in the minichannels. Local values of the heat transfer coefficient were calculated from the Robin boundary condition. The foil temperature distribution and the derivative of the foil temperature were obtained by solving the two-dimensional inverse heat conduction problem, due to measurements obtained by IRT. Calculations was carried out by the method based on the approximation of the solution of the problem using a linear combination of Trefftz functions. The basic property of this functions is they satisfy the governing equation. Unknown coefficients of linear combination of Trefftz functions are calculated from the minimization of the functional that expresses the mean square error of the approximate solution on the boundary. The results presented as IR thermographs, two-phase flow structure images and the heat transfer coefficient as a function of the distance from the channel inlet, were analyzed.
A Rahmatnezamabad
2014-11-01
Full Text Available In this paper photonic band gaps of 1D photonic crystal are compared by using transfer matrix method and Fresnel coefficients method. In Fresnel coefficients method, the refractive indices of each layer and incidence light angle to the surface are used for calculating Fresnel coefficients, and then the necessary and sufficient condition for a 100% reflection from the surface of double layer dielectrics is applied in such a way that reflection coefficient tends to unity so that photonic band gaps are determined. But in transfer matrix method there are some complications needed for solving quadratic partial differential equations and applying continuity of tangent components of fields and Bloch’s condition, though the results are the same
Maciejewska, Beata; Piasecka, Magdalena
2016-08-01
The paper presents an application of the semi-analytical method, called the non-continuous Trefftz method, to the calculation of the heat transfer coefficients. It is very effective method for solving direct and inverse problems. The results obtained by this method are consistent with the results obtained by using complicated methods: the FEM and Beck method. Sought local heat transfer coefficients between the heating surface and the boiling liquid flowing through 1 mm deep minichannel were calculated from the Robin boundary condition. The temperature of the heating surface and the derivative of the temperature were was found from solving the inverse problem. The study is limited to the identification of the heat transfer coefficient in the subcooled and the saturated nucleate boiling regions. The article presents also the measurement stand and methodology of conducting the experiment. Presented issues allows verification of state-of-the-art methods of solving the inverse problem by using the authors' empirical data from the experiment.
On the reliable estimation of heat transfer coefficients for nanofluids in a microchannel
Irwansyah, Ridho; Cierpka, Christian; Kähler, Christian J.
2016-09-01
Nanofluids (base fluid and nanoparticles) can enhance the heat transfer coefficient h in comparison to the base fluid. This open the door for the design of efficient cooling system for microelectronics component for instance. Since theoretical Nusselt number correlations for microchannels are not available, the direct method using an energy balance has to be applied to determine h. However, for low nanoparticle concentrations the absolute numbers are small and hard to measure. Therefore, the study examines the laminar convective heat transfer of Al2O3-water nanofluids in a square microchannel with a cross section of 0.5 × 0.5 mm2 and a length of 30 mm under constant wall temperature. The Al2O3 nanoparticles have a diameter size distribution of 30-60 nm. A sensitivity analysis with error propagation was done to reduce the error for a reliable heat transfer coefficient estimation. An enhancement of heat transfer coefficient with increasing nanoparticles volume concentration was confirmed. A maximum enhancement of 6.9% and 21% were realized for 0.6% Al2O3-water and 1% Al2O3-water nanofluids.
Enhancement of solubility and mass transfer coefficient of salicylic acid through hydrotropy
S.THENESHKUMAR; D.GNANAPRAKASH; N.NAGENDRA GANDHI
2009-01-01
This study deals with the effect of hydrotropes on the solubility and mass transfer coefficient of salicylic acid.The solubility and mass transfer studies were performed using the hydrotropes,i.e.,sodium acetate,sodium salicylate,citric acid,and urea at concentrations of 0～3.0 mol/L and system temperatures of 303-333 K.It was found that the solubility and mass transfer coefficient of salicylic acid increases with increase in hydrotrope concentration and also with system temperature.All hydrotropes used in this work showed an enhancement in solubility and mass transfer coefficient to difierent degrees.The maximum enhancement factor values were determined for all hydrotropes used in this study.The highest value was 28.08 for solubility studies and 10.42 for mass trailsfer studies.The performance of hydrotropes Was measured in terms of the Setschenow constant(Ks).The highest value observed was 0.696.
Guo Zerong
2016-01-01
Full Text Available To study the effect of variable heat transfer coefficient of fireworks and crackers on thermal explosion critical ambient temperature and time to ignition, considering the heat transfer coefficient as the power function of temperature, mathematical thermal explosion steady state and unsteady-state model of finite cylindrical fireworks and crackers with complex shell structures are established based on two-dimensional steady state thermal explosion theory. The influence of variable heat transfer coefficient on thermal explosion critical ambient temperature and time to ignition are analyzed. When heat transfer coefficient is changing with temperature and in the condition of natural convection heat transfer, critical ambient temperature lessen, thermal explosion time to ignition shorten. If ambient temperature is close to critical ambient temperature, the influence of variable heat transfer coefficient on time to ignition become large. For firework with inner barrel in example analysis, the critical ambient temperature of propellant is 463.88 K and the time to ignition is 4054.9s at 466 K, 0.26 K and 450.8s less than without considering the change of heat transfer coefficient respectively. The calculation results show that the influence of variable heat transfer coefficient on thermal explosion time to ignition is greater in this example. Therefore, the effect of variable heat transfer coefficient should be considered into thermal safety evaluation of fireworks to reduce potential safety hazard.
Raseelo J. Moitsheki
2008-01-01
Full Text Available Lie point symmetry analysis is performed for an unsteady nonlinear heat diffusion problem modeling thermal energy storage in a medium with a temperature-dependent power law thermal conductivity and subjected to a convective heat transfer to the surrounding environment at the boundary through a variable heat transfer coefficient. Large symmetry groups are admitted even for special choices of the constants appearing in the governing equation. We construct one-dimensional optimal systems for the admitted Lie algebras. Following symmetry reductions, we construct invariant solutions.
Seyed Ali Aghayan
2013-01-01
Full Text Available A novel scheme to obtain the optimum tissue heating condition during hyperthermia treatment is proposed. To do this, the effect of the controllable overall heat transfer coefficient of the cooling system is investigated. An inverse problem by a conjugated gradient with adjoint equation is used in our model. We apply the finite difference time domain method to numerically solve the tissue temperature distribution using Pennes bioheat transfer equation. In order to provide a quantitative measurement of errors, convergence history of the method and root mean square of errors are also calculated. The effects of heat convection coefficient of water and thermal conductivity of casing layer on the control parameter are also discussed separately.
Henningsen, Poul; Hattel, Jesper Henri; Wanheim, Tarras
1998-01-01
. The thermocouples are welded to the end of grooves milled in a small plug, which is pressed into a hold in the punch nose. All the temperature measurements in the tool and the workpiece are compared with a number of finite element (FE) simulations computed with different heat transfer coefficients. The current heat...... transfer coefficient (HTC) is then determined by the least square method...
Numerical prediction of nucleate pool boiling heat transfer coefficient under high heat fluxes
Pezo Milada L.; Stevanović Vladimir D.
2016-01-01
This paper presents CFD (Computational Fluid Dynamics) approach to prediction of the heat transfer coefficient for nucleate pool boiling under high heat fluxes. Three-dimensional numerical simulations of the atmospheric saturated pool boiling are performed. Mathematical modelling of pool boiling requires a treatment of vapor-liquid two-phase mixture on the macro level, as well as on the micro level, such as bubble growth and departure from the heating surfa...
Determination of the mass-transfer coefficient in liquid phase in a stream-bubble contact device
Dmitriev, A. V.; Dmitrieva, O. S.; Madyshev, I. N.
2016-09-01
One of the most effective energy saving technologies is the improvement of existing heat and mass exchange units. A stream-bubble contact device is designed to enhance the operation efficiency of heat and mass exchange units. The stages of the stream-bubble units that are proposed by the authors for the decarbonization process comprise contact devices with equivalent sizes, whose number is determined by the required performance of a unit. This approach to the structural design eliminates the problems that arise upon the transition from laboratory samples to industrial facilities and makes it possible to design the units of any required performance without a decrease in the effectiveness of mass exchange. To choose the optimal design that provides the maximum effectiveness of the mass-exchange processes in units and their intensification, the change of the mass-transfer coefficient is analyzed with the assumption of a number of parameters. The results of the study of the effect of various structural parameters of a stream-bubble contact device on the mass-transfer coefficient in the liquid phase are given. It is proven that the mass-transfer coefficient increases in the liquid phase, in the first place, with the growth of the level of liquid in the contact element, because the rate of the liquid run-off grows in this case and, consequently, the time of surface renewal is reduced; in the second place, with an increase in the slot diameter in the downpipe, because the jet diameter and, accordingly, their section perimeter and the area of the surface that is immersed in liquid increase; and, in the third place, with an increase in the number of slots in the downpipe, because the area of the surface that is immersed in the liquid of the contact element increases. Thus, in order to increase the mass-transfer coefficient in the liquid phase, it is necessary to design the contact elements with a minimum width and a large number of slots and their increased diameter; in
Development and calibration of heat transfer coefficient sensor for rotational state
QUAN Yong-kai; XU Guo-qiang; LUO Xiang; ZHANG Da
2011-01-01
A novel heat transfer coefficient sensor is introduced and the design,manufacture,and calibration are described.The intended application of this instrument was on a high rotational speed test disc.In the experiments,the heat transfer coefficient sensor was calibrated under static state and rotational state respectively.The calibration under the static state was accomplished in a pipe： the inside diameter（ID） was 0.048m and the total length was 4m,the distance between the sensor and the inlet of the pipe was 3.5m;the standard value was measured using a self-made calibrator.The calibration under the rotational state was accomplished using a rotating disc： the diameter and thickness of the stainless disc were 800mm and 25mm,respectively;the sensor was installed at the location of r=250mm;the rotating disc driven by a 30kW direct current motor can supply the maximum rotational speed of 3000r/min.The standard value under rotational state was provided by an approximate empirical formula.The results show that the designed sensor can measure heat transfer coefficient directly under rotational state and static state with good accuracy and stability;the correlation factor of K are constant under static state and rotational state.
Lüpkes, Christof; Gryanik, Vladimir M.
2015-01-01
The interaction between sea ice and atmosphere depends strongly on the near-surface transfer coefficients for momentum and heat. A parametrization of these coefficients is developed on the basis of an existing parametrization of drag coefficients for neutral stratification that accounts for form drag caused by the edges of ice floes and melt ponds. This scheme is extended to better account for the dependence of surface wind on limiting cases of high and low ice concentration and to include near-surface stability effects over open water and ice on form drag. The stability correction is formulated on the basis of stability functions from Monin-Obukhov similarity theory and also using the Louis concept with stability functions depending on the bulk Richardson numbers. Furthermore, a parametrization is proposed that includes the effect of edge-related turbulence also on heat transfer coefficients. The parametrizations are available in different levels of complexity. The lowest level only needs sea ice concentration and surface temperature as input, while the more complex level needs additional sea ice characteristics. An important property of our parametrization is that form drag caused by ice edges depends on the stability over both ice and water which is in contrast to the skin drag over ice. Results of the parametrization show that stability has a large impact on form drag and, thereby, determines the value of sea ice concentration for which the transfer coefficients reach their maxima. Depending on the stratification, these maxima can occur anywhere between ice concentrations of 20 and 80%.
Koetsier, W.T.; Thoenes, D.
1973-01-01
The liquid phase mass transfer coefficient kL for the absorption of oxygen in tap water and in ionic solutions has been calculated from the quotien It is concluded that the liquid phase mass transfer coefficient is roughly proportional to the stirrer speed. The gas fraction e apparently has little
Analytical Study on Impingement Heat Transfer with Single—Phase Free—Surface Circular Liquid Jets
C.F.Ma; T.Masuoka; 等
1996-01-01
An analytical research was conducted to study heat transfer from horizontal surfaces to normally impinging circular jets under arbitrary-heat-flux conditions.The laminar thermal and hydraulic bound ary layers were divided into five regions of flow.General expressions of heat transfer coefficients were obtained in all the four regions of stagnation and wall jet zones before the hydraulic jump.
Amarante, A.; Lanoiselle, J.L.; Ramirez, A.
2003-10-01
Heat exchange is often complex to assess in freezing equipment. Either the extensive calculation procedures based on product time-temperature data, or the lack of accurate thermophysical properties, or even the non-uniform processing conditions in industrial equipment, results in increased difficulty in calculating accurate heat exchange parameters. The present study aims to solve this kind of problem by introducing the use of heat flux sensors (or fluxmeters) for an online measurement of heat exchange parameters during freezing processes. Since food products often have irregular, moist and greasy surfaces, bad attachment of the sensors can lead to low accuracy in heat flux measurement. First, a technique was improved in this particular and a numerical procedure based on matching the experimental and simulated temperature histories was used to calibrate the sensors attached to Tylose gels submitted to freezing and thawing cycles. Following this, the sensors were applied directly to a vegetable product undergoing freezing in a static freezer to measure the instantaneous product heat release rate and the local heat transfer coefficient. A fluxmeter-plastic transducer was also developed and used, coupled to an anemometer to map axially and transversally the local effective heat transfer coefficient and air speed profiles in a Super-Contact freezing tunnel. Results were compared with numerical simulations and showed good agreement. Irregular air speed distribution and low efficiency heat transfer zones were accurately detected, providing information for equipment optimization. (author)
Mass transfer coefficient in ginger oil extraction by microwave hydrotropic solution
Handayani, Dwi; Ikhsan, Diyono; Yulianto, Mohamad Endy; Dwisukma, Mandy Ayulia
2015-12-01
This research aims to obtain mass transfer coefficient data on the extraction of ginger oil using microwave hydrotropic solvent as an alternative to increase zingiberene. The innovation of this study is extraction with microwave heater and hydrotropic solvent,which able to shift the phase equilibrium, and the increasing rate of the extraction process and to improve the content of ginger oil zingiberene. The experiment was conducted at the Laboratory of Separation Techniques at Chemical Engineering Department of Diponegoro University. The research activities carried out in two stages, namely experimental and modeling work. Preparation of the model postulated, then lowered to obtain equations that were tested and validated using data obtained from experimental. Measurement of experimental data was performed using microwave power (300 W), extraction temperature of 90 ° C and the independent variable, i.e.: type of hydrotropic, the volume of solvent and concentration in order, to obtain zingiberen levels as a function of time. Measured data was used as a tool to validate the postulation, in order to obtain validation of models and empirical equations. The results showed that the mass transfer coefficient (Kla) on zingiberene mass transfer models ginger oil extraction at various hydrotropic solution attained more 14 ± 2 Kla value than its reported on the extraction with electric heating. The larger value of Kla, the faster rate of mass transfer on the extraction process. To obtain the same yields, the microwave-assisted extraction required one twelfth time shorter.
The influence of a heat transfer coefficient probe on fluid flow near wall
Mareš Martin
2012-04-01
Full Text Available Good knowledge of the convective boundary condition is necessary for finite element analysis of thermal deformation behavior in machine tools. There are a number of correlation equations for natural and forced convection and several correlations for mixed convection. Due to a relatively wide range of dimensions, temperatures and speeds, all regimes of convective heat transfer can be observed in machine tools, including the transition region between laminar and turbulent free convection, characterized by Rayleigh number values ranging between Ra = 108 – 109. Since convection in machine tools is highly influenced by external and internal factors, the heat transfer coefficient characterizing convective heat transfer and its changes has to be evaluated experimentally. An experimental technique for evaluating the heat transfer coefficient on the wall and its changes between the wall and the ambient air, based on an active sensor, is being developed. Since the probe dimensions are not negligible, given the fluid motion structures near the wall which are induced by buoyancy or by forced flow, the influence of the probe has to be considered. Paper deals with latest experimental results and summarizes previous work.
Mobile, Michael; Widdowson, Mark; Stewart, Lloyd; Nyman, Jennifer; Deeb, Rula; Kavanaugh, Michael; Mercer, James; Gallagher, Daniel
2016-04-01
Better estimates of non-aqueous phase liquid (NAPL) mass, its persistence into the future, and the potential impact of source reduction are critical needs for determining the optimal path to clean up sites impacted by NAPLs. One impediment to constraining time estimates of source depletion is the uncertainty in the rate of mass transfer between NAPLs and groundwater. In this study, an innovative field test is demonstrated for the purpose of quantifying field-scale NAPL mass transfer coefficients (kl(N)) within a source zone of a fuel-contaminated site. Initial evaluation of the test concept using a numerical model revealed that the aqueous phase concentration response to the injection of clean groundwater within a source zone was a function of NAPL mass transfer. Under rate limited conditions, NAPL dissolution together with the injection flow rate and the radial distance to monitoring points directly controlled time of travel. Concentration responses observed in the field test were consistent with the hypothetical model results allowing field-scale NAPL mass transfer coefficients to be quantified. Site models for groundwater flow and solute transport were systematically calibrated and utilized for data analysis. Results show kl(N) for benzene varied from 0.022 to 0.60d(-1). Variability in results was attributed to a highly heterogeneous horizon consisting of layered media of varying physical properties.
Mobile, Michael; Widdowson, Mark; Stewart, Lloyd; Nyman, Jennifer; Deeb, Rula; Kavanaugh, Michael; Mercer, James; Gallagher, Daniel
2016-04-01
Better estimates of non-aqueous phase liquid (NAPL) mass, its persistence into the future, and the potential impact of source reduction are critical needs for determining the optimal path to clean up sites impacted by NAPLs. One impediment to constraining time estimates of source depletion is the uncertainty in the rate of mass transfer between NAPLs and groundwater. In this study, an innovative field test is demonstrated for the purpose of quantifying field-scale NAPL mass transfer coefficients (klN) within a source zone of a fuel-contaminated site. Initial evaluation of the test concept using a numerical model revealed that the aqueous phase concentration response to the injection of clean groundwater within a source zone was a function of NAPL mass transfer. Under rate limited conditions, NAPL dissolution together with the injection flow rate and the radial distance to monitoring points directly controlled time of travel. Concentration responses observed in the field test were consistent with the hypothetical model results allowing field-scale NAPL mass transfer coefficients to be quantified. Site models for groundwater flow and solute transport were systematically calibrated and utilized for data analysis. Results show klN for benzene varied from 0.022 to 0.60 d- 1. Variability in results was attributed to a highly heterogeneous horizon consisting of layered media of varying physical properties.
Heat Transfer in Bubble Columns with High Viscous and Low Surface Tension Media
Kim, Wan Tae; Lim, Dae Ho; Kang, Yong [Chungnam National University, Daejeon (Korea, Republic of)
2014-08-15
Axial and overall heat transfer coefficients were investigated in a bubble column with relatively high viscous and low surface tension media. Effects of superficial gas velocity (0.02-0.1 m/s), liquid viscosity (0.1-3 Pa·s) and surface tension (66.1-72.9x10{sup -3} N/m) on the local and overall heat transfer coefficients were examined. The heat transfer field was composed of the immersed heater and the bubble column; a vertical heater was installed at the center of the column coaxially. The heat transfer coefficient was determined by measuring the temperature differences continuously between the heater surface and the column which was bubbling in a given operating condition, with the knowledge of heat supply to the heater. The local heat transfer coefficient increased with increasing superficial gas velocity but decreased with increasing axial distance from the gas distributor and liquid surface tension. The overall heat transfer coefficient increased with increasing superficial gas velocity but decreased with increasing liquid viscosity or surface tension. The overall heat transfer coefficient was well correlated in terms of operating variables such as superficial gas velocity, liquid surface tension and liquid viscosity with a correlation coefficient of 0.91, and in terms of dimensionless groups such as Nusselt, Reynolds, Prandtl and Weber numbers with a correlation of 0.92; h=2502U{sub G}{sup 0.236}{sub L}{sup -0.250}{sub L}{sup -}0{sup .028} Nu=3.25Re{sup 0.180}Pr{sup -0.067}We{sup 0.028}.
Fast liquid transfer between two surfaces
Chen, Huanchen; Tang, Tian; Amirfazli, Alidad
2014-11-01
Liquid transfer process between two surfaces typically ends by breaking of a stretched liquid bridge. The amount of liquid remaining on each of the surfaces relative to total volume is usually of interest in applications (e.g. offset or electronic printing, wet adhesion systems, etc.). Literature shows that depending on stretching velocity, U, surface wettability and liquid properties, the behaviour of the liquid bridge can be categorized into: quasi-static where the surface force dominates and dynamic where contributions from viscous and inertia forces are not negligible. Through a systematic experimental study, we demonstrate for the first time that the division of liquid between surfaces in the quasi-static regime is a constant which depends on the receding contact angles. In the dynamic regime (fast transfer), liquid division takes a complicated form. An analytical-empirical model is developed and verified by experimental results that can predict splitting of the liquid between two surfaces as a function of U, surface wettability and liquid viscosity. The model also successfully predicts an even split between surfaces at extremely high velocities as it was observed by us and others.
Er. Shivesh Kumar
2016-09-01
Full Text Available Since centuries steam is being used in power generating system. The steam leaving the power unit is reconverted into water in a condenser designed to transfer heat from the steam to the cooling water as rapidly and as efficiently as possible. The efficiency of condenser depends on rate of condensation and mode of condensation of steam in the condenser. The increase in efficiency of the condenser enhances the heat transfer co-efficient which in turn results in economic design of condenser and reduced pumping power for a desired output. Higher heat transfer coefficient in condensers is beneficial in the industrial applications e.g., Sugar industry, ships propulsion, nuclear power reactor, power generating system, production of Liquefied petroleum gases, liquid nitrogen and liquid oxygen. In the present experimental study, comparison of heat transfer coefficients of silver coated and chromium coated copper tubes of condenser have been performed. it has been observed that inside heat transfer coefficient (hᵢ, outside heat transfer coefficient (h₀ and overall heat transfer coefficient (U associated with silver coated condenser made of copper is more than that of chromium coated condenser made of copper. It is also observed that all the three types of heat transfer coefficient increases with increase of steam pressure [1].
Heat Transfer in a Liquid-Solid Circulating Fluidized Bed Reactor with Low Surface Tension Media
HR Jin; H Lim; DH Lim; Y Kang; Ki-Won Jun
2013-01-01
Heat transfer characteristics between the immersed heater and the bed content were studied in the riser of a liquid-solid circulating fluidized bed, whose diameter and height were 0.102 m (ID) and 2.5 m, respectively. Effects of liquid velocity, particle size, surface tension of liquid phase and solid circulation rate on the overall heat transfer coefficient were examined. The heat transfer coefficient increased with increasing particle size or solid cir-culation rate due to the higher potential of particles to contact with the heater surface and promote turbulence near the heater surface. The value of heat transfer coefficient increased gradually with increase in the surface tension of liquid phase, due to the slight increase of solid holdup. The heat transfer coefficient increased with the liquid veloc-ity even in the higher range, due to the solid circulation prevented the decrease in solid holdup, in contrast to that in the conventional liquid-solid fluidized beds. The values of heat transfer coefficient were well correlated in terms of dimensionless groups as well as operating variables.
EMILA ŽIVKOVIĆ
2009-04-01
Full Text Available The evaporation heat transfer coefficient of the refrigerant R-134a in a vertical plate heat exchanger was investigated experimentally. The area of the plate was divided into several segments along the vertical axis. For each of the segments, the local value of the heat transfer coefficient was calculated and presented as a function of the mean vapor quality in the segment. Owing to the thermocouples installed along the plate surface, it was possible to determine the temperature distribution and vapor quality profile inside the plate. The influences of the mass flux, heat flux, pressure of system and the flow configuration on the heat transfer coefficient were also taken into account and a comparison with literature data was performed.
Enhanced convective and film boiling heat transfer by surface gas injection
Duignan, M.R.; Greene, G.A. (Brookhaven National Lab., Upton, NY (United States)); Irvine, T.F., Jr. (State Univ. of New York, Stony Brook, NY (United States). Dept. of Mechanical Engineering)
1992-04-01
Heat transfer measurements were made for stable film boiling of water over a horizontal, flat stainless steel plate from the minimum film boiling point temperature, T{sub SURFACE} {approximately}500K, to T{sub SURFACE} {approximately}950K. The pressure at the plate was approximately 1 atmosphere and the temperature of the water pool was maintained at saturation. The data were compared to the Berenson film-boiling model, which was developed for minimum film-boiling-point conditions. The model accurately represented the data near the minimum film-boiling point and at the highest temperatures measured, as long it was corrected for the heat transferred by radiation. On the average, the experimental data lay within {plus minus}7% of the model. Measurements of heat transfer were made without film boiling for nitrogen jetting into an overlying pool of water from nine 1-mm- diameter holes, drilled in the heat transfer plate. The heat flux was maintained constant at approximately 26.4 kW/m{sup 2}. For water-pool heights of less than 6cm the heat transfer coefficient deceased linearly with a decrease in heights. Above 6cm the heat transfer coefficient was unaffected. For the entire range of gas velocities measured (0 to 8.5 cm/s), the magnitude of the magnitude of the heat transfer coefficient only changed by approximately 20%. The heat transfer data bound the Konsetov model for turbulent pool heat transfer which was developed for vertical heat transfer surfaces. This agreement suggests that surface orientation may not be important when the gas jets do not locally affect the surface heat transfer. Finally, a database was developed for heat transfer from the plate with both film boiling and gas jetting occurring simultaneously, in a pool of water maintained at its saturation temperature. The effect of passing nitrogen through established film boiling is to increase the heat transfer from that surface. 60 refs.
Enhanced convective and film boiling heat transfer by surface gas injection
Duignan, M.R.; Greene, G.A. [Brookhaven National Lab., Upton, NY (United States); Irvine, T.F., Jr. [State Univ. of New York, Stony Brook, NY (United States). Dept. of Mechanical Engineering
1992-04-01
Heat transfer measurements were made for stable film boiling of water over a horizontal, flat stainless steel plate from the minimum film boiling point temperature, T{sub SURFACE} {approximately}500K, to T{sub SURFACE} {approximately}950K. The pressure at the plate was approximately 1 atmosphere and the temperature of the water pool was maintained at saturation. The data were compared to the Berenson film-boiling model, which was developed for minimum film-boiling-point conditions. The model accurately represented the data near the minimum film-boiling point and at the highest temperatures measured, as long it was corrected for the heat transferred by radiation. On the average, the experimental data lay within {plus_minus}7% of the model. Measurements of heat transfer were made without film boiling for nitrogen jetting into an overlying pool of water from nine 1-mm- diameter holes, drilled in the heat transfer plate. The heat flux was maintained constant at approximately 26.4 kW/m{sup 2}. For water-pool heights of less than 6cm the heat transfer coefficient deceased linearly with a decrease in heights. Above 6cm the heat transfer coefficient was unaffected. For the entire range of gas velocities measured [0 to 8.5 cm/s], the magnitude of the magnitude of the heat transfer coefficient only changed by approximately 20%. The heat transfer data bound the Konsetov model for turbulent pool heat transfer which was developed for vertical heat transfer surfaces. This agreement suggests that surface orientation may not be important when the gas jets do not locally affect the surface heat transfer. Finally, a database was developed for heat transfer from the plate with both film boiling and gas jetting occurring simultaneously, in a pool of water maintained at its saturation temperature. The effect of passing nitrogen through established film boiling is to increase the heat transfer from that surface. 60 refs.
Diazo transfer for azido-functional surfaces
Laura Russo
2011-04-01
Full Text Available Preparation of azido-functionalized polymers is gaining increasing attention. We wish to report an innovative, novel strategy for azido functionalization of polymeric materials, coupling plasma technology and solution processed diazo transfer reactions. This novel approach allows the azido group to be introduced downstream of the material preparation, thus preserving its physicochemical and mechanical characteristics, which can be tailored a priori according to the desired application. The whole process involves the surface plasma functionalization of a material with primary amino groups, followed by a diazo transfer reaction, which converts the amino functionalities into azido groups that can be exploited for further chemoselective reactions. The diazo transfer reaction is performed in a heterogeneous phase, where the azido group donor is in solution. Chemical reactivity of the azido functionalities was verified by subsequent copper-catalyzed azide-alkyne cycloaddition.
Sotelo, S.S.; Romero, R.J. [Univ. Autonoma del Estado de Morelos, Cuernavaca Morelos (Mexico). Centro di Investigacion en Ingeneria y Ciencias Aplicadas; Best, R. [Univ. Autonoma de Mexico, Temixco, Morelos (Mexico). Centro de Investigacion en Energie
2009-07-01
A mathematical model was used to characterize the thermal behaviour of a steam generator in an alternative energy upgrade system. A thermodynamic cycle was used to increase the temperatures produced by solar, geothermal, and waste heat from industrial processes. The absorption heat transformer (AHT) process can be used in industrial processes where low temperature heat flows occur. Alternative energy was supplied to the generator where the working fluid was condensed and then transported to the evaporator through an expansion valve. Vapor was then transported to the absorber in order to deliver heat at a higher temperature. The solution was then returned to the generator in order to start the cycle again. A heat exchanger was placed between the absorber and the generator in order to preheat incoming solutions from the generator. The mathematical model was used to simulate heat transfer in the generator in order to determine optimal operating conditions. Heat transfer coefficients were calculated using equations reported for single phase flow. It was concluded that the highest heat transfer coefficients were obtained for a Reynolds number of 2300 with an alternative energy source of 90 degrees C at mass flows of 4 L/m. 33 refs., 14 figs.
Hippensteele, Steven A.; Poinsatte, Philip E.
1993-01-01
In this transient technique the preheated isothermal model wall simulates the classic one-dimensional, semi-infinite wall heat transfer conduction problem. By knowing the temperature of the air flowing through the model, the initial temperature of the model wall, and the surface cooling rate measured at any location with time (using the fast-response liquid-crystal patterns recorded on video tape), the heat transfer coefficient can be calculated for the color isothermal pattern produced. Although the test was run transiently, the heat transfer coefficients are for the steady-state case. The upstream thermal boundary condition was considered to be isothermal. This transient liquid-crystal heat-transfer technique was used in a transient air tunnel in which a square-inlet, 3-to-1 exit transition duct was placed. The duct was preheated prior to allowing room temperature air to be suddenly drawn through it. The resulting isothermal contours on the duct surfaces were revealed using a surface coating of thermochromic liquid crystals that display distinctive colors at particular temperatures. A video record was made of the temperature and time data for all points on the duct surfaces during each test. The duct surfaces were uniformly heated using two heating systems: the first was an automatic temperature-controlled heater blanket completely surrounding the test duct like an oven, and the second was an internal hot-air loop through the inside of the test duct. The hot-air loop path was confined inside the test duct by insulated heat dams located at the inlet and exit ends of the test duct. A recirculating fan moved hot air into the duct inlet, through the duct, out of the duct exit, through the oven, and back to the duct inlet. The temperature nonuniformity of the test duct model wall was held very small. Test results are reported for two inlet Reynolds numbers of 200,000 and 1,150,000 (based on the square-inlet hydraulic diameter) and two free-stream turbulence
A model for calculating heat transfer coefficient concerning ethanol-water mixtures condensation
Wang, J. S.; Yan, J. J.; Hu, S. H.; Yang, Y. S.
2010-03-01
The attempt of the author in this research is made to calculate a heat transfer coefficient (HTC) by combining the filmwise theory with the dropwise notion for ethanol-water mixtures condensation. A new model, including ethanol concentration, vapor pressure and velocity, is developed by introducing a characteristic coefficient to combine the two mentioned-above theories. Under different concentration, pressure and velocity, the calculation is in comparison with experiment. It turns out that the calculation value is in good agreement with the experimental result; the maximal error is within ±30.1%. In addition, the model is applied to calculate related experiment in other literature and the values obtained agree well with results in reference.
Effect of pressure on heat transfer coefficient at the metal/mold interface of A356 aluminum alloy
Fardi Ilkhchy, A.; Jabbari, Masoud; Davami, P.
2012-01-01
conduction problem (IHCP) method. The method covers the expedient of comparing theoretical and experimental thermal histories. Temperature profiles obtained from thermocouples were used in a finite difference heat flow program to estimate the transient heat transfer coefficients. The new simple formula......The aim of this paper is to correlate interfacial heat transfer coefficient (IHTC) to applied external pressure, in which IHTC at the interface between A356 aluminum alloy and metallic mold during the solidification of casting under different pressures were obtained using the inverse heat...... was presented for correlation between external pressure and heat transfer coefficient. Acceptable agreement with data in literature shows the accuracy of the proposed formula....
Mario Arias Zabala
2011-12-01
Full Text Available In this paper the volumetric oxygen transfer (kLa and overall heat transfer (Ua coefficients were determined in flasks which were subjected to rotary shaker action, also provided with a temperature control chamber. Likewise, it was determined the effect over such coefficients of some parameters like surrounding temperature, shaking speed, closure type, liquid volume, capacity and baffles presence or absence in each flask, to determine the optimal work conditions in the rotary shaker. The used liquid in these experiments was distilled water. The kLa and Ua coefficients were also determined in the alcoholic fermentation of glucose by Saccharomyces cerevisiae yeast, in order to establish comparison standards. The maximum and minimum values of referred coefficients to distilled water and the operation conditions were: kLa of 6.2 x 10-3 s-1, working at 25 ºC, 100 rpm, 50 ml of liquid volume, erlenmeyer of 500 ml with baffles and plastic closure. kLa of 4.107 x 10-3 s-1, working at 45 ºC, 60 rpm, 150 ml of liquid volume, erlenmeyer of 250 ml without baffles and cotton closure. Ua of 31.9963 J/min °C, working at 45 ºC, 150 rpm, 150 ml of liquid volume, erlenmeyer of 500 ml with baffles and cotton closure. Ua of 6.0179 J/min °C, working at 35 ºC, 60 rpm, 50 ml of liquid volume, erlenmeyer of 250 ml without baffles and plastic closure. The kLa and Ua values in the alcoholic fermentation and the operation conditions were: kLa of 2.6 x 10-4 s-1 and Ua of 12.8907 J/min °C, working at 35 °C, 150 rpm, 150 ml of liquid volume, Erlenmeyer of 250 ml, with baffles and cotton closure.
Effect of Mixed Working Fluid Composition on Binary Cycle Condenser Heat Transfer Coefficients
Dan Wendt; Greg Mines
2011-10-01
Effect of Mixed Working Fluid Composition on Binary Cycle Condenser Heat Transfer Coefficients Dan Wendt, Greg Mines Idaho National Laboratory The use of mixed working fluids in binary power plants can provide significant increases in plant performance, provided the heat exchangers are designed to take advantage of these fluids non-isothermal phase changes. In the 1980's testing was conducted at DOE's Heat Cycle Research Facility (HCRF) where mixtures of different compositions were vaporized at supercritical pressures and then condensed. This testing had focused on using the data collected to verify that Heat Transfer Research Incorporated (HTRI) codes were suitable for the design of heat exchangers that could be used with mixtures. The HCRF data includes mixture compositions varying from 0% to 40% isopentane and condenser tube orientations of 15{sup o}, 60{sup o}, and 90{sup o} from horizontal. Testing was performed over a range of working fluid and cooling fluid conditions. Though the condenser used in this testing was water cooled, the working fluid condensation occurred on the tube-side of the heat exchanger. This tube-side condensation is analogous to that in an air-cooled condenser. Tube-side condensing heat transfer coefficient information gleaned from the HCRF testing is used in this study to assess the suitability of air-cooled condenser designs for use with mixtures. Results of an air-cooled binary plant process model performed with Aspen Plus indicate that that the optimal mixture composition (producing the maximum net power for the scenario considered) is within the range of compositions for which data exist. The HCRF data is used to assess the impact of composition, tube orientation, and process parameters on the condensing heat transfer coefficients. The sensitivity of the condensing coefficients to these factors is evaluated and the suitability of air-cooled condenser designs with mixtures is assessed. This paper summarizes the evaluation
Three-fluid plasmas in star formation II. Momentum transfer rate coefficients
Pinto, Cecilia
2008-01-01
The charged component of the insterstellar medium consists of atomic and molecular ions, electrons, and charged dust grains, coupled to the local Galactic magnetic field. Collisions between neutral particles (mostly atomic or molecular hydrogen) and charged species, and between the charged species themselves, affect the magnetohydrodynamical behaviour of the medium and the dissipation of electric currents. The friction force due to elastic collisions between particles of different species in the multi-component interstellar plasma is a nonlinear function of the temperature of each species and the Mach number of the relative drift velocity. The aim of this paper is to provide an accurate and, as far as possible, complete set of momentum transfer rate coefficients for magnetohydrodynamical studies of the interstellar medium. Momentum transfer rates are derived from available experimental data and theoretical calculations of cross sections within the classic approach developed by Boltzmann and Langevin for a wid...
Assessment of Real Heat Transfer Coefficients through Shell and Tube and Plate Heat Exchangers
Dan CONSTANTINESCU
2011-07-01
Full Text Available The purpose of this paper is to present a procedure used in the assessment of the real heat transfer characteristic of shell and tube and plate heat exchangers. The theoretical fundamentals of the procedure are introduced as well as the measured data collection and processing. The theoretical analysis is focused on the adoption of criterial equations which, subjected to certain verification criteria presented in the paper, provide the most credible value of the convection heat transfer coefficients inside the circular and flat tubes. In the end two case studies are presented, one concerning a shell and tube heat exchanger operational at INCERC Thermal Substation and the other concerning a plate heat exchanger tested on the Laboratory Stand of the Department of Building Services and Efficient Use of Energy in Buildings of INCERC Bucharest.
Experimental apparatus for measuring heat transfer coefficients by the Wilson plot method
Fernandez-Seara, Jose [Area de Maquinas y Motores Termicos, Escuela Superior de Ingenieros Industriales, Campus Lagoas-Marcosende, No 9, 36200 Vigo (Spain); UhIa, Francisco Jose [Area de Maquinas y Motores Termicos, Escuela Superior de Ingenieros Industriales, Campus Lagoas-Marcosende, No 9, 36200 Vigo (Spain); Sieres, Jaime [Area de Maquinas y Motores Termicos, Escuela Superior de Ingenieros Industriales, Campus Lagoas-Marcosende, No 9, 36200 Vigo (Spain); Campo, Antonio [Mechanical Engineering Department, University of Vermont, Burlington, VT 05405 (United States)
2005-05-01
The Wilson plot is a technique to estimate the film coefficients in several types of heat transfer processes and to obtain general heat transfer correlations. This method is an outstanding tool in practical applications and in laboratory research activities that involve analysis of heat exchangers. Moreover, the application of this method is simple enough to be taught in laboratory practices for students at university and doctoral level of physics and engineering. Therefore, an experimental apparatus has been designed and built in our laboratory that allows the students to carry out experiments based on the application of the Wilson plot method. In this note, the principles of the method are explained, the experimental apparatus is described and representative results of the experimental data taken from the apparatus and the application of the Wilson plot method are shown. (note)
Bennion, Kevin; Moreno, Gilberto
2015-09-29
Thermal management for electric machines (motors/ generators) is important as the automotive industry continues to transition to more electrically dominant vehicle propulsion systems. Cooling of the electric machine(s) in some electric vehicle traction drive applications is accomplished by impinging automatic transmission fluid (ATF) jets onto the machine's copper windings. In this study, we provide the results of experiments characterizing the thermal performance of ATF jets on surfaces representative of windings, using Ford's Mercon LV ATF. Experiments were carried out at various ATF temperatures and jet velocities to quantify the influence of these parameters on heat transfer coefficients. Fluid temperatures were varied from 50 degrees C to 90 degrees C to encompass potential operating temperatures within an automotive transaxle environment. The jet nozzle velocities were varied from 0.5 to 10 m/s. The experimental ATF heat transfer coefficient results provided in this report are a useful resource for understanding factors that influence the performance of ATF-based cooling systems for electric machines.
Evaluation of heat transfer surfaces for compact recuperator using a CFD code
Ashok Babu, T. P.; Talekala, Mohammad Shekoor
2009-04-01
Exhaust recovery recuperator is mandatory in order to realize a thermal efficiency of 30% or higher for micro turbines. In this work an attempt is made to select the cross corrugated heat transfer surface with minimum core volume of a recuperator matrix using a CFD code. Analysis is carried out for selected cross corrugated heat transfer surface configurations. The relation between the minimum core volume from design calculation and average skin friction coefficient from CFD analysis has been established.
Baojin, Qi; Li, Zhang; Hong, Xu; Yan, Sun [State-Key Laboratory of Chemical Engineering, School of Mechanical and Power Engineering, East China University of Science and Technology, Shanghai 200237 (China)
2011-01-15
Visual experiments were employed to investigate heat transfer characteristics of steam on vertical titanium plates with/without surface modifications for different surface energies. Stable dropwise condensation and filmwise condensation were achieved on two surface modification titanium plates, respectively. Dropwise and rivulet filmwise co-existing condensation form of steam was observed on unmodified titanium surfaces. With increase in the surface subcooling, the ratio of area ({eta}) covered by drops decreased and departure diameter of droplets increased, resulting in a decrease in condensation heat transfer coefficient. Condensation heat transfer coefficient decreased sharply with the values of {eta} decreasing when the fraction of the surface area covered by drops was greater than that covered by rivulets. Otherwise, the value of {eta} had little effect on the heat transfer performance. Based on the experimental phenomena observed, the heat flux through the surface was proposed to express as the sum of the heat flux through the dropwise region and rivulet filmwise region. The heat flux through the whole surface was the weighted mean value of the two regions mentioned above. The model presented explains the gradual change of heat transfer coefficient for transition condensation with the ratio of area covered by drops. The simulation results agreed well with the present experimental data when the subcooling temperature is lower than 10 C. (author)
肖薇; 刘寿东; 李旭辉; 王伟; 胡凝; 江晓东; 李永秀; 徐向华; 张雪松
2012-01-01
湖泊水面与大气之间垂直方向的动量、水汽和热量通量与风速、湿度和温度梯度之间存在比例关系,因此在湖泊水气相互作用研究中,这比例系数(交换系数)是关键因子.在以往的研究中,交换系数通常直接采用水面梯度观测法或海洋大气近地层的参数化方案进行计算本文采用涡度相关系统和小气候系统仪器在太湖平台上直接观测的通量和气象要素,对上述交换系数(最小均方差原则)进行优化,结果为:动量交换系数CDION=1.52×10-1、水汽变换系数CEION=0.82×10-3、热量交换系数CHION=1.02×10-3,与其他内陆湖泊涡度相关观测数据的推导结果一致.本文的研究结果表明:与海洋参数化方案相比,在相同的风速条件下,湖面的空气动力学粗糙度比海洋高,这可能是由于受到水深的影响；如果采用海洋参数化方案,会导致湖泊年蒸发量的估算值偏大40％.太湖的动量、水汽和热量交换系数可以视为常数,可以不考虑稳定度和风速的影响.这是因为本文中83％的数据为近中性条件.敏感性分析表明:如果考虑稳定度的影响,LE模拟值的平均误差降低了0.5 W/m2,H的平均误差降低了0.4 W/m2,u*的计算值没有变化；如果考虑风速的影响,u*模拟值的平均误差降低了 0.004 m/s,LE的平均误差升高了1.3 W/m2,H的模拟结果几乎不受影响.这一结果能为湖气相互作用研究提供参考.%In studies of lake-atmosphere interactions, the fluxes of momentum, water vapor and heat (latent ami sensible heat) are parameterized as being proportional to the differences in Mind, humiclily and air temperature between the water surface and a reference height above the surface. The proportionality or transfer coefficients are often assumed to follow the gradient observation above lake surface or the parameterizations established for the marine atmospheric surface layer. Optimization against the eddy covariance
Low-Flow Film Boiling Heat Transfer on Vertical Surfaces
Munthe Andersen, J. G.; Dix, G. E.; Leonard, J. E.
1976-01-01
The phenomenon of film boiling heat transfer for high wall temperatures has been investigated. Based on the assumption of laminar flow for the film, the continuity, momentum, and energy equations for the vapor film are solved and a Bromley-type analytical expression for the heat transfer...... length, an average film boiling heat transfer coefficient is obtained....
An instrument to measure the convective heat transfer coefficient on large vessels.
Miguel, Alaor Faria; de O Nascimento, Francisco Assis; da Rocha, Adson Ferreira; dos Santos, Icaro
2008-01-01
Hepatocellular carcinoma is one of the most common malignancies worldwide. During radiofrequency hepatic ablation, the tumor is heated by means of radiofrequency energy. The heating causes necrosis of the malignant tumor. Thus, if the procedure is successful it can cure the patient. Studies have shown that recurrences occur after the treatment and these recurrences frequently take place next to the hepatic artery and portal vein. The recurrences occur due to the high convective loss on these vessels. This work proposed, developed and tested an instrument for the measurement of the convective heat transfer coefficient (h) in large vessels. Moreover, this work developed a mechanical simulator and validated an equation developed by Consiglieri et al, which analytically determines the value of h. The instrument was tested using a mechanical simulator that reproduces the flow conditions and the geometry of large vessels in the liver. A flow velocity of 0.2 m/s was simulated in order to mock the typical flow at the portal vein. The average value of h using the experimental apparatus was 2130+/-40 W.m(-2).K(-1) (mean+/-SD). The results showed that the error of the proposed method is approximately 22%. This work showed that the instrument can be used for measuring h in vitro and that the Consiglieri's equation can be used to determine the convective heat transfer coefficient on large vessels.
Guo Zerong; Xia Quan; Yan Peiyu; Du Zhiming
2016-01-01
To study the effect of variable heat transfer coefficient of fireworks and crackers on thermal explosion critical ambient temperature and time to ignition, considering the heat transfer coefficient as the power function of temperature, mathematical thermal explosion steady state and unsteady-state model of finite cylindrical fireworks and crackers with complex shell structures are established based on two-dimensional steady state thermal explosion theory. T...
Brice Pêtre; Eva Dorignac; Jean Jacques Vullierme
2003-01-01
Walls'cooling of aeronautic propeller combustion chamber is performed with the injection, through the combustion chamber wall, of a part of the air coming from compressors placed upstream. Measurements of the wall thermal fields are made by infrared thermography along the injection wall. This injection wall is pierced by 9 rows of 8 holes (α=90°) in staggered configuration (p/D=s/D=6). We propose a model using two heat transfer coefficients to represent the convective exchanges. The results are non-dimensioned and presented in comparison with the case without holes. The use of this model allows us to define 4 zones. Those 4 zones exist for the 5 blowing rates.
Chabi, A. R.; Zarrinabadi, S.; Peyghambarzadeh, S. M.; Hashemabadi, S. H.; Salimi, M.
2017-02-01
Forced convective heat transfer in a microchannel heat sink (MCHS) using CuO/water nanofluids with 0.1 and 0.2 vol% as coolant was investigated. The experiments were focused on the heat transfer enhancement in the channel entrance region at Re Hydraulic performance of the MCHS was also estimated by measuring friction factor and pressure drop. Results showed that higher convective heat transfer coefficient was obtained at the microchannel entrance. Maximum enhancement of the average heat transfer coefficient compared with deionized water was about 40 % for 0.2 vol% nanofluid at Re = 1150. Enhancement of the convective heat transfer coefficient of nanofluid decreased with further increasing of Reynolds number.
LI Yan-bao; JIANG Xue-lian; GUO Hong-yi
2005-01-01
Experimental studies on the friction coefficient between concrete and the top surface of a rubble mound foundation in China are reviewed. Through comparison of different test results, the development of this research is comprehensively analyzed. An experiment is carried out in the condition similar to prototype. The process curve of friction coefficient with the test block sliding is analyzed and a standard for determination of the friction coefficient is defined. The variation features of the friction coefficient are analyzed on the basis of the present experimental results and other studies in China. It is shown that the friction coefficient between concrete and the top surface of a rubble mound foundation decreases with the increase of the foundation pressure, and the friction coefficient for a very fine leveling bed is smaller than that for a fine leveling bed.
Hindasageri, V.; Vedula, R. P.; Prabhu, S. V.
2013-02-01
Temperature measurement by thermocouples is prone to errors due to conduction and radiation losses and therefore has to be corrected for precise measurement. The temperature dependent emissivity of the thermocouple wires is measured by the use of thermal infrared camera. The measured emissivities are found to be 20%-40% lower than the theoretical values predicted from theory of electromagnetism. A transient technique is employed for finding the heat transfer coefficients for the lead wire and the bead of the thermocouple. This method does not require the data of thermal properties and velocity of the burnt gases. The heat transfer coefficients obtained from the present method have an average deviation of 20% from the available heat transfer correlations in literature for non-reacting convective flow over cylinders and spheres. The parametric study of thermocouple error using the numerical code confirmed the existence of a minimum wire length beyond which the conduction loss is a constant minimal. Temperature of premixed methane-air flames stabilised on 16 mm diameter tube burner is measured by three B-type thermocouples of wire diameters: 0.15 mm, 0.30 mm, and 0.60 mm. The measurements are made at three distances from the burner tip (thermocouple tip to burner tip/burner diameter = 2, 4, and 6) at an equivalence ratio of 1 for the tube Reynolds number varying from 1000 to 2200. These measured flame temperatures are corrected by the present numerical procedure, the multi-element method, and the extrapolation method. The flame temperatures estimated by the two-element method and extrapolation method deviate from numerical results within 2.5% and 4%, respectively.
Hindasageri, V; Vedula, R P; Prabhu, S V
2013-02-01
Temperature measurement by thermocouples is prone to errors due to conduction and radiation losses and therefore has to be corrected for precise measurement. The temperature dependent emissivity of the thermocouple wires is measured by the use of thermal infrared camera. The measured emissivities are found to be 20%-40% lower than the theoretical values predicted from theory of electromagnetism. A transient technique is employed for finding the heat transfer coefficients for the lead wire and the bead of the thermocouple. This method does not require the data of thermal properties and velocity of the burnt gases. The heat transfer coefficients obtained from the present method have an average deviation of 20% from the available heat transfer correlations in literature for non-reacting convective flow over cylinders and spheres. The parametric study of thermocouple error using the numerical code confirmed the existence of a minimum wire length beyond which the conduction loss is a constant minimal. Temperature of premixed methane-air flames stabilised on 16 mm diameter tube burner is measured by three B-type thermocouples of wire diameters: 0.15 mm, 0.30 mm, and 0.60 mm. The measurements are made at three distances from the burner tip (thermocouple tip to burner tip/burner diameter = 2, 4, and 6) at an equivalence ratio of 1 for the tube Reynolds number varying from 1000 to 2200. These measured flame temperatures are corrected by the present numerical procedure, the multi-element method, and the extrapolation method. The flame temperatures estimated by the two-element method and extrapolation method deviate from numerical results within 2.5% and 4%, respectively.
Immersion Condensation on Oil-Infused Heterogeneous Surfaces for Enhanced Heat Transfer
Xiao, Rong; Miljkovic, Nenad; Enright, Ryan; Wang, Evelyn N.
2013-06-01
Enhancing condensation heat transfer is important for broad applications from power generation to water harvesting systems. Significant efforts have focused on easy removal of the condensate, yet the other desired properties of low contact angles and high nucleation densities for high heat transfer performance have been typically neglected. In this work, we demonstrate immersion condensation on oil-infused micro and nanostructured surfaces with heterogeneous coatings, where water droplets nucleate immersed within the oil. The combination of surface energy heterogeneity, reduced oil-water interfacial energy, and surface structuring enabled drastically increased nucleation densities while maintaining easy condensate removal and low contact angles. Accordingly, on oil-infused heterogeneous nanostructured copper oxide surfaces, we demonstrated approximately 100% increase in heat transfer coefficient compared to state-of-the-art dropwise condensation surfaces in the presence of non-condensable gases. This work offers a distinct approach utilizing surface chemistry and structuring together with liquid-infusion for enhanced condensation heat transfer.
Immersion condensation on oil-infused heterogeneous surfaces for enhanced heat transfer.
Xiao, Rong; Miljkovic, Nenad; Enright, Ryan; Wang, Evelyn N
2013-01-01
Enhancing condensation heat transfer is important for broad applications from power generation to water harvesting systems. Significant efforts have focused on easy removal of the condensate, yet the other desired properties of low contact angles and high nucleation densities for high heat transfer performance have been typically neglected. In this work, we demonstrate immersion condensation on oil-infused micro and nanostructured surfaces with heterogeneous coatings, where water droplets nucleate immersed within the oil. The combination of surface energy heterogeneity, reduced oil-water interfacial energy, and surface structuring enabled drastically increased nucleation densities while maintaining easy condensate removal and low contact angles. Accordingly, on oil-infused heterogeneous nanostructured copper oxide surfaces, we demonstrated approximately 100% increase in heat transfer coefficient compared to state-of-the-art dropwise condensation surfaces in the presence of non-condensable gases. This work offers a distinct approach utilizing surface chemistry and structuring together with liquid-infusion for enhanced condensation heat transfer.
Surface-particle-emulsion heat transfer model between fluidized bed and horizontal immersed tube
无
2002-01-01
A mathematical model, surface-particle-emulsion heat transfer model, is presented by considering voidage variance in emulsion in the vicinity of an immersed surface. Heat transfer near the surface is treated by dispersed particles touching the surface and through the emulsion when the distance from the surface is greater than the diameter of a particle. A film with an adjustable thickness which separates particles from the surface is not introduced in this model. The coverage ratio of particles on the surface is calculated by a stochastic model of particle packing density on a surface. By comparison of theoretical solutions with experimental data from some references, the mathematical model shows better qualitative and quantitative prediction for local heat transfer coefficients around a horizontal immersed tube in a fluidized bed.
Leung, Juliana Y; Srinivasan, Sanjay
2016-09-01
Modeling transport process at large scale requires proper scale-up of subsurface heterogeneity and an understanding of its interaction with the underlying transport mechanisms. A technique based on volume averaging is applied to quantitatively assess the scaling characteristics of effective mass transfer coefficient in heterogeneous reservoir models. The effective mass transfer coefficient represents the combined contribution from diffusion and dispersion to the transport of non-reactive solute particles within a fluid phase. Although treatment of transport problems with the volume averaging technique has been published in the past, application to geological systems exhibiting realistic spatial variability remains a challenge. Previously, the authors developed a new procedure where results from a fine-scale numerical flow simulation reflecting the full physics of the transport process albeit over a sub-volume of the reservoir are integrated with the volume averaging technique to provide effective description of transport properties. The procedure is extended such that spatial averaging is performed at the local-heterogeneity scale. In this paper, the transport of a passive (non-reactive) solute is simulated on multiple reservoir models exhibiting different patterns of heterogeneities, and the scaling behavior of effective mass transfer coefficient (Keff) is examined and compared. One such set of models exhibit power-law (fractal) characteristics, and the variability of dispersion and Keff with scale is in good agreement with analytical expressions described in the literature. This work offers an insight into the impacts of heterogeneity on the scaling of effective transport parameters. A key finding is that spatial heterogeneity models with similar univariate and bivariate statistics may exhibit different scaling characteristics because of the influence of higher order statistics. More mixing is observed in the channelized models with higher-order continuity. It
Leung, Juliana Y.; Srinivasan, Sanjay
2016-09-01
Modeling transport process at large scale requires proper scale-up of subsurface heterogeneity and an understanding of its interaction with the underlying transport mechanisms. A technique based on volume averaging is applied to quantitatively assess the scaling characteristics of effective mass transfer coefficient in heterogeneous reservoir models. The effective mass transfer coefficient represents the combined contribution from diffusion and dispersion to the transport of non-reactive solute particles within a fluid phase. Although treatment of transport problems with the volume averaging technique has been published in the past, application to geological systems exhibiting realistic spatial variability remains a challenge. Previously, the authors developed a new procedure where results from a fine-scale numerical flow simulation reflecting the full physics of the transport process albeit over a sub-volume of the reservoir are integrated with the volume averaging technique to provide effective description of transport properties. The procedure is extended such that spatial averaging is performed at the local-heterogeneity scale. In this paper, the transport of a passive (non-reactive) solute is simulated on multiple reservoir models exhibiting different patterns of heterogeneities, and the scaling behavior of effective mass transfer coefficient (Keff) is examined and compared. One such set of models exhibit power-law (fractal) characteristics, and the variability of dispersion and Keff with scale is in good agreement with analytical expressions described in the literature. This work offers an insight into the impacts of heterogeneity on the scaling of effective transport parameters. A key finding is that spatial heterogeneity models with similar univariate and bivariate statistics may exhibit different scaling characteristics because of the influence of higher order statistics. More mixing is observed in the channelized models with higher-order continuity. It
Julia, J. E.; Hernández, L.; Martínez-Cuenca, R.; Hibiki, T.; Mondragón, R.; Segarra, C.; Jarque, J. C.
2012-11-01
Forced convective heat transfer coefficient and pressure drop of SiO2- and Al2O3-water nanofluids were characterized. The experimental facility was composed of thermal-hydraulic loop with a tank with an immersed heater, a centrifugal pump, a bypass with a globe valve, an electromagnetic flow-meter, a 18 kW in-line pre-heater, a test section with band heaters, a differential pressure transducer and a heat exchanger. The test section consists of a 1000 mm long aluminium pipe with an inner diameter of 31.2 mm. Eighteen band heaters were placed all along the test section in order to provide a uniform heat flux. Heat transfer coefficient was calculated measuring fluid temperature using immersed thermocouples (Pt100) placed at both ends of the test section and surface thermocouples in 10 axial locations along the test section (Pt1000). The measurements have been performed for different nanoparticles (Al2O3 and SiO2 with primary size of 11 nm and 12 nm, respectively), volume concentrations (1% v., 5% v.), and flow rates (3 103Re<105). Maximum heat transfer coefficient enhancement (300%) and pressure drop penalty (1000%) is obtained with 5% v. SiO2 nanofluid. Existing correlations can predict, at least in a first approximation, the heat transfer coefficient and pressure drop of nanofluids if thermal conductivity, viscosity and specific heat were properly modelled.
Dependence of dose coefficients for {sup 239}Pu on transfer rates and absorption parameters
Suzuki, K.; Sekimoto, H. [Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, Tokyo (Japan); Ishigure, N. [Division of Radiotoxicology and Protection, National Institute of Radiological Sciences, Chiba (Japan)
2000-05-01
As it is reported of the biokinetic models and parameter values of the International Commission on Radiological Protection (ICRP) for dose estimation have uncertainties owing to insufficiency of human data. For most radionuclides, the data underlying such models and parameters of ICRP usually depend on animal experiments. Moreover, these values or model parameter are also greatly different between mammalian species. Recently, various radiation protection organizations are considering the biokinetic uncertainties from standpoints of data's sources, quality and completeness. In practice, a sensitivity analysis of doses to parameters is significant for the purpose of risk assessment. In general, movement or material in the body is depicted as a system of first-order processes, and parameter values are expressed as transfer rates between compartments. In this study, we made a code to reproduce the ICRP's dose coefficients for {sup 239}Pu, which is one of the most important elements for occupational exposure and its effective dose is much concerned with its own distribution in the body for dominance of alpha-decay. By using this code, we modified each transfer rate in a factor of 2, 3 and 4 in order to evaluate the effects, and calculated the sensitivities of effective doses due to these changes. Additionally, we examined the effects of modification of absorption parameters f{sub r}, S{sub r} and S{sub s}, which represent the absorption of particles from respiratory tract into blood. Consequently, the transfer rates that give a large sensitivity were specified, and it was shown that changes of transfer rates and absorption parameters are not so influential on effective doses for {sup 239}Pu in many cases. (author)
Kwang-Il Choi
2013-01-01
Full Text Available Experimental data of heat transfer coefficient during evaporation of R-1234yf, R-134a, and R-22 in horizontal circular small tubes are compared. The local heat transfer coefficient is obtained for heat fluxes ranging from 10 to 35 kW m−2, mass fluxes ranging from 100 to 650 kg m−2 s−1, saturation temperatures of 5, 10, and 15°C, and quality up to 1.0. The test sections are made of stainless steel tubes with inner diameters of 1.5 and 3.0 mm, the lengths of 1000 and 2000. Effects of heat flux, inner tube diameter, and saturation temperature on heat transfer coefficient are reported in the present study. Nucleate boiling heat transfer contribution is predominant, especially at low quality region, and laminar flow appears in the evaporative small tubes. The experimental results are compared against four existing heat transfer coefficients, and the modified correlation of heat transfer coefficient is developed with good prediction.
Characterization of the interfacial heat transfer coefficient for hot stamping processes
Luan, Xi; Liu, Xiaochuan; Fang, Haomiao; Ji, Kang; El Fakir, Omer; Wang, LiLiang
2016-08-01
In hot stamping processes, the interfacial heat transfer coefficient (IHTC) between the forming tools and hot blank is an essential parameter which determines the quenching rate of the process and hence the resulting material microstructure. The present work focuses on the characterization of the IHTC between an aluminium alloy 7075-T6 blank and two different die materials, cast iron (G3500) and H13 die steel, at various contact pressures. It was found that the IHTC between AA7075 and cast iron had values 78.6% higher than that obtained between AA7075 and H13 die steel. Die materials and contact pressures had pronounced effects on the IHTC, suggesting that the IHTC can be used to guide the selection of stamping tool materials and the precise control of processing parameters.
Lee, Sin Pyo [Kyonggi Univ., Suwon (Korea, Republic of)
2016-02-15
Fine wires made from platinum have been used as sensors to evaluate the convection performance of nanofluids. However, the wire sensor is difficult to handle due to its fragility. Additionally, an unrealistic convective heat transfer coefficient (h) is obtained if a rigorous calibration process combined with precision equipment is not used for measurement. This paper proposes a new evaluation apparatus for h of nanofluids that uses a thermistor sensor instead of the platinum wire. The working principles are also explained in detail. Validation experiments for pure engine oil comparing h from the two sensors confirmed numerous practical benefits of the thermistor. The proposed system can be used as a useful tool to justify the adoption of developed nanofluids.
Caron, Etienne; Daun, Kyle J.; Wells, Mary A.
2013-04-01
The heat transfer coefficient (HTC) between the sheet metal and the cold tool is required to predict the final microstructure and mechanical properties of parts manufactured via hot forming die quenching. Temperature data obtained from hot stamping experiments conducted on boron steel blanks were processed using an inverse heat conduction algorithm to calculate heat fluxes and temperatures at the blank/die interface. The effect of the thermocouple response time on the calculated heat flux was compensated by minimizing the heat imbalance between the blank and the die. Peak HTCs obtained at the end of the stamping phase match steady-state model predictions. At higher blank temperatures, the time-dependent deformation of contact asperities is associated with a transient regime in which calculated HTCs are a function of the initial stamping temperature.
Retrieval of ocean surface wind stress and drag coefficient from spaceborne SAR
杨劲松; 黄韦艮; 周长宝
2001-01-01
A model for retrieval of wind stress and drag coefficient on the sea surface with the data measured by spacebome synthetic aperture radar (SAR) has been developed based on the SAR imaging mechanisms of ocean surface capillary waves and short gravity waves. This model consists of radiometric calibration, wind speed retrieval and wind stress and drag coefficient calculation. A Radarsat SAR image has been used to calculate wind stress and drag coeffi cient. Good results have been achieved.
Cao, Yongyou; Guo, Zhipeng; Xiong, Shoumei
2012-07-01
High-pressure die cast B390 alloy was prepared on a 350 ton cold chamber die casting machine. The metal/die interfacial heat transfer coefficient of the alloy was investigated. Considering the filling process, a "finger"-shaped casting was designed for the experiments. This casting consisted of five plates with different thicknesses (0.05 inch or 1.27 mm to 0.25 inch or 6.35 mm) as well as individual ingates and overflows. Experiments under various operation conditions were conducted, and temperatures were measured at various specific locations inside the die. Based on the results, the interfacial heat transfer coefficient and heat flux were determined by solving the inverse heat transfer problem. The influence of the mold-filling sequence, sensor locations, as well as processing parameters including the casting pressure, die temperature, and fast/slow shot speeds on the heat transfer coefficient were discussed.
Sakuma, Hiroshi
2013-12-01
frictional strength of faults is a critical factor that contributes to continuous fault slip and earthquake occurrence. Frictional strength can be reduced by the presence of sheet-structured clay minerals. In this study, two important factors influencing the frictional coefficient of minerals were quantitatively analyzed by a newly developed computational method based on a combination of first-principles study and thermodynamics. One factor that helps reduce the frictional coefficient is the low adhesion energy between the layers under dry conditions. Potassium ions on mica surfaces are easily exchanged with sodium ions when brought into contact with highly concentrated sodium-halide solutions. We found that the surface ion exchange with sodium ions reduces the adhesion energy, indicating that the frictional coefficient can be reduced under dry conditions. Another factor is the lubrication caused by adsorbed water films on mineral surfaces under wet conditions. Potassium and sodium ions on mica surfaces have a strong affinity for water molecules. In order to remove the adsorbed water molecules confined between mica surfaces, a differential compressive stress of the order of tens of gigapascals was necessary at room temperature. These water molecules inhibit direct contact between mineral surfaces and reduce the frictional coefficient. Our results imply that the frictional coefficient can be modified through contact with fluids depending on their salt composition. The low adhesion energy between fault-forming minerals and the presence of an adsorbed water film is a possible reason for the low frictional coefficient observed at continuous fault slip zones.
THE EFFECT OF THE ALUMINIUM ALLOY SURFACE ROUGHNESS ON THE RESTITUTION COEFFICIENT
Stanisław Bławucki
2015-08-01
Full Text Available The paper presents the results of research on the effect of the surface roughness of aluminum alloy on its coefficient of restitution. It describes the current method of finishing the workpiece surface layer after cutting and innovative measuring device which was used in the research. The material used in the research was aluminium alloy EN AW 7075. The paper also presents a relationship between the coefficient of restitution and surface roughness of the milled samples as well as impressions left by bead in function of velocity and a sample surface roughness.
Experimental study on convective heat transfer coefficient around a vertical hexagonal rod bundle
Makhmalbaf, M. H. M.
2012-06-01
Research on convective heat transfer coefficient around a rod bundle has many diverse applications in industry. So far, many studies have been conducted in correlations related to internal and turbulent fully-developed flow. Comparison shows that Dittus-Boelter, Sieder-Tate and Petukhov have so far been the most practical correlations in fully-developed turbulent fluid flow heat transfer. The present study conducts an experimental examination of the validity of these frequently-applied correlations and introduces a manufactured test facility as well. Due to its generalizibility, the unique geometry of this test facility (hexagonal arranged, 7 vertical rods in a hexagonal tube) can fulfil extensive applications. The paper also studies the major deviation sources in data measurements, calibrations and turbulence of fluid flow in this. Finally, regarding to sufficient number of experiments in a vast fluid mean velocity range (3,800 < Re < 40,000), a new curve and correlation are presented and the results are compared with the above mentioned commonly-applied correlations.
Heat and mass transfer rates during flow of dissociated hydrogen gas over graphite surface
Nema, V. K.; Sharma, O. P.
1986-01-01
To improve upon the performance of chemical rockets, the nuclear reactor has been applied to a rocket propulsion system using hydrogen gas as working fluid and a graphite-composite forming a part of the structure. Under the boundary layer approximation, theoretical predictions of skin friction coefficient, surface heat transfer rate and surface regression rate have been made for laminar/turbulent dissociated hydrogen gas flowing over a flat graphite surface. The external stream is assumed to be frozen. The analysis is restricted to Mach numbers low enough to deal with the situation of only surface-reaction between hydrogen and graphite. Empirical correlations of displacement thickness, local skin friction coefficient, local Nusselt number and local non-dimensional heat transfer rate have been obtained. The magnitude of the surface regression rate is found low enough to ensure the use of graphite as a linear or a component of the system over an extended period without loss of performance.
EMRULLAH YA¸SAR; YAKUP YILDIRIM; ILKER BURAK GIRESUNLU
2016-08-01
Fin materials can be observed in a variety of engineering applications. They are used to ease the dissipation of heat from a heated wall to the surrounding environment. In this work, we consider a nonlinear fin problem with temperature-dependent thermal conductivity and heat transfer coefficient. The equation(s) under study are highly nonlinear. Both the thermal conductivity and the heat transfer coefficient are given as arbitrary functions of temperature. Firstly, we consider the Lie group analysis for different cases of thermal conductivity and the heat transfer coefficients. These classifications are obtained from the Lie group analysis. Then, the first integrals of the nonlinear straight fin problem are constructed by three methods, namely, Noether’s classical method, partial Noether approach and Ibragimov’s nonlocal conservation method. Some exact analytical solutions are also constructed. The obtained result is also compared with the result obtained by other methods.
The influence of surface preparation on the absorption coefficient of laser radiation
Kurp, Piotr; Mucha, Zygmunt; Mulczyk, Krystian; Gradoń, Ryszard; Trela, Paweł
2016-12-01
The absorption coefficient of the surface of a workpiece is of importance in laser treatment, particularly in the treatment where the temperature of an element must be strictly controlled. Laser surface treatment (such as hardening, metallic glazing) and laser forming can be primarily included in this type of technology. In another case, surface temperature must be precisely controlled, especially if structural changes are to be avoided. There are a number of ways to increase the absorption coefficient of the surface of an element. Since the laser forming is the research subject of the authors of the presented paper, it was necessary to determine the absorption coefficient for the different surfaces preparation of workpieces. Raw surface, oxidized surface, sandblasted surface, black enamel covered surface and waterglass covered surface were examined, respectively. The experiment was performed using a CO2 laser with a head for a surface treatment which generates a rectangular beam of dimensions 2x20 mm, and the samples were made of X5CrNi18-10 stainless steel.
Iguchi, Tadashi; Anoda, Yoshinari [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment; Iwaki, Chikako [Toshiba Corp., Tokyo (Japan)
2002-02-01
Authors performed post-CHF experiments under wider pressure ranges of 2 MPa - 18 MPa, wider mass flux ranges of 33 kg/m{sup 2}s - 1651 kg/m{sup 2}s and wider superheat of heaters up to 500 K in comparison to experimental ranges at previous post-CHF experiments. Data on boiling transition, critical heat flux and post-CHF heat transfer coefficient were obtained. Used test section was 4x4-rod bundle with heaters, which diameter and length were the same as those of BWR nuclear fuels. As the result of the experiments, it was found that the boiling transition occurred just below several grid spacers, and that the fronts of the boiling transition region proceeded lower with increase of heated power. Heat transfer was due to nucleate boiling above grid spacers, while it was due to film boiling below grid spacers. Consequently, critical heat flux is affected on the distance from the grid spacers. Critical heat flux above the grid spacers was about 15% higher than that below the grid spacers, by comparing them under the same local condition. Heat transfer by steam turbulent flow was dominant to post-CHF heat transfer, when superheat of heaters was sufficiently high. Then, post-CHF heat transfer coefficient was predicted with heat transfer correlations for single-phase flow. On the other hand, when superhead of heaters was not sufficiently high, post-CHF heat transfer coefficient was higher than the prediction with heat transfer correlations for single-phase flow. Mass flux effect on post-CHF heat transfer coefficient was described by standardization of post-CHF heat transfer coefficient with the prediction for single-phase flow. However, pressure effect, superheat effect and effect of position were not described. Authors clarified that those effects could be described with functions of heater temperature and position. Post-CHF heat transfer coefficient was lowest just blow the grid spacers, and it increased with the lower positions. It increased by about 30% in one span of
Impact of External Pressure on the Heat Transfer Coefficient during Solidification of Al-A356 Alloy
Jabbari, Masoud; Ilkhchy, A.Fardi; Moumani, E.
In this paper the interfacial heat transfer coefficient (IHTC) is correlated to applied external pressure, in which IHTC at the interface between A356 aluminum alloy and metallic mold during the solidification of the casting under different pressures were obtained using the Inverse Heat Conduction...... Problem (IHCP) method. The method covers the expedient of comparing theoretical and experimental thermal histories. Temperature profiles obtained from thermocouples were used in a finite difference heat flow program to estimate the transient heat transfer coefficients. The new simple formula was presented...
Komov, A. T.; Varava, A. V.; Zakharenkov, A. V.; Dedov, A. V.; Boltenko, E. A.; Agishev, B. Y.
2016-10-01
The work is a continuation of the experimental studies on the enhancement of heat transfer in the fuel assembly on the experimental stand in National Research University "Moscow Power Engineering Institute". The description of the experimental setup, construction and main geometrical parameters of intensifier are presented. The new experimental data on the pressure loss and heat transfer coefficient using an edge enhancer - twisted wire single-phase convection mode are presented. In the research, the range mode parameters and geometric characteristics of the intensifier were extended. The relation of the coefficients of hydraulic resistance and the Nusselt number of steps twist twisted wire was found, the effect of the ribs on the heat transfer coefficient was shown. It is found that for any twist pitch ranging from 20 to 100 mm corresponds to a maximum heat transfer rib height H = 0,35. An increase in the heat transfer coefficient in the convex heating surface was experimentally obtained.
A modified stanton number for heat transfer through fabric surface
Zhang Shen-Zhong
2015-01-01
Full Text Available The Stanton number was originally proposed for describing heat transfer through a smooth surface. A modified one is suggested in this paper to take into account non-smooth surface or fractal surface. The emphasis is put on the heat transfer through fabrics.
Tuning apparent friction coefficient by controlled patterning bulk metallic glasses surfaces
Li, Ning; Xu, Erjiang; Liu, Ze; Wang, Xinyun; Liu, Lin
2016-12-01
Micro-honeycomb structures with various pitches between adjacent cells were hot-embossed on Zr35Ti30Cu8.25Be26.75 bulk metallic glass surface. The effect of pitch geometry on the frictional behavior of metallic glass surface was systematically investigated. The results revealed that all textured metallic glass surfaces show a reduction in friction coefficient compared to smooth surface. More intriguingly, the friction coefficient first decreased and then increased gradually with increasing pitches. Such unique behavior can be understood fundamentally from the perspective of competing effects between contact area and local stress level with increasing pitches. This finding not only enhance the in-depth understanding of the mechanism of the significant role of surface topography on the frictional behavior of metallic glass surface, but also opens a new route towards other functional applications for bulk metallic glasses.
A. C. Rizzi Jr.
2009-09-01
Full Text Available This work is aimed at modeling the heat transfer mechanism in a fluidized bed of grass seeds (Brachiaria brizantha for supporting further works on simulating the drying of these seeds in such a bed. The three-phase heat transfer model, developed by Vitor et al. (2004, is the one used for this proposal. This model is modified to uncouple one of the four adjusted model parameters from the gas temperature. Using the first set of experiments, carried out in a laboratory scale batch fluidized bed, the four adjusted model parameters are determined, generating the heat transfer coefficient between particles and gas phase, as well as the heat transfer coefficient between the column wall and ambient air. The second set of experiments, performed in the same unit at different conditions, validates the modified model.
DR. S.N. Sapali
2009-11-01
Full Text Available Two phase heat transfer coefficients and pressure drops of R-404A in a smooth (8.56 mm ID and micro-fin tube (8.96 mm ID are experimentally investigated. Different from previous studies, the present experiments are performed for different condensing temperatures, with superheating and sub cooling and using hermetically sealed compressor. The test runs are done at average saturated condensing temperatures ranging from 35oC to 60oC. The mass fluxes are between 90 and 800 kg m-2s-1 . The experimental results from both smooth and micro-fin tubes show that the average heat transfer coefficient and pressure drop increases with mass flux but decreases with increasing condensing temperature. The average heat transfer coefficient is 30-210% higher for micro-fin tube than that of smooth tube, with moderate increase in pressure drop ranging from 10-55%. New correlations based on the data gathered during the experimentation for predicting condensation heat transfer coefficients are proposed for wide range of practical applications.
SUI Da-shan; CUI Zhen-shan
2007-01-01
The accurate material physical properties, initial and boundary conditions are indispensable to the numerical simulation in the casting process, and they are related to the simulation accuracy directly.The inverse heat conduction method can be used to identify the mentioned above parameters based on the temperature measurement data.This paper presented a new inverse method according to Tikhonov regularization theory.A regularization functional was established and the regularization parameter was deduced, the Newton-Raphson iteration method was used to solve the equations.One detailed case was solved to identify the thermal conductivity and specific heat of sand mold and interfacial heat transfer coefficient (IHTC) at the meantime.This indicates that the regularization method is very efficient in decreasing the sensitivity to the temperature measurement data, overcoming the illposedness of the inverse heat conduction problem (IHCP) and improving the stability and accuracy of the results.As a general inverse method, it can be used to identify not only the material physical properties but also the initial and boundary conditions' parameters.
Mass Transfer Coefficient During Cathodic Protectionof Low Carbon Steel in Seawater
Ameel Mohammed Rahman
2009-01-01
Full Text Available The aim of this research is to calculate mass transfer coefficient, kd, during cathodic protection of low carbon steel in neutral seawater (3.5% W/V NaCl in distilled water with pH = 7. Two types of cathodic protection were used:First: Sacrificial anode cathodic protection (SACP were a pipeline of steel carrying seawater using zinc as a sacrificial anode and with variable temperatures ranged (0 45oC and volumetric flow rate ranged (5 900 lit/hr. It was found that the kd increases with increasing temperature and volumetric flow rate of seawater, where kd ranged (0.24×10-6 41.6×10-6 m/s.Second: Impressed current cathodic protection (ICCP technique adopting a rotating vertical steel cylinder in seawater with variable temperatures ranged (0 45oC and rotating velocity ranged (0 400 rpm. It was found that the kd increases with increasing temperature and rotating velocity, where kd ranged (7.25×10-6 36.82×10-6 m/s.
Experimentally Determined Overall Heat Transfer Coefficients for Spacesuit Liquid Cooled Garments
Bue, Grant; Rhodes, Richard; Anchondo, Ian; Westheimer, David; Campbell, Colin; Vogel, Matt; Vonaue, Walt; Conger, Bruce; Stein, James
2015-01-01
A Human-In-The-Loop (HITL) Portable Life Support System 2.0 (PLSS 2.0) test has been conducted at NASA Johnson Space Center in the PLSS Development Laboratory from October 27, 2014 to December 19, 2014. These closed-loop tests of the PLSS 2.0 system integrated with human subjects in the Mark III Suit at 3.7 psi to 4.3 psi above ambient pressure performing treadmill exercise at various metabolic rates from standing rest to 3000 BTU/hr (880 W). The bulk of the PLSS 2.0 was at ambient pressure but effluent water vapor from the Spacesuit Water Membrane Evaporator (SWME) and the Auxiliary Membrane Evaporator (Mini-ME), and effluent carbon dioxide from the Rapid Cycle Amine (RCA) were ported to vacuum to test performance of these components in flight-like conditions. One of the objectives of this test was to determine the overall heat transfer coefficient (UA) of the Liquid Cooling Garment (LCG). The UA, an important factor for modeling the heat rejection of an LCG, was determined in a variety of conditions by varying inlet water temperature, flow rate, and metabolic rate. Three LCG configurations were tested: the Extravehicular Mobility Unit (EMU) LCG, the Oceaneering Space Systems (OSS) LCG, and the OSS auxiliary LCG. Other factors influencing accurate UA determination, such as overall heat balance, LCG fit, and the skin temperature measurement, will also be discussed.
Vaporization heat transfer of dielectric liquids on enhanced surfaces covered with screen wicks
Gu, C. B.; Chow, L. C.; Pais, M. R.; Baker, K.
1993-01-01
Experiments were conducted to investigate the vaporization heat transfer characteristics for the dielectric liquid FC-72 on several wicking surfaces which may be used in flat-plate heat pipes. The wicking materials studied included microstructure enhanced surfaces and coarse surfaces covered with screen meshes. Experimental data for q versus deltaT curves and critical heat fluxes were obtained for the two different operating conditions of a heat pipe, evaporation, and shallow pool boiling. When the liquid level was above the heated surface, the height of the liquid level above the surface was varied from 0 to 10 mm. When the liquid level was below the heated surface, the distance from the liquid level to the edge of the surface was adjusted from 0 to 15 mm. Experimental results revealed that for shallow pool boiling when the heated surface was covered with a wire screen mesh, the heat transfer coefficient increased at lower heat fluxes but the critical heat flux (CHF) decreased for all the surfaces tested. In the case of evaporation, both CHF and the heat transfer coefficient increased as the microstructure surfaces were covered with screen meshes.
Inversion of dielectric constant and moisture of bare soil surface from backscattering coefficient
李宗谦; 冯孔豫
1997-01-01
An inverse method of dielectric constant and moisture of bare wet soil surface from backscattering coefficients is presented, which is based upon the small perturbation model of electromagnetic wave scattering from rough surfaces and the empirical and dielectric mixing models of wet soil. Some sets of curves which describe the relation between the moisture of soil and the ratio of like polarization backscattering coefficients σvv and σhh are obtained, and some principles on how to choose the incident frequencies and the incident angles of the electromagnetic wave are given Analysis and calculation show that the mam advantage of this inverse method is its efficiency and simplicity.
Chakravarthii, M. K. Dheepan; Mutharasu, D.; Shanmugan, S.
2017-01-01
The major challenge in microelectronic chips is to eliminate the generated heat for stable and reliable operation of the devices. Microchannel heat sinks are efficient method to dissipate high heat flux. The pressure drop and heat transfer coefficient are the important parameters which determine the thermal-hydraulic performance of the microchannel heat sink. In this study, a converging-diverging (CD) microchannel heat sink was experimentally investigated for the variation of pressure drop and heat transfer coefficient. De-ionized water was considered as the working fluid. Experiments were conducted for single phase fluid flow with mass flow rate and heat flux ranging from 0.001232 to 0.01848 kg/s and 10-50 W/cm2 respectively. The fluid and solid temperature were measured to calculate the heat transfer coefficients. Numerical results were computed using the CFD software and validated against the experimental results. The CD microchannel possesses high heat transfer coefficient than the straight microchannels. Theoretical correlations were proposed for comparing the experimental Nusselt number of CD microchannel. Evaluation of thermal-hydraulic performance of CD microchannel is important to quantify its applications in electronics cooling.
YangDu; MingDaoXin
1999-01-01
This paper developed a new type of three dimensional inner microfin tube,The experimental results of the flow patterns for the horizontal condensation inside these tubes are reported in the paper,The flow patterns for the hirizontal condensation inside the new made tubes are divided into annular flow stratified flow and intermittent flow within the test conditions.The experiments of the local heat transfer coefficients for the different flow patterns have been systematically caried out ,The experiments of the local heat transfer coefficients changing with the vapor dryness fraction have also been carried out.As compared with the heat transfer coefficients of the two dimensional inner microfin tubes,those of the three dimensional inner microfin tubes increase 47-127% for the annular flow region,38-183% for the stratified flow and 15-75%,for the intermittent flow,respectively.The enhancement factor of the local heat transfer coefficients is from 1\\8-6\\9 for the vapor dryness fraction from 0.05 to 1.
Ratkovich, Nicolas Rios; Berube, P.R.; Nopens, I.
2011-01-01
) cannot be applied directly. As an alternative, in this work, a multidisciplinary approach was selected, by exploiting dimensionless analysis using the Sherwood number. Mass transfer coefficients were measured at various superficial velocities of gas and liquid flow in a tubular system. Due...
Clinic based transfer of the N(D,W)(60Co) calibration coefficient using a linear accelerator.
Abdel-Rahman, W; Evans, M D C; Serré, L; McCaffrey, J P; Podgorsak, E B; Seuntjens, J P
2009-03-01
Ionization chambers used for reference dosimetry require a local secondary standard ionization chamber with a 60Co absorbed dose to water calibration coefficient N(D,W)(60Co) traceable to a national primary standards dosimetry laboratory or an accredited secondary dosimetry calibration laboratory. Clinic based (in-house) transfer of this coefficient to tertiary reference ionization chambers has traditionally been accomplished with chamber cross calibration in water using a 60Co beam; however, access to 60Co teletherapy machines has become increasingly limited for clinic based physicists. In this work, the accuracy of alternative methods of transferring the N(D,W)(60Co) calibration coefficient using 6 and 18 MV photon beams from a linear accelerator in lieu of 60Co has been investigated for five different setups and four commonly used chamber types.
EMILA DJORDJEVIC; STEPHAN KABELAC; SLOBODAN SERBANOVIC
2007-01-01
In this study the transfer coefficient of evaporation heat of the refrigerant 1,1,1,2-tetrafluoroethane (R-134a) in a vertical plate heat exchanger was experimentally investigated. The results are presented as the dependancy of the mean heat transfer coefficient for the whole heat exchanger on the mean vapor quality. The influences of mass flux, heat flux and flow configuration on the heat transfer coefficient were also taken into account and a comparison with previously published experimenta...
Karunakara, N; Ujwal, P; Yashodhara, I; Rao, Chetan; Sudeep Kumara, K; Dileep, B N; Ravi, P M
2013-10-01
Detailed studies were carried out to establish site-specific soil to grass transfer factors (Fv) and grass to cow milk transfer coefficients (Fm) for radioactive cesium ((137)Cs) and stable cesium (Cs) for Kaiga region, where a nuclear power station has been in operation for more than 10 years. The study included adopted cows, cows of local farmers, and cows from the dairy farm. A grass field was developed specifically for the study and 2 local breed cows were adopted and allowed to graze in this grass field. The soil and grass samples were collected regularly from this field and analyzed for the concentrations of (137)Cs and stable Cs to evaluate the soil to grass Fv values. The milk samples from the adopted cows were analyzed for the (137)Cs and stable Cs concentrations to evaluate Fm values. For comparison, studies were also carried out in dominant grazing areas in different villages around the nuclear power plant and the cows of local farmers which graze in these areas were identified and milk samples were collected and analyzed regularly. The geometric mean values of Fv were found to be 1.1 × 10(-1) and 1.8 × 10(-1) for (137)Cs and stable Cs, respectively. The Fm of (137)Cs had geometric mean values of 1.9 × 10(-2) d L(-1) and 4.6 × 10(-2) d L(-1), respectively, for adopted Cows 1 and 2; 1.7 × 10(-2) d L(-1) for the cows of local farmers, and 4.0 × 10(-3) d L(-1) for the dairy farm cows. The geometric mean values of Fm for stable Cs were similar to those of (137)Cs. The Fm value for the dairy farm cows was an order of magnitude lower than those for local breed cows. The Fm values observed for the local breed cows were also an order of magnitude higher when compared to the many values reported in the literature and in the IAEA publication. Possible reasons for this higher Fm values were identified. The correlation between Fv and Fm values for (137)Cs and stable Cs and their dependence on the potassium content ((40)K and stable K) in
Junghui Chen; Kuan-Po Wang [Chung-Yuan Christian University (China). Dept. of Chemical Engineering; Ming-Tsai Liang [I-Shou University (China). Dept. of Chemical Engineering
2005-06-01
An overlapped type of local neural network is proposed to improve accuracy of the heat transfer coefficient estimation of the supercritical carbon dioxide. The idea of this work is to use the network to estimate the heat transfer coefficient for which there is no accurate correlation model due to the complexity of the thermo-physical properties involved around the critical region. Unlike the global approximation network (e.g. backpropagation network) and the local approximation network (e.g. the radial basis function network), the proposed network allows us to match the quick changes in the near-critical local region where the rate of heat transfer is significantly increased and to construct the global smooth perspective far away from that local region. Based on the experimental data for carbon dioxide flowing inside a heated tube at the supercritical condition, the proposed network significantly outperformed some the conventional correlation method and the traditional network models. (Author)
Whitesides, R. Harold; Majumdar, Alok K.; Jenkins, Susan L.; Bacchus, David L.
1990-01-01
A series of cold flow heat transfer tests was conducted with a 7.5-percent scale model of the Space Shuttle Rocket Motor (SRM) to measure the heat transfer coefficients in the separated flow region around the nose of the submerged nozzle. Modifications were made to an existing 7.5 percent scale model of the internal geometry of the aft end of the SRM, including the gimballed nozzle in order to accomplish the measurements. The model nozzle nose was fitted with a stainless steel shell with numerous thermocouples welded to the backside of the thin wall. A transient 'thin skin' experimental technique was used to measure the local heat transfer coefficients. The effects of Reynolds number, nozzle gimbal angle, and model location were correlated with a Stanton number versus Reynolds number correlation which may be used to determine the convective heating rates for the full scale Space Shuttle Solid Rocket Motor nozzle.
Le Dreau, Jerome; Heiselberg, Per; Jensen, Rasmus Lund
2013-01-01
Night-time ventilation is a promising approach to reduce the energy needed for cooling buildings without reducing thermal comfort. Nevertheless actual building simulation tools have showed their limits in predicting accurately the efficiency of night-time ventilation, mainly due to inappropriate...... air and the room, and floor emissivities. This extensive experimental study enabled a detailed analysis of the convective and radiative flow at the different surfaces of the room. The experimentally derived convective heat transfer coefficients (CHTC) have been compared to existing correlations...... ventilation, the convective heat transfer was well predicted by existing correlations. Nevertheless the change of floor emissivity influenced the CHTC at the surface of interest....
Aspects of radiation heat transfer in arrays of fixed discrete surfaces
Drost, M.K.; Palmer, B.J. [Pacific Northwest Lab., Richland, WA (United States); Welty, J.R. [Oregon State Univ., Corvallis, OR (United States)
1993-08-01
Arrays of fixed discrete surfaces are encountered in a number of important applications. Evaluating radiant heat transfer in an array of fixed discrete surfaces is challenging because array optical properties are often nonhomogeneous and anisotropic. This article presents the results of a Monte Carlo simulation of radiation heat transfer in several array geometries. The results show that for the array geometries included in the study, the extinction coefficient is strongly anisotropic and that optical properties are dependent on both the geometric arrangement of the elements and the scattering characteristics of individual elements.
Effect of Lubricant Viscosity and Surface Roughness on Coefficient of Friction in Rolling Contact
S.G. Ghalme
2013-12-01
Full Text Available The main objective of this paper is to investigate the effect of surface roughness and lubricant viscosity on coefficient of friction in silicon nitride- steel rolling contact. Two samples of silicon nitride with two different values of surface roughness were tested against steel counter face. The test was performed on four ball tester in presence of lubricant with two different values of viscosity. Taguchi technique a methodology in design of experiment implemented to plan the experimentation and same is utilized to evaluate the interacting effect of surface roughness and lubricant viscosity. Analysis of experimental results presents a strong interaction between surface roughness and lubricant viscosity on coefficient of friction in rolling contact.
Convective Heat Transfer from Castings of Ice Roughened Surfaces in Horizontal Flight
Dukhan, Nihad; Vanfossen, G. James, Jr.; Masiulaniec, K. Cyril; Dewitt, Kenneth J.
1995-01-01
A technique was developed to cast frozen ice shapes that had been grown on a metal surface. This technique was applied to a series of ice shapes that were grown in the NASA Lewis Icing Research Tunnel on flat plates. Eight different types of ice growths, characterizing different types of roughness, were obtained from these plates, from which aluminum castings were made. Test strips taken from these castings were outfitted with heat flux gages, such that when placed in a dry wind tunnel, they could be used to experimentally map out the convective heat transfer coefficient in the direction of flow from the roughened surfaces. The effects on the heat transfer coefficient for parallel flow, which simulates horizontal flight, were studied. The results of this investigation can be used to help size heaters for wings, helicopter rotor blades, jet engine intakes, etc., or de-icing for anti-icing applications where the flow is parallel to the iced surface.
Nogueira, Bruno L; Pérez, Julio; van Loosdrecht, Mark C M; Secchi, Argimiro R; Dezotti, Márcia; Biscaia, Evaristo C
2015-09-01
In moving bed biofilm reactors (MBBR), the removal of pollutants from wastewater is due to the substrate consumption by bacteria attached on suspended carriers. As a biofilm process, the substrates are transported from the bulk phase to the biofilm passing through a mass transfer resistance layer. This study proposes a methodology to determine the external mass transfer coefficient and identify the influence of the mixing intensity on the conversion process in-situ in MBBR systems. The method allows the determination of the external mass transfer coefficient in the reactor, which is a major advantage when compared to the previous methods that require mimicking hydrodynamics of the reactor in a flow chamber or in a separate vessel. The proposed methodology was evaluated in an aerobic lab-scale system operating with COD removal and nitrification. The impact of the mixing intensity on the conversion rates for ammonium and COD was tested individually. When comparing the effect of mixing intensity on the removal rates of COD and ammonium, a higher apparent external mass transfer resistance was found for ammonium. For the used aeration intensities, the external mass transfer coefficient for ammonium oxidation was ranging from 0.68 to 13.50 m d(-1) and for COD removal 2.9 to 22.4 m d(-1). The lower coefficient range for ammonium oxidation is likely related to the location of nitrifiers deeper in the biofilm. The measurement of external mass transfer rates in MBBR will help in better design and evaluation of MBBR system-based technologies.
Accurate measurement of the kinetic coefficient of friction between a surface and a granular mass
Rademacher, F.J.C.
1978-01-01
A device has been developed for correct measurement of the kinematic coefficient of friction between a cohesionless granular material and a surface. Particle size may range from 0.5 up to about 9 mm, depending somewhat on the desired accuracy. Sliding velocity of the granules with respect to the sur
Study on Absorption Heat transfer of Two-Dimensionally Constant Curvature Surface Tubes-1
Ogawa, Kiyoshi; Isshiki, Naotsugu
In order to get better heat transfer coefficient of absorption in actual apparatus, it is considered that the wettability of the surface should be high, and that the thickness of liquid film should not be too thin or too thick all over the surface. So, new conception of two-dimensionally constant curvature surface (CCS) for absorption heat transfer has been introduced for the first time by the authors. First, theoretical CCS section curves of CCS tubes were calculated, and some of them were manufactured for the test. The wettability of CCS is tested and compared to the other finned tubes (radial fin tubes of triangular and rectangular profiles). As may be seen from photographs and compared to the other finned tubes, on the CCS surface, the thickness of liquid has shown to be even all over the surface without creating paticulary thick or thin place, so that, liquid films are very wettable on the CCS surface.
MASS TRANSFER COEFFICIENTS FOR A NON-NEWTONIAN FLUID AND WATER WITH AND WITHOUT ANTI-FOAM AGENTS
Leishear, R.
2009-09-09
Mass transfer rates were measured in a large scale system, which consisted of an 8.4 meter tall by 0.76 meter diameter column containing one of three fluids: water with an anti-foam agent, water without an anti-foam agent, and AZ101 simulant, which simulated a non-Newtonian nuclear waste. The testing contributed to the evaluation of large scale mass transfer of hydrogen in nuclear waste tanks. Due to its radioactivity, the waste was chemically simulated, and due to flammability concerns oxygen was used in lieu of hydrogen. Different liquids were used to better understand the mass transfer processes, where each of the fluids was saturated with oxygen, and the oxygen was then removed from solution as air bubbled up, or sparged, through the solution from the bottom of the column. Air sparging was supplied by a single tube which was co-axial to the column, the decrease in oxygen concentration was recorded, and oxygen measurements were then used to determine the mass transfer coefficients to describe the rate of oxygen transfer from solution. Superficial, average, sparging velocities of 2, 5, and 10 mm/second were applied to each of the liquids at three different column fill levels, and mass transfer coefficient test results are presented here for combinations of superficial velocities and fluid levels.
octanol/water partition coefficient using solvation free energy and solvent-accessible surface area
无
2001-01-01
The regression model for octanol/water partition coefficients (Kow ), is founded with only two molecular descriptors available through quantum chemical calculations: solvation free energy (△ Gs ), and solvent-accessible surface area (SASA). For the properties of 47 organic compounds from 17 types, the model gives a oonection coefficient (adjusted for degrees of freedom) of 0.959 and a standard error of 0.277 log unit. It is a suitable way to predict the partition properties that are related to solute-solvent interactions in the water phase.
Transient radiative heat transfer in an inhomogeneous participating medium with Fresnel’s surfaces
2008-01-01
This paper studies the radiative heat transfer within an inhomogeneous and isot- ropically scattering medium with reflecting Fresnel’s surfaces. Thermal radiation transfers in a curve inside a medium with an inhomogeneous distribution of a re- fractive index. The inhomogenous medium is divided into n homogenous isother- mal sub-layers and in each sub-layer the radiation transfers in a straight line. By adopting a multilayer radiative transfer model and using a ray-tracing/nodal- ana- lyzing method, a radiative transfer model is built for the inhomogenous participat- ing medium. In the multilayer model, a criterion for refraction / total reflection at the interfaces between neighboring sub-layers is introduced, avoiding the integral singularity and reflection at physically inexistent interfaces (only the total reflection is considered). Transient thermal behavior is examined when the parameters of the radiative properties such as refractive indexes, extinction coefficients, and sin- gle-scattering albedoes vary continually along the thickness direction.
Sabatier, Romuald; Fossati, Caroline; Bourennane, Salah; Di Giacomo, Antonio
2008-10-01
Model Based Optical Proximity Correction (MBOPC) is since a decade a widely used technique that permits to achieve resolutions on silicon layout smaller than the wave-length which is used in commercially-available photolithography tools. This is an important point, because masks dimensions are continuously shrinking. As for the current masks, several billions of segments have to be moved, and also, several iterations are needed to reach convergence. Therefore, fast and accurate algorithms are mandatory to perform OPC on a mask in a reasonably short time for industrial purposes. As imaging with an optical lithography system is similar to microscopy, the theory used in MBOPC is drawn from the works originally conducted for the theory of microscopy. Fourier Optics was first developed by Abbe to describe the image formed by a microscope and is often referred to as Abbe formulation. This is one of the best methods for optimizing illumination and is used in most of the commercially available lithography simulation packages. Hopkins method, developed later in 1951, is the best method for mask optimization. Consequently, Hopkins formulation, widely used for partially coherent illumination, and thus for lithography, is present in most of the commercially available OPC tools. This formulation has the advantage of a four-way transmission function independent of the mask layout. The values of this function, called Transfer Cross Coefficients (TCC), describe the illumination and projection pupils. Commonly-used algorithms, involving TCC of Hopkins formulation to compute aerial images during MBOPC treatment, are based on TCC decomposition into its eigenvectors using matricization and the well-known Singular Value Decomposition (SVD) tool. These techniques that use numerical approximation and empirical determination of the number of eigenvectors taken into account, could not match reality and lead to an information loss. They also remain highly runtime consuming. We propose an
Matteoni, G.; Georgakis, C.T.
2012-01-01
Theoretical and experimental investigations to date have assumed that bridge cables can be modeled as ideal circular cylinders and the associated aerodynamic coefficients are invariant with the wind angle-of-attack. On the other hand, bridge cables are normally characterized by local alterations...... of their inherent surface roughness and shape, which might present a significant disturbance for the surrounding wind flow. The present study focuses on the experimental determination, based on static wind tunnel tests, of the aerodynamic coefficients of full-scale bridge cable section models both perpendicular...... and inclined to the flow, for varying wind angles-of-attack. The wind tunnel test results demonstrate that the aerodynamic coefficients of bridge cables can be significantly affected by the wind angle-of-attack....
Orgill, James J; Atiyeh, Hasan K; Devarapalli, Mamatha; Phillips, John R; Lewis, Randy S; Huhnke, Raymond L
2013-04-01
Trickle-bed reactor (TBR), hollow fiber membrane reactor (HFR) and stirred tank reactor (STR) can be used in fermentation of sparingly soluble gasses such as CO and H2 to produce biofuels and bio-based chemicals. Gas fermenting reactors must provide high mass transfer capabilities that match the kinetic requirements of the microorganisms used. The present study compared the volumetric mass transfer coefficient (K(tot)A/V(L)) of three reactor types; the TBR with 3 mm and 6 mm beads, five different modules of HFRs, and the STR. The analysis was performed using O2 as the gaseous mass transfer agent. The non-porous polydimethylsiloxane (PDMS) HFR provided the highest K(tot)A/V(L) (1062 h(-1)), followed by the TBR with 6mm beads (421 h(-1)), and then the STR (114 h(-1)). The mass transfer characteristics in each reactor were affected by agitation speed, and gas and liquid flow rates. Furthermore, issues regarding the comparison of mass transfer coefficients are discussed.
Yao, Kangning; Chi, Yong; Wang, Fei; Yan, Jianhua; Ni, Mingjiang; Cen, Kefa
2016-01-01
A commonly used aeration device at present has the disadvantages of low mass transfer rate because the generated bubbles are several millimeters in diameter which are much bigger than microbubbles. Therefore, the effect of a microbubble on gas-liquid mass transfer and wastewater treatment process was investigated. To evaluate the effect of each bubble type, the volumetric mass transfer coefficients for microbubbles and conventional bubbles were determined. The volumetric mass transfer coefficient was 0.02905 s(-1) and 0.02191 s(-1) at a gas flow rate of 0.67 L min(-1) in tap water for microbubbles and conventional bubbles, respectively. The degradation rate of simulated municipal wastewater was also investigated, using aerobic activated sludge and ozone. Compared with the conventional bubble generator, the chemical oxygen demand (COD) removal rate was 2.04, 5.9, 3.26 times higher than those of the conventional bubble contactor at the same initial COD concentration of COD 200 mg L(-1), 400 mg L(-1), and 600 mg L(-1), while aerobic activated sludge was used. For the ozonation process, the rate of COD removal using microbubble generator was 2.38, 2.51, 2.89 times of those of the conventional bubble generator. Based on the results, the effect of initial COD concentration on the specific COD degradation rate were discussed in different systems. Thus, the results revealed that microbubbles could enhance mass transfer in wastewater treatment and be an effective method to improve the degradation of wastewater.
Alkali halide solutions under thermal gradients: soret coefficients and heat transfer mechanisms.
Römer, Frank; Wang, Zilin; Wiegand, Simone; Bresme, Fernando
2013-07-11
We report an extensive analysis of the non-equilibrium response of alkali halide aqueous solutions (Na(+)/K(+)-Cl(-)) to thermal gradients using state of the art non-equilibrium molecular dynamics simulations and thermal diffusion forced Rayleigh scattering experiments. The coupling between the thermal gradient and the resulting ionic salt mass flux is quantified through the Soret coefficient. We find the Soret coefficient is of the order of 10(-3) K(-1) for a wide range of concentrations. These relatively simple solutions feature a very rich behavior. The Soret coefficient decreases with concentration at high temperatures (higher than T ∼ 315 K), whereas it increases at lower temperatures. In agreement with previous experiments, we find evidence for sign inversion in the Soret coefficient of NaCl and KCl solutions. We use an atomistic non-equilibrium molecular dynamics approach to compute the Soret coefficients in a wide range of conditions and to attain further microscopic insight on the heat transport mechanism and the behavior of the Soret coefficient in aqueous solutions. The models employed in this work reproduce the magnitude of the Soret coefficient, and the general dependence of this coefficient with temperature and salt concentration. We use the computer simulations as a microscopic approach to establish a correlation between the sign and magnitude of the Soret coefficients and ionic solvation and hydrogen bond structure of the solutions. Finally, we report an analysis of heat transport in ionic solution by quantifying the solution thermal conductivity as a function of concentration. The simulations accurately reproduce the decrease of the thermal conductivity with increasing salt concentration that is observed in experiments. An explanation of this behavior is provided.
Studying heat transfer enhancement for water boiling on a surface with micro- and nanorelief
Kuzma-Kichta, Yu. A.; Lavrikov, A. V.; Shustov, M. V.; Chursin, P. S.; Chistyakova, A. V.; Zvonarev, Yu. A.; Zhukov, V. M.; Vasil'eva, L. T.
2014-03-01
We present the results from a study of heat transfer enhancement for bulk water boiling at atmospheric pressure on a surface with micro- and nanorelief, including a relief formed from silicon carbide and aluminum oxide nanoparticles. Horizontally oriented steel tube 1.2 mm in diameter and copper plate 15 × 3 mm in size were selected as test sections. The process was recorded by means of a video camera, and the values of heat transfer, critical heat fluxes, and contact angles were measured. The use of surface with micro- and nanorelief makes it possible to obtain a significantly higher critical heat flux and boiling heat transfer coefficient owing to a change of surface wettability. The results of investigations can find use in compact heat exchangers, refrigerating plants, heat pipes, in the mirrors of high-capacity lasers, in the targets and resonators of charged particle accelerators and for external cooling of reactor vessels under emergency conditions.
Boiling Heat Transfer on Porous Surfaces with Vapor Channels
吴伟; 杜建华; 王补宣
2002-01-01
Boiling heat transfer on porous coated surfaces with vapor channels was investigated experimentally to determine the effects of the size and density of the vapor channels on the boiling heat transfer. Observations showed that bubbles escaping from the channels enhanced the heat transfer. Three regimes were identified: liquid flooding, bubbles in the channel and the bottom drying out region. The maximum heat transfer occurred for an optimum vapor channel density and the boiling heat transfer performance was increased if the channels were open to the bottom of the porous coating.
Investigation of Enhanced Boiling Heat Transfer from Porous Surfaces
LinZhiping; MaTongze; 等
1994-01-01
Experimental investigations of boiling heat transfer from porous surfaces at atmospheric pressure were performne.The porous surfaces are plain tubes coverd with metal screens.V-shaped groove tubes covered with screens,plain tubes sintered with screens.and V-shaped groove tubes sintered with screens,The experimental results show that sintering metal screens around spiral V-shaped groove tubes can greatly improve the boiling heat transfer,The boiling hystesis was observed in the experiment.This paper discusses the mechanism of the boiling heat transfer from those kinds of porous surfaces stated above.
Effects of surface wettability on fast liquid transfer
Chen, H.; Tang, T.; Amirfazli, A.
2015-11-01
A systematic experimental study was performed to understand the role of surface contact angles in affecting the process of fast liquid transfer. Surfaces with different wettabilities were used, and the transfer ratio (α, the amount of liquid transferred to the acceptor surface over the total amount of liquid) was measured for each pair of surfaces. A numerical model based on the volume of fluid method was developed to help understand the experimental results. The surface wettability was shown to significantly affect the boundaries between three regimes based on stretching speeds: quasi-static (surface force dominated), transition (surface/viscous/inertia forces all important) and dynamic (viscous/inertia forces dominated). Specifically, the values of the boundary speeds were found to increase with |α0 - 0.5|, where α0 is the transfer ratio in the quasi-static regime, and α0 is governed by the surface receding contact angles. Based on our results, an empirical equation to describe the transfer ratio as function of stretching speed was proposed. This equation can also be used as a prediction tool for the value of α for a fast transfer system.
Webster John G
2006-10-01
Full Text Available Abstract Background We need a sensor to measure the convective heat transfer coefficient during ablation of the heart or liver. Methods We built a minimally invasive instrument to measure the in vivo convective heat transfer coefficient, h in animals, using a Wheatstone-bridge circuit, similar to a hot-wire anemometer circuit. One arm is connected to a steerable catheter sensor whose tip is a 1.9 mm × 3.2 mm thin film resistive temperature detector (RTD sensor. We used a circulation system to simulate different flow rates at 39°C for in vitro experiments using distilled water, tap water and saline. We heated the sensor approximately 5°C above the fluid temperature. We measured the power consumed by the sensor and the resistance of the sensor during the experiments and analyzed these data to determine the value of the convective heat transfer coefficient at various flow rates. Results From 0 to 5 L/min, experimental values of h in W/(m2·K were for distilled water 5100 to 13000, for tap water 5500 to 12300, and for saline 5400 to 13600. Theoretical values were 1900 to 10700. Conclusion We believe this system is the smallest, most accurate method of minimally invasive measurement of in vivo h in animals and provides the least disturbance of flow.
P. Raveendiran
2015-06-01
Full Text Available The heat transfer coefficients and friction factors of a baffled shell and heat pipe heat exchanger with various inclination angles were determined experimentally; using methanol as working fluid and water as heat transport fluid were reported. Heat pipe heat exchanger reported in this investigation have inclination angles varied between 15o and 60o for different mass flow rates and temperature at the shell side of the heat exchanger. All the required parameters like outlet temperature of both hot and cold side of heat exchanger and mass flow rate of fluids were measured using an appropriate instrument. Different tests were performed from which condenser side heat transfer coefficient and friction factor were calculated. In all operating conditions it has been found that the heat transfer coefficient increases by increasing the mass flow rate and angle of inclination. The reduction in friction factor occurs when the Reynolds number is increased. The overall optimum experimental effectiveness of GABSHPHE has found to be 42% in all operating conditioning at ψ = 45o.
Heat transfer between elastic solids with randomly rough surfaces.
Volokitin, A I; Lorenz, B; Persson, B N J
2010-01-01
We study the heat transfer between elastic solids with randomly rough surfaces.We include both the heat transfer from the area of real contact, and the heat transfer between the surfaces in the non-contact regions.We apply a recently developed contact mechanics theory, which accounts for the hierarchical nature of the contact between solids with roughness on many different length scales. For elastic contact, at the highest (atomic) resolution the area of real contact typically consists of atomic (nanometer) sized regions, and we discuss the implications of this for the heat transfer. For solids with very smooth surfaces, as is typical in many modern engineering applications, the interfacial separation in the non-contact regions will be very small, and for this case we show the importance of the radiative heat transfer associated with the evanescent electromagnetic waves which exist outside of all bodies.
Modeling of ultrasound contrast agents bubble dynamics with modified surface tension coefficient
ZHENG LuJie; TU Juan; CHEN WeiZhong
2009-01-01
The current work proposes a model describing the dynamics of coated microbubbles, which simplifies the traditional three-layer model to a two-layer one by introducing a visco-elastic interface with variable surface tension coefficients to connect the gas zone and the liquid zone. In the modified model, the traditional two interfaces boundary conditions are combined into one to simplify the description of the bubble. Moreover, the surface tension coefficient is defined as a function of bubble radius with lower and upper limits, which are related to the buckling and rupture mechanisms of the bubble. Further discussion is made regarding the effects resulting from the change of the surface tension coefficient on bubble dynamics. The dynamic responses of Optison and Sonozoid microbubbles, measured experimentally based on light scattering technology (adapted from previously published work), are simulated using both classic three-layer models (e.g. Church's model) and simplified model. The resuits show that our simplified model works as well as the Church's model.
Determination of interface heat-transfer coefficients for permanent-mold casting of Ti-6Al-4V
Kobryn, P. A.; Semiatin, S. L.
2001-08-01
Interface heat-transfer coefficients ( h 0) for permanent-mold casting (PMC) of Ti-6Al-4V were established as a function of casting surface temperature using a calibration-curve technique. Because mold geometry has a strong effect on h 0, values were determined for both of the two limiting interface types, “shrink-off” and “shrink-on.” For this purpose, casting experiments with instrumented molds were performed for cylinder- and pipe-shaped castings. The measured temperature transients were used in conjunction with two-dimensional (2-D) axisymmetric finite-element method (FEM) simulations to determine h 0( T). For the shrink-off interface type, h 0 was found to decrease linearly from 2000 to 1500 W/m2 K between the liquidus and the solidus, from 1500 to 325 W/m2 K between the solidus and the gap-formation temperature, and at a rate of 0.3 W/m2 K/K thereafter. For the shrink-on interface type, h 0 was found to increase linearly from 2000 to 2500 W/m2 K between the liquidus and the solidus temperatures, from 2500 to 5000 W/m2 K between the solidus and the gap-formation temperature, and to remain constant thereafter. The shrink-on values were up to 100 times the shrink-off values, indicating the importance of accounting for the interface geometry in FEM simulations of this process. The FEM-predicted casting and mold temperatures were found to be insensitive to certain changes in the h 0 values and sensitive to others. A comparison to published h 0 values for PMC of aluminum alloys showed some similarities and some differences.
Gilles Hebrard
2009-11-01
Full Text Available The objective of this present paper is to propose a new theoretical prediction method of the volumetric mass transfer coefficient (k_{L}a occurring in a gas-liquid contactor based on the dissociation of the liquid-side mass transfer coefficient (k_{L} and the interfacial area (a. The calculated results have been compared with those obtained with the experimental process in a small-scale bubble column. Tap water was used as liquid phase and an elastic membrane with a single orifice as gas sparger. Only the dynamic bubble regime was considered in this work (Re_{OR}= 1501000 and We = 0.0024. This study has clearly shown that, whatever the operating conditions under test, the generated bubble diameters (d
Heat transfer enhancement and surface thermostabilization for pool boiling on porous structures
Wojcik Tadeusz Michal
2012-04-01
Full Text Available The scope of the article includes the description of the experimental setup, methodology of the experimental studies, the study results for pool boiling heat transfer coefficient encountered on sintered capillary porous coverings. The results of own studies presented here refer to the boiling in a large volume on copper fibrous coverings. Hysteresis type I, II and III were described. Several examples of capillary porous surface coverings applications in purposely chosen complex boiling heat transfer processes have been presented based on Wojcik and Poniewski patents.
Surface diffusion coefficient of Au atoms on single layer graphene grown on Cu
Ruffino, F., E-mail: francesco.ruffino@ct.infn.it; Cacciato, G.; Grimaldi, M. G. [Dipartimento di Fisica ed Astronomia-Universitá di Catania, via S. Sofia 64, 95123 Catania, Italy and MATIS IMM-CNR, via S. Sofia 64, 95123 Catania (Italy)
2014-02-28
A 5 nm thick Au film was deposited on single layer graphene sheets grown on Cu. By thermal processes, the dewetting phenomenon of the Au film on the graphene was induced so to form Au nanoparticles. The mean radius, surface-to-surface distance, and surface density evolution of the nanoparticles on the graphene sheets as a function of the annealing temperature were quantified by scanning electron microscopy analyses. These quantitative data were analyzed within the classical mean-field nucleation theory so to obtain the temperature-dependent Au atoms surface diffusion coefficient on graphene: D{sub S}(T)=[(8.2±0.6)×10{sup −8}]exp[−(0.31±0.02(eV)/(at) )/kT] cm{sup 2}/s.
Flow and heat transfer in compact offset strip fin surfaces
Junqi DONG; Jiangping CHEN; Zhijiu CHEN
2008-01-01
Experimental studies of air-side heat transfer and pressure drop characteristics of offset strip fins and flat tube heat exchangers were performed. A series of tests were conducted for 9 heat exchangers with different fin space, fin height, fin strip length and flow length, at a constant tube-side water flow rate of 2.5 m3/h. The char-acteristics of the heat transfer and pressure drop of differ-ent fin space, fin height and fin length were analyzed and compared. The curves of the heat transfer coefficients vs. The pumping power per unit frontal area were then plot-ted. Moreover, the enhanced heat transfer mechanism of offset strip fins was analyzed using field synergy theory. The results showed that fin length and flow length have more obviously effect on the thermal hydraulic character-istics of offset strip fins.
Rocha, Alan Carlos Bueno da
1997-07-01
A heat transfer (condenser) of a domestic freezer was tested in a vertical channel in order to study the influence of the chimney effect in the optimization of the heat transfer coefficient. The variation of the opening of the channel, position and the heating power of the heat exchanger in the heat transfer coefficient was considered. The influence of the surface emissivity on the heat transfer by thermal radiation was studied with the heat exchanger testes without paint and with black paint. The air velocity entering the channel was measured with a hot wire anemometer. In order to evaluate the chimney effect, the heat exchanger was testes in a open ambient. This situation simulates its operational conditions when installed on the freezer system. The variables collected in the experimental procedures was gathered in the form of dimensionless parameters as Nusselt, Rayleigh, Grashof and Prandtl numbers, and dimensional parameters of the convection. The results showed that the highest heat transfer value occurred when both a specific position and a specific channel opening were used. The experiments pointed out that the radiation contribution must be considered in heat transfer calculations. The conclusions showed that different channel openings can improve the heat transfer coefficient in this heat transfer exchanger. (author)
Oxygen transfer in circular surface aeration tanks.
Rao, Achanta Ramakrishna; Patel, Ajey Kumar; Kumar, Bimlesh
2009-06-01
Surface aeration systems employed in activated sludge plants are the most energy-intensive units of the plants and typically account for a higher percentage of the treatment facility's total energy use. The geometry of the aeration tank imparts a major effect on the system efficiency. It is said that at optimal geometric conditions, systems exhibits the maximum efficiency. Thus the quantification of the optimal geometric conditions in surface aeration tanks is needed. Optimal geometric conditions are also needed to scale up the laboratory result to the field installation. In the present work, experimental studies have been carried out on baffled and unbaffled circular surface aeration tanks to ascertain the optimal geometric conditions. It is found that no optimal geometric conditions exist for the liquid/water depth in circular surface aeration tanks; however, for design purposes, a standard value has been assumed. Based on the optimal geometric conditions, a scale-up equation has been developed for the baffled circular surface aeration tanks.
Unsteady convection flow and heat transfer over a vertical stretching surface.
Wenli Cai
Full Text Available This paper investigates the effect of thermal radiation on unsteady convection flow and heat transfer over a vertical permeable stretching surface in porous medium, where the effects of temperature dependent viscosity and thermal conductivity are also considered. By using a similarity transformation, the governing time-dependent boundary layer equations for momentum and thermal energy are first transformed into coupled, non-linear ordinary differential equations with variable coefficients. Numerical solutions to these equations subject to appropriate boundary conditions are obtained by the numerical shooting technique with fourth-fifth order Runge-Kutta scheme. Numerical results show that as viscosity variation parameter increases both the absolute value of the surface friction coefficient and the absolute value of the surface temperature gradient increase whereas the temperature decreases slightly. With the increase of viscosity variation parameter, the velocity decreases near the sheet surface but increases far away from the surface of the sheet in the boundary layer. The increase in permeability parameter leads to the decrease in both the temperature and the absolute value of the surface friction coefficient, and the increase in both the velocity and the absolute value of the surface temperature gradient.
Unsteady convection flow and heat transfer over a vertical stretching surface.
Cai, Wenli; Su, Ning; Liu, Xiangdong
2014-01-01
This paper investigates the effect of thermal radiation on unsteady convection flow and heat transfer over a vertical permeable stretching surface in porous medium, where the effects of temperature dependent viscosity and thermal conductivity are also considered. By using a similarity transformation, the governing time-dependent boundary layer equations for momentum and thermal energy are first transformed into coupled, non-linear ordinary differential equations with variable coefficients. Numerical solutions to these equations subject to appropriate boundary conditions are obtained by the numerical shooting technique with fourth-fifth order Runge-Kutta scheme. Numerical results show that as viscosity variation parameter increases both the absolute value of the surface friction coefficient and the absolute value of the surface temperature gradient increase whereas the temperature decreases slightly. With the increase of viscosity variation parameter, the velocity decreases near the sheet surface but increases far away from the surface of the sheet in the boundary layer. The increase in permeability parameter leads to the decrease in both the temperature and the absolute value of the surface friction coefficient, and the increase in both the velocity and the absolute value of the surface temperature gradient.
Ben Yaghlene, H; Leguerinel, I; Hamdi, M; Mafart, P
2009-07-31
In this study, predictive microbiology and food engineering were combined in order to develop a new analytical model predicting the bacterial growth under dynamic temperature conditions. The proposed model associates a simplified primary bacterial growth model without lag, the secondary Ratkowsky "square root" model and a simplified two-parameter heat transfer model regarding an infinite slab. The model takes into consideration the product thickness, its thermal properties, the ambient air temperature, the convective heat transfer coefficient and the growth parameters of the micro organism of concern. For the validation of the overall model, five different combinations of ambient air temperature (ranging from 8 degrees C to 12 degrees C), product thickness (ranging from 1 cm to 6 cm) and convective heat transfer coefficient (ranging from 8 W/(m(2) K) to 60 W/(m(2) K)) were tested during a cooling procedure. Moreover, three different ambient air temperature scenarios assuming alternated cooling and heating stages, drawn from real refrigerated food processes, were tested. General agreement between predicted and observed bacterial growth was obtained and less than 5% of the experimental data fell outside the 95% confidence bands estimated by the bootstrap percentile method, at all the tested conditions. Accordingly, the overall model was successfully validated for isothermal and dynamic refrigeration cycles allowing for temperature dynamic changes at the centre and at the surface of the product. The major impact of the convective heat transfer coefficient and the product thickness on bacterial growth during the product cooling was demonstrated. For instance, the time needed for the same level of bacterial growth to be reached at the product's half thickness was estimated to be 5 and 16.5 h at low and high convection level, respectively. Moreover, simulation results demonstrated that the predicted bacterial growth at the air ambient temperature cannot be assumed to be
Jianyin Xiong
Full Text Available The diffusion coefficient (D(m and material/air partition coefficient (K are two key parameters characterizing the formaldehyde and volatile organic compounds (VOC sorption behavior in building materials. By virtue of the sorption process in airtight chamber, this paper proposes a novel method to measure the two key parameters, as well as the convective mass transfer coefficient (h(m. Compared to traditional methods, it has the following merits: (1 the K, D(m and h(m can be simultaneously obtained, thus is convenient to use; (2 it is time-saving, just one sorption process in airtight chamber is required; (3 the determination of h(m is based on the formaldehyde and VOC concentration data in the test chamber rather than the generally used empirical correlations obtained from the heat and mass transfer analogy, thus is more accurate and can be regarded as a significant improvement. The present method is applied to measure the three parameters by treating the experimental data in the literature, and good results are obtained, which validates the effectiveness of the method. Our new method also provides a potential pathway for measuring h(m of semi-volatile organic compounds (SVOC by using that of VOC.
Radiative transfer modeling of surface chemical deposits
Reichardt, Thomas A.; Kulp, Thomas J.
2016-05-01
Remote detection of a surface-bound chemical relies on the recognition of a pattern, or "signature," that is distinct from the background. Such signatures are a function of a chemical's fundamental optical properties, but also depend upon its specific morphology. Importantly, the same chemical can exhibit vastly different signatures depending on the size of particles composing the deposit. We present a parameterized model to account for such morphological effects on surface-deposited chemical signatures. This model leverages computational tools developed within the planetary and atmospheric science communities, beginning with T-matrix and ray-tracing approaches for evaluating the scattering and extinction properties of individual particles based on their size and shape, and the complex refractive index of the material itself. These individual-particle properties then serve as input to the Ambartsumian invariant imbedding solution for the reflectance of a particulate surface composed of these particles. The inputs to the model include parameters associated with a functionalized form of the particle size distribution (PSD) as well as parameters associated with the particle packing density and surface roughness. The model is numerically inverted via Sandia's Dakota package, optimizing agreement between modeled and measured reflectance spectra, which we demonstrate on data acquired on five size-selected silica powders over the 4-16 μm wavelength range. Agreements between modeled and measured reflectance spectra are assessed, while the optimized PSDs resulting from the spectral fitting are then compared to PSD data acquired from independent particle size measurements.
Laser texturing of Hastelloy C276 alloy surface for improved hydrophobicity and friction coefficient
Yilbas, B. S.; Ali, H.
2016-03-01
Laser treatment of Hastelloy C276 alloy is carried out under the high pressure nitrogen assisting gas environment. Morphological and metallurgical changes in the laser treated layer are examined using the analytical tools including, scanning electron and atomic force microscopes, X-ray diffraction, energy dispersive spectroscopy, and Fourier transform infrared spectroscopy. Microhardness is measured and the residual stress formed in the laser treated surface is determined from the X-ray data. The hydrophibicity of the laser treated surface is assessed using the sessile drop method. Friction coefficient of the laser treated layer is obtained incorporating the micro-tribometer. It is found that closely spaced laser canning tracks create a self-annealing effect in the laser treated layer and lowers the thermal stress levels through modifying the cooling rates at the surface. A dense structure, consisting of fine size grains, enhances the microhardness of the surface. The residual stress formed at the surface is compressive and it is in the order of -800 MPa. Laser treatment improves the surface hydrophobicity significantly because of the formation of surface texture composing of micro/nano-pillars.
Lewandowska, Monika; Malinowski, Leszek
2016-01-01
The data resulting from the thermal-hydraulic test of the ITER TF CICC are used to determine the flow partition and the overall effective heat transfer coefficient (hBC) between bundle and central channel in a direct way, i.e. by analysis of the heat transfer between both flow channels, based on the mass and energy balance equations and the readings of thermometers located inside the cable. In cases without a local heat source in the considered cable segment the obtained hBC values were consistent with those obtained in earlier studies by analysis of experimental data using indirect methods. It was also observed that the transverse heat transfer was strongly enhanced in a cable segment heated from outside. This phenomenon results from the mass transfer from the bundle region to the central channel. The experimental hBC data obtained for the case without a heat source in the considered segment were also compared with those calculated using various heat transfer correlations.
Improvement of dropwise condensation heat transfer using hydrophobic nano porous surfaces
Kim, Sang Eun; Kim, Hyun Dae [Kyung Hee Univ., Seoul (Korea, Republic of)
2012-10-15
Recently interest of passive system in thermal hydraulic safety system of nuclear power plants has been increased. Passive residual heat removal system (PRHRS) is applied to SMART and APR+ for providing the sufficient cooling capacity against accident conditions. PRHRS is a device for removing the decay heat that cools steam through condensation heat transfer in emergency tank. Condensation is one of most important heat transfer methods in almost industry including the PRHRS. Condensation is classified, according to shape of condensate, into drop-wise condensation and film wise condensation. Drop-wise condensation (DWC) exhibits a significantly higher heat transfer coefficient than film wise condensation (FWC). Whether DWC or FWC occurs in a heat transfer surface is strongly affected by wettability of a surface. It is known that DWC is appears on low wettability surfaces while FWC is appears on high wettability one. In this study, nano-porous hydrophobic surfaces were prepared and tested for the improvement of dropwise condensation heat transfer performance.
Partition coefficients for the SAMPL5 challenge using transfer free energies
Jones, Michael R.; Brooks, Bernard R.; Wilson, Angela K.
2016-11-01
SAMPL challenges (Mobley et al. in J Comput Aided Mol Des 28:135-150, 2014; Skillman in J Comput Aided Mol Des 26:473-474, 2012; Geballe in J Comput Aided Mol Des 24:259-279, 2010; Guthrie in J Phys Chem B 113:4501-4507, 2009) provide excellent opportunities to assess theoretical approaches on new data sets with a goal of gaining greater insight towards protein and ligand modeling. In the SAMPL5 experiment, cyclohexane-water partition coefficients were determined using a vertical solvation scheme in conjunction with the SMD continuum solvent model. Several DFT functionals partnered with correlation consistent basis sets were evaluated for the prediction of the partition coefficients. The approach chosen for the competition, a B3PW91 vertical solvation scheme, yields a mean absolute deviation of 1.9 logP units and performs well at estimating the correct hydrophilicity and hydrophobicity for the full SAMPL5 molecule set.
Miles, Rachael E H; Davies, James F; Reid, Jonathan P
2016-07-20
We explore the dependence of the evaporation coefficient of water from aqueous droplets on the composition of a surface film, considering in particular the influence of monolayer mixed component films on the evaporative mass flux. Measurements with binary component films formed from long chain alcohols, specifically tridecanol (C13H27OH) and pentadecanol (C15H31OH), and tetradecanol (C14H29OH) and hexadecanol (C16H33OH), show that the evaporation coefficient is dependent on the mole fractions of the two components forming the monolayer film. Immediately at the point of film formation and commensurate reduction in droplet evaporation rate, the evaporation coefficient is equal to a mole fraction weighted average of the evaporation coefficients through the equivalent single component films. As a droplet continues to diminish in surface area with continued loss of water, the more-soluble, shorter alkyl chain component preferentially partitions into the droplet bulk with the evaporation coefficient tending towards that through a single component film formed simply from the less-soluble, longer chain alcohol. We also show that the addition of a long chain alcohol to an aqueous-sucrose droplet can facilitate control over the degree of dehydration achieved during evaporation. After undergoing rapid gas-phase diffusion limited water evaporation, binary aqueous-sucrose droplets show a continued slow evaporative flux that is limited by slow diffusional mass transport within the particle bulk due to the rapidly increasing particle viscosity and strong concentration gradients that are established. The addition of a long chain alcohol to the droplet is shown to slow the initial rate of water loss, leading to a droplet composition that remains more homogeneous for a longer period of time. When the sucrose concentration has achieved a sufficiently high value, and the diffusion constant of water has decreased accordingly so that bulk phase diffusion arrest occurs in the monolayer
Jebaraj Johnley Muthuraj, Josiah
Cathodic protection is widely used for corrosion prevention. However, this process generates hydrogen at the protected metal surface, and diffusion of hydrogen through the metal may cause hydrogen embrittlement or hydrogen induced stress corrosion cracking. Thus the choice of a metal for use as fasteners depends upon its hydrogen uptake, permeation, diffusivity and trapping. The diffusivity of hydrogen through four high strength alloys (AISI 4340, alloy 718, alloy 686, and alloy 59) was analyzed by an electrochemical method developed by Devanathan and Stachurski. The effect of plasma nitriding and microstructure on hydrogen permeation through AISI 4340 was studied on six different specimens: as-received (AR) AISI 4340, nitrided samples with and without compound layer, samples quenched and tempered (Q&T) at 320° and 520°C, and nitrided samples Q&T 520°C. Studies on various nitrided specimens demonstrate that both the gamma'-Fe 4N rich compound surface layer and the deeper N diffusion layer that forms during plasma nitriding reduce the effective hydrogen diffusion coefficient, although the gamma'-Fe4N rich compound layer has a larger effect. Multiple permeation transients yield evidence for the presence of only reversible trap sites in as-received, Q&T 320 and 520 AISI 4340 specimens, and the presence of both reversible and irreversible trap sites in nitrided specimens. Moreover, the changes in microstructure during the quenching and tempering process result in a significant decrease in the diffusion coefficient of hydrogen compared to as-received specimens. In addition, density functional theory-based molecular dynamics simulations yield hydrogen diffusion coefficients through gamma'- Fe4N one order of magnitude lower than through α-Fe, which supports the experimental measurements of hydrogen permeation. The effect of microstructure and trapping was also studied in cold rolled, solutionized, and precipitation hardened Inconel 718 foils. The effective hydrogen
Determination of Heat Transfer Coefficient in a Gun Barrel from Experimental Data
1985-01-01
Barrels, BRL-R- 1740, September 1974. AD #BOOO71L. Mark W. Zemansky , Heat and Thermodynamics, McGraw-Hill Book Company Inc., New York, 1957. 3 Max Jacob...September 1974. AD #BOO17lL. 2. Mark W. Zemansky , Heat and Thermodynamics, McGraw-Hill Book Company Inc., New York, 1957. 3. Max Jacob, Heat Transfer, Vol. 1
Ng, Y C; Colsher, C S; Quinn, D J; Thompson, S E
1977-07-15
This document presents tables of diet-to-milk transfer coefficients for radioactive and stable isotopes in the cow. The values are based on an extensive literature review of the secretion of radioisotopes in milk and the concentrations of radioactive or stable isotopes in milk and feed. Transfer coefficients were compiled and tabulated for isotopes of more than 70 elements. The values are summarized in a table of elemental transfer coefficients and also organized into separate tables that reveal their elemental systematics and the effects of physical and chemical form.
Noroviruses on surfaces: Detection, transfer and inactivation
RÃ¶nnqvist, Maria
2014-01-01
Human noroviruses (HuNoVs) are a leading cause of foodborne gastroenteritis worldwide and spread easily among humans via the faecal-oral route. A low infective dose, a high viral load in the vomit and faeces of infected persons, a lack of long-term immunity following previous infection, and a high environmental stability of the viruses all enhance the spreading of HuNoV in the population. The aim of this doctoral thesis is to investigate the prevalence of HuNoVs on environmental surfaces...
Enrique Torres‐Tamayo
2014-01-01
Full Text Available La pérdida de eficiencia del proceso de enfriamiento del licor amoniacal, mediante el uso de intercambiadores de calor de placas, está asociada a imprecisiones en la estimación de los coeficientes de transferencia de calor y la acumulación de incrustaciones en la superficie de intercambio. El objetivo de la investigación es determinar los coeficientes de transferencia de calor y la influencia de lasincrustaciones en la pérdida de eficiencia de la instalación. Mediante un procedimiento iterativo se estableció la ecuación del número de Nusselt y su relación con el número de Reynolds y Prandtl. Se utilizó un diseño experimental multifactorial. Los resultados predicen el conocimiento de los coeficientespara el cálculo del número de Nusselt en ambos fluidos. Los valores de los coeficientes del licor amoniacal son inferiores, ello se debe a la presencia de componentes gaseosos. La ecuación obtenida muestra correspondencia con el modelo de Buonapane, el error comparativo es del 3,55 %.Palabras claves: intercambiador de calor de placas, coeficientes de transferencia de calor, eficiencia térmica.______________________________________________________________________________AbstractThe loss of efficiency of the ammonia liquor cooling process, by means of the plate heat exchanger, is associated to the incorrect estimate of the heat transfer coefficients and the accumulation of inlays in the exchange surface. The objective of the investigation is to determine the transfer coefficients and the influence of the inlays in the efficiency loss of the installation. By means of an iterative procedure was obtained the Nusselt number equation and the relationship with the Reynolds and Prandtl number, for it was used it a design experimental multifactorial. The results predict the knowledge of the coefficients forthe calculation of the Nusselt number for both fluids. The ammonia liquor coefficients values are inferior, due to the presence of gassy
Kandouci Chahr-Eddine; Adjal Yassine
2014-01-01
This present paper deals with a mathematical description of linear axial and torsional vibrations. The normal and tangential stress tensor components produced by axial-torsional deformations and vibrations in the propeller and intermediate shafts, under the influence of propeller-induced static and variable hydrodynamic excitations are also studied. The transfer matrix method related to the constant coefficients of differential equation solutions is used. The advantage of the latter as compared with a well-known method of transfer matrix associated with state vector is the possibility of reducing the number of multiplied matrices when adjacent shaft segments have the same material properties and diameters. The results show that there is no risk of buckling and confirm that the strength of the shaft line depends on the value of the static tangential stresses which is the most important component of the stress tensor.
Liebert, Curt H.; Ehlers, Robert C.
1961-01-01
Local experimental heat-transfer coefficients were measured in the chamber and throat of a 2400-pound-thrust ammonia-oxygen rocket engine with a nominal chamber pressure of 600 pounds per square inch absolute. Three injector configurations were used. The rocket engine was run over a range of oxidant-fuel ratio and chamber pressure. The injector that achieved the best performance also produced the highest rates of heat flux at design conditions. The heat-transfer data from the best-performing injector agreed well with the simplified equation developed by Bartz at the throat region. A large spread of data was observed for the chamber. This spread was attributed generally to the variations of combustion processes. The spread was least evident, however, with the best-performing injector.
Testing of heat transfer coefficient of photovoltaic components%光伏构件的传热系数检测
林磊
2013-01-01
本文首先阐述了建筑围护结构对光伏构件传热性能的要求，然后根据相关标准测试了三种光伏构件，分析影响传热系数的原因，最后分析了三种光伏构件在全国各气候分区的适应性。%In this article, the author described the requirements on the heat transfer performance of photovoltaic component architecture firstly, and then tested three photovoltaic components according to the relevant standard , and the factors which influencing heat transfer co-efficient had been analyzed .Finally, the climate adaptability of three kinds of photovoltaic component had been evaluated .
C. M. Raguraman
2013-01-01
Full Text Available Heat transfer in stirred vessels is important because process fluid temperature in the vessel is one of the most significant factors for controlling the outcome of process. In this study, the effects of some important design parameters for coal-water slurry in agitated vessel used in coal gasification such as stirrer speed, location of stirrer, D/d ratio, and coal-water ratio were investigated and optimized using the Taguchi method. The experiments were planned based on Taguchi’s orthogonal array with each trial performed under different levels of design parameter. Signal-to-noise (S/N analysis and analysis of variance (ANOVA were carried out in order to determine the effects of process parameter and optimal factor’s level settings. Finally, confirmation tests verified that the Taguchi method achieved optimization of heat transfer coefficient in agitated vessel.
Chen, Shi; Zhang, Yinhong; Lin, Shuyu; Fu, Zhiqiang
2014-02-01
The electromechanical coupling coefficient of Rayleigh-type surface acoustic waves in semi-infinite piezoelectrics/non-piezoelectrics superlattices is investigated by the transfer matrix method. Research results show the high electromechanical coupling coefficient can be obtained in these systems. The optimization design of it is also discussed fully. It is significantly influenced by electrical boundary conditions on interfaces, thickness ratios of piezoelectric and non-piezoelectric layers, and material parameters (such as velocities of pure longitudinal and transversal bulk waves in non-piezoelectric layers). In order to obtain higher electromechanical coupling coefficient, shorted interfaces, non-piezoelectric materials with large velocities of longitudinal and transversal bulk waves, and proper thickness ratios should be chosen.
Experiment study on heat transfer coefficient in climbing film plate heat exchanger%升膜式板式换热器的换热性能研究
高晓凯; 陶乐仁; 高立博; 黄理浩
2013-01-01
升膜蒸发是在换热器表面形成一层薄液膜,薄膜蒸发能够强化换热.文中研究采用光滑铜板的板式升膜蒸发器,以去离子水作为介质,在不同进水流量、不同加热量(热流密度)下,测定换热器某些点的局部换热系数,计算出总的换热系数,研究影响板式换热器升膜蒸发的因素和变化趋势.%A thin liquid film can be formed on the outer surface in the heat exchanger and can enhance heat transfer. This paper focused on studying smooth plate of copper in plate heat exchanger for deion - water as working fluids. Based on the different inlet - water flow and the different heat - flow density, the heat - transfer coefficients in partial positions were measured and the oveall coefficient could be concluded. The factors of affect the climbing film evaporation in plate heat exchanger and trendency were also analyzed.
Sundus Hussein Abd
2012-01-01
Full Text Available In this research, an experimental study was conducted to high light the impact of the exterior shape of a cylindrical body on the forced and free convection heat transfer coefficients when the body is hold in the entrance of an air duct. The impact of changing the body location within the air duct and the air speed are also demonstrated. The cylinders were manufactured with circular, triangular and square sections of copper for its high thermal conductivity with appropriate dimensions, while maintaining the surface area of all shapes to be the same. Each cylinder was heated to a certain temperature and put inside the duct at certain locations. The temperature of the cylinder was then monitored. The heat transfer coefficient were then calculated for forced convection for several Reynolds number (4555-18222.The study covered free convection impact for values of Rayleigh number ranging between (1069-3321. Imperical relationships were obtained for all cases of forced and free convection and compared with equations of circular cylindrical shapes found in literature. These imperical equations were found to be in good comparison with that of other sources.
Li, Zhengqiang; Li, Kaitao; Li, Donghui; Yang, Jiuchun; Xu, Hua; Goloub, Philippe; Victori, Stephane
2016-09-20
The Cimel new technologies allow both daytime and nighttime aerosol optical depth (AOD) measurements. Although the daytime AOD calibration protocols are well established, accurate and simple nighttime calibration is still a challenging task. Standard lunar-Langley and intercomparison calibration methods both require specific conditions in terms of atmospheric stability and site condition. Additionally, the lunar irradiance model also has some known limits on its uncertainty. This paper presents a simple calibration method that transfers the direct-Sun calibration constant, V0,Sun, to the lunar irradiance calibration coefficient, CMoon. Our approach is a pure calculation method, independent of site limits, e.g., Moon phase. The method is also not affected by the lunar irradiance model limitations, which is the largest error source of traditional calibration methods. Besides, this new transfer calibration approach is easy to use in the field since CMoon can be obtained directly once V0,Sun is known. Error analysis suggests that the average uncertainty of CMoon over the 440-1640 nm bands obtained with the transfer method is 2.4%-2.8%, depending on the V0,Sun approach (Langley or intercomparison), which is comparable with that of lunar-Langley approach, theoretically. In this paper, the Sun-Moon transfer and the Langley methods are compared based on site measurements in Beijing, and the day-night measurement continuity and performance are analyzed.
M. Dieng
2013-02-01
Full Text Available The aim of this study is to characterize thermal insulating local material, kapok, from a study in 3 dimensions in Cartesian coordinate and in dynamic frequency regime. From a study a 3 dimensional the heat transfer through a material made of wool kapok (thermal conductivity: &lambda = 0,035 W/m/K; density: &rho = 12, 35 kg/m3; thermal diffusivity: &alpha = 17, 1.10-7 m2 /s is presented. The evolution curves of temperature versus convective heat transfer coefficient have helped highlight the importance of pulse excitation and the depth in the material. The thermal impedance is studied from representations of Nyquist and Bode diagrams allowing characterizing the thermal behavior from thermistors. The evolution of the thermal impedance with the thermal capacity of the material is presented.
Santos-Martins, Diogo; Fernandes, Pedro Alexandrino; Ramos, Maria João
2016-11-01
In the context of SAMPL5, we submitted blind predictions of the cyclohexane/water distribution coefficient (D) for a series of 53 drug-like molecules. Our method is purely empirical and based on the additive contribution of each solute atom to the free energy of solvation in water and in cyclohexane. The contribution of each atom depends on the atom type and on the exposed surface area. Comparatively to similar methods in the literature, we used a very small set of atomic parameters: only 10 for solvation in water and 1 for solvation in cyclohexane. As a result, the method is protected from overfitting and the error in the blind predictions could be reasonably estimated. Moreover, this approach is fast: it takes only 0.5 s to predict the distribution coefficient for all 53 SAMPL5 compounds, allowing its application in virtual screening campaigns. The performance of our approach (submission 49) is modest but satisfactory in view of its efficiency: the root mean square error (RMSE) was 3.3 log D units for the 53 compounds, while the RMSE of the best performing method (using COSMO-RS) was 2.1 (submission 16). Our method is implemented as a Python script available at https://github.com/diogomart/SAMPL5-DC-surface-empirical.
OGO-6 gas-surface energy transfer experiment
Mckeown, D.; Dummer, R. S.; Bowyer, J. M., Jr.; Corbin, W. E., Jr.
1973-01-01
The kinetic energy flux of the upper atmosphere was analyzed using OGO-6 data. Energy transfer between 10 microwatts/sq cm and 0.1 W/sq cm was measured by short-term frequency changes of temperature-sensitive quartz crystals used in the energy transfer probe. The condition of the surfaces was continuously monitored by a quartz crystal microbalance to determine the effect surface contamination had on energy accommodation. Results are given on the computer analysis and laboratory tests performed to optimize the operation of the energy transfer probe. Data are also given on the bombardment of OGO-6 surfaces by high energy particles. The thermoelectrically-cooled quartz crystal microbalance is described in terms of its development and applications.
Marquardt, Katharina; Dohmen, Ralf; Wagner, Johannes
2014-05-01
Diffusion along interface and grain boundaries provides an efficient pathway and may control chemical transport in rocks as well as their mechanical strength. Besides the significant relevance of these diffusion processes for various geologic processes, experimental data are still very limited (e.g., Dohmen & Milke, 2010). Most of these data were measured using polycrystalline materials and the formalism of LeClaire (1951) to fit integrated concentration depth profiles. To correctly apply this formalism, certain boundary conditions of the diffusion problem need to be fulfilled, e.g., surface diffusion is ignored, and furthermore the lattice diffusion coefficient has to be known from other studies or is an additional fitting parameter, which produces some ambiguity in the derived grain boundary diffusion coefficients. We developed an experimental setup where we can measure the lattice and grain boundary diffusion coefficients simultaneously but independent and demonstrate the relevance of surface diffusion for typical grain boundary diffusion experiments. We performed Mg2SiO4 bicrystal diffusion experiments, where a single grain boundary is covered by a thin-film of pure Ni2SiO4 acting as diffusant source, produced by pulsed laser deposition. The investigated grain boundary is a 60° (011)/[100]. This specific grain boundary configuration was modeled using molecular dynamics for comparison with the experimental observations in the transmission electron microscope (TEM). Both, experiment and model are in good agreement regarding the misorientation, whereas there are still some disagreements regarding the strain fields along the grain boundary that are of outmost importance for the strengths of the material. The subsequent diffusion experiments were carried out in the temperature range between 800° and 1450° C. The inter diffusion profiles were measured using the TEMs energy dispersive x-ray spectrometer standardized using the Cliff-Lorimer equation and EMPA
Shivanian, Elyas; Hosseini Ghoncheh, S. J.
2017-02-01
In this paper, the nonlinear fin problem with temperature-dependent thermal conductivity and heat transfer coefficient is revisited. In this problem, it has been assumed that the heat transfer coefficient is expressed in a power-law form and the thermal conductivity is a linear function of temperature. A method based on the traditional shooting method and the homotopy analysis method is applied, the so-called shooting homotopy analysis method (SHHAM), to the governing nonlinear differential equation. In this technique, more high-order approximate solutions are computable and multiple solutions are easily searched and discovered due to being free of the symbolic variable. It is found that the solution might be empty, unique or dual depending on the values of the parameters of the model. Furthermore, corresponding fin efficiencies with high accuracy are computed. As a consequence, a new branch solution for this nonlinear problem by a new proposed method, based on the traditional shooting method and the homotopy analysis method, is obtained.
Giraud, Florine; Hamitouche, Yacine; Vallon, Pierrick; Tremeac, Brice
2017-02-01
Compact evaporator like plate heat exchangers can play a significant role in reducing the investment cost of low cooling power sorption systems. However, when water is used as refrigerant, the working pressure is very low and vaporization phenomena are really different than vaporization phenomena occurring at higher pressures. Few studies focus on this subject and there is a lack of knowledge about vaporization (boiling or evaporation) phenomena occurring in compact evaporators at low pressure. The design of such evaporators remain manly empirical. There is thus a need of better characterization of the influence of the driving parameters in order to optimize the evaporator design. The objective of this article is thus to go further in the understanding of phenomena occurring in compact plate-type evaporators. In that goal, an experimental campaign was conducted to study continuously the performance of a smooth plate type evaporator as a function of the filling levels. The influence of the saturation pressure and the secondary fluid temperature on an overall heat transfer coefficient is studied. It is show that there is a dependence of the maximal overall heat transfer coefficient to these parameters. It is also shown that there seems to be a strong dependence between phenomena observed and phenomena that happens before. Thus, dynamic and inertia effects must be taken into account and model developed in absorption configuration cannot be applied for this study.
Lu, C.-H.; Beckmann, M.; Unz, S.; Gloess, D.; Frach, P.; Holst, E.; Lasagni, A.; Bieda, M.
2016-01-01
It is well known that dropwise condensation corresponds to a high heat transfer coefficient. The high performance enhancement of dropwise condensation in comparison to filmwise condensation is attributed to the ability of non-wetting droplets to be shed from the surface by gravity, therefore reducing the overall thermal resistance. The common treatments to carry out the hydrophobic surface for dropwise condensation are coating and structure. The improvement of heat transfer efficiency by combination of surface treatments with coating and groove structure has been proved compared of surface with single surface treatment by coating or groove structure. Based on this result, in this study presents a model developed to predict the heat transfer efficiency of dropwise condensation for surface with coating and groove structure features. The model is established by heat transfer though a single droplet with the drop size distribution. The heat transfer of single drop is not only analyzed as combination of thermal resistances, but also considered capillary effect of droplet due to groove geometry and properties of surface. In addition, the model results are validated with experimental data which is investigated by varied modification of vapor side metallic surface properties at low absolute pressure. It can be a reference to design industrial condensers of heat exchangers in the future. Further to optimize the surface properties and improve the higher heat transfer performance of dropwise condensation.
Heat Transfer Enhancement in Turbulent Flows by Blocked Surfaces
Onur YEMENİCİ
2013-04-01
Full Text Available In this study, the heat transfer analyses over flat and blocked surfaces were carried out in turbulent flow under the influence of the block height. A constant-temperature hot wire anemometer was used to the velocity and turbulent intensity measurements, while temperature values were measured by copper-constantan thermocouples. The average Stanton numbers for block heights of 15 and 25 mm were higher than those of flat surface by %38 and %84, respectively. The results showed that the presence of the blocks increased the heat transfer and the enhancement rose with block heights
Bishay, A.G. [Engineering Mathematics and Physics Department, Faculty of Engineering, Ain Shams University, Cairo (Egypt); El-Gamal, S., E-mail: samyelgamal@gmail.co [Physics Department, Faculty of Education, Ain Shams University, Cairo (Egypt)
2011-05-15
Three sets (A, B and C) of two-dimensional island platinum films (2D-I(Pt)Fs) were prepared via the thermal evaporation technique, where the substrates are corning 7059 glass slides. The mass thickness (d{sub m}) of the films of different sets is 5, 10 and 20 A, respectively. The Pt films were exposed to {gamma}-rays from {sup 137}Cs (0.662 MeV) radiation source of dose rate 0.5 Gy/min. and the different doses are 100, 200, 300, 500 and 700 Gy. The dependence of the surface resistivity ({rho}) on temperature over the range of 100-300 K was undertaken at different d{sub m} and doses then the temperature coefficient of surface resistivity ({alpha}) was deduced. It was found that; (i) for particular d{sub m} and T, the absolute value of {alpha} decreases as the dose increases (ii) for particular dose and T, the absolute value of {alpha} decreases as d{sub m} increases (iii) for particular dose and d{sub m}, the absolute value of {alpha} decreases as T increases. Qualitative interpretation for the results was offered on the ground that the electrons transfer among islands takes place by the activated tunneling mechanism and the {gamma}-irradiation has changed the shape of islands from spherical to prolate spheroid.
Enhanced surface friction coefficient and hydrophobicity of TPE substrates using an APPJ system
Sainz-García, Elisa, E-mail: elisa.sainzg@unirioja.es; Alba-Elías, Fernando, E-mail: fernando.alba@unirioja.es; Múgica-Vidal, Rodolfo, E-mail: rodolfo.mugica@alum.unirioja.es; González-Marcos, Ana, E-mail: ana.gonzalez@unirioja.es
2015-02-15
Highlights: • Coatings on thermoplastic elastomers by atmospheric pressure plasma jet. • Study of influence of APTES and FLUSI percentage on the coating's properties. • The best sample (AF{sub 75}) used 75% of APTES and 25% of FLUSI as precursor mixture. • Sample AF{sub 75} reduced a 51.5% the FC and increased a 4.4% the WCA. - Abstract: An APPJ system was used to deposit a coating that combines a low friction coefficient with a high water contact angle (WCA) on a thermoplastic elastomer substrate (TPE) that is used in automotive profiling. The main drawback of this research is that groups that improve the hydrophobicity of the surface worsen its tribological properties. To overcome this, this study explored the use of various mixtures of differing proportions of two precursors. They were a siloxane, aminopropyltriethoxysilane (APTES) that was used to reduce the friction coefficient by its content of SiO{sub x} and a fluorinated compound, (heptadecafluoro-1,1,2,2-tetrahydrodecyl)trimethoxysilane (FLUSI) that was used to improve the water-repellency characteristics, due to the presence of CF{sub 2} long chains. The coatings were characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), X-ray Photoelectron Spectroscopy (XPS), dynamic Water Contact Angle (WCA), stability tests and tribological tests. It was found that an increase of the absorbance area under the SiOSi peak and inorganic groups is related to lower friction coefficients. On the other hand, the higher the CF{sub 2} percentage is, the higher the WCA is. The sample that was coated with 25% of FLUSI and 75% of APTES combined the improvements of both functional properties, the friction coefficient and the WCA. It has an average friction coefficient that is (0.530 ± 0.050) 51.5% lower and a WCA that is (θ{sub adv} = 119.8° ± 4.75) 4.4% higher than the uncoated TPE sample. A satisfactory
Serrating Nozzle Surfaces for Complete Transfer of Droplets
Kim, Chang-Jin " CJ" Yi, Uichong
2010-01-01
A method of ensuring the complete transfer of liquid droplets from nozzles in microfluidic devices to nearby surfaces involves relatively simple geometric modification of the nozzle surfaces. The method is especially applicable to nozzles in print heads and similar devices required to dispense liquid droplets having precise volumes. Examples of such devices include heads for soft printing of ink on paper and heads for depositing droplets of deoxyribonucleic acid (DNA) or protein solutions on glass plates to form microarrays of spots for analysis. The main purpose served by the present method is to ensure that droplets transferred from a nozzle have consistent volume, as needed to ensure accuracy in microarray analysis or consistent appearance of printed text and images. In soft printing, droplets having consistent volume are generated inside a print head, but in the absence of the present method, the consistency is lost in printing because after each printing action (in which a drop is ejected from a nozzle), a small residual volume of liquid remains attached to the nozzle. By providing for complete transfer of droplets (and thus eliminating residual liquid attached to the nozzle) the method ensures consistency of volume of transferred droplets. An additional benefit of elimination of residue is prevention of cross-contamination among different liquids printed through the same nozzle a major consideration in DNA microarray analysis. The method also accelerates the printing process by minimizing the need to clean a printing head to prevent cross-contamination. Soft printing involves a hydrophobic nozzle surface and a hydrophilic print surface. When the two surfaces are brought into proximity such that a droplet in the nozzle makes contact with the print surface, a substantial portion of the droplet becomes transferred to the print surface. Then as the nozzle and the print surface are pulled apart, the droplet is pulled apart and most of the droplet remains on the
Natural convection heat transfer on surfaces of copper micro-wires
Guan, Ning; Liu, Zhigang; Zhang, Chengwu; Jiang, Guilin
2014-02-01
The natural convection heat transfer characteristics and mechanism for copper micro-wires in water and air were investigated experimentally and numerically. The wires with diameters of 39.9, 65.8 and 119.1 μm were placed horizontally in water inside of a sealed tube and in air of a large room, respectively. Using Joule heating, the heat transfer coefficients and Nusselt numbers of natural convection for micro-wires in ultra pure water and air were obtained. A three dimensional incompressible numerical model was used to investigate the natural convection, and the prediction with this model was in reasonable accordance with the experimental results. With the decrease of micro-wire diameter, the heat transfer coefficient of natural convection on the surface of micro-wire becomes larger, while the Nu number of natural convection decreases in water and air. Besides, the change rate of Nu number in water decreases apparently with the increase of heat flux and the decrease of wire diameter, which is larger than that in air. The thickness of boundary layer on the wall of micro-wire becomes thinner with the decrease of diameter in both water and air, but the ratio of boundary layer thickness in water to the diameter increases. However, there is almost no change of this ratio for natural convection in air. As a result, the proportion of conduction in total heat transfer of natural convection in water increases, while the convective heat transfer decreases. The velocity distribution, temperature field and the boundary layer in the natural convection were compared with those of tube with conventional dimension. It was found that the boundary layer around the micro-wire is an oval-shaped film on the surface, which was different from that around the conventional tube. This apparently reduces the convection strength in the natural convection, thus the heat transfer presents a conduction characteristic.
Zhu, Jie; Luo, Yuting; Tian, Jian; Li, Juan; Gao, Xuefeng
2015-05-27
We report that the dropwise condensation heat transfer (DCHT) effectiveness of copper surfaces can be dramatically enhanced by in situ grown clustered ribbed-nanoneedles. Combined experiments and theoretical analyses reveal that, due to the microscopically rugged and low-adhesive nature of building blocks, the nanosamples can not only realize high-density nucleation but constrain growing condensates into suspended microdrops via the self-transport and/or self-expansion mode for subsequently self-propelled jumping, powered by coalescence-released excess surface energy. Consequently, our nanosample exhibits over 125% enhancement in DCHT coefficient. This work helps develop advanced heat-transfer materials and devices for efficient thermal management and energy utilization.
Tan, Benjamin
1995-01-01
Using thermochromatic liquid crystal to measure surface temperature, an automated transient method with time-varying free-stream temperature is developed to determine local heat transfer coefficients. By allowing the free-stream temperature to vary with time, the need for complicated mechanical components to achieve a step temperature change is eliminated, and by using the thermochromatic liquid crystals as temperature indicators, the labor intensive task of installing many thermocouples is omitted. Bias associated with human perception of the transition of the thermochromatic liquid crystal is eliminated by using a high speed digital camera and a computer. The method is validated by comparisons with results obtained by the steady-state method for a circular Jet impinging on a flat plate. Several factors affecting the accuracy of the method are evaluated.
Ameel Mohammed Rahman Al-Mayah
2014-06-01
Full Text Available The study of oxygen mass transfer was conducted in a laboratory scale 5 liter stirred bioreactor equipped with one Rushton turbine impeller. The effects of superficial gas velocity, impeller speed, power input and liquid viscosity on the oxygen mass transfer were considered. Air/ water and air/CMC systems were used as a liquid media for this study. The concentration of CMC was ranging from 0.5 to 3 w/v. The experimental results show that volumetric oxygen mass transfer coefficient increases with the increase in the superficial gas velocity and impeller speed and decreases with increasing liquid viscosity. The experimental results of kla were correlated with a mathematical correlation describing the influences of the considered factors (the overall power input and the superficial gas velocity over the studied rages. The predicted kla values give acceptable results compared with the experimental values. The following correlations were obtained: Air/water system Air/CMC system (0.5w/v Air/CMC system (1w/v Air/CMC system (2w/v Air/CMC system (3w/v
A Theory for the Scalar Roughness and the Scalar Transfer Coefficients over Snow and Sea Ice,
1986-09-01
and camphor ... 7 4. Model predictions for an aerodynamically rough surface compared with the ex- perimental data of Dipprey and Sabersky (1963...stability 4.,. Ls Latent heat of sublimation of ice , . Pr v/D, Prandtl number Q Water vapor density Qr Water vapor density at an arbitrary reference height...specific heat of air at constant pressure L, = latent heat of sublimation of ice. Equations 1-3 define the roughness lengths. z0 is the familiar
Toghraie, D.
2016-10-01
In this study, a numerical method for simulation of flow boiling through subcooled jet on a hot surface with 800 °C has been presented. Volume fraction (VOF) has been used to simulate boiling heat transfer and investigation of the quench phenomena through fluid jet on a hot horizontal surface. Simulation has been done in a fixed Tsub=55 °C, Re=5000 to Re=50,000 and also in different Tsub =Tsat -Tf between 10 °C and 95 °C. The effect of fluid jet velocity and subcooled temperature on the rewetting temperature, wet zone propagation, cooling rate and maximum heat flux has been investigated. The results of this study show that by increasing the velocity of fluid jet of water, convective heat transfer coefficient at stagnation point increases. More ever, by decreasing the temperature of the fluid jet, convective heat transfer coefficient increases.
Perceptual learning: tactile letter recognition transfers across body surfaces.
Arnold, Gabriel; Auvray, Malika
2014-01-01
Visual-to-tactile sensory substitution devices are designed to assist visually impaired people by converting visual stimuli into tactile stimuli. The important claim has been made that, after training with these devices, the tactile stimuli can be moved from one body surface to another without any decrease in performance. This claim, although recurrent, has never been empirically investigated. Moreover, studies in the field of tactile perceptual learning suggest that performance improvement transfers only to body surfaces that are closely represented in the somatosensory cortex, i.e. adjacent or homologous contralateral body surfaces. These studies have however mainly used discrimination tasks of stimuli varying along only one feature (e.g., orientation of gratings) whereas, in sensory substitution, tactile information consists of more complex stimuli. The present study investigated the extent to which there is a transfer of tactile letter learning. Participants first underwent a baseline session in which the letters were presented on their belly, thigh, and shin. They were subsequently trained on only one of these body surfaces, and then re-tested on all of them, as a post-training session. The results revealed that performance improvement was the same for both the trained and the untrained surfaces. Moreover, this transfer of perceptual learning was equivalent for adjacent and non-adjacent body surfaces, suggesting that tactile learning transfer occurs independently of the distance on the body. A control study consisting of the same baseline and post-training sessions, without training in between, revealed weaker improvement between the two sessions. The obtained results support the claim that training with sensory substitution devices results in a relative independence from the stimulated body surface.
吴静; 李选友; 陈宝明; 高玲; 王瑞雪; 赵改菊; 王成运
2014-01-01
Heat transfer coefficient is one of the most crucial parameters in thermal calculation and design for an externally heated rotary kiln. Suitably designed kiln dimensions, structure and operating parameters rely on the accuracy of the employed heat transfer coefficient. For an externally heated kiln, heat transfers from an outside source to inside particles through a wall. Generally, the filling ratio in an externally heated rotary kiln is low. So, the heat transfer mechanism for large particles with a low filling ratio in an externally heated rotary kiln is quite different from that in an internally heated rotary kiln, whose filling ratio is usually more than 15 percent. Despite the existence of some achievements in particles motion behavior and heat transfer mechanisms in an internally heated rotary kiln, so far, there is no reliable heat transfer model to describe the heat transfer process between the kiln’s surface and particles in an externally heated rotary kiln with low filling large particles. As a result, the main approach of heat transfer coefficient determination is still an experimental test. On the basis of heat transfer mechanism analysis, this paper regards the heat transfer process between the kiln’s surface and large particles as consisting of heat conduction between the kiln’s surface and gas film, heat convection between the gas film and particles, and heat radiation between the kiln’s surface and particles. Finally, a mathematical model is created for the prediction of the heat transfer coefficient between the kiln’s surface and large particles. To validate the developed model, a series of experimental tests are performed. Alumina spherical grains with a diameter of 6 mm are used as testing particles. When the filling ratio is 5 percent, the heat transfer coefficients are measured in the range of 220℃-420℃ at 20℃ surface temperature intervals, corresponding to the rotary speeds of 1r/min, 2r/min, and 3r/min, respectively. The
Freche, John C; Schum, Eugene F
1951-01-01
Blade-to-coolant convective heat-transfer coefficients were obtained on a forced-convection water-cooled single-stage turbine over a large laminar flow range and over a portion of the transition range between laminar and turbulent flow. The convective coefficients were correlated by the general relation for forced-convection heat transfer with laminar flow. Natural-convection heat transfer was negligible for this turbine over the Grashof number range investigated. Comparison of turbine data with stationary tube data for the laminar flow of heated liquids showed good agreement. Calculated average midspan blade temperatures using theoretical gas-to-blade coefficients and blade-to-coolant coefficients from stationary-tube data resulted in close agreement with experimental data.
Triangulating Nucleic Acid Conformations Using Multicolor Surface Energy Transfer.
Riskowski, Ryan A; Armstrong, Rachel E; Greenbaum, Nancy L; Strouse, Geoffrey F
2016-02-23
Optical ruler methods employing multiple fluorescent labels offer great potential for correlating distances among several sites, but are generally limited to interlabel distances under 10 nm and suffer from complications due to spectral overlap. Here we demonstrate a multicolor surface energy transfer (McSET) technique able to triangulate multiple points on a biopolymer, allowing for analysis of global structure in complex biomolecules. McSET couples the competitive energy transfer pathways of Förster Resonance Energy Transfer (FRET) with gold-nanoparticle mediated Surface Energy Transfer (SET) in order to correlate systematically labeled points on the structure at distances greater than 10 nm and with reduced spectral overlap. To demonstrate the McSET method, the structures of a linear B-DNA and a more complex folded RNA ribozyme were analyzed within the McSET mathematical framework. The improved multicolor optical ruler method takes advantage of the broad spectral range and distances achievable when using a gold nanoparticle as the lowest energy acceptor. The ability to report distance information simultaneously across multiple length scales, short-range (10-50 Å), mid-range (50-150 Å), and long-range (150-350 Å), distinguishes this approach from other multicolor energy transfer methods.
Torrella, Enrique [Department of Applied Thermodynamics, Camino de Vera, 14, Polytechnic University of Valencia, E-46022 Valencia (Spain); Navarro-Esbri, Joaquin; Cabello, Ramon [Department of Technology, Campus de Riu Sec,University Jaume I, E-12071 Castellon (Spain)
2006-03-01
The present paper presents experimental results obtained from a refrigerating vapour-compression plant's shell-and-tube (1-2) evaporator working with R407C. Several tests have been carried out to study the influence of the evaporating pressure and the refrigerant's mass flow rate on the refrigerant's boiling heat-transfer coefficient inside horizontal tubes. This work has been performed by analyzing the variations of the evaporator's overall thermal-resistance, computed using the effectiveness-NTU method, considering the influence of pressure drops and glide at the evaporator, and finally transferring the results and conclusions to the boiling heat-transfer coefficient. It has been observed that the variations of the boiling heat-transfer coefficient show a dependence on the evaporating temperature and the refrigerant's mass-flow rate, which has been analyzed in the test range. [Author].
Shitzer, Avraham
2006-03-01
The wind-chill index (WCI), developed in Antarctica in the 1940s and recently updated by the weather services in the USA and Canada, expresses the enhancement of heat loss in cold climates from exposed body parts, e.g., face, due to wind. The index provides a simple and practical means for assessing the thermal effects of wind on humans outdoors. It is also used for indicating weather conditions that may pose adverse risks of freezing at subfreezing environmental temperatures. Values of the WCI depend on a number of parameters, i.e, temperatures, physical properties of the air, wind speed, etc., and on insolation and evaporation. This paper focuses on the effects of various empirical correlations used in the literature for calculating the convective heat transfer coefficients between humans and their environment. Insolation and evaporation are not included in the presentation. Large differences in calculated values among these correlations are demonstrated and quantified. Steady-state wind-chill-equivalent temperatures (WCETs) are estimated by a simple, one-dimensional heat-conducting hollow-cylindrical model using these empirical correlations. Partial comparison of these values with the published "new" WCETs is presented. The variability of the estimated WCETs, due to different correlations employed to calculate them, is clearly demonstrated. The results of this study clearly suggest the need for establishing a "gold standard" for estimating convective heat exchange between exposed body elements and the cold and windy environment. This should be done prior to the introduction and adoption of further modifications to WCETs and indices. Correlations to estimate the convective heat transfer coefficients between exposed body parts of humans in windy and cold environments influence the WCETs and need to be standardized.
Heat mass transfer model of fouling process of calcium carbonate on heat transfer surface
2008-01-01
A new heat mass transfer model was developed to predict the fouling process of calcium carbonate on heat transfer surface. The model took into account not only the crystallization fouling but also the particle fouling which was formed on the heat transfer surface by the suspension particles of calcium carbonate in the su- persaturated solution. Based on experimental results of the fouling process, the deposition and removal rates of the mixing fouling were expressed. Furthermore, the coupling effect of temperature with the fouling process was considered in the physics model. As a result the fouling resistance varying with time was obtained to describe the fouling process and the prediction was compared with experimental data under same conditions. The results showed that the present model could give a good prediction of fouling process, and the deviation was less than 15% of the experimental data in most cases. The new model is credible to predict the fouling process.
Fifth-order field aberration coefficients for an optical surface of rotational symmetry.
Gaj, M
1971-07-01
The approximate formulas for the principal ray parameters, such as directional cosines and heights of incidence, as well as for the paraxial sagittal quantities h(s) and H (s) have been expressed by paraxial quantities and Seidel aberrations to fifth-order accuracy. On the basis of these relations an expression for the sagittal radius of curvature r(s), (for a given y ) has been obtained. These quantities are used to derive fifth-order field aberration coefficients for arbitrary surfaces of rotational symmetry by using the wave aberration formula for sagittal focus {M. Gaj, Opt. Spectrosk. 21, 373 (1966) [Opt. Spectrosc. 21, 209 (1966)]}. The resulting expression has four terms. The first one depends only on asphericity and tends to equal zero when the surface becomes spherical. The second is a disturbance term and disappears in the Seidel region. The third and fourth terms may be treated as a generalization of the Petzval curvature and of the Seidel astigmatism, respectively. The limits of the terms, when h tends to zero, has been examined.
Van Fossen, G. James; De Witt, Kenneth J.; Newton, James E.; Poinsatte, Phillip E.
1988-01-01
Wind tunnels typically have higher free stream turbulence levels than are found in flight. Turbulence intensity was measured to be 0.5 percent in the NASA Lewis Icing Research Tunnel (IRT) with the cloud making sprays off and around 2 percent with cloud making equipment on. Turbulence intensity for flight conditions was found to be too low to make meaningful measurements for smooth air. This difference between free stream and wind tunnel conditions has raised questions as to the validity of results obtained in the IRT. One objective of these tests was to determine the effect of free stream turbulence on convective heat transfer for the NASA Lewis LEWICE ice growth prediction code. These tests provide in-flight heat transfer data for a NASA-0012 airfoil with a 533 cm chord. Future tests will measure heat transfer data from the same airfoil in the Lewis Icing Research Tunnel. Roughness was obtained by the attachment of small, 2 mm diameter hemispheres of uniform size to the airfoil in three different patterns. Heat transfer measurements were recorded in flight on the NASA Lewis Twin Otter Icing Research Aircraft. Measurements were taken for the smooth and roughened surfaces at various aircraft speeds and angles of attack up to four degrees. Results are presented as Frossling number versus position on the airfoil for various roughnesses and angles of attack.
Newton, James E.; Vanfossen, G. James; Poinsatte, Phillip E.; Dewitt, Kenneth J.
1988-01-01
Wind tunnels typically have higher free stream turbulence levels than are found in flight. Turbulence intensity was measured to be 0.5 percent in the NASA Lewis Icing Research Tunnel (IRT) with the cloud making sprays off and around 2 percent with cloud making equipment on. Turbulence intensity for flight conditions was found to be too low to make meaningful measurements for smooth air. This difference between free stream and wing tunnel conditions has raised questions as to the validity of results obtained in the IRT. One objective of these tests was to determine the effect of free stream turbulence on convective heat transfer for the NASA Lewis LEWICE ice growth prediction code. These tests provide in-flight heat transfer data for a NASA-0012 airfoil with a 533 cm chord. Future tests will measure heat transfer data from the same airfoil in the Lewis Icing Research Tunnel. Roughness was obtained by the attachment of small, 2 mm diameter hemispheres of uniform size to the airfoil in three different patterns. Heat transfer measurements were recorded in flight on the NASA Lewis Twin Otter Icing Research Aircraft. Measurements were taken for the smooth and roughened surfaces at various aircraft speeds and angles of attack up to four degrees. Results are presented as Frossling number versus position on the airfoil for various roughnesses and angles of attack.
Flow, heat transfer, and free surface shape during the optical fiber drawing process
Xiao, Zhihui
1997-12-01
A two-dimensional finite element model is introduced for analyzing glass and gas flows, heat transfer, and fiber formation during the optical fiber drawing process. This study consists of simulations in three different areas: the upper region, the tip region, and the whole furnace region. Conjugating the glass and gas flows and heat transfer, the shapes of an optical fiber as free surfaces in the upper neck-down and the tip regions are separately obtained by solving the coupled continuity, momentum, and energy equations. In the upper region simulation, a surface-to-surface radiation model is used for the enclosure which consists of the wall and the glass surface, and the Rosseland approximation radiation model is employed to account for the radiation effect in the glass region. In the tip region simulation, only the glass fiber region is considered and a convective heat transfer model on the fiber surface is employed to account for the energy exchange between the fiber surface and the purge gas. In the fiber, radiation in the axial direction is included. The whole furnace simulation uses a calculated fiber neck-down shape and an assumed fiber tip shape as a fixed interface and computes the convective heat transfer coefficient profile in the tip region which was used in the tip region simulation. The glass viscosity is temperature-dependent and significantly affects the fiber shape. The finite element code FIDAP is used in the study. The effects of various operating conditions such as draw speed, wall temperature distribution, and gas flow rate are studied.
Nonlinear Radiative Heat Transfer in Blasius and Sakiadis Flows Over a Curved Surface
Naveed, M.; Abbas, Z.; Sajid, M.
2017-01-01
This study investigates the heat transfer characteristics for Blasius and Sakiadis flows over a curved surface coiled in a circle of radius R having constant curvature. Effects of thermal radiation are also analyzed for nonlinear Rosseland approximation which is valid for all values of the temperature difference between the fluid and the surface. The considered physical situation is represented by a mathematical model using curvilinear coordinates. Similar solutions of the developed partial differential equations are evaluated numerically using a shooting algorithm. Fluid velocity, skin-friction coefficient, temperature and local Nusselt number are the quantities of interest interpreted for the influence of pertinent parameters. A comparison of the present and the published data for a flat surface validates the obtained numerical solution for the curved geometry.
A Novel Surface Aeration Configuration for Improving Gas—Liquid Mass Transfer
YUGengzhi; MAZaisha; 等
2002-01-01
A novel surface aeration configuration featured with a self-rotating and floating baffle (SRFB) and a Rushton disk turbine (DT) with a perforated disk has been developed. The SRFB, consisted of 12 fan blades twisted by an angle of 30° to the horizontal plane, is incorporated onto the impeller shaft to improve gas entrainment, bubble breakup, mixing in a φ154mm agitated vessel. This new configuration is compared to the conventional DT surface aeration experimentally. The results suggest that the critical impeller speed for onset of gas entrainments is lower for the new configuration and it demands greater power consumption. Moreover, the SRFB system produces 30%-68% higher volumetric mass transfer coefficient per unit power input than that obtained in the conventional DT surface aerator under the same operation conditions.
Rubio Cerda, Eduardo; Porta Gandara, Miguel A [CIBNOR, Mexico D.F (Mexico); Fernandez Zayas, Jose Luis [UNAM Mexico, D.F. (Mexico)
2000-07-01
This work reports an experimental method that allows to estimate the heat transfer coefficients in the neighborhood of walls or flat plates subject to convective transport phenomena. This method can be applied to a great variety of thermal systems since it is based on the knowledge of the border condition for the temperature at the surface of the plate, and the temperature profile that characterize the dimensionless coefficient of heat transfer in the fluid, according to its definition given by the Nusselt number. The approach of this work are the foundations of the method and the system that has been developed to apply it, that incorporates automatic acquisition equipment for continuos monitoring of the information and elements to control the parameters of interest. In addition, the experimental cavities on which the method will be evaluated are discussed, considering two different scales, as well as experiments in cavities filled with air, and with a mixture of air and steam water, as is the case for solar distillation. [Spanish] En este trabajo se presenta un metodo que permite determinar de manera experimental coeficientes de transferencia de calor por conveccion. Este metodo puede ser aplicado a una gran variedad de sistemas termicos ya que se fundamenta en el conocimiento de la condicion de frontera para la temperatura en la superficie de la placa, y del perfil de temperaturas que caracteriza el coeficiente adimensional de transferencia de calor en el fluido, de acuerdo a la definicion de este, dada por el numero de Nusselt. El trabajo que aqui se reporta esta enfocado a la fundamentacion del metodo y al equipamiento que se ha desarrollado para instrumentarlo, que incorpora equipos automaticos de adquisicion continua de informacion y elementos de control para los parametros de interes. Se presentan ademas, las cavidades experimentales sobre las que sera evaluado el metodo, que considera dos escalas diferentes, asi como experimentos en cavidades llenas de aire
Boiling heat transfer enhancement of nanofluids on a smooth surface with agitation
Kong, Xin; Qi, Baojin; Wei, Jinjia; Li, Wei; Ding, Jie; Zhang, Yonghai
2016-12-01
The pool boiling heat transfer performance on a smooth silicon chip surface with agitation was experimentally investigated in this study. The nanofluids (Ag/alcohol) of 0.02 % volume concentration and ethyl alcohol with purification over 99.9 % were the two contrast working fluids. For each group, subcoolings of 40, 50 and 60 K were conducted under atmospheric pressure. To enhance the heat transfer performance, an agitating device was fixed above the top of the chip. The experimental results indicated that nanofluids could enhance the heat transfer performance especially in the nucleate boiling region. The heat transfer coefficient was significantly increased with nanofluids, while the critical heat flux (CHF) was nearly not changed. In the agitation Reynolds number of 20,300, the heat transfer performance of nanofluids was significantly enhanced in the convection region, and the CHF was increased by more than 25 % for all groups. This boiling phenomenon was observed for both nanofluids and alcohol groups. Meanwhile, the boiling curves of different liquid subcoolings in the nucleate region were quite similar to each other under agitation.
Transient radiative heat transfer in an inhomogeneous participating medium with Fresnel's surfaces
YI HongLiang; TAN HePing
2008-01-01
This paper studies the radiative heat transfer within an inhomogeneous and isot-ropically scattering medium with reflecting Fresnel's surfaces. Thermal radiation transfers in a curve inside a medium with an inhomogeneous distribution of a re-fractive index. The inhomogenous medium is divided into n homogenous isother-mal sub-layers and in each sub-layer the radiation transfers in a straight line. By adopting a multilayer radiative transfer model and using a ray-tracing/nodal-ana-lyzing method, a radiative transfer model is built for the inhomogenous participat-ing medium. In the muItilayer model, a criterion for refraction / total reflection at the interfaces between neighboring sub-layers is introduced, avoiding the integral singularity and reflection at physically inexistent interfaces (only the total reflection is considered). Transient thermal behavior is examined when the parameters of the radiative properties such as refractive indexes, extinction coefficients, and sin-gle-scattering albedoes vary continually along the thickness direction.
邓运来; 贺有为; 曹盛强; 张新明
2011-01-01
建立一种多喷嘴同时喷射淬火冷却的数学模型,通过实测冷却曲线分析计算厚板驻点区与紊流区换热系数分布规律,基于ABAQUS模拟软件模拟验证模型.结果表明:驻点与紊流点处的换热系数随时间分布是不均匀的,在10～20s内出现峰值,随后呈上下波动变化的规律；实测(或计算)试样心部与表面的冷却曲线与模拟的吻合较好,验证了多喷嘴同时喷射下的换热系数分布模型.%The quenched cooling heat transfer process of the thick plate by multi-nozzle jet impinging is extremely complicated, thus it is difficult to establish a model of the surface heat transfer coefficient distribution, which reveals the speed of the heat transfer on the jet impinging surface. In this paper, the mathematical model of multi-nozzle jet simultaneously impinging quenched cooling has been established, coefficient distribution law at the stagnation and turbulent zone has been calculated by actual measurement of the cooling curve and has been verified based on the ABAQUS simulation software. The results show that the coefficient distribution at the stagnation and turbulent zone is uneven over time, and the peak appeared within 10 to 20 seconds, and then comes to the variation of the next waves. The actual measurement(or calculation) of the cooling curves at the sample' s center and surface is at a very good match state with that of simulation, therefore it verifies the heat transfer coefficient distribution model under the multi-nozzle jet simultaneously impinging.
anjali devi
2015-01-01
Full Text Available The effects of nonlinear radiation on hydromagnetic boundary layer flow and heat transfer over a shrinking surface is investigated in the present work. Using suitable similarity transformations, the governing nonlinear partial differential equations are transformed into nonlinear ordinary differential equations. The resultant equations which are highly nonlinear are solved numerically using Nachtsheim Swigert shooting iteration scheme together with Fourth Order Runge Kutta method. Numerical solutions for velocity, skin friction coefficient and temperature are obtained for various values of physical parameters involved in the study namely Suction parameter, Magnetic parameter, Prandtl number, Radiation parameter and Temperature ratio parameter. Numerical values for dimensionless rate of heat transfer are also obtained for various physical parameters and are shown through tables. The analytical solution of the energy equation when the radiation term is taken in linear form is obtained using Confluent hypergeometric function.
Fernandes Filho, Francisco
1991-03-01
The work presents a study on heat transfer between gas and solid phases for fixed beds in the absence of mass transfer and chemical reactions. Mathematical models presented in the literature were analyzed concerning to the assumptions made on axial dispersion in the fluid phase and interparticle thermal conductivity. Heat transfer coefficients and their dependency on flow conditions, particles and packed bed characteristics were experimentally determined through the solution of the previous mathematical models. Pressure drop behaviour for the packed beds used for the heat transfer study was also included. (author) 32 refs., 12 figs.
Evolution of the transfer function characterization of surface scatter phenomena
Harvey, James E.; Pfisterer, Richard N.
2016-09-01
Based upon the empirical observation that BRDF measurements of smooth optical surfaces exhibited shift-invariant behavior when plotted versus o , the original Harvey-Shack (OHS) surface scatter theory was developed as a scalar linear systems formulation in which scattered light behavior was characterized by a surface transfer function (STF) reminiscent of the optical transfer function (OTF) of modern image formation theory (1976). This shift-invariant behavior combined with the inverse power law behavior when plotting log BRDF versus log o was quickly incorporated into several optical analysis software packages. Although there was no explicit smooth-surface approximation in the OHS theory, there was a limitation on both the incident and scattering angles. In 1988 the modified Harvey-Shack (MHS) theory removed the limitation on the angle of incidence; however, a moderate-angle scattering limitation remained. Clearly for large incident angles the BRDF was no longer shift-invariant as a different STF was now required for each incident angle. In 2011 the generalized Harvey-Shack (GHS) surface scatter theory, characterized by a two-parameter family of STFs, evolved into a practical modeling tool to calculate BRDFs from optical surface metrology data for situations that violate the smooth surface approximation inherent in the Rayleigh-Rice theory and/or the moderate-angle limitation of the Beckmann-Kirchhoff theory. And finally, the STF can be multiplied by the classical OTF to provide a complete linear systems formulation of image quality as degraded by diffraction, geometrical aberrations and surface scatter effects from residual optical fabrication errors.
Najeeb, Umair
This thesis experimentally investigates the enhancement of single-phase heat transfer, frictional loss and pressure drop characteristics in a Single Heater Element Loop Tester (SHELT). The heater element simulates a single fuel rod for Pressurized Nuclear reactor. In this experimental investigation, the effect of the outer surface roughness of a simulated nuclear rod bundle was studied. The outer surface of a simulated fuel rod was created with a three-dimensional (Diamond-shaped blocks) surface roughness. The angle of corrugation for each diamond was 45 degrees. The length of each side of a diamond block is 1 mm. The depth of each diamond block was 0.3 mm. The pitch of the pattern was 1.614 mm. The simulated fuel rod had an outside diameter of 9.5 mm and wall thickness of 1.5 mm and was placed in a test-section made of 38.1 mm inner diameter, wall thickness 6.35 mm aluminum pipe. The Simulated fuel rod was made of Nickel 200 and Inconel 625 materials. The fuel rod was connected to 10 KW DC power supply. The Inconel 625 material of the rod with an electrical resistance of 32.3 kO was used to generate heat inside the test-section. The heat energy dissipated from the Inconel tube due to the flow of electrical current flows into the working fluid across the rod at constant heat flux conditions. The DI water was employed as working fluid for this experimental investigation. The temperature and pressure readings for both smooth and rough regions of the fuel rod were recorded and compared later to find enhancement in heat transfer coefficient and increment in the pressure drops. Tests were conducted for Reynold's Numbers ranging from 10e4 to 10e5. Enhancement in heat transfer coefficient at all Re was recorded. The maximum heat transfer co-efficient enhancement recorded was 86% at Re = 4.18e5. It was also observed that the pressure drop and friction factor increased by 14.7% due to the increased surface roughness.
Arun Kumar Pujari
2014-01-01
Full Text Available A computational study on conjugate heat transfer is carried out to present the behavior of nondimensional temperature and heat transfer coefficient of a Nozzle Guide Vane (NGV leading edge. Reynolds number of both mainstream flow and coolant impinging jets are varied. The NGV has five rows of film cooling holes arranged in shower head manner and four rows of impingement holes arranged in staggered manner. The results are presented by considering materials of different thermal conductivity. The results show that the mainstream flow affects the temperature distribution on the interior side of the vane leading edge for high conductivity material whereas it has negligible effects for low conductivity material. The effect of changing blowing ratio on internal heat transfer coefficient and internal surface temperature is also presented.
高朋; 刘宏民; 于丙强; 陈军平; 王超
2014-01-01
在中厚板生产中，高压水除鳞对流换热系数是轧制前温度场数学模型的重要参数。目前国内外研究学者在计算高压水除鳞对流换热系数仅考虑了两个因素的影响，计算出的换热系数偏小或者偏大。本文同时考虑了高压水喷嘴距连铸坯表面距离、喷嘴出口速度、连铸坯表面温度3个因素对高压水除鳞对流换热系数的影响，并通过FLUENT软件计算出高压水除鳞对流换热系数，然后通过MATLAB软件非线性回归方法回归出高压水除鳞对流换热系数的数学模型。针对鞍钢中厚板生产现场，使用此数学模型计算出对应工况的对流换热系数，然后将此换热系数输入MARC有限元软件中进行温度场分析。对鞍钢生产现场的连铸坯温度进行了实测，理论计算值与实测值最大误差为19℃，最小误差为5℃，吻合较好，结果证明回归出的高压水对流换热系数数学模型比较合理。%In medium plate production, high pressure water descaling convection heat transfer coefficient is an important parameter of the mathematical model of the temperature field. At present, two factors are considered as calculating high pressure water de-scaling convection heat transfer coefficient, the calculated value of convection heat transfer coefficient is too small or too large. The influence of three factors including the high-pressure water spray nozzle from the billet surface distance, nozzle outlet velocity, the billet surface temperature are considered in the process of calculating high pressure water convective heat transfer coefficient. The high pressure water coefficient of convective heat transfer is calculated using FLUENT software in this paper. A regression mathematical model of high pressure water heat transfer coefficient convection is established using the nonlinear regression method in Matlab. The established mathematical model is used to calculate the convection heat
Jakkareddy, Pradeep S.; Balaji, C.
2016-09-01
This paper employs the Bayesian based Metropolis Hasting - Markov Chain Monte Carlo algorithm to solve inverse heat transfer problem of determining the spatially varying heat transfer coefficient from a flat plate with flush mounted discrete heat sources with measured temperatures at the bottom of the plate. The Nusselt number is assumed to be of the form Nu = aReb(x/l)c . To input reasonable values of ’a’ and ‘b’ into the inverse problem, first limited two dimensional conjugate convection simulations were done with Comsol. Based on the guidance from this different values of ‘a’ and ‘b’ are input to a computationally less complex problem of conjugate conduction in the flat plate (15mm thickness) and temperature distributions at the bottom of the plate which is a more convenient location for measuring the temperatures without disturbing the flow were obtained. Since the goal of this work is to demonstrate the eficiacy of the Bayesian approach to accurately retrieve ‘a’ and ‘b’, numerically generated temperatures with known values of ‘a’ and ‘b’ are treated as ‘surrogate’ experimental data. The inverse problem is then solved by repeatedly using the forward solutions together with the MH-MCMC aprroach. To speed up the estimation, the forward model is replaced by an artificial neural network. The mean, maximum-a-posteriori and standard deviation of the estimated parameters ‘a’ and ‘b’ are reported. The robustness of the proposed method is examined, by synthetically adding noise to the temperatures.
Choi, Dong jae; Jang, Yeong jun; Lee, Yeon-Gun [Jeju National University, Jeju (Korea, Republic of); Kim, Sin [Chung-Ang University, Seoul (Korea, Republic of)
2015-10-15
The Passive Containment Cooling System (PCCS) to be introduced in advanced LWRs removes released energy to an external heat sink by a naturally driven flow. Containment through the condensation heat transfer phenomenon in the event of the loss of coolant accident (LOCA) or main steam line break (MSLB). As the released steam pressurizes the containment, the PCCS will activate to transport the decay heat In this study, a numerical analysis of the condensation heat transfer coefficients on the PCCS condenser tube is conducted using the MARS-KS code. The condensation heat transfer coefficients are obtained from JNU condensation tests performed on a 1000 long and 40 mm O.D. tube. The analysis condition covers 2 and 4 bar for the air mass fraction ranging from 0.1 to 0.8. The JNU single vertical condensation experimental results, Uchida's and Dehbi's correlation compared with the MARS-KS code's results at 2 and 4 bar. Experimental results and MARS-KS predicted heat transfer coefficient is different from the thermal resistances and Wall subcooling. An average relative error is 18.8% and 15% at 2 and 4 bar, respectively. Uchida's correlation is considered the noncondensable gas mass fraction only. Therefore, that is lower than MARS-KS results at 4 bar. Dehbi's correlation affected by ratio of the height-to-diameter, so its results are higher condensation heat transfer coefficient than MARS-KS predicted results.
Information Exchange via Surface Modified Resonance Energy Transfer
Boström, Mathias; Huang, Dan; Ninham, Barry W; Sernelius, Bo E
2013-01-01
The theory is presented for resonance interaction between two atoms in an excited configuration: one atom, the "receptor" of information (i.e. energy), adsorbed on a phospholipid surface and the other atom, the "emitter" of information (i.e. energy), a long distance away. The dielectric function for a specific phospholipid membrane is obtained from density functional theory calculations. We present numerical results comparing the range and magnitude of non-specific Casimir-Polder interactions with the much more long-ranged, and highly specific, resonance interaction. A study of the resonance interaction with one or both atoms adsorbed on a phospholipid membrane surface reveals a possibility to have a cross over from attraction to repulsion or from repulsion to attraction at separations between receptor and emitter atoms exceeding several hundred {\\AA}ngstr\\"oms. The energy transfer and the observed transitions in the sign of the interaction energies near surfaces provide potential new ways to start recognitio...
Roy, Arindam; Ramasubramaniam, Rajagopal; Gaonkar, Harshavardhan A.
2012-11-01
Kubelka-Munk (K-M) theory is a phenomenological light transport theory that provides analytical expressions for reflectance and transmittance of diffusive substrates such as tissues. Many authors have derived relations between coefficients of K-M theory and that of the more fundamental radiative transfer equations. These relations are valid only in diffusive light transport regime where scattering dominates over absorption. They also fail near boundaries where incident beams are not diffusive. By measuring total transmittance and total reflectance of tissue phantoms with varying optical parameters, we have obtained empirical relations between K-M coefficients and the radiative transport coefficients for integrating sphere-based spectrophotometers that use uniform, nondiffusive incident beams. Our empirical relations show that the K-M scattering coefficients depend only on reduced scattering coefficient (μs‧), whereas the K-M absorption coefficient depends on both absorption (μa) and reduced scattering (μs‧) coefficients of radiative transfer theory. We have shown that these empirical relations are valid in both the diffusive and nondiffusive regimes and can predict total reflectance within an error of 10%. They also can be used to solve the inverse problem of obtaining multiple optical parameters such as chromophore concentration and tissue thickness from the measured reflectance spectra with a maximum accuracy of 90% to 95%.
RAFT microemulsion polymerization with surface-active chain transfer agent
El-Hedok, Ibrahim Adnan
The work described in this dissertation focuses on enhancing the polymer nanoparticle synthesis using RAFT (reversible-addition fragmentation chain transfer) in microemulsion polymerization in order to achieve predetermined molecular weight with narrow molecular weight polydispersity. The hypothesis is that the use of an amphiphilic chain transfer agent (surface-active CTA) will confine the CTA to the surface of the particle and thermodynamically favor partitioning of the CTA between micelles and particles throughout the polymerization. Thus, the CTA diffusion from micelles to polymer particles would be minimized and the breadth of the CTA per particle distribution would remain low. We report the successful improved synthesis of poly(butyl acrylate), poly(ethyl acrylate), and poly(styrene) nanoparticles using the RAFT microemulsion polymerization with surface-active CTA. The polymerization kinetics, polymer characteristics and latex size experimental data are presented. The data analysis indicates that the CTA remains partitioned between the micelles and particles by the end of the polymerization, as expected. We also report the synthesis of well-defined core/shell poly(styrene)/poly(butyl acrylate) nanoparticle, having polydispersity index value of 1.1, using semi-continuous microemulsion polymerization with the surface-active CTA. The surface-active CTA restricts the polymerization growth to the surface of the particle, which facilitates the formation of a shell block co-polymers with each subsequent second monomer addition instead of discrete homopolymers. This synthesis method can be used to create a wide range of core/shell polymer nanoparticles with well-defined morphology, given the right feeding conditions.
Turbulent mass transfer through a flat shear-free surface
Magnaudet, Jacques; Calmet, Isabelle
2006-04-01
Mass transfer through the flat shear-free surface of a turbulent open-channel flow is investigated over a wide range of Schmidt number (1 ≤ Sc ≤ 200) by means of large-eddy simulations using a dynamic subgrid-scale model. In contrast with situations previously analysed using direct numerical simulation, the turbulent Reynolds number Re is high enough for the near-surface turbulence to be fairly close to isotropy and almost independent of the structure of the flow in the bottom region (the statistics of the velocity field are identical to those described by I. Calmet & J. Magnaudet J. Fluid Mech. vol. 474, 2003, p. 355). The main statistical features of the concentration field are analysed in connection with the structure of the turbulent motion below the free surface, characterized by a velocity macroscale u and an integral length scale L. All near-surface statistical profiles are found to be Sc-independent when plotted vs. the dimensionless coordinate Sc({1) / 2}yu/nu (y is the distance to the surface and nu is the kinematic viscosity). Mean concentration profiles are observed to be linear throughout an inner diffusive sublayer whose thickness is about one Batchelor microscale, i.e. LSc({) - 1 / 2 }Re({) - 3 / 4}. In contrast, the concentration fluctuations are found to reach their maximum near the edge of the outer diffusive layer which scales as LSc({) - 1 / 2}Re({) - 1 / 2}. Instantaneous views of the near-surface isovalues of the concentration and vertical velocity are used to reveal the influence of the Schmidt number. In particular, it is observed that at high Schmidt number, the tiny concentration fluctuations that subsist in the diffusive sublayer just mirror the divergence of the two-component surface velocity field. Co-spectra of concentration and vertical velocity fluctuations indicate that the main contribution to the turbulent mass flux is provided by eddies whose horizontal size is close to L, which strongly supports the view that the mass
da Silva, Wilton Pereira; E Silva, Cleide M D P S
2014-09-01
Cooling of fruits and vegetables, immediately after the harvest, has been a widely used method for maximizing post-harvest life. In this paper, an optimization algorithm and a numerical solution are used to determine simultaneously the convective heat transfer coefficient, hH, and the thermal diffusivity, α, for an individual solid with cylindrical shape, using experimental data obtained during its cooling. To this end, the one-dimensional diffusion equation in cylindrical coordinates is discretized and numerically solved through the finite volume method, with a fully implicit formulation. This solution is coupled to an optimizer based on the inverse method, in which the chi-square referring to the fit of the numerical simulation to the experimental data is used as objective function. The optimizer coupled to the numerical solution was applied to experimental data relative to the cooling of a cucumber. The obtained results for α and hH were coherent with the values available in the literature. With the results obtained in the optimization process, the cooling kinetics of cucumbers was described in details.
Rotational Energy Transfer of N2 Determined Using a New Ab Initio Potential Energy Surface
Huo, Winifred M.; Stallcop, James R.; Partridge, Harry; Langhoff, Stephen R. (Technical Monitor)
1997-01-01
A new N2-N2 rigid-rotor surface has been determined using extensive Ab Initio quantum chemistry calculations together with recent experimental data for the second virial coefficient. Rotational energy transfer is studied using the new potential energy surface (PES) employing the close coupling method below 200 cm(exp -1) and coupled state approximation above that. Comparing with a previous calculation based on the PES of van der Avoird et al.,3 it is found that the new PES generally gives larger cross sections for large (delta)J transitions, but for small (delta)J transitions the cross sections are either comparable or smaller. Correlation between the differences in the cross sections and the two PES will be attempted. The computed cross sections will also be compared with available experimental data.
M. T. Schobeiri
2000-01-01
Full Text Available Aerodynamic and heat transfer investigations were done on a constant curvature curved plate in a subsonic wind tunnel facility for various wake passing frequencies and zero pressure gradient conditions. Steady and unsteady boundary layer transition measurements were taken on the concave surface of the curved plate at different wake passing frequencies where a rotating squirrel-cage generated the unsteady wake flow. The data were analyzed using timeaveraged and ensemble-averaged techniques to provide insight into the growth of the boundary layer and transition. Ensemble-averaged turbulence intensity contours in the temporal spatial domain showed that transition was induced for increasing wake passing frequency and structure. The local heat transfer coefficient distribution for the concave and convex surface was determined at those wake passing frequencies using a liquid crystal heat transfer measurement technique. Detailed aerodynamic and heat transfer investigations showed that higher wake passing frequency caused transition to occur earlier on the concave surface. Local Stanton numbers were also calculated on the concave surface and compared with Stanton numbers predicted using a differential boundary layer and heat transfer calculation method. On the convex side, no effect of wake passing frequency on heat transfer was observed due to a separation bubble that induced transition.
Das, Sudev; Bhaumik, Swapan
2016-04-01
The influence of coating thickness and surface roughness on pool boiling heat transfer is experimentally studied over a range of surface roughness values with varied coating thickness with water at atmospheric pressure. Test surfaces used in this experiment are namely, untreated surface (Ra = 0.0899 µm), polished surface (Ra = 0.0493 µm), TiO2 nanoparticle coated surface with a roughness (Ra) ranging from 0.0338 to 0.289 µm. The surfaces were characterized with respect to contact angle, surface roughness and coating thickness. The contact angle, surface roughness and coating thickness were measured by sessile drop method, optical surface profiler and instrument thickness monitor respectively. Heat fluxes observed ranged from 52.63 to 144.73 W/cm2. Different trends were observed in the Heat Transfer Coefficient (HTC) with respect to the surface roughness and coating thickness values on the same set of heat flux. The HTC was found to increase with increasing the roughness values for untreated and polish surface but nanoparticle coated surfaces displayed different trend in HTCs. The HTC was found to increase with increasing coating thickness with all wall superheat.
2014-04-01
Introduction A tropical cyclone can be viewed as a complex heat engine that extracts heat energy from the sea surface, mainly in the form of latent heat, and...Quarterly Journal of the Royal Meteorological Society Q. J. R. Meteorol. Soc. 140: 792–804, April 2014 Sensitivity of tropical- cyclone models to the...study of the sensitivity of tropical- cyclone intensification to the surface drag coefficient in a three-dimensional model by Montgomery et al. is
Tsukamoto, Takamasa; Ramasamy, Elamparuthi; Shimada, Tetsuya; Takagi, Shinsuke; Ramamurthy, V
2016-03-29
Three coumarin derivatives (7-propoxy coumarin, coumarin-480, and coumarin-540a, 2, 3, and 4, respectively) having different absorption and emission spectra were encapsulated within a water-soluble organic capsule formed by the two positively charged ammonium-functionalized cavitand octaamine (OAm, 1). Guests 2, 3, and 4 absorb in ultraviolet, violet, and blue regions and emit in violet, blue, and green regions, respectively. Energy transfer between the above three coumarin@(OAm)2 complexes assembled on the surface of a saponite clay nanosheet was investigated by steady-state and time-resolved emission techniques. Judging from their emission and excitation spectra, we concluded that the singlet-singlet energy transfer proceeded from 2 to 3, from 2 to 4, and from 3 to 4 when OAm-encapsulated 2, 3, and 4 were aligned on a clay surface as two-component systems. Under such conditions, the energy transfer efficiencies for the paths 2* to 3, 2* to 4, and 3* to 4 were calculated to be 33, 36, and 50% in two-component systems. When all three coumarins were assembled on the surface and 2 was excited, the energy transfer efficiencies for the paths 2* to 3, 2* to 4, and 3* to 4 were estimated to be 32, 34, and 33%. A comparison of energy transfer efficiencies of the two-component and three-component systems revealed that excitation of 2 leads to emission from 4. Successful merging of supramolecular chemistry and surface chemistry by demonstrating novel multi-step energy transfer in a three-component dye encapsulated system on a clay surface opens up newer opportunities for exploring such systems in an artificial light-harvesting phenomenon.
S.P. Anjali Devi
2010-01-01
Full Text Available Viscous and Joule dissipation effects are considered on MHD nonlinear flow and heat transfer past a stretching porous surface embedded in a porous medium under a transverse magnetic field. Analytical solutions of highly nonlinear momentum equation and confluent hypergeometric similarity solution of heat transfer equations in the case when the plate stretches with velocity varying linearly with distance are obtained. The effect of various parameters like suction parameter, Prandtl number, Magnetic parameter, and Eckert number entering into the velocity field, temperature distribution and skin friction co-efficient at the wall are discussed with the aid of graphs.
Heat mass transfer model of fouling process of calcium carbonate on heat transfer surface
QUAN ZhenHua; CHEN YongChang; MA ChongFang
2008-01-01
A new heat mass transfer model was developed to predict the fouling process of calcium carbonate on heat transfer surface.The model took into account not only the crystallization fouling but also the particle fouling which was formed on the heat transfer surface by the suspension particles of calcium carbonate in the su-persaturated solution.Based on experimental results of the fouling process,the deposition and removal rates of the mixing fouling were expressed.Furthermore,the coupling effect of temperature with the fouling process was considered in the physics model.As a result the fouling resistance varying with time was obtained to describe the fouling process and the prediction was compared with experimental data under same conditions.The results showed that the present model could give a good prediction of fouling process,and the deviation was less than 15% of the experimental data in most cases.The new model is credible to predict the fouling process.
Yasin, Muhammad; Park, Shinyoung; Jeong, Yeseul; Lee, Eun Yeol; Lee, Jinwon; Chang, In Seop
2014-10-01
This study proposed a submerged hollow fibre membrane bioreactor (HFMBR) system capable of achieving high carbon monoxide (CO) mass transfer for applications in microbial synthesis gas conversion systems. Hydrophobic polyvinylidene fluoride (PVDF) membrane fibres were used to fabricate a membrane module, which was used for pressurising CO in water phase. Pressure through the hollow fibre lumen (P) and membrane surface area per unit working volume of the liquid (A(S)/V(L)) were used as controllable parameters to determine gas-liquid volumetric mass transfer coefficient (k(L)a) values. We found a k(L)a of 135.72 h(-1) when P was 93.76 kPa and AS/VL was fixed at 27.5m(-1). A higher k(L)a of 155.16 h(-1) was achieved by increasing AS/VL to 62.5m(-1) at a lower P of 37.23 kPa. Practicality of HFMBR to support microbial growth and organic product formation was assessed by CO/CO2 fermentation using Eubacterium limosum KIST612.
Breman, B.B; Beenackers, A.A C M; Bouma, M.J; VanderWerf, M.H.
1996-01-01
Data on the volumetric liquid-side gas-liquid mass transfer coefficient, k(L)a, in a Multi-stage Agitated Contractor (MAC) are reported for three gas-liquid systems (air-water, helium-n-octane, and air-Monoethylene Glycol (MEG)). k(L)a (s(-1)) was determined using a dynamic method with moderately so
The Henry’s law constant (HLC) and the overall mass transfer coefficient are both important parameters for modeling formaldehyde emissions from aqueous solutions. In this work, the apparent HLCs for aqueous formaldehyde solutions were determined in the concentration range from 0....
胡中爱; 吴红英
2000-01-01
The relationship between osmotic pressure difference across the membrane and mass transfer coefficient is developed in this paper. On the basis of this relationship, a method for measuring mass transfer coefficient by using experimental data on reverse osmosis is established. Pitzer's equations are used to calculate osmotic pressure differences in order to assure accuracy of results. Under the conditions of constant operating pressure and bulk flow, mass transfer coefficient is scarcely affected by membrane structure, but decreases slightly with increasing feed concentration. The solute concentration in the polarization layer is calculated by using the measured values of mass transfer coefficient. Polarization layer concentration increases with augmentation in bulk concentration. However, their difference increases with increasing bulk concentration until a maximum difference is reached, and then decreases. Mass transfer coefficient increases with higher velocity of bulk flow. If mass transfer coefficient is so large that the ratio(PwΔπσ/k)becomes very small, polarization could be neglected.
Abdel-Rahman, W.; Evans, M. D. C.; Serre, L.; McCaffrey, J. P.; Podgorsak, E. B.; Seuntjens, J. P. [Department of Medical Physics, McGill University Health Centre, 1650 Avenue Cedar, Montreal, Quebec H3G 1A4 (Canada); Windsor Regional Cancer Center, 2220 Kildre Road, Windsor, Ontario N8W 2X3 (Canada); Ionizing Radiation Standards, National Research Council of Canada, Ottawa, Ontario K1A 0R6 (Canada); Department of Medical Physics, McGill University Health Centre, 1650 Avenue Cedar, Montreal, Quebec H3G 1A4 (Canada)
2009-03-15
Ionization chambers used for reference dosimetry require a local secondary standard ionization chamber with a {sup 60}Co absorbed dose to water calibration coefficient N{sub D,w}{sup 6{sup 0Co}} traceable to a national primary standards dosimetry laboratory or an accredited secondary dosimetry calibration laboratory. Clinic based (in-house) transfer of this coefficient to tertiary reference ionization chambers has traditionally been accomplished with chamber cross calibration in water using a {sup 60}Co beam; however, access to {sup 60}Co teletherapy machines has become increasingly limited for clinic based physicists. In this work, the accuracy of alternative methods of transferring the N{sub D,w}{sup 6{sup 0Co}} calibration coefficient using 6 and 18 MV photon beams from a linear accelerator in lieu of {sup 60}Co has been investigated for five different setups and four commonly used chamber types.
张时锋; 李自良
2011-01-01
Heat transfer coefficient is the main parameters of assessing the cooling capacity of quenching cooling medium, and it also is the key parameters of establishing the thermal boundary conditions. Using the inverse method for heat transfer coefficient, the heat transfer coefficient is taken as the unknown variables to solve the problem, which is classified as inverse heat conduction problems. Such problems have the extremely vital significance in practical engineering application research. This article presented a program of the inverse method for heat transfer coefficient using MATLAB software. The program based on the finite element method verified by Ansys software simulations and experiments. The results show that the method described in this article is a kind of effective method of calculating heat transfer coefficient.%换热系数是评定淬火介质冷却能力的主要参数,也是建立热边界条件的关键参数.换热系数反求法就是把换热系数作为未知量来求解,属于反向热传导问题,这类问题的研究在实际工程应用中具有十分重要的意义.本文用Matlab编写了基于有限元的换热系数反求法程序,用Ansys软件模拟和试验相结合的方法,进行了相应的验证,结果表明,本文所述的方法是一种有效的计算换热系数的方法.
Radiative transfer through an array of discrete surfaces. Final report
Welty, J.R.
1995-08-01
The aim of this research has been to examine how the transfer of radiant energy through a two-dimensional array of typical packing elements is affected by geometric variables (spacing, packing arrangement, and element shapes). The information resulting from this study will be relevant to a spectrum of applications including fibrous insulation, ceramic fabrics, and air heating solar receivers. Computational and experimental results will also be useful in establishing criteria for the valid application of participating media models to systems of discrete surfaces. Additional studies, related to the principal goal, were undertaken as the research effort progressed. These side-issues resulted in three out of the total of 12 publications that resulted from this effort. Collaboration between OSU and PNL has been interactive regarding the experimental and numerical modeling phases of this effort with the results of one group offering guidance to the other. Accomplishments achieved during the course of this effort include the following: (1) a state-of-the-art bidirectional reflectometer was designed, constructed and operated, (2) measurements were made and the results characterized of the bidirectional reflectance of several materials, (3) it was demonstrated that there is a need for information on the full bidirectional reflectance distribution function (BDRF) to describe radiant interchange involving striated surfaces, and (4) validation of results using the two-dimensional Monte Carlo code, developed at PNL, was achieved and the code was used to extend the results of a classic geometric problem in the radiant heat transfer literature.
Choi, Myung Soo; Yang, Kyong Uk [Chonnam National University, Yeosu (Korea, Republic of); Kondou, Takahiro [Kyushu University, Fukuoka (Japan); Bonkobara, Yasuhiro [University of Miyazaki, Miyazaki (Japan)
2016-03-15
We developed a method for analyzing the free vibration of a structure regarded as a distributed system, by combining the Wittrick-Williams algorithm and the transfer dynamic stiffness coefficient method. A computational algorithm was formulated for analyzing the free vibration of a straight-line beam regarded as a distributed system, to explain the concept of the developed method. To verify the effectiveness of the developed method, the natural frequencies of straight-line beams were computed using the finite element method, transfer matrix method, transfer dynamic stiffness coefficient method, the exact solution, and the developed method. By comparing the computational results of the developed method with those of the other methods, we confirmed that the developed method exhibited superior performance over the other methods in terms of computational accuracy, cost and user convenience.
间接加热式列管回转干燥机传热系数模型构建%Modeling for heat transfer coefficient in indirect-heating tube rotary dryer
吴静; 李选友※; 陈宝明; 王瑞雪; 马晓旭; 高玲
2013-01-01
传热系数是列管回转干燥机设计和热工计算所必须的至关重要的设计参数之一，其精度的高低决定了干燥机尺寸、结构设计以及操作参数的合理性。目前还没有一种能够确切描述其加热管与物料颗粒传热过程的可靠而实用的传热模型。该文在对列管回转干燥机传热机理分析的基础上，提出了列管与颗粒间换热的基本构成为：列管管壁与气体介质间对流、气体介质与颗粒间的导热以及列管管壁与颗粒间的辐射换热；通过对列管回转干燥机内料层膨胀的试验研究，分析了颗粒对列管气膜边界层的影响；在此基础上，建立了预测列管外壁与颗粒间总传热系数的数学模型，并以2 mm直径的陶瓷球为物料，在6个转速条件下测量了管壁与颗粒间的换热系数，对模型进行验证；试验结果表明，模型预测的误差小于13%，可满足工程计算的精度要求。研究结果可为列管回转干燥机传热机理的深入研究提供参考。% Heat transfer coefficient is one of the most crucial parameters in thermal calculation and design for a tube rotary dryer. The dimension, structure and operating parameters of a suitably designed dryer rely on the accuracy of the employed heat transfer coefficient. Because of the existence of tubes, particles’ motion behavior and heat transfer mechanism in a tube rotary dryer are more complicated than in a conventional rotary dryer. So far, there is no reliable heat transfer model to describe the heat transfer process between the tubes’ surface and particles in a tube rotary dryer. As a result, the main approach of heat transfer coefficient determination is still an experimental test. The main reason is the insufficiency of understanding on the mechanism of heat transfer between heating tube’s surface and particles. Our experimental investigation showed that heat transfer between tubes’ surface and
Effects of mass transfer between Martian satellites on surface geology
Nayak, Michael; Nimmo, Francis; Udrea, Bogdan
2016-03-01
Impacts on planetary bodies can lead to both prompt secondary craters and projectiles that reimpact the target body or nearby companions after an extended period, producing so-called "sesquinary" craters. Here we examine sesquinary cratering on the moons of Mars. We model the impact that formed Voltaire, the largest crater on the surface of Deimos, and explore the orbital evolution of resulting high-velocity ejecta across 500 years using four-body physics and particle tracking. The bulk of mass transfer to Phobos occurs in the first 102 years after impact, while reaccretion of ejecta to Deimos is predicted to continue out to a 104 year timescale (cf. Soter, S. [1971]. Studies of the Terrestrial Planets. Cornell University). Relative orbital geometry between Phobos and Deimos plays a significant role; depending on the relative true longitude, mass transfer between the moons can change by a factor of five. Of the ejecta with a velocity range capable of reaching Phobos, 25-42% by mass reaccretes to Deimos and 12-21% impacts Phobos. Ejecta mass transferred to Mars is caused by Deimos material. However the high-velocity ejecta mass reaccreted to Deimos from a Voltaire-sized impact is comparable to the expected background mass accumulated on Deimos between Voltaire-size events. Considering that the high-velocity ejecta contains only 0.5% of the total mass sent into orbit, sesquinary ejecta from a Voltaire-sized impact could feasibly resurface large parts of the Moon, erasing the previous geological record. Dating the surface of Deimos may be more challenging than previously suspected.
Cleide M. D. P. da S. e Silva
2012-04-01
Full Text Available In this article, a methodology is used for the simultaneous determination of the effective diffusivity and the convective mass transfer coefficient in porous solids, which can be considered as an infinite cylinder during drying. Two models are used for optimization and drying simulation: model 1 (constant volume and diffusivity, with equilibrium boundary condition, and model 2 (constant volume and diffusivity with convective boundary condition. Optimization algorithms based on the inverse method were coupled to the analytical solutions, and these solutions can be adjusted to experimental data of the drying kinetics. An application of optimization methodology was made to describe the drying kinetics of whole bananas, using experimental data available in the literature. The statistical indicators enable to affirm that the solution of diffusion equation with convective boundary condition generates results superior than those with the equilibrium boundary condition.Neste artigo, é usada uma metodologia para a determinação simultânea da difusividade efetiva e do coeficiente de transferência convectivo de massa em sólidos porosos que possam ser considerados como um cilindro infinito, durante sua secagem. Dois modelos são utilizados para a otimização e a simulação do processo de secagem: o modelo 1 (volume e difusividade constantes, com condição de contorno de equilíbrio; e o modelo 2 (volume e difusividade constantes, com condição de contorno convectiva. Algoritmos de otimização por varredura, baseados no método inverso, foram acoplados às soluções analíticas referentes aos dois modelos utilizados, possibilitando ajustar tais soluções aos dados experimentais da cinética de secagem em camada fina de produtos com a forma cilíndrica. Foi feita uma aplicação da metodologia de otimização na descrição da cinética de secagem de bananas inteiras, usando dados experimentais disponíveis na literatura. Os indicadores estat
Khaiyer, Mandana M.; Doelling, David R.; Chan, Pui K.; Nordeen, MIchele L.; Palikonda, Rabindra; Yi, Yuhong; Minnis, Patrick
2006-01-01
Satellites can provide global coverage of a number of climatically important radiative parameters, including broadband (BB) shortwave (SW) and longwave (LW) fluxes at the top of the atmosphere (TOA) and surface. These parameters can be estimated from narrowband (NB) Geostationary Operational Environmental Satellite (GOES) data, but their accuracy is highly dependent on the validity of the narrowband-to-broadband (NB-BB) conversion formulas that are used to convert the NB fluxes to broadband values. The formula coefficients have historically been derived by regressing matched polarorbiting satellite BB fluxes or radiances with their NB counterparts from GOES (e.g., Minnis et al., 1984). More recently, the coefficients have been based on matched Earth Radiation Budget Experiment (ERBE) and GOES-6 data (Minnis and Smith, 1998). The Clouds and the Earth's Radiant Energy Budget (CERES see Wielicki et al. 1998)) project has recently developed much improved Angular Distribution Models (ADM; Loeb et al., 2003) and has higher resolution data compared to ERBE. A limited set of coefficients was also derived from matched GOES-8 and CERES data taken on Topical Rainfall Measuring Mission (TRMM) satellite (Chakrapani et al., 2003; Doelling et al., 2003). The NB-BB coefficients derived from CERES and the GOES suite should yield more accurate BB fluxes than from ERBE, but are limited spatially and seasonally. With CERES data taken from Terra and Aqua, it is now possible to derive more reliable NB-BB coefficients for any given area. Better TOA fluxes should translate to improved surface radiation fluxes derived using various algorithms. As part of an ongoing effort to provide accurate BB flux estimates for the Atmospheric Radiation Measurement (ARM) Program, this paper documents the derivation of new NB-BB coefficients for the ARM Southern Great Plains (SGP) domain and for the Darwin region of the Tropical Western Pacific (DTWP) domain.
张靖周; 李立国
2001-01-01
A high-resolution testing technique named liquid crystal thermography is used for the experimental study on jet array impingement to map out the distribution of heat transfer coefficients on the cooling surface. Effects of the impingement distance, the impinging hole arrangement and the initial crossflow on heat transfer characteristics are investigated. The thermal images show truly the features of local heat transfer for each jet impingement cooling. The applications of thermochromic liquid crystal are successful in the qualitative and quantitative measurement for heat transfer coefficients distribution%采用高精度热色液晶测试技术对阵列射流冲击的冷却表面局部换热系数分布进行试验研究。研究了射流冲击间距、射流孔排列方式和初始横流等因素对换热特性的影响。热图像真实地反映出每一股射流的冲击冷却局部换热特征。热色液晶用于换热系数分布的定性和定量测试是非常有效的。
Sterling, N C
2011-01-01
We present total and final-state resolved charge transfer (CT) rate coefficients for low-charge Ge, Se, Br, Kr, Rb, and Xe ions reacting with neutral hydrogen over the temperature range 10^2--10^6 K. Each of these elements has been detected in ionized astrophysical nebulae, particularly planetary nebulae. CT rate coefficients are a key ingredient for the ionization equilibrium solutions needed to determine total elemental abundances from those of the observed ions. A multi-channel Landau Zener approach was used to compute rate coefficients for projectile ions with charges q=2-5, and for singly-charged ions the Demkov approximation was utilized. Our results for five-times ionized species are lower limits, due to the incompleteness of level energies in the NIST database. In addition, we computed rate coefficients for charge transfer ionization reactions between the neutral species of the above six elements and ionized hydrogen. The resulting total and state-resolved CT rate coefficients are tabulated and availa...
Moradkhani, Hamed; Izadkhah, Mir-Shahabeddin; Anarjan, Navideh
2017-02-01
In this work, gas dispersion in a two-phase partitioning bioreactor is analyzed by calculating volumetric oxygen mass transfer coefficient which is modeled using a commercial computational fluid dynamics (CFD), code FLUENT 6.2. Dispersed oxygen bubbles dynamics is based on standard "k-ε" Reynolds-averaged Navier-Stokes (RANS) model. This paper describes a three-dimensional CFD model coupled with population balance equations (PBE) in order to get more confirming results of experimental measurements. Values of k L a are obtained using dynamic gassing-out method. Using the CFD simulation, the volumetric mass transfer coefficient is calculated based on Higbie's penetration theory. Characteristics of mass transfer coefficient are investigated for five configurations of impeller and three different aeration flow rates. The pitched six blade type, due to the creation of downward flow direction, leads to higher dissolved oxygen (DO) concentrations, thereby, higher values of k L a compared with other impeller compositions. The magnitude of dissolved oxygen percentage in the aqueous phase has direct correlation with impeller speed and any increase of the aeration magnitude leads to faster saturation in shorter periods of time. Agitation speeds of 300 to 800 rpm are found to be the most effective rotational speeds for the mass transfer of oxygen in two-phase partitioning bioreactors (TPPB).
Computational flow and heat transfer of a row of circular jets impinging on a concave surface
Kumar, B.V.N.R.; Prasad, B.V.S.S.S. [Indian Institute of Technology Madras, Thermal Turbomachines Lab, Chennai (India)
2008-04-15
A computational investigation is carried out to study the flow and heat transfer from a row of circular jets impinging on a concave surface. The computational domain simulates the impingement cooling zone of a gas turbine nozzle guide vane. The parameters, which are varied in the study include jet Reynolds number (Re{sub d} = 5000-67800), inter-jet distance to jet diameter ratio (c/d = 3.33 and 4.67) and target plate distance to jet diameter ratio (H/d = 1, 3 and 4). The flow field, predicted with K-{omega} turbulence model and using Fluent 6.2.16, is characterized with the presence of a pair of counter rotating vortices, an upwash fountain flow and entrainment. The local pressure coefficient and Nusselt number variations along the concave plate are presented and these values are found to under predict the available experimental data by about 12%. (orig.)
Lee, Dorothy B; Faget, Maxime A
1956-01-01
A modified method of Van Driest's flat-plate theory for turbulent boundary layer has been found to simplify the calculation of local skin-friction coefficients which, in turn, have made it possible to obtain through Reynolds analogy theoretical turbulent heat-transfer coefficients in the form of Stanton number. A general formula is given and charts are presented from which the modified method can be solved for Mach numbers 1.0 to 12.0, temperature ratios 0.2 to 6.0, and Reynolds numbers 0.2 times 10 to the 6th power to 200 times 10 to the 6th power.
Taha, T.J.; Thakur, D.B.; Meer, van der T.H.
2012-01-01
In this work, heat transfer surface modification and heat transfer measurement technique is developed. Heat transfer investigation was aimed to study the effect of carbon nano fibers (extremely high thermal conductive material) on the enhancement level in heat transfer. Synthesis of these carbon nan
Two—parameter—dependent Drag Coefficient Over Sea Surface by Turbulent Modeling
JiachunLI; ZifanZHANG
1999-01-01
A new model accounting for both turbulence and sea state effects has been proposed in the current paper to describe momentum exchange through air-sea interface.While long wave components mainly change air flow profile,short wave components exert their influences on the momentum exchange via turbulent stress,which leads to the growth of drag coefficients by a factor of two in young wave age circumstances,As a typical case study,we have considered neutral ABL over a representative regular wave with roughness due to short capillary wves riding over it.The results by the pressent model are in reasonable agreement with Maat's analysis numerically fitted by HEXMAX data and Janssen's results.Two parameter dependence of drag coefficient can resolve the existing discrepency between theory and observations.
Buchachenko, A. A.; Kroupnov, A. A.; Kovalev, V. L.
2015-08-01
Elementary stage rate coefficients of the full system of kinetic equations describing heterogeneous catalytic recombination of the dissociated air on the surfaces of thermal protective ceramic coatings of β-cristobalite and α-Al2O3 are determined using the quantum-mechanical calculations within the framework of cluster models and literature data. Both the impact and associative recombination processes of adsorbed oxygen and nitrogen atoms are taken into account.
Condensation heat transfer on micro and nano structured super hydrophobic surface
Kim, Donghyun; Hwang, Kyung Won; Park, Hyun Sun; Kim, Moo Hwan [POSTECH, Pohang (Korea, Republic of)
2014-05-15
Condensation phenomena occur during the PCCS operation cooling the containment through phase change heat transfer. Accordingly it is important to enhance the condensation heat transfer performance. Condensation mode is commonly classified as filmwise condensation (FWC) and dropwise condensation (DWC). DWC heat transfer performance has an order of magnitude higher than FWC heat transfer performance. In DWC process, condensed liquid droplets attach to the surface and prevent transfer of heat to the cooled surface. Generally the condensate is removed by gravity. When removal rate of condensate is high, DWC heat transfer performance will be enhanced. In terms of removal rate, superhydrophobic surface, which is recently in the spotlight, is expected to have capability to enhance the DWC heat transfer efficiency by reducing droplet size. In this study, we investigated condensation heat transfer performance on micro and nano structured superhydrophobic surface. Condensation experiments on the micro and nano structured superhydrophobic surface were carried out and compared with those on the smooth hydrophobic surface in terms of heat transfer performance and condensed droplet morphologies. Through the experiments, we found that superhydrophobicity disappeared under the condensation circumstance. As a result, heat transfer performance on the superhydro-phobic structured surface decreased compared with that on the smooth hydrophobic surface. In order to enhance the condensation heat transfer performance with superhydrophobic property, condensation mechanism on superhydrophobic surface and the conditions for sustaining superhydrophobicity should be studied more.
Sing, M.; Schwingenschlögl, U.; Claessen, R.;
2003-01-01
diagnostic tool. We show that the observation of generic one-dimensional signatures in photoemission spectra of the valence band close to the Fermi level can be strongly affected by surface effects. Especially, great care must be exercised taking evidence for an unusual one-dimensional many-body state......We have thoroughly characterized the surfaces of the organic charge-transfer salts TTF-TCNQ and (TMTSF)(2)PF6 which are generally acknowledged as prototypical examples of one-dimensional conductors. In particular x-ray-induced photoemission spectroscopy turns out to be a valuable nondestructive...
GUO Zhi-peng
2007-02-01
Full Text Available The high pressure die casting (HPDC process is one of the fastest growing and most efficient methods for the production of complex shape castings of magnesium and aluminum alloys in today’s manufacturing industry.In this study, a high pressure die casting experiment using AZ91D magnesium alloy was conducted, and the temperature profiles inside the die were Measured. By using a computer program based on solving the inverse heat problem, the metal/die interfacial heat transfer coefficient (IHTC was calculated and studied. The results show that the IHTC between the metal and die increases right after the liquid metal is brought into the cavity by the plunger,and decreases as the solidification process of the liquid metal proceeds until the liquid metal is completely solidified,when the IHTC tends to be stable. The interfacial heat transfer coefficient shows different characteristics under different casting wall thicknesses and varies with the change of solidification behavior.
杨雁鸣; 马敬环; 刘莹
2013-01-01
分别用经过脱硬预处理的海水和传统预处理的海水(以下称海水)进行水平管降膜蒸发实验.研究结果表明,在沸点低于70℃时,随着沸点的升高,两者的传热系数都逐渐增大,但脱硬后海水的传热系数略高于海水;在沸点高于70℃时,脱硬后海水的传热系数远远大于海水.也就是说,脱硬后海水可以在高温时也达到很高的传热系数,从而为脱硬预处理与多效蒸发系统相结合提供实验与设计基础.%In this paper,seawater with simple pretreatment and seawater with softening pretreatment were used to horizontal tube falling film evaporation experiments respectively.Experimentalresults showed that these two heat-transfer coefficients gradually increased with boiling point rising,and the heat-transfer seawater s when the boiling coefficient of seawater with softening pretreatment was slightly higher than seawater'point was below 70 ℃.The heat-transfer coefficient of seawater with softening pretreatment was much higher than the seawater' s when the boiling point was above 70 ℃.In an other word,seawater with softening pretreatment could achieve high heat-transfer coefficient at high temperatures.The experiment provided the experimental and designed base for the combination of softening pretreatment and multiple effect evaporation system.
New sensitive micro-measurements of dynamic surface tension and diffusion coefficients
Kinoshita, Koji; Ortiz, Elisa Parra; Needham, David
2017-01-01
. These limitations create inconsistencies for the kinetic analysis of surfactant adsorption/desorption, especially significant for ionic surfactants. Here, the “micropipette interfacial area-expansion method” was introduced and validated as a new DST measurement having a high enough sensitivity to detect diffusion...... controlled molecular adsorption at the air-water interfaces. To validate the new technique, the diffusion coefficient of 1-Octanol in water was investigated with existing models: the Ward Tordai model for the long time adsorption regime (1–100 s), and the Langmuir and Frumkin adsorption isotherm models...
Zhu, Lianjie; Koper, Ger J M; Bedeaux, Dick
2006-03-23
The surface temperature and surface mole fractions are calculated for a catalytic hydrogen oxidation reaction over a Pt/Al2O3 catalyst pellet. The thermodynamics of irreversible processes was used in order to ensure the correct introduction of coupled heat and mass transfer. Two pathways, one using the 4 x 4 resistivity matrix and the other using a simplified effective conductivity matrix, were proven to yield equivalent results. By using expressions for the thermal diffusion coefficients, heats of transfer, and the Maxwell-Stefan diffusion coefficients given in the literature, available experimental data could be reproduced. The Dufour effect was found to be negligible for the prediction of the surface temperature. Neglecting the Soret effect would increase the predicted value of the surface temperature significantly-more than 30 K out of an average of about 400 K. It is found that the reaction rate can be used to predict the surface temperature.
Li-Hua Yu
2015-09-01
Full Text Available In recent years, water (R718 as a kind of natural refrigerant—which is environmentally-friendly, safe and cheap—has been reconsidered by scholars. The systems of using water as the refrigerant, such as water vapor compression refrigeration and heat pump systems run at sub-atmospheric pressure. So, the research on water boiling heat transfer at sub-atmospheric pressure has been an important issue. There are many research papers on the evaporation of water, but there is a lack of data on the characteristics at sub-atmospheric pressures, especially lower than 3 kPa (the saturation temperature is 24 °C. In this paper, the experimental research on water boiling heat transfer on a horizontal copper rod surface at 1.8–3.3 kPa is presented. Regression equations of the boiling heat transfer coefficient are obtained based on the experimental data, which are convenient for practical application.
Knežević Milena M.
2014-01-01
Full Text Available Distribution of gas bubbles and volumetric mass transfer coefficient, Kla, in a three phase system, with different types of solid particles at different operation conditions were studied in this paper. The ranges of superficial gas and liquid velocities used in this study were 0,03-0,09 m/s and 0-0,1 m/s, respectively. The three different types of solid particles were used as a bed in the column (glass dp=3 mm, dp=6 mm; ceramic dp=6 mm. The experiments were carried out in a 2D plexiglas column, 278 x 20,4 x 500 mm and in a cylindrical plexiglas column, with a diameter of 64 mm and a hight of 2000 mm. The Kla coefficient increased with gas and liquid velocities. Results showed that the volumetric mass transfer coefficient has a higher values in three phase system, with solid particles, compared with two phase system. The particles properties (diameter and density have a major impact on oxygen mass transfer in three phase systems.
Marcos, J.D. [Escuela Tecnica Superior Ingenieria Industrial, UNED, c/Juan del Rosal 12, 28040 Madrid (Spain); Izquierdo, M. [Instituto de Ciencias de la Construccion Eduardo Torroja (CSIC), c/Serrano Galvache 4, 28033 Madrid (Spain); Escuela Politecnica Superior, Universidad Carlos III de Madrid, Avenida de la Universidad 30, 28911 Leganes, Madrid (Spain); Lizarte, R. [Escuela Politecnica Superior, Universidad Carlos III de Madrid, Avenida de la Universidad 30, 28911 Leganes, Madrid (Spain); Palacios, E. [Escuela Universitaria Ingenieria Tecnica Industrial, Universidad Politecnica de Madrid, C/ Ronda de Valencia 3, 28012 Madrid (Spain); Infante Ferreira, C.A. [Delft University of Technology, Engineering Thermodynamics, Leeghwaterstraat 44, 2628 CA Delft (Netherlands)
2009-06-15
The aim of this work is to determine the boiling heat transfer coefficients in the high temperature desorber (HTD) of an air-cooled double effect lithium bromide/water absorption prototype. The HTD is a plate heat exchanger (PHE) with thermal oil on one side, and a lithium bromide solution on the other side. Several experiments were performed with this PHE while the prototype was working with an outdoor dry bulb temperature around 42 C and condensation temperature around 55 C. The registered data allowed to calculate the global heat transfer coefficient and the heat transfer coefficient for the LiBr/water mixture in forced convective boiling. The pressure drop produced by the boiling of the refrigerant has been calculated as well. It has been verified that the largest part of the heat supplied in the generator is required for desorbing the refrigerant (except for the maximum solution mass flow), while the sensible heat varies from 10% to 50% of the total heat supplied. (author)
1976-03-01
A compilation is presented of heat transfer and pressure drop data which were collected from literature reports on extended surface heat exchangers. The type of extended surfaces considered are tubular finned tubes as distinct from compact heat exchangers. These surfaces have a base tube to which additional surface was added by mechanical means. This additional surface is in the form of fins attached to the outside surface of the tube. These tubes are normally employed for heat transfer between a liquid and a gas. The liquid flows inside the tubes and the gas, normally air, flows outside the tubes. The fins are oriented so that their surface is transverse to the axis of the tubes. The gas flows across the tubes in a direction parallel to the fin surface.
The influence of a radiated heat exchanger surface on heat transfer
Morel Sławomir
2015-09-01
Full Text Available The experiment leads to establish the influence of radiated surface development heat exchangers on the values of heat flux transferred with water flowing through the exchangers and placed in electric furnace chamber. The values of emissivity coefficients are given for the investigated metal and ceramic coatings. Analytical calculations have been made for the effect of the heating medium (flame – uncoated wall and then heating medium (flame – coated wall reciprocal emissivity coefficients. Analysis of the values of exchanged heat flux were also realized. Based on the measurement results for the base coating properties, these most suitable for spraying the walls of furnaces and heat exchangers were selected, and determined by the intensification of heat exchange effect. These coatings were used to spray the walls of a laboratory waste-heat boiler, and then measurements of fluxes of heat absorbed by the cooling water flowing through the boiler tubes covered with different type coatings were made. Laboratory tests and calculations were also confirmed by the results of full-scale operation on the metallurgical equipment.
The influence of a radiated heat exchanger surface on heat transfer
Morel, Sławomir
2015-09-01
The experiment leads to establish the influence of radiated surface development heat exchangers on the values of heat flux transferred with water flowing through the exchangers and placed in electric furnace chamber. The values of emissivity coefficients are given for the investigated metal and ceramic coatings. Analytical calculations have been made for the effect of the heating medium (flame) - uncoated wall and then heating medium (flame) - coated wall reciprocal emissivity coefficients. Analysis of the values of exchanged heat flux were also realized. Based on the measurement results for the base coating properties, these most suitable for spraying the walls of furnaces and heat exchangers were selected, and determined by the intensification of heat exchange effect. These coatings were used to spray the walls of a laboratory waste-heat boiler, and then measurements of fluxes of heat absorbed by the cooling water flowing through the boiler tubes covered with different type coatings were made. Laboratory tests and calculations were also confirmed by the results of full-scale operation on the metallurgical equipment.
Ehrlich, Stephan; Moellmann, Jonas; Reckien, Werner; Bredow, Thomas; Grimme, Stefan
2011-12-09
Dispersion-corrected density functional theory calculations (DFT-D3) were performed for the adsorption of CO on MgO and C(2) H(2) on NaCl surfaces. An extension of our non-empirical scheme for the computation of atom-in-molecules dispersion coefficients is proposed. It is based on electrostatically embedded M(4)X(4) (M=Na, Mg) clusters that are used in TDDFT calculations of dynamic dipole polarizabilities. We find that the C(MM)(6) dispersion coefficients for bulk NaCl and MgO are reduced by factors of about 100 and 35 for Na and Mg, respectively, compared to the values of the free atoms. These are used in periodic DFT calculations with the revPBE semi-local density functional. As demonstrated by calculations of adsorption potential energy curves, the new C(6) coefficients lead to much more accurate energies (E(ads)) and molecule-surface distances than with previous DFT-D schemes. For NaCl/C(2) H(2) we obtained at the revPBE-D3(BJ) level a value of E(ads) =-7.4 kcal mol(-1) in good agreement with experimental data (-5.7 to -7.1 kcal mol(-1)). Dispersion-uncorrected DFT yields an unbound surface state. For the MgO/CO system, the computed revPBE-D3(BJ) value of E(ads) =-4.1 kcal mol(-1) is also in reasonable agreement with experimental results (-3.0 kcal mol(-1)) when thermal corrections are taken into account. Our new dispersion correction also improves computed lattice constants of the bulk systems significantly compared to plain DFT or previous DFT-D results. The extended DFT-D3 scheme also provides accurate non-covalent interactions for ionic systems without empirical adjustments and is suggested as a general tool in surface science.
Pikal, Michael J; Bogner, Robin; Mudhivarthi, Vamsi; Sharma, Puneet; Sane, Pooja
2016-11-01
This report presents calculations of the difference between the vial heat transfer coefficient of the "edge vial" and the "center vial" at all scales. The only scale-up adjustment for center vials is for the contribution of radiation from the shelf upon which the vial sits by replacing the emissivity of the laboratory dryer shelf with the emissivity of the production dryer shelf. With edge vials, scales-up adjustments are more complex. While convection is not important, heat transfer from the wall to the bands (surrounding the vial array) by radiation and directly from the band to the vials by both radiation and conduction is important; this radiation heat transfer depends on the emissivity of the vial and the bands and is nearly independent of the emissivity of the dryer walls. Differences in wall temperatures do impact the edge vial effect and scale-up, and estimates for wall temperatures are needed for both laboratory and manufacturing dryers. Auto-loading systems (no bands) may give different edge vial heat transfer coefficients than when operating with bands. Satisfactory agreement between theoretical predictions and experimental values of the edge vial effect indicate that results calculated from the theory are of useful accuracy.
Equations of atrazine transfer from agricultural land to surface water
Cann, C.
1995-08-01
As atrazine, the most widely used herbicide in agriculture, makes problems for water supply, the Cemagref study its transfer from lands to surface water. On a small basin of central Brittany, soil and water contents of atrazine have been monitored from 1991 to 1994. Data show that atrazine content of the top layer of soil decreases slowly after spreading. Degradation works more than leaching for this decrease. There is always atrazine in the water of the stream at the outlet of the basin. The concentration of atrazine in water increase sharply in every flood and then decrease slowly. The maximum level of concentration in each flood is very well correlated with the ratio of maximum discharge to the base flow. It means that quick superficial flow of water is the most contaminated water. It brings most of the total flow of atrazine which can be measured in the stream. However, this flow represent only a very small part of the spread atrazine on the basin: less than 1%.
Sustained frictional instabilities on nanodomed surfaces: Stick-slip amplitude coefficient
Quignon, Benoit; Pilkington, Georgia A.; Thormann, Esben
2013-01-01
of the nanodomed surfaces cannot be fully described by the framework of Amontons' laws of friction and that additional parameters (e.g., σf and SSAC) are required, when their friction, lubrication, and wear properties are important considerations in related nanodevices. © 2013 American Chemical Society....
Kabeel, A. E.; Abdelgaied, Mohamed
2016-08-01
Nano-fluids are used to improve the heat transfer rates in heat exchangers, especially; the shell-and-tube heat exchanger that is considered one of the most important types of heat exchangers. In the present study, an experimental loop is constructed to study the thermal characteristics of the shell-and-tube heat exchanger; at different concentrations of Al2O3 nonmetallic particles (0.0, 2, 4, and 6 %). This material concentrations is by volume concentrations in pure water as a base fluid. The effects of nano-fluid concentrations on the performance of shell and tube heat exchanger have been conducted based on the overall heat transfer coefficient, the friction factor, the pressure drop in tube side, and the entropy generation rate. The experimental results show that; the highest heat transfer coefficient is obtained at a nano-fluid concentration of 4 % of the shell side. In shell side the maximum percentage increase in the overall heat transfer coefficient has reached 29.8 % for a nano-fluid concentration of 4 %, relative to the case of the base fluid (water) at the same tube side Reynolds number. However; in the tube side the maximum relative increase in pressure drop has recorded the values of 12, 28 and 48 % for a nano-material concentration of 2, 4 and 6 %, respectively, relative to the case without nano-fluid, at an approximate value of 56,000 for Reynolds number. The entropy generation reduces with increasing the nonmetallic particle volume fraction of the same flow rates. For increase the nonmetallic particle volume fraction from 0.0 to 6 % the rate of entropy generation decrease by 10 %.
Santos, M V; Sansinena, M; Zaritzky, N; Chirife, J
2012-01-01
In oocyte vitrification, plunging directly into liquid nitrogen favor film boiling and strong nitrogen vaporization. A survey of literature values of heat transfer coefficients (h) for film boiling of small metal objects with different geometries plunged in liquid nitrogen revealed values between 125 to 1000 W per per square m per K. These h values were used in a numerical simulation of cooling rates of two oocyte vitrification devices (open-pulled straw and Cryotop), plunged in liquid and slush nitrogen conditions. Heat conduction equation with convective boundary condition was considered a linear mathematical problem and was solved using the finite element method applying the variational formulation. COMSOL Multiphysics was used to simulate the cooling process of the systems. Predicted cooling rates for OPS and Cryotop when cooled at -196 degree C (liquid nitrogen) or -207 degree C (average for slush nitrogen) for heat transfer coefficients estimated to be representative of film boiling, indicated lowering the cooling temperature produces only a maximum 10 percent increase in cooling rates; confirming the main benefit of plunging in slush over liquid nitrogen does not arise from their temperature difference. Numerical simulations also demonstrated that a hypothetical four-fold increase in the cooling rate of vitrification devices when plunging in slush nitrogen would be explained by an increase in heat transfer coefficient. This improvement in heat transfer (i.e., high cooling rates) in slush nitrogen is attributed to less or null film boiling when a sample is placed in slush (mixture of liquid and solid nitrogen) because it first melts the solid nitrogen before causing the liquid to boil and form a film.
Derivation of Regression Coefficients for Sea Surface Temperature Retrieval over East Asia
Myoung-Hwan AHN; Eun-Ha SOHN; Byong-Jun HWANG; Chu-Yong CHUNG; Xiangqian WU
2006-01-01
Among the regression-based algorithms for deriving SST from satellite measurements, regionally optimized algorithms normally perform better than the corresponding global algorithm. In this paper,three algorithms are considered for SST retrieval over the East Asia region (15°-55°N, 105°-170°E),including the multi-channel algorithm (MCSST), the quadratic algorithm (QSST), and the Pathfinder algorithm (PFSST). All algorithms are derived and validated using collocated buoy and Geostationary Meteorological Satellite (GMS-5) observations from 1997 to 2001. An important part of the derivation and validation of the algorithms is the quality control procedure for the buoy SST data and an improved cloud screening method for the satellite brightness temperature measurements. The regionally optimized MCSST algorithm shows an overall improvement over the global algorithm, removing the bias of about -0.13℃ and reducing the root-mean-square difference (rmsd) from 1.36℃ to 1.26℃. The QSST is only slightly better than the MCSST. For both algorithms, a seasonal dependence of the remaining error statistics is still evident. The Pathfinder approach for deriving a season-specific set of coefficients, one for August to October and one for the rest of the year, provides the smallest rmsd overall that is also stable over time.
Kubota, Y; Katano, H; Senda, M
2001-01-01
The ion-transfer reaction of local anesthetics at an organic solvent/water interface has been studied using cyclic voltammetry (CV) with a stationary nitrobenzene (NB)/water (W) interface. Procaine and seven other local anesthetics gave reversible or quasi-reversible voltammograms at the NB/W interface in the pH range between 0.9 and 9.6. These drugs are present in aqueous solution in either neutral or ionic form, or both forms. The half-wave potential, as determined by the midpoint potential in CV, vs. pH curves, were determined and analyzed to determine the partition coefficients of both neutral and ionic forms of the drugs between NB and W. The partition coefficients of the ionic forms were derived from their formal potential of transfer at an NB/W interface. The dissociation constants of ionic forms of the drugs in NB were also deduced. A high correlation between the pharmacological activity and the partition coefficient of the ionic form of amide-linked local anesthetics has been shown.
Liquid transfer between two solid surfaces with the effect of contact angle hysteresis
Chen, Huanchen; Tang, Tian; Amirfazli, Alidad
2013-11-01
Drop transfer from one solid surface to another (e.g. due to the approach of a surface from top to a sessile drop resting on a lower surface) is widely observed in many industrial areas, e.g. offset printing. This process is governed by many factors such as the contact angle (CA) and contact angle hysteresis (CAH) of surfaces, viscosity of the liquid and the rate at which the donor and acceptor surfaces are separated. In this work, an experimental apparatus is developed to study the transfer of liquid drop between surfaces, with the particular focus on addressing the effect of the surfaces' CAH when the loading speed is low (transfer is quasi-static). In the experiment, a liquid bridge between the two surfaces is first formed by compression; then stretched to the point of breakage. By using surfaces that have similar CA but dissimilar CAH, the liquid transfer ratio (the amount of liquid transferred to the acceptor surface over the total amount of liquid) is found to be significantly influenced by CAH. In addition, as a result of CAH, the maximum compression of the liquid bridge is found to play an important role in determining the transfer ratio. These findings can be very helpful for the design of surfaces and loading conditions to achieve desired transfer ratios in practice.
Energy analysis of the engineering-economic optimization of convective heat-transfer surfaces
Stoyanov, N. M.
1991-07-01
The influence of the specific costs of the heat transfer surface, 1 kW of installed power of the blower and motor, 1 kW·h of electrical energy consumption by it, operating time of the surface, and other factors on the optimum specific power expenditure to force heat-transfer fluids through the ducts of heattransfer surfaces is investigated. The minimum engineering-economically justified operating time of the surface is determined.
X. Y. Ji
2010-12-01
Full Text Available The gas-liquid two-phase mass transfer process in microchannels is complicated due to the special dynamical characteristics. In this work, a novel method was explored to measure the liquid side volumetric mass transfer coefficient kLa. Pressure transducers were utilized to measure the pressure variation of upward gas-liquid two-phase flow in three vertical rectangular microchannels and the liquid side volumetric mass transfer coefficient kLa was calculated through the Pressure-Volume-Temperature correlation of the gas phase. Carbon dioxide-water, carbon dioxide-ethanol and carbon dioxide-n-propanol were used as working fluids, respectively. The dimensions of the microchannels were 40 µm×240 µm (depth×width, 100 µm×800 µm and 100 µm×2000 µm, respectively. Results showed that the channel diameter and the capillary number influence kLa remarkably and that the maximum value of kLa occurs in the annular flow regime. A new correlation of kLa was proposed based on the Sherwood number, Schmidt number and the capillary number. The predicted values of kLa agreed well with the experimental data.
Shizhen Xu; Xiaotao Zu; Xiaodong Yuan
2011-01-01
The lifetime of optical components in high-fluence ultraviolet (UV) laser applications is typically limited by laser-initiated damage and its subsequent growth. Using 10.6-μm CO2 laser pulses, we successfully mitigate 355-nm laser induced damage sites on fused silica surface with dimensions less than 200 μm.The damage threshold increases and the damage growth mitigates. However, the growth coefficients of new damage on the CO2 laser processed area are higher than those of the original sample. The damage grows with crack propagation for residual stress after CO2 laser irradiation. Furthermore, post-heating is beneficial to the release of residual stress and slows down the damage growth.%@@ The lifetime of optical components in high-fluence ultraviolet (UV) laser applications is typically limited by laser-initiated damage and its subsequent growth.Using 10.6-μm CO2 laser pulses, we successfully mitigate 355-nm laser induced damage sites on fused silica surface with dimensions less than 200 μm.The damage threshold increases and the damage growth mitigates.However, the growth coefficients of new damage on the CO2 laser processed area are higher than those of the original sample.The damage grows with crack propagation for residual stress after CO2 laser irradiation.Furthermore, post-heating is beneficial to the release of residual stress and slows down the damage growth.
Anderson, Troy P.; Wilson, Chris; Zuhlke, Craig A.; Kruse, Corey; Hassebrook, Anton; Somanas, Isra; Ndao, Sidy; Gogos, George; Alexander, Dennis
2014-03-01
Femtosecond Laser Surface Processing (FLSP) is a powerful technique for the fabrication of self-organized multiscale surface structures on metals that are critical for advanced control over energy transfer at a liquid/solid interface in applications such as electrolysis. The efficiency of the hydrogen evolution reaction on stainless steel 316 electrodes in a 1 molar potassium hydroxide solution is used to analyze the role of surface geometry to facilitate the phase conversion of the liquid to a gaseous state in the vicinity of the interface. It is found that the efficiency of the electrolysis process is directly related to the separation of micro-scale features on an electrode surface. The enhancement is attributed to the size of the valleys between microstructures controlling the contact between an evolving vapor bubble and the electrode surface. The results suggest an alternative pathway for the tailoring of interfacial energy transfer on structured surfaces separate from traditional benchmarks such as surface area and contact angle.
Perez Galindo, Jose Arturo; Garcia Gutierrez, Alonso [Instituto de Investigaciones Electricas, Cuernavaca (Mexico)
1985-12-31
This work describes the experimental technique for the sublimation of naphthalene in air which measures heat transfer coefficients through the use of the analogy between the transference phenomena of heat and mass. The technique used to substitute the experimental measurements of heat transfer, in which it is difficult to control the border thermal conditions, when they are dimmed by the omnipresent problem of heat conduction through the walls of the transference surfaces. Two examples are included of the application technique and its potential is outlined. [Espanol] En este trabajo se describe la tecnica experimental de la sublimacion de naftalina en aire mediante la que se miden coeficientes de transferencia de masa. Los datos asi obtenidos pueden convertirse en coeficientes de transferencia de calor a traves del uso de la analogia entre los fenomenos de transferencia de calor y masa. La tecnica se utiliza para substituir las mediciones experimentales de transferencia de calor, en las que es dificil controlar las condiciones termicas de frontera, cuando las empana el problema omnipresente de la conduccion de calor a traves de las paredes de las superficies de transferencia. Se incluyen dos ejemplos de la aplicacion de la tecnica y se destaca su potencial.
Radiative heat transfer at nanoscale mediated by surface plasmons for highly doped silicon.
Rousseau, Emmanuel; Laroche, Marine; Greffet, Jean-Jacques
2009-01-01
International audience; In this letter, we revisit the role of surface plasmons for nanoscale radiative heat transfer between doped silicon surfaces. We derive a new accurate and closed-form expression of the radiative near-field heat transfer. We also analyse the flux and find that there is a doping level that maximizes the heat flux.
Heat transfer in the Knudsen layer
Sharipov, Felix
2004-06-01
A concept of the surface heat conductivity determining a heat transfer in the Knudsen layer was introduced. It has the same order with respect to the Knudsen number as the bulk heat transfer and must be taken into account in practical calculations. Using the Onsager principle the coefficient of the surface heat conductivity was related to the thermal slip coefficient.
Zhipeng Qu
2017-02-01
Full Text Available The new Heliosat‑4 method estimates the downwelling shortwave irradiance received at ground level in all sky conditions. It provides the global irradiance and its direct and diffuse components on a horizontal plane and the direct irradiance for a plane normal to sun rays. It is a fully physical model using a fast, but still accurate approximation of radiative transfer modelling and is therefore well suited for geostationary satellite retrievals. It can also be used as a fast radiative transfer model in numerical weather prediction models. It is composed of two models based on abaci, also called look-up tables: the already-published McClear model calculating the irradiance under cloud-free conditions and the new McCloud model calculating the extinction of irradiance due to clouds. Both have been realized by using the libRadtran radiative transfer model. The main inputs to Heliosat‑4 are aerosol properties, total column water vapour and ozone content as provided by the Copernicus Atmosphere Monitoring Service (CAMS every 3 h. Cloud properties are derived from images of the Meteosat Second Generation (MSG satellites in their 15 min temporal resolution using an adapted APOLLO (AVHRR Processing scheme Over cLouds, Land and Ocean scheme. The 15 min means of irradiance estimated by Heliosat‑4 are compared to corresponding measurements made at 13 stations within the Baseline Surface Radiation Network and being located in the field of view of MSG and in various climates. The bias for global irradiance is comprised between 2 and 32 W m−2. The root mean square error (RMSE ranges between 74 and 94 W m−2. Relative RMSE values range between 15 % and 20 % of the mean observed irradiance for stations in desert and Mediterranean climates, and between 26 % and 43 % for rainy climates with mild winters. Correlation coefficients between 0.91 and 0.97 are found. The bias for the direct irradiance at normal incidence is comprised
Yu-zeng Zhao; Xin-lin Yang; Feng Bai; Wen-qiang Huang
2005-01-01
Grafting of polystyrene with narrowly dispersed polymer microspheres through surface-initiated atom transfer radical polymerization (ATRP) was investigated. Polydivinylbenzene (PDVB) microspheres were prepared by dispersion polymerization with poly(N-vinyl pyrrolidone) (PVP) as stabilizer. The surfaces of PDVB microspheres were chloromethylated by chloromethyl methyl ether in the presence of zinc chloride as catalyst to form chloromethylbenzene initiating core sites for subsequent ATRP grafting of styrene using CuC1/bpy as catalytic system. Polystyrene was found to be grafted not only from the particle surfaces but also from within a thin shell layer, resulting in the formation of particles size increased from 2.38-2.58 μm, which can further grow to 2.93 μm during secondary grafting polymerization of styrene. This demonstrates that grafting polymerization proceeds through a typical ATRP procedure with living nature. All of the prepared microspheres have narrow particle size distribution with coefficient of variation around 10%.
Doménech-Carbó, A; Doménech-Carbó, M T; Gimeno-Adelantado, J V; Bosch-Reig, F; Saurí-Peris, M C; Casas-Catalán, M J
2001-04-01
The alteration of copper pigments in art samples was studied by linear scan and cyclic voltammetry using sample-modified Elvacite 2044 film electrodes on the basis of two-dimensional diagrams of charge transfer coefficients calculated from Tafel plots of reductive dissolution processes vs. peak potential. Characteristic voltammetric peaks were obtained for pigments used in the baroque vault frescoes of the Basílica de la Virgen de los Desamparados painted by Antonio Palomino. Results obtained by voltammetric techniques were compared with those from SEM/EDX and FT-IR analysis obtaining a good agreement and leaving to an unambiguous identification of pigments used by Palomino and their alteration products.
魏博; 胡申华; 黄龙; 樊小朝; 何伟
2012-01-01
The analysis method of exergy transfer pay more attention to the quality of the energy in process of energy transferring than the method of energy equilibrium. This article borrowed the expression of the thickness of liquid film and the heat transfer coefficient from the analytical solution for laminar film condensation of vapor which studied by Nusselt. Through lead into the research method of the theory of the exergy transfer, the local resistance coefficient of the expression of exergy transfer during thevertical surface condensation can concluded. Calculate the thinkness of liquid film, coefficient of the heat transfer and exergy transfer at the different condenser depression on the surface, will reach a conclusion of that if the condenser depression is largen the coefficient of the heat transfer will reduce, and the coefficient of the exergy transfer will raise. So increase the condenser depression will raise the amount of the exergy transfer, achieve the goal of enhance the heat transfer.%(火用)传递的分析方法比能量平衡的分析方法更加关注能量品质的蜕变规律.借鉴努塞尔蒸汽层流膜状凝结的分析解中竖直平壁凝结液膜的厚度与传热系数表达式,引入(火用)传递理论的研究方法,得到竖直平壁凝结换热局部(火用)传递系数表达式,通过对不同壁面过冷度情况下对壁面液膜厚度、传热系数及(火用)传递系数计算,结果显示过冷度越大,壁面厚度增大,传热系数减小,但(火用)传递系数变大.通过对计算结果的分析可知,壁面过冷度增加可增加传(火用)量,达到强化换热的目的.
Sieres, Jaime; Fernandez-Seara, Jose [University of Vigo, Area de Maquinas y Motores Termicos, E.T.S. de Ingenieros Industriales, Vigo (Spain)
2008-08-15
The ammonia purification process is critical in ammonia-water absorption refrigeration systems. In this paper, a detailed and a simplified analytical model are presented to characterize the performance of the ammonia rectification process in packed columns. The detailed model is based on mass and energy balances and simultaneous heat and mass transfer equations. The simplified model is derived and compared with the detailed model. The range of applicability of the simplified model is determined. A calculation procedure based on the simplified model is developed to determine the volumetric mass transfer coefficients in the vapour phase from experimental data. Finally, the proposed model and other simple calculation methods found in the general literature are compared. (orig.)
Yuan, Zhang Fu; Mukai, Kusuhiro; Takagi, Katsuhiko; Ohtaka, Masahiko; Huang, Wen Lai; Liu, Qiu Sheng
2002-10-15
The surface tension of molten tin has been determined by the sessile drop method at temperatures ranging from 523 to 1033 K and in the oxygen partial pressure (P(O(2))) range from 2.85 x 10(-19) to 8.56 x 10(-6) MPa, and its dependence on temperature and oxygen partial pressure has been analyzed. At P(O(2))=2.85 x 10(-19) and 1.06 x 10(-15) MPa, the surface tension decreases linearly with the increase of temperature and its temperature coefficients are -0.151 and -0.094 mN m(-1) K(-1), respectively. However, at high P(O(2)) (3.17 x 10(-10), 8.56 x 10(-6) MPa), the surface tension increases with the temperature near the melting point (505 K) and decreases above 723 K. The surface tension decrease with increasing P(O(2)) is much larger near the melting point than at temperatures above 823 K. The contact angle between the molten tin and the alumina substrate is 158-173 degrees, and the wettability is poor.
Interaction of NO2 with TiO2 surface under UV irradiation: measurements of the uptake coefficient
Y. Bedjanian
2012-01-01
Full Text Available The interaction of NO2 with TiO2 solid films was studied under UV irradiation using a low pressure flow reactor (1–10 Torr combined with a modulated molecular beam mass spectrometer for monitoring of the gaseous species involved. The NO2 to TiO2 reactive uptake coefficient was measured from the kinetics of NO2 loss on TiO2 coated Pyrex rods as a function of NO2 concentration, irradiance intensity (JNO2 = 0.002–0.012 s−1, relative humidity (RH = 0.06–69 %, temperature (T = 275–320 K and partial pressure of oxygen (0.001–3 Torr. TiO2 surface deactivation upon exposure to NO2 was observed. The initial uptake coefficient of NO2 on illuminated TiO2 surface (with 90 ppb of NO2 and JNO2≅0.006 s−1 was found to be γ0 = (1.2±0.4 ×10−4 (calculated using BET surface area under dry conditions at T = 300 K. The steady state uptake, γ, was several tens of times lower than the initial one, independent of relative humidity, and was found to decrease in the presence of molecular oxygen. In addition, it was shown that γ is not linearly dependent on the photon flux and seems to level off under atmospheric conditions. Finally, the following expression for γ was derived, γ = 2.3×10−3 exp(−1910/T/(1 + P0.36 (where P is O2 pressure in Torr, and recommended for atmospheric applications (for any RH, near 90 ppb of NO2 and JNO2 = 0.006 s−1.
Josué Imbert‐González
2014-08-01
Full Text Available La transferencia de calor incrementada por métodos pasivos se emplea en diversosintercambiadores de calor de alta efectividad. El objetivo del trabajo presentado fue la evaluación del estado de las investigaciones en el campo de la transferencia de calor mejorada en espacios anulares, a partir del empleo de elementos turbulizadores helicoidales como técnicas pasivas. La revisión se centró en el empleo de láminas helicoidales y espirales, la obtención de ecuaciones de correlación del coeficiente de transferencia de calor incrementado, el coeficiente de fricción y la evaluación que se realiza de este proceso por parte de diferentes autores. El análisis crítico permitió realizar valoraciones integradas y recomendar sobre los aspectos que podrían ser analizados en el futuro en esta temática.Palabras claves: transferencia de calor incrementada, láminas helicoidales, espirales, espacios anulares, métodos pasivos._______________________________________________________________________________AbstractThe transfer enhancement by passive methods is used in several heat exchanger of high effectiveness. The objective of the presented work was the evaluation of the state of the investigations in heat transfer enhancement in annular spaces, from the employment of elements helical. The revision was centered in the employment of twisted tape and wire coil in spiral, the equations of correlation obtained of the coefficient of transfer of increased heat, the coefficient of friction and the evaluation that was carried out of this process on the part of different authors. From the critical analysis of the published results, the authors recommend on the topics that can be analyzed in the future in this area.Key words: heat transfer enhancement, twisted tape, helical springs, annular spaces, passive methods.
Qu Wei; Ma Tongze
2001-01-01
The surface of capillary wall can be treated to have a periodic microrelief mathematically. The roughness is micro enough compared with the thickness of the liquid film. So, the surface roughness only exerts influence on the adsorptive potential. Macroscopically, the flow field of the liquid film can be considered as that when the rough surface has an equivalent smooth surface, whose position is at the crests of the microrelief. The mechanism of heat transfer is in connection with two resistances: the thermal resistance of the liquid film conduction and the thermal resistance of the interfacial evaporation. The capillary pressure between the two sides of the vapor-liquid interface due to the interfacial curvature and the disjoining pressure owing to the thin liquid film are considered simultaneously. Several micro tubes with different micro rough surfaces are studied. The length of the evaporating interfacial region decreases with the increase of roughness angle and/or the increase of the roughness height. The heat transfer coefficient and the temperature of the vapor-liquid interface will change to fit the constant mass flow rate.
Zupančič, Matevž; Može, Matic; Gregorčič, Peter; Golobič, Iztok
2017-03-01
Microstructured uniformly and non-uniformly wettable surfaces were created on 25-μm-thin stainless steel foils by laser texturing using a marking nanosecond Nd:YAG laser (λ = 1064 nm) and utilizing various laser fluences and scan line separations. High-speed photography and high-speed IR thermography were used to investigate nucleate boiling heat transfer on the microstructured surfaces. The most pronounced results were obtained on a surface with non-uniform microstructure and non-uniform wettability. The obtained results show up to a 110% higher heat transfer coefficients and 20-40 times higher nucleation site densities compared to the untextured surface. We show that the number of active nucleation sites is significantly increased in the vicinity of microcavities that appeared in areas with the smallest (10 μm) scan line separation. Furthermore, this confirms the predictions of nucleation criteria and proves that straightforward, cost-effective nanosecond laser texturing allows the production of cavities with diameters of up to a few micrometers and surfaces with non-uniform wettability. Additionally, this opens up important possibilities for a more deterministic control over the complex boiling process.
Wang, B.; Liao, Q.; Fillingham, J. H.; Bootsma, H. A.
2013-12-01
Parameterization of air-sea gas transfer velocity was routinely made with wind speed. Near surface turbulent dissipation rate has been shown to have better correlation with the gas transfer velocity in a variety of aquatic environments (i.e., the small eddy model) while wind speed is low to moderate. Wind speed model may underestimate gas transfer velocity at low to moderate winds when the near surface turbulence is produced by other environmental forcing. We performed a series of field experiments to measure the CO2 transfer velocity, and the statistics of turbulence immediately below the air-water interface using a novel floating PIV and chamber system. The small eddy model was evaluated and the model coefficient was found to be a non-constant, and it varies with the local turbulent level (figure 1). Measure results also suggested an appropriate scaling of the vertical dissipation profile immediately below the interface under non-breaking conditions, which can be parameterized by the wind shear, wave height and wave age (figure 2). Figure 1. Relation between the coefficient of the small eddy model and dissipation rate. The data also include Chu & Jirka (2003) and Vachon et al. (2010). The solid regression line: α = 0.188log(ɛ)+1.158 Figure 2. Non-dimensional dissipation profiles. Symbols: measured data with the floating PIV. Solid line: regression of measured data with a -0.79 decaying rate. Dash line with -2 slope: Terray et al. (1996) relation. Dash line with two layer structure: Siddiqui & Loewen (2007) relation.
Cavadias, S; Cauquot, P; Amouroux, J
1997-01-01
Space shuttle overheating during the re-entry phase, due to catalytic oxygen recombination on the thermal protection system, is a problem of practical and theoretical interest. The energy transfer is characterised by the product of the accommodation and the recombination coefficients. Previous measu
Jianping; Ping; Lin; Yunlin
2000-07-01
The local overall volumetric gas-liquid mass transfer coefficients at the specified point in a gas-liquid-solid three-phase reversed flow jet loop bioreactor (JLB) with a non-Newtonian fluid was experimentally investigated by a transient gassing-in method. The effects of liquid jet flow rate, gas jet flow rate, particle density, particle diameter, solids loading, nozzle diameter and CMC concentration on the local overall volumetric gas-liquid mass transfer coefficient (K(L)a) profiles were discussed. It was observed that local overall K(L)a profiles in the three-phase reversed flow JLB with non-Newtonian fluid increased with the increase of gas jet flow rate, liquid jet flow rate, particle density and particle diameter, but decreased with the increase of the nozzle diameter and CMC concentration. The presence of solids at a low concentration increased the local overall K(L)a profiles, and the optimum of solids loading for a maximum profile of the local overall K(L)a was found to be 0.18x10(-3)m(3) corresponding to a solids volume fraction, varepsilon(S)=2.8%.
Amanifard, N.; Nariman-Zadeh, N.; Borji, M.; Khalkhali, A.; Habibdoust, A. [Department of Mechanical Engineering, The University of Guilan, P.O. Box 3756, Rasht (Iran)
2008-02-15
Three-dimensional heat transfer characteristics and pressure drop of water flow in a set of rectangular microchannels are numerically investigated using Fluent and compared with those of experimental results. Two metamodels based on the evolved group method of data handling (GMDH) type neural networks are then obtained for modelling of both pressure drop ({delta}P) and Nusselt number (Nu) with respect to design variables such as geometrical parameters of microchannels, the amount of heat flux and the Reynolds number. Using such obtained polynomial neural networks, multi-objective genetic algorithms (GAs) (non-dominated sorting genetic algorithm, NSGA-II) with a new diversity preserving mechanism is then used for Pareto based optimization of microchannels considering two conflicting objectives such as ({delta}P) and (Nu). It is shown that some interesting and important relationships as useful optimal design principles involved in the performance of microchannels can be discovered by Pareto based multi-objective optimization of the obtained polynomial metamodels representing their heat transfer and flow characteristics. Such important optimal principles would not have been obtained without the use of both GMDH type neural network modelling and the Pareto optimization approach. (author)
Coherent motions and time scales that control heat and mass transfer at wind-swept water surfaces
Turney, D. E.
2016-12-01
Forecast of the heat and chemical budgets of lakes, rivers, and oceans requires improved predictive understanding of air-water interfacial transfer coefficients. Here we present laboratory observations of the coherent motions that occupy the air-water interface at wind speeds (U10) 1.1-8.9 m/s. Spatiotemporal near-surface velocity data and interfacial renewal data are made available by a novel flow tracer method. The relative activity, velocity scales, and time scales of the various coherent interfacial motions are measured, namely for Langmuir circulations, streamwise streaks, nonbreaking wind waves, parasitic capillary waves, nonturbulent breaking wind waves, and turbulence-generating breaking wind waves. Breaking waves exhibit a sudden jump in streamwise interfacial velocity wherein the velocity jumps up to exceed the wave celerity and destroys nearby parasitic capillary waves. Four distinct hydrodynamic regimes are found to exist between U10 = 0 and 8.9 m/s, each with a unique population balance of the various coherent motions. The velocity scales, time scales, and population balance of the different coherent motions are input to a first-principles gas transfer model to explain the waterside transfer coefficient (kw) as well as experimental patterns of temperature and gas concentration. The model mixes concepts from surface renewal and divergence theories and requires surface divergence strength (β), the Lagrangian residence time inside the upwelling zone (tLu), and the total lifetime of new interface before it is downwelled (tLT). The model's output agrees with time-averaged measurements kw, patterns of temperature in infrared photographs, and spatial patterns of gas concentration and kw from direct numerical simulations. Several nondimensional parameters, e.g. βtLu and τstLT where τs is the interfacial shear rate, determine the effectiveness of a particular type of coherent motion for affecting kw.
李明明; 李强; 李琳; 邹宗树
2012-01-01
为了研究冶金反应器内渣-金界面的传质,设计了研究液-液流动边界层传质实验.实验在保证油-水界面稳定的情况下,研究了苯甲酸钠示踪物质在油-水界面的传质现象.通过改变水流量Q（0.44~1.60m3/h）,利用电导率仪测量苯甲酸钠示踪物质在水中的浓度变化,实验确定了液-液界面流动边界层传质系数的准数方程式,并尝试性地给出了液体黏度以及表面张力与传质系数之间的准数关系式.实验结果与液体流过平板边界层的传质过程作了比较讨论.%Experiment research concerning the mass transfer of flowing boundary layer on a liquid-liquid interface was performed to discuss the mass transfer on the molten slag-metal interface in metallurgical reactor.The mass transfer phenomenon of sodium benzoate on the oil-water interface was analyzed in the condition of keeping oil-water interface flat.The concentration change of sodium benzoate with time in water was measured by conductivity meter when the volume flow of water varied from 0.44 to 1.60 m3/h.A dimensionless number equation with respect to the mass transfer coefficient of flowing boundary layer on the liquid-liquid interface was obtained.Then,a dimensionless number equation between the mass transfer coefficient and viscosity as well as surface tension was given tentatively.The results were compared with the mass transfer of boundary layer in the case of fluid flowing through a flat.
GUO Bing; LI Zhi-Hong; LIU Wei-Ping; BAI Xi-Xiang
2007-01-01
The asymptotic normalization coefficients (ANCs) for the virtual decay 17O→16O+n are derived from the angular distributions of the 16O(d, p)17O reaction leading to the ground and first excited states of 17O, respectively, using the distorted wave Born approximation and the adiabatic wave approximation. The ANCs of 17F are then extracted according to charge symmetry of mirror nuclei and used to calculate the astrophysical S-factors of 16O(p,γ)17F leading to the first two states of 17F. The present results are in good agreement with those from the direct measurement. This provides a test of this indirect method to determine direct astrophysical S-factors of(p, γ) reaction. In addition, the S-factors at zero energy for the direct captures to the ground and first excited states of 17F are presented, without the uncertainty associated with the extrapolation from higher energies in direct measurement.
Fristrup, Charlotte Juel; Jankova Atanasova, Katja; Hvilsted, Søren
2009-01-01
The initial formation of initiating sites for atom transfer radical polymerization (ATRP) on various polymer surfaces and numerous inorganic and metallic surfaces is elaborated. The subsequent ATRP grafting of a multitude of monomers from such surfaces to generate thin covalently linked polymer...
Taha, T. J.; Thakur, D. B.; Van der Meer, T. H.
2012-11-01
In this work, heat transfer surface modification and heat transfer measurement technique is developed. Heat transfer investigation was aimed to study the effect of carbon nano fibers (extremely high thermal conductive material) on the enhancement level in heat transfer. Synthesis of these carbon nano structures is achieved using thermal catalytic chemical vapor deposition process (TCCVD) on a 50 μm pure nickel (Ni270) wire. The micro wire samples covered with CNF layers were subjected to a uniform flow from a nozzle. Heat transfer measurement was achieved by a controlled heat dissipation through the micro wire to attain a constant temperature during the flow. This measurement technique is adopted from hot wire anemometry calibration method. Synthesis of carbon nano structures, heat transfer surface characterization and measurement technique are evaluated. Preliminary results indicate that an average enhancement in Nusselt Number of 17% is achieved.
Deridder, Sander; Desmet, Gert
2012-03-02
Numerical calculations of the mobile zone mass transfer rate in a variety of ordered 2D and 3D structures are presented. These calculations are in line with earlier theoretical and experimental findings made in the field of chemical engineering and suggest that the Sherwood-number (Sh(m)) appearing in the mobile phase mass transfer term of the general plate height expression of liquid chromatography is not correctly predicted by the Wilson-Geankoplis--or the Kataoka--or the penetration model expression that have been used up to now to in the field of LC, and that at least more research is needed before these expressions can be continued to be used with confidence. The aforementioned expressions were obtained by neglecting the effect of axial dispersion on the mass transfer process, and it seems that they therefore underestimate the true Sh(m)-number by a factor of 2-5 around the minimum of the van Deemter-curve. New correlations describing the variation of the Sh(m)-coefficient as a function of the reduced velocity for a number of other packing geometries (tetrahedral monolith, 2D pillar array) are proposed. These correlations are in agreement with earlier theoretical and experimental studies showing that at low velocities the local-driving force-based Sh(m)-value is of the order of 10-20 in a packed bed column with an external porosity on the order of 35-40%.
Niu, Zhijun; Zhao, Yang; Sun, Wei; Shi, Suqing; Gong, Yongkuan
2016-11-01
Biomimetic surface modification of polypropylene (PP) is conducted by surface chain transfer reaction based on the mussel-inspired versatile adhesion technology and thiol chemistry, using 2-methacryloyloxyethylphosphorylcholine (MPC) as a hydrophilic monomer mimicking the cell outer membrane structure and 2,2-azobisisobutyronitrile (AIBN) as initiator in ethanol. A layer of polydopamine (PDA) is firstly deposited onto PP surface, which not only offers good interfacial adhesion with PP, but also supplies secondary reaction sites (-NH2) to covalently anchor thiol groups onto PP surface. Then the radical chain transfer to surface-bonded thiol groups and surface re-initiated polymerization of MPC lead to the formation of a thin layer of polymer brush (PMPC) with cell outer membrane mimetic structure on PP surface. X-ray photoelectron spectrophotometer (XPS), atomic force microscopy (AFM) and water contact angle measurements are used to characterize the PP surfaces before and after modification. The protein adsorption and platelet adhesion experiments are also employed to evaluate the interactions of PP surface with biomolecules. The results show that PMPC is successfully grafted onto PP surface. In comparison with bare PP, the resultant PP-PMPC surface exhibits greatly improved protein and platelet resistance performance, which is the contribution of both increased surface hydrophilicity and zwitterionic structure. More importantly, the residue thiol groups on PP-PMPC surface create a new pathway to further functionalize such zwitterion modified PP surface.
Thermal and Fluid Dynamic Performance of Pin Fin Heat Transfer Surfaces
Sahiti, Naser
2006-01-01
This thesis is organized into nine Chapters. Chapter 2 gives an overview of some highly effec-tive heat transfer surfaces used basically for the enhancement of single-phase convective heat transfer in the air conditioning, refrigeration, unit air heater and automobile industries. It follows the analysis of basic parameters that influence the performance of the fins and at the end a rela-tively simple analytical method for the assessment of the order of the magnitude of heat transfer enhanceme...
Second law analysis of heat transfer surfaces in circulating fluidized beds
Gungor, Afsin [Department of Mechanical Engineering, Faculty of Engineering and Architecture, Nigde University, 51100 Nigde (Turkey)
2009-07-15
The correct sizing of the heat transfer surfaces is important to ensure proper operation, load turndown, and optimization of circulating fluidized beds (CFBs). From this point of view, in this study, the thermodynamic second law analysis of heat transfer surfaces in CFBs is investigated theoretically in order to define the parameters that affect the system efficiency. Using a previously developed 2D CFB model which uses the particle-based approach and integrates and simultaneously predicts the hydrodynamics and combustion aspects, second law efficiency and entropy generation values are obtained at different height and volume ratios of the heat transfer surfaces for CFBs. Besides that, the influences of the water flow rates and heat exchanger tube diameters on the second law efficiency are investigated. Through this analysis, the dimensions, arrangement and type of the heat transfer surfaces which achieve maximum efficiency are obtained. (author)
汪贺模; 蔡庆伍; 余伟; 苏岚
2012-01-01
Establishing an accuracy relationship between the convective heat transfer coefficient and cooling process is the key to improve the laminar cooling control model, The convective heat transfer coefficient and corresponding surface temperature were calculated by the finite difference method and the inverse heat conduction method. The effects of cooling water jet flow rate on the heat transfer coefficient and surface temperature was investigated when the cooling water jet flow rate varied from 0. 9 to 2, 1 m3 · h -1. It is found that the convective heat transfer coefficient is a nonlinear function of the surface temperature during laminar flow cooling. Within a distance of 70 mm from the stagnation line, the cooling flow rate has no effect on the heat transfer coefficient and surface temperature. But outside 70 mm, the heat transfer coefficient ratio becomes smaller with increasing distance from the stagnation line, It is also shown that relatively good agreement is obtained between the calculated and measured curves.%提高带钢层流冷却控制模型的精度，关键是建立精确的对流换热系数与冷却工艺之间的关系．采用有限差分法和反向热传导法，获得了实验条件下钢板表面的对流换热系数及表面温度．研究了不同水流量（0．9—2．1m3·h-1）对换热系数与表面温度变化规律的影响．在层流冷却过程中，对流换热系数与表面温度呈非线性关系；在距离驻点70mm内，水流量对换热系数随表面温度变化规律没影响；远离驻点70mm外，对流换热系数比随远离冲击区驻点距离的增加而减小．采用所确定的换热系数计算得到的温降曲线与实测曲线吻合较好．
Surface-to-food pesticide transfer as a function of moisture and fat content.
Vonderheide, Anne P; Bernard, Craig E; Hieber, Thomas E; Kauffman, Peter E; Morgan, Jeffrey N; Melnyk, Lisa Jo
2009-01-01
Transfer of pesticides from household surfaces to foods may result in excess dietary exposure in children (i.e., beyond that inherent in foods due to agricultural application). In this study, transfer was evaluated as a function of the moisture and fat content of various foods. Surfaces chosen for investigation were those commonly found in homes and included Formica, ceramic tile, plastic, carpet, and upholstery fabric. Each surface type was sprayed with an aqueous emulsion of organophosphates, fipronil, and synthetic pyrethroids. In the first phase of the study, multiple foods (apples, watermelon, wheat crackers, graham crackers, white bread, flour tortillas, bologna, fat-free bologna, sugar cookies, ham, Fruit Roll-ups, pancakes, and processed American cheese) were categorized with respect to moisture and fat content. All were evaluated for potential removal of applied pesticides from a Formica surface. In the second phase of the study, representative foods from each classification were investigated for their potential for pesticide transfer with an additional four surfaces: ceramic tile, plastic, upholstery, and carpet. Moisture content, not fat, was found to be a determining factor in most transfers. For nearly all surfaces, more efficient transfer occurred with increased hardness (Formica and ceramic tile). Comparatively, the polymer composition of the plastic delivered overall lower transfer efficiencies, presumably due to an attraction between it and the organic pesticides of interest.
Niu, Zhijun; Zhao, Yang; Sun, Wei; Shi, Suqing, E-mail: shisq@nwu.edu.cn; Gong, Yongkuan
2016-11-15
Highlights: • Biomimetic surface modification of PP was successfully conducted by integrating mussel-inspired technology, thiol chemistry and cell outer membranes-like structures. • The resultant biomimetic surface exhibits good interface and surface stability. • The obvious suppression of protein adsorption and platelet adhesion is also achieved. • The residue thoil groups on the surface could be further functionalized. - Abstract: Biomimetic surface modification of polypropylene (PP) is conducted by surface chain transfer reaction based on the mussel-inspired versatile adhesion technology and thiol chemistry, using 2-methacryloyloxyethylphosphorylcholine (MPC) as a hydrophilic monomer mimicking the cell outer membrane structure and 2,2-azobisisobutyronitrile (AIBN) as initiator in ethanol. A layer of polydopamine (PDA) is firstly deposited onto PP surface, which not only offers good interfacial adhesion with PP, but also supplies secondary reaction sites (-NH{sub 2}) to covalently anchor thiol groups onto PP surface. Then the radical chain transfer to surface-bonded thiol groups and surface re-initiated polymerization of MPC lead to the formation of a thin layer of polymer brush (PMPC) with cell outer membrane mimetic structure on PP surface. X-ray photoelectron spectrophotometer (XPS), atomic force microscopy (AFM) and water contact angle measurements are used to characterize the PP surfaces before and after modification. The protein adsorption and platelet adhesion experiments are also employed to evaluate the interactions of PP surface with biomolecules. The results show that PMPC is successfully grafted onto PP surface. In comparison with bare PP, the resultant PP-PMPC surface exhibits greatly improved protein and platelet resistance performance, which is the contribution of both increased surface hydrophilicity and zwitterionic structure. More importantly, the residue thiol groups on PP-PMPC surface create a new pathway to further functionalize such
Heat transfer effect of an extended surface in downward-facing subcooled flow boiling
Khan, Abdul R., E-mail: khan@vis.t.u-tokyo.ac.jp [Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Erkan, Nejdet, E-mail: erkan@vis.t.u-tokyo.ac.jp [Nuclear Professional School, School of Engineering, The University of Tokyo, 2-22 Shirakata, Tokai-mura, Ibaraki, 319-1188 (Japan); Okamoto, Koji, E-mail: okamoto@n.t.u-tokyo.ac.jp [Nuclear Professional School, School of Engineering, The University of Tokyo, 2-22 Shirakata, Tokai-mura, Ibaraki, 319-1188 (Japan)
2015-12-15
Highlights: • Compare downward-facing flow boiling results from bare and extended surfaces. • Upstream and downstream temperatures were measured on the extended surface. • Downstream temperatures exceed upstream temperatures for all flow rates. • Bubble accumulation occurs downstream on extended surface. • Extended surface heat transfer lower than bare surface as flow rate reduced. - Abstract: New BWR containment designs are considering cavity flooding as an accident management strategy. Unlike the PWR, the BWR has many Control Rod Guide Tube (CRGT) penetrations in the lower head. During a severe accident scenario with core melt in the lower plenum along with cavity flooding, the penetrations may affect the heat transfer on the ex-vessel surface and disrupt fluid flow during the boiling process. A small-scale experiment was performed to investigate the issues existing in downward-facing boiling phenomenon with an extended surface. The results were compared with a bare (flat) surface. The mass flux of 244 kg/m{sup 2} s, 215 kg/m{sup 2} s, and 177 kg/m{sup 2} s were applied in this study. CHF conditions were observed only for the 177 kg/m{sup 2} s case. The boiling curves for both types of surfaces and all flow rates were obtained. The boiling curves for the highest flow rate showed lower surface temperatures for the extended surface experiments when compared to the bare surface. The downstream location on the extended surface yielded the highest surface temperatures as the flow rate was reduced. The bubble accumulation and low velocity in the wake produced by flow around the extended surface was believed to have caused the elevated temperatures in the downstream location. Although an extended surface may enhance the overall heat transfer, a reduction in the local heat transfer was observed in the current experiments.
Consalvi, J. L.; Nmira, F.
2016-03-01
The main objective of this article is to quantify the influence of the soot absorption coefficient-Planck function correlation on radiative loss and flame structure in an oxygen-enhanced propane turbulent diffusion flame. Calculations were run with and without accounting for this correlation by using a standard k-ε model and the steady laminar flamelet model (SLF) coupled to a joint Probability Density Function (PDF) of mixture fraction, enthalpy defect, scalar dissipation rate, and soot quantities. The PDF transport equation is solved by using a Stochastic Eulerian Field (SEF) method. The modeling of soot production is carried out by using a flamelet-based semi-empirical acetylene/benzene soot model. Radiative heat transfer is modeled by using a wide band correlated-k model and turbulent radiation interactions (TRI) are accounted for by using the Optically-Thin Fluctuation Approximation (OTFA). Predicted soot volume fraction, radiant wall heat flux distribution and radiant fraction are in good agreement with the available experimental data. Model results show that soot absorption coefficient and Planck function are negatively correlated in the region of intense soot emission. Neglecting this correlation is found to increase significantly the radiative loss leading to a substantial impact on flame structure in terms of mean and rms values of temperature. In addition mean and rms values of soot volume fraction are found to be less sensitive to the correlation than temperature since soot formation occurs mainly in a region where its influence is low.
Residual strain evaluation of curved surface by grating-transferring technique and GPA
无
2011-01-01
This paper investigates an advanced grating-transferring technique combined with geometric phase analysis (GPA) for residual strain evaluation of curved surface.A standard holographic grating is first transferred to a pre-produced epoxy resin film and then consolidated to a test region of curved surface.With a rubber mold and silicone rubber the deformed grating is replicated to a sheet metal after hole-drilling for release of residual stress.After that the grating is transferred from the sheet metal to the...
CHEN Zhen; LI Hong-Lang; YAN Li; CHEN Xiao-Yang; LU Da-Cheng; WANG Xiao-Hui; LIU Xiang-Lin; HAN Pei-De; YUAN Hai-Rong; WANG Du; WANG Zhan-Guo; HE Shi-Tang
2001-01-01
High-quality and high-resistivity GaN films were grown on (0001) sapphire face by metal-organic vapour phase epitaxy. To measure the surface acoustic wave properties accurately, we deposited metallized interdigital trans ducers on the GaN surface. The acoustic surface wave velocity and electromechanical coupling coefficient were measured, respectively, to be 5667m/s and 1.9% by the pulse method.
Maunu KUOSA; Petri SALLINEN; Arttu REUNANEN; Jari BACKMAN; Jaakko LARJOLA; Lasse KOSKELAINEN
2005-01-01
The study deals with the cooling of a high-speed electric machine through an air gap with numerical and experimental methods. The rotation speed of the test machine is between 5000～40000 r/min and the machine is cooled by a forced gas flow through the air gap. In the previous part of the research the friction coefficient was measured for smooth and grooved stator cases with a smooth rotor. The heat transfer coefficient was recently calculated by a numerical method and measured for a smooth stator-rotor combination. In this report the cases with axial groove slots at the stator and/or rotor surfaces are studied. Numerical flow simulations and measurements have been done for the test machine dimensions at a large velocity range. At constant mass flow rate the heat transfer coefficients by the numerical method attain bigger values with groove slots on the stator or rotor surfaces. The results by the numerical method have been confirmed with measurements. The RdF-sensor was glued to the stator and rotor surfaces to measure the heat flux through the surface, as well as the temperature.
Sujith Kumar, C.S., E-mail: sujithdeepam@gmail.com [Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli 620015, Tamil Nadu (India); Suresh, S., E-mail: ssuresh@nitt.edu [Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli 620015, Tamil Nadu (India); Aneesh, C.R., E-mail: aneeshcr87@gmail.com [Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli 620015, Tamil Nadu (India); Santhosh Kumar, M.C., E-mail: santhoshmc@nitt.edu [Department of Physics, National Institute of Technology, Tiruchirappalli 620015, Tamil Nadu (India); Praveen, A.S., E-mail: praveen_as_1215@yahoo.co.in [Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli 620015, Tamil Nadu (India); Raji, K., E-mail: raji.kochandra@gmail.com [School of Nano Science and Technology, National Institute of Technology, Calicut 673601, Kerala (India)
2015-04-15
Graphical abstract: - Highlights: • Fe–Al{sub 2}O{sub 3}–TiO{sub 2} composite coatings were coated on the copper using spray pyrolysis. • Effect of Fe doping on porosity was determined using AFM. • Effect of Fe doping on hydrophilicity was determined. • Higher enhancement in CHF was obtained for 7.2 at% Fe doped coated sample. - Abstract: In the present work, flow boiling experiments were conducted to study the effect of spray pyrolyzed Fe doped Al{sub 2}O{sub 3}–TiO{sub 2} composite coatings over the copper heater blocks on critical heat flux (CHF) and boiling heat transfer coefficient. Heat transfer studies were conducted in a mini-channel of overall dimension 30 mm × 20 mm × 0.4 mm using de-mineralized water as the working fluid. Each coated sample was tested for two mass fluxes to explore the heat transfer performance. The effect of Fe addition on wettability and porosity of the coated surfaces were measured using the static contact angle metre and the atomic force microscope (AFM), and their effect on flow boiling heat transfer were investigated. A significant enhancement in CHF and boiling heat transfer coefficient were observed on all coated samples compared to sand blasted copper surface. A maximum enhancement of 52.39% and 44.11% in the CHF and heat transfer coefficient were observed for 7.2% Fe doped TiO{sub 2}–Al{sub 2}O{sub 3} for a mass flux of 88 kg/m{sup 2} s.
Chifflard, P.; Kohl, B.; Markart, G.; Kirnbauer, R.
2009-04-01
Modelling the runoff of a catchment in a high spatial resolution, you need to know the potential of a single plot to generate surface runoff. The portion of surface runoff is highly significant for storm runoff events, accordingly, it mainly forms the hydrograph. In this study, the influence of vegetation, soil features and antecedent soil moisture on generating surface runoff at the plot scale have been analysed. To achieve an appropriate fit of the plots, a plot sizes between 50 and 400 m² were chosen. The rainfall intensities ranged between 10 mm/h and 100 mm/h. Based on 260 rain simulations with a transportable sprinkling instrumentation on representative plots in the eastern Alps (Austria, Italy, Germany), including investigations on land-use, vegetation cover and soil physical characteristics, various soil-vegetation complexes and their surface runoff processes have been be analysed. Additionally, we investigated flow paths, travel distance, infiltration hindrance, flow resistance and overland flow velocity. The soil water status was monitored by using TDR-probes, which had been installed in two profiles within the plot in different depths ranging from 5 cm to 40 cm. For every sprinkling experiment, a surface runoff coefficient was calculated as the ratio between total rainfall amount and surface runoff. With this substantial dataset, the regression analysis was used to examine the influence of the hydrological key factors as soil, vegetation and initial soil moisture condition on the distribution functions of the surface runoff coefficient. The first results show that the vegetation cover is very important for the surface runoff. If initial soils are covered by alpine or sub-alpine pioneering vegetation surface runoff can be found very scarce. If these initial soils are covered i.e. by subalpine nardus grasslands the surface runoff coefficients range from 0.1 up to 0.8. On the other hand it can be shown that soils with a high bulk density mainly generate
Chavan, Shreyas; Cha, Hyeongyun; Orejon, Daniel; Nawaz, Kashif; Singla, Nitish; Yeung, Yip Fun; Park, Deokgeun; Kang, Dong Hoon; Chang, Yujin; Takata, Yasuyuki; Miljkovic, Nenad
2016-08-09
Understanding the fundamental mechanisms governing vapor condensation on nonwetting surfaces is crucial to a wide range of energy and water applications. In this paper, we reconcile classical droplet growth modeling barriers by utilizing two-dimensional axisymmetric numerical simulations to study individual droplet heat transfer on nonwetting surfaces (90° distribution theory is incorporated to show that previous modeling approaches underpredict the overall heat transfer by as much as 300% for dropwise and jumping-droplet condensation. To verify our simulation results, we study condensed water droplet growth using optical and environmental scanning electron microscopy on biphilic samples consisting of hydrophobic and nanostructured superhydrophobic regions, showing excellent agreement with the simulations for both constant base area and constant contact angle growth regimes. Our results demonstrate the importance of resolving local heat transfer effects for the fundamental understanding and high fidelity modeling of phase change heat transfer on nonwetting surfaces.
Convective Heat Transfer Between the Wall Surface of a Cavity and the External Main Stream
Yoshiwara, Masahiro; Katto, Yoshiro; Yokoyama, Masanori
An experimental study has been made under the following conditions for convective heat transfer between the wall surface of a cavity of which both width and depth are 25 mm and the external main stream; the range of Reynolds numbers is from 104 to 105, and the ratio of tripping wire diameter to cavity width is 0.08. The oncoming boundary layer to a cavity is turbulent by the tripping wire with the existing study. Convective heat transfer between a cavity wall surface and the external main stream is treated by the following two phenomena; one is the heat transfer which is related to the temperature difference between the wall surface and the fluid in the cavity, and the other the heat transfer which is related to the temperature difference between the fluid in a cavity and the external mainstream. Experimental data obtained for the foregoing conditions is almost coincide with the existing dimensionless correlations of two of the authors.
Fabrication of "petal effect" surfaces by femtosecond laser-induced forward transfer
Li, Hong-Jin; Fan, Wen-Zhong; Pan, Huai-Hai; Wang, Cheng-Wei; Qian, Jing; Zhao, Quan-Zhong
2017-01-01
Superhydrophobic adhesive glass surfaces with polystyrene has been obtained via femtosecond laser induced forward transfer (LIFT). Using this facile method, we obtained composite structures on the glass surface, achieving the transformation from hydrophilicity to superhydrophobicity with contact angle from 36.22° on the glass surface to 159.19° on the LIFT modified glass surface. Analogous to the "petal effect", the obtained superhydrophobic surface also shows high adhesion. Furthermore, the wettability of LIFT modified glass surface can be tuned by changing the interval width of laser scanning, which can be explained by the Cassie impregnating wetting model.
Hsu, Chin-Chi
2012-06-01
This study investigates the effects of surface wettability on pool boiling heat transfer. Nano-silica particle coatings were used to vary the wettability of the copper surface from superhydrophilic to superhydrophobic by modifying surface topography and chemistry. Experimental results show that critical heat flux (CHF) values are higher in the hydrophilic region. Conversely, CHF values are lower in the hydrophobic region. The experimental CHF data of the modified surface do not fit the classical models. Therefore, this study proposes a simple model to build the nexus between the surface wettability and the growth of bubbles on the heating surface. © 2012 Elsevier Ltd. All rights reserved.
Optimization of convective heat transfer coefficient in water jet cooled mirror%射流式水冷镜对流换热系数的优化
李斌; 焦路光; 刘亮; 李兰; 周琼; 袁圣付; 刘文广
2011-01-01
介绍了射流水冷技术并将其应用到高能激光器反射镜的冷却中,设计了射流式水冷镜.采用计算流体力学的方法,利用通用有限元软件ANSYS的流体分析模块FLOTRAN对单孔内射流进行了数值模拟,详细讨论了各孔参数对换热性能的影响.实现了孔参数的优化.结果表明:在水冷镜中采用射流技术可以获得很好的对流换热效果,换热系数可达100 KW/(m·K)以上,且具有结构简单、可控性强等特点.%The jet cooling technology was introduced and used in the cooling of high power laser mirror, then the water jet cooled mirror was designed.Computational fluid dynamics method was adopted to simulate the jet in a hole by the fluid analysis module FLOTRAN of the finite element analysis software ANSYS, then the influence on the capability of heat transfer of the parameters of the hole was discussed and optimization of the parameters was achieved.The results show that great capability of heat transfer can be achieved by using the jet cooling technology, with simple structure and good controllability, and the heat transfer coefficient can be higher than 100 kW/(m2 · K).
Yifat, Jonathan; Gannot, Israel
2015-03-01
Early detection of malignant tumors plays a crucial role in the survivability chances of the patient. Therefore, new and innovative tumor detection methods are constantly searched for. Tumor-specific magnetic-core nano-particles can be used with an alternating magnetic field to detect and treat tumors by hyperthermia. For the analysis of the method effectiveness, the bio-heat transfer between the nanoparticles and the tissue must be carefully studied. Heat diffusion in biological tissue is usually analyzed using the Pennes Bio-Heat Equation, where blood perfusion plays an important role. Malignant tumors are known to initiate an angiogenesis process, where endothelial cell migration from neighboring vasculature eventually leads to the formation of a thick blood capillary network around them. This process allows the tumor to receive its extensive nutrition demands and evolve into a more progressive and potentially fatal tumor. In order to assess the effect of angiogenesis on the bio-heat transfer problem, we have developed a discrete stochastic 3D model & simulation of tumor-induced angiogenesis. The model elaborates other angiogenesis models by providing high resolution 3D stochastic simulation, capturing of fine angiogenesis morphological features, effects of dynamic sprout thickness functions, and stochastic parent vessel generator. We show that the angiogenesis realizations produced are well suited for numerical bio-heat transfer analysis. Statistical study on the angiogenesis characteristics was derived using Monte Carlo simulations. According to the statistical analysis, we provide analytical expression for the blood perfusion coefficient in the Pennes equation, as a function of several parameters. This updated form of the Pennes equation could be used for numerical and analytical analyses of the proposed detection and treatment method.
Linek, V., E-mail: linekv@vscht.cz [Prague Institute of Chemical Technology, Department of Chemical Engineering, CZ-166 28 Prague 6 (Czech Republic); Košek, L. [Research Centre Řež, CZ-250 68 Husinec-Řež (Czech Republic); Moucha, T.; Rejl, F.J.; Kordač, M.; Valenz, L.; Opletal, M. [Prague Institute of Chemical Technology, Department of Chemical Engineering, CZ-166 28 Prague 6 (Czech Republic)
2014-11-15
Highlights: • The model of hydrogen isotopes desorption from lead lithium alloy in packed column is presented. • Mass transfer coefficient k{sub L}a are evaluated from Alpy's Melodie loop experiments. • Packing height and efficiency of packed columns in DEMO plant for DCLL and HCLL are evaluated. • Effects of liquid phase axial dispersion, surface tension and wettability of packing are evaluated. • Effect of flow rate of the purge gas on packing height and desorption efficiency is evaluated. - Abstract: The model of the desorption of hydrogen isotopes from lead lithium alloy in a packed column is derived from the first principles using the plug flow in the liquid phase either the plug flow or ideal mixing in the gas phases. Sievert's law of non-linear equilibrium is followed. The volumetric mass transfer coefficient k{sub L}a and its dependence on the liquid metal flow rate are evaluated on the basis of the Melodie loop experiments. The presented model is used for evaluation of the minimum flow rate of the purge gas for which the concentration of the isotope in the gas leaving the column is at its highest, while the driving force of the interfacial transport of the isotope is still not reduced and the tritium desorption efficiency is therefore retained. The potential effect of the axial dispersion in the gas and liquid phase is evaluated. Highlighted are the issues of the optimum packing geometric surface area, above which the efficiency starts to decrease, and of the role of the surface tension and the contact angle with regard to the wettability of the packing. On the basis of the findings related to these factors, the Mellapak 500 Y and Mellapak packings with flat surfaces are recommended for the tests aiming to intensify the tritium desorption efficiency in the packed columns. The models were used for the engineering sizing of the packed columns in two breeding blanket concepts for the DEMO plant – utilizing DCLL (dual coolant lead lithium
江宁; 曹祖庆
2001-01-01
The concept and physical meanings of condenser’s cleanness coefficient and the modified coefficient of air content in the steam side of condensers have been described,It is suggested to use the measured standard heat transfer coefficient in good state of condensers as a standard for comparison with heat transfer coefficient of condensers.The calculation method of standard heat transfer coefficient has been analyzed,a modified calculation method of test condition for water temperature and water volume etc.in the HEI formula is put forward,a method for on-line calculating the cleanness coefficient of the condenser and modified coefficient of air content at the steam side is put forward as well.%对凝汽器清洁系数和汽侧空气量修正系数的概念与物理意义进行了论述，提出了以良好状态实测标准传热系数作为凝汽器传热系数的比较标准，分析了标准传热系数的计算方法，提出了在HEI公式中对水温、水量等试验条件的修正算法，以及在线计算凝汽器清洁系数、汽侧空气量修正系数的方法。
Physisorption on flat surfaces and inside square wells: a transfer matrix study
Cheng, E.; Banavar, J. R.; Cole, M. W.; Toigo, F.
1992-01-01
Calculations are performed with the transfer matrix method to predict adsorption on a flat surface and on a pore-like well on the surface. In the flat case, temperature-dependent deviation from the Frenkel-Halsey-Hill theory is seen. For numerical reasons the calculations are done for a two-dimensional "world".
The role of a convective surface in models of the radiative heat transfer in nanofluids
Rahman, M.M., E-mail: mansurdu@yahoo.com; Al-Mazroui, W.A.; Al-Hatmi, F.S.; Al-Lawatia, M.A.; Eltayeb, I.A.
2014-08-15
Highlights: • The role of a convective surface in modelling with nanofluids is investigated over a wedge. • Surface convection significantly controls the rate of heat transfer in nanofluid. • Increased volume fraction of nanoparticles to the base-fluid may not always increase the rate of heat transfer. • Effect of nanoparticles solid volume fraction depends on the types of constitutive materials. • Higher heat transfer in nanofluids is found in a moving wedge rather than in a static wedge. - Abstract: Nanotechnology becomes the core of the 21st century. Nanofluids are important class of fluids which help advancing nanotechnology in various ways. Convection in nanofluids plays a key role in enhancing the rate of heat transfer either for heating or cooling nanodevices. In this paper, we investigate theoretically the role of a convective surface on the heat transfer characteristics of water-based nanofluids over a static or moving wedge in the presence of thermal radiation. Three different types of nanoparticles, namely copper Cu, alumina Al{sub 2}O{sub 3} and titanium dioxide TiO{sub 2} are considered in preparation of nanofluids. The governing nonlinear partial differential equations are made dimensionless with the similarity transformations. Numerical simulations are carried out through the very robust computer algebra software MAPLE 13 to investigate the effects of various pertinent parameters on the flow field. The obtained results presented graphically as well as in tabular form and discussed from physical and engineering points of view. The results show that the rate of heat transfer in a nanofluid in the presence of thermal radiation significantly depends on the surface convection parameter. If the hot fluid side surface convection resistance is lower than the cold fluid side surface convection resistance, then increased volume fraction of the nanoparticles to the base fluid may reduces the heat transfer rate rather than increases from the surface of
Surface chemistry effects in finite element modeling of heat transfer in (micron)-fuel cells
Havstad, M
2000-12-07
Equations for modeling surface chemical kinetics by the interaction of gaseous and surface species are presented. The formulation is embedded in a finite element heat transfer code and an ordinary differential equation package is used to solve the surface system of chemical kinetic equations for each iteration within the heat transfer solver. The method is applied to a flow which includes methane and methanol in a microreactor on a chip. A simpler more conventional method, a plug flow reactor model, is then applied to a similar problem. Initial results for steam reforming of methanol are given.
Hijikata, K.; Nakabeppu, O. (Tokyo Inst. of Technology, Tokyo (Japan)); Wang, P.
1991-05-25
A model of finned tubes is developed to predict condensation performance of R-tubes with radial ridges circumferential fin surfaces. Results predicted by this model make an accurate explanation of experimental data, and the condensation mechanism of R-tubes and freon {prime} s condensation heat transfer to R-tubes are predicted by the model R-tubes have high condensation heat transfer coefficients because the ridges on the fin surfaces of the R-tube extend the thin condensate film area and also promote convective heat transfer in the film. In condensation of high performance finned tubes, load values like local temperature differences, local heat flux, local heat transfer coefficient change circumferentially. Therefore, it is necessary to consider this change using theoretical models. 17 refs., 9 figs.
Baier, Tobias; Hardt, Steffen
2014-01-01
The velocity distribution of a gas confined between surfaces held at different temperatures shows a significant deviation from the Maxwell distribution as long as the mean free path of the molecules is comparable to the channel dimensions. When one of the surfaces is suitably structured, this non-equilibrium distribution can be exploited to transfer momentum in tangential direction between the two surfaces. This opens up the possibility to extract work from the system which operates as a heat engine. Since both surfaces are held at constant temperatures, the mode of momentum transfer is different from thermal creep flow that has gained more attention so far. This situation is studied in the limit of free-molecular flow for the case that an unstructured surface is allowed to move tangentially with respect to a structured surface. Parameter studies are conducted, and configurations with maximum thermodynamic efficiency are identified. Overall, it is shown that significant efficiencies can be obtained by tangent...
Privman, V.; Svrakic, N.M.
1989-02-01
Two- and three-dimensional Ising-type systems are considered in the finite-cross-section cylindrical geometry. An interface is forced along the cylinder (strip in 2d) by the antiperiodic or /plus minus/ boundary conditions. Detailed predictions are presented for the largest asymptotically degenerate set of the transfer matrix eigenvalues. For rough interfaces, i.e., for O < T < T/sub c/ in 2d, T/sub R/ < T < T/sub c/ in 3d, the eigenvalues are split algebraically, and the spectral gaps are governed by the surface stiffness coefficient. For rigid interfaces, i.e., O < T < T /sub R/ in 3d, the eigenvalues are split exponentially, with the gaps determined by the step free energy.
J. Prakash Maran
2013-09-01
Full Text Available In this study, a comparative approach was made between artificial neural network (ANN and response surface methodology (RSM to predict the mass transfer parameters of osmotic dehydration of papaya. The effects of process variables such as temperature, osmotic solution concentration and agitation speed on water loss, weight reduction, and solid gain during osmotic dehydration were investigated using a three-level three-factor Box-Behnken experimental design. Same design was utilized to train a feed-forward multilayered perceptron (MLP ANN with back-propagation algorithm. The predictive capabilities of the two methodologies were compared in terms of root mean square error (RMSE, mean absolute error (MAE, standard error of prediction (SEP, model predictive error (MPE, chi square statistic (χ2, and coefficient of determination (R2 based on the validation data set. The results showed that properly trained ANN model is found to be more accurate in prediction as compared to RSM model.
Fristrup, Charlotte Juel; Jankova Atanasova, Katja; Hvilsted, Søren
2010-01-01
Surface-Initiated Atom Transfer Radical Polymerization (SI-ATRP) has been exploited to hydrophilize PEEK. The ketone groups on the PEEK surface were reduced to hydroxyl groups which were converted to bromoisobutyrate initiating sites for SI-ATRP. The modification steps were followed by contact an...... in the surface topography. Two possible applications arose from the hydrophilization of PEEK, metal deposition and protein repellency. The performed modification allowed for successful electroless deposition and good adhesion of nickel as well as copper....
Lin, Albert; Fu, Sze-Ming; Chung, Yen-Kai; Lai, Shih-Yun; Tseng, Chi-Wei
2013-01-14
Surface plasmon enhancement has been proposed as a way to achieve higher absorption for thin-film photovoltaics, where surface plasmon polariton(SPP) and localized surface plasmon (LSP) are shown to provide dense near field and far field light scattering. Here it is shown that controlled far-field light scattering can be achieved using successive coupling between surface plasmonic (SP) nano-particles. Through genetic algorithm (GA) optimization, energy transfer between discrete nano-particles (ETDNP) is identified, which enhances solar cell efficiency. The optimized energy transfer structure acts like lumped-element transmission line and can properly alter the direction of photon flow. Increased in-plane component of wavevector is thus achieved and photon path length is extended. In addition, Wood-Rayleigh anomaly, at which transmission minimum occurs, is avoided through GA optimization. Optimized energy transfer structure provides 46.95% improvement over baseline planar cell. It achieves larger angular scattering capability compared to conventional surface plasmon polariton back reflector structure and index-guided structure due to SP energy transfer through mode coupling. Via SP mediated energy transfer, an alternative way to control the light flow inside thin-film is proposed, which can be more efficient than conventional index-guided mode using total internal reflection (TIR).
Bacon, D H
2013-01-01
Basic Heat Transfer aims to help readers use a computer to solve heat transfer problems and to promote greater understanding by changing data values and observing the effects, which are necessary in design and optimization calculations.The book is concerned with applications including insulation and heating in buildings and pipes, temperature distributions in solids for steady state and transient conditions, the determination of surface heat transfer coefficients for convection in various situations, radiation heat transfer in grey body problems, the use of finned surfaces, and simple heat exc
Whicker, Jeffrey J; Pinder, John E; Ibrahim, Shawki A; Stone, James M; Breshears, David D; Baker, Kristine N
2007-07-01
The environmental mobility of newly deposited radionuclides in surface soil is driven by complex biogeochemical relationships, which have significant impacts on transport pathways. The partition coefficient (Kd) is useful for characterizing the soil-solution exchange kinetics and is an important factor for predicting relative amounts of a radionuclide transported to groundwater compared to that remaining on soil surfaces and thus available for transport through erosion processes. Measurements of Kd for 238U are particularly useful because of the extensive use of 238U in military applications and associated testing, such as done at Los Alamos National Laboratory (LANL). Site-specific measurements of Kd for 238U are needed because Kd is highly dependent on local soil conditions and also on the fine soil fraction because 238U concentrates onto smaller soil particles, such as clays and soil organic material, which are most susceptible to wind erosion and contribute to inhalation exposure in off-site populations. We measured Kd for uranium in soils from two neighboring semiarid forest sites at LANL using a U.S. Environmental Protection Agency (EPA)-based protocol for both whole soil and the fine soil fraction (diametersKd values, which are those specified in the EPA protocol, ranged from 276-508 mL g-1 for whole soil and from 615-2249 mL g-1 for the fine soil fraction. Unexpectedly, the 30-d Kd values, measured to test for soil-solution exchange equilibrium, were more than two times the 7-d values. Rates of adsorption of 238U to soil from solution were derived using a 2-component (FAST and SLOW) exponential model. We found significant differences in Kd values among LANL sampling sites, between whole and fine soils, and between 7-d and 30-d Kd measurements. The significant variation in soil-solution exchange kinetics among the soils and soil sizes promotes the use of site-specific data for estimates of environmental transport rates and suggests possible differences in
Tiwari, Akhilesh; Kondjoyan, Alain; Fontaine, Jean-Pierre
2012-07-01
The phenomenon of heat and mass transfer by condensation of water vapour from humid air involves several key concepts in aerobic bioreactors. The high performance of bioreactors results from optimised interactions between biological processes and multiphase heat and mass transfer. Indeed in various processes such as submerged fermenters and solid-state fermenters, gas/liquid transfer need to be well controlled, as it is involved at the microorganism interface and for the control of the global process. For the theoretical prediction of such phenomena, mathematical models require heat and mass transfer coefficients. To date, very few data have been validated concerning mass transfer coefficients from humid air inflows relevant to those bioprocesses. Our study focussed on the condensation process of water vapour and developed an experimental set-up and protocol to study the velocity profiles and the mass flux on a small size horizontal flat plate in controlled environmental conditions. A closed circuit wind tunnel facility was used to control the temperature, hygrometry and hydrodynamics of the flow. The temperature of the active surface was controlled and kept isothermal below the dew point to induce condensation, by the use of thermoelectricity. The experiments were performed at ambient temperature for a relative humidity between 35-65% and for a velocity of 1.0 ms⁻¹. The obtained data are analysed and compared to available theoretical calculations on condensation mass flux.
Heat Transfer from a dc Laminar Plasma-Jet Flow to Different Solid Surfaces
孟显; 潘文霞; 吴承康
2003-01-01
The heat flux distributions were measured by using transient method for an argon dc laminar plasma-jet flow impinging normally on a plate surface embedded with copper probes. Different powders were coated on the probe surfaces and the effect of powder coatings on the heat transfer from jet flow to the probe surface was examined.Experimental results show that the maximum values of the heat flux to the probe increase with the coating of fine metal powders, while for the surfaces coated with fine ceramic powders, the maximum values of heat flux decrease, compared with that to the bare copper probe surface.
Technologies for Lunar Surface Power Systems Power Beaming and Transfer
Marzwell, Neville; Pogorzelski, Ronald J.; Chang, Kai; Little, Frank
2008-01-01
steering for microwave power transmission (the ability to accurately track a moving receiver) has been demonstrated at Texas A&M. It is proposed that the next step in development of this concept is a modest scale up from 25 elements to 435 followed by a further scale up using such 435 element arrays as subarrays for a still larger retrodirective system. Ultimately, transmit antenna sizes on the order of 100 meters are envisioned permitting transfer levels on the order of 30 kW to aerial vehicles up to 20 km.
Seghir, S.; Stein, N. [Institut Jean Lamour - Electrochimie des Materiaux, Nancy-Universite, Universite Paul Verlaine Metz, CNRS, 1 Bd. Arago, F-57078 Metz (France); Boulanger, C., E-mail: clotilde.boulanger@univ-metz.f [Institut Jean Lamour - Electrochimie des Materiaux, Nancy-Universite, Universite Paul Verlaine Metz, CNRS, 1 Bd. Arago, F-57078 Metz (France); Lecuire, J.-M. [Institut Jean Lamour - Electrochimie des Materiaux, Nancy-Universite, Universite Paul Verlaine Metz, CNRS, 1 Bd. Arago, F-57078 Metz (France)
2011-02-15
The molybdenum chalcogenides Mo{sub 6}X{sub 8} (X = S, Se) offer the possibility of intercalation/de-intercalation processes by chemical or electrochemical way. Besides the different applications of so-called Chevrel phases, we have proposed an electrochemical transfer junction for selective recovery of metallic cations in the perspective of recycling of industrial liquid mineral wastes. Thus, the knowledge of the diffusion properties of cations in the Chevrel phases is essential. Here we report on the electrochemical determination of diffusion coefficients of Co{sup 2+}, Ni{sup 2+}, Fe{sup 2+}, Cd{sup 2+}, Zn{sup 2+}, Mn{sup 2+} and Cu{sup 2+} for Mo{sub 6}S{sub 8} and Mo{sub 6}Se{sub 8} matrices. Experiments were realized on samples with compactness of 50% and 96-98%. They point out that the lower compactness is unfavorable to the mobility of the cobalt ions. From potential step chronoamperometry and electrochemical impedance spectroscopy, the diffusion coefficients were found around 10{sup -9} cm{sup 2} s{sup -1}, even 10{sup -6} cm{sup 2} s{sup -1} for copper. These results confirm the high mobility of transition metal ions in studied phases and complete the data for Co, Fe or Mn-Mo{sub 6}S{sub 8} system and Mn-Mo{sub 6}Se{sub 8} system. For the sulfide phase, the following sequence for D-tilde is observed Ni < Co < Fe < Cd < Zn < Mn << Cu and can be explained in regards with structural considerations and repulsion effects for copper.
Rotational Energy Transfer of N2 Gas Determined Using a New Ab Initio Potential Energy Surface
Huo, Winifred M.; Stallcop, James R.; Partridge, Harry; Langhoff, Stephen R. (Technical Monitor)
1997-01-01
Rotational energy transfer between two N2 molecules is a fundamental process of some importance. Exchange is expected to play a role, but its importance is somewhat uncertain. Rotational energy transfer cross sections of N2 also have applications in many other fields including modeling of aerodynamic flows, laser operations, and linewidth analysis in nonintrusive laser diagnostics. A number of N2-N2 rigid rotor potential energy surface (PES) has been reported in the literature.
Evgeny Epelbaum
2005-05-01
The proton to proton polarization transfer coefficients K{sub x}{sup x'}, K{sub y}{sup y'}, K{sub z}{sup x'} and the proton to deuteron polarization transfer coefficients K{sub x}{sup x'}, K{sub y}{sup y'}, K{sub z}{sup x'}, K{sub x}{sup y'z'}, K{sub y}{sup z'z'}, K{sub z}{sup y'z'}, K{sub y}{sup x'z'} and K{sub y}{sup x'x'-y'y'} have been measured in d({rvec p}, {rvec p})d and d({rvec p}, {rvec d})p reactions at E{sub p}{sup lab} = 22.7 MeV, respectively. The data have been compared to predictions of modern nuclear forces obtained by solving the three-nucleon Faddeev equations in momentum space. Realistic (semi) phenomenological nucleon-nucleon potentials combined with model three-nucleon forces and modern chiral nuclear forces have been used. The AV18, CD Bonn, Nijm I and II nucleon-nucleon interactions have been applied alone or combined with the Tucson-Melbourne 99 three-nucleon force, adjusted separately for each potential to reproduce the triton binding energy. For the AV18 potential also the Urbana IX three-nucleon force have been used. In addition chiral NN potentials in the next-to-leading-order and chiral two- and three-nucleon forces in the next-to-next-to-leading-order have been applied. Only when three-nucleon forces are included a satisfactory description of all data results. For the chiral approach the restriction to the forces in the next-to-leading order is insufficient. Only when going over to the next-to-next-to-leading order one gets a satisfactory description of the data, similar to the one obtained with the (semi) phenomenological forces.
表面张力系数实验的应用研究%On the Application of Liquid Surface Tension Coefficient Experiment
葛素红; 孙桂华; 王雅丽
2014-01-01
The surface tension coefficient of saline water and sweet water in the same temperature and different densities was measured using the FD-NST-I liquid surface tension coefficient measuring instrument. And the surface tension coefficient of tap -water and purified water in different temperatures was also measured using the same instrument. Results show that the surface tension coefficient is related to temperature and density.%应用拉脱法测量了食盐和白糖溶液的表面张力系数，发现：盐溶液的表面张力系数随着溶液密度的增大而增大，糖溶液的表面张力系数随着浓度的增大而减小。测量了自来水与纯净水在不同环境温度下的表面张力系数，验证了液体表面张力系数随着温度的升高而降低的物理规律。
Resonance Energy Transfer in Hybrid Devices in the Presence of a Surface
Kopylov, Oleksii; Huck, Alexander; Kadkhodazadeh, Shima
2014-01-01
We have studied room-temperature, nonradiative resonant energy transfer from InGaN/GaN quantum wells to CdSe/ZnS nanocrystals separated by aluminum oxide layers of different thicknesses. Nonradiative energy transfer from the quantum wells to the nanocrystals at separation distances of up...... to approximately 10 nm was observed. By comparing the carrier dynamics of the quantum wells and the nanocrystals, we found that nonradiative recombination via surface states, generated during dry etching of the wafer, counteracts the nonradiative energy-transfer process to the nanocrystals and therefore decreases...
Zheng, Junwei [Iowa State Univ., Ames, IA (United States)
1999-11-08
Surface plasmon resonance was utilized to enhance the electron transfer at silver/solution interfaces. Photoelectrochemical reductions of nitrite, nitrate, and CO_{2} were studied on electrochemically roughened silver electrode surfaces. The dependence of the photocurrent on photon energy, applied potential and concentration of nitrite demonstrates that the photoelectrochemical reduction proceeds via photoemission process followed by the capture of hydrated electrons. The excitation of plasmon resonances in nanosized metal structures resulted in the enhancement of the photoemission process. In the case of photoelectrocatalytic reduction of CO_{2}, large photoelectrocatalytic effect for the reduction of CO_{2} was observed in the presence of surface adsorbed methylviologen, which functions as a mediator for the photoexcited electron transfer from silver metal to CO_{2} in solution. Photoinduced reduction of microperoxidase-11 adsorbed on roughened silver electrode was also observed and attributed to the direct photoejection of free electrons of silver metal. Surface plasmon assisted electron transfer at nanostructured silver particle surfaces was further determined by EPR method.
Zheng, Junwei
1999-11-08
Surface plasmon resonance was utilized to enhance the electron transfer at silver/solution interfaces. Photoelectrochemical reductions of nitrite, nitrate, and CO{sub 2} were studied on electrochemically roughened silver electrode surfaces. The dependence of the photocurrent on photon energy, applied potential and concentration of nitrite demonstrates that the photoelectrochemical reduction proceeds via photoemission process followed by the capture of hydrated electrons. The excitation of plasmon resonances in nanosized metal structures resulted in the enhancement of the photoemission process. In the case of photoelectrocatalytic reduction of CO{sub 2}, large photoelectrocatalytic effect for the reduction of CO{sub 2} was observed in the presence of surface adsorbed methylviologen, which functions as a mediator for the photoexcited electron transfer from silver metal to CO{sub 2} in solution. Photoinduced reduction of microperoxidase-11 adsorbed on roughened silver electrode was also observed and attributed to the direct photoejection of free electrons of silver metal. Surface plasmon assisted electron transfer at nanostructured silver particle surfaces was further determined by EPR method.
Surface energy equation for heat transfer process in a pebble fuel
Espinosa-Paredes, G., E-mail: gepe@xanum.uam.mx [Área de Ingeniería en Recursos Energéticos, Universidad Autónoma Metropolitana-Iztapalapa, Av. San Rafael Atlixco 186 Col. Vicentina, México, DF 09340 (Mexico); Castillo-Jiménez, V. [Área de Ingeniería en Recursos Energéticos, Universidad Autónoma Metropolitana-Iztapalapa, Av. San Rafael Atlixco 186 Col. Vicentina, México, DF 09340 (Mexico); Herranz-Puebla, L.E. [División de Fisión Nuclear, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, Avda. Complutense, 22, 28040 Madrid (Spain); Vázquez-Rodríguez, R. [Área de Ingeniería en Recursos Energéticos, Universidad Autónoma Metropolitana-Iztapalapa, Av. San Rafael Atlixco 186 Col. Vicentina, México, DF 09340 (Mexico)
2014-12-15
Highlights: • Steady and transient behaviors of the interfacial heat transfer in a fuel element. • Non-local averaging volume method for deriving the surface energy equation. • The method captures significant physical phenomena of the interfacial heat transfer. • Closure relationships are proposed in order to obtain the temperatures distribution. • The derived average equation represents an upscaling regarding the local description. - Abstract: In this paper the surface energy equation for the heat transfer process (HT) between the mixture of fuel (TRISO particles and graphite matrix) and coating in a fuel pebble is derived. The fuel pebble can be treated as a heterogeneous region (mixture of microspheres and graphite) interacting thermally with the homogeneous region (the coating or cladding). These two regions are separated by a boundary region where the properties and behavior differ from those of the adjoining regions. The methodology applied for deriving the surface energy equation is based on the classical theory on interfacial transport phenomena. The surface energy equation derived in this work is an average equation that represents an upscaling respect to the local description. The regions around the surface where changes in the physical phenomena are important are of the order of microns, in contrast with interfacial mass transfer between phases that may be several molecular diameters. The numerical analysis regarding the application of surface energy equation is presented in this work.
Heat transfer of impinging jet-array over convex-dimpled surface
Chang, Shyy Woei [Thermal Fluids Laboratory, National Kaohsiung Marine University, No. 142, Haijhuan Road, Nanzih District, Kaohsiung City 81143, Taiwan (China); Jan, Yih Jena; Chang, Shuen Fei [Department of Marine Engineering, National Kaohsiung Marine University, No. 142, Haijhuan Road, Nanzih District, Kaohsiung City 81143, Taiwan (China)
2006-08-15
A detailed heat transfer measurement over a convex-dimpled surface of impinging jet-array with three eccentricities (E/H) between jet-centre and dimple-centre is performed. These surface dimples considerably modify heat transfers from smooth-walled scenarios due to different impinging topologies for jet array with modified inter-jet reactions. Heat transfer variations caused by adjusting jet Reynolds number (Re) and separation distance (S/D{sub j}) over the ranges of 5000=
Phillip Burgers
Full Text Available For a century, researchers have used the standard lift coefficient C(L to evaluate the lift, L, generated by fixed wings over an area S against dynamic pressure, ½ρv(2, where v is the effective velocity of the wing. Because the lift coefficient was developed initially for fixed wings in steady flow, its application to other lifting systems requires either simplifying assumptions or complex adjustments as is the case for flapping wings and rotating cylinders.This paper interprets the standard lift coefficient of a fixed wing slightly differently, as the work exerted by the wing on the surrounding flow field (L/ρ·S, compared against the total kinetic energy required for generating said lift, ½v(2. This reinterpreted coefficient, the normalized lift, is derived from the work-energy theorem and compares the lifting capabilities of dissimilar lift systems on a similar energy footing. The normalized lift is the same as the standard lift coefficient for fixed wings, but differs for wings with more complex motions; it also accounts for such complex motions explicitly and without complex modifications or adjustments. We compare the normalized lift with the previously-reported values of lift coefficient for a rotating cylinder in Magnus effect, a bat during hovering and forward flight, and a hovering dipteran.The maximum standard lift coefficient for a fixed wing without flaps in steady flow is around 1.5, yet for a rotating cylinder it may exceed 9.0, a value that implies that a rotating cylinder generates nearly 6 times the maximum lift of a wing. The maximum normalized lift for a rotating cylinder is 1.5. We suggest that the normalized lift can be used to evaluate propellers, rotors, flapping wings of animals and micro air vehicles, and underwater thrust-generating fins in the same way the lift coefficient is currently used to evaluate fixed wings.
Nucleate boiling heat transfer from a structured surface - Effect of liquid intake
Das, A.K.; Das, P.K.; Bhattacharyya, S.; Saha, P. [Department of Mechanical Engineering, Indian Institute of Technology, Kharagpur 721 302 (India)
2007-04-15
A model of the suction evaporation mode in nucleate boiling from tunnel and pore structures is presented. The model is based on the analysis by Nakayama et al. [W. Nakayama, T. Daikoku, H. Kuwahara, T. Nakajima, Dynamic model of enhanced boiling heat transfer on porous surfaces - Part II. Analytical model, ASME J. Heat Transfer 102 (3) (1980) 451-456] and L.H. Chein and R.L. Webb [A nucleate boiling model for structured enhanced surfaces, Int. J. Heat Mass Transfer 41 (14) (1998) 2183-2195]. Additionally, a detailed phenomenological model of liquid refill has been developed. It has been shown that the process of liquid refill and the time needed for it is strongly dependent on pool height. Effect of liquid pool height on bubble frequency has also been discussed. Finally, a generalized methodology is given for the prediction of boiling data from a structured surface. (author)
Nascimento, Fellype do; Canesqui, Mara A; Moshkalev, Stanislav
2016-01-01
In this work we studied processing of poly(dimethylsiloxane) (PDMS) surfaces using dielectric barrier discharge (DBD) plasma in two different assemblies, one using the primary plasma jet obtained from a conventional DBD and the other using a DBD plasma jet transfer. The evolution of water contact angle (WCA) in function of plasma processing time and in function of aging time as well as the changes in the surface roughness of PDMS samples for both plasma treatments have been studied. We also compared vibrational and rotational temperatures for both plasmas and for the first time the vibrational temperature (T_vib) for the transferred plasma jet has been shown to be higher as compared with the primary jet. The increment in the T_vib value seems to be the main reason for the improvements in adhesion properties and surface wettability for the transferred plasma jet. Possible explanations for the increase in the vibrational temperature are presented.
Szillat, Florian; Fechner, Renate; Mayr, Stefan G
2013-09-01
Pattern transfer during deposition of oligomeric bisphenol A (OBA) on pre-structured Cu surfaces is investigated by means of a combined experimental-computational approach. Aiming for quantitative prediction of experiments, as characterized by atomic force microscopy (AFM), we explore the capabilities of stochastic rate equations to quantitatively account for the spatio-temporal evolution of surface topography. While surface diffusion and deposition noise constitute the main mechanisms, pattern transfer is affected by the inclusion of retardation in the interface potential, which appears to be necessary beyond a critical initial surface slope. In addition, routes for successful surface fixation by cross-linking are also demonstrated, which may pave the way for further technological use.
Saltiel, S; Ducloy, M; Bloch, Daniel; Ducloy, Martial; Saltiel, Solomon
2006-01-01
The near-field interaction of an atom with a dielectric surface is inversely proportional to the cube to the distance to the surface, and its coupling strength depends on a dielectric image coefficient. This coefficient, simply given in a pure electrostatic approach by (eps-1) / (eps+1) with eps the permittivity, is specific to the frequency of each of the various relevant atomic transition : it depends in a complex manner from the bulk material properties, and can exhibit resonances connected to the surface polariton modes. We list here the surface resonances for about a hundred of optical windows whose bulk properties are currently tabulated. The study concentrates on the infrared domain because it is the most relevant for atom-surface interaction. Aside from this tabulation, we discuss simple hints to estimate the position of surface resonances, and how uncertainties in the bulk data for the material dramatically affect the predictions for the image coefficient. We also evaluate the contribution of UV reso...
Sergeev, Daniil; Troitskaya, Yuliya; Vdovin, Maxim
2015-04-01
Investigation of small scale transfer processes between the ocean and atmosphere in the boundary and its parameterization on the meteorological conditions (wind and surface waves parameters) is very important for weather forecasts modeling [1]. The accuracy of the predictions taking in to account the so named bulk-formulas strongly depends on the quality empirical data. That is why the laboratory modeling sometimes is preferable (see [2]) then in situ measurements for obtaining enough ensembles of the data with a good accuracy in control conditions, first of all in a case of severe conditions (strong winds with intensive wave breaking and sprays generation). In this investigation laboratory modeling was performed on the Thermostratified Wind-Wave Channel of the IAP RAS (see. [3]). Experiments were carried out for the wind speeds up to 18.5 m/s (corresponding the equivalent 10-m wind speed 30 m/s). For the possibility of varying parameters of surface roughness independently on the wind flow a special system basing on the submerged mosquito mesh (cell of 2*2 mm) was used (see [4]). The roughness was controlled by the depth of the mesh installation under the free surface (no waves when the mesh was on the surface and maximum wave amplitude for the maximum depth). So, for each wind speed several cases of the waves parameters were investigated. During experiments a stable stratification of the boundary layer of air flow was obtained. Temperature of the heating air was 33-37 degrees (depending on the reference wind speed), and the water temperature was 14-16 degrees. The Pitote gauge and hotwire were used together for measuring velocity and temperature profiles. Also indirect estimations of the total volume of the phase of sprays were obtained by analyzing hotwire signals errors during droplets hits. Then aerodynamic drag CD and heat transfer Ch coefficients were obtained by profiling method. It was shown that that these parameters are very sensitive to the intensity of
Zhang Di
2015-01-01
Full Text Available Dynamic mesh methods and user defined functions are adopted and the shear stress transport k-ω turbulent model has been used in the numerical investigation of heat transfer performance of synthetic jet impingement onto dimple/protrusioned surface. The results show that the local time-averaged Nusselt number of the dimpled/protrusioned target surface tends to be much closer with that of flat cases with increasing of frequency. The heat transfer performance gets better when frequency increases. The area-averaged time-averaged Nusselt number of protrusioned target surface is the most close to that of flat cases when f = 320 Hz while it is the smallest among the synthetic jet cases in dimpled target surface. The heat transfer enhancement performance of synthetic jet is 30 times better than that of natural convection. The time-averaged Nusselt number of stagnation point in the protrusioned target surface is higher than that of flat target surface while it is lower in the dimpled surface than that of flat surface no matter in the synthetic jet, steady jet or natural convection cases. Meanwhile, the timeaveraged Nusselt number of stagnation point in the synthetic jet cases increases with the increasing of frequency. It is worth pointing out that the time-averaged Nusselt number of stagnation point is lower than that of steady cases when the frequency is low. However, it shows a bit higher than that of steady cases when f = 320 Hz.
解旭斌; 王维城; 王栋
2000-01-01
Using HFC134a and HCFC22 as the working fluid, the comparative experimentalstudies on horizontal condensation in smooth tube and two other augumented heattransfer tubes with different groove shapes (DAE-2 tube and DAEC tube)areconducted. As the experimental results indicated, compared with the smoothtube, the average heat transfer coefficient of DAE-2 is improved by140%to 170% and the pressure drop per unit length increased by 50%to100%. In addition, the average heat transfer coefficient of DAEC tube isenhanced by 160%to 200% and the pressure drop per unit length increased by70% to 130%. Further more, the empirical formulas about average heat transfercoefficient and pressure drop of the DAE-2 tube and DAEC tube are given inthis paper，which can be used to design condensers%本文以HFC134a和HCFC22为工质对光管及两种不同槽型的强化传热管(DAE-2管与DAEC管)的水平管内凝结换热进行了对比实验研究。研究发现，DAE-2管平均换热系数比光管提高了140%170%, 而单位长度阻力损失增加了50%100%, DAEC管平均换热系数比光管提高了160%200%, 同时单位长度阻力损失增加了70%130%。此外，本文给出了DAE-2管和DAEC管平均换热系数及阻力损失的计算关联式,可用于冷凝器设计
Garcia Gonzalez, Raquel; Verhoef, Anne; Luigi Vidale, Pier; Braud, Isabelle
2012-05-01
This study focuses on the mechanisms underlying water and heat transfer in upper soil layers, and their effects on soil physical prognostic variables and the individual components of the energy balance. The skill of the JULES (Joint UK Environment Simulator) land surface model (LSM) to simulate key soil variables, such as soil moisture content and surface temperature, and fluxes such as evaporation, is investigated. The Richards equation for soil water transfer, as used in most LSMs, was updated by incorporating isothermal and thermal water vapor transfer. The model was tested for three sites representative of semiarid and temperate arid climates: the Jornada site (New Mexico, USA), Griffith site (Australia), and Audubon site (Arizona, USA). Water vapor flux was found to contribute significantly to the water and heat transfer in the upper soil layers. This was mainly due to isothermal vapor diffusion; thermal vapor flux also played a role at the Jornada site just after rainfall events. Inclusion of water vapor flux had an effect on the diurnal evolution of evaporation, soil moisture content, and surface temperature. The incorporation of additional processes, such as water vapor flux among others, into LSMs may improve the coupling between the upper soil layers and the atmosphere, which in turn could increase the reliability of weather and climate predictions.
Stevenson, Gareth P; Lee, Chong-Yong; Kennedy, Gareth F; Parkin, Alison; Baker, Ruth E; Gillow, Kathryn; Armstrong, Fraser A; Gavaghan, David J; Bond, Alan M
2012-06-26
A detailed analysis of the cooperative two-electron transfer of surface-confined cytochrome c peroxidase (CcP) in contact with pH 6.0 phosphate buffer solution has been undertaken. This investigation is prompted by the prospect of achieving a richer understanding of this biologically important system via the employment of kinetically sensitive, but background devoid, higher harmonic components available in the large-amplitude Fourier transform ac voltammetric method. Data obtained from the conventional dc cyclic voltammetric method are also provided for comparison. Theoretical considerations based on both ac and dc approaches are presented for cases where reversible or quasi-reversible cooperative two-electron transfer involves variation in the separation of their reversible potentials, including potential inversion (as described previously for solution phase studies), and reversibility of the electrode processes. Comparison is also made with respect to the case of a simultaneous two-electron transfer process that is unlikely to occur in the physiological situation. Theoretical analysis confirms that the ac higher harmonic components provide greater sensitivity to the various mechanistic nuances that can arise in two-electron surface-confined processes. Experimentally, the ac perturbation with amplitude and frequency of 200 mV and 3.88 Hz, respectively, was employed to detect the electron transfer when CcP is confined to the surface of a graphite electrode. Simulations based on cooperative two-electron transfer with the employment of reversible potentials of 0.745 ± 0.010 V, heterogeneous electron transfer rate constants of between 3 and 10 s(-1) and charge transfer coefficients of 0.5 for both processes fitted experimental data for the fifth to eighth ac harmonics. Imperfections in theory-experiment comparison are consistent with kinetic and thermodynamic dispersion and other nonidealities not included in the theory used to model the voltammetry of surface
Effect of Surface Defect States on Valence Band and Charge Separation and Transfer Efficiency
Xu, Juan; Teng, Yiran; Teng, Fei
2016-09-01
Both energy band and charge separation and transfer are the crucial affecting factor for a photochemical reaction. Herein, the BiOCl nanosheets without and with surface bismuth vacancy (BOC, V-BOC) are prepared by a simple hydrothermal method. It is found that the new surface defect states caused by bismuth vacancy have greatly up-shifted the valence band and efficiently enhanced the separation and transfer rates of photogenerated electron and hole. It is amazing that the photocatalytic activity of V-BOC is 13.6 times higher than that of BOC for the degradation methyl orange (MO). We can develop an efficient photocatalyst by the introduction of defects.
Marzieh Alikhasi; Hakimeh Siadat; Elaheh Beyabanaki; Mohammad Javad Kharazifard
2015-01-01
Objectives: The purpose of this study was to compare the accuracy of implant position transfer and surface detail reproduction using two impression techniques and materials.Materials and Methods: A metal model with two implants and three grooves of 0.25, 0.50 and 0.75 mm in depth on the flat superior surface of a die was fabricated. Ten regular-body polyether (PE) and 10 regular-body polyvinyl siloxane (PVS) impressions with square and conical transfer copings using open tray and closed tray ...
Liu, Siyu; Zhao, Ning; Cheng, Zhen; Liu, Hongguang
2015-04-21
Amino-functionalized fluorescent carbon dots have been prepared by hydrothermal treatment of glucosamine with excess pyrophosphate. The produced carbon dots showed stabilized green emission fluorescence at various excitation wavelengths and pH environments. Herein, we demonstrate the surface energy transfer between the amino-functionalized carbon dots and negatively charged hyaluronate stabilized gold nanoparticles. Hyaluronidase can degrade hyaluronate and break down the hyaluronate stabilized gold nanoparticles to inhibit the surface energy transfer. The developed fluorescent carbon dot/gold nanoparticle system can be utilized as a biosensor for sensitive and selective detection of hyaluronidase by two modes which include fluorescence measurements and colorimetric analysis.
Mounsef, Jihane Rahbani; Salameh, Dominique; Louka, Nicolas; Brandam, Cedric; Lteif, Roger
2015-09-20
The aeration is a key factor for Bacillus thuringiensis growth, sporulation and δ-endotoxins production. The objective of our work was to study the effect of aeration on the fermentation kinetics of Bacillus thuringiensis kurstaki (Btk), cultivated in a cereal milling byproduct (CMB) mono-component medium, in order to improve the δ-endotoxins productivity. Aeration conditions were systematically characterized by the volumetric mass transfer coefficient KLa. In the 6% CMB culture medium, different values of the maximal specific oxygen uptake rate were obtained at different values of KLa. For KLa of 7.2 h(-1), the growth was inhibited and the sporulation was defective. There was a linear increase of the average specific growth rate and faster sporulation and liberation of spores and δ-endotoxins crystals when KLa was increased between 13.3 h(-1) and 65.5 h(-1). Similar kinetic was observed in cultures performed at KLa equal to 65.5 h(-1) and 106.2 h(-1). The highest toxins productivity of 96.1 mg L(-1) (h)-1 was obtained in the 9% CMB culture medium for KLa of 102 h(-1). It was possible to track the evolution of the bacterial cells between vegetative growth, sporulation and liberation of mature spores by following the variation of the CO2 percent in the effluent gas.
Pillai, Indu M Sasidharan; Gupta, Ashok K
2017-05-15
A continuous flow electrochemical reactor was developed, and its application was tested for the treatment of textile wastewater. A parallel plate configuration with serpentine flow was chosen for the continuous flow reactor. Uniparameter optimization was carried out for electrochemical oxidation of synthetic and real textile wastewater (collected from the inlet of the effluent treatment plant). Chemical Oxygen Demand (COD) removal efficiency of 90% was achieved for synthetic textile wastewater (initial COD - 780 mg L(-1)) at a flow rate of 500 mL h(-1) (retention time of 6 h) and a current density of 1.15 mA cm(-2) and the energy consumption for the degradation was 9.2 kWh (kg COD)(-1). The complete degradation of real textile wastewater (initial COD of 368 mg L(-1)) was obtained at a current density of 1.15 mA cm(-2), NaCl concentration of 1 g L(-1) and retention time of 6 h. Energy consumption and mass transfer coefficient of the reactions were calculated. The continuous flow reactor performed better than batch reactor with reference to energy consumption and economy. The overall treatment cost for complete COD removal of real textile wastewater was 5.83 USD m(-3).
Endo, Satoru; Kajimoto, Tsuyoshi; Shizuma, Kiyoshi
2013-02-01
The transfer coefficient (TF) from soil to rice plants of (134)Cs and (137)Cs in the form of radioactive deposition from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in March 2011 was investigated in three rice paddy fields in Minami-Soma City. Rice crops were planted in the following May and harvested at the end of September. Soil cores of 30-cm depth were sampled from rice-planted paddy fields to measure (134)Cs and (137)Cs radioactivity at 5-cm intervals. (134)Cs and (137)Cs radioactivity was also measured in rice ears (rice with chaff), straws and roots. The rice ears were subdivided into chaff, brown rice, polished rice and rice bran, and the (134)Cs and (137)Cs radioactivity concentration of each plant part was measured to calculate the respective TF from the soil. The TF of roots was highest at 0.48 ± 0.10 in the field where the (40)K concentration in the soil core was relatively low, in comparison with TF values of 0.31 and 0.38 in other fields. Similar trends could be found for the TF of whole rice plants, excluding roots. The TF of rice ears was relatively low at 0.019-0.026. The TF of chaff, rice bran, brown rice and polished rice was estimated to be 0.049, 0.10-0.16, 0.013-0.017 and 0.005-0.013, respectively.
Claret, A.
2017-03-01
Aims: We present new gravity and limb-darkening coefficients for a wide range of effective temperatures, gravities, metallicities, and microturbulent velocities. These coefficients can be used in many different fields of stellar physics as synthetic light curves of eclipsing binaries and planetary transits, stellar diameters, line profiles in rotating stars, and others. Methods: The limb-darkening coefficients were computed specifically for the photometric system of the space mission tess and were performed by adopting the least-square method. In addition, the linear and bi-parametric coefficients, by adopting the flux conservation method, are also available. On the other hand, to take into account the effects of tidal and rotational distortions, we computed the passband gravity-darkening coefficients y(λ) using a general differential equation in which we consider the effects of convection and of the partial derivative (∂lnI(λ) /∂lng)Teff. Results: To generate the limb-darkening coefficients we adopt two stellar atmosphere models: atlas (plane-parallel) and phoenix (spherical, quasi-spherical, and r-method). The specific intensity distribution was fitted using five approaches: linear, quadratic, square root, logarithmic, and a more general one with four terms. These grids cover together 19 metallicities ranging from 10-5 up to 10+1 solar abundances, 0 ≤ log g ≤ 6.0 and 1500 K ≤Teff ≤ 50 000 K. The calculations of the gravity-darkening coefficients were performed for all plane-parallel ATLAS models. Tables 2-29 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/600/A30
Miljkovic, Nenad; Enright, Ryan; Wang, Evelyn N
2012-02-28
Condensation on superhydrophobic nanostructured surfaces offers new opportunities for enhanced energy conversion, efficient water harvesting, and high performance thermal management. These surfaces are designed to be Cassie stable and favor the formation of suspended droplets on top of the nanostructures as compared to partially wetting droplets which locally wet the base of the nanostructures. These suspended droplets promise minimal contact line pinning and promote passive droplet shedding at sizes smaller than the characteristic capillary length. However, the gas films underneath such droplets may significantly hinder the overall heat and mass transfer performance. We investigated droplet growth dynamics on superhydrophobic nanostructured surfaces to elucidate the importance of droplet morphology on heat and mass transfer. By taking advantage of well-controlled functionalized silicon nanopillars, we observed the growth and shedding behavior of suspended and partially wetting droplets on the same surface during condensation. Environmental scanning electron microscopy was used to demonstrate that initial droplet growth rates of partially wetting droplets were 6× larger than that of suspended droplets. We subsequently developed a droplet growth model to explain the experimental results and showed that partially wetting droplets had 4-6× higher heat transfer rates than that of suspended droplets. On the basis of these findings, the overall performance enhancement created by surface nanostructuring was examined in comparison to a flat hydrophobic surface. We showed these nanostructured surfaces had 56% heat flux enhancement for partially wetting droplet morphologies and 71% heat flux degradation for suspended morphologies in comparison to flat hydrophobic surfaces. This study provides insights into the previously unidentified role of droplet wetting morphology on growth rate, as well as the need to design Cassie stable nanostructured surfaces with tailored droplet
Sun, Xuefei; Liu, Jikun; Lee, Milton L
2008-02-01
Fabrication of microfluidic systems from polymeric materials is attractive because of simplicity and low cost. Unfortunately, the surfaces of many polymeric materials can adsorb biological samples. Therefore, it is necessary to modify their surfaces before these polymeric materials can be used for separation and analysis. Oftentimes it is difficult to modify polymeric surfaces because of their resistance to chemical reaction. Recently, we introduced a surface-reactive acrylic polymer, poly(glycidyl methacrylate-co-methyl methacrylate) (PGMAMMA), which can be modified easily and is suitable for fabrication of microfluidic devices. Epoxy groups on the surface can be activated by air plasma treatment, hydrolysis, or aminolysis. In this work, the resulting hydroxyl or amino groups were reacted with 2-bromoisobutylryl bromide to introduce an initiator for surface-initiated atom-transfer radical polymerization (SI-ATRP). Polyethylene glycol (PEG) layers grown on the surface using this method were uniform, hydrophilic, stable, and resistant to protein adsorption. Contact angle measurement and X-ray photoelectron spectroscopy (XPS) were used to characterize activated polymer surfaces, initiator-bound surfaces, and PEG-grafted surfaces. We obtained excellent capillary electrophoresis (CE) separations of proteins and peptides with the PEG-modified microchips. A separation efficiency of 4.4 x 10(4) plates for a 3.5 cm long separation channel was obtained.
Fielitz, Peter; Borchardt, Günter
2016-08-10
In the dedicated literature the oxygen surface exchange coefficient KO and the equilibrium oxygen exchange rate [Fraktur R] are considered to be directly proportional to each other regardless of the experimental circumstances. Recent experimental observations, however, contradict the consequences of this assumption. Most surprising is the finding that the apparent activation energy of KO depends dramatically on the kinetic regime in which it has been determined, i.e. surface exchange controlled vs. mixed or diffusion controlled. This work demonstrates how the diffusion boundary condition at the gas/solid interface inevitably entails a correlation between the oxygen surface exchange coefficient KO and the oxygen self-diffusion coefficient DO in the bulk ("on top" of the correlation between KO and [Fraktur R] for the pure surface exchange regime). The model can thus quantitatively explain the range of apparent activation energies measured in the different regimes: in the surface exchange regime the apparent activation energy only contains the contribution of the equilibrium exchange rate, whereas in the mixed or in the diffusion controlled regime the contribution of the oxygen self-diffusivity has also to be taken into account, which may yield significantly higher apparent activation energies and simultaneously quantifies the correlation KO ∝ DO(1/2) observed for a large number of oxides in the mixed or diffusion controlled regime, respectively.
Li, Yaqin; Sun, Zhigang; Jiang, Bin; Xie, Daiqian; Dawes, Richard; Guo, Hua
2014-08-28
The kinetics and dynamics of several O + O2 isotope exchange reactions have been investigated on a recently determined accurate global O3 potential energy surface using a time-dependent wave packet method. The agreement between calculated and measured rate coefficients is significantly improved over previous work. More importantly, the experimentally observed negative temperature dependence of the rate coefficients is for the first time rigorously reproduced theoretically. This negative temperature dependence can be attributed to the absence in the new potential energy surface of a submerged "reef" structure, which was present in all previous potential energy surfaces. In addition, contributions of rotational excited states of the diatomic reactant further accentuate the negative temperature dependence.
Ellwood, R; Stratoudaki, T; Sharples, S D; Clark, M; Somekh, M G
2014-03-01
The third-order elastic constants of a material are believed to be sensitive to residual stress, fatigue, and creep damage. The acoustoelastic coefficient is directly related to these third-order elastic constants. Several techniques have been developed to monitor the acoustoelastic coefficient using ultrasound. In this article, two techniques to impose stress on a sample are compared, one using the classical method of applying a static strain using a bending jig and the other applying a dynamic stress due to the presence of an acoustic wave. Results on aluminum samples are compared. Both techniques are found to produce similar values for the acoustoelastic coefficient. The dynamic strain technique however has the advantages that it can be applied to large, real world components, in situ, while ensuring the measurement takes place in the nondestructive, elastic regime.
Teodori, E.; Palma, T.; Valente, T.; Moita, A. S.; Moreira, A. L. N.
2016-09-01
This paper proposes a detailed analysis of bubble dynamics to describe pool boiling heat transfer in extreme wetting scenarios (superhydrophobic vs hydrophilic). A mechanistic approach, based on extensive post-processing allows quantifying the relative advantage of the superhydrophobic surfaces to endorse the onset of boiling at very low superheats (1-2K) vs their worse heat transfer performance associated to the swift formation of an insulating vapour film. Based on this analysis, a simple biphilic surface is created. The results suggest that for high heat fluxes, bubble dynamics is dominated by the emission of very small bubbles, which seems to affect the interaction mechanisms, precluding the emission of the large bubbles from the surface, thus compromising the good performance of the biphilic surfaces.
LARGE EDDY SIMULATION OF FREE SURFACE TURBULENT CHANNEL FLOW WITH HEAT TRANSFER
无
2002-01-01
In this paper, the Large Eddy Simulation (LES) was used to study the free-surface turbulent channel flow with passive heat transfer. The three-dimensional filtered incompressible Navier-Stokes equations and energy equation were numerically solved with dynamic Subgrid Scale (SGS) models for modeling turbulent stresses and heat flux. To compare the turbulent behavior of the free-surface and two-walled channel flows, the LES of two-walled turbulent channel flow was performed. The statistical quantities and flow structures of the free-surface turbulence with heat transfer in the vicinity of the free-surface were investigated. The results are also in good agreement with theoretical analysis and available results by Direct Numerical Simulation (DNS).
Direct Observation of Molecular Preorganization for Chirality Transfer on a Catalyst Surface
Demers-Carpentier, Vincent; Goubert,, Guillaume; Masini, Federico
2011-01-01
The chemisorption of specific optically active compounds on metal surfaces can create catalytically active chirality transfer sites. However, the mechanism through which these sites bias the stereoselectivity of reactions (typically hydrogenations) is generally assumed to be so complex that conti......The chemisorption of specific optically active compounds on metal surfaces can create catalytically active chirality transfer sites. However, the mechanism through which these sites bias the stereoselectivity of reactions (typically hydrogenations) is generally assumed to be so complex...... functional theory calculations reveals the stereodirecting forces governing preorganization into precise chiral modifier-substrate bimolecular surface complexes. The study shows that the chiral modifier induces prochiral switching on the surface and that different prochiral ratios prevail at different...
Microscale heat transfer in a free jet against a plane surface
Shu, Jian-Jun
2014-01-01
A new two-layer model has been proposed to study microscale heat transfer associated with a developing flow boundary layer. As an example, a cold, microscale film of liquid impinging on an isothermal hot, horizontal surface has been investigated. The boundary layer is divided into two regions: a micro layer at microscale away from the surface and a macro layer at macroscale away from the surface. An approximate solution for the velocity and temperature distributions in the flow along the horizontal surface is developed, which exploits the hydrodynamic similarity solution for microscale film flow. The approximate solution may provide a valuable basis for assessing microscale flow and heat transfer in more complex settings.
Jang, Heejun; Kang, Il-Suk; Lee, Youngbok; Cha, Yun Jeong; Yoon, Dong Ki; Ahn, Chi Won; Lee, Wonhee
2016-09-01
The direct transfer of graphene using polydimethylsiloxane (PDMS) stamping has advantages such as a ‘pick-and-place’ capability and no chemical residue problems. However, it is not easy to apply direct PDMS stamping to graphene grown via chemical vapor deposition on rough, grainy metal surfaces due to poor contact between the PDMS and graphene. In this study, graphene consisting of a mixture of monolayers and multiple layers grown on a rough Ni surface was directly transferred without the use of an adhesive layer. Liquid PDMS was cured on graphene to effect a conformal contact with the graphene. A fast release of graphene from substrate was achieved by carrying out wet-etching-assisted mechanical peeling. We also carried out a thermal post-curing of PDMS to control the level of adhesion between PDMS and graphene and hence facilitate a damage-free release of the graphene. Characterization of the transferred graphene by micro-Raman spectroscopy, SEM/EDS and optical microscopy showed neither cracks nor contamination from the transfer. This technique allows a fast and simple transfer of graphene, even for multilayer graphene grown on a rough surface.
Ultrafast Electron Transfer Between Dye and Catalyst on a Mesoporous NiO Surface.
Brown, Allison M; Antila, Liisa J; Mirmohades, Mohammad; Pullen, Sonja; Ott, Sascha; Hammarström, Leif
2016-07-01
The combination of molecular dyes and catalysts with semiconductors into dye-sensitized solar fuel devices (DSSFDs) requires control of efficient interfacial and surface charge transfer between the components. The present study reports on the light-induced electron transfer processes of p-type NiO films cosensitized with coumarin C343 and a bioinspired proton reduction catalyst, [FeFe](mcbdt)(CO)6 (mcbdt = 3-carboxybenzene-1,2-dithiolate). By transient optical spectroscopy we find that ultrafast interfacial electron transfer (τ ≈ 200 fs) from NiO to the excited C343 ("hole injection") is followed by rapid (t1/2 ≈ 10 ps) and efficient surface electron transfer from C343(-) to the coadsorbed [FeFe](mcbdt)(CO)6. The reduced catalyst has a clear spectroscopic signature that persists for several tens of microseconds, before charge recombination with NiO holes occurs. The demonstration of rapid surface electron transfer from dye to catalyst on NiO, and the relatively long lifetime of the resulting charge separated state, suggests the possibility to use these systems for photocathodes on DSSFDs.
Effect of Favorable Pressure Gradients on Turbine Blade Pressure Surface Heat Transfer
Boyle, Robert J.; Giel, P. W.
2002-01-01
Recent measurements on a turbine rotor showed significant relaminarization effects. These effects were evident on the pressure surface heat transfer measurements. The character of the heat transfer varied with Reynolds number. Data were obtained for exit Reynolds numbers between 500,000 and 880,000. Tests were done with a high level of inlet turbulence, 7.5%. At lower Reynolds numbers the heat transfer was similar to that for laminar flow, but at a level higher than for laminar flow. At higher Reynolds numbers the heat transfer was similar to turbulent flow, when the acceleration parameter, K, was sufficiently small. The proposed paper discusses the experimental results, and also discusses approaches to calculating the surface heat transfer for the blade surface. Calculations were done using a three-dimensional Navier-Stokes CFD analysis. The results of these tests, when compared with previous blade tests in the same facility, illustrate modeling difficulties that were encountered in CFD predictions. The two blades were in many ways similar. However, the degree of agreement between the same analysis and the experimental data was significantly different. These differences are highlighted to illustrate where improvements in modeling approaches are needed for transitional flows.
Catalytic surface effect on ceramic coatings for an aeroassisted orbital transfer vehicle
Steward, D. A.; Leiser, D. B.
1984-01-01
Surface catalytic efficiencies of glassy coatings were determined from a reaction boundary layer computation and arc-jet data. The catalytic efficiencies of the various coatings examined are discussed in terms of their reaction-rate constants. These constants are a function of the wall temperature (1290 K to 2000 K). In addition, the advantage of a thermal protection system for a bent biconic, aeroassisted orbital transfer vehicle with a low surface catalytic efficiency is discussed.
Four-stream Radiative Transfer Parameterization Scheme in a Land Surface Process Model
ZHOU Wenyan; GUO Pinwen; LUO Yong; Kuo-Nan LIOU; Yu GU; Yongkang XUE
2009-01-01
Accurate estimates of albedos are required in climate modeling. Accurate and simple schemes for radiative transfer within canopy are required for these estimates, but severe limitations exist. This paper developed a four-stream solar radiative transfer model and coupled it with a land surface process model. The radiative model uses a four-stream approximation method as in the atmosphere to obtain analytic solutions of the basic equation of canopy radiative transfer. As an analytical model, the four-stream radiative transfer model can be easily applied efficiently to improve the parameterization of land surface radiation in climate models. Our four-stream solar radiative transfer model is based on a two-stream short wave radiative transfer model. It can simulate short wave solar radiative transfer within canopy according to the relevant theory in the atmosphere. Each parameter of the basic radiative transfer equation of canopy has special geometry and optical characters of leaves or canopy. The upward or downward radiative fluxes are related to the diffuse phase function, the G-function, leaf reflectivity and transmission, leaf area index, and the solar angle of the incident beam.The four-stream simulation is compared with that of the two-stream model. The four-stream model is proved successful through its consistent modeling of canopy albedo at any solar incident angle. In order to compare and find differences between the results predicted by the four-and two-stream models, a number of numerical experiments are performed through examining the effects of different leaf area indices, leaf angle distributions, optical properties of leaves, and ground surface conditions on the canopy albcdo. Parallel experiments show that the canopy albedos predicted by the two models differ significantly when the leaf angle distribution is spherical and vertical. The results also show that the difference is particularly great for different incident solar beams.One additional
Comparison of Exact Solutions for Heat Transfer in Extended Surfaces of Different Geometries
K. J. Moleofane
2014-01-01
nonlinear steady state problem is linearizable provided that the thermal conductivity is the differential consequence of the term involving the heat transfer coefficient. As such, one is able to construct exact solutions. On the other hand, we employ the Lie point symmetry methods when the problem is not linearizable. Some interesting results are obtained and analyzed. The effects of the parameters such as thermogeometric fin parameter and the exponent on temperature are studied. Furthermore, fin efficiency and heat flux along the fin length of a spherical geometry are also studied.
Kumar, Ravi; Varma, H.K.; Agrawal, K.N.; Mohanty, Bikash
2001-03-01
In the present investigation a comprehensive study of the modified Wilson plot technique has been made and a stepwise methodology has been evolved. This technique can be used to determine the condensing-side heat transfer coefficient during condensation of vapor over a horizontal tube. The necessary experimental data have been acquired by conducting experiments for the condensation of steam and R-134a over a plain tube and different finned tubes (CIFTs and SIFTs). The experimental heat transfer coefficient, based on the test-section wall temperature measurement (wall temperature was measured with thermocouples), h{sub o}, has been compared with that predicted by the modified Wilson plot technique, h{sub mw}. The modified Wilson plot technique underpredicted the condensing-side heat transfer coefficient for the condensation of steam in a range of 7.5-15%. The heat transfer coefficient for the condensation of R-134a is also underpredicted in a range of 13-25% by this technique. (Author)
Synthesis, Phase Transfer and Surface Modification of Hydrophobic Quantum Dots for Bioapplications
Zhang, Ruili; Zhang, Xiao; Li, Xiaoyu; Yang, Ping
2013-04-01
We review the preparation, phase transfer, surface modification and possible bioapplications of hydrophobic CdSe based quantum dots (QDs). CdSe cores with rod and spherical morphologies were prepared through adjusting preparation conditions. The photoluminescence (PL) of the QDs depended strongly on preparation conditions. The QDs were coated with semiconductor shells to improve their PL properties. Anisotropic growth occurred during shell coating. Core/shell QDs revealed tunable PL and high PL efficiencies up to 90%. The phase transfer of QDs from oil phase to water phase was carried out via polymer or a sol-gel process. The silanization of the QDs plays an important role for the sol-gel process. Because of a SiO2 coating, the surface modification of the QDs for bioapplications became easy. After transferring into water phase, the QDs still retained high PL efficiency. Because of their high PL, these biofunctional materials could provide a platform for various applications.
Near-field radiative heat transfer between arbitrarily-shaped objects and a surface
Edalatpour, Sheila
2016-01-01
A fluctuational electrodynamics-based formalism for calculating near-field radiative heat transfer between objects of arbitrary size and shape and an infinite surface is presented. The surface interactions are treated analytically via Sommerfeld's theory of electric dipole radiation above an infinite plane. The volume integral equation for the electric field is discretized using the thermal discrete dipole approximation (T-DDA). The framework is verified against exact results in the sphere-surface configuration, and is applied to analyze near-field radiative heat transfer between a complex-shaped probe and an infinite plane both made of silica. It is found that when the probe tip size is approximately equal to or smaller than the gap d separating the probe and the surface, coupled localized surface phonon (LSPh)-surface phonon-polariton (SPhP) mediated heat transfer occurs. In this regime, the net spectral heat rate exhibits four resonant modes due to LSPhs along the minor axis of the probe while the net tota...
Vermeltfoort, PBJ; van der Mei, HC; Busscher, HJ; Hooymans, JMM; Bruinsma, GM
2004-01-01
The aim of this study was to determine the transfer of Pseudomonas aeruginosa No. 3 and Staphylococcus aureus 835 from contact lenses to surfaces with different hydrophobicity and roughness. Bacteria were allowed to adhere to contact lenses (Surevue, PureVision, or Focus Night & Day) by incubating t
Evaluation of Salmonella biofilm cell transfer from contact surfaces to beef products
Introduction: Meat contamination by Salmonella enterica is a serious food safety concern. One common transmission route that leads to cross contamination in meat plants is bacteria transfer from biofilms on contact surfaces to meat products via direct contact. Many factors could affect biofilm tra...
Javakhishvili, Irakli; Dimitrov, Ivaylo; Tynelius, Oskar
2016-01-01
Proton exchange membranes for fuel cell applications are synthesized by surface-initiated(SI) atom transfer radical polymerization (ATRP). Poly(vinylidene fluoride-co-chlorotrifluoroethylene)is electrospun into 50 μm thick mat, which is then employed as multifunctionalinitiator for copper...
2011-01-01
Source: US2012184029A The present invention relates to preparation of a polymer coating comprising or consisting of polymer chains comprising or consisting of units of 2-methoxyethyl acrylate synthesized by Surface-Initiated Atom Transfer Radical Polymerization (SI ATRP) such as ARGET SI ATRP...... or AGET SI ATRP and uses of said polymer coating....
Fristrup, Charlotte Juel; Jankova Atanasova, Katja; Eskimergen, Rüya
2012-01-01
Grafting of poly(ethylene glycol)methacrylate (PEGMA) and N,N-dimethylacrylamide (DMAAm) from UV-initiator modified polypropylene (PP) was performed by Surface-Initiated Atom Transfer Radical Polymerization (SI-ATRP). The modification and hydrophilization of the PP substrates were confirmed...
Sérgio Nepomuceno Pereira
2014-01-01
Full Text Available Measurements of the aerosol absorption coefficient, between 2007 and 2013, were made at the ground level in Évora, a Portuguese small town located in the southwestern Iberia Peninsula. Such a relatively long time series of absorbing aerosols is unique in Portugal and uncommon elsewhere. The average aerosol absorption coefficient was close to 9 Mm−1 and clear cycles at both daily and seasonal time scales were found. An average increase by a factor of two (from 6 to 12 Mm−1 was observed in winter if compared to summer season. The daily variations were similarly shaped for all seasons, with two morning and afternoon peaks, but with magnitudes modulated by the seasonal evolution. That was not the case if Sundays were considered. These variations can be explained in terms of the impact of local particle sources, related mainly to traffic and biomass burning and upward mixing of the aerosol due to variable mixing layer heights, either daily or seasonally. Also, a strong negative correlation between the aerosol absorption coefficient and the wind speed was verified, and an exponential decay function was found to fit very well to the data. The wind direction seems to be not correlated with the aerosol absorption coefficient.
Armando Alvis
2010-01-01
Full Text Available Se describe un procedimiento de evaluación del coeficiente de transferencia de calor en operaciones industriales. Se presenta un modelo matemático sencillo de determinación del coeficiente convectivo de transferencia de calor usando el software DCAL (Determinación de Coeficiente de Transferencia de Calor durante un Calentamiento. Para validar el modelo se usaron datos experimentales de muestras procesadas por tratamiento térmico, utilizando diferentes temperaturas y tiempos de proceso. Los datos experimentales fueron procesados automáticamente por el software, para la generación de gráficas y determinación de un coeficiente de transferencia de calor optimizado. Se concluye que la metodología descrita sirve para el cálculo del coeficiente convectivo cuando no hay resistencia interna a la transferencia de calor.The evaluation of the heat transfer coefficient for its use in industrial operations is described. A simple mathematical model to determine the heat transfer convective coefficient using the DCAL software (Determination of Heat Transfer Coefficient during a Heating. To valídate the model experimental data of samples processed by thermal treatment using different temperatures and process time were used. The experimental data was automatically processed by the software, to genérate graphs and to determine an optimum heat transfer coefficient. The main conclusión was that the methodology described is useful to the compute of convective coefficient when there is no inside heat transfer resistance.
Sharma, P.K.; Knuth, E.L.
1977-12-01
Spatial and energy distributions of helium atoms scattered from an anodized 1235-0 aluminum surface as well as the tangential and normal momentum accommodation coefficients calculated from these distributions are reported. A procedure for calculating drag coefficients from measured values of spatial and energy distributions is given. The drag coefficient calculated for a 6061 T-6 aluminum sphere is included.
Piston surface heat transfer during combustion in large marine diesel engines
Jensen, Michael Vincent; Walther, Jens Honore
2010-01-01
In the design process of large marine diesel engines information on the maximum heat load on the piston surface experienced during the engine cycle is an important parameter. The peak heat load occurs during combustion when hot combustion products impinge on the piston surface. Although the maximum...... with burning off piston surface material. In this work the peak heat load on the piston surface of large marine diesel engines during combustion was investigated. Measurements of the instantaneous surface temperature and surface heat flux on pistons in large marine engines are difficult due to expensive...... was calculated under different conditions in the numerical setup in order to obtain information of the actual peak heat flux experienced at the piston in large marine diesel engines during combustion. The variation of physical parameters influencing the heat transfer during combustion included a variation...
Jun, Yong-Du [Department of Mechanical and Automotive Engineering, Kongju National University, Kongju, Chungnam, 314-701 (Korea); Kim, Kwang J.; Kennedy, John M. [Department of Mechanical Engineering, University of Nevada-Reno, MS 312, Reno, NV 89557 (United States)
2010-03-15
Additives are often effectively used in enhancing heat transfer by creating a surface tension gradient on the surface of a condensate film to induce Marangoni driven ''dropwise-like'' condensation. The objective of the current study is to use the Maximum Bubble Pressure Method (MBPM) to evaluate dynamic behavior of the surface tension of solutions of three different additives (2-ethoxy ethanol, isobutylamine, and 2-ethyl-1-hexanol) of varying concentrations with water. It was shown that the effects of 2-ethoxy ethanol on surface tension was primarily dependent on solute concentration and showed little dependence on time (i.e. surface age of bubble). While both isobutylamine and 2-ethyl-1-hexanol showed strong dependence on both concentration and time, the effects of the later were far more dramatic. The results for all solutions are presented as functions of concentration and time (i.e. surface age of bubble). (author)
Vaporization heat transfer of dielectric liquids on a wick-covered surface
Gu, C. B.; Chow, L. C.; Baker, K.
1993-01-01
Vaporization heat transfer characteristics were measured for the dielectric liquid FC-72 on a horizontal heated surface covered with wire screen wicks with the mesh number for the screens varying from 24 to 100. In such a situation the liquid level can be either higher or lower than the heated surface. When the liquid level was above the heated surface (shallow pool boiling), the height of the liquid level above the surface, h, was varied from 0 to 10 mm. When the liquid level was below the heated surface (evaporation through capillary pumping), the distance from the liquid level to the edge of the surface, L, was adjusted from 0 to 15 mm. Experimental data revealed that the critical heat flux (CHF) decreases as the mesh number is increased from 24 to 100 for both vaporation and shallow pool boiling, showing that the vapor-escaping limit is more important than the capillary limit in flat plate heat pipe application.
Wan, Z.; Ng, D.; Dozier, J.
1994-01-01
Spectral radiance measurements have been made in the laboratory and in the field for deriving spectral emissivities of some land cover samples with a spectroradiometer and an auxiliary radiation source in the wavelength range 2.5-14.5 micrometers. A easy and quick four-step method (four steps to measure the sample and a diffuse reflecting plate surface under sunshine and shadowing conditions, respectively) has been used for simultaneous determination of surface temperature and emissivity. We emphasized in-situ measurements in combination with radiative transfer simulations, and an error analysis for basic assumptions in deriving spectral emissivity of land-surface samples from thermal infrared measurements.
Fristrup, Charlotte Juel; Eskimergen, Rüya; Burkrinsky, J.T.
2008-01-01
-modified PEEK using Surface-Initiated Atom Transfer Radical Polymerization (SI ATRP). Surface reduction of PEEK to form hydroxyl groups [1, 2, 3] was .performed prior to the attachment of 2-bromoisobutyrate initiating groups. Each modification step of PEEK as well as the polymer grafting was followed...... and confirmed by ATR FTIR, water contact ang;le, and Thermal Gravimetric Analysis (TGA). The surface topography was evaluated by "Atomic Force Microscopy (AFM). X-ray Photoelectron Spectroscopy (XPS) has been used to investigate the degree of functionalization. The performed modification allowed for successful...
Heat Transfer Measurement and Modeling in Rigid High-Temperature Reusable Surface Insulation Tiles
Daryabeigi, Kamran; Knutson, Jeffrey R.; Cunnington, George R.
2011-01-01
Heat transfer in rigid reusable surface insulations was investigated. Steady-state thermal conductivity measurements in a vacuum were used to determine the combined contribution of radiation and solid conduction components of heat transfer. Thermal conductivity measurements at higher pressures were then used to estimate the effective insulation characteristic length for gas conduction modeling. The thermal conductivity of the insulation can then be estimated at any temperature and pressure in any gaseous media. The methodology was validated by comparing estimated thermal conductivities with published data on a rigid high-temperature silica reusable surface insulation tile. The methodology was also applied to the alumina enhanced thermal barrier tiles. Thermal contact resistance for thermal conductivity measurements on rigid tiles was also investigated. A technique was developed to effectively eliminate thermal contact resistance on the rigid tile s cold-side surface for the thermal conductivity measurements.
2009-01-01
infer the momentum accommodation coefficients. II . RADIOMETRIC APPROACH TO MOMENTUM ACCOMMODATION STUDY The radiometric forces on a heated plate may...total radiometric force that includes the force resulting from the pressure difference between the hot and the cold sides of the vane, and ii the shear...Klinkrad, M. Ivanov, and A. Kashkovsky, “A rarefied aerodynamic modelling system for earth satel- lites RAMSES ,” Proceedings of the 19th International
Dissolved organic matter in sea spray: a transfer study from marine surface water to aerosols
Schmitt-Kopplin, P.; Liger-Belair, G.; Koch, B. P.; Flerus, R.; Kattner, G.; Harir, M.; Kanawati, B.; Lucio, M.; Tziotis, D.; Hertkorn, N.; Gebefügi, I.
2012-04-01
Atmospheric aerosols impose direct and indirect effects on the climate system, for example, by absorption of radiation in relation to cloud droplets size, on chemical and organic composition and cloud dynamics. The first step in the formation of Organic primary aerosols, i.e. the transfer of dissolved organic matter from the marine surface into the atmosphere, was studied. We present a molecular level description of this phenomenon using the high resolution analytical tools of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and nuclear magnetic resonance spectroscopy (NMR). Our experiments confirm the chemoselective transfer of natural organic molecules, especially of aliphatic compounds from the surface water into the atmosphere via bubble bursting processes. Transfer from marine surface water to the atmosphere involves a chemical gradient governed by the physicochemical properties of the involved molecules when comparing elemental compositions and differentiating CHO, CHNO, CHOS and CHNOS bearing compounds. Typical chemical fingerprints of compounds enriched in the aerosol phase were CHO and CHOS molecular series, smaller molecules of higher aliphaticity and lower oxygen content, and typical surfactants. A non-targeted metabolomics analysis demonstrated that many of these molecules corresponded to homologous series of oxo-, hydroxy-, methoxy-, branched fatty acids and mono-, di- and tricarboxylic acids as well as monoterpenes and sugars. These surface active biomolecules were preferentially transferred from surface water into the atmosphere via bubble bursting processes to form a significant fraction of primary organic aerosols. This way of sea spray production leaves a selective biological signature of the surface water in the corresponding aerosol that may be transported into higher altitudes up to the lower atmosphere, thus contributing to the formation of secondary organic aerosol on a global scale or transported laterally with
Li, Juan; Hong, Cheng-Yi; Wu, Shu-Xian; Liang, Hong; Wang, Li-Ping; Huang, Guoming; Chen, Xian; Yang, Huang-Hao; Shangguan, Dihua; Tan, Weihong
2016-01-01
Hydrophobic nanoparticles have shown substantial potential for bioanalysis and biomedical applications. However, their use is hindered by complex phase transfer and inefficient surface modification. This paper reports a facile and universal strategy for phase transfer and surface biofunctionalization of hydrophobic nanomaterials using aptamer-pendant DNA tetrahedron nanostructures (Apt-tet). The Janus DNA tetrahedron nanostructures are constructed by three carboxyl group modified DNA strands and one aptamer sequence. Each tetrahedron edge is an 18-base-pair double helix, making the tetrahedral edges about 5.8 nm in length. The pendant linear sequence is an aptamer, in this case AS1411, known to specifically bind nucleolin, typically overexpressed on the plasma membranes of tumor cells. The incorporation of the aptamers adds targeting ability and also enhances intracellular uptake. Phase-transfer efficiency using Apt-tet is much higher than that achieved using single-stranded DNA. In addition, the DNA tetrahedron nanostructures can be programmed to permit the incorporation of other functional nucleic acids, such as DNAzymes, siRNA, or antisense DNA, allowing, in turn, the construction of promising theranostic nanoagents for bioanalysis and biomedical applications. Given these unique features, we believe that our strategy of surface modification and functionalization may become a new paradigm in phase-transfer-agent design and further expand biomedical applications of hydrophobic nanomaterials. PMID:26302208
Li, Juan; Hong, Cheng-Yi; Wu, Shu-Xian; Liang, Hong; Wang, Li-Ping; Huang, Guoming; Chen, Xian; Yang, Huang-Hao; Shangguan, Dihua; Tan, Weihong
2015-09-01
Hydrophobic nanoparticles have shown substantial potential for bioanalysis and biomedical applications. However, their use is hindered by complex phase transfer and inefficient surface modification. This paper reports a facile and universal strategy for phase transfer and surface biofunctionalization of hydrophobic nanomaterials using aptamer-pendant DNA tetrahedron nanostructures (Apt-tet). The Janus DNA tetrahedron nanostructures are constructed by three carboxyl group modified DNA strands and one aptamer sequence. The pendant linear sequence is an aptamer, in this case AS1411, known to specifically bind nucleolin, typically overexpressed on the plasma membranes of tumor cells. The incorporation of the aptamers adds targeting ability and also enhances intracellular uptake. Phase-transfer efficiency using Apt-tet is much higher than that achieved using single-stranded DNA. In addition, the DNA tetrahedron nanostructures can be programmed to permit the incorporation of other functional nucleic acids, such as DNAzymes, siRNA, or antisense DNA, allowing, in turn, the construction of promising theranostic nanoagents for bioanalysis and biomedical applications. Given these unique features, we believe that our strategy of surface modification and functionalization may become a new paradigm in phase-transfer-agent design and further expand biomedical applications of hydrophobic nanomaterials.