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 and...... moisture transfer coefficients. The research showed that the developed model gives good agreement with the local convective surface transfer coefficients predicted from CFD. The main advantage of the presented (sub)zonal airflow model is that the computational effort is relatively small, while the...
The heat transfer coefficient on film cooled surfaces
Ammari, H.D.
1989-01-01
A systematic investigation of the effects of coolant-to-mainstream density ratio and mainstream acceleration on the heat transfer following injection through a row of holes in a flat plate into a turbulent boundary layer is described. A mass transfer technique was employed which uses a swollen polymer surface and laser holographic interferometry. The constant concentration of the test surface simulated isothermal conditions. Density ratios in excess of unity, representative of gas turbine ope...
Steskens, Paul Wilhelmus Maria Hermanus; Janssen, Hans; Rode, Carsten
2009-01-01
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...... 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...... influence on the predicted hygrothermal conditions at the surface of a building component and on the heat and vapour exchange with the indoor environment....
Critical thickness of an optimum extended surface characterized by uniform heat transfer coefficient
Leontiou, Theodoros; Fyrillas, Marios M.
2015-01-01
We consider the heat transfer problem associated with a periodic array of extended surfaces (fins) subjected to convection heat transfer with a uniform heat transfer coefficient. Our analysis differs from the classical approach as (i) we consider two-dimensional heat conduction and (ii) the base of the fin is included in the heat transfer process. The problem is modeled as an arbitrary two-dimensional channel whose upper surface is flat and isothermal, while the lower surface has a periodic a...
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.
CFD Analysis of Convective Heat Transfer Coefficient on External Surfaces of Buildings
Andrea de Lieto Vollaro; Giorgio Galli; Andrea Vallati
2015-01-01
Convective heat transfer coefficients for external building surfaces are essential in building energy simulation (BES) to calculate convective heat gains and losses from building facades and roofs to the environment. These coefficients are complex functions of: building geometry, building surroundings, local air flow patterns and temperature differences. A microclimatic analysis in a typical urban configuration, has been carried out using Ansys Fluent Version 14.0, an urban street canyon, wit...
Critical thickness of an optimum extended surface characterized by uniform heat transfer coefficient
Leontiou, Theodoros
2015-01-01
We consider the heat transfer problem associated with a periodic array of extended surfaces (fins) subjected to convection heat transfer with a uniform heat transfer coefficient. Our analysis differs from the classical approach as (i) we consider two-dimensional heat conduction and (ii) the base of the fin is included in the heat transfer process. The problem is modeled as an arbitrary two-dimensional channel whose upper surface is flat and isothermal, while the lower surface has a periodic array of extensions/fins which are subjected to heat convection with a uniform heat transfer coefficient. Using the generalized Schwarz-Christoffel transformation the domain is mapped onto a straight channel where the heat conduction problem is solved using the boundary element method. The boundary element solution is subsequently used to pose a shape optimization problem, i.e. an inverse problem, where the objective function is the normalized Shape Factor and the variables of the optimization are the parameters of the Sch...
Hay, N.; Lampard, D.; Maali, R.; Burns, I.
A method permitting the simultaneous determination of the heat transfer coefficient and adiabatic wall effectiveness for film cooled surfaces has been developed. The swollen polymer technique, together with laser holographic interferometry, is employed in measuring the mass transfer from a film cooled surface, and the heat transfer coefficient and effectiveness are deduced through the heat-mass transfer analogy. A tangential slot injection geometry has been used in demonstrating the potential of the method for the rapid acquisition of comprehensive heat transfer data on film cooled surfaces.
The present paper deals with a sodium water reaction (SWR) in a steam generator (SG) of sodium-cooled fast reactor (SFR). When a heat transfer tube in the SG fails, SWR would take place. This reaction occurs rapidly and accompanies a high temperature jet. This jet would cover up the neighboring tubes and the tubes have possibilities to fail secondarily by an overheated rupture. Therefore, the quantification of the heat transfer from the fluid to the tube in the SWR is important from the view point of safety evaluation. To obtain knowledge on the SWR phenomenon, experiments with SWAT-1R test facility were carried out at Japan Atomic Energy Agency (JAEA). In the experiment, thermocouples were installed at 6 locations on a tube placed for measurement in the SWR reacting zone and the temperature histories were measured. In the present study, the heat transfer coefficient has been evaluated by solving one-dimensional inverse problem of heat transfer based on the SWAT-1R experimental result. And the flow characteristics such as a void fraction and a fluid velocity, at the surface of the heat transfer tube have been speculated from the magnitude of heat transfer coefficient. Furthermore, one-dimensional thermal hydraulics simulation has been performed based on a boundary layer approximation. In the analyses, the fluid velocity at out of the boundary layer and the void fraction condition are given as a parameter. As a result, the correlation diagram between the heat transfer coefficient and the flow characteristics has been evaluated so as to investigate the flow characteristics in the SWAT-1R experiment. (author)
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-Îµ 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.
Variation of Local Pool Boiling Heat Transfer Coefficient On 3-Degree Inclined Tube Surface
Experimental studies on both subcooled and saturated pool boiling of water were performed to obtain local heat transfer coefficients on a 3 .deg. inclined tube of 50.8 mm diameter at atmospheric pressure. The local values were determined at every 45 .deg. from the very bottom to the uppermost of the tube periphery. The maximum and minimum local coefficients were observed at the azimuthal angles of 0 .deg. and 180 .deg., respectively, in saturated water. The locations of the maxima and the minima were dependent on the inclination angle of the tube as well as the degree of subcooling. The major heat transfer mechanisms were considered to be liquid agitation generated by the sliding bubbles and the creation of big size bubbles through bubble coalescence. As a way of quantifying the heat transfer coefficients, an empirical correlation was suggested
Convective heat transfer at exterior building surfaces has an impact on the design and performance of building components such as double-skin facades, solar collectors, solar chimneys and ventilated photovoltaic arrays, and also affects the thermal climate and cooling load in urban areas. In this study, an overview is given of existing correlations of the exterior convective heat transfer coefficient (CHTC) with the wind speed, indicating significant differences between these correlations. As an alternative to using existing correlations, the applicability of CFD to obtain forced CHTC correlations is evaluated, by considering a cubic building in an atmospheric boundary layer. Steady Reynolds-averaged Navier-Stokes simulations are performed and, instead of the commonly used wall functions, low-Reynolds number modelling (LRNM) is used to model the boundary-layer region for reasons of improved accuracy. The flow field is found to become quasi independent of the Reynolds number at Reynolds numbers of about 105. This allows limiting the wind speed at which the CHTC is evaluated and thus the grid resolution in the near-wall region, which significantly reduces the computational expense. The distribution of the power-law CHTC-U10 correlation over the windward and leeward surfaces is presented (U10 = reference wind speed at 10 m height). It is shown that these correlations can be accurately determined by simulations with relatively low wind speed values, which avoids the use of excessively fine grids for LRNM, and by using only two or three discrete wind speed values, which limits the required number of CFD simulations.
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. PMID:25322139
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...
Santos, Jane Meri; Kreim, Virginie; Guillot, Jean-Michel; Reis, Neyval Costa; de Sá, Leandro Melo; Horan, Nigel John
2012-12-01
This study has investigated overall mass transfer coefficients of hydrogen sulphide from quiescent liquid surfaces under simulated laboratory conditions. Wind flow (friction velocity) has been correlated with the overall mass transfer coefficient (KL) of hydrogen sulphide in the liquid phase using a wind tunnel study. The experimental values for this coefficient have been compared with predicted KL values obtained from three different emission models that are widely used to determine volatilization rates from the quiescent surfaces of wastewater treatment unit processes. Friction velocity (in a range of 0.11 and 0.27 m s-1) was found to have a negligible influence on the overall mass transfer coefficients for hydrogen sulphide but by contrast two of the models predicted a stronger influence of friction velocity and overestimate the KL values by up to a factor of 12.5, thus risking unnecessary expenditure on odour control measures. However, at low wind speeds or friction velocities, when more odour complaints might be expected due to poor atmospheric dispersion, a better agreement of emission rates with experimental data was found for all the models.
Mass transfer coefficients and the film cooling effectiveness are measured downstream of a single row of holes inclined 30 degrees with the surface and inline with the main turbulent boundary layer flow. The mass transfer coefficients (based on the difference between the free stream and the surface concentrations) are measured using a naphthalene sublimation technique. The effectiveness is determined through the injection of a trace gas into the secondary (cooling jets) flow and measuring its concentration at the impermeable wall. Experiments are carried out in a subsonic, zero pressure gradient turbulent boundary layer, under isothermal conditions with three blowing ratios: 0.4, 0.8, and 1.2. The data is collected in a region 7 to 80 jet diameters downstream of the injection location
Because convective heat transfer is enhanced in flow past rough surfaces, much experimental and analytical effort over the past several decades has been devoted to the evaluation of artificial roughening for potential application to the heat transfer surfaces of gas-cooled reactors. Unfortunately, much of the analytical development in this field has been inadequately explained in the literature; this has led to misinterpretation of some of the subsequent experimental findings, compounding the uncertainty. This work provides a critical review of the underlying assumptions, theoretical foundations, and supporting experimental evidence for the analytical procedures in current use for the evaluation of roughness effects. It is a concise presentation of the available formulations with recommendations concerning their applicability to rough rod bundles
Wanninger, Andreas; Ceuca, Sabin Cristian; Macian-Juan, Rafael [Technische Univ. Muenchen, Garching (Germany). Dept. of Nuclear Engineering
2013-07-01
Different approaches for the calculation of Direct Contact Condensation (DCC) using Heat Transfer Coefficients (HTC) based on the Surface Renewal Theory (SRT) are tested using the CFD simulation tool ANSYS CFX. The present work constitutes a preliminary study of the flow patterns and conditions observed using different HTC models. A complex 3D flow pattern will be observed in the CFD simulations as well as a strong coupling between the condensation rate and the two-phase flow dynamics. (orig.)
Different approaches for the calculation of Direct Contact Condensation (DCC) using Heat Transfer Coefficients (HTC) based on the Surface Renewal Theory (SRT) are tested using the CFD simulation tool ANSYS CFX. The present work constitutes a preliminary study of the flow patterns and conditions observed using different HTC models. A complex 3D flow pattern will be observed in the CFD simulations as well as a strong coupling between the condensation rate and the two-phase flow dynamics. (orig.)
Chan, T. L.
This paper presents the effect of viewing-angle variations on the accuracy of transient and heated-coating liquid-crystal methods for determining the local heat transfer coefficients on a curved surface. A developed liquid-crystal calibration technique using a true-color image processing system has been used to alleviate the effect of viewing angle on oblique/curved surfaces. The accuracy of heat transfer coefficients improved significantly with careful correction of the viewing-angle effect on the surface geometry. It is crucial to ensure the implementation of the suggested calibration technique to be used in wideband thermochromic liquid-crystal applications on the non-orthogonal surface.
A critical review of the assumptions, theoretical foundations, and supporting experimental evidence for the analytical procedures in current use for evaluation of the effects of artificial surface roughening on friction factor and Stanton number is provided. Recommendations are given concerning the application of these procedures to rough rod bundles. A new method is demonstrated for determination of the slope and intercept of the universal logarithmic dimensionless velocity distribution law for fully rough flow past roughened surfaces without the need for experimental measurement of the velocity profile. The slope is shown to vary with the nature of the roughened surface and to deviate significantly from the slope for turbulent flow past smooth walls in some cases. It is further shown that the intercept, which is a boundary condition equivalent to the roughness parameter for friction, is independent of the width of the velocity profile. A similar method is developed for determination of the slope and intercept of the temperature distribution law, but additional experimental investigation is required before the efficacy of this application can be conclusively established
Hodge, S.A.; Sanders, J.P.; Klein, D.E.
1979-11-01
A critical review of the assumptions, theoretical foundations, and supporting experimental evidence for the analytical procedures in current use for evaluation of the effects of artificial surface roughening on friction factor and Stanton number is provided. Recommendations are given concerning the application of these procedures to rough rod bundles. A new method is demonstrated for determination of the slope and intercept of the universal logarithmic dimensionless velocity distribution law for fully rough flow past roughened surfaces without the need for experimental measurement of the velocity profile. The slope is shown to vary with the nature of the roughened surface and to deviate significantly from the slope for turbulent flow past smooth walls in some cases. It is further shown that the intercept, which is a boundary condition equivalent to the roughness parameter for friction, is independent of the width of the velocity profile. A similar method is developed for determination of the slope and intercept of the temperature distribution law, but additional experimental investigation is required before the efficacy of this application can be conclusively established.
Inverse determination of local heat transfer coefficient
The naphtalene sublimation and transient methods are widely used techniques which are particularly useful in complex flows and solid shapes. Both techniques have been widely used with considerable success but they are not appropriate for high temperatures. An alternative method to obtain the local convective heat transfer coefficient, that does not have any disadvantages noted above, is the inverse procedure. Determination of the space-variable heat transfer coefficient on a complex shape surface requires the solution of the nonlinear inverse heat conduction problem. The distribution of the heat transfer coefficient is calculated from temperature measurements at interior points of the solid and measured fluid temperature. The unknown parameters associated with the solution are selected to achieve the closest agreement in a least squares sense between the computed and measured temperatures using the Levenberg - Marquardt method. The nonlinear least - squares problem is parameterized by assuming the staircase changes of heat transfer coefficient on the boundary or expressing the space variations of the heat transfer coefficient in the functional form. The uncertainties in the estimated components of the heat transfer coefficient or in the estimated parameters are determined for the temperature measurements with known and unknown standard deviations. 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. The experimental results reported herein are among the first that show the variation of the local heat transfer coefficients over the circumference of the finned tube. Most data reported previously were acquired for smooth tubes at low temperatures. The main advantage of the method is that it does not require any knowledge, or solution to, the complex fluid flow field. It should be noted that determining unknown steady distribution of heat transfer coefficients by using the developed method is inexpensive, since it requires only one fluid temperature probe and a few thermocouples for temperature measurements inside the solid. Refs. 4 (author)
In fire engineering analysis, one of the open problem is the transfer of thermal parameters obtained by fire CFD model to FEM models for structural analysis. In this study the new useful concept of â€œAdiabatic Surface Temperatureâ€ or more commonly known as AST, introduced by WickstrÃ¶m, is investigated. The adiabatic surface temperature offers the opportunity to transfer both thermal information of the gas and the net heat flux to the solid phase model, obtained by CFD analysis. In this study two CFD analyses are carried out in order to evaluate the effect of emissivity and of convective heat transfer coefficient to determine the AST. First one CFD analysis simulating a fire scenario, â€œconjugate heat transferâ€, with a square steel beam exposed to hot surface is carried out to calculate AST, heat convective coefficient and temperature field in the beam. Second one, a conductive analysis is carried out on â€œstandalone beamâ€ imposing a third type boundary condition on its boundaries assuming the AST, evaluated in the conjugate analysis, as external temperature. Different heat convective coefficients are imposed on the beam walls. The comparison between results obtained by means of the two proposed analyses shows the use of AST as transfer thermal parameter between CFD (Computational Fluid Dynamic) and FEM (Finite Element Method) models is appropriate when the convective heat transfer coefficient is properly evaluated. -- Highlights: â–º An open problem is to transfer parameters obtained by thermal to structural models. â–º The useful concept of â€œAdiabatic Surface Temperatureâ€ (AST) is investigated. â–º The AST use is right for properly evaluated convective heat transfer coefficient
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 made for the mathematical tooth model, the results predicted with this model were compared with those of an experiment using mercury as the tooth surrounding medium. For all the other thermal loadin...
Chan, T.L. [Dept. of Mechanical Engineering, Hong Kong Polytechnic Univ., Kowloon (Hong Kong)
2001-10-01
This paper presents the effect of viewing-angle variations on the accuracy of transient and heated-coating liquid-crystal methods for determining the local heat transfer coefficients on a curved surface. A developed liquid-crystal calibration technique using a true-color image processing system has been used to alleviate the effect of viewing angle on oblique/curved surfaces. The accuracy of heat transfer coefficients improved significantly with careful correction of the viewing-angle effect on the surface geometry. It is crucial to ensure the implementation of the suggested calibration technique to be used in wideband thermochromic liquid-crystal applications on the non-orthogonal surface. (orig.)
Coefficients of heat transfer in condensation
The authors analyze the problem of determining the coefficients of heat transfer in the condensation of steam on vertical walls in terms of the Prandtl hypothesis and the Reynolds analogy for distribution of the turbulent thermal conductivity across the condensate film. From the assumed model the authors derived expressions for the heat transfer coefficients
Heat transfer coefficient for boiling carbon dioxide
Knudsen, Hans JÃ¸rgen HÃ¸gaard; Jensen, Per Henrik
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...... between the measured and the calculated heat transfer coefficient is nearly constant and equal 1.9. With this factor the correlation predicts the measured data within 14% (RMS). The pressure drop is of the same order as the measuring uncertainty and the pressure drop has not been compared with correlation's....
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). PMID:23812315
Transfer coefficients for turbulent flow between parallel plates
Average transfer coefficients in the turbulent forced convection entrance region between parallel plates, with asymmetrical conditions of the concentration profile, were determined experimentaly with the Naphthalene Sublimation Technique. In accordance with the analogy between heat and mass transfer, the tests correspond to a heat-transfer problem with uniform surface temperature at one plate and the other insulated. The Reynolds number ranges from 10900 to 91700. (Author)
Determination of the heat transfer coefficients in transient heat conduction
The determination of the space- or time-dependent heat transfer coefficient which links the boundary temperature to the heat flux through a third-kind Robin boundary condition in transient heat conduction is investigated. The reconstruction uses average surface temperature measurements. In both cases of the space- or time-dependent unknown heat transfer coefficient the inverse problems are nonlinear and ill posed. Least-squares penalized variational formulations are proposed and new formulae for the gradients are derived. Numerical results obtained using the nonlinear conjugate gradient method combined with a boundary element direct solver are presented and discussed. (paper)
Hay, N.; Lampard, D.; Saluja, C. L.
1984-06-01
This paper describes an investigation of the sensitivity of the heat transfer coefficient under the film to the state of the approach boundary layer for injection through a row of holes on a flat plate. The investigation is done for a range of blowing parameters using a heat-mass transfer analogy. Injection angles of 35 deg and 90 deg are covered. Additionally, for the same injection geometries, the effect of injection in the presence of mild adverse, mild favorable, and strong favorable mainstream pressure gradients is investigated. The results indicate that the heat transfer coefficient under the film is sensitive neither to the condition of the approach boundary layer nor to the presence of a mild adverse pressure gradient, but it is significantly lowered by a favorable pressure gradient, particularly at low blowing parameters.
Transfer coefficients in elliptical tubes and plate fin heat exchangers
Mean transfer coefficients in elliptical tubes and plate fin heat exchangers were determined by application of heat and mass transfer analogy in conjunction with the naphthalene sublimation technique. The transfer coefficients are presented in a dimensionless form as functions of the Reynolds number. By using the least squares method analytical expressions for the transfer coefficients were determined with low scattering. (E.G.)
Heat transfer coefficient between UO2 and Zircaloy-2
This paper provides some experimental values of the heat-transfer coefficient between UO2 and Zircaloy-2 surfaces in contact under conditions of interfacial pressure, temperature, surface roughness and interface atmosphere, that are relevant to UO2/Zircaloy-2 fuel elements operating in pressurized-water power reactors. Coefficients were obtained from eight UO2/ Zircaloy-2 pairs in atmospheres of helium, argon, krypton or xenon, at atmosphere pressure and in vacuum. Interfacial pressures were varied from 50 to 550 kgf/cm2 while surface roughness heights were in the range 0.2 x 10-4 to 3.5 x 10-4 cm. The effect on the coefficients of cycling the interfacial pressure, of interface gas pressure and of temperature were examined. The experimental values of the coefficients were used to test the predictions of expressions for the heat-transfer between two solids in contact. For the particular UO2/ Zircaloy-2 pairs examined, numerical values were assigned to several parameters that related the surface roughnesses to either the radius of solid/solid contact spots or to the mean thickness of the interface voids and that accounted for the imperfect accommodation of the void gas on the test surfaces. (author)
The heat (mass) transfer characteristics on the blade surface of a high-turning first-stage turbine rotor for power generation has been investigated by employing the naphthalene sublimation technique. A four-axis profile measurement system is developed successfully for the measurements of local sublimation depth on the curved surface. In the leading edge region, there is a good agreement between the present heat (mass) transfer data and the previous result on a turbine blade with a moderate turning angle, but come discrepancies are found in the mid-chord heat (mass) transfer between the two results. The local heat (mass) transfer on the present suction surface is greatly enhanced due to an earlier boundary transition, compared with that on a turbine blade with a moderate turning angle, meanwhile there is only a slight change in the pressures-side heat (mass) transfer between the two different turbine rotors. In general, the heat (mass) transfer augmentation by the endwall vortices is found much higher on the suction surface than on the pressure surface
Distortion effects on the spin transfer coefficient
Lee, S E; Hong, S W; Kim, B T
1999-01-01
We investigated the distortion effects on the spin transfer coefficient D sub n sub n for the intermediate energy (p,n) charge exchange reactions leading to the Gamow-Teller resonance in the continuum region. When the distortion is included, the imaginary parts of both the central and the tensor direct contributions are significantly changed. Also, the magnitude of T sub 0 sub 0 becomes smaller, which results in larger D sub n sub n values. We also found that when the distortion is included the phase difference between T sub 0 sub 0 and T sub 2 sub 0 in the complex plane remains almost the same for different Q-values.
Transfer coefficients for terrestrial foodchain: their derivation and limitations
Transfer coefficients to predict the passage of isotopes from the environment to terrestrial foods have been derived for various radionuclides of importance in the nuclear fuel cycle. These data update and extend previously recommended handbook values. We derive transfer coefficients to terrestrial foods and describe the systematics of the derived transfer coefficients. Suggestions are offered for changes in the values of transfer coefficients to terrestrial foods that now appear in federal regulatory guides. Deficiencies in our present knowledge concerning transfer coefficients and limitations in the use of these values to ensure compliance with radiation protection standards are discussed
Paper presents an analytical solution of the problem to determine the efficiency coefficient of a constant section fin at heat transfer coefficient changing along fin height. It is determined, that the commonly applied assumption about the constancy of a convectional coefficient of heat emission when calculating the efficiency of a fin based on the value of the reduced coefficient of heat emission results in the error reaching 15%. It is shown that to reduce it up to 2-3% when calculating the efficiency coefficient of a fin one should have the experimental values of both the reduced coefficient of heat emission and the convectional coefficient of heat emission at a surface supporting the fins
Radionuclide transfer to animal products: revised recommended transfer coefficient values
Howard, B.J. [Centre for Ecology and Hydrology, Lancaster Environment Centre, Library Avenue, Bailrigg, Lancaster LAI 4AP (United Kingdom)], E-mail: bjho@ceh.ac.uk; Beresford, N.A.; Barnett, C.L. [Centre for Ecology and Hydrology, Lancaster Environment Centre, Library Avenue, Bailrigg, Lancaster LAI 4AP (United Kingdom); Fesenko, S. [International Atomic Energy Agency, 1400 Vienna (Austria)
2009-03-15
A compilation has been undertaken of data which can be used to derive animal product transfer coefficients for radionuclides, including an extensive review of Russian language information. The resultant database has been used to provide recommended transfer coefficient values for a range of radionuclides to (i) cow, sheep and goat milk, (ii) meat (muscle) of cattle, sheep, goats, pigs and poultry and (iii) eggs. The values are used in a new IAEA handbook on transfer parameters which replaces that referred to as 'TRS 364'. The paper outlines the approaches and procedures used to identify and collate data, and assumptions used. There are notable differences between the TRS 364 'expected' values and the recommended values in the revised Handbook from the new database. Of the recommended values, three milk values are at least an order of magnitude higher than the TRS 364 values (Cr, Pu (cow) Pu (sheep)) and one milk value is lower (Ni (cow)). For meat, four values (Am, Cd, Sb (beef) I (pork)) are at least an order of magnitude higher than the TRS 364 values and eight values are at least an order of magnitude lower (Ru, Pu (beef), Ru, Sr, Zn (sheep), Ru, Sr (pork), Mn (poultry)). Many data gaps remain.
Condensation heat transfer coefficients of flammable refrigerants
Dongsoo Jung; Soonam Chae; Dongsoo Bae [Inha University, Incheon (Korea). Department of Mechanical Engineering; Sukjae Oho [TechnoChem Co. Ltd., Kyunggi-Do (Korea)
2004-05-01
In this study, external condensation heat transfer coefficients (HTCs) of six flammable refrigerants of propylene (R1270), propane (R290), isobutane (R600a), butane (R600), dimethylether (RE170), and HFC32 were measured at the vapor temperature of 39 {sup o}C on a plain tube of 19.0 mm outside diameter with a wall subcooling of 3-8 {sup o}C under a heat flux of 7-23 kW m{sup -2}. Test results showed a typical trend that external condensation HTCs decrease with the wall subcooling. No unusual behavior or phenomenon was observed for these flammable refrigerants during experiments. HFC32 and DME showed 28-44% higher HTCs than those of HCFC22 due to their excellent thermophysical properties. Propylene and butane showed the similar HTCs as those of HCFC22 while propane and isobutane showed 9% lower HTCs than those of HCFC22. Finally, a general correlation was made by modifying Nusselt's equation based upon the measured data of eleven fluids of various vapor pressures including halogenated refrigerants. The general equation showed an excellent agreement with all data exhibiting a deviation of less than 3%. (author)
The impact of air flow to the distribution of heat transfer coefficient on circular cylinder
Beran, P. (Pavel)
2015-01-01
To study the temperature effects which cause degradation of building materials in exterior is necessary to know the coefficient of heat transfer on its surface during the cross-flow. In this paper the values of heat transfer coefficient on circular cylinder for the cross-flow of air characterized by Reynolds number 78 200 were determined. The values of heat transfer coefficient were obtained by comparing numerically computed temperatures in several points in cylinder with measured values ...
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.
Semi-empirical model for heat transfer coefficient in liquid metal turbulent flow
The heat transfer by forced convection in a metal liquid turbulent flow for circular ducts is analyzed. An analogy between the momentum and heat in the wall surface, is determined, aiming to determine an expression for heat transfer coefficient in function of the friction coefficient. (E.G.)
Analysis of the heat transfer coefficient during potato frying
Costa, Rui M.; Oliveira, Fernanda A.R.; Delaneya, Olivia; Gekas, Vassilis
2001-01-01
The objective of this work was to study the dependence of the heat transfer coefficient (h) on the water loss rate of potato during frying. An indirect method was used where a metal piece with the same geometry of the potato pieces was placed on top of various potato samples at different frying times, and its temperature was recorded for 20â€“30 s. Another method consisted of direct recording of the temperature within a potato slice, close to the surface. Water loss rate was estimated by image ...
Overall mass-transfer coefficients in non-linear chromatography
Mollerup, JÃ¸rgen; 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 HenryÂ´s law relationship...... can be applied, the over-all mass-transfer coefficient will be concentration independent. However, in mass-transfer operations, a linear equilibrium relationship is in most cases not a valid approximation wherefore the over-all mass-transfer coefficient becomes strongly concentration dependent as...... shown in this paper. In this case one has to discard the use of over-all mass-transfer coefficients and calculate the rate of mass transfer from the two film theory using the appropriate non-linear relationship to calculate the equilibrium ratio at the interface between the two films....
Experimental evaluation of heat transfer coefficients between radiant ceiling and room
Causone, Francesco; Corgnati, Stefano P.; Filippi, Marco; Olesen, Bjarne W.
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 and...
Transfer coefficients for plate fin and elliptical tube heat exchangers
In order to determine transfer coefficients for plate fin and elliptical tube exchangers, mass transfer experiments have been performed using the naphthalene sublimation technique. By means of the heat-mass transfer analogy, the results can be converted to heat transfer results. The transfer coefficients were compared with those for circular tube exchangers and the comparison revealed no major differences. This is a positive outcome, since the use of elliptical tubes may reduce substantially the pressure drop, without affecting the transfer characteristics.(Author)
Tests were performed in a transient heat transfer tunnel in which the model under test was preheated prior to allowing room temperature air to be suddenly drawn over the model. The resulting movement of isothermal contours on the model is revealed using a surface coating of thermochromic liquid crystals that display distinctive colors at particular temperatures. A video record is obtained of a temperature and time data pair for all points on the model during a single test. Experiments on a duct model are reported in which the model was preheated using a hot air stream. A manner in which initial model temperature nonuniformities could be taken into account was investigated. The duct model was also tested with a steady-state measurement technique and results were compared with the transient measurements, but recognizing that differences existed between the upstream thermal boundary conditions. The steady-state and transient measurements were shown to be consistent with predicted values. The main advantage of this transient heat transfer technique using liquid crystals is that since the test model need not be actively heated, high-resolution measurements on surfaces with complex shapes may be obtained
Jones, Terry V.; Hippensteele, Steven A.
1988-01-01
Tests were performed in a transient heat transfer tunnel in which the model under test was preheated prior to allowing room temperature air to be suddenly drawn over the model. The resulting movement of isothermal contours on the model is revealed using a surface coating of thermochromic liquid crystals that display distinctive colors at particular temperatures. A video record is obtained of a temperature and time data pair for all points on the model during a single test. Experiments on a duct model are reported in which the model was preheated using a hot air stream. A manner in which initial model temperature nonuniformities could be taken into account was investigated. The duct model was also tested with a steady-state measurement technique and results were compared with the transient measurements, but recognizing that differences existed between the upstream thermal boundary conditions. The steady-state and transient measurements were shown to be consistent with predicted values. The main advantage of this transient heat transfer technique using liquid crystals is that since the test model need not be actively heated, high-resolution measurements on surfaces with complex shapes may be obtained.
Local heat transfer coefficient for turbulent flow in rod bundles
The correlation of the local heat transfer coefficients in heated triangular array of rod bundles, in terms of the flow hydrodynamic parameters is presented. The analysis is made first for fluid with Prandtl numbers varying from moderated to high (Pr>0.2), and then extended to fluids with low Prandtl numbers (0.004< Pr<0.2). Results of temperature and velocity fields distribution of slip coefficients and local heat transfer coefficients are obtained. (E.G.)
Heat transfer coefficient for F.E analysis in the warm forging process
S.S. Kang
2007-01-01
Full Text Available Purpose: The Purpose of this paper is to obtain suitable convection and contact heat transfer coefficient forone-time finite element analysis in the warm forging process.Design/methodology/approach: To do this, the temperature of the tool used in the operation was measured witha thermocouple and repeated finite element analysis(FEA was performed using the experimentally calculatedcontact and cooling heat transfer coefficient. Also the surface temperature of the active tool was obtained bycomparing the measurement and analysis results and finally the contact heat transfer coefficient for one-time FEAwas completed by comparing the surface temperature between the repeated FEA and one-time FEA results.Findings: The acceptable convection heat transfer coefficients are from 0.3 to 0.8N/mm/s/K and the contactheat transfer coefficient of 6~9N/mm/s/K is appropriate for the warm forging process with flow-typelubrication conditions.Practical implications: A comparison of the temperatures from the repeated and one-time analysis allows anoptimum contact heat transfer coefficient for the one time finite element analysis to be determined.Originality/value: Several studies have been conducted with different conditions such as applied pressure andkind of lubricant, but no research has been conducted concerning the convection heat transfer coefficient in thewarm forging process. Also, comparative analysis concerning the reason for difference between experimentallydetermined contact heat transfer coefficient and practically adapted one has not been conducted, yet.
Dateo, Christopher E.; Arnold, James O. (Technical Monitor)
1994-01-01
A new analytic global potential energy surface describing the hydroperoxyl radical system H((sup 2)S) + O2(X (sup 3)Sigma((sup -)(sub g))) (reversible reaction) HO2 ((X-tilde) (sup 2)A'') (reversible reaction) O((sup 3)P) + O H (X (sup 2)Pi) has been fitted using the ab initio complete active space SCF (self-consistent-field)/externally contracted configuration interaction (CASSCF/CCI) energy calculations of Walch and Duchovic. Results of quasiclassical trajectory studies to determine the rate coefficients of the forward and reverse reactions at combustion temperatures will be presented. In addition, vibrational energy levels were calculated using the quantum DVR-DGB (discrete variable representation-distributed Gaussian basis) method and the splitting due to H atom migration is investigated. The material of the proposed presentation was reviewed and the technical content will not reveal any information not already in the public domain and will not give any foreign industry or government a competitive advantage.
Correlation of heat transfer coefficient for quench front
The heat transfer coefficient at the quench front during quenching is one of the important parameters for researching the quenching processes, one of the main variables for the movement velocity of quenching front, too. A transient hot-patch test technique and unsteady state two-dimensional numerical technique is adopted to investigate the heat transfer coefficient at the quench front under the top-quenching, low pressure and low mass flux in a tube. Based on a suitable physical model, a multi-variables nonlinear regression method is used to analysis the effect of relevant parameters on the heat transfer coefficient and obtained the final empirical correlation under the experimental condition
Estimation of Volumetric Mass Transfer Coefficient in Bioreactor
Zainab Yaquob Atiya
2012-01-01
Full Text Available This study is concentrated to investigate the effects of aeration and stirring speed on the volumetric mass transfer coefficient (KLa. A dynamic technique was used in estimating KLa values in order to achieve the aim of this study.This study was done in 10L bioreactor by using two medias:-1. Dionized water2. Xanthan solution (1 g /LMoreover, the research covered a comparison between the obtained values of KLa.The Xanthan solution was used because of its higher viscosity in comparison with water. It behaves similarly to the cultivation medium when organisms are cultivated in a bioreactor. Growth of organisms in the reactor leads to a change in the viscosity of the medium which affects the mass transfer.Two variables, the effect of air flow rate (3-20 L/min and the effect of stirring speed (250-700rpm on KLa value were studied. Other parameters such as temperature, liquid volume, and stirrer shape and stirrer position were held constant; the results demonstrated an increase in KLa Â– value and mass transfer with increasing stirrer speed. Thus at higher speed, better dispersion of the bubbles was obtained. Therefore, that increased the surface / volume ratio which increased the mass transfer area i.e. KLa value.
This paper is described for the measurement technique for local heat transfer coefficients using a copper sensor in rod bundles with mixing vanes. A copper sensor is defined as the device to measure the convective heat transfer coefficient using constant heat flux and surface temperatures. The copper sensor consists of a cartridge heater and four pieces of thermocouple. The copper sensors located at axial positions of rod bundles are able to measure the local heat transfer coefficients at its positions. The effect of local heated and full heated of copper sensors for rod bundles is investigated using CFD analysis. The decay of local heat transfer coefficients of locally heating condition such as a copper sensor is estimated to be higher value than that of fully heating condition. The calibration curve for local heat transfer coefficients measured is presented
A study on the evaporative heat transfer coefficient in PCCS
In advanced nuclear reactors, the passive containment cooling has been suggested in AP600 to enhance the safety. The passive cooling has two mechanisms, air natural convection and water cooling with evaporation. To conform the coolability of PCCS, many works have been performed experimentally and numerically. In this study, the water cooling test was performed in scaled down segment type PCCS facility, which have the same configuration with AP600 prototype containment, to obtain the evaporative heat transfer coefficients. In the experiment air-steam mixture temperature and velocity, relative humidity and wall heat flux are measured. The local heat transfer coefficients are calculated and averaged through the vertical plate part of the facility. To convince the measured heat transfer coefficients, an analytical model for the local evaporative heat transfer is developed and compared with experimental data. From the comparison, the predicted coefficients are quite well agreed with measured values
Using a special rod built with a stack of UO2 pellets inside a thick Zircaloy clad, the authors report the measurement of the fuel-clad heat transfer coefficient when water vapour in intentionally introduced in the fuel rod at the beginning of its life. They describe the irradiation device, the measurement method (acquired data and mathematical determination of various values: temperature of the inner surface of the cladding, integrated thermal conductivity, fuel surface temperature, fuel-cladding heat transfer coefficient, thermal expansion of the cladding inner radius, UO2 thermal expansion). They finally report the experiment
Measurement of heat transfer coefficient using termoanemometry methods
Dan?ová 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.
Measurement of heat transfer coefficient using termoanemometry methods
Dan?ová P.; Sitek P; Vít T.
2014-01-01
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.
Heat transfer coefficient for F.E analysis in the warm forging process
Kang, S S; Kang, J. H.; Lee, K. O.
2007-01-01
Purpose: The Purpose of this paper is to obtain suitable convection and contact heat transfer coefficient forone-time finite element analysis in the warm forging process.Design/methodology/approach: To do this, the temperature of the tool used in the operation was measured witha thermocouple and repeated finite element analysis(FEA) was performed using the experimentally calculatedcontact and cooling heat transfer coefficient. Also the surface temperature of the active tool was obtained bycom...
Overall Heat and Mass Transfer Coefficient of Water Vapor Adsorption
Hamamoto, Yoshinori; Mori, Hideo; Godo, Masazumi; Miura, Kunio; Watanabe, Yutaka; Ishizawa, Toshihiko; Takatsuka, Takeshi
A fundamental investigation was performed to develop a compact and simple desiccant ventilation unit which is one of the main components of a novel energy saving air-conditioning system. Water vapor in the air is adsorbed and/or desorbed to be controlled the humidity of supply air through a unit of an adsorbent rotor. A numerical simulation helps to understand the phenomena of heat and mass transfer in the rotor block. Overall transfer coefficients were estimated by performing both experiment and calculation. It was examined that the transient overall equivalent heat and mass transfer coefficient was not constant. It seems that both film fluid and diffusion resistance govern the coefficients in the block, and the influence of air flow on the time averaged coefficients is estimated by a considering the laminar forced convection from a flat plate. There is little difference of the coefficient between adsorption and desorption process. The correlation and fitting parameters are presented for prediction of the overall heat and mass transfer coefficients. The estimation accuracy was improved.
Calculation of time-dependent heat transfer coefficients during rewetting of highly heated tubes
The computer program INSTHTC was developed to calculate the time-dependent local heat transfer coefficients. The model was applied to calculate the rewetting experiments performed in connection with the BMFT-Research Projekt RS 62. In the advanced version INSTHTC 2 the insulation of the heated tube was also simulated. The presence of an air gap between the outer surface of the tube and the insulation was taken into account. The calculated surface temperature of the insulation agrees well with the one derived from caloric measurements. The influence of radiant heat-transfer through the air gap was studied. The time-dependent heat-transfer coefficient at the inner surface of the tube was calculated using the appropriate saturation temperature of the water according to the measured pressure. The causes for the oscillation of the calculated heat-transfer coefficients are discussed in detail. (orig.)
Local heat transfer coefficient near the spacer grids
The paper presents the experimental data of the local heat transfer in the fuel rod assembly with honeycomb type spacer grids. It was established experimentally that the separation of the boundary layer behind the spacer grid increases the inter-channel coefficient of transverse mixing of flow, and therefore, the local heat transfer. If the distance between the spacer grids is relatively small, they influence one another through the redistribution of mass flow in elementary channels. The local heat transfer behind the spacer grid varies with a distance from it. The local heat transfer can be determined within ± 3% using similar equations for any elementary cell. (orig.)
Identification of MIMO systems with sparse transfer function coefficients
Qiu, Wanzhi; Saleem, Syed Khusro; Skafidas, Efstratios
2012-12-01
We study the problem of estimating transfer functions of multivariable (multiple-input multiple-output--MIMO) systems with sparse coefficients. We note that subspace identification methods are powerful and convenient tools in dealing with MIMO systems since they neither require nonlinear optimization nor impose any canonical form on the systems. However, subspace-based methods are inefficient for systems with sparse transfer function coefficients since they work on state space models. We propose a two-step algorithm where the first step identifies the system order using the subspace principle in a state space format, while the second step estimates coefficients of the transfer functions via L1-norm convex optimization. The proposed algorithm retains good features of subspace methods with improved noise-robustness for sparse systems.
The use of steady state heat transfer coefficients in transient calculations
It is generally not possible to develop fully time-variant analyses for rapid changes of conditions within a reactor. This leads to the use of steady state heat transfer coefficients as an approximation in such calculations. Criteria are set for the validity of using these steady-state heat transfer coefficients in transient calculations. In particular, criteria are given for using a steady state coefficient during a rapid decrease in heat flux. The analysis is based on a solution of the energy equation given by Stein (1971) for a heat flux which is both axially and time dependent. Criteria are given both for smooth and roughened heat transfer surfaces. It is demonstrated that use of the steady state heat transfer coefficient is valid for a set of prescribed AGR conditions. Consideration has been given to the more difficult case of rapid changes in coolant velocity. (U.K.)
Heat transfer coefficient determination for flow boiling in vertical and horizontal minichannels
Piasecka Magdalena; Maciejewska Beata
2014-01-01
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...
Estimation of bulk transfer coefficient for latent heat flux (Ce)
Sadhuram, Y.
The bulk transfer coefficient for latent heat flux (Ce) has been estimated over the Arabian Sea from the moisture budget during the pre-monsoon season of 1988. The computations have been made over two regions (A: 0-8 degrees N: 60-68 degrees E: B: 0...
Measurement of the convective heat-transfer coefficient
Conti, Rosaria; Gallitto, Aurelio Agliolo; 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.
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...
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.
3D measurements and numerical computations of heat transfer coefficients on spheres in an array
The focus of this paper is to investigate the heat transfer coefficient distributions on the spheres in a three-dimensional (3-D) array. This arrangement is an essential geometry in pebble bed reactors (PBRs) that are generally adopted in the chemical and the nuclear engineering. Understanding the thermal-hydraulic characteristics of the pebbles is important for the design of reactors. Using the transient liquid crystal technique, an experimental device is set up to measure the transient wall temperature on the surface of spheres arranged in an array, as heated air flows across. Based on the measured temperature distributions on the sphere surfaces, the heat transfer coefficient can be derived. A 3-D transient computational fluid dynamics (CFD) model with different turbulence models is also developed and assessed using the measured heat transfer coefficient distributions. Five turbulence models are considered in this study: the standard k-Îµ low-Re, AKN k-Îµ low-Re, standard k-Îµ two-layer, realizable k-Îµ two-layer, and v2-bar-f turbulence models, respectively. Comparisons of the predicted heat transfer coefficient distributions and those in the experimental data reveal that the v2-bar-f turbulence model is more suitable for simulating flow and heat transfer characteristics in a sphere array. In addition, the beneficial effect of Rein on the heat transfer coefficient distribution is captured by both experimental measurements and CFD predictions. (authors)
Subcooled boiling heat transfer on a finned surface
Experimental and numerical studies have been performed to determine the heat transfer coefficients from a finned cylindrical surface to subcooled boiling water. The heat transfer rates were measured in an annular test section consisting of an electrically heated fuel element simulator (FES) with eight longitudinal, rectangular fins enclosed in a glass tube. A two-dimensional finite-element heat transfer model using the Galerkin method was employed to determine the heat transfer coefficients along the periphery of the FES surface. An empirical correlation was developed to predict the heat transfer coefficients during subcooled boiling. The correlation agrees well with the measured data. (6 figures) (Author)
Transfer coefficients of radionuclides from feed to livestock products
The accumulation of data on radionuclide transfer are poor in Japan and those are limited to 90Sr, 137Cs and 131I released from the previous atomic bomb experiments. However, in Europe, intensive studies on environment RI level which affects the restriction of the intake for meats and milk products have been made as the measures against the environment radioactivity due to Chernobyl accident. The transfer coefficients of radionuclides to meats and milk products were estimated on a basis of the data published in the Science of the Total Environment vol.85(1989), Oxford University and CEC Radiation Protection, EUR 12608 EN, Luxembourg, 1990 in addition to the data on Exclusion of Radioactivity from foods, Environment Parameter, series No. 4. On the other hand, the transfer coefficients for Japanese were estimated using the concerned data from published reports and the environment radioactivity data reported by national and local government bodies. In this book, many new data of transfer coefficient are presented in tables along with the previous data collected by international nuclear energy agencies and respective national facilities concerned. (M.N.)
Sodium-water reaction (SWR) in a steam generator of sodium-cooled fast reactor (SFR) is a significant phenomenon for safety assessment of the system. One of the top concerns in the SWR is an overheating rupture phenomenon in which a neighbor heat transfer tube fails instantaneously because of a deterioration of structural integrity under a high temperature condition. Hence, the heat transfer coefficient on the tube surface is of importance. Since hydrogen gas is generated in the SWR and liquid water will evaporate quickly due to depressurization, the reaction region is covered with a multi-phase flow structure, and thus the value of the heat transfer coefficient will vary widely. In the present paper, a correlation diagram has been developed between the heat transfer coefficient and the void fraction based on one dimensional homogeneous flow simulation. Furthermore, the transient of void fraction in SWAT-1R experiment is investigated using the diagram. (author)
Finite element model for beef chilling using CFD-generated heat transfer coefficients
Pham, Q.T. [University of New South Wales, Sydney, NSW 2052 (Australia); Trujillo, F.J. [Food Science Australia, 11 Julius Avenue, North Ryde, NSW 2113 (Australia); McPhail, N. [Food Science Australia, P.O. Box 3312, Tingalpa DC, Brisbane, QLD 4173 (Australia)
2009-01-15
A combined model of the beef chilling process is presented, in which computational fluid dynamics (CFD) was used to estimate the local heat and mass transfer coefficients, assuming uniform surface temperatures, and a set of 2-D finite element grids was used to solve the heat transfer equation in the product, which has an elongated shape. Another set of 1-D grids was used to solve the water transport equation near the surface of the meat. The surface transfer coefficients were calculated for various combinations of air orientations and speeds, and summarised in a set of regression equations. The model was verified by existing and new data on heat load, temperatures, weight loss and surface water activity. (author)
Inverse estimation of the local heat transfer coefficient in curved tubes: a numerical validation
Wall curvature represents one of the most used passive techniques to enhance convective heat transfer. The effectiveness of wall curvature is due to the fact that it gives origin to the centrifugal force: this phenomenon induces local maxima in the velocity distribution that locally increase the temperature gradients at the wall by then maximizing the heat transfer. This fact brings to a significant variation of the wall temperature and of the wall heat flux along the circumferential coordinate. The convective heat transfer coefficient is consequently not uniformly distributed along the tube's perimeter and is characterized by higher values at the extrados wall surface in comparison to the ones at the intrados wall surface. Therefore, for predicting the overall performance of heat transfer apparatuses that involve the use of curved tubes, it becomes important to know the local distribution of the convective heat transfer coefficient not only along the axis of the heat transfer section, but also on the internal tube's surface along the cross section circumference. The present paper is intended to the assessment of a procedure developed to evaluate the local convective heat transfer coefficient, along the circumferential coordinate, at the internal wall of a coiled pipe.
Measurement and modeling of interface heat transfer coefficients
The results of preliminary work on the modeling and measurement of the heat transfer coefficients of metal/mold interfaces is reported. The system investigated is the casting of uranium in graphite molds. The motivation for the work is primarily to improve the accuracy of process modeling of prototype mold designs at the Los Alamos Foundry. The evolution in design of a suitable mold for unidirectional solidification is described, illustrating the value of simulating mold designs prior to use. Experiment indicated a heat transfer coefficient of 2 kW/m2/K both with and without superheat. It was possible to distinguish between solidification due to the mold and that due to radiative heat loss. This permitted an experimental estimate of the emissivity, epsilon = 0.2, of the solidified metal
Automatic optimization of the heat transfer coefficient in boiler setups
Automatic optimization of a boiler setup can be based on features of its static characteristic having the form of a maximum in the coefficient of heat transfer from the heater to evaporated medium. This is illustrated by the example of a conventional industrial vaporizer setup used for concentrating aqueous solutions of heavy metal salts, in which case the economy of a heating steam reaches 10 percent
INFLTB, Dosimetric Mass Energy Transfer and Absorption Coefficient
1 - Description of program or function: INFLTB calculates mass energy transfer and mass energy absorption coefficients between 1 keV and 100 MeV for 29 elements and 14 mixtures and compounds of general dosimetric interest. Elements: hydrogen, helium, lithium, beryllium, carbon, graphite, nitrogen, oxygen, fluorine, neon, aluminum, silicon, sulfur, argon, calcium, titanium, iron, copper, germanium, krypton, molybdenum, tin, iodine, barium, gadolinium, tungsten, platinum, uranium, silver, lead. Mixtures and compounds: A-150 tissue-equivalent plastic, adipose tissue (ICRP), adipose tissue (ICRU, 1986), air, dry (near sea level), bone, compact (ICRU), bone, cortical (ICRP), bone, cortical (ICRU, 1986), calcium fluoride, calcium fluoride, ferrous sulfate (standard Fricke) dosimeter solution, ferrous sulfate ('super' Fricke) dosimeter solution, glass, borosilicate ('Pyrex', corning 7740), lithium fluoride, muscle, skeletal (ICRP), muscle, skeletal (ICRU, 1986), muscle, striated (ICRU), polyethylene, polymethyl methacrylate, 'Lucite', 'Perspex', 'Plexiglas', polystyrene, polytetrafluoroethylene, 'Teflon', water, liquid, water vapor, Te gas(methane). 2 - Method of solution: The mass energy transfer coefficient is calculated from the sum of the interaction cross sections (atomic photo effect, Compton scattering, and pair plus triplet production) multiplied by their respective average fractions of energy transferred to electrons and positrons. The mass energy absorption coefficient is the product of the mass energy transfer coefficient and 1 - G, where G is the average fraction of the secondary electron (or positron) kinetic energy that is spent in Bremsstrahlung production and in-flight positron annihilation. 3 - Restrictions on the complexity of the problem: Photon source energies are limited to values between 1 keV and 100 MeV. Radiation yield files are available only for 29 element and 14 compounds and mixtures
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.
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 manikinâ€™s body was as the skin temp...
Heat transfer coefficient for lead matrixing in disposal containers for used reactor fuel
In the Canadian Nuclear Fuel Waste Management Program, metal matrices with low melting points are being evaluated for their potential to provide support for the shell of disposal containers for used fuel, and to act as an additional barrier to the release of radionuclides. The metal matrix would be incorporated into the container by casting. To study the heat transfer processes during solidification, a steady-state technique was used, involving lead as the cast metal, to determine the overall heat transfer coefficient between the lead and some of the candidate container materials. The existence of an air gap between the cast lead and the container material appeared to control the overall heat transfer coefficient. The experimental observations indicated that the surface topography of the container material influences the heat transfer and that a smoother surface results in a greater heat transfer than a rough surface. The experimental results also showed an increasing heat transfer coefficient with increasing temperature difference across the container base plates; a model developed to base-plate bending can explain the observed results
Microscale surface modifications for heat transfer enhancement.
Bostanci, Huseyin; Singh, Virendra; Kizito, John P; Rini, Daniel P; Seal, Sudipta; Chow, Louis C
2013-10-01
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 2.8Ã— compared to the projected base area, and the arithmetic mean roughness value (Ra) was determined to vary from 0.3 Î¼m for the reference smooth surface to 19.5 Î¼m 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. PMID:24003985
Rewetting of a finite rod an arbitrary space-dependent heat transfer coefficient
Two-dimensional rewetting models usually assume two or three regions, with different boundary conditions specified at the solid surface. The more advanced analytical solutions by eigenfunction expansions obtain a formed expression of the temperature distribution in each sub region with a constant heat transfer coefficient. This expression contains some, yet, unknown constants which are determined by matching the temperatures and their axial gradients at the interface between adjacent sub domains. As far as we know, to date there does not exist an analytical solution of a rewetting model with an arbitrary space-dependent heat transfer coefficient. Moreover, eigenfunction expansions solutions of models with a discontinuous heat transfer coefficient have been shown to impede convergence of the series and to decrease the solution accuracy. In the present study, we solve by eigenfunction expansions a two-dimensional model of rewetting of a finite length slab or cylindrical rod, with an arbitrary space-dependent heat transfer coefficient. The unique features of the present approach are the simplicity of the solution, which does not necessitates a tedious splitting of the solution domain into sub domains, and avoiding the convergence problem associated with cases of discontinuous heat transfer coefficients. (authors); 5 refs
NORMATIVE HEAT-TRANSFER COEFFICIENT OF THE RESIDENTIAL BUILDING
A. E. Piir
2015-10-01
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.
Taslim, M. E.; V. Nezym
2007-01-01
Heat transfer coefficients in the cooling cavities of turbine airfoils are greatly enhanced by the presence of discrete ribs on the cavity walls. These ribs introduce two heat transfer enhancing features: a significant increase in heat transfer coefficient by promoting turbulence and mixing, and an increase in heat transfer area. Considerable amount of data are reported in open literature for the heat transfer coefficients both on the rib surface and on the floor area betw...
Hay, N.; Lampard, D.; Saluja, C. L.
1984-06-01
The influence of injection of cooling films through a row of holes on the heat transfer coefficient on a flat plate is investigated for a range of mass flux ratio using a heat-mass transfer analogy. Injection angles of 35 deg and 90 deg are covered. The experimental technique employed uses a swollen polymer surface and laser holographic interferometry. The results presented show the change in local heat transfer coefficient over the no-injection values at the centerline and off-centerline locations for various streamwise stations. The effect of injection on laterally averaged heat transfer coefficients is also assessed.
The difficulty in solving heat transfer tasks in machine structures is often involved in determination of heat transfer coefficient on the surface of the given part. The method considered enables this calculation when based only on values of temperature, measured at several arbitrary points within the part. The points may be placed even outside the exposed region. Let us consider a body of general shape with heat transfer on its surface S. Boundary conditions on the part S(4) of the surface S may be known, and on the other part S(B) of the surface S are given either in terms of surrounding temperature, which is supposed to be known, and of heat transfer coefficient. The spatially variable distribution of the latter can be expressed by Langrange's polynomial, determined by unknown values of the heat transfer coefficient in several points on the surface S(B). These values form the vector V, that describes the heat transfer coefficient distribution with accuracy, proportional to the chosen dimension of the vector. In this way the vector defines also a temperature field of the given body. the task is now to find a vector determining such temperature field, that proves the best agreement with experimental results. This is performed by Nelder and Meads direct search optimizing method. The method requires the evaluation of temperature fields, corresponding to the initial set of vectors V. The temperature field is computed by the finite element method using triangular elements with linear approximation of temperatures. In accordance with the foregoing outlines a FORTRAN program for the ICL 1905 computer was written
A correlation to the heat transfer coefficient in nucleate boiling
Nucleate boiling heat transfer is a complex phenomenon, making the development of a correlation for the heat transfer coefficient rather cumbersome due to the number of physical parameters involved in it. Some authors have followed a pragmatic approach to the problem by correlating the heat transfer coefficient in terms of reduced primitive properties. Two of the most knowledgeable authors who have followed this approach are Gorenflo and Cooper. Comparisons have been performed among results from the correlations proposed by these researchers and experimental results obtained elsewhere for refrigerants R-11, R-113 and R-114. These comparisons have shown that Cooper's correlation is best fitted for halocarbon refrigerants. The correlation proposed by Gorenflo ads the difficulty of including a numerical factor specific for each fluid. Leiner modified Gorenflo's correlation to determine the numerical factor as a function of known physical parameters of the fluid. In present study, the form of this function has been investigated for halocarbon refrigerants. The obtained correlation is written in terms of the following parameters: reduced pressure, eccentric and compressibility factors at the critical state, and a dimensionless specific heat of the vapor phase. The correlation compares well with experimental results. (author)
Power co-efficient using lumped heat transfer model
Generalised methodology is derived to determine the power coefficients between any two asymptotic states. Methodology is derived by simplifying heat transfer equations into lumped parameter model. If the reactor coolant flow and thermo physical properties are assumed to be constant, change in reactivity at a given reactor location is purely a function of linear power, and the net change in reactivity is a function of net change in total power. Power coefficient is almost a constant value, when it is calculated between any two asymptotic states, except the Doppler contribution, a non linear reactivity component. It is verified between zero power and nominal power, and between zero power and 50 % of nominal power. (author)
The Heat Transfer Coefficient of Recycled Concrete Bricks Combination with EPS Insulation Board Wall
Jianhua Li; Wanlin Cao
2015-01-01
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 coefficien...
Heung-Kyu Kim; Seong Hyeon Lee; Hyunjoo Choi
2015-01-01
Using an inverse analysis technique, the heat transfer coefficient on the die-workpiece contact surface of a hot stamping process was evaluated as a power law function of contact pressure. This evaluation was to determine whether the heat transfer coefficient on the contact surface could be used for finite element analysis of the entire hot stamping process. By comparing results of the finite element analysis and experimental measurements of the phase transformation, an evaluation was perfor...
Local heat transfer coefficient in a fluidized bed
This paper presents an experimental study for the local heat transfer coefficient. The experiments was conducted inside a reactor with inner diameter (I D = 142mm) at atmospheric conditions (temperature mean value = 29 deg.) The bed was heated by means of a parochial electric heater with a diameter of (dh = 29 mm) and a constant power of 5W. The following factors varied: particles type and diameter, fluid velocity, bed height and heater position inside the reactor. The results were presented and discussed. (author). 15 refs., 7 figs
Estimation of Volumetric Mass Transfer Coefficient in Bioreactor
Zainab Yaquob Atiya
2012-01-01
This study is concentrated to investigate the effects of aeration and stirring speed on the volumetric mass transfer coefficient (KLa). A dynamic technique was used in estimating KLa values in order to achieve the aim of this study.This study was done in 10L bioreactor by using two medias:-1. Dionized water2. Xanthan solution (1 g /L)Moreover, the research covered a comparison between the obtained values of KLa.The Xanthan solution was used because of its higher viscosity in comparison with w...
Identification of the capillary transfer coefficient in porous building materials
Vala, J.; Jarošová, P.
2013-10-01
Physical description of the capillary transfer of water (or other liquids) in porous building material comes out from the thermomechanical principle of mass balance and from the Fick law, nonlinear only in the multiplicative capillary transfer coefficient. However, such seemingly simple formulation leads to the non-trivial theory of solvability and convergence of sequences of approximate solutions even for direct problems. The analysis of inverse problems relies on various simplified approaches, whose mutual relations, including those to the related direct problems, are not very transparent: some additional least squares, regression, etc. tricks are often hidden in computational algorithms. This paper demonstrates the general formulation, containing most identification approaches used in practice as certain special cases, both those using the 3-dimensional integration and those relying on (semi-)analytical formulae relying on the very special geometrical configurations. An illustrative example shows the possibility of implementation of the sketched algorithms in the MATLAB environment.
Nucleate boiling heat transfer coefficients of flammable refrigerants
Jung, Dongsoo [Inha Univ., Incheon (Korea). Dept. of Mechanical Engineering; Lee, Heungseok; Bae, Dongsoo [Inha Univ., Incheon (Korea); Oho, Sukjae [TechnoChem Co. Ltd., Kyunggi-Do (Korea)
2004-06-01
Nucleate boiling heat transfer coefficients (HTCs) of propylene (R1270), propane (R290), isobutane (R600a), butane (R600), and dimethylether (RE170) on a horizontal smooth tube of 19.0 mm outside diameter have been measured. The experimental apparatus was specially designed to accommodate high vapor pressure refrigerants such as propylene and propane with a sight glass. A cartridge heater was used to generate uniform heat flux on the tube. Data were taken in the order of decreasing heat flux from 80 kW m{sup -2} to 10 kW m{sup -2} with an interval of 10 kW m{sup -2} in the pool temperature of 7 {sup o}C. Test results exhibited a typical trend that HTCs of flammable refrigerants increase with increasing vapor pressure. Existing nucleate boiling heat transfer correlations showed up to 80% deviation as compared to the present data. Hence a new correlation was developed through a regression analysis taking into account dimensionless variables affecting nucleate boiling heat transfer. The new correlation showed a good agreement with data for flammable refrigerants as well as halogenated refrigerants with a deviation of 5.3%. (author)
Confirmation of selected milk and meat radionuclide transfer coefficients. Progress report
The objectives are to determine transfer coefficients to milk, beef and chicken of four radionuclides for which transfer coefficients were either indetermined or based upon secondary data. The radionuclides are 99Mo, 99Tc, 140Ba, and 131Te. The transfer coefficient for 133I to eggs was also determined, because again only limited data was available in the literature
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.
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...
Efficiency analysis of straight fin with variable heat transfer coefficient and thermal conductivity
Sadri, Somayyeh; Raveshi, Mohammad Reza; Amiri, Shayan [K.N. Toosi University of Technology, Tehran (Iran, Islamic Republic of)
2012-04-15
In this study, one type of applicable analytical method, differential transformation method (DTM), is used to evaluate the efficiency and behavior of a straight fin with variable thermal conductivity and heat transfer coefficient. Fins are widely used to enhance heat transfer between primary surface and the environment in many industrial applications. The performance of such a surface is significantly affected by variable thermal conductivity and heat transfer coefficient, particularly for large temperature differences. General heat transfer equation related to the fin is derived and dimensionalized. The concept of differential transformation is briefly introduced, and then this method is employed to derive solutions of nonlinear equations. Results are evaluated for several cases such as: laminar film boiling or condensation, forced convection, laminar natural convection, turbulent natural convection, nucleate boiling, and radiation. The obtained results from DTM are compared with the numerical solution to verify the accuracy of the proposed method. The effects of design parameters on temperature and efficiency are evaluated by some figures. The major aim of the present study, which is exclusive for this article, is to find the effect of the modes of heat transfer on fin efficiency. It has been shown that for radiation heat transfer, thermal efficiency reaches its maximum value.
Efficiency analysis of straight fin with variable heat transfer coefficient and thermal conductivity
In this study, one type of applicable analytical method, differential transformation method (DTM), is used to evaluate the efficiency and behavior of a straight fin with variable thermal conductivity and heat transfer coefficient. Fins are widely used to enhance heat transfer between primary surface and the environment in many industrial applications. The performance of such a surface is significantly affected by variable thermal conductivity and heat transfer coefficient, particularly for large temperature differences. General heat transfer equation related to the fin is derived and dimensionalized. The concept of differential transformation is briefly introduced, and then this method is employed to derive solutions of nonlinear equations. Results are evaluated for several cases such as: laminar film boiling or condensation, forced convection, laminar natural convection, turbulent natural convection, nucleate boiling, and radiation. The obtained results from DTM are compared with the numerical solution to verify the accuracy of the proposed method. The effects of design parameters on temperature and efficiency are evaluated by some figures. The major aim of the present study, which is exclusive for this article, is to find the effect of the modes of heat transfer on fin efficiency. It has been shown that for radiation heat transfer, thermal efficiency reaches its maximum value
Confirmation of selected milk and meat radionuclide-transfer coefficients
The elements selected for study of their transfer coefficients to eggs, poultry meat, milk and beef were Mo, Tc, Te, and Ba. The radionuclides used in the study were the gamma-emitting radionuclides 99Mo, /sup 123m/Te and 133Ba. 133Ba was selected because 140Ba-140La is produced infrequently and availability was uncertain. 133Ba has a great advantage for our type of experiment because of its longer physical half-life. 99Tc is a pure beta-emitter and was used in the first three animal experiments because we could not obtain the gamma-emitting /sup 95m/Tc. A supply of this nuclide was recently obtained, however, for the second cow experiment
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.
Dimethylsulfide gas transfer coefficients from algal blooms in the Southern Ocean
Bell, T. G.; W. De Bruyn; C. A. Marandino; Miller, S. D.; C. S. Law; Smith, M.J.; Saltzman, E. S.
2015-01-01
Airâ€“sea dimethylsulfide (DMS) fluxes and bulk airâ€“sea gradients were measured over the Southern Ocean in Februaryâ€“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 sâˆ’1. Bi...
DMS gas transfer coefficients from algal blooms in the Southern Ocean
Bell, T. G.; W. De Bruyn; C. A. Marandino; Miller, S. D.; C. S. Law; Smith, M.J.; Saltzman, E. S.
2014-01-01
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 ...
Carneiro, O. S.; NÃ³brega, J. M.; Mota, Armando R.; Silva, Carolina
2013-01-01
The extrusion of technical thermoplastics profiles generally uses a dry calibration/cooling system, composed by one or several calibrators in series. One of the major difficulties to be faced when modelling this important stage is an adequate prescription of the heat transfer coefficient, hinterface, between the plastic profile surface and the cooling medium, which must include the effect of the interface contact resistance. This is the motivation that led the present research ...
Li, Huiping; He, Lianfang; Zhang, Chunzhi; Cui, Hongzhi
2015-06-01
The thermal physical parameters have significant effects on the calculation accuracy of physical fields, and the boundary heat transfer coefficient between the die and water is one of the most important thermal physical parameters in the hot stamping. In order to attain the boundary heat transfer coefficient, the testing devices and test procedures are designed according to the characteristic of heat transfer in the hot stamping die. A method of estimating the temperature-dependent boundary heat transfer coefficient is presented, and an inverse heat conduction software is developed based on finite element method, advance-retreat method and golden section method. The software is used to calculate the boundary heat transfer coefficient according to the temperatures measured by NiCr-NiSi thermocouples in the experiment. The research results show that, the convergence of the method given in the paper is well, the surface temperature of sample has a significant effect on the boundary heat transfer coefficient between the die and water. The boundary heat transfer coefficient increases as the surface temperature of sample reduces, and the variation is nonlinear.
Li, Huiping; He, Lianfang; Zhang, Chunzhi; Cui, Hongzhi
2016-04-01
The thermal physical parameters have significant effects on the calculation accuracy of physical fields, and the boundary heat transfer coefficient between the die and water is one of the most important thermal physical parameters in the hot stamping. In order to attain the boundary heat transfer coefficient, the testing devices and test procedures are designed according to the characteristic of heat transfer in the hot stamping die. A method of estimating the temperature-dependent boundary heat transfer coefficient is presented, and an inverse heat conduction software is developed based on finite element method, advance-retreat method and golden section method. The software is used to calculate the boundary heat transfer coefficient according to the temperatures measured by NiCr-NiSi thermocouples in the experiment. The research results show that, the convergence of the method given in the paper is well, the surface temperature of sample has a significant effect on the boundary heat transfer coefficient between the die and water. The boundary heat transfer coefficient increases as the surface temperature of sample reduces, and the variation is nonlinear.
Krupiczka, R.; Rotkegel, A.; Ziobrowski, Z. [Polish Academy of Sciences, Institute of Chemical Engineering, Gliwice (Poland)
1999-07-01
The paper describes a mathematical model of the process based on the multicomponent mass transfer theory which enables to the effect to be predicted of mass transport on the boiling heat transfer coefficient. The results of calculation were compared with our own experimental pool boiling data for the ternary system methanol-isopropanol-water and with Grigoriev's data obtained for the system acetone-methanol-water. The good accuracy was obtained when the ratio of the tube to the bubbles surface, which touch the heater at that moment, was considered as a parameter of the model. (authors)
In this study, the relation between radiative and convective heat transfer coefficient at the ceiling is determined for a cooled ceiling room of which floor surface is isolated. Firstly, convective heat transfer is simulated numerically neglecting the radiative heat transfer at the surfaces (Îµw = Îµc = 0) for different room dimensions (3 x 3 x 3, 4 x 3 x 4 and 6 x 3 x 4 m) and thermal conditions (Tc = 0-25 deg. C, Tw = 28-36 deg. C). Then, radiative heat transfer is calculated theoretically for different surface emissivities (Îµw = Îµc = 0.7, 0.8 and 0.9). Numerical data are compared with the results of correlations based on experimental data given in literature. New correlations for convective and radiative heat transfer coefficients at the ceiling are found in the current study. The ratio of radiative heat transfer coefficients to convective heat transfer coefficients (hcr/hcc) is determined. It was seen that the ratios range from 0.7 to 2.3 depending on the temperature difference. The ratios increase as the temperature differences increase. Therefore, a new correlation between the coefficients is developed depending on temperature difference at the ceiling
Karadag, Refet [Department of Mechanical Engineering, Harran University, Osmanbey Kampusu, 63300 Sanliurfa (Turkey)
2009-01-15
In this study, the relation between radiative and convective heat transfer coefficient at the ceiling is determined for a cooled ceiling room of which floor surface is isolated. Firstly, convective heat transfer is simulated numerically neglecting the radiative heat transfer at the surfaces ({epsilon}{sub w} = {epsilon}{sub c} = 0) for different room dimensions (3 x 3 x 3, 4 x 3 x 4 and 6 x 3 x 4 m) and thermal conditions (T{sub c} = 0-25 C, T{sub w} = 28-36 C). Then, radiative heat transfer is calculated theoretically for different surface emissivities ({epsilon}{sub w} = {epsilon}{sub c} = 0.7, 0.8 and 0.9). Numerical data are compared with the results of correlations based on experimental data given in literature. New correlations for convective and radiative heat transfer coefficients at the ceiling are found in the current study. The ratio of radiative heat transfer coefficients to convective heat transfer coefficients (h{sub cr}/h{sub cc}) is determined. It was seen that the ratios range from 0.7 to 2.3 depending on the temperature difference. The ratios increase as the temperature differences increase. Therefore, a new correlation between the coefficients is developed depending on temperature difference at the ceiling. (author)
In a steam generator of FBR, a high pressured water flows inside of heat transfer tubes and exchanges its heat with sodium through the tubes. When a tube fails, water would leak into sodium, and react with sodium (Sodium Water Reaction; SWR). This reaction occurs rapidly and accompanies a high temperature jet. The jet has possibilities to cause a secondary failure of neighboring tubes. With regard to the secondary failure caused by deterioration of tube material due to high temperature (overheating rupture), quantification of heat transfer from fluid to the tube is important perspective of safety evaluation. The SWR experiments with SWAT-1R test facility was performed at Japan Atomic Energy Agency (JAEA). In the experiment, the SWR was produced by feeding water vapor from one tube toward a test section of pin bundle with 43 tubes. Thermo couples (T/Cs) were installed and temperature transient was measured in a certain tube near the reacting zone. In the present study, the heat transfer coefficient on the heat transfer tube has been investigated numerically based on the experimental temperature. Furthermore, we also have made an investigation of the flow characteristic on the heat transfer tube, taking into account the variation of the heat transfer coefficient. (author)
Mass-transfer coefficients at the uranium adsorption from solution on ion exchange resins
The process of uranium adsorption on ion exchange resins is a mass-transfer process of solid-liquid nature asociated with chemical reaction. Mathematical models used in these studies considers a spherical ion exchange resin grain where on its surface and its pores is taking place the chemical reaction. This paper presents experimental data of the uranium adsorption from alkaline solutions on a strong basic ion exchange resin, second type in chlorine form. The resin and the solution are contacting in two ways: fixed bed and perfect mixing. The optimal resin size and mass transfer coefficient was established for uranium adsorption from alkaline solutions. Also, criterial relation were established between mass-transfer process variables, impulse transfer, equipment geometry used for the experiments. (orig.)
Heat transfer coefficient in pool boiling for an electrically heated tube at various inclinations
An experimental investigation is carried out study the behaviour of heat transfer in pool boiling from a vertical and inclined heated tube at atmospheric pressure. An imperial correlation joining the different parameters affecting the heat transfer coefficient in pool boiling for an electrically heated tube at various inclinations is developed. Two test sections (zircaloy-4 and stainless steel) of 16 n n outer diameter and 120 nm length are investigated. Four levels of heat flux are used for heating the two lest sections (e.g. 381, 518, 721 and 929 k.watt/n 2). The maximum surface temperature achieved is 146.5 degree c for both materials, and the maximum bulk temperature is 95 degree C. It is found that the average heat transfer coefficient is inversely proportional with heated length l, where it reaches a constant value in the horizontal position. The heat transfer coefficient curves at various inclinations with respect to the heated tube length pass around one point which is defined as limit length
Nonstationary Mass Transfer Near the Surface of a Cylindrical Body
Rudobashta, S. P.; Kosheleva, M. K.; Kartashov, Ã‰. M.
2015-11-01
The problem of nonstationary diffusion of the target component to a phase that is external relative to the surface of a cylindrical body has been formulated and solved analytically. From the found solution the dependences have been obtained for calculating the instantaneous mass transfer coefficient and the phase-contact-time mean mass transfer coefficient, on the basis of which the process of extraction of technological pollutants from fibrous materials has been analyzed.
Modeling the Effect of Internal Convection Currents on Heat Transfer Coefficient of Liquid Foods
SAJID ALI
2013-04-01
Full Text Available The internal convection currents generated during the cooling process affect convective heat transfer coefficient from the surface of the container, these convection currents may increase the effective value of the surface film conductance (h. Therefore, in such situation the Nu-Re correlations, which are generally used to predict h-values, may not yield realistic results. In the present work, this effect has been investigated by using the empirical correlation developed through Temperature-Time measurements at the centre of liquid food containers during cooling .The main concern of the present work is about considering the heat transfer behaviour for liquid foods for which a cylindrical shape container of brass metal have taken, in this work the transient Time-Temperature relation is utilized to calculate the value of convection heat transfer coefficient (h for each measured temperature at the centre of the cylinder (rÂ¬Â¬o=0. Then after plotting the graph between â€˜hâ€™ and â€˜Tâ€™ an expression between h and T is obtained, which is fed back in the programme developed with the help of finite difference method by which Time-Temperature variation is obtained. Experimental procedure was used to determine surface film conductance of cylindrical Apple and Orange juice container, calculated temperatures have been compared with the experimental results when the measured surface film conductance were used to solve the transient heat conduction equation in cylindrical coordinates. A consistently excellent agreement was observed.
Determining heat transfer coefficients in radial flow through a polyethylene packed
LuÃs PatiÃ±o
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 modelâ€™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 fluidâ€™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.
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.
The heat-transfer coefficients around a workpiece immersed in an electrically heated heat treatment fluidised bed were studied. A suspension probe designed to simulate a workpiece of complex geometry was developed to measure local total and radiative heat-transfer coefficients at a high bed temperature. The probe consisted of an energy-storage region separated by insulation from the fluidised bed, except for the measuring surface, and a multi-thermocouple measurement system. Experiments in the fluidised bed were performed for a fluidising medium of 120-mesh alumina, a wide temperature range of 110-1050 deg. C and a fluidising number range of 1.18-4.24. It was found that the workpiece surface temperature has a more significant effect on heat transfer than the bed temperature. The total heat-transfer coefficient at the upper surface of the workpiece sharply decreased at the start of heating, and then steadily increased as heating progressed, while a sharp decrease became a rapid increase and then a slow increase for the radiative heat-transfer coefficient. A great difference in the heat-transfer coefficients around the workpiece was observed
Dimethylsulfide gas transfer coefficients from algal blooms in the Southern Ocean
Bell, T. G.; De Bruyn, W.; Marandino, C. A.; Miller, S. D.; Law, C. S.; Smith, M. J.; Saltzman, E. S.
2015-02-01
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 show 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.
DMS gas transfer coefficients from algal blooms in the Southern Ocean
Bell, T. G.; De Bruyn, W.; Marandino, C. A.; Miller, S. D.; Law, C. S.; Smith, M. J.; Saltzman, E. S.
2014-11-01
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.
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 sâˆ’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.
Mass transfer coefficient for volatilization of volatile organic compounds from wastewater
Intamanee, J.
2006-09-01
Full Text Available Volatilization of volatile organics compounds (VOCs from wastewater is recognized as an important source that caused air pollution today. In air pollution management regarding VOCs emission to atmosphere, the amount of VOCs that released from wastewater needs to be known. A model for predicting of VOCs volatilized from wastewater is then necessary. The aim of this research was to develop the gas-film (kGa,VOC and liquid-film (kLa,VOC mass transfer coefficients from volatilization of VOCs from wastewater. The volatilization experiments were performed in a pilot volatilization tank with a volume of 100 L. The wind speed over the water surface, measured at 10 cm above water surface (U10cm, was the main parameter which investigated in this work. The U10cm were varied from 0 to 4.42 m/s. VOCs used in this investigation were methanol, toluene and methyl ethyl ketone.The results revealed that the gas-film coefficient of methanol increased linearly with increasing U10cm over the investigated range of U10cm whereas the liquid-film coefficient of toluene fell into two regimes with a break at the U10cm of 2.4 m/s. The correlations of kGa,VOC and kLa,VOC were developed from gas-film and liquid-film coefficient of methanol and toluene, respectively, and verified by predicting overall mass transfer coefficient (KOLa of MEK. It was found that the correlations of kGa,VOC and kLa,VOC predicted the mass transfer coefficient of MEK which volatilized from wastewater quite well but underestimated KOLa of MEK volatilized from pure water. Since the mass transfer coefficient of VOCs volatilized from pure water were significant higher than that of wastewater as found in this work, the kGa,VOC and kLa,VOC developed based on wastewater is recommended for prediction of VOCs emission rate from wastewater rather than the correlation previously developed based on pure water.
A study to measure the transfer of radiocaesium to adult female sheep through a breeding cycle is described. The transfer of radiocaesium from the diet to muscle (estimated as the equilibrium transfer coefficient) was significantly lower to pregnant, and especially lactating, animals compared to non-lactating and barren animals. High dry matter intake rates were also associated with significantly lower transfer coefficients. Known relationships between dry matter intake rates and protein turnover could credibly explain some of these differences. However, when described as the concentration ratio, radiocaesium transfer to meat was apparently highest during lactation. The apparent difference in results obtained by the two approaches of determining transfer is the consequence of daily dry matter intake being a denominator within the estimation of transfer coefficient. A wider discussion of transfer coefficients and concentration ratios leads us to suggest that the concentration ratio is the more robust and potentially generic parameter
Wang, Z.; Ireland, P.T.; Jones, T.V. [Univ. of Oxford (United Kingdom). Dept. of Engineering Science
1995-04-01
Short pin-fin and pin-fin arrays are frequently used in turbine blade internal cooling systems to enhance cooling and stiffen the structure. The present work has shown that a knowledge of the detailed heat transfer coefficient distribution is required to predict the cooling effect of such devices accurately. The heat flow process has been numerically modeled at typical engine conditions with the detailed heat transfer distribution measured by the transient heat transfer method being used as the thermal boundary conditions. The heat transfer coefficient over the surface of a pedestal with fillet radii has been measured using thermochromic liquid crystals and the transient heat transfer method. The tests were performed at engine representative Reynolds numbers for a geometry typical of those used in turbine blade cooling systems. The heat conduction process that occurs in the engine was subsequently modeled numerically with a finite element discretization of the solid pedestal. The measured heat transfer coefficients were used to derive the exact boundary conditions applicable to the engine. The temperature field within the pedestal, calculated using the correct heat transfer coefficient distribution, is compared to that calculated using an area-averaged heat transfer coefficient. Metal temperature differences of 90 K are predicted across the blade wall.
Heat transfer coefficients were measured in a channel with one side dimpled surface. The sphere type dimples were fabricated, and the diameter (D) and the depth of dimple was 16 mm and 4 mm, respectively. Two channel heights of about 0.6D and 1.2D, two dimple configurations were tested. The Reynolds number based on the channel hydraulic diameter was varied from 30000 to 50000. The improved hue detection based transient liquid crystal technique was used in the heat transfer measurement. Heat transfer measurement results showed that high heat transfer was induced downstream of the dimples due to flow reattachment. Due to the flow recirculation on the upstream side in the dimple, the heat transfer coefficient was very low. As the Reynolds increased, the overall heat transfer coefficients also increased. With the same dimple arrangement, the heat transfer coefficients and the thermal performance factors were higher for the lower channel height. As the distance between the dimples became smaller, the overall heat transfer coefficient and the thermal performance factors increased
Shin, So Min; Lee, Ki Seon; Park, Seoung Duck; Kwak, Jae Su [Korea Aerospace University, Goyang (Korea, Republic of)
2009-03-15
Heat transfer coefficients were measured in a channel with one side dimpled surface. The sphere type dimples were fabricated, and the diameter (D) and the depth of dimple was 16 mm and 4 mm, respectively. Two channel heights of about 0.6D and 1.2D, two dimple configurations were tested. The Reynolds number based on the channel hydraulic diameter was varied from 30000 to 50000. The improved hue detection based transient liquid crystal technique was used in the heat transfer measurement. Heat transfer measurement results showed that high heat transfer was induced downstream of the dimples due to flow reattachment. Due to the flow recirculation on the upstream side in the dimple, the heat transfer coefficient was very low. As the Reynolds increased, the overall heat transfer coefficients also increased. With the same dimple arrangement, the heat transfer coefficients and the thermal performance factors were higher for the lower channel height. As the distance between the dimples became smaller, the overall heat transfer coefficient and the thermal performance factors increased
Condensation in the presence of noncondensible gases play 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 and mass transfer analogy since it considers the sensible and condensation heat transfer simultaneously. This model was found to perform much better than the reduction factor approach. The calculation using the new model was found to be in much better agreement with the experimental values. (author)
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.
Hao, Weiqiang; Wang, Junde; Zhang, Xiangmin
2006-12-01
In order to investigate the concentration dependence of mass transfer coefficients in RPLC, experimental breakthrough curves obtained by staircase frontal analysis (FA) were fitted to the simplified models such as multiplate (MP) model, equilibrium dispersive (ED) model, and transport model, and the sophisticated models such as lumped pore diffusion (POR) model and general rate (GR) model. The MP model was used to obtain the initial guesses of the parameters of the ED and the transport models. Then the best values were obtained by minimizing the differences between theoretical and experimental values with a nonlinear fitting procedure. The values of the parameters of the POR and the GR models can be calculated by using the expressions derived from the plate height equations, which was further validated by using the fitting method. It was found that the mass transfer coefficients would depend on the solute concentration. This can be ascribed to the surface diffusivity, which correlates with the concentration and is lumped into the mass transfer coefficients for both simplified and sophisticated models. PMID:17305235
In - line determination of heat transfer coefficients in a plate heat exchanger
Sotelo, S. Silva; DomÃnguez, R. J. Romero
This paper shows an in - line determination of heat transfer coefficients in a plate heat exchanger. Water and aqueous working solution of lithium bromide + ethylene glycol are considered. Heat transfer coefficients are calculated for both fluids. "Type T" thermocouples were used for monitoring the wall temperature in a plate heat exchanger, which is one of the main components in an absorption system. Commercial software Agilent HP Vee Pro 7.5 was used for monitoring the temperatures and for the determination of the heat transfer coefficients. There are not previous works for heat transfer coefficients for the working solution used in this work.
Study on grey model in the heat transfer coefficient of supercritical water
Heat transfer coefficient is an important feature factor to describe supercritical water reactor(SCWR). With experimental data as basic, using Grey model to analyze the relationship between heat transfer coefficient and other influential factors, studying the inside law of heat transfer coefficient variation of supercritical water, so as to differ the traditional method that get the equations from fitting experimental data. Comparing it to other traditional equations, the results indicates that the data which are calculated by GM model are close to experimental data, GM model can describe the variation of supercritical water's heat transfer coefficient with other influential factors well
Effect of design and operation parameters on heat transfer coefficient in condensers
Accurate and optimum usage of energy sources is gaining importance all over the world due to the increase of energy need and limited energy sources. Increasing condenser efficiency, reduce both the dimensions and the material usage and also the investment cost of the devices. This can be maintained by increasing the heat transfer coefficient in condensers. Generally, tubes having plain inner surfaces are mounted horizontally in serpentine type condenser applications and due to the performance loss results from the congestion in serpentine connections, vertical tube mounting is not preferred. Due to the complexity of the two-phase flow, a single set of correlation for heat transfer cannot be used. Average and local heat transfer coefficient for condensers are determined. Moreover, for each experiments flow pattern is determined and the validity of the correlations are compared according to that flow pattern. In Table 2, some of the experiments for R134a are listed. Local heat transfer coefficient is also important for condenser design. As a result, to design effective condensers the accuracy of the correlations is very important. When all the experiments are taken into account, it is seen that deviation of the correlations differs according to the refrigerant type, tube dimensions, mass flux, saturation temperature and flow pattern. For high mass flux (>400 kg/m2s) Traviss (1973) correlation failed. For small diameters (<3.14 mm) Tandon (1985) correlation estimate the heat transfer coefficient with a high deviation. Most accurate results are obtained for Akers et al. (1959), M.M. Shah (1978), Cavallini and Zecchlin (1974), J.R. Thome - J. El Hajal - A. Cavallini (2003) correlations. For high mass flux and annular flow, M.M. Shah (1978) correlation estimates the heat transfer coefficient with high precision. However, as the tube diameter decrease, this deviation increases. For small tube diameter such as 0.691 mm Cavallini and Zecchlin (1974) gives the most accurate results. J.R. Thome - J. El Hajal - A. Cavallini (2003) correlations are classified according to the flow pattern. For stratified flow the accuracy of that correlation is much better than the others. (author)
Varga, Szabolcs; Oliveira, Jorge C
2000-01-01
The external heat transfer coefficient in steam retort processing was determined experimentally in a pilot scale retort. The heat transfer equations were solved applying finite elements and using the actual retort temperature profile as boundary condition. The instantaneous values of the heat transfer coe cient were determined, to analyse its time-variability along a retort cycle. It was found that reliable results for the external heat transfer coefficient at time t could be obtaine...
Estimation of grass to cow's milk transfer coefficients for emergency situations
Several studies have been reported on soil to grass equilibrium transfer factors and grass to cow's milk transfer coefficients for 137Cs for the environs of different nuclear power plants of both India and other parts of the world. In such studies, the activity concentration of 137Cs is measured in grass collected from different places. Cow's milk samples are collected from nearby localities or from milk dairies and analyzed for 137Cs and the grass to cow's milk transfer coefficient is estimated. In situation where 137Cs is not present in measurable activity concentrations, its stable counterpart (Cs) is measured for the estimation of transfer coefficients. These transfer coefficient values are generally used in theoretical models to estimate the dose to the population for hypothetical situation of emergency. It should be noted that the transfer coefficients obtained for equilibrium conditions may not be totally applicable for emergency situation. However, studies aimed at evaluating transfer coefficients for emergency situations are sparse because nuclear power plants do not release 137Cs during normal operating situations and therefore simulating situation of emergency release is not possible. Hence, the only method to estimate the grass to milk transfer coefficient for emergency situation is to spike the grass with small quantity of stable Cs. This paper reports the results of grass to milk transfer coefficients for stable isotope of Cesium (Cs) for emergency situation
Branco, J. F.; Pinho, C. T.; Figueiredo, R. A.
2000-01-01
The conduction phenomenon in an insulated sphere is re-worked through a dimensionless approach, where the heat transfer coefficient dependence on the external radius and on the surface temperature, as in the case of forced and free convection, is taken into account. Assuming a power law variation of the convection coefficient [1, 2], and using the results of Sparrow [3], equations and graphs for the most important dimensionless parameters are presented. The developed equations show, for examp...
Effect of Film Injection Location on Local Heat Transfer Coefficient on a Gas Turbine Blade
Anant B. Mehendale; H. Wanda Jiang; Srinath V. Ekkad; Je-Chin Han
1998-01-01
Experiments were performed to study the effect of film hole location on local heat transfer coefficient distribution of a turbine blade model with air or CO2 film injection to simulate coolant density effect. Tests were performed on a five blade linear cascade at the chord Reynolds number of 3×105 at cascade inlet. The test blade had three rows of film holes in the leading edge region and two rows each on the pressure and suction surfaces. Film hole locations were varied by leaving the desire...
Dimethylsulfide gas transfer coefficients from algal blooms in the Southern Ocean
Bell, TG; W. De Bruyn; Marandino, CA; Miller, SD; Law, CS; Smith, MJ; Saltzman, Es
2015-01-01
Â© Author(s) 2015. 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. Bi...
Boiling Heat Transfer on Superhydrophilic, Superhydrophobic, and Superbiphilic Surfaces
Betz, Amy Rachel; Kim, Chang-Jin 'CJ'; Attinger, Daniel
2012-01-01
With recent advances in micro- and nanofabrication, superhydrophilic and superhydrophobic surfaces have been developed. The statics and dynamics of fluids on these surfaces have been well characterized. However, few investigations have been made into the potential of these surfaces to control and enhance other transport phenomena. In this article, we characterize pool boiling on surfaces with wettabilities varied from superhydrophobic to superhydrophilic, and provide nucleation measurements. The most interesting result of our measurements is that the largest heat transfer coefficients are reached not on surfaces with spatially uniform wettability, but on biphilic surfaces, which juxtapose hydrophilic and hydrophobic regions. We develop an analytical model that describes how biphilic surfaces effectively manage the vapor and liquid transport, delaying critical heat flux and maximizing the heat transfer coefficient. Finally, we manufacture and test the first superbiphilic surfaces (juxtaposing superhydrophobic ...
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
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.
The tritium bred in a deuterium-tritium fusion reactor is removed from its blanket by using helium sweep gas. From the viewpoint of adsorption capacity and pressure of tritium at release, a cryosorption bed, which uses molecular sieves or activated carbon at the temperature of liquid nitrogen, is attractive for the recovery of this tritium. The mass transfer coefficients required to predict the breakthrough curve are experimentally discussed. The overall mass transfer coefficient KFav, in the cryosorption of hydrogen isotopes on molecular sieves or activated carbon at 77 K consists of a mass transfer coefficient that represents the transfer from the bulk gas flow to the surface of the adsorbent through the boundary layer kfav, a mass transfer coefficient that represents the axial dispersion in the packed bed kzav, and a mass transfer coefficient that represents the intraparticle diffusion through micro pores in the adsorbent particle Î’ks av. The value of Î’ksav is confirmed to be 1 to 50 s-1, which decreases with an increase of hydrogen partial pressure, and the rate-controlling step is Î’ksav when the hydrogen partial pressure is higher than several hundred pascals, and kzav, becomes the rate-controlling step when the hydrogen partial pressure is low and gas velocity is slow. 7 refs., 10 figs., 4 tabs
Heat transfer coefficient for flow boiling in an annular mini gap
HoÅ¼ejowska 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 â€“ 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 twoâ€“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.
PARTITION COEFFICIENTS FOR METALS IN SURFACE WATER, SOIL, AND WASTE
This report presents metal partition coefficients for the surface water pathway and for the source model used in the Multimedia, Multi-pathway, Multi-receptor Exposure and Risk Assessment (3MRA) technology under development by the U.S. Environmental Protection Agency. Partition ...
A novel approach to determine the heat transfer coefficient in directional solidification furnaces
Banan, Mohsen; Gray, Ross T.; Wilcox, William R.
1990-01-01
The heat transfer coefficient between a molten charge and its surroundings in a Bridgman furnace was determined using an approach utilizing 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 value estimated by standard heat transfer calculations.
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.
Experimental study on the critical heat flux and heat transfer coefficient in nanofluid pool boiling
Nanofluid is the liquid with dilute dispersion of nano-meter sized solid particles. It is know that the critical heat flux in pool boiling is usually enhanced and the heat transfer coefficient changes rather complicatedly in the nanofluid comparing with the pure liquid. At present, it is believed that the CHF enhancement can mainly be attributed to the nano-particle layer formed on the heated surface during nucleate boiling. Since nano-particles are often agglomerated in the base liquid, it is expected that the dispersion condition of nano-particles in the base liquid has some impact on the formation process of the nano-particle layer and consequently the value of CHF. In this experimental work, systematic investigation was carried out for the effect of the particle dispersion condition in the base liquid on the CHF and the heat transfer coefficient in nucleate pool boiling of water-based nanofluids. In the present experiments using TiO2 nanofluids as the test fluid, the CHF was not influenced significantly by the particle dispersion condition whilst noticeable deterioration of the boiling heat transfer took place only in the case of fine particle dispersion. (author)
During the process of setting and hardening in concrete, the temperature profile shows a gradual nonlinear distribution due to the development of heat of hydration in cement. At early ages of concrete structures, this nonlinear distribution can have a large influence on crack evolution. It is thus important to obtain an accurate temperature history, and to do this, it is necessary to examine the thermal properties of the concrete. In this study, the convective heat transfer coefficient, which represents the heat transfer between a concrete surface and ambient air, was experimentally investigated with test variables such as the velocity of wind, the curing conditions, and the ambient temperature. For analyses using the thermal equilibrium boundary condition, it is generally noted that most of the heat release by the evaporation of moisture occurs at an early stage. To consider this phenomenon, the existing thermal equilibrium boundary condition has been modified so as to consider the evaporation quantity due to the evaporation effect. Convective heat transfer coefficients for a specific case were then calculated from the modified thermal equilibrium boundary condition using experimental results
BoÅ¾idar LiÅ¡ÄiÄ‡
2012-02-01
Full Text Available This paper explains the need for a database of cooling intensities for liquid quenchants, in order to predict the quench hardness, microstructure, stresses and distortion, when real engineering components of complex geometry are quenched. The existing laboratory procedures for cooling intensity evaluation, using small test specimens, and Lumped-Heat-Capacity Method for calculation of heat transfer coefficient, are presented. Temperature Gradient Method for heat transfer calculation in workshop conditions, when using the Liscic/Petrofer probe, has been elaborated. Critical heat flux densities and their relation to the initial heat flux density, is explained. Specific facilities for testing quenching intensity in workshop conditions, are shown. The two phase project of the International Federation for Heat Treatment and Surface Engineering (IFHTSE, as recently approved, is mentioned.
Mass transport effect on the heat transfer coefficient during boiling of multicomponent mixture
Krupiczka, Roman; Rotkegel, Adam; Ziobrowski, Zenon [Polish Academy of Sciences, Institute of Chemical Engineering, Gliwice (Poland)
2009-05-15
In this work a simplified calculation method taking into account the effect of mass transport on the heat transfer coefficient (HTC) during boiling of multicomponent mixture has been elaborated. The calculation results were compared with own experimental data for ternary system methanol-isopropanol-water and Grigoriev data [1] (acetone-methanol-water). The experiments were performed in different hydrodynamic conditions such as: pool boiling and liquid evaporation at the free surface of the falling film. The experimental data covered wide range of heat fluxes from 6 to 30 kW/m{sup 2} in the case of liquid evaporation from the falling film and from 30 to 240 kW/m{sup 2} for pool boiling. The analysis of the results indicates that the mass transfer resistance in the liquid phase caused a significant reduction of experimental value HTC in comparison to so-called ideal HTC. (orig.)
Di Natale, Francesco; Nigro, Roberto
2012-05-01
In this work, experimental values of local heat transfer coefficients around a horizontal cylinder immersed in a bubbling fluidized bed are reported for three types of bed materials classified as Geldart B particles, fluidized with air at ambient pressure and temperature. Results are interpreted in light of a model for heat transfer coefficient in order to estimate the time-average bed porosity profile close to the exchange surface. These angular profiles of bed porosity are compared with former experiments to verify the correctness of the adopted model, and are used to provide a physical interpretation of the experimental results.
Heat transfer from rough surfaces
The transformation of the friction data obtained with experiments in annuli can be performed either with the assumption of universal logarithmic velocity profile or of an universal eddy momentum diffusivity profile. For the roughness of practical interest both methods, when properly applied, give good results. For these roughnesses the transformed friction factors seem not to be unduly affected if one assumes a constant slope of the velocity profile equal to 2.5. All the transformation methods of the heat transfer data so far proposed predict too high wall temperatures in the central channels of a 19-rod bundle with three-dimensional roughness. Preliminary calculations show that the application of the superimposition principle with the logarithmic temperature profiles gives good results for the three-dimensional roughness as well. Although the measurements show that the slope of the logarithmic temperature profiles is different from 2.5, the assumption of a constant slope equal to 2.5 does not affect the transformed heat transfer data appreciably. For moderately high roughness ribs the turbulent Prandtl number, averaged over the cross section of a tube, is about the same (approx. 0.8) for rough as for smooth surfaces. The temperature effect on the heat transfer data with air cooling is stronger than originally assumed in the general correlation of Dalle Donne and Meyer. With helium cooling this temperature effect is even stronger. (orig.)
A Comparative Study of Heat Transfer Coefficients for Film Condensation
Wei, Xiaoyong; Fang, Xiande; Rongrong SHI
2012-01-01
Film condensation heat transfer has wide applications in a variety of industrial systems. A number of film condensation heat transfer correlations (FCHTCs) have been proposed. However, their predictions are often inconsistent. This paper presents a comparative study of existing FCHTCs. Totally 1214 experimental data points are obtained from 10 published papers, and 14 FCHTCs are reviewed, among which four correlations are used for horizontal flow outside smooth tubes, three for flow ...
The tritium bred in a DT fusion reactor is taken out of its blanket using helium sweep gas. The cryosorption bed using molecular sieves or activated carbon at liquid nitrogen temperature is attractive for recovery of this tritium from the view point of adsorption capacity and pressure of tritium at release. The mass transfer coefficients required to predict the breakthrough curve are discussed in this paper. The surface diffusivity included in one of them is quantitated. Its value is dependent on the adsorption site. The rate controlling step changes with the equilibrium partial pressure of the hydrogen isotope, because the mass transfer coefficient representing the intraparticle diffusion decreases with increasing equilibrium pressure. The mass transfer coefficients in desorption are estimated to be the same as those in adsorption. 6 refs., 8 figs., 1 tab
Two-phase flow heat transfer has been exhaustively studied over recent years. However, in this field several questions remain unanswered. Heat transfer coefficient prediction related to nucleate and convective boiling have been studied using different approaches, numerical, analytical and experimental. In this work, an experimental analysis, data representation and heat transfer coefficient prediction on two-phase heat transfer on nucleate and convective boiling are presented. An empirical correlation is obtained based on genetic algorithms search engine over a dimensional analysis of the two-phase flow heat transfer problem. (author)
The usage of transfer coefficients to describe radionuclide transport from a cow's diet to its milk
The terms 'transfer coefficient', 'transfer function' and 'transfer rate' are used to describe the transport of radionuclides from a cow's diet to her milk. Simple derivation of these parameters, their interpretations and interrelationships are given, and possible misinterpretations of published values due to imprecise definitions or incorrectly supplied or omitted units are reviewed. (author)
Most of the previous convection experiments for nanofluids have been performed for internal tube flow with constant heat flux boundary condition. In contrast, a simple experimental apparatus measuring convective heat transfer coefficient from a heated wire to external nanofluids is proposed and its working principles are explained in detail. The convective heat transfer coefficient provided by the present system might be used as a useful indication justifying the adoption of prepared nanofluids as new efficient heat transfer fluids. Validation experiments by comparing convective heat transfer coefficients between the conventional correlation and measured values are carried out for base fluids. Also the effect of increased thermal conductivity of nano lubrication oil on the enhancement of convective heat transfer coefficient is investigated
Estimating the workpiece-backingplate heat transfer coefficient in friction stirwelding
Larsen, Anders; Stolpe, Mathias; Hattel, Jesper Henri
2012-01-01
Purpose - The purpose of this paper is to determine the magnitude and spatial distribution of the heat transfer coefficient between the workpiece and the backingplate in a friction stir welding process using inverse modelling. Design/methodology/approach - The magnitude and distribution of the heat...... yields optimal values for the magnitude and distribution of the heat transfer coefficient. Findings - It is found that the heat transfer coefficient between the workpiece and the backingplate is non-uniform and takes its maximum value in a region below the welding tool. Four different parameterisations...... 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...
Evaluation of the heat transfer coefficient in thermal shock of alumina disks
Disks of a high-purity commercial alumina powder were fabricated by slip casting, pre-calcined, sintered and machined with SiC paper (120 and 320 grit). The specimens were tested in thermal shock conditions from several temperatures (Ti) between 870 and 980 C using a high-velocity air jet at room temperature (T0). The temperature differential between the disk and the air jet was incremented in 10 C until crack propagation was detected. During the air impinging, the temperature was recorded on the lower specimen surface at the central point and at a peripheral one. The coefficient governing the convective heat transfer on the specimen surface, h, was estimated by fitting the calculated temperature profiles with those measured during the test. Three alternative models were proposed for the temperature calculations using a finite element analysis. (orig.)
Measurement of heat transfer coefficient using termoanemometry methods
DanÄovÃ¡, Petra; Sitek, P.; VÃt, T.
Liberec : Technical University of Liberec, 2013 - (VÃt, T.; DanÄovÃ¡, P.; NovotnÃ½, P.), s. 152-155 ISBN 978-80-260-5375-0. [Experimental Fluid Mechanics 2013. KutnÃ¡ hora (CZ), 19.11.2013-22.11.2013] Institutional support: RVO:61388998 Keywords : syntetic jet * thermoanemometry * heat transfer Subject RIV: BJ - Thermodynamics
Measurement of the Convective Heat-Transfer Coefficient
Conti, Rosaria; Gallitto, Aurelio Agliolo; Fiordilino, Emilio
2014-01-01
We propose an experiment for investigating how objects cool down toward the thermal equilibrium with their surroundings. We describe the time dependence of the temperature difference of the cooling objects and the environment with an exponential decay function. By measuring the thermal constant t, we determine the convective heat-transfer…
M. E. Taslim
2007-08-01
Full Text Available Heat transfer coefficients in the cooling cavities of turbine airfoils are greatly enhanced by the presence of discrete ribs on the cavity walls. These ribs introduce two heat transfer enhancing features: a significant increase in heat transfer coefficient by promoting turbulence and mixing, and an increase in heat transfer area. Considerable amount of data are reported in open literature for the heat transfer coefficients both on the rib surface and on the floor area between the ribs. Many airfoil cooling design software tools, however, require an overall average heat transfer coefficient on a rib-roughened wall. Dealing with a complex flow circuit in conjunction with 180Ã¢ÂˆÂ˜ bends, numerous film holes, trailing-edge slots, tip bleeds, crossover impingement, and a conjugate heat transfer problem; these tools are not often able to handle the geometric details of the rib-roughened surfaces or local variations in heat transfer coefficient on a rib-roughened wall. On the other hand, assigning an overall area-weighted average heat transfer coefficient based on the rib and floor area and their corresponding heat transfer coefficients will have the inherent error of assuming a 100% fin efficiency for the ribs, that is, assuming that rib surface temperature is the same as the rib base temperature. Depending on the rib geometry, this error could produce an overestimation of up to 10% in the evaluated rib-roughened wall heat transfer coefficient. In this paper, a correction factor is developed that can be applied to the overall area-weighted average heat transfer coefficient that, when applied to the projected rib-roughened cooling cavity walls, the net heat removal from the airfoil is the same as that of the rib-roughened wall. To develop this correction factor, the experimental results of heat transfer coefficients on the rib and on the surface area between the ribs are combined with about 400 numerical conduction models to determine an overall equivalent heat transfer coefficient that can be used in airfoil cooling design software. A well-known group method of data handling (GMDH scheme was then utilized to develop a correlation that encompasses most pertinent parameters including the rib geometry, rib fin efficiency, and the rib and floor heat transfer coefficients.
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)
The object of the experiments was to choose suitable particulate materials for a fluidised bed cooler, to test a deep fluidised bed for uniformity of heat transfer coefficient, and to explore the temperature distribution in a centrally heated annular fluidised bed. This memorandum records the techniques used and some of the practical aspects involved, together with the performance results obtained, for the assistance of other experimenters who may wish to use fluidised beds as a laboratory technique. Mathematical correlation of the results has not been attempted since some of the properties of the bed material were not known and to determine them was beyond the scope of the work programme. Rather, we have compared our results with those of other experimenters. Graphite tubes, for use in steady state thermal stress experiments, are to be heated by a graphite radiant heater situated in the bore and cooled on the outer surface. The tubes are 2 cm. bore, 8 cm. outside diameter and 48 cm. long. The outside temperature of the tubes is to be between 500 deg. C. and 1500 deg. C. It is estimated that the heat transfer rate required for fracture at the outer surface is 30 watts/cm2. This could readily be achieved by cooling with liquid metals, water or high velocity gas. However, serious problems of either materials compatibility or mechanical complexity make these undesirable. A water-cooled fluidised bed of compatible solids fluidised with nitrogen gas can overcome most of these problems and give heat transfer coefficients close to that required, vis. about 0.1 w/cm C . A coolant bed about 20'' long would be required and an annulus of about 2'' radial width round the specimen was considered to be practicable
137Cs transfer coefficients from fodder to cow milk
The transfer of 137Cs from the components of cows' diets to milk was followed in detail on 10 farms in the north-eastern region of Italy (Friuli-Venezia Giulia) from June to July 1988. Samples of milk, grass and other components of the cows' diet were collected regularly and analysed for radiocaesium content. The transfer factors, calculated for 137Cs after a four-week feeding period with contaminated silage, were higher (0.0064) than those calculated in 1987 in the same area (0.0030). This may be attributable to the fact that the 137Cs associated to the forage administrated to cows in 1988 was completely incorporated in the plant and thus more assimilable to the cattle. (Author)
Accurate modeling of thermal shock induced stresses has become ever most important to emerging accident-tolerant ceramic cladding concepts, such as silicon carbide (SiC) and SiC coated zircaloy. Since fractures of ceramic (entirely ceramic or coated) occur by excessive tensile stresses with linear elasticity, modeling transient stress distribution in the material provides a direct indication of the structural integrity. Indeed, even for the current zircaloy cladding material, the oxide layer formed on the surface - where cracks starts to develop upon water quenching - essentially behaves as a brittle ceramic. Hence, enhanced understanding of thermal shock fracture of a brittle material would fundamentally contribute to safety of nuclear reactors for both the current fuel design and that of the coming future. Understanding thermal shock fracture of a brittle material requires heat transfer rate between the solid and the fluid for transient temperature fields of the solid, and structural response of the solid under the obtained transient temperature fields. In water quenching, a solid experiences dynamic time-varying heat transfer rates with phase changes of the fluid over a short quenching period. Yet, such a dynamic change of heat transfer rates during the water quenching transience has been overlooked in assessments of mechanisms, predictability, and uncertainties for thermal shock fracture. Rather, a time-constant heat transfer coefficient, named 'effective heat transfer coefficient' has become a conventional input to thermal shock fracture analysis. No single constant heat transfer could suffice to depict the actual stress evolution subject to dynamic heat transfer coefficient changes with fluid phase changes. Use of the surface temperature dependent heat transfer coefficient will remarkably increase predictability of thermal shock fracture of brittle materials and complete the picture of stress evolution in the quenched solid. The presented result with Al2O3 shows stress prediction around - 90% of the actual fracture stress with the use of the actual surface temperature dependent heat transfer coefficient. Hence, this work formerly informs thermal shock community that the surface temperature dependent heat transfer coefficient h(Ts) should be used for thermal shock fracture analysis and prediction. Yet, it is remarkable to note how widely, without technical consciousness, the use of a constant heat transfer coefficient has been practiced in the field of thermal shock fracture studies. A surface temperature dependent heat transfer coefficient h(Ts) is dependent on a number of parameters, including water bath temperature, pressure, specimen size and shape, and surface characteristics including wettability, nucleation site density, and pore structures. Hence, for a thermal shock fracture analysis, those non-strength related thermal shock fracture parameters should be accounted in h(Ts). Consequently, increasing efforts should be made on understanding transient boiling heat transfer rates of brittle materials to advance our understanding of thermal shock fracture, which will fundamentally contribute to safety of nuclear reactors
Lee, Youho; Lee, Jeong Ik; Cheon, Hee [KAIST, Daejeon (Korea, Republic of)
2015-05-15
Accurate modeling of thermal shock induced stresses has become ever most important to emerging accident-tolerant ceramic cladding concepts, such as silicon carbide (SiC) and SiC coated zircaloy. Since fractures of ceramic (entirely ceramic or coated) occur by excessive tensile stresses with linear elasticity, modeling transient stress distribution in the material provides a direct indication of the structural integrity. Indeed, even for the current zircaloy cladding material, the oxide layer formed on the surface - where cracks starts to develop upon water quenching - essentially behaves as a brittle ceramic. Hence, enhanced understanding of thermal shock fracture of a brittle material would fundamentally contribute to safety of nuclear reactors for both the current fuel design and that of the coming future. Understanding thermal shock fracture of a brittle material requires heat transfer rate between the solid and the fluid for transient temperature fields of the solid, and structural response of the solid under the obtained transient temperature fields. In water quenching, a solid experiences dynamic time-varying heat transfer rates with phase changes of the fluid over a short quenching period. Yet, such a dynamic change of heat transfer rates during the water quenching transience has been overlooked in assessments of mechanisms, predictability, and uncertainties for thermal shock fracture. Rather, a time-constant heat transfer coefficient, named 'effective heat transfer coefficient' has become a conventional input to thermal shock fracture analysis. No single constant heat transfer could suffice to depict the actual stress evolution subject to dynamic heat transfer coefficient changes with fluid phase changes. Use of the surface temperature dependent heat transfer coefficient will remarkably increase predictability of thermal shock fracture of brittle materials and complete the picture of stress evolution in the quenched solid. The presented result with Al{sub 2}O{sub 3} shows stress prediction around - 90% of the actual fracture stress with the use of the actual surface temperature dependent heat transfer coefficient. Hence, this work formerly informs thermal shock community that the surface temperature dependent heat transfer coefficient h(T{sub s}) should be used for thermal shock fracture analysis and prediction. Yet, it is remarkable to note how widely, without technical consciousness, the use of a constant heat transfer coefficient has been practiced in the field of thermal shock fracture studies. A surface temperature dependent heat transfer coefficient h(T{sub s}) is dependent on a number of parameters, including water bath temperature, pressure, specimen size and shape, and surface characteristics including wettability, nucleation site density, and pore structures. Hence, for a thermal shock fracture analysis, those non-strength related thermal shock fracture parameters should be accounted in h(T{sub s}). Consequently, increasing efforts should be made on understanding transient boiling heat transfer rates of brittle materials to advance our understanding of thermal shock fracture, which will fundamentally contribute to safety of nuclear reactors.
Van Treuren, K.W.; Wang, Z.; Ireland, P.T.; Jones, T.V. (Univ. of Oxford (United Kingdom). Dept. of Engineering Science)
1994-07-01
A transient method of measuring the local heat transfer under an array of impinging jets has been developed. The use of a temperature-sensitive coating consisting of three encapsulated thermochromic liquid crystal materials has allowed the calculation of both the local adiabatic wall temperature and the local heat transfer coefficient over the complete surface of the target plate. The influence of the temperature of the plate through which the impingment gas flows on the target plate heat transfer has been quantified. Results are presented for a single in-line array configuration over a range of jet Reynolds numbers.
Hoelzer, Karin; Pouillot, Régis; Gallagher, Daniel; Silverman, Meryl B; Kause, Janell; Dennis, Sherri
2012-07-01
Listeria monocytogenes is readily found in the environment of retail deli establishments and can occasionally contaminate food handled in these establishments. Here we synthesize the available scientific evidence to derive probability distributions and mathematical models of bacterial transfers between environmental surfaces and foods, including those during slicing of food, and of bacterial removal during cleaning and sanitizing (models available at www.foodrisk.org). Transfer coefficients varied considerably by surface type, and after log(10) transformation were best described by normal distributions with means ranging from -0.29 to -4.96 and standard deviations that ranged from 0.07 to 1.39. 'Transfer coefficients' during slicing were best described by a truncated logistic distribution with location 0.07 and scale 0.03. In the absence of protein residues, mean log inactivation indicated a greater than 5 log(10) reduction for sanitization with hypochlorite (mean: 6.5 log(10); 95% confidence interval (CI): 5.0-8.1 log(10)) and quaternary ammonium compounds (mean: 5.5 log(10); 95% CI: 3.6-7.3 log(10)), but in the presence of protein residues efficacy reduced dramatically for hypochlorite (mean: 3.8 log(10); 95% CI: 2.1-5.4 log(10)) as well as quaternary ammonium compounds (mean: 4.4log(10); 95% CI: 2.5-6.4 log(10)). Overall, transfer coefficients are therefore low, even though cross-contamination can be extremely efficient under certain conditions. Dozens of food items may consequently be contaminated from a single contaminated slicer blade, albeit at low concentrations. Correctly performed sanitizing efficiently reduces L. monocytogenes contamination in the environment and therefore limits cross-contamination, even though sanitization is only performed a few times per day. However, under unfavorable conditions reductions in bacterial concentration may be far below 5 log(10). The probability distributions and mathematical models derived here can be used to evaluate L. monocytogenes cross-contamination dynamics in environments where foods are handled, and to assess the potential impact of different intervention strategies. PMID:22704063
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.
Study of Oxygen Mass Transfer Coefficient in Microbial Leaching of Uranium
Oxygen mass transfer coefficient is one of the most important parameters in the design of aerobic process bioreactor, which is represented by the overall volumetric oxygen mass transfer. The purpose of this article was the investigation of the mass transfer coefficient in the vast range of operational parameters in a stirred tank reactor. The effects of cell concentration, stirred power consumption and apparent air velocity on the mass transfer coefficient show that oxygen mass transfer in microbial leaching of uranium and in this range of parameter is not limited in these experiments. The overall volumetric oxygen mass transfer was determined in the range of 36-84 hr-1. Agreements of the suggested mathematical correlation for predicting the mass transfer were also evaluated. The results showed that the equation based on the rpm and/or power consumption and apparent air velocity specifies a good agreement with the experimental results with the coefficient of determination of R2=94.2 and 93.4. It was concluded that the introduced models are suitable for evaluation of the mass transfer coefficient in the microbial leaching of uranium.
Measurement of Average Pool Boiling Heat Transfer Coefficient on Near-Horizontal Tube
An experimental study is performed to obtain an average heat transfer coefficient around the perimeter of a near horizontal tube. For the test a stainless steel tube of 50.8 mm diameter submerged in water at atmospheric pressure is used. Both subcooled and saturated pool boiling conditions are considered and the inclination angle of the tube is changed from the horizontal position to 9 .deg. in steps of 3 .deg.. In saturated water, the local boiling heat transfer coefficient at the azimuthal angle of 90 .deg. from the tube bottom can be regarded as the average of the coefficients regardless of the tube inclination angles. However, when the water is subcooled the location for the average heat transfer coefficient depends on the inclination angle and the heat flux. It is explained that the major mechanisms changing the heat transfer are closely related with the intensity of the liquid agitation and the generation of big size bubbles through bubble coalescence
Kadhim S. K.
2016-01-01
Full Text Available The aim of this work is to investigate experimentally the effect of the forced vibrations on the free convection heat transfer coefficient using heated longitudinally finned cylinder made of Aluminium. The effect of the vibration frequency ranged from 2 to16 Hz with various heat fluxes ranged from 500-1500 W/m2. It was found that, the relation between the heat transfer coefficient and amplitude of vibration increased for all inclination angles from (0Â°-45Â°, while the increment of inclination angle decreases the values of convection heat transfer coefficient. The results show that the heat transfer coefficient ratio (hv/ho of longitudinal finned cylinders in (0Â° angle was (8% and (30% greater than those for the (30Â° and (45Â° respectively.
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.
Aliaga, David Alfredo
Convective heat transfer over ribbed surfaces is a very complex process that requires detailed measurements for further understanding. Recent developments in infrared detector designs, optical attachments and computer and video capabilities have produced accurate infrared thermography systems with the spatial resolution required to obtain local heat transfer measurements on surfaces of complex geometry. Thus infrared thermography represents an attractive alternative to existing methods for heat transfer measurements (i.e. thermocouples, naphthalene sublimation, or liquid crystal measurements). The present investigation describes a new experimental method which uses infrared thermography in a subsonic wind tunnel to obtain detailed temperature measurements over ribbed plates with constant heat flux. The infrared system used in this study incorporated an infrared detector with a closed cycle microcooler which permitted the infrared camera to be positioned at arbitrary viewing angles. This flexibility permitted direct observations of the ribbed surface without the use of reflective optics that would have increased the inaccuracy of the procedure. Reference thermocouples placed at strategic locations over the ribbed plates were used to correct temperature readings of the infrared system in order to minimize measurement errors. Three ribbed plates were tested. Plates A and B had ribs of square cross section. The rib spacing (pitch) on plate A was designed so that regions of separation and reattachment would occur on the plate between ribs whereas plate B was designed to produce only regions of separation and recirculation. Plate C was constructed as an improved version of plate A and included trapezoidal ribs. The rib height and pitch on plate C was the same as on plate A. The trapezoidal shape of the rib for plate C was designed to minimize the recirculation regions in the front and back of the ribs while allowing reattachment at the base surface of the plate. Local heat transfer coefficients surrounding the ribs are presented and comparisons between plates are drawn. It is shown that the new method of heat transfer measurement is able to detect numerous small scale features of the complex flow field and consequent heat transfer distribution around ribs of arbitrary shape.
HengLiang Zhang; Shi Liu; Danmei Xie; Yangheng Xiong; Yanzhi Yu; Yan Zhou; Rui Guo
2013-01-01
Thermal stress failure caused by alternating operational loads is the one of important damage mechanisms in the nuclear power plants. To evaluate the thermal stress responses, the Green’s function approach has been generally used. In this paper, a method to consider varying heat transfer coefficients when using the Green’s function method is proposed by using artificial parameter method and superposition principle. Time dependent heat transfer coefficient has been treated by using a modified ...
M. Pakdemirli; Sahin, A.
2006-01-01
A nonlinear fin equation in which thermal conductivity is an arbitrary function of temperature and, heat transfer coefficient is an arbitrary function of spatial variable is considered. Scaling transformation is applied to the equations to determine the specific forms of these functions for which the equation admits such type of transformation. It is found that for arbitrary heat conduction function, scaling transformation exists for an inverse square heat transfer coefficient. Selecting also...
Lauret, Philippe; Miranville, Frédéric; Boyer, Harry; Garde, Francois; Adelard, Laetitia
2006-01-01
This paper deals with the application of Bayesian methods to the estimation of two convective heat transfer coefficients of a roof-mounted radiant barrier system (RBS). As part of an empirical validation of the thermal model of the roofing complex, a parametric sensitivity analysis highlighted the importance of convective coefficients in the thermal behavior of a roofing complex. A parameter estimation method is then used in order to find the values of the coefficients that lead to an improve...
Measurement and Prediction of the Average Heat Transfer Coefficient on a Tube
Most results are for horizontal tubes of diameter ranging 7.6âˆ¼51 mm. Only Seethes et al. studied variations in local heat transfer coefficients along the tube periphery while controlling the inclination angle. The main result of the previous investigations is that there is a considerable difference among the local heat transfer coefficients along a tube periphery. This has been the major cause of the discrepancy among the results. It is very important to predict the exact heat transfer coefficient on a tube for the thermal design of tubular type heat exchangers. No results have been reported about the way to predict the average value on a tube except Kang who suggested a method for the horizontal tube. The present study is aimed to find out a way of predicting the average heat transfer coefficient with considering the degree of subcooling and the inclination angle. The average heat transfer coefficient was observed at Î¸ =90 .deg in the saturated water regardless of the tube inclination angle. However, as the water was subcooled the location for the average heat transfer coefficient moves to the lower region of the tube
Transfer coefficients have become virtually indispensible in the study of the fate of radioisotopes released from nuclear installations. These coefficients are used in equilibrium assessment models where they specify the degree of transfer in food chains of individual radioisotopes from soil to plant products and from feed or forage and drinking water to animal products and ultimately to man. Information on transfer coefficients for terrestrial food chain models is very piecemeal and occurs in a wide variety of journals and reports. To enable us to choose or determine suitable values for assessments, we have addressed the following aspects of transfer coefficients on a very broad scale: (1) definitions, (2) equilibrium assumption, which stipulates that transfer coefficients be restricted to equilibrium or steady rate conditions, (3) assumption of linearity, that is the idea that radioisotope concentrations in food products increase linearly with contamination levels in the soil or animal feed, (4) methods of determination, (5) variability, (6) generic versus site-specific values, (7) statistical aspects, (8) use, (9) sources of currently used values, (10) criteria for revising values, (11) establishment and maintenance of files on transfer coefficients, and (12) future developments. (auth)
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.
Investigation of heat transfer coefficient during quenching in various cooling agents
Highlights: â€¢ The highest HTC during quenching in mineral oils occur in temperature 520â€“550 Â°C. â€¢ The peaks of HTC for polymers exist at lower temperature compared to mineral oils. â€¢ Temperature and utilization time of coolant affect the heat transfer coefficient. â€¢ Ageing of mineral oils affects their severities; a direction of change is equivocal. -- Abstract: Heat transfer coefficients, HTCs, at the surface of a metal sample during immersion quenching were measured and evaluated using numerical procedures. The boundary inverse heat conduction problem has been defined and solved. A FEM self-developed computer code has been used to obtain a solution to the direct problem. The sensitivity of the method enabled us to examine the effect of various quenching parameters on the heat transfer for two mineral oils and a polymer quenchant. At 800 Â°C the HTC values were equal to âˆ¼0.5 kW/(m2 K) and âˆ¼3.2 kW/(m2 K), for mineral oils and a polymer coolant, respectively. They increased to âˆ¼4.7 kW/(m2 K) â€“ oil A, âˆ¼6.0 kW/(m2 K) â€“ oil B and âˆ¼7.4 kW/(m2 K) â€“ polymer, respectively. The peak of HTC was sharp and occurred at a narrow temperature interval between 520 and 550 Â°C for the oils, whereas for the polymer, the peak was lower by approx. 100 K and flat over 100â€“120 K interval. Subsequently HTC decreased, and at âˆ¼150 Â°C the values were âˆ¼0.5 kW/(m2 K) and âˆ¼2.0 kW/(m2 K), for mineral oils and a water polymer coolant, respectively
Sputtered metal source for rate coefficient measurements of asymmetric charge transfer reactions
Complete text of publication follows. Asymmetric charge transfer (ACT) reactions between noble gas ions and metal atoms play an important role in numerous glow discharge applications. Due to the sputtering effect of ions impinging on the cathode surface significant metal density can be created in the cathode area of dc noble gas discharges. These metal atoms are then ionized and excited in the negative glow region, which is utilized in glow discharge spectroscopy (GDS) applications. ACT represents an important source of excited metal ions in the negative glow. Numerical modeling of the cathode region of a sputtering discharge requires rate coefficient values of ACT reactions as input data [Bogaerts et al. J. Anal. Atom. Spectrom. 11 (1996) 841]. There are rate coefficient values available in the literature only for volatile metals - in combination with different noble gas ions - that can be evaporated at relatively low temperatures (e.g. Hg, Zn, Cd etc.). However, data for other metals (Cu, Fe, Ag, etc.) have not been measured yet. The aim of this work is to build a metal source that can be applied for rate coefficient measurements of ACT reactions. The new sputtered metal source operates at room temperature creating homogeneous spatial distribution of metal atoms in a 9 cm3 region. Four hollow-cathode discharges - placed symmetrically around the central region - provide the needed metal density in the order of 5 x 1011 cm-3 as determined by atomic absorption spectroscopy. The future work focuses on the ACT rate coefficient measurements. The authors kindly acknowledge the support by the MRTN-CT-035459.
A new interpretation of internal heat transfer coefficients of porous media
Dybbs, A.; Kar, K.; Groeneweg, M.; Ling, J. X.; Naraghi, M.
1984-01-01
The results of laser anemometer and flow visualization based fluid mechanics studies of porous media are used to obtain heat transfer coefficients for porous materials. Average pore flow Re ranging from 0.16-700 were examined. Darcy, inertial steady laminar, unsteady laminar and turbulent flow regimes were detected. A passage length model was devised to derive the heat transfer coefficient. Sample data from flows through porous metals composed of powders and fibers validated the passage length for Darcy and inertial flow regimes. Unsteady laminar and turbulent flow coefficients require the identification of new parameters.
Heat Transfer Coefficient Analysis for Coolant Channels in a VHTR
A very high temperature reactor (VHTR) is graphite moderated and helium cooled reactor and selected as a next generation nuclear reactor for its ultimate safety among various advantages. This type reactor has become of great interest in terms of using a process heat. To utilize VHTR safely and practically, optimized heat flux analysis is necessary. Empirical correlations for a Nusselt number have widely been applied to predict the convective heat transfer in coolant channels of a prismatic VHTR. This approach has advantages of fast computation. However, there has been no in-depth study on their applicability to the thermo-fluid conditions of coolant channels of a prismatic VHTR. Therefore, this paper investigates the applicability of well-known empirical correlations to the coolant channels of a prismatic VHTR by using the detailed numerical results obtained from the 3-D computational fluid dynamics (CFD) analysis. In particular, the effect of two different wall heating condition on the applicability of empirical correlations is focused in this paper
Study of the measurement about the apparent heat transfer coefficient of solid uranium hexafluoride
In order to provide the conditions for designing the congealed accept container of uranium hexafluoride, a set of experiment system of measuring apparent heat transfer coefficient in which the small-sized congealed accept container was considered as main equipment was set up. Then the experiments of loading and unloading uranium hexafluoride were carried out. The process of loading and unloading uranium hexafluoride in small-sized congealed accept container were simulated by the barrel model of steady heat transfer in this paper, and the apparent heat transfer coefficient of solid uranium hexafluoride was obtained. (authors)
Balkan, F.; Sezar, M.H.
2007-01-01
It is shown that there exists an optimal spacing of thermo-sensors in the determination of the experimental heat transfer coefficient of a fluid flowing over a plate. The problem is considered as an inverse heat transfer problem with long thin fin model. The heat transfer coefficient of the fluid is estimated from simulated steady-state temperature measurements along the plate. It is shown theoretically that the inner product of the sensitivity vector, JTJ, should be maximum and the group m n...
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
2015-08-01
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.
Ã–zdemir Mustafa
2015-01-01
Full Text Available In this study, the heat transfer mechanism under agitated pool boiling was examined experimentally. Aqueous sugar solutions were used in a centrically agitated vessel. The effects of the gap which is between the impeller edge and the flat bottom of the agitated vessel, the rotational impeller speed and impeller size were studied on the boiling heat transfer coefficient. A new Nusselt function depending on the Peclet number was suggested for the heat transfer mechanism.
This paper presents a procedure for determining the transient heat transfer coefficient in cylindrical, thick-walled pressure parts. From theoretical considerations, the temperatures can be predicted at discrete locations throughout the wall, when input data such as thermocouple responses are known at one or several interior locations. Special emphasis is placed on the dynamic response of the thermometer, which measures the temperature, of the inside fluid, to enable exact determination of both heat transfer coefficient and fluid temperature. The transient response of a thermocouple in a convectional thermowell (pocket) is described by the first-order convective heat transfer model in which the rate of thermoelement temperature change is proportional to the instantaneous difference between the thermoelement and fluid temperatures. Several numerical examples show the effect of different time constants or thermal capacitances of thermometers on the calculated heat transfer coefficients and fluid temperatures. (orig.)
Dynamics of liquid nitrogen cooling process of solid surface at wetting contact coefficient
Smakulski, P.; Pietrowicz, S.
2015-12-01
Liquid cryogens cooling by direct contact is very often used as a method for decreasing the temperature of electronic devices or equipment i.e. HTS cables. Somehow, cooldown process conducted in that way could not be optimized, because of cryogen pool boiling characteristic and low value of the heat transfer coefficient. One of the possibilities to increase the efficiency of heat transfer, as well as the efficiency of cooling itself, it is to use a spray cooling method. The paper shows dynamics analysis of liquid nitrogen cooling solid surface process. The model of heat transfer for the single droplet of liquid nitrogen, which hits on a flat and smooth surface with respect to the different Weber numbers, is shown. Temperature profiles in calculation domains are presented, as well as the required cooling time. The numerical calculations are performed for different initial and boundary conditions, to study how the wetting contact coefficient is changing, and how it contributed to heat transfer between solid and liquid cryogen.
Prediction of overall heat transfer coefficient for RMI insulation using the test and analysis
Both parts of shell and layers have different thermal transfer flow; shell-part is conductivity loss, layer is convective and radiative loss that would contribute to calculate the total heat value with difficulty. We developed the new method about prediction of RMI's total value by separating the shell and layer as a function of heat resistivity. Whereas heat transfer value at the insulation shell is calculated by CFD analysis according to various insulation sizes, multi-layer would be done by thermal test. These predicted models are compared with final insulation sample of overall heat transfer value for the validation. RMI insulation was investigated by GHP (guarded hot plate) measuring instrument (inner-layer) and thermal analysis simulation(CFD method) to predict the approximate value of overall heat transfer. The results are as follows. - Thickness of out-shell as same meaning of outshell ratio is determined very carefully at RMI design. Because it can lead to very large changes in heat transfer. For example, whereas thickness of out-shell with 0.1mm(0.13%) shows 0.16 W/m2K through surface of out-shell, that of 0.4mm(0.53%) thickness is 0.49 W/m2K which is increased nonlinearly. - Inner-layer and out-shell of RMI is arranged in parallel, so that overall heat transfer coefficient would be written with sum of each part. For example, at the condition of 70 .deg. C, inner-layer part(0.06mm) is 0.56 W/m2K and out-shell part(0.7mm) is 0.72 W/m2K, and overall value is 1.28 W/m2K. - We could expect that heat transfer value is changed according to out-shell ratio, because out-shell ratio as conductivity loss is connected with insulation size and inner-layer as radiation blocking is independent
Tube length effect on the nucleate pool boiling heat transfer coefficient
The effect of a vertically installed condenser tube length on the nucleate pool boiling heat transfer under atmospheric pressure has been obtained using various combination of major parameters for application to the advanced light water reactors (e.g., passive residual heat removal system (PRHRS) heat exchanger of Westinghouse AP600 and passive secondary condensing system (PSCS) condenser of Korean Next Generation Reactor (KNGR)). To quantify length effect, a new empirical correlation has been developed based on the experimental data bank for the pool boiling heat transfer and some parametric studies have been done using the newly developed empirical correlation to broaden its applicability. The experimental data for q' versus ?T test are counted as 1,063 points and can cover the extent of D=14.0 ? 25.4 mm, ?=15.1 ? 60.9 mm, H=5.25 ? 30.93, and q'?160 kW/m2. The uncertainty in q', T, and ? is estimated to be ±1.0%, ±1.0, and ±5.0 nm, respectively. The newly developed empirical correlation has the form of q'=0.019?0.579?T4.679/(D1.238H0.072) and can predict the experimental data within ±20% bound. Through the detailed investigation of the experimental data and photographs taken from the experiment four mechanisms of (1) bubble generation and growth through the tube length, (2) bubble stay duration on the tube surface, (3) liquid agitation due to bubble detachment, and (4) bubble coalescence on the tube surface (especially, top region of the tube length) are considered as the most visible phenomena to explain the change of the heat transfer coefficient due to tube length change. The effect of the tube length is greatly observed before H(=L/D) gets 50. After that, the heat flux decreases linearly with H increase. (author)
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.
Estimation of grass to milk transfer coefficient for Strontium for emergency situations
The grass to milk transfer coefficient is usually represented as Fm values. This paper reports the results of grass to cow milk transfer coefficients (Fm) for Strontium for emergency situation. An experimental grass field was developed in Kaiga region and 2 cows were adopted for collecting milk samples regularly. Grass was cut from the field and spiked with very low concentration of stable Strontium, taken in the form of Sr(No3)2, to simulate a sudden deposition of Strontium on grass and fed to the adopted cows. The milk samples were collected during normal milking periods (morning and evening) for several days and analyzed. The peak concentration of Sr in milk was observed during time period 12-36 hrs after the intake of spiked grass. The mean value of transfer coefficient was found to be 1.4 x 10-3 d L-1. The grass to milk transfer coefficient values observed under spiked conditions were similar to that observed for equilibrium transfer coefficient for Kaiga region. (author)
This technique provides a method of obtaining average fuel to coolant heat transfer coefficients for individual fuel subassemblies in fast reactors. A series of experiments on the UK prototype fast reactor (PFR) over the period 1977-1979 have demonstrated that the technique is simple, requires no special instrumentation other than thermocouples to monitor coolant outlet temperatures, and the measurement can be made during normal reactor operation. Thus it is possible to determine how heat transfer coefficients change with operating conditions and with the degree of burn-up in the fuel. The analysis of a single experiment is presented to illustrate the technique. This was conducted at a single reduced power level of 200 thermal megawatts for two different primary coolant flow rates, both steady fractions of the maximum (0.88 and 0.47). Cyclic and single-step perturbations of about 10% amplitude were impressed on the steady power and the delayed coolant temperature response at subassembly outlets was monitored. Burn-ups in the subassemblies ranged between 1.0% and 4.7%. From the measured delays at the two flows it was possible to determine the fuel time-constant and hence the fuel-to-coolant heat transfer coefficient. It was also shown that a simple, lumped-element, heat transfer model can be used to obtain sufficiently accurate estimates from measurements at just one coolant flow. Fuel surface-to-coolant thermal conductances (i.e. gap conductances) were subsequently derived from the heat transfer coefficients. These ranged between 2.4 kW m-2K-1 and 3.3 kW m-2K-1 with the smaller conductances being obtained for those fuel elements with the larger degree of burn-up. These values are lower than expected but consistent with a higher than expected value for the negative power coefficient of reactivity feedback which has been observed at reduced power. (orig.)
In-reactor measurement of fuel-to-sheath heat transfer coefficients between UO2 and stainless steel
An experimental technique has been developed to measure the fuel-to-sheath heat transfer coefficient in operating UO2 fuel elements in a more direct manner than previously possible. During in-reactor operation, the thermal response of the fuel (measured by thermocouples placed near the outer surface of the UO2 pellets) and the dimensional response of the sheathing (measured by attached strain gauges) were monitored while varying either the element internal gas pressure or the element power. Detailed quantitative analysis yields both the solid and fluid components of fuel-to-sheath heat transfer as a function of gap width, gas pressure and composition, and interfacial pressure. (author)
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 ?g/cm2 and 0 to 25 ?g/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 ?g/cm2 for hexadecanol and 15 ?g/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.
Enhancement of pool boiling heat transfer by surface micro-structuring
The present paper addresses the use of surfaces structured with arrays of square micro-cavities to enhance pool boiling heat transfer. The heat transfer performance, obtained with the structured surfaces is evaluated based on the measured boiling curves and on the heat transfer coefficients. Two new parameters are suggested to relate the bubble dynamics (and consequently the surface topography) with the heat transfer coefficients: the modified dimensionless cavity spacing and the dimensionless distance, which cover the governing parameters of the phenomena. Correlations of these parameters with the heat transfer coefficients allowed to identify the best performing patterns, from those tested so far. Based on this progress it is expected that optimization of these relations will lead to precise relations which allow a systematic optimization of the surface pattern leading to an effective heat transfer enhancement, for situations involving high heat fluxes.
Rahbar-Kelishami Ahmad
2015-03-01
Full Text Available The calculation of column’s height plays an important role in packed columns precise design. This research is based on experimentally measurement of mass transfer coefficients in different heights of packed column to predict its height. The objective of presented work is to introduce a novel conceptual method to predict column height via new correlation for mass transfer coefficient. As the mass transfer coefficient is decreased with increase of column height, the HTU’s are not constant figures along the column so this new approach is called increasing HTU’s. The results of the proposed idea were compared with other correlations and the conventional method i.e. constant HTU’s. Since the results are in very good agreement with experimental data comparing to conventional method, it seems this approach can be a turning point in design of all differential columns like packed columns. Making use of this method is suggested for design of differential columns.
M. Torab-Mostaedi
2009-12-01
Full Text Available The volumetric overall mass transfer coefficients have been measured in a pulsed packed extraction column using diffusion model for two different liquid-liquid systems. The effects of operational variables such as pulsation intensity and dispersed and continuous phase flow rates on volumetric overall mass transfer coefficients have been investigated. Effective diffusivity is substituted for molecular diffusivity in the Gröber equation for prediction of dispersed phase overall mass transfer coefficients. The enhancement factor is determined experimentally and therefrom an empirical correlation is derived for prediction of effective diffusivity as a function of Reynolds number, Schmidt number and viscosity ratio. Good agreement between prediction and experiments was found for all operating conditions that were investigated.
Molecular dynamics calculation of the sticking coefficient of gases to surfaces
The Molecular dynamics method has been employed to calculate the sticking coefficient of He, Ar and CO2 molecules to the surface and of carbon clusters and to the graphite surface. The computed coefficients are compared with experimental results. (orig.)
Transfer coefficient study of Sr-90 in the soil-grass-milk chain for Cuba
One of the most important problems in modern radioecology is the lack of able information about the features of radionuclide migration in tropical and subtropical environment. The development of nuclear energy and the enhancing in the applications of nuclear techniques in those latitudes indicate that studies in this area are necessary. Cuba is carrying out studies on radioecological characterization of the principal food chains in the country. One of the objectives of these studies is to define the values of the transfer coefficients to be used in the evaluation programs for the assessment of the radiological impact of practices which involve ionizing radiation. This paper shows the results obtained in the determination of Sr-90 transfer coefficients in soil-grass-milk food chain in 'La Quebrada', a place near the Havana City where an important part of the milk that the citizens consume is produced. Transfer coefficients for Sr-90 were calculated on the basis of data collected during 5 years in the region. Soil-grass transfer coefficients are in the range 0.18-5 while grass-milk coefficients are in the range of 1.2x10-4 - 6x10-3 day/L. These values are in accordance with values reported by other authors in the literature. (authors). 4 refs., 2 tabs
Spin transfer coefficients for the (p suprho,n suprho) reaction in the plane wave approximation
Lee, H S; Kim, B T
1998-01-01
The spin transfer coefficients D sub n sub n (theta=0 .deg. ) for the intermediate energy charge exchange reaction (p suprho,n suprho) leading to the giant resonances in the continuum region are investigated. The dependence of the spin transfer coefficients on the nuclear wave function, the reaction Q-value, and the effective two-body interaction are studied using the plane wave approximation. It is shown that both the direct and the exchange parts of the tensor interaction play important roles in determining the D sub n sub n value.
Defining the transfer coefficient in electrochemistry: An assessment (IUPAC Technical Report)
Guidelli, Rolando; Compton, Richard G.; Feliu, Juan M.; Gileadi, Eliezer; Lipkowski, Jacek; Schmickler, Wolfgang; Trasatti, Sergio
2014-01-01
The transfer coefficient Î± is a quantity that is commonly employed in the kinetic investigation of electrode processes. In the 3rd edition of the IUPAC Green Book, the cathodic transfer coefficient Î±c is defined as â€“(RT/nF)(dlnkc/dE), where kc is the electroreduction rate constant, E is the applied potential, and R, T, and F have their usual significance. This definition is equivalent to the other, -(RT/nF)(dln|jc|/dE), where jc is the cathodic current density corrected for any changes in the...
Experimental determination of heat transfer coefficients in uranium zirconium hydride fuel rod
This work presents the experiments and theoretical analysis to determine the temperature parameter of the uranium zirconium hydride fuel elements, used in the TRIGA IPR-R1 Research Nuclear Reactor. The fuel thermal conductivity and the heat transfer coefficient from the cladding to the coolant were evaluated experimentally. It was also presented a correlation for the gap conductance between the fuel and the cladding. In the case of nuclear fuels the heat parameters become functions of the irradiation as a result of change in the chemical and physical composition. The value of the heat transfer coefficients should be determined experimentally. (author)
The determination of the heat transfer coefficient of the pins of the Spallation Neutron Source is a very important problem for the development of this facility, as data for thermal and structural studies. For this purpose, a test apparatus was built, in scale 1:1, for the simulation of the thermal and hydraulical conditions of the Neutron Source. This apparatus is a pin bank, with one of the pins electrically heated. Performance of measurements gave the values for the heat transfer coefficient, here presented in the Nusselt Number form, and its local distribution. Results show the linear dependence of Nusselt Number on Reynolds Number, for a constant heat production. (orig.)
Kadhim S. K.; Nasif M. S.
2016-01-01
The aim of this work is to investigate experimentally the effect of the forced vibrations on the free convection heat transfer coefficient using heated longitudinally finned cylinder made of Aluminium. The effect of the vibration frequency ranged from 2 to16 Hz with various heat fluxes ranged from 500-1500 W/m2. It was found that, the relation between the heat transfer coefficient and amplitude of vibration increased for all inclination angles from (0°-45°), while the increment of inclination...
Hydrogen is expected to serve as a clean secondary energy, because it can be manufactured from water, used in a variety of energy end-use sectors as fuel, and returned to water after burning. For the realization of hydrogen energy system, development of efficient and economical hydrogen production methods is required to meet the future huge demand of hydrogen. The Iodine-Sulfur (IS) process is a promising candidate of such hydrogen production methods, in which water reacts with iodine and sulfur dioxide to produce hydrogen iodide and sulfuric acid (Bunsen reaction) and the produced acids are then decomposed to produce hydrogen and oxygen, respectively. This study is concerned with the development of IS process equipment named direct contact sulfuric acid concentrator, in which gaseous mixture produced by thermal decomposition of sulfuric acid contacts directly with sulfuric acid solution. In the concentrator, the high temperature heat of the decomposed gas is recovered and used to concentrate sulfuric acid solution and, at the same time, the undecomposed sulfuric acid is condensed and separated from the decomposition products of sulfur dioxide and oxygen. Although the concept is very attractive from the viewpoint of the development of compact and efficient sulfuric acid concentrator, little is known on the heat and mass transfer relevant to the concentrator. Therefore, experimental methods were discussed to acquire the gas-phase mass transfer coefficient required for the optimal design of the concentrator. Assuming the use of wetted-wall column and also of the sulfuric acid of azeotropic composition as the test solution which could eliminate the liquid-phase mass transfer resistance, the column specification and the measurement conditions were determined by which flooding could be avoided and surface wetting could be assured, as well. (author)
Local Mass Transfer Coefficient for Idealized 2D Urban Street Canyon Models
Leung, Ka Kit; Liu, Chun-Ho
2011-09-01
Human activities in urban areas is one of the major sources of anthropogenic releases in the atmospheric boundary layer (ABL). The mechanism of urban morphology for the heat and mass transfer in built environment is thus an attractive topic in the research community. In this paper, a series of laboratory measurements is conducted to elucidate the mass transfer from hypothetical urban roughness constructed by idealized 2D street canyons. The experiments are carried out in the wind tunnel in the University of Hong Kong. The urban ABL structure inside the wind tunnel is controlled by placing small cubic Styrofoam blocks upstream of the test section. The street canyons are fabricated by movable rectangular acrylic blocks so that different building height to street width (aspect) ratios are examined. The height of building blocks is kept minimum to make sure that the urban ABL over the street canyons is high enough for fully developed turbulent flows. The prevailing wind is normal to the street axis, demonstrating the scenario of least pollutant removal from the street canyons to the urban ABL. The sample street canyon is covered by soaked filter papers to represent uniform mass concentrations on the building facades and ground surface. The wet bulb temperature of the filter papers is continuously monitored to ensure saturated conditions. Their weight before and after an experiment is used to measure the amount of water evaporated. Preliminary results illustrate the local mass transfer coefficient distribution for aspect ratios 1/4, 1/2, 1, and 2, which are comparable with those available in literuatre.
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)
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)
In designing extraction columns many parameters must be considered such as mass transfer coefficients during formation, rising or falling and coalescence time, holdup, drop size and size distribution. Prediction of dispersed phase holdup is one of the most important parameter mentioned above. A laboratory spray column was constructed in our experimental works. Mass transfer coefficients, extraction percentage and local dispersed phase holdup were studied. Three physical systems with different physical properties and wide range of interfacial tensions, the most important physical property in our experiments, were used. It was found that the size of the mother drops produced by nozzles strongly depends on nozzle diameter. Most part of the mass transfer takes place in the nozzle tip and it increases as nozzles diameter decreases. Using multi orifices and single nozzles mass transfers were compared, taking into account the variation of dispersed phase hold up along the column
Estimation of gap conductance in nuclear reactor fuel rods requires values for thermal accommodation coefficients of several gases on Zircaloy, uraniumdioxide, stainless steel, and other surfaces. These values for Zircaloy-2 have now been obtained by observing cooling rates of a Zircaloy sphere suspended in the several gases. These measurements are on so-called engineering surfaces, and no special attempt other than baking under high vacuum pumping was used to clean the surfaces. It is found, however, that if the recent kinetic theory results of Cercignani and Pagani on heat transfer from a sphere are used, then quite constant values for accommodation coefficients on a range of pressures are obtained
Determination of the heat-transfer coefficient and current density profile of gas-discharge plasma
The spatial distribution of gas temperature in a cylindrical discharge tube is theoretically investigated in respect of heat transfer due to gas thermal conduction and heat exchange with surrounding medium. Based on the obtained results the facilities for experimental determination of the heat-transfer coefficient of gas-discharge plasma and radial profiles of the electron density, discharge current density and radiants are shown
Božidar Liš?i?; Tomislav Filetin
2012-01-01
This paper explains the need for a database of cooling intensities for liquid quenchants, in order to predict the quench hardness, microstructure, stresses and distortion, when real engineering components of complex geometry are quenched. The existing laboratory procedures for cooling intensity evaluation, using small test specimens, and Lumped-Heat-Capacity Method for calculation of heat transfer coefficient, are presented. Temperature Gradient Method for heat transfer calculation in worksho...
Seyed Ali Aghayan; Dariush Sardari; Seyed Rabii Mahdi Mahdavi; Mohammad Hasan Zahmatkesh
2013-01-01
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 measur...
Moitsheki, Raseelo J.
2008-01-01
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...
Ã–zdemir Mustafa; Durmaz Ufuk
2015-01-01
In this study, the heat transfer mechanism under agitated pool boiling was examined experimentally. Aqueous sugar solutions were used in a centrically agitated vessel. The effects of the gap which is between the impeller edge and the flat bottom of the agitated vessel, the rotational impeller speed and impeller size were studied on the boiling heat transfer coefficient. A new Nusselt function depending on the Peclet number was suggested for the heat transfe...
Powell, W. B.
1973-01-01
A methodology is described for the analysis of a transient temperature measurement made in a flat or curved plate subjected to convective heat transfer, such that the surface heat flux, the hot-gas temperture, and the gas heat transfer coefficient can be determined. It is shown that if the transient temperature measurement is made at a particular point located nearly midway in the thickness of the plate there is an important simplification in the data analysis process, in that the factor relating the surface heat flux to the measured rate of rise of temperature becomes invariant for a Fourier Number above 0.60 and for all values of the Biot Number. Parameters are derived, tabulated, and plotted which enable straightforward determination of the surface heat flux, the hot-gas temperature, of the plate, the rate of rise of temperature, the plate thickness and curvature, and the mean thermal properties of the plate material at the test temperature.
Thermal accommodation coefficient of gases on controlled solid surfaces: Argon-tungsten system
Saxena, S. C.; Afshar, R.
1985-03-01
The knowledge of the thermal accommodation coefficient for gases on well-controlled surfaces as a function of temperature is imperative to understanding the mechanism of interphase heat transfer on the microscopic level. With this goal in view, a heat transfer column instrument is designed, fabricated, assembled, and tested for the specific case a argon—tungsten system. With 99.9999%, pure argon, six sets of data are taken in the rarefied gas region in the maximum temperature range of 500 1500 K. Four sets of these measurements are in the temperature-jump region and are analyzed by the constant-power method to compute the thermal accommodation coefficient of argon on a controlled tungsten surface. The other two sets are taken under free-molecular flow conditions and are interpreted in accordance with the man-free-path kinetic theory for the low-pressure regime. These data are compared and discussed in the context of reported data in the literature and interpreted in the light of the surface condition and finish of the tungsten wire.
Pool boiling heat transfer from enhanced surfaces to dielectric fluids
Pool boiling heat-transfer measurements were made using a 15.8 mm o.d. plain copper tube and three copper enhanced surfaces: a Union Carbide High Flux surface, a Hitachi Thermoexcell-E surface and a Wieland Gewa-T surface. The dielectric fluids were Freon-113 and Fluorinert FC-72, a perfluorinated organic compound manufactured to cool electronic equipment. Data were taken at atmospheric pressure, and at heat fluxes from 100 W/m2 to 200,000 W/m2. Prior to operation, each test surface was subjected to one of three aging procedures to observe the effect of surface past history upon boiling incipience. For Freon-113 the enhanced surfaces showed a two to tenfold increase in the heat-transfer coefficient when compared to a plain tube, whereas for FC-72 an increase of two to five was measured. The High Flux surface gave the best performance over the range of heat fluxes. The Gewa-T surface did not show as much of an enhancement at low fluxes as the other two surfaces, but at high fluxes its performance improved. In fact, it was the only surface tested which delayed the onset of film boiling with FC-72. The degree of superheat required to activate the enhanced surfaces was sensitive to both past history of the surface and to fluid properties
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, Kolmogorovâ€™s isotropic turbulence theory with Higbieâ€™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.
Evaluation of convective heat transfer coefficient of various crops in cyclone type dryer
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/m2 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
Kato, Hideki
2014-07-01
Photon mass energy transfer coefficient is an essential factor when converting photon energy fluence into kinetic energy released per unit mass (kerma). Although mass attenuation coefficient and mass energy absorption coefficients can be looked up in databases, the mass energy transfer coefficient values are still controversial. In this paper, the photon mass energy transfer coefficients for elements Z=1-92 were calculated based on cross-sectional data for each photon interaction type. Mass energy transfer coefficients for 48 compounds and/or mixtures of dosimetric interest were calculated from coefficient data for elements using Bragg's additivity rule. We additionally developed software that can search these coefficient data for any element or substance of dosimetric interest. The database and software created in this paper should prove useful for radiation measurements and/or dose calculations. PMID:25055949
The effect of mechanical vibrations of a heated string on the heat transfer coefficient ? at various heat fluxes has been studied experimentally. An empirical relation between the coefficient ? and the vibration frequency and amplitude with unchanged q has been found
Evaluation of the heat transfer coefficient at the metal-mould interface during flow
Z. Konopka
2007-12-01
Full Text Available Calculation results concerning the heat transfer coefficient at the metal-mould interface during flow of the AlMg10 alloy in the channel-like cavity of the spiral castability test mould. The experimental cooling curve as well as changes of metal flow velocity have been determined on the basis of the measured metal temperature during flow. The cooling curve equation for the examined alloy, derived from the heat balance condition in a casting-mould system and taking into account experimental data concerning changes in metal temperature and its flow velocity, has enabled evaluation of the heat transfer coefficient at a chosen point of a metal stream along the mould channel. Graphic representations of changes of this coefficient against time and the channel length have been shown.
The prediction of heat transfer coefficient in circulating fluidized bed combustors
In the present work, a theoretical study is performed to modify an existing model that is used to predict the heat transfer coefficient in circulating fluidized bed combustors. In the model, certain parameters were used as being of constant values, which leads to an error in the obtained value of the heat transfer coefficient. In this study and as a first step, the model is thoroughly studied and then the variation of the coefficient with these parameters is presented. Having done that, correlation for these parameters are obtained and then used in the model. Finally the modified model was tested against previously experimental and theoretical data that is available in literature. It was found that the accuracy of the model has been improved after it has been modified
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.
The present work is to improve our understanding and analysis of direct contact condensation on the gravity injection of CMTs and to measure the heat transfer coefficients around steam bubbles using the holographic interferometry and the high speed camera. The condensation regime map associated with the downward injection of steam into water through the steam pipe is investigated to understand the mechanism of the direct contact condensation. The present map shows that the boundary of chugging and subsonic jetting with the larger diameter pipe is shifted to the larger steam mass flux. Steam cavity mode, ever not found in the literature and the unique mode of downward injection for the present geometry, is observed at the low subcooled water temperature. With the holographic interferometry and the high speed camera, the heat transfer mechanism for the direct contact condensation in CMTs is understood and the heat transfer coefficients are measured
The present work is to improve our understanding and analysis of direct contact condensation on the gravity injection of CMTs and to measure the heat transfer coefficients around steam bubbles using the holographic interferometer and high speed camera. The condensation regime map associated with the downward injection of steam into water through the steam pipe is investigated to understand the mechanism of the direct contact condensation. The present map shows that the boundary of chugging and subsonic jetting with the larger diameter pipe is shifted to the larger steam mass flux. Steam cavity mode, not found in the literature, and the unique mode of downward injection for the present geometry, is observed at the low subcooled water temperature. With the holographic interferometry and the high speed camera, the heat transfer mechanism for the direct contact condensation in CMTs is understood and the heat transfer coefficients are measured. (orig.)
Calculating the heat transfer coefficient of frame profiles with internal cavities
NoyÃ©, Peter Anders; Laustsen, Jacob Birck; Svendsen, Svend
2004-01-01
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...... 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 of the...... correspondence between measured and calculated values. Hence, when determining the heat transfer coefficient of frame profiles with internal cavities by calculations, it is necessary to apply a more detailed radiation exchange model than described in the prEN ISO 10077-2 standard. The ISO-standard offers such an...
An experimental test to study natural convection heat transfer to air within a trapezoidal channel area was carried out, heating one of its faces. The temperature in different points along the heated face, inlet and outlet air temperature, environment temperature, the current and voltage supplied to the heater were measured. From the measures, the power applied and the average heat transfer coefficient in the channel were determined. During the experimental test the power applied, channel inclination and the air entrance and exit position, were changed. The values obtained from the different test modes show that the heat transfer coefficient is independent of the power and strongly dependent of the channel inclination and channel position. (author)
A Study of the Heat Transfer Coefficient of a Mini Channel Evaporator with R-134a as Refrigerant
Dollera, E. B.; Villanueva, E. P.
2015-09-01
The present study is to evaluate the heat transfer coefficient of the minichannel copper blocks used as evaporator with R-134a as the refrigerant. Experiments were conducted using three evaporator specimens of different channel hydraulic diameters (1.0mm, 2.0mm, 3.0mm). The total length for each channel is 640 mm. The dimension of each is 100mm.x50mm.x20mm. and the outside surfaces were machined to have fins. They were connected to a standard vapour compression refrigeration system. During each run of the experiment, the copper block evaporator was placed inside a small wind tunnel where controlled flow of air from a forced draft fan was introduced for the cooling process. The experimental set-up used data acquisition software and computer-aided simulation software was used to simulate the pressure drop and temperature profiles of the evaporator during the experimental run. The results were then compared with the Shah correlation. The Shah correlation over predicted and under predicted the values as compared with the experimental results for all of the three diameters and high variation for Dh=1.0mm. This indicates that the Shah correlation at small diameters is not the appropriate equation for predicting the heat transfer coefficient. The trend of the heat transfer coefficient is increasing as the size of the diameter increases.
Determination of heat transfer coefficient between a fluid and a wall
The authors show the extent to which one can assume the existence of a constant heat transfer coefficient between a fluid and a wall in transient thermal conditions, and the means of estimating it. After reviewing investigations reported in the literature (coefficient assumed constant or not), they present two models based on a pulse method: sudden increase in wall temperature, cooling by fluid flow, temperature recording of the wall face not in contact with the fluid-wether or not the fluid is heated. They present the experimental system, define the tranfer coefficient, and make the calculation from the thermogram obtained. For water and air, they analyze the variations in coefficient as a function of fluid flow rate, initial pulse, temperature detector position, and show that the method proposed yields reproducible results
In this study, radiative and convective heat transfer coefficients at the ceiling are determined for a cooled ceiling room. Firstly, convective heat transfer is simulated numerically neglecting the radiative heat transfer at the surfaces (Îµf = Îµw = Îµc = 0), then, radiative heat transfer is calculated theoretically for different surface emissivities (Îµf = Îµw = Îµc = 0.5, 0.6, 0.7, 0.8 and 0.9) for different room dimensions (3 x 3 x 3, 4 x 3 x 4 and 6 x 3 x 4 m) and thermal conditions (Tf = 25 deg. C, Tw = 28-36 deg. C and Tc = 0-25 deg. C). Numerical data is compared with the results of correlations based on experimental data given in literature. New equations related to convective and total (including the effect of convection and radiation) heat transfer coefficients for ceiling are found in the current study
This paper is concerned with the development of an experimental setup and Finite Element (FE) modeling of dry sliding of metals to estimate interface heat transfer coefficient. Heat transfer between the chip, the tool, and the environment during the metal machining process has an impact on temperatures, wear mechanisms and hence on tool-life and on the accuracy of the machined component. For modeling of the metal machining process, the interface heat transfer coefficient is an important input parameter to quantify the transfer of heat between the chip and the tool and to accurately predict the temperature distribution within the cutting tool. In previous studies involving FE analysis of metal machining process, the heat transfer coefficient has been assumed to be between 10-500 kW/m/sup 2/ deg. C (0.49-24.5 BTU/sec/ft/sup 2//degree F), with a background from metal forming processes (especially forging). Based on the operating characteristics, metal forming and machining processes are different in nature. Hence there was a need to develop a procedure close to metal machining process, to estimate this parameter in order to increase the reliability of FE models. To this end, an experimental setup was developed, in which an uncoated cemented carbide pin was rubbed against a steel work piece while the later was rotated at speeds similar to the cutting tests. This modified pin-on-disc set-up was equipped with temperature and force monitoring equipment. A FE model was constructed for heat generation and frictional contact. The experimental and modeling results of the dry sliding process yield the interface heat transfer coefficient for a range of rubbing speeds. (author)
Condensation heat transfer coefficients of flammable refrigerants on various enhanced tubes
Park, Ki Jung; Jung, Dong Soo [Inha Univ., Incheon (Korea, Republic of)
2005-10-15
In this study, external condensation Heat Transfer Coefficients (HTCs) of six flammable refrigerants of propylene (R1270), propane (R290), isobutane (R600a), butane (R600), dimethylether (RE170), and HFC32 were measured at the vapor temperature of 39 .deg. C on a 1023 fpm low fin and turbo-C tubes. All data were taken under the heat flux of 32{approx}116 and 42{approx}142 kW/m{sup 2} for the low fin and turbo-C tubes respectively. Flammable refrigerants' data obtained on enhanced tubes showed a typical trend that external condensation HTCs decrease with increasing wall subcooling. HFC32 and DME showed up to 30% higher HTCs than those of HCFC22 due to their excellent thermophysical properties. Propylene, propane, isobutane, and butane showed similar or lower HTCs than those of HCFC22. Beatty and Katz' correlation predicted the HTCs of the flammable refrigerants obtained on a low fin tube within a mean deviation of 7.3%. Turbo-C tube showed the best performance due to its 3 dimensional surface geometry for fast removal of condensate.
Condensation heat transfer coefficients of flammable refrigerants on various enhanced tubes
In this study, external condensation Heat Transfer Coefficients (HTCs) of six flammable refrigerants of propylene (R1270), propane (R290), isobutane (R600a), butane (R600), dimethylether (RE170), and HFC32 were measured at the vapor temperature of 39 .deg. C on a 1023 fpm low fin and turbo-C tubes. All data were taken under the heat flux of 32âˆ¼116 and 42âˆ¼142 kW/m2 for the low fin and turbo-C tubes respectively. Flammable refrigerants' data obtained on enhanced tubes showed a typical trend that external condensation HTCs decrease with increasing wall subcooling. HFC32 and DME showed up to 30% higher HTCs than those of HCFC22 due to their excellent thermophysical properties. Propylene, propane, isobutane, and butane showed similar or lower HTCs than those of HCFC22. Beatty and Katz' correlation predicted the HTCs of the flammable refrigerants obtained on a low fin tube within a mean deviation of 7.3%. Turbo-C tube showed the best performance due to its 3 dimensional surface geometry for fast removal of condensate
A recent VAMP (Validation of Environmental Model Predictions) report collated values for aggregated transfer coefficients (Tag) which can describe the integrated transfer of radiocaesium to food products from semi-natural ecosystems. Further Tag data are presented for sheep and mushrooms which suggest that subdivision of Tag values to take soil type and seasonal variation into account is potentially valuable. For sheep, Tag values for organic soils are generally one to two orders of magnitude higher than those for sandy and clay soils. For most other semi-natural foodstuffs there are currently inadequate data to make such subdivisions. (author). 19 refs, 1 fig., 4 tabs
Krupiczka, R.; Rotkegel, A.; Ziobrowski, Z. [Polish Academy of Sciences, Institute of Chemical Engineering, Gliwice (Poland)
2000-06-01
The paper describes a mathematical model of the process based on multicomponent mass transfer theory which enables the effect to be predicted of mass transport on the boiling heat transfer coefficient. The results of calculations were compared with our own experimental pool boiling data for the ternary system methanol-isopropanol-water and with Grigoriev's data obtained for the system acetone-methanol-water. The good accuracy was obtained when the ratio of the tube surface area to the surface area of the bubbles, which touch the heater at that moment, was considered as a parameter of the model. Based on our own experimental pool boiling data for the system methanol-isopropanol-water and the corresponding binary systems the triangular diagram of the ratio {alpha}{sub exp}/{alpha}{sub id} as a function of the liquid compositions is presented. (authors)
Determination of drying kinetics and convective heat transfer coefficients of ginger slices
Akpinar, Ebru Kavak; Toraman, Seda
2015-12-01
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 Â°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 (Ï‡ 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 Ã— 10-10 to 6.977 Ã— 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 Â°C.
Charge transfer kinetics from surface plasmon resonance voltammetry.
Lu, Jin; Li, Jinghong
2014-04-15
On the basis of a quantitative relationship between surface plasmon resonance signal and electrochemical current in the electrochemical surface plasmon resonance (EC-SPR), EC-SPR signal measures the semi-integral of faradaic current. We theoretically discussed the electrode potential and charge transfer kinetics to be determined from surface plasmon resonance voltammetry (or potential sweep EC-SPR) signals for the fully reversible, quasi-reversible, and irreversible redox reactions. The results indicated that the electroanalysis of EC-SPR signal is more straightforward than conventional electrochemical current. Then, we studied two model redox reactions of hexaammineruthenium chloride and 4-nitrotoluene, to obtain half wave potential of quasi-reversible redox reaction, transfer coefficient, and standard rate constant of irreversible redox reaction from EC-SPR signals. PMID:24654883
In a high-level waste (HLW) repository, heat is generated by the radioactive decay of the waste. This can affect the safety of the repository because the surrounding environment can be changed by the heat transfer through the rock. Thus, it is important to determine the heat transfer coefficient of the atmosphere in the underground repository. In this study, the heat transfer coefficient was estimated by measuring the indoor environmental factors in the Korea Atomic Energy Research Institute Underground Research Tunnel (KURT) under forced convection. For the experiment, a heater of 5 kw capacity, 2 meters long, was inserted through the tunnel wall in the heating section of KURT in order to heat up the inside of the rock to 90 .deg. C, and fresh air was provided by an air supply fan connected to the outside of the tunnel. The results showed that the average air velocity in the heating section after the provision of the air from outside of the tunnel was 0.81 m/s with the Reynolds number of 310,000 âˆ¼ 340,000. The seasonal heat transfer coefficient in the heating section under forced convection was 7.68 W/m2 K in the summer and 7.24 W/mm2 K in the winter
Yoon, Chan Hoon; Hwang, In Phil; Kim, Jin [Inha University, Incheon (Korea, Republic of); Kwon, Sang Ki [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)
2010-09-15
In a high-level waste (HLW) repository, heat is generated by the radioactive decay of the waste. This can affect the safety of the repository because the surrounding environment can be changed by the heat transfer through the rock. Thus, it is important to determine the heat transfer coefficient of the atmosphere in the underground repository. In this study, the heat transfer coefficient was estimated by measuring the indoor environmental factors in the Korea Atomic Energy Research Institute Underground Research Tunnel (KURT) under forced convection. For the experiment, a heater of 5 kw capacity, 2 meters long, was inserted through the tunnel wall in the heating section of KURT in order to heat up the inside of the rock to 90 .deg. C, and fresh air was provided by an air supply fan connected to the outside of the tunnel. The results showed that the average air velocity in the heating section after the provision of the air from outside of the tunnel was 0.81 m/s with the Reynolds number of 310,000 {approx} 340,000. The seasonal heat transfer coefficient in the heating section under forced convection was 7.68 W/m{sup 2} K in the summer and 7.24 W/mm{sup 2} K in the winter.
Study for transfer coefficient of iodine from grass to cow milk
Radioiodine (131I) is one of the radio nuclides likely to get released into the atmosphere in case of a reactor accident, though chances of such an accident are very remote due to stringent engineering safety features. During the short initial phase of accidental release of radioactivity, 131I is transferred through grass-cow milk pathway, leading to significant thyroid dose to those consuming milk, especially infant and children. Transfer coefficients are important for quick evaluation of environmental contamination, during both normal and abnormal operational phases of a nuclear facility. Transfer coefficient of iodine from grass to milk is defined as ratio of iodine concentration in milk (Bq.L-1) obtained at equilibrium for a constant rate of intake of iodine in (Bq.D-1). During normal operation conditions of nuclear power reactor, the release of radioactive iodine isotopes is are too low that they are not present in measurable concentrations in the environment. Hence, studies are to be performed using stable iodine to estimate the transfer coefficient. A method has been developed based on thermal neutron activation analysis (NAA) to estimate the stable iodine concentration present in grass and cow milk. The method involves pre-concentration from matrix, neutron activation and gamma spectrometry and these were standardized
Integration Of Heat Transfer Coefficient In Glass Forming Modeling With Special Interface Element
Numerical modeling of the glass forming processes requires the accurate knowledge of the heat exchange between the glass and the forming tools. A laboratory testing is developed to determine the evolution of the heat transfer coefficient in different glass/mould contact conditions (contact pressure, temperature, lubrication...). In this paper, trials are performed to determine heat transfer coefficient evolutions in experimental conditions close to the industrial blow-and-blow process conditions. In parallel of this work, a special interface element is implemented in a commercial Finite Element code in order to deal with heat transfer between glass and mould for non-meshing meshes and evolutive contact. This special interface element, implemented by using user subroutines, permits to introduce the previous heat transfer coefficient evolutions in the numerical modelings at the glass/mould interface in function of the local temperatures, contact pressures, contact time and kind of lubrication. The blow-and-blow forming simulation of a perfume bottle is finally performed to assess the special interface element performance
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 Blochâ€™s condition, though the results are the same
Lee, C. M.; Addy, H. E.; Bond, T. H.; Chun, K. S.; Lu, C. Y.
1987-01-01
The main objective of this report was to derive equations to estimate heat transfer coefficients in both the combustion chamber and coolant pasage of a rotary engine. This was accomplished by making detailed temperature and pressure measurements in a direct-injection stratified-charge rotary engine under a range of conditions. For each sppecific measurement point, the local physical properties of the fluids were calculated. Then an empirical correlation of the coefficients was derived by using a multiple regression program. This correlation expresses the Nusselt number as a function of the Prandtl number and Reynolds number.
The effect of inclination angle on the heat transfer and pressure drop characteristics of brazed aluminum heat exchangers was experimentally investigated under wet conditions. Three samples having different fin pitches (1.25, 1.5 and 2.0 mm) were tested. Results show that heat transfer coefficients are not affected by the inclination angle. However, friction factors increase as the inclination angle increases with negligible difference between the forward and backward inclination. The effect of fin pitch on the heat transfer coefficient and on the pressure drop is also discussed. Comparison of the dry and wet surface heat transfer coefficients reveals that dry surface heat transfer coefficients are significantly larger than wet surface heat transfer coefficients. Possible explanation is provided by considering the condensate drainage pattern. The data are also compared with the existing correlation
Ratkovich, Nicolas Rios; Berube, P.R.; Nopens, I.
2011-01-01
One of the operational challenges associated with membrane bioreactors (MBRs) is the fouling of the membranes. In tubular side-stream MBRs, fouling reduction can be achieved through controlling the hydrodynamics of the two-phase slug flow near the membrane surface. The two-phase slug flow induces......). A semi-empirical relationship based on the LÃ©vÃªque relationship for the Sherwood number (mass transfer coefficient) was formulated for the laminar regime. A test case comparison between water and activated sludge was performed based on full-scale airlift MBR operational conditions. It was found that...
Baskakov, A. P.; Rakov, O. A.
2013-01-01
The analytical equations for the steady-state heat-and-mass transfer in the steam evaporation/condensation processes from the steam-gas mixtures on the planar and spherical surfaces are derived. The vapor flow through the motionless dry gas is considered according to the method proposed by Maxwell for the solution of the diffusion problems. The relationships for the calculation of the coefficients taking into account an increase in the mass output and an increase or a decrease in the heat emi...
Numerical study of surface heat transfer enhancement in an impinging solar receiver
Li, Lifeng
2014-01-01
During the impinging heat transfer, a jet of working fluid, either gas or liquid, will besprayed onto the heat transfer surface. Due to the high turbulence of the fluid, the heat transfer coefficient between the wall and the fluid will be largely enhanced. Previously, an impinging type solar receiver with a cylindrical cavity absorber was designed for solar dish system. However, non-uniform temperature distribution in the circumferential direction was found on absorber surface from the numeri...
Single-phase ambient and cryogenic temperature heat transfer coefficients in microchannels
Baek, S.; Bradley, P. E.
2015-12-01
Micro-scaling cryogenic refrigerators, in particular the Joule-Thomson (JT) variety require very good information about heat transfer characteristics of the refrigerants flowing in the microchannels for optimal design and performance. The extremely low Reynolds flow is present in a micro JT cryocooler, the heat transfer characteristics at these conditions require investigation. There are numerous studies regarding heat transfer coefficient measurements of liquid flow in microchannels at/near ambient temperature and high Reynolds flow (Re>2000), that agree well with the conventional correlations. However, results from previous studies of gaseous flow in microchannels at low Reynolds flow (Reperformed at cryogenic temperatures are quite limited in number. In this paper, the single-phase heat transfer coefficients and friction factors for nitrogen are measured at ambient and cryogenic temperatures. The hydraulic diameters for this study are 60, 110 and 180 ?m for circular microchannels. The Reynolds numbers varied from a very low value of 10 to 3000. The measured friction factors are comparable to those in macro-scale tubes. The experimental results of the heat transfer indicate that Nusselt numbers derived from measurements are significantly affected by axial conduction at low Reynolds flow (Re1000) follow conventional theory. The detailed experiment, procedure, and measured results are presented in this paper and discussed regarding deviation from ideal theory at low Reynolds flow.
The impact of air flow to the distribution of heat transfer coefficient on circular cylinder
Beran, Pavel
Vol. 1648. Melville, NY : AIP Publishing, 2015 - (Simos, T.; Tsitouras, C.), ÄŒ. 090006 ISBN 978-0-7354-1287-3. ISSN 0094-243X. - (AIP Conference Proceedings. 1648). [International Conference on Numerical Analysis and Applied Mathematics (ICNAAM). Rhodes (GR), 22.09.2014-28.09.2014] R&D Projects: GA ÄŒR(CZ) GBP105/12/G059 Keywords : transient heat transfer * heat transfer coefficient * air flow * finite element method * Reynolds number * climatic tunnel Subject RIV: JN - Civil Engineering http://scitation.aip.org/content/aip/proceeding/aipcp/10.1063/1.4912394
The effect of gas dissolved in the water on heat transfer coefficients in nuclear reactors
Experimental data on the effect of dissolved nitrogen on heat removal from fuel rod bundles are presented. In it is shown that the coefficients of heat transfer in the gas liberation zone, produced by the rise of the cooling-water temperature as it approaches its saturation temperature, become abnormally low. The normal explanation of the effect of the dissolved nitrogen on the boiling crisis is incorrect. At high vapor contents of the cooling-water flow all the dissolved gas becomes liberated, and has no effect on the heat transfer
Chung, S.
1973-01-01
Heat transfer phenomena of rarefied gas flows is discussed based on a literature survey of analytical and experimental rarefied gas dynamics. Subsonic flows are emphasized for the purposes of meteorological thermometry in the high atmosphere. The heat transfer coefficients for three basic geometries are given in the regimes of free molecular flow, transition flow, slip flow, and continuum flow. Different types of heat phenomena, and the analysis of theoretical and experimental data are presented. The uncertainties calculated from the interpolation rule compared with the available experimental data are discussed. The recovery factor for each geometry in subsonic rarefied flows is also given.
The impact of air flow to the distribution of heat transfer coefficient on circular cylinder
Beran, Pavel
Vol. 1648. Melville, NY : AIP Publishing, 2015 - (Simos, T.; Tsitouras, C.), 090006 ISBN 978-0-7354-1287-3. ISSN 0094-243X. - (AIP Conference Proceedings. 1648). [International Conference on Numerical Analysis and Applied Mathematics 2014. ICNAAM-2014. Rhodes (GR), 22.09.2014-28.09.2015] R&D Projects: GA ÄŒR(CZ) GBP105/12/G059 Keywords : transient heat transfer * heat transfer coefficient * air flow * finite element method * Reynolds number * climatic tunnel Subject RIV: JN - Civil Engineering http://scitation.aip.org/content/aip/proceeding/aipcp/10.1063/1.4912394
A hybrid diagnostic agent system is developed to detect and identify early an anomaly that happens in the fast-breeder reactor 'Monju'. The system outputs a diagnostic result by integrating the results of diagnosis by four diagnostic software agents. They are (1) an estimation agent of overall heat transfer coefficient of evaporator and superheater, (2) a state identification agent based on SVM (Support Vector Machine), (3) an anomaly detection agent by WT (Wavelet Transformation), and (4) a CBR (Case-Based Reasoning) agent using several attributes in both time and frequency domain. This paper describes the whole system and the estimation technique of overall heat transfer coefficient by simple physical models from 'Monju' process signals. (author)
The influence of temperature and concentration measurement errors on experimental determination of mass and heat transfer coefficients is analysed. Calculus model of coefficients and of measurement errors, the experimental data obtained on the water isotopic distillation plant and the results of determinations are presented. The experimental distillation column, with inner diameter of 108 mm, have been equipped with B7 structured packing on a height of 14 m. This column offers the possibility to measure vapour temperature and isotopic concentration in 12 locations. For error propagation analysis, the parameters measured for each packing bed, namely temperature and isotopic concentration of the vapour, were used. A relation for calculation of maximum error of experimental determinations of mass and heat transoprt coefficients is given. The experimental data emphasize the 'ending effects' and regions with bad thermal insulation. (author)
E. Hetmaniok; D. SÅ‚ota; A. Zielonka
2012-01-01
A procedure based on the Artificial Bee Colony algorithm for solving the two-phase axisymmetric one-dimensional inverse Stefanproblem with the third kind boundary condition is presented in this paper. Solving of the considered problem consists in reconstruction of the function describing the heat transfer coefficient appearing in boundary condition of the third kind in such a way that the reconstructed values of temperature would be as closed as possible to the measurements of temperature giv...
Retrieving the heat transfer coefficient for jet impingement from transient temperature measurements
Highlights: ? Heat transfer coefficient for impinging air jet is retrieved. ? Searched boundary condition approximated by spatial and temporal functions. ? Nonlinearity of problem bypassed by Newton's cooling law. ? Enforced temporal invariability of heat transfer coefficient stabilize solution. ? Results outperforms standard inverse approach. - Abstract: Algorithm of retrieving the heat transfer coefficient (HTC) from transient temperature measurements is presented. The unknown distributions of two types of boundary conditions: the temperature and heat flux are parameterized using a small number of user defined functions. The solutions of the direct heat conduction problems with known boundary temperature and flux are expressed as a superposition of auxiliary temperature fields multiplied by unknown parameters. Inverse problem is formulated as a least squares fit of calculated and measured temperatures and is cast in a form of a sum of two objective functions. The first results originates from an inverse problem for retrieving the boundary temperature the second comes from the inverse problem for reproducing the boundary heat flux. The final form of the objective function is obtained by enforcing constant in time value of the heat transfer coefficient. This approach leads to substantial regularization of the results, when compared with the standard technique, where HTC is calculated from separately reconstructed temperature and heat flux on the boundary. The validation of the numerical procedure is carried out by reconstructing a known distribution of the HTC using simulated measurements laden by stochastic error. The proposed approach is also used to reconstruct the distribution of the HTC in a physical experiment of heating a cylindrical sample using an impinging jet.
Correlations for the Prediction of NTU and Mass Transfer Coefficient for a VPE
Rathilal, S.; ÄŒÃ¡rskÃ½, M.; Heyberger, AleÅ¡; RouskovÃ¡, Milena
Praha : Process Engineering Publisher, 2010, s. 411. ISBN 978-80-02-02247-3. [International Congress of Chemical and Process Engineering CHISA 2010 and 7th European Congress of Chemical Engineering ECCE-7 /19./. Prague (CZ), 28.08.2010-01.09.2010] Institutional research plan: CEZ:AV0Z40720504 Keywords : mass transfer coefficient * liquid-liquid extraction * acetone-toluene-water system Subject RIV: CI - Industrial Chemistry, Chemical Engineering www.chisa.cz/2010, www.ecce7.com
Evaluation of heat transfer coefficient of tungsten filaments at low pressures and high temperatures
The paper presents an experimental method for the evaluation of the heat transfer coefficient of tungsten filaments at low pressures and high temperatures. For this purpose an electrode of a T5 fluorescent lamp was tested under low pressures with simultaneous heating in order to simulate the starting conditions in the lamp. It was placed in a sealed vessel in which the pressure was varied from 1 kM (kilo micron) to 760 kM. The voltage applied to the electrode was in the order of the filament's voltage of the lamp at the normal operation with the ballast during the preheating process. The operating frequency ranged from DC to 50 kHz. The experiment targeted on estimating the temperature of the electrode at the end of the first and the ninth second after initiating the heating process. Next, the heat transfer coefficient was calculated at the specific experimental conditions. A mathematical model based on the results was developed that estimates the heat transfer coefficient. The experiments under different pressures confirm that the filament's temperature strongly depends on the pressure.
Mirmanto, M.
2016-01-01
Experiments to investigate local pressure distribution and local heat transfer coefficients during flow boiling of water in a microchannel were performed. The hydraulic diameter of the channel was 0.635 mm. The nominal mass fluxes used were varied from 200 to 700 kg/m2 s and heat fluxes ranging from 171 to 685 kW/m2 were applied. An inlet fluid temperature of 98 °C and pressure of 125 kPa were maintained at the microchannel entrance. There were six pressure tappings inserted into the channel to measure the local pressures and six thermocouple inserted into the channel block with equally distances to measure the wall local temperatures. The local pressure measurements during flow boiling show a non linear line connecting each local pressure, especially at higher heat fluxes or pressure drops. The non linear local pressure influences the value of the estimated local heat transfer coefficient. The effects of mass flux and heat flux on local heat transfer coefficient are also discussed.
NikoliÄ‡ Z.S.
2007-01-01
Full Text Available In this paper a numerical model will be adopted to analyze the heat transfer process during rapid solidification of a spherical sample placed on a metallic substrate cooled by water. The interfacial heat transfer coefficient between the sample and the substrate will be evaluated by matching model calculations with the surface temperature history recorded by a digital camera during solidification of a sample melted in an Arc-image furnace. .
NikoliÄ‡ Z.S.; Yoshimura M.; Araki S.; Fujiwara T.
2007-01-01
In this paper a numerical model will be adopted to analyze the heat transfer process during rapid solidification of a spherical sample placed on a metallic substrate cooled by water. The interfacial heat transfer coefficient between the sample and the substrate will be evaluated by matching model calculations with the surface temperature history recorded by a digital camera during solidification of a sample melted in an Arc-image furnace. .
Te-Wen Tu; Sen-Yung Lee
2015-01-01
An analytical solution for the heat transfer in hollow cylinders with time-dependent boundary condition and time-dependent heat transfer coefficient at different surfaces is developed for the first time. The methodology is an extension of the shifting function method. By dividing the Biot function into a constant plus a function and introducing two specially chosen shifting functions, the system is transformed into a partial differential equation with homogenous boundary conditions only. The ...
A look-up table for film-boiling heat-transfer coefficients in tubes with vertical upward flow
A look-up table of film-boiling heat-transfer coefficients has been developed for steam-water flow inside vertical tubes, using a methodology similar to that for the look-up table of critical heat flux. The film-boiling look-up table provides heat-transfer coefficients at discrete values of pressure, mass flux, heat flux and thermodynamic quality, covering both the inverted annular-flow film-boiling (IAFB) and the dispersed-flow film-boiling (DFFB) regions. The table values are established using 14 687 film-boiling heat-transfer data points for tubes compiled in the AECL film-boiling data bank. At conditions where no data are available, these values are calculated using the Groeneveld-Delorme correlation (for the DFFB region) and the Hammouda model (for the IAFB region). The film-boiling look-up table and other leading film-boiling prediction methods have been assessed using the available data base. The look-up table predicts the surface-temperature data with a root-mean-square error of 6.73% and an average error of 1.2%, which is an improvement over that of other prediction methods. In addition, the film-boiling look-up table covers a wide range of flow conditions, provides a smooth transition between IAFB and DFFB regions, requires little computing time, and exhibits correct asymptotic and parametric trends. (author)
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.
Comparison of boiling heat transfer coefficient and pressure drop correlations for evaporators
Evaporator design is an important aspect for the HVAC industry. As the demand for more efficient and compact heat exchangers increase, researches on estimation of two-phase flow heat transfer and pressure drop gain importance. Due to complexity of the hydrodynamic and heat transfer of the two-phase flow, there are many experimental studies available for refrigerants int he literature. In this study, a model for boiling heat transfer in a horizontal tube has been developed and the simulation results are compared with experimental ones published in the literature. In these comparisons, heat transfer coefficient is calculated by using Kattan-Thome-Favrat (1998), Shah (1982), Kandilikar (1990), Chaddock and Brunemann (1967) correlations under different operational conditions such as saturation pressure, mass flux, the type of refrigerant and two phase flow pattern. Besides that flow pattern has also been considered in the simulation by using Thome and El Hajal (2002) model. For pressure drop Lockhart-Martinelli (1949), Mueller-Steinhagen-Hack (1986) and Groennerund (1979) correlations are used in simulations. Local vapor quality change at each experimental condition through the model is determined. Roughness is an important parameter for frictional pressure drop. Friction coefficient is determined by using Churchill (1977) model. (author)
Evaluation of Heat and Mass Transfer Coefficients for R134a/DMF Bubble Absorber
M. Suresh
2011-01-01
Full Text Available The Vapour Absorption Refrigeration System (VARS has generated renewed interest and is being viewed as one of the alternatives for vapour compression refrigeration due to its potential for waste heat utilization. To improve the efficiency of these systems, it is necessary to study heat and mass transfer processes in absorption system components. The absorber, one of the crucial components in VARS is considered for study. Experimental investigation is carried out to study heat and mass transfer characteristics in a glass absorber. A new combination of R134a/DMF is used as the working fluid to overcome the limitations of well known working pairs, ammonia-water and lithium bromide-water. The effects of parameters viz., gas flow rate, solution initial concentration, solution pressure and solution temperature on absorber performance are analyzed. Heat and mass transfer coefficients evaluated from the experiments are compared with the numerical model and it is found that agreement is good. Heat and mass transfer coefficients increase as the gas flow rate, solution initial concentration and solution temperature increase whereas they decrease as the solution pressure increases. Sherwood number and Nusselt number evaluated from the experimental data are compared with those obtained from the numerical correlations developed earlier by the authors.
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 Â° 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 Â± 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.
Evaluation of condensation heat transfer coefficient in AC600 passive containment cooling system
The author gives a warranty to choice condensation heat transfer correlation (HTC) in AC600 passive containment cooling system (PCCS) analysis by comparing some most useful condensation HTC used in PCCSAC-MD code which is a multi-dimensional thermal-hydraulic analysis code for AC600 PCCS. These correlations include Uchida correlation, Gido-Koestl correlation, Tagami correlation and heat-mass transfer analogy correlation using the heat transfer coefficient on the vapor side of the interface. The author gets the conclusion that the Uchida correlation based on steady state data of experiment is more conservative than the Gido-Koestl correlation. The difference of peak pressure value of AC600 containment under double ended cold leg loss of coolant accident or main steam line break accident calculated by different correlation is similar while for double ended hot leg loss of coolant accident the difference is big, Although different correlation gets different heat transfer coefficient. The Tagami correlation is the most conservative one in the main steam line break accident calculated
Condensation heat transfer coefficients of R1234yf on plain, low fin, and Turbo-C tubes
Park, Ki-Jung; Kang, Dong Gyu; Jung, Dongsoo [Department of Mechanical Engineering, Inha University, Incheon 402-751 (Korea, Republic of)
2011-01-15
In this study, external condensation heat transfer coefficients (HTCs) of HFC134a and R1234yf are measured on a plain, low fin, and Turbo-C tubes at the saturated vapor temperature of 39 C with the wall subcooling of 3-8 C. R1234yf is a new alternative refrigerant of low greenhouse warming potential for replacing HFC134a, one of the greenhouse gases in Kyoto protocol, used extensively in automobile air conditioners and other refrigeration systems. Test results show that the condensation HTCs of R1234yf are very similar to those of HFC134a for all three surfaces tested. For the development of heat transfer correlations, thorough property measurements are needed for R1234yf in the near future. (author)
Nielsen, Anders Michael; Nielsen, Lars Peter; Feilberg, Anders; Christensen, Knud Villy
2009-01-01
sulfur gases and to provide toluene retention profiles for the model to determine the air velocity and overall mass-transfer coefficient of toluene. The mass-transfer coefficient of toluene was used as a reference for determining the mass transfer of sulfur gases. By presenting the model to scenarios of...... a filter bed with a consortium of effective sulfur oxidizers, the most likely mechanism for incomplete removal of sulfur compounds from the exhaust air was elucidated. This was found to be insufficient mass transfer and not inadequate bacterial activity as anticipated by the manager of the BF. Thus......, knowing the relationship between mass-transfer coefficients and air velocity for a given type of BF allows for an improved dimensioning and managing of this and similar BFs. This research demonstrates that it is possible to estimate mass-transfer coefficients and air velocity in BFs using MIMS in...
Parvataneni
2013-09-01
Full Text Available The present theoretical investigation deals with the problem of free convective heat transfer from a vertical plate having linear temperature gradient along its surface to the surrounding thermally stratified fluid. Integral method of analysis is adopted to investigate the effect of four parameters viz., the gradients of temperature in the fluid and the wall, Grashof number and Prandtl number on heat transfer coefficients. It is observed from the numerical results that an increase in the surface temperature gradient would result in higher heat transfer coefficients than those observed in isothermal wall case.
Prediction of the heat transfer coefficient for ice slurry flows in a horizontal pipe
Kousksou, T.; Jamil, A.; Zeraouli, Y. [Laboratoire de Thermique Energetique et Procedes, Avenue de l' Universite, BP 1155, 64013 Pau Cedex (France); El Rhafiki, T. [Laboratoire de Thermique Energetique et Procedes, Avenue de l' Universite, BP 1155, 64013 Pau Cedex (France); Laboratoire d' Energetique, Mecanique des Fluides et Sciences des Materiaux, Universite AbdelMalek Essaidi, 90000 Tetouan (Morocco)
2010-06-15
In this study, heat transfer for ice slurry flows was investigated. For the experiments, ice slurry was made from 9% ethanol-water solution flow in a 20 mm internal diameter, 1000 mm long horizontal copper tube. The ice slurry was heated by a cylindrical electrical resistance. Experiments of the melting process were conducted with changing the ice slurry mass flux rate and the heat flux. The enthalpy-porosity formulation was used to predict the ice slurry temperature and the local values of heat transfer coefficient in the exchanger. Measurements and data acquisition of ice slurry temperature and mass flow rate at the inlet and outlet are performed. It was found that the heat transfer rates increase with the mass flow rate, the ice fraction and the heat flux density. However, the effect of ice fraction appears not to be significant at high mass flow rates. In addition, the correlation proposed by Christensen and Kauffeld gives good agreement with numerical results. (author)
Prediction of the heat transfer coefficient for ice slurry flows in a horizontal pipe
In this study, heat transfer for ice slurry flows was investigated. For the experiments, ice slurry was made from 9% ethanol-water solution flow in a 20 mm internal diameter, 1000 mm long horizontal copper tube. The ice slurry was heated by a cylindrical electrical resistance. Experiments of the melting process were conducted with changing the ice slurry mass flux rate and the heat flux. The enthalpy-porosity formulation was used to predict the ice slurry temperature and the local values of heat transfer coefficient in the exchanger. Measurements and data acquisition of ice slurry temperature and mass flow rate at the inlet and outlet are performed. It was found that the heat transfer rates increase with the mass flow rate, the ice fraction and the heat flux density. However, the effect of ice fraction appears not to be significant at high mass flow rates. In addition, the correlation proposed by Christensen and Kauffeld gives good agreement with numerical results.
Sensitivity analysis of dose coefficients for 239Pu to transfer rates
It is reported that 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. A code has been developed to reproduce the ICRP's dose coefficient for 239Pu, 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, each transfer rate was modified by a factor of 2, 3 and 4, and the sensitivities of effective doses due to these changes calculated. Consequently, the transfer rates that give a large sensitivity were specified, and it was shown that in many cases changes of transfer rates are not very influential on effective doses for 239Pu. (author)
Heat Transfer in Bubble Columns with High Viscous and Low Surface Tension Media
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 PaÂ·s) and surface tension (66.1-72.9x10-3 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=2502UG0.236L-0.250L-0.028 Nu=3.25Re0.180Pr-0.067We0.028
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 PaÂ·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}.
EMILA ŽIVKOVI?
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.
Behzadian, Farnaz; Yerushalmi, Laleh; Alimahmoodi, Mahmood; Mulligan, Catherine N
2013-08-01
The hydrodynamic characteristics and the overall volumetric oxygen transfer coefficient of a new multi-environment bioreactor which is an integrated part of a wastewater treatment system, called BioCAST, were studied. This bioreactor contains several zones with different environmental conditions including aerobic, microaerophilic and anoxic, designed to increase the contaminant removal capacity of the treatment system. The multi-environment bioreactor is designed based on the concept of airlift reactors where liquid is circulated through the zones with different environmental conditions. The presence of openings between the aerobic zone and the adjacent oxygen-depleted microaerophilic zone changes the hydrodynamic properties of this bioreactor compared to the conventional airlift designs. The impact of operating and process parameters, notably the hydraulic retention time (HRT) and superficial gas velocity (U(G)), on the hydrodynamics and mass transfer characteristics of the system was examined. The results showed that liquid circulation velocity (V(L)), gas holdup (Îµ) and overall volumetric oxygen transfer coefficient (k(L)a(L)) increase with the increase of superficial gas velocity (U(G)), while the mean circulation time (t(c)) decreases with the increase of superficial gas velocity. The mean circulation time between the aerobic zone (riser) and microaerophilic zone (downcomer) is a stronger function of the superficial gas velocity for the smaller openings (1/2 in.) between the two zones, while for the larger opening (1 in.) the mean circulation time is almost independent of U(G) for U(G) â‰¥ 0.023 m/s. The smaller openings between the two zones provide higher mass transfer coefficient and better zone generation which will contribute to improved performance of the system during treatment operations. PMID:23142846
Although the heat transfer problem of pressurized supercritical water (SCW) flows in around tube has been studied for decades, the subject is still considerably of interest nowadays. This is partly because of the expanded investigation of using SCW for nuclear engineering applications like SCWR which is generation IV reactor and promising advanced nuclear systems because of their high thermal efficiency(i.e., about 45% as opposed to about 33% efficiency for current light water reactors LWRs) and considerable plant simplification. Literature survey shows that heat transfer coefficient (HTC) is sharply enhanced near the pseudo critical temperature. As the heat flux increases, the peak of the HTC decreases. When the heat flux reaches to some high values, heat transfer deterioration (HTD) occurs. CFD code with various turbulence models are being used to evaluate HTC. Modeling of Yamagata's experiment has been carried out for evaluation of HTC using CFD code FLUENT with standard kÎµ turbulence model, nonequilibrium wall function,viscous heating, full buoyancy effect and including wall roughness effect.In this paper model constants for standard kÎµ model have been derived. In the Yamagata experiment, investigations were made for HTC to supercritical water flowing vertically upward in vertical tubes of 10 and 7.5mm internal diameter, at pressures 22.6, 24.5 and 29.5 MPa, bulk temperature from 230 to 540 oC, heat flux 233, 465, 698 and 930kW/m2 and mass flux 1200 kg/m2.s. Two dimensional axisymmetry grid generation has been done using GAMBIT. Inbuilt boundary conditions in the FLUENT are invoked for mass flow rate at inlet,pressure outlet at the outlet of the tube and wall at the cylindrical surface where heat flux is given. Thermo-physical properties are taken from the (IAPWSIF97) and piecewise linear variation are given in the FLUENT for 30 temperature points. Bulk fluid temperature is obtained using user defined function. HTC are obtained based on heat flux, surface temperature and bulk fluid temperature. The calculated HTC is compared with the experimental results and also compared with the results of the other authors. It is observed in both experimental and code calculated values that peak HTC decreases for increase in heat flux for constant mass flux and it is also noticed that peak HTC decreases with the increase in system pressure for constant heat flux. However, it is noticed that magnitude of peak HTC calculated by code is higher than the experimental data especially for higher heat flux and rate of decrease of peak HTC with increase in heat flux is lesser with compared to experimental results. It is observed that peak HTC increases with increase in wall roughness of the tube. It is also observed that HTC calculated by FLUENTcode is in good agreement with the HTC calculated by other authors using CFD code with various turbulence models. (author)
Using GIS to produce impervious surface coefficients from National Land Cover Data National Laud Cover Data (NLCD) and county level planimetric impervious surface data were utilized to derive an impervious coefficient per NLCD class. Results show that coefficients fall in...
Heat transfer of coolant flow through the automobile radiators is of great importance for the optimization of fuel consumption. In this study, the heat transfer performance of the automobile radiator is evaluated experimentally by calculating the overall heat transfer coefficient (U) according to the conventional Îµ-NTU technique. Copper oxide (CuO) and Iron oxide (Fe2O3) nanoparticles are added to the water at three concentrations 0.15, 0.4, and 0.65 vol.% with considering the best pH for longer stability. In these experiments, the liquid side Reynolds number is varied in the range of 50â€“1000 and the inlet liquid to the radiator has a constant temperature which is changed at 50, 65 and 80 Â°C. The ambient air for cooling of the hot liquid is used at constant temperature and the air Reynolds number is varied between 500 and 700. However, the effects of these variables on the overall heat transfer coefficient are deeply investigated. Results demonstrate that both nanofluids show greater overall heat transfer coefficient in comparison with water up to 9%. Furthermore, increasing the nanoparticle concentration, air velocity, and nanofluid velocity enhances the overall heat transfer coefficient. In contrast, increasing the nanofluid inlet temperature, lower overall heat transfer coefficient was recorded. -- Highlights: â–º Overall heat transfer coefficient in the car radiator measured experimentally. â–º Nanofluids showed greater heat transfer performance comparing with water. â–º Increasing liquid and air Re increases the overall heat transfer coefficient. â–º Increasing the inlet liquid temperature decreases the overall heat transfer coefficient
In the Loss-of-RHR accident during mid-loop operation reflux condensation in U-tube riser is experimentally studied. The present experimental study handles with the reflux condensation in the presence of noncondensable gas in a vertical tube. The main interest is to investigate the parametric effects such as inlet air mass fraction, system pressure and inlet steam flow rate on reflux condensation heat transfer. The test facility is mainly composed of two parts: an air-steam mixture generation part and a reflux condensation part(test section). Air is used as a noncondensable gas. Experiments are performed under the system pressure of 1 âˆ¼ 2.5bar, inlet steam flow rate of 1.04 âˆ¼ 2.15kg/hr and inlet air mass fraction of 0 âˆ¼ 57.9%. From experimental results, several characteristics of parametric effects are confirmed. The presence of air causes a decrease in heat transfer coefficients and, as a result, increases the active condensation length. As the inlet steam flow rate increases, the active length slightly increases during reflux condensation. As the system pressure increases, the active condensation length somehow decreases with an increase in heat transfer coefficients in that zone. And the flooding limit for inlet mixture flow rate is much less than that of Wallis' flooding formula
Condition monitoring of steam generator by estimating the overall heat transfer coefficient
This study develops a technique for monitoring in on-line the state of the steam generator of the fast-breeder reactor (FBR) â€œMonjuâ€. Because the FBR uses liquid sodium as coolant, it is necessary to handle liquid sodium with caution due to its chemical characteristics. The steam generator generates steam by the heat of secondary sodium coolant. The sodium-water reaction may happen if a pinhole or crack occurs at the thin metal tube wall that separates the secondary sodium coolant and water/steam. Therefore, it is very important to detect an anomaly of the wall of heat transfer tubes at an early stage. This study aims at developing an on-line condition monitoring technique of the steam generator by estimating overall heat transfer coefficient from process signals. This paper describes simplified mathematical models of superheater and evaporator to estimate the overall heat transfer coefficient and a technique to diagnose the state of the steam generator. The applicability of the technique is confirmed by several estimations using simulated process signals with artificial noises. The results of the estimations show that the developed technique can detect the occurrence of an anomaly. (author)
Transient measurement of dual channel CICC heat transfer coefficients on a full size ITER conductor
Dual channel Cable-In-Conduit Conductors (CICC) provide low hydraulic resistance and faster central channel circulation, limiting superconductors temperature rise. The Poloidal Field Insert Sample (PFIS) was tested in the SULTAN facility to evaluate the thermal coupling between the CICC channels upon an experimental heat transfer coefficient assessment. Simple assumptions on the flow homogeneous central and annular temperatures, no jacket conduction, no steel inertia and diffusivity lead to a one-dimensional thermal model fully solved in its transient response to a Heavy-side temperature evolution at the inlet, using a Laplace transformation. Transient temperature step data fitted with the analytical resolution provide heat transfer coefficients as a function of mass flow rate, compared to crude predictions and steady state evaluations, where annular and central temperatures are homogenized in compliance with the CICC heat transfer characteristic length. The transient measurements are subject to the inertia and diffusivity of the conductor, whereas comparable steady state measures suffer from annular isothermal assumption. Recommendations are made for the thermohydraulic instrumentation of future conductor samples. (authors)
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.
Relationship between soil surface roughness and hydraulic roughness coefficient on sloping farmland
Zi-cheng ZHENG; Shu-qin HE; Fa-qi WU
2012-01-01
The soil surface roughness and hydraulic roughness coefficient are important hydraulic resistance characteristic parameters. Precisely estimating the hydraulic roughness coefficient is important to understanding mechanisms of overland flow. Four tillage practices, including cropland raking, artificial hoeing, artificial digging, and straight slopes, were considered based on the local agricultural conditions to simulate different values of soil surface roughness in the Loess Plateau. The objec...
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.
The friction coefficient between surfaces depends not only on their roughness but also on their relative speed. The aim of this work is to show how the friction coefficient would vary with the relative speed of the two rough surfaces provided accounting affects of their reciprocal correlation. The reciprocal spectral density of the two surfaces is studied in addition to their structure function. It is shown that the reciprocal spectral density has important impacts on the friction coefficient of the surfaces, in a sense that a positive or a negative reciprocal correlation would cause a decrease or an increase in the friction coefficient. In addition, the friction is studied in the context of the relaxation time. It is shown that there is a threshold for the relative velocity of the two surfaces, where by exceeding the threshold velocity the friction coefficient would not increase, but decrease
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: Â kLa of 6.2 x 10-3 s-1, working at 25 ÂºC, 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 ÂºC, 60 rpm, 150 ml of liquid volume, erlenmeyer of 250 ml without baffles and cotton closure. Ua of 31.9963 J/min Â°C, working at 45 ÂºC, 150 rpm, 150 ml of liquid volume, erlenmeyer of 500 ml with baffles and cotton closure. Ua of 6.0179 J/min Â°C, working at 35 ÂºC, 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 Â°C, working at 35 Â°C, 150 rpm, 150 ml of liquid volume, Erlenmeyer of 250 ml, with baffles and cotton closure. Â
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
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...... 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 for correlation between external pressure and heat transfer coefficient. Acceptable agreement with data in literature shows the accuracy of the proposed formula....
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 intensities of about 1 percent, which is typical of wind tunnels, and up to 20 percent (using a grid), which is typical of real engine conditions.
Hippensteele, Steven A.; Poinsatte, Philip E.
1993-08-01
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 intensities of about 1 percent, which is typical of wind tunnels, and up to 20 percent (using a grid), which is typical of real engine conditions.
Mass transfer coefficient factor in pipe bend - 3 D CFD analysis
In power industries Flow Accelerated Corrosion (FAC) has been a concern for pipe wall thinning where high velocity fluid at elevated temperatures is used. Even straight pipes are found to have non uniform corrosion and this is enhanced in junctions such as bends, orifices etc. Mass transfer coefficient (MTC) which defines the amount of corrosion changes from its value in straight pipe (with same fluid parameters) for flow in bends, orifice etc due to changes in velocity profile in axial direction. In this paper, 3 D computational fluid dynamics (CFD) simulation is carried out for an experiment on 58Â° bend angle and 2D bend radius circular carbon steel pipe carrying water at 120Â°C under neutral pH conditions. The turbulent model K-Ï‰ with shear stress transport was used for this purpose. The mass transfer boundary layer (MTBL) thickness Î´mtbl depends on Schmidt number (Sc), as Î´mtbl âˆ¼ Î´h/(Sc1/3). MTBL is significantly smaller than hydrodynamic boundary layer Î´h for large Sc, hence boundary layer meshing was carried out deep into Î´mtbl. Uniform velocity was applied at the inlet. The flow velocity was 3 m/s at room temperature while the experimental fluid velocity was 7 m/s. Lower value of fluid velocity is chosen due to the limitations of grid size since it depends inversely on fluid velocity. The ratio of MTC in bend to straight pipe is not strongly dependent on Sc. CFD simulation at lower temperature is sufficient to get approximate MTC in bends. The ratio of the mass transfer coefficient at some locations in bend to the straight pipe coefficient (MTCR) is determined through simulation. The MTC increased in the extrados of the bend towards the outlet. (author)
After TMI and Chernobyl accidents, many efforts have been made to enhance the nuclear safety with passive features. Among such passive features, the passive containment cooling system (PCCS) has been suggested by Westinghouse in the AP600 plant. The containment with PCCS is a dual containment, and consists of a stainless steel vessel and a concrete wall. In the gap between these structures, air and water can counter-currently pass and cool the steel surface. This paper experimentally investigates evaporative heat and mass transfer at the surface of a falling water film with counter-current air flow in a vertical duct with one-side heated plate. Experiments included various conditions of mass flow rate of film and air. Experimental results show the strong effects of water temperature and air mass flow rate, but little effect of the water flow rate. Also, simple analyses based on heat and mass transfer analogy were performed to evaluate the experimental results. With experimental data, a new correlation on evaporative mass transfer coefficient was developed, and with the correlation, the containment pressure and temperature was calculated for the design basis accident of AP600 by the use of CONTEMPT4/MOD5 code implementation
Program FREG series calculate temperature distribution in a fuel rod and the stored energy based on the distribution. The temperature distribution is calculated accordance with the fuel rod irradiation history. The temperature in the fuel rod is severely influenced with gap heat transfer coefficients between fuel pellet surface and cladding inner surface. Enphasis is placed on how to find the gap heat transfer coefficients. FREG-4 is a version-up program of FREG-3. Major modification from FREG-3 is handlings of fission product gas release, which have influences on the gap heat transfer. FREG-4 distingushed fission-product isotopes remained in pellets and fission-product gaseous isotopes released from the pellets, and considers that the released isotopes are transported for plenums to balance whole fuel rod internal pressure and transformed into another isotopes due to decay and the nuetron absorptions. The present report describes modified models from FREG-3 and user's manual for FREG-4. (author)
Mass Transfer Coefficient During Cathodic Protectionof Low Carbon Steel in Seawater
Ameel Mohammed Rahman; Anees Abdullah Khadom; Khalid W. Hameed
2009-01-01
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 i...
Evaluation of heat transfer coefficient of tungsten filaments at low pressures and high temperatures
Chondrakis, N.G.; Topalis, F.V.
2010-01-01
Abstract The paper presents an experimental method for the evaluation of the heat transfer coefficient of tungsten filaments at low pressures and high temperatures. For this purpose an electrode of a T5 fluorescent lamp was tested under low pressures with simultaneous heating in order to simulate the starting conditions in the lamp. It was placed in a sealed vessel in which the pressure was varied from 1 kM (kilo micron) to 760 kM. The voltage applied to the electrode was in the or...
JuraÅ¡Äik, M.; Sikula, I.; Rosenberg, M.; J. MarkoÅ¡
2007-01-01
This study deals with the measurement of volumetric mass transfer coefficients (kLa) in the internal loop airlift reactors (ILALRs) of different volumes (12 dm3, 40 dm3 and 200 dm3) using the glucose oxidase method. The experimental results of this work were compared with those kLa obtained for the same ILALRs by applying different other methods. Results of this work showed a good agreement with the published results obtained by applying other methods on the non-coalescent medium. The init...
KÃ¡rÃ¡szovÃ¡, Magda; Å imÄÃk, Miroslav; Friess, K.; RandovÃ¡, A.; Jansen, J. C.; RÅ¯Å¾iÄka, Marek; SedlÃ¡kovÃ¡, Zuzana; IzÃ¡k, Pavel
2013-01-01
RoÄ. 118, 30 OCT (2013), s. 255-263. ISSN 1383-5866 R&D Projects: GA ÄŒR GAP106/10/1194; GA MÅ k(CZ) 7C11009 Grant ostatnÃ: RFCS(XE) RFCR-CT-2010-00009; INP(IT) PON01_01840; HA MÅ k(CZ) CZ.1.05/2.1.00/03.0071 Institutional support: RVO:67985858 Keywords : biogas purification * supported ionic liquid membranes * mass transfer coefficients Subject RIV: CI - Industrial Chemistry, Chemical Engineering Impact factor: 3.065, year: 2013
A review of measured values of the milk transfer coefficient (fsub(m)) for iodine
Most published assessments of the environmental transport of iodine have used a value of 1 X 10-2 days per litre (d/1) for the transfer coefficient (fsub(m)) which relates the concentration per litre of milk to the daily amount of the element ingested by a cow. However, the USNRC has recommended (USNRC 77) a value of 0.6 X 10-2 d/1 for the transfer of iodine to cow's milk and 6 X 10-2 d/1 for goat's milk. A literature survey of published values of fsub(m) leads to a recommendation which deviates from the values chosen by the USNRC. An fsub(m) of 0.5 d/1 for goat's milk and an fsub(m) of 1 X 10-2 for cow's milk appear to be more appropriate. (author)
Highlights: â–º Mass transfer coefficient does not depend on biomass concentration. â–º The pulp density has a negative effect on mass transfer coefficient. â–º The pulp density is the unique factor that affects maximum OUR. â–º In this work, Nealeâ€™s correlation is corrected for prediction of mass transfer coefficient. â–º Biochemical reaction is a limiting factor in the uranium bioleaching process. - Abstract: In this work, the volumetric oxygen mass transfer coefficient and the oxygen uptake rate (OUR) were studied for uranium ore bioleaching process by Acidthiobacillus ferrooxidans in a stirred tank reactor. The Box-Bohnken design method was used to study the effect of operating parameters on the oxygen mass transfer coefficient. The investigated factors were agitation speed (rpm), aeration rate (vvm) and pulp density (% weight/volume) of the stirred tank reactor. Analysis of experimental results showed that the oxygen mass transfer coefficient had low dependence on biomass concentration but had higher dependence on the agitation speed, aeration rate and pulp density. The obtained biological enhancement factors were equal to ones in experiments. On the other hand, the obtained values for Damkohler number (Da < 0.468) indicated that the process was limited by the biochemical reaction rate. Experimental results obtained for oxygen mass transfer coefficient were correlated with the empirical relations proposed by Garcia-Ochoa and Gomez (2009) and Neale and Pinches (1994). Due to the high relative error in the correlation of Neale and Pinches, that correlation was corrected and the coefficient of determination was calculated to be 89%. The modified correlation has been obtained based on a wide range of operating conditions, which can be used to determine the mass transfer coefficient in a bioreactor
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.
Graphical abstract: - Highlights: â€¢ Application of enhanced surfaces in boiling heat transfer. â€¢ Flow and pool boiling heat transfer on the heating surfaces with mini-recesses. â€¢ Minichannel (horizontal) with the enhanced heating wall. â€¢ Determination of heat transfer coefficients and boiling curves. â€¢ Comparative experimental data analysis for flow and pool boiling heat transfer. - Abstract: The paper focuses on the analysis of the enhanced surfaces in such applications as boiling heat transfer. The surfaces have similar geometric parameters for the surface development. Two testing measurement modules with enhanced heating surfaces are used independently, one for flow boiling and the other â€“ for pool boiling research. The heating surfaces with mini-recesses which contact boiling liquid are made by spark erosion. Flow boiling is studied when FC-72 flows through a horizontally positioned minichannel and its bottom wall is heated. These experiments were carried out during under a pressure slightly higher than the atmospheric one. Pool boiling experiments were conducted with FC-72 at atmospheric pressure in the vessel using enhanced sample as the bottom heating surface. Comparison of results for flow and pool boiling indicates that obtained heat transfer coefficients are a few times higher for pool boiling in the boiling incipience conditions. There are basic differences in the local heat transfer coefficients during the development of flow boiling in a minichannel, depending on the location along the flow in the channel. In the subcooled boiling area, heat transfer coefficients are low. In developed boiling, they are high, but they decrease when the amount of vapour in the liquidâ€“vapour mixture rises
Marinucci, C; Bruzzone, P; Stepanov, B
2007-01-01
This paper describes a new method to determine the equivalent heat transfer coefficients, i.e., radial and azimuthal, in CICC’s with parallel cooling channels. The method is based on the measurement of the steady state temperature response to a step heating. The experiment is modelled by a set of transport equations for the temperature distribution that contain explicitly the parametric dependence on the transverse heat transfer coefficients. The equations are solved analytically and the values of the equivalent transverse heat transfer coefficients are obtained as the best fit of the experimental temperature distributions. We show the results obtained with the method by application to a short length sample experiment in the SULTAN test facility using an ITER-type CICC with special instrumentation, and with heaters to generate a variety of heat slugs. The values of heat transfer coefficient are consistent with expected values, based in particular on the theory of dispersion in porous media.
S. I. ANWAR
2012-10-01
Full Text Available In this paper, convective heat transfer coefficient of Indian gooseberry (Emblica officinalis, in three different forms (shreds, slices and pieces, under forced convection mode has been determined. These forms were dried in laboratory drier. Values of constants C and n have been determined using experimental data and regression analysis for calculating values of convective heat transfer coefficient. It was found that the convective heat transfer coefficient varies with form of commodity being dried and decreases as the drying progresses. The value of convective heat transfer coefficient was highest for shredded form (30.39 W/m2oC followed by slices (25.88 W/m2oC and pieces (18.67 W/m2oC when compared at certain final moisture content. The data were also analyzed for per cent uncertainty.
THE EFFECT OF THE ALUMINIUM ALLOY SURFACE ROUGHNESS ON THE RESTITUTION COEFFICIENT
StanisÅ‚aw BÅ‚awucki; Kazimierz Zaleski
2015-01-01
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 ...
Volumetric mass transfer coefficient and hydrodynamic study of a new self-inducing turbine
Highlights: • Experimental study of a new self inducing turbine. • Hydrodynamic parameters study of the generated flow. • Experimental study of the evolution of kLa and we give an empirical correlation. • Comparing our results to a previous research [17]. • Find a good agreements, with better performances of our turbine. - Abstract: The self-inducing turbines are among mobile agitations which present a very interesting potential in terms of energy in the field of wastewater treatment by activated sludge. Often, the reactions involved in this type of contactors are limited by the gas–liquid mass transfer. The objective of this experimental work is the determination of the oxygenation capacity of a new self-inducing turbine, a holed hollow cylinder, having a thickness of W = 1.5 cm and a diameter D = 9 cm, with 6 holes having a diameter of 0.5 cm each. During this experimental work, we evaluated the volumetric mass transfer coefficient kLa, which is directly related to the oxygenation capacity (OC) and this for various rotational speeds of the turbine as well as for various submergences. We finally succeeded to find an empirical correlation for our new self inducing turbine. The most common method used to estimate experimentally the coefficient kLa is the technique of dynamic oxygenation and deoxygenation. We finally concluded that this new turbine had a satisfying aeration capacity, which increases with the increase of the rotational speed, and decreases when increasing the submergence of the impeller
Reconstruction of the heat transfer coefficient on the grounds of experimental data
D. SÅ‚ota
2009-05-01
Full Text Available Purpose: Solidification of pure metal can be modelled by a two-phase Stefan problem, in which the distribution of temperature in the solid and liquid phases is described by the heat conduction equation with initial and boundary conditions. The inverse Stefan problem can be applied to solve design problems in casting process.Design/methodology/approach: In numerical calculations the alternating phase truncation method, the Tikhonov regularization and the genetic algorithm were used. The featured examples of calculations show a very good approximation of the experimental data.Findings: The verification of the method of reconstructing the cooling conditions during the solidification of pure metals. The solution of the problem consists of selecting the heat transfer coefficient on the boundary, so that the temperature in selected points on the boundary of the domain assumes given values.Research limitations/implications: The method requires that it must be possible to describe the sought boundary condition by means of a finite number of parameters. It is not necessary, that the sought boundary condition should be linearly dependent on those parameters.Practical implications: The presented method can be easy applied to solve design problems of different types, e.g. for the design of continuous casting installations (incl. the selection of the length of secondary cooling zones, the number of jets installed in individual zones, etc..Originality/value: Verification, on the grounds of experimental data, the formerly devised method of determining the heat transfer coefficient during the solidification of pure metals.
Kandlikar, S. G.
2013-02-01
Evaporation momentum force arises due to the difference in liquid and vapor densities at an evaporating interface. The resulting rapid interface motion increases the microconvection heat transfer around a nucleating bubble in pool boiling. Microstructure features are developed on the basis of this hypothesis to control the bubble trajectory for (i) enhancing the heat transfer coefficient, and (ii) creating separate liquid and vapor pathways that result in an increased critical heat flux (CHF). An eightfold higher heat transfer coefficient (629 000 W/m2 Â°C) and two-and-half times higher CHF (3 MW/m2) over a plain copper surface were achieved with water.
Leblay, P.; Henry, J.F.; Caron, D; Leducq, D.; Bontemps, A.; Fournaison, L
2012-01-01
A methodology has been developed based on periodic excitation by Joule effect and infrared thermography measurement. It has been applied to measure heat transfer coefficients of water flowing in a round tube and in a multiport-flat tube. Models were developed to deduce heat transfer coefficient from wall temperature amplitude and heat flux measurement. For the round tube and for the multiport flat tubes, Reynolds number investigated ranges respectively from 2000 to 14000 and from 800 to 10000...
Low-Flow Film Boiling Heat Transfer on Vertical Surfaces
Munthe Andersen, J. G.; Dix, G. E.; Leonard, J. E.; Sun, K. H.
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....
With the cost of water quality research at the watershed level, modeling has become an important tool for researchers. When modeling nitrate transport within drainage networks, denitrification within the sediments needs to be accounted for. Birgand et al. developed an equation using a term called a ...
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. PMID:23464237
The role of surface energy coefficients and nuclear surface diffuseness in the fusion of heavy-ions
Dutt, Ishwar; Puri, Rajeev K.
2010-01-01
We discuss the effect of surface energy coefficients as well as nuclear surface diffuseness in the proximity potential and ultimately in the fusion of heavy-ions. Here we employ different versions of surface energy coefficients. Our analysis reveals that these technical parameters can influence the fusion barriers by a significant amount. A best set of these parameters is also given that explains the experimental data nicely.
This paper presents a comparison of the measured horizontal, smooth-tube, flow boiling heat transfer coefficient of R11 to that of its proposed ozone safe replacement R123. The fluid properties of R11 and R123 are similar. The flow boiling data for the two fluids are similar for the convective region. However, the heat transfer coefficient for R11 in the nucleate flow boiling region was consistently observed to be, on average, 8.5% to 33% larger than that for R123. The influence of Reynolds number and heat flux on the heat transfer-thermodynamic quality relationship is also presented. Predictions of the heat transfer coefficient with two open literature flow boiling correlations were compared to the measured data. The heat transfer coefficients predicted with the correlations were, on average from 13% to 57% greater than the measured heat transfer coefficients. Not until recently has there been sufficient thermodynamic or transport data for R123 to perform an accurate heat transfer analysis for that fluid. Great care was taken to ensure that the most carefully measured property data were used for this analysis. For the convenience of the reader, both the R123 and R11 property data used in this study are presented
Extensive studies on transfer of 131I through grass-cow-milk pathway after the Chernobyl accident were reported. But, under nor mal operational conditions of a power reactor, 131I is not present in measurable concentration in environmental matrices around a nuclear power generating station. Hence, database on 131I transfer coefficients for grass-cow-milk pathway in equilibrium conditions in the environment of a nuclear power plant are sparse. One of method to estimate the equilibrium transfer coefficient is to use stable iodine, which is present naturally in very low levels in the environmental matrices. By measuring the concentration of stable iodine concentration in grass and cow milk, the grass-to-milk transfer coefficient of iodine can be estimated. Since the metabolism of stable and radioiodine is same, the data obtained for transfer coefficient of stable iodine could be used for predicting the transfer for radioiodine to cow milk. The measurement of stable iodine in the environmental sample is very challenging because of its extremely low concentration. Neutron Activation Analysis (NAA) can be used to estimate stable iodine in the environment matrices after suitably optimizing the condition to minimize interferences. This paper presents the results of a systematic study on the transfer coefficients for grass-cow milk pathway of iodine in normal (equilibrium) situations as well as for a postulated (simulated) emergency condition in Kaiga region
Several experiments and theoretical researches have been performed to calculate condensation heat transfer and many correlations have been suggested. Generally, correlations are largely divided into two groups: applicable to laminar flow or turbulent flow. That is because, depending on whether flow is laminar or turbulent, flow characteristics and phenomena which play major role in heat transfer process are greatly different. Film Reynolds number is widely used to determine whether flow is laminar or turbulent. MARS code uses two condensation heat transfer coefficient(HTC) correlations: Nusselt's correlation for laminar flow and Shah's for turbulent. Condensation HTCs are calculated by using both correlations and the larger one is taken, that is, Film Reynolds number is not used to determine flow condition and select HTC correlation. This means that a correlation may be able to be incorrectly used just because its HTC is larger, though a correlation is not in an applicable range. In this paper, simulation results of two condensation experiments using MARS code are discussed. It is shown that, though flow condition is similar, different correlation can be used and how much calculated results are differentiated from experimental data
Heat transfer coefficient calculation for analysis of ITER shield block using CFX and ANSYS
Highlights: â†’ Benchmark HTC modeling in CFX and compare this modeling with empirical formulas. â†’ Given the error formulas derived from theory. â†’ Benchmark HTC modeling in ANSYS and the results is consistent with the conclusion of error estimate from theory. - Abstract: In thermal-mechanical analysis of ITER shield block using ANSYS code, it needs the real heat transfer coefficient (HTC) values which are computed by CFX. Because two kinds of HTC values can be gotten from CFX and which has some difference with ANSYS, so it is necessary to estimate the error caused by HTC transferred from CFX to ANSYS. In this paper, HTC values got from CFX was firstly benchmarked with the results got from empirical formulas, then estimated the error caused by HTC transferred from theory and gave the expressions of the error, thirdly benchmark work of ANSYS results in 4 cases was done, then compared the error with former error estimated formula derived from theory. In the end, conclusions will be given based on above benchmark works.
The paper analyses the influence of measuring errors of the operation parameters (flows, temperatures, pressures, and concentrations) in the experimental determination of the mass and heat transfer coefficients. Data obtained on experimental plants for hydrogen isotopes separation, by hydrogen distillation and water distillation, and calculus model for errors propagation are presented. The results are tabulated. The variation intervals of transfer coefficients are marked graphically. The study of the measuring errors is an intermediate stage, extremely important, in experimental determination of criterion relation coefficients, specific relations for B7 structured packing. (authors)
Determination of the pressure drop and the heat transfer coefficient in a gas-solid two-phase flow
An experimental study was developed for a vertical gas solid two phase flow with heat transfer by analysing the gradient of both static pressure and temperature alongside the system. The measurements were used to produce the isothermal hydrodynamic entry lenght and the gas-solid heat transfer coefficient as well as the influence of the solid particle. (Author)
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. PMID:23759735
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 103Re5). 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 239Pu on transfer rates and absorption parameters
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 239Pu, 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 fr, Sr and Ss, 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 239Pu in many cases. (author)
Comparison of the methods for calculating the interfacial heat transfer coefficient in hot stamping
This paper presents a hot stamping experimentation and three methods for calculating the Interfacial Heat Transfer Coefficient (IHTC) of 22MnB5 boron steel. Comparison of the calculation results shows an average error of 7.5% for the heat balance method, 3.7% for the Beck's nonlinear inverse estimation method (the Beck's method), and 10.3% for the finite-element-analysis-based optimization method (the FEA method). The Beck's method is a robust and accurate method for identifying the IHTC in hot stamping applications. The numerical simulation using the IHTC identified by the Beck's method can predict the temperature field with a high accuracy. - Highlights: â€¢ A theoretical formula was derived for direct calculation of IHTC. â€¢ The Beck's method is a robust and accurate method for identifying IHTC. â€¢ Finite element method can be used to identify an overall equivalent IHTC
Distribution coefficient and transfer factor of stable iodine in agricultural soils in Aomori, Japan
Soil-to-solution distribution coefficient (Kd) and soil-to-plant transfer factor (TF) were determined for agricultural soils and selected plants in Aomori Prefecture, Japan, by means of analysis of stable I in soil and plant samples. The concentration of I in the soil samples varied between 0.52 and 82.8 mg kg-1 (geometric mean of 4.4 mg kg-1). The Kd, which was defined as the ratio of I concentration in soil to that in water extracted from the soil, was 1.5 x 103 in geometric mean (L/kg). The TF value was defined as the ratio of I concentration in plant to that in soil. Geometric means of the TF on dry weight base obtained in this study were 3.2 x 10-2 for komatsuna, 2.0 x 10-2 for Japanese radish and 2.3 x 10-2 for pasture grass. (author)
E. Hetmaniok
2012-12-01
Full Text Available A procedure based on the Artificial Bee Colony algorithm for solving the two-phase axisymmetric one-dimensional inverse Stefanproblem with the third kind boundary condition is presented in this paper. Solving of the considered problem consists in reconstruction of the function describing the heat transfer coefficient appearing in boundary condition of the third kind in such a way that the reconstructed values of temperature would be as closed as possible to the measurements of temperature given in selected points of the solid. A crucial part of the solution method consists in minimizing some functional which will be executed with the aid of one of the swarm intelligence algorithms - the ABC algorithm.
Enrichment factors and transfer coefficients from soil to rye plants by INAA
An extensive investigation of elemental levels in cereals and their cultivation soils has been going on across the main production areas of mainland Portugal, with a view to an eventual biofortification of major cultivars through agronomic practices. Cereals are an obvious choice as primary vehicles for food-supplementation programs, especially in countries where they definitely weigh in the dietary intake (like Portugal), and regions whose geographical and/or pedological features may account for nutrient deficiencies in typical diets. Mature rye plants (Secale cereale L.; roots and grains) and local soils were collected in the summer of 2009 from two regions of northern Portugal, and put through k0-standardized, instrumental neutron activation analysis (k0-INAA). Overall, the results (elemental concentrations, enrichment factors, transfer coefficients) seem to confirm an efficient uptake of elements from soil and their translocation to the aerial parts of the plants, notably to the ones that really matter in human nutrition (grains). (author)
Some studies on direct-contact condensation in cocurrent stratified flow of steam and subcooled water were reviewed. Several approaches have been performed to develop the condensation heat transfer coefficient relationship. The local Nusselt number is correlated in terms of the local water Reynolds and Prandtl numbers as well as the steam Froude number. In addition, a turbulence-centered model, developed principally for gas absorption in several geometries, is modified by using calculated interfacial parameters for the turbulent velocity and length scales. These approaches result in a fairly good agreement with the data, whereas, the turbulence-centered model is here recommended since it is based on the turbulent properties which may be closely related to the condensation phenomena. (Author)
Boiling on free-falling spheres; Drag and heat transfer coefficients
Zvirin, Y. (Technion-Israel Inst. of Tech., Haifa (Israel). Dept. of Mechanical Engineering); Hewitt, G.F. (Imperial Coll. of Science and Technology, London (UK). Dept. of Chemical Engineering and Chemical Technology); Kenning, D.B.R. (Oxford Univ. (UK). Dept. of Engineering Science)
1990-01-01
Experiments have been conducted to measure drag (c{sub D}) and heat transfer coefficients (h) and to study the boiling nature on heated spheres free-falling in saturated and subcooled water. Simultaneous measurements of the transient sphere velocity and temperature during the fall enabled calculation of c{sub D}, heat fluxes, and h values. It has been found that the drag decreases with the initial sphere temperature, T{sub 0}. The measured results, as well as still and motion photography, show that at T{sub 0} {gt} 450{degrees}C film boiling prevails, with low heat fluxes at the beginning of the transient. In some cases the film collapses, leading to a transition to disturbed-film and micro-bubble regimes, associated with larger heat fluxes and also solid-liquid interactions, with lateral motion of the sphere (shoot-off).
Mechanistic model of iodine mass transfer at pool surfaces
Mass transfer of molecular iodine (I2) at the water poolâ€“gas interface can be modeled by means of a water surface film renewal model superimposed to the established two-film theory, where the water-side I2 mass transfer coefficient kw is related to the I2 molecular diffusivity in water D and the airâ€“water contact time a according to The present paper describes a mechanistic approach to determine the contact time from the water flow distribution. The method makes use of a numerical simulation of the poolwater flow, and a numerical evaluation of the contact time distribution at the pool surface. Owing to the numerical treatment it can be applied to pool geometries of any kind, which makes it applicable for nuclear reactor safety studies in general kw=âˆš(D/Ï€a) The present paper describes a mechanistic approach to determine the contact time from the water flow distribution. The method makes use of a numerical simulation of the poolwater flow, and a numerical evaluation of the contact time distribution at the pool surface. Owing to the numerical treatment it can be applied to pool geometries of any kind, which makes it applicable for nuclear reactor safety studies in general
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.
THE EFFECT OF THE ALUMINIUM ALLOY SURFACE ROUGHNESS ON THE RESTITUTION COEFFICIENT
StanisÅ‚aw BÅ‚awucki
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.
New potential energy surface for the HCS+â€“He system and inelastic rate coefficients
A new high quality potential energy surface is calculated at a coupled-cluster single double triple level with an aug-cc-pV5Z basis set for the HCS+â€“He system. This potential energy surface is used in low energy quantum scattering calculations to provide a set of (de)-excitation cross sections and rate coefficients among the first 20 rotational levels of HCS+ by He in the range of temperature from 5 K to 100 K. The paper discusses the impact of the new ab initio potential energy surface on the cross sections at low energy and provides a comparison with the HCO+â€“He system. The HCS+â€“He rate coefficients for the strongest transitions differ by factors of up to 2.5 from previous rate coefficients; thus, analysis of astrophysical spectra should be reconsidered with the new rate coefficients
New potential energy surface for the HCS(+)-He system and inelastic rate coefficients.
Dubernet, Marie-Lise; Quintas-SÃ¡nchez, Ernesto; Tuckey, Philip
2015-07-28
A new high quality potential energy surface is calculated at a coupled-cluster single double triple level with an aug-cc-pV5Z basis set for the HCS(+)-He system. This potential energy surface is used in low energy quantum scattering calculations to provide a set of (de)-excitation cross sections and rate coefficients among the first 20 rotational levels of HCS(+) by He in the range of temperature from 5 K to 100 K. The paper discusses the impact of the new ab initio potential energy surface on the cross sections at low energy and provides a comparison with the HCO(+)-He system. The HCS(+)-He rate coefficients for the strongest transitions differ by factors of up to 2.5 from previous rate coefficients; thus, analysis of astrophysical spectra should be reconsidered with the new rate coefficients. PMID:26233137
Effect of heat transfer coefficient on sheath and fuel centreline temperatures in SCWRS
SuperCritical Water-cooled nuclear Reactors (SCWRs) utilize light water above the pseudocritical point as a reactor coolant. This Generation IV reactor concept is currently in its preliminary design phase. This paper discusses the variables that influence heat transfer from the fuel. The coolant Heat Transfer Coefficient (HTC). Axial Heat Flux Profile (AHFP), sheath (clad) geometry and fuel thermal conductivity all impact the sheath and fuel centreline temperatures. The presented analysis utilizes the most recent HTC correlation developed for supercritical water, the Mokry et al. correlation (2009). The proposed sheath geometry is based on smaller diameter fuel elements than that of the current design to accommodate more fuel rods. Both uniform and cosine AHFPs, at average channel power, are applied. The results presented describe a sensitivity analysis of the effect of incrementing the HTC on sheath and fuel centreline temperatures. With a uniform AHFP and increasing HTC increments from 50 - 200% HTC the average temperature difference compared to 100% HTC are decreases from 13 to -18%. With a cosine AHFP and HTC incremented from 50 - 200% HTC the average temperature difference compared to 100% HTC have the range of 20 to -10%. (author)
Degradation of condensation HTC (Heat Transfer Coefficient) under an air presence in a vertical tube was explored both experimentally and analytically, with the aim of developing evaluation methods for the design of passive containment cooling systems in the next generation reactors. Measurements were done using a stainless steel tube of 49.5 mm I.D. and 2.0 m length, enclosed by a cooling jacket. Flow rates of steam, air and cooling water, and the system pressure were varied as the experimental parameters. First, condensation HTC was correlated to a function of mixture Reynolds number and air partial pressure ratio, in which thermal resistance of the condensate film was excluded. Secondly, an analogy between heat and mass transfer was applied. The calculated values agreed well with the measured values of condensation HTCs in turbulent flow, while an obvious underestimation was observed for the flow in which mixture Reynolds number was lower than 2,300. Finally, ratios of calculated to experimental HTCs, which include thermal resistances of the condensate film, averaged 1.01 for turbulent steam flow. (author)
In this study, the air side heat transfer coefficient of an aluminium mini-channel heat exchanger was investigated for single-phase flow in the mini-channel, with water in the tubes and air on the outside. Research methods included hydraulic tests on a single mini-channel tube, Wilson Plot experiments and experiment validation. Results obtained from the hydraulic test showed that turbulent flow occurred in the tube at a Reynolds number of 830. Wilson Plot experiments were conducted to determine air side heat transfer coefficient of the heat exchanger. The tube side Reynolds number was maintained above 1000 to ensure turbulent flow and tube side heat transfer coefficient was calculated using Gnielinski equation for turbulent flow. The air side heat transfer coefficients obtained from the Wilson Plot experiments were in good agreement with known correlations. The outcome of this study is to use the air side heat transfer coefficient to calculate the performance of refrigerant condensers for different tube pass ratios and flow pass configurations
Pronobis, M.; Kalisz, S.; Wejkowski, R.
The paper presents the results of an investigation concerning heat transfer and pressure loss in air crossflow of diagonally shaped membrane heating surfaces. The heat and mass transfer analogy by means of naphthalene sublimation technique is used in order to evaluate mean Nusselt number values in such tube banks. The effect of tube bank arrangement on heat transfer coefficients and flow resistance is discussed. Convective heat transfer and pressure loss characteristics of diagonally shaped membrane tube banks, plain tube banks and ordinary membrane tube banks are compared.
A correlation for free convection heat transfer from vertical wavy surfaces
Ashjaee, M.; Amiri, M.; Rostami, J. [University of Tehran, Department of Mechanical Engineering, Tehran (Iran)
2007-11-15
Free convection heat transfer along an isothermal vertical wavy surface was studied experimentally and numerically. A Mach-Zehnder Interferometer was used in the experiment to determine the local heat transfer coefficients. Experiments were done for three different amplitude-wavelength ratios of {alpha} = 0.05, 0.1, 0.2 and the Rayleigh numbers ranging from Ra{sub l} = 2.9 x 10 {sup 5} to 5.8 x 10 {sup 5}. A finite-volume based code was developed to verify the experimental study and obtain the results for all the amplitude-wavelength ratios between {alpha} = 0 to 0.2. It is found that the numerical results agree well with the experimental data. Results indicate that the frequency of the local heat transfer rate is the same as that of the wavy surface. The average heat transfer coefficient decreases as the amplitude-wavelength ratio increases and there is a significant difference between the average heat transfer coefficients of the surface with {alpha} = 0.2 and those surfaces with {alpha} = 0.05 and 0.1. The experimental data are correlated with a single equation which gives the local Nusselt number along the wavy surface as a function of the amplitude-wavelength ratio and the Rayleigh number. (orig.)
Reactions involving electron transfer at semiconductor surfaces
Rapid isotopic equilibration was observed upon contacting an equimolar mixture of (16O2 + 18O2) at 295 or 77 K with oxygen-deficient surfaces of pure and doped zinc oxides from which light was excluded at all stages. Kinetic expressions for opposing second-order reactions accurately described variations in mole fraction of 16O2, 16O18O and 18O2 in the gas phase during the approach to full isotopic equilibration at 295 or 77 K. Rate constants thereby derived for this R0-type exchange did not correlate with reported concentrations of conduction-band electrons for the zinc oxides, indicating that the rate-determining process for exchange was not collective-electron type charge transfer at the oxygen-deficient surfaces in the absence of illumination. Surfaces could be rendered inactive by extensive preoxidation in 16O2 at 650 K in the dark, but heating for 2 h periods in the dark under continuous evacuation restored activity to a progressively increasing extent at temperatures of 400 to 650 K. Preadsorption of H2O, H2 or (CH3)2CHOH at 295 K strongly inhibited activity. An explanation of the observed results is developed. (author)
Electron transfer in gas surface collisions
In this thesis electron transfer between atoms and metal surfaces in general is discussed and the negative ionization of hydrogen by scattering protons at a cesiated crystalline tungsten (110) surface in particular. Experimental results and a novel theoretical analysis are presented. In Chapter I a theoretical overview of resonant electron transitions between atoms and metals is given. In the first part of chapter II atom-metal electron transitions at a fixed atom-metal distance are described on the basis of a model developed by Gadzuk. In the second part the influence of the motion of the atom on the atomic charge state is incorporated. Measurements presented in chapter III show a strong dependence of the fraction of negatively charged H atoms scattered at cesiated tungsten, on the normal as well as the parallel velocity component. In chapter IV the proposed mechanism for the parallel velocity effect is incorporated in the amplitude method. The scattering process of protons incident under grazing angles on a cesium covered surface is studied in chapter V. (Auth.)
Heat transfer during cooling of hot surfaces by water nozzles
M. Pøíhoda
2009-10-01
Full Text Available Method of cooling in a secondary zone of continuous casting of steel has a significant influence on a quality of continuously cast products mainly from the point of view of internal and surface defects as well as zonal segregations. At the department of thermal engineering, a physical model of the secondary zone has been developed, which enables testing of both water and water-air nozzles. During laboratory measurements cooling effects of a cone nozzle have been expressed by means of three parameters. Most commonly used parameter is an admission characteristic, infrequently heat transfer coefficient is determined and newly a measuring of dynamic impact of the cooling water has been introduced.
Karadag, Refet [Department of Mechanical Engineering, Harran University, Osmanbey Kampusu, 63300 Sanliurfa (Turkey)], E-mail: rkaradag21@yahoo.com
2009-06-15
In this study, radiative and convective heat transfer coefficients at the ceiling are determined for a cooled ceiling room. Firstly, convective heat transfer is simulated numerically neglecting the radiative heat transfer at the surfaces ({epsilon}{sub f} = {epsilon}{sub w} = {epsilon}{sub c} = 0), then, radiative heat transfer is calculated theoretically for different surface emissivities ({epsilon}{sub f} = {epsilon}{sub w} = {epsilon}{sub c} = 0.5, 0.6, 0.7, 0.8 and 0.9) for different room dimensions (3 x 3 x 3, 4 x 3 x 4 and 6 x 3 x 4 m) and thermal conditions (T{sub f} = 25 deg. C, T{sub w} = 28-36 deg. C and T{sub c} = 0-25 deg. C). Numerical data is compared with the results of correlations based on experimental data given in literature. New equations related to convective and total (including the effect of convection and radiation) heat transfer coefficients for ceiling are found in the current study.
Parvataneni
2013-01-01
The present theoretical investigation deals with the problem of free convective heat transfer from a vertical plate having linear temperature gradient along its surface to the surrounding thermally stratified fluid. Integral method of analysis is adopted to investigate the effect of four parameters viz., the gradients of temperature in the fluid and the wall, Grashof number and Prandtl number on heat transfer coefficients. It is observed from the numerical results that an increase in the su...
Heat transfer and friction coefficients for air flow in a smooth annulus
In the Heat Transfer Laboratory of INR various experiments on single rough or smooth rods contained in smooth annuli have been performed in the past. These experiments have been performed with rods of large diameters. Recently however a series of experiments with rough rods of 8 mm O.D. has been carried out. To check if the new experimental apparatus and the experimental techniques used were correct, an experiment was performed with an inner heated tube of 8 mm O.D. contained in the smooth outer tube of 16 mm I.D. used in the experiments with the rough rods. The results of this experiment are reported in the present paper. The friction and heat transfer data obtained with the turbulent flow runs of the present experiment agree well with previous experiments performed at INR with larger smooth annuli. The smaller size of the annulus and the improvements in mass flow and pressure drop measurements have allowed to extend the investigations to laminar flow. The laminar flow friction data can be correlated in terms of fsub(B) versus Re-sub(W), where the gas physical properties in Re-sub(W) are evaluated at the temperature T-sub(W), average between the temperature of the inner surface and the outer surface of the annulus, weighted over the two surfaces. This correlation method has been already suggested by us for rough rods in a smooth tube. The laminar flow heat transfer data, correlated in terms of Nusub(B) versus Gr-sub(W) tend to be lower than the analytical prediction of Heaton, Reynolds and Kays, a fact which could be explained by the superposition of natural convection. (orig.)
Determination of surface tension coefficient of liquids by diffraction of light on capillary waves
This paper describes a simple technique for determining the coefficient of the surface tension of liquids, based on laser light diffraction on capillary waves. Capillary waves of given frequency are created by an exciter needle acting on the surface of liquid and represent a reflective diffraction grating, the constant of which (the wavelength of capillary waves) can be determined based on a known incidence angle of light (grazing angle). We obtain the coefficient of the surface tension of liquids by applying the dispersion relation for capillary waves and analyze the difficulties that arise when setting up and conducting the experiment in detail. (paper)
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.
Intelligent tires for identifying coefficient of friction of tire/road contact surfaces
Matsuzaki, Ryosuke; Kamai, Kazuto; Seki, Ryosuke
2015-03-01
Intelligent tires equipped with sensors as well as the monitoring of the tire/road contact conditions are in demand for improving vehicle control and safety. With the aim of identifying the coefficient of friction of tire/road contact surfaces during driving, including during cornering, we develop an identification scheme for the coefficient of friction that involves estimation of the slip angle and applied force by using a single lightweight three-axis accelerometer attached on the inner surface of the tire. To validate the developed scheme, we conduct tire-rolling tests using an accelerometer-equipped tire with various slip angles on various types of road surfaces, including dry and wet surfaces. The results of these tests confirm that the estimated slip angle and applied force are reasonable. Furthermore, the identified coefficient of friction by the developed scheme agreed with that measured by standardized tests.
The friction factor and Stanton number for flow past a roughened surface are determined by the parameters A and R(h+) of the universal law of friction and A/sub H/ and G(h+) of the universal law of heat transfer. The methods to be used for determination of these parameters for the particular roughness to be used in the Core Flow Test Loop (CFTL) are presented. Examples are given concerning the application of these methods to both transitional and fully rough flow using experimental results taken from the literature
Kim, D.S. [arsenal research, Sustainable Energy Systems, Giefinggasse 2, 1210 Vienna (Austria); Infante Ferreira, C.A. [Delft University of Technology, Engineering Thermodynamics, Leeghwaterstraat 44, 2628 CA Delft (Netherlands)
2009-01-15
The effects of the surface geometry and of a surfactant on the characteristics of LiBr-water solution falling films are experimentally investigated. Two different surfaces (flat copper plate and the same copper plate covered with a copper wire screen) are tested with four fluids (pure water and 50% lithium bromide-water solution with or without 100 ppm of 2-ethyl-1-hexanol) for Reynolds numbers from 40 to 110. Flow patterns and heat and mass transfer coefficients are discussed. Marangoni convection was observed in water-cooled LiBr-water flows resulting in significant heat and mass transfer enhancement. 2-ethyl-1-hexanol enhances heat and mass transfer in LiBr-water flows by more than a factor of two. 2-ethyl-1-hexanol in water makes copper surface strongly hydrophobic. The wire screen promotes absorption process in adiabatic conditions but hinders the process in non-adiabatic conditions by reducing the Marangoni convection induced by 2-ethyl-1-hexanol. The experimental heat and mass transfer coefficients are presented in dimensionless forms. (author)
Heat Transfer and Pressure Drop with Rough Surfaces, a Literature Survey
This literature survey deals with changes in heat transfer coefficient and friction factor with varying nature and degree of roughness. Experimental data cover mainly the turbulent flow region for both air and water as flow mediums. Semiempirical analysis about changes in heat transfer coefficient due to roughness has been included. An example of how to use these data to design a heat exchanger surface is also cited. The extreme case of large fins has not been considered. Available literature between 1933 - 1963 has been covered
Highlights: â–º Measured subcooled boiling pressure drop and local heat transfer coefficient in horizontal tubes. â–º Infra-red thermal imaging is used for wall temperature measurement. â–º Developed correlations for pressure drop and local heat transfer coefficient. -- Abstract: Horizontal flow is commonly encountered in boiler tubes, refrigerating equipments and nuclear reactor fuel channels of pressurized heavy water reactors (PHWR). Study of horizontal flow under low pressure and low flow (LPLF) conditions is important in understanding the nuclear core behavior during situations like LOCA (loss of coolant accidents). In the present work, local heat transfer coefficient and pressure drop are measured in a horizontal tube under LPLF conditions of subcooled boiling. Geometrical parameters covered in this study are diameter (5.5 mm, 7.5 mm and 9.5 mm) and length (550 mm, 750 mm and 1000 mm). The operating parameters varied are mass flux (450â€“935 kg/m2 s) and inlet subcooling (29 Â°C, 50 Â°C and 70 Â°C). Infra-red thermography is used for the measurement of local wall temperature to estimate the heat transfer coefficient in single phase and two phase flows with water as the working medium at atmospheric pressure. Correlation for single phase diabatic pressure drop ratio (diabatic to adiabatic) as a function of viscosity ratio (wall temperature to fluid temperature) is presented. Correlation for pressure drop under subcooled boiling conditions as a function of Boiling number (Bo) and Jakob number (Ja) is obtained. Correlation for single phase heat transfer coefficient in the thermal developing region is presented as a function of Reynolds number (Re), Prandtl number (Pr) and z/d (ratio of axial length of the test section to diameter). Correlation for two phase heat transfer coefficient under subcooled boiling condition is developed as a function of boiling number (Bo), Jakob number (Ja) and Prandtl number (Pr)
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 the grid spacers, which length was about 50 cm. (author)
Authors performed post-CHF experiments under wider pressure ranges of 2 MPa - 18 MPa, wider mass flux ranges of 33 kg/m2s - 1651 kg/m2s 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 the grid spacers, which length was about 50 cm. (author)
Heat/Mass Transfer Measurement on The Tip Surface Of Rotor Blade With Squlear Rim
Park, Jun Su; Lee, Dong Hyun; Lee, Woo Jin; Cho, Hyung Hee; Rhee, Dong-Ho; Kang, Shin-Hyung
2010-06-01
The present study investigates local heat/mass transfer characteristics on blade tip surface with squealer rim. A linear cascade experimental setup consists of three large scale airfoils was used. The axial chord length and turning angle of test blade are 237 mm and 126Â°, respectively. Heat/mass transfer coefficients were measured with three different rim heights (3%, 6% and 9% of axial chord length) and fixed tip clearance (2% of axial chord length). Main flow Reynolds number based on axial chord length is 1.5Ã—105. Naphthalene sublimation method is used to measure the detailed mass transfer coefficient on the blade tip surface. The heat/mass transfer results show that as the rim height increases, the peak values on the upstream region of the tip surface decreases and moves to the suction side rim. At the downstream region of the tip surface, the pitch-wise averaged heat/mass transfer coefficients increases as the rim height increases.
Cho, Mintaek; Lee, Taehoon; Shin, Youngjoon; Lee, Kiyoung; Kim, Yongwan [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Chang, Jiwoon; Lee, Youngjune [Chungnam National Univ., Daejeon (Korea, Republic of)
2013-05-15
In this paper, a sensitivity analysis on the overall heat transfer coefficient has been carried out as a function of operation temperature and pressure. The sulfur-iodine (SI) cycle and Westinghouse sulfur hybrid cycle, combined with a very high temperature gas-cooled reactor (VHTR), are well-known as feasible technologies for hydrogen production. The SI process consists of a Bunsen reactor; H{sub 2}SO{sub 4}, SO{sub 3}, and HIx decomposers; and a HI pre-heater. The overall heat transfer coefficient of the process heat exchanger (PHE) used in the SI process is a very important factor when sizing the PHE.
Webster John G; Chachati Louay; Tangwongsan Chanchana; Farrell Patrick V
2006-01-01
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 Ã— 3.2 mm thin film resistive temperature detector (RTD) sensor. We used a circulation system t...
Oleksandr I. Brunetkin
2015-06-01
Full Text Available The article highlights the reason of complication of usage of alternative fuel gases on the installed equipment — the organization of effective process of their combustion. As one of the parameters affecting the dynamic characteristics of the control object, the coefficient of convective heat transfer is considered. The effect of changes of physical characteristics of heat and rate of combustion products arising from the use of various combustible gases on it is determined. It is found that the main cause of the change of heat transfer coefficient is the presence of flammable gases of carbon monoxide and hydrogen in the mixture.
In this paper, a sensitivity analysis on the overall heat transfer coefficient has been carried out as a function of operation temperature and pressure. The sulfur-iodine (SI) cycle and Westinghouse sulfur hybrid cycle, combined with a very high temperature gas-cooled reactor (VHTR), are well-known as feasible technologies for hydrogen production. The SI process consists of a Bunsen reactor; H2SO4, SO3, and HIx decomposers; and a HI pre-heater. The overall heat transfer coefficient of the process heat exchanger (PHE) used in the SI process is a very important factor when sizing the PHE
Gilles Hebrard; Marupatch Jamnongwong; Jidapa Wachirasak; Pisut Painmanakul
2009-01-01
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...
A technique is described which provides a method of obtaining average fuel-to-coolant heat-transfer coefficients for individual fuel subassemblies in fast reactors. A series of experiments on the UK prototype fast reactor over the period 1977-1979 has demonstrated that the technique is simple, requires no special instrumentation other than thermocouples to monitor coolant outlet temperatures, and that the measurement can be made during normal reactor operation. Thus it is possible to determine how heat-transfer coefficients change with operating conditions and with the degree of burn up in the fuel. (U.K.)
An experimental study on forced convection in a four-cusp duct simulating a typical nuclear reactor channel degraded by accident is presented. Transfer coefficients were obtained by using the analogy between heat and mass tranfer, with the naphtalene sublimation technique. The experiment consisted in forcing air past a four-cusp naphthalene moulded duct. Mass transfer coefficients were determined in nondimensional form as Sherwood number. Experimental curves correlating the Sherwood number with a nondimensional length, x+, were obtained for Reynolds number varying from 891 to 30.374. This range covers typical flow rates that are expected to exist in a degraded nuclear reactor core. (Author)
Kwang-Il Choi; Nguyen-Ba Chien; Jong-Taek Oh
2013-01-01
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 35â€‰kWâ€‰mâˆ’2, mass fluxes ranging from 100 to 650â€‰kgâ€‰mâˆ’2â€‰sâˆ’1, saturation temperatures of 5, 10, and 15Â°C, and quality up to 1.0. The test sections are made of stainless steel tubes with inner diameters of 1.5 and 3.0â€‰mm, the lengths of 1000 and 2000. Effects of heat flux,...
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...
Pressure-induced absorption coefficients for radiative transfer calculations in Titan's atmosphere
The semiempirical theory of Birnbaum and Cohen (1976) is used to calculate the FIR pressure-induced absorption (PIA) spectra of N2, CH4, N2 + Ar, N2 + CH4, and N2 + H2 under conditions like those in the Titan troposphere. The results are presented graphically and compared with published data from laboratory measurements of PIA in the same gases and mixtures (Dagg et al., 1986; Dore et al., 1986). Good agreement is obtained, with only a slight underestimation of PIA at 300-400/cm in the case of CH4. The absorption coefficients are presented in tables, and it is suggested that the present findings are of value for evaluating the effects of tropospheric clouds on the Titan FIR spectrum and studying the greenhouse effect near the Titan surface. 24 references
Transfer coefficients (the equilibrium ratio be-tween radionuclide activity concentration in milk or meat and the daily intake of radionuclide) are widely used to predict the contamination of animal products following the release of radionuclides into the environment. For a transfer coefficient to be generally applicable, its value must be constant for a range of circumstances. However, this is not the case for radiostrontium, the behaviour of which is strongly influenced by that of the homeostatically controlled nutrient, calcium. In this study, a relationship is derived between radiostrontium transfer coefficients and dietary calcium intake which takes into account the observed ratio for strontium:calcium transfer to milk. This relationship is tested against a range of observed data collated from the literature (n = 30) and found to account for 93% of the variability in transfer coefficient values. Model calculations show that a reduction in Fm of at least 40%-60% would be expected if dairy cattle, fed rations typical for well-managed herds, were supplemented with 100-200 g per day. Larger reductions would be predicted when dietary calcium intake is low. (orig.). With 3 figs., 1 tab
In this paper, a study of convective mass transfer coefficient and rate of moisture removal from cabbage and peas for open sun drying and inside greenhouse drying has been performed as a function of climatic parameters. The hourly data for the rate of moisture removal, crop temperature, relative humidity inside and outside the greenhouse and ambient air temperature for complete drying have been recorded. The experiments were conducted after the crop harvesting season from September to December 2001. These data were used for determination of the coefficient of convective mass transfer and then for development of the empirical relation of convective mass transfer coefficient with drying time under natural and forced modes. The empirical relations with convective mass transfer for open and greenhouse drying have been compared. The convective mass transfer coefficient was lower for drying inside the greenhouse with natural mode as compared to open sun drying. Its value was doubled under the forced mode inside the greenhouse drying compared to natural convection in the initial stage of drying
In this study, the interfacial heat transfer coefficient (IHTC) for vertically upward unidirectional solidification of a eutectic Al-Si casting on water cooled copper and steel chills was measured during solidification. A finite difference method (FDM) was used for solution of the inverse heat conduction problem (IHCP). Six computer guided thermocouples were connected with the chill and casting, and the time-temperature data were recorded automatically. The thermocouples were placed, located symmetrically, at 5 mm, 37.5 mm and 75 mm from the interface. As the lateral surfaces are very well heat isolated, the unidirectional solidification process starts vertically upward at the interface surface. The measured time-temperature data files were used by a FDM using an explicit technique. A heat flow computer program has been written to estimate the transient metal-chill IHTC in the IHCP. The experimental and calculated temperatures have shown excellent agreement. The IHTC during vertically upward unidirectional solidification of an Al-Si casting on copper and steel chills have varied between about 19-9.5 kW/m2 K and 6.5-5 kW/m2 K, respectively
Heat transfer in an unwetted zone in hot-surface cooling
Pin cladding overheating may occur because of increasing power or reduction in coolant flow rate, which perturb normal working conditions. Conditions return to normal after the perturbation only if the heat output in a pin corresponds to the heat removed by the coolant. It is necessary to calculate the heat transfer at all stages in such a situation to provide nuclear safety. At present, little is known about heat transfer when hot pins are cooled by underheated water or steam-water mixtures with low steam contents in particular because measurements are difficult. Under stationary conditions, the high critical heat fluxes mean that the temperatures in the transfer surfaces beyond the crisis zone become too high, which leads to failure. When measurements are made with hot surfaces cooling, the relatively high transfer coefficients at high mass flow rates mean that the cooling lasts only some seconds. As the cooling time shortens, the equipment specifications tighten, and there is a marked increase in the error in determining the transfer coefficients. To overcome these difficulties, a hot-spot method has been proposed, which under stationary conditions gives a flow structure as in nonstationary cooling. However, it is impossible to estimate the amount of heat transferred to the flow from the hot spot, so it is virtually impossible to calculate the two-phase flow parameters. The authors have made measurements on the heat-transfer coefficients in the unwetted zone when the hot surface is cooled by pressurized water at high mass speeds. The relatively high heat deposition rate in the working section produced quasistationary cooling conditions, which enabled them to determine the transfer coefficients with acceptable accuracy
For the future upgrade of inner vessel components (CIEL project) a guard limiter for plasma ramp-up and disruption protection will be installed on the high field side of the vacuum vessel. Among transient heat loads, this structure has to sustain a moderate heat flux in the range of ?0.5 MW/m2 during quasi steady state operation (1000 s). A bolted carbon-carbon (C-C) tile is preferred compared with a brazed tile solution due to the expected moderate heat fluxes, costs and the possibility of rapid replacement of individual tiles. Large flat tile assemblies require a sufficient soft and conductive compliant layer enclosed between tile and heat sink in order to avoid thermal contact loss of the assembly during heat loads and therefore minimising the tile surface temperature. The global heat transfer coefficient (Hgl) under vacuum at low contact pressures (0.5-1.5 MPa) between C-C and CuCrZr heat sink substrata has been measured in the experimental device, installation of contact heat transfer measurements (ITTAC), using different compliant materials. It appears that the best compliant layer is a graphite sheet (PAPYEX), compared with copper-felt/foam material. As an example, a Hgl number of ?104 W/m2 K at an average contact pressure of 0.5 MPa has been measured near room temperature between C-C (SEP N11) and CuCrZr substrata using a 0.5-mm thick PAPYEX layer. Thermohydraulic calculations (2D) of the guard limiter design show an expected tile surface temperature of about 550 deg. C in steady state regime for an incident heat flux of 0.5 MW/m2
Mastrullo, R.; Mauro, A.W.; Rosato, A. [D.E.TE.C., Facolta di Ingegneria, Universita degli Studi di Napoli Federico II, p.le Tecchio 80, 80125 Napoli (Italy); Vanoli, G.P. [Dipartimento di Ingegneria, Universita degli Studi del Sannio, corso Garibaldi 107, Palazzo dell' Aquila Bosco Lucarelli, 82100 Benevento (Italy)
2010-09-15
Among the alternatives to the HCFCs and HFCs, carbon dioxide emerged as one of the most promising environmentally friendly refrigerants. In past years many works were carried out about CO{sub 2} flow boiling and very different two-phase flow characteristics from conventional fluids were found. In order to assess the best predictive methods for the evaluation of CO{sub 2} heat transfer coefficients and pressure gradients in macro-channels, in the current article a literature survey of works and a collection of the results of statistical comparisons available in literature are furnished. In addition the experimental data from University of Naples are used to run a deeper analysis. Both a statistical and a direct comparison against some of the most quoted predictive methods are carried out. Methods implemented both for low-medium pressure refrigerants and specifically developed for R744 are used in the comparison. Some general indications about the choice of the predictive methods dependently on the operating conditions are given. (author)
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.
Boissieux, X.; Heikal, M.R.; Johns, R.A. [University of Brighton (United Kingdom). School of Engineering
2000-08-01
This paper presents local heat transfer results obtained during the condensation of Isceon 59, R407C and R404A in a smooth horizontal tube. The results have been compared with existing correlations for condensation heat transfer to assess the validity of these models for refrigerant mixtures. Two correlations (Dobson MK, Chato JC. Condensation in smooth horizontal tubes. Journal of Heat Transfer, Transactions of ASME 1998; 120: 193-213, Shah MM. A general correlation for heat transfer during film condensation inside pipes. Int J Heat and Mass Transfer 1979; 22: 547-56) have been considered because they deal with refrigerant blends and their range of applicability suited the experimental test conditions. The Dobson and Chato correlation provided the best prediction for these refrigerant mixtures. The Shah correlation fitted the measurements of the local heat transfer coefficients well and seem to cope well with refrigerant mixtures. (author)
Research on heat transfer characteristics of nano-structured surface
Heat transfer enhancement at nano-structured surfaces on SUS316 substrate is experimentally investigated. In this study, slurry coating and dip-coating of nano-particles on the substrate and ion beam irradiation are applied as the fabrication technique of such surfaces. All of these surfaces shows the heat transfer enhancement with the factor ranging from 1.4 to 2. (author)
Estimation of the friction coefficient between wheel and rail surface using traction motor behaviour
The friction coefficient between a railway wheel and rail surface is a crucial factor in maintaining high acceleration and braking performance of railway vehicles thus monitoring this friction coefficient is important. Restricted by the difficulty in directly measuring the friction coefficient, the creep force or creepage, indirect methods using state observers are used more frequently. This paper presents an approach using a Kalman filter to estimate the creep force and creepage between the wheel and rail and then to identify the friction coefficient using the estimated creep force-creepage relationship. A mathematic model including an AC motor, wheel and roller is built to simulate the driving system. The parameters are based on a test rig at Manchester Metropolitan University. The Kalman filter is designed to estimate the friction coefficient based on the measurements of the simulation model. Series of residuals are calculated through the comparison between the estimated creep force and theoretical values of different friction coefficient. Root mean square values of the residuals are used in the friction coefficient identification.
Estimation of the friction coefficient between wheel and rail surface using traction motor behaviour
Zhao, Y.; Liang, B.; Iwnicki, S.
2012-05-01
The friction coefficient between a railway wheel and rail surface is a crucial factor in maintaining high acceleration and braking performance of railway vehicles thus monitoring this friction coefficient is important. Restricted by the difficulty in directly measuring the friction coefficient, the creep force or creepage, indirect methods using state observers are used more frequently. This paper presents an approach using a Kalman filter to estimate the creep force and creepage between the wheel and rail and then to identify the friction coefficient using the estimated creep force-creepage relationship. A mathematic model including an AC motor, wheel and roller is built to simulate the driving system. The parameters are based on a test rig at Manchester Metropolitan University. The Kalman filter is designed to estimate the friction coefficient based on the measurements of the simulation model. Series of residuals are calculated through the comparison between the estimated creep force and theoretical values of different friction coefficient. Root mean square values of the residuals are used in the friction coefficient identification.
SAFARI 2000 Surface Atmospheric Radiative Transfer (SMART), Dry Season 2000
National Aeronautics and Space Administration â€” ABSTRACT: Surface-sensing Measurements for Radiative Transfer (SMART) and Chemical, Optical, and Microphysical Measurements of In-situ Troposphere (COMMIT) consist...
Using 86Rb as a tracer the effective diffusion coefficient in the resin phase has been determined by direct measurement of the change in the ion concentration. The evaluation of the charging curves was carried out graphically by comparing the experimental curves with theoretical ones, taking into account liquid phase mass transfer
Miyabe, K; Guiochon, G
1999-01-01
The experimental results of a previous study of the mass transfer kinetics of bovine serum albumin (BSA) in ion-exchange chromatography under nonlinear conditions are reevaluated. The analysis of the concentration dependence of the lumped mass-transfer rate coefficient (k(m,L)) provides information on the kinetics of axial dispersion, fluid-to-particle mass transfer, intraparticle mass transfer, and adsorption/desorption. The new analysis shows that the contribution of intraparticle mass transfer is the dominant one. Similar to k(m,L), the surface diffusivity (D(s)) of BSA increases with increasing concentration. The linear concentration dependence of k(m,L) seems to originate in a similar dependence of D(s). The use of an heterogeneous-surface model for the anion-exchange resin provides an explanation of the positive concentration dependence of D(s). This work illustrates how frontal analysis data can be used for a detailed investigation of the kinetics of mass transfer between the phases of a chromatographic column, in addition to its conventional use in the determination of the thermodynamic characteristics of the phase equilibrium. PMID:10441366
Highlights: â–º Partition coefficients octanol/buffer of new drug-like spiro-derivatives were determined. â–º Thermodynamic functions of transfer were calculated. â–º The correlations partition coefficients and molecular descriptors are discussed. -- Abstract: Temperature dependences of partition coefficient for 11 drug-like spiro-derivatives of 1,3-thiazine in the system aqueous phosphate buffer/organic phase (hexane, octanol) have been determined over the temperature range (293.15 to 315.15) K by the isothermal saturation method. The effects of aliphatic chain substituent structure and introduction of oxygen, chlorine, bromine and fluorine atoms on the partitioning processes of the substances studied were examined. It has been established that among the substances investigated halogen derivatives possess the lowest partition coefficients in buffer/hexane system and the highest ones in buffer/octanol system. Regularities between the partition coefficients and the descriptors reflecting the capability of the solutes to undergo specific and nonspecific interactions with solvent molecules were revealed. The thermodynamic functions describing the partitioning process were calculated. It was found that differences in the partition coefficients depend on the enthalpies of transfer
Pinheiro Cleber
2008-07-01
Full Text Available Abstract Background One of the current shortcomings of radiofrequency (RF tumor ablation is its limited performance in regions close to large blood vessels, resulting in high recurrence rates at these locations. Computer models have been used to determine tissue temperatures during tumor ablation procedures. To simulate large vessels, either constant wall temperature or constant convective heat transfer coefficient (h have been assumed at the vessel surface to simulate convection. However, the actual distribution of the temperature on the vessel wall is non-uniform and time-varying, and this feature makes the convective coefficient variable. Methods This paper presents a realistic time-varying model in which h is a function of the temperature distribution at the vessel wall. The finite-element method (FEM was employed in order to model RF hepatic ablation. Two geometrical configurations were investigated. The RF electrode was placed at distances of 1 and 5 mm from a large vessel (10 mm diameter. Results When the ablation procedure takes longer than 1â€“2 min, the attained coagulation zone obtained with both time-varying h and constant h does not differ significantly. However, for short duration ablation (5â€“10 s and when the electrode is 1 mm away from the vessel, the use of constant h can lead to errors as high as 20% in the estimation of the coagulation zone. Conclusion For tumor ablation procedures typically lasting at least 5 min, this study shows that modeling the heat sink effect of large vessels by applying constant h as a boundary condition will yield precise results while reducing computational complexity. However, for other thermal therapies with shorter treatment using a time-varying h may be necessary.
FREG-3 predicts the temperature distribution in a fuel rod and the stored energy based on the distribution. The temperature distribution is calculated in accordance with fuel-rod irradiation history under normal operating conditions. An important factor in obtaining the temperature distribution is the gap heat transfer coefficient between pellet outer surface and cladding inner surface. To obtain the proper coefficient, the program incorporates submodels and correlations. Purpose of the program is to evaluate stored energy in the fuel rod preceding the initiation of the LOCA. The estimated stored energy is a significant key parameter in safety evaluation of the fuel rod. The program can also be used as the best estimate code, if calculation models or correlations are appropriately chosen. The calculation procedure and the models used are described. (auth.)
The purpose has been to describe an approach suggested for constructing generalized closure relationships for local and subchannel wall friction, heat and mass transfer coefficients, with not only axial and transversal parameters taken into account, but azimuthal substance transfer effects as well. These constitutive relations that are primary for description of one- and two-phase one-dimensional flow models can be derived from the initial 3-D drift flux formulation. The approach is based on the Reynolds flux, boundary layer and generalized coefficient of substance transfer. One more task has been to illustrate the validity of the 'conformity principle' for the limiting cases. The method proposed is based on the similarity theory, boundary layer model, and a phenomenological description of the regularities of the substance transfer (momentum, heat, and mass), as well as on an adequate simulation of the forms of flow structure by a generalized approach to build (an integrated in form and semi-empirical in maintenance structure) analytical relationships for wall friction, heat and mass transfer coefficients. (author)
Wen, D.S.; Yan Youyou; Kenning, D.B.R
2004-06-01
Time-averaged local heat transfer coefficients were measured during flow boiling of water at atmospheric pressure in a vertical channel of rectangular cross-section 2 mm by 1 mm for ranges of mass flux 57-211 kg/m{sup 2} s, heat flux 27-160 kW/m{sup 2}, thermodynamic quality 0-0.3 and inlet subcooling 1-12 K. The heat transfer coefficients were found to increase nearly with the square root of the heat flux. There was little effect of mass flux at 107, 134 and 211 kg/m{sup 2} s; lower heat transfer coefficients at 57 kg/m{sup 2} s were probably due to transient local dryout. Local time-averaged quality and different inlet conditions of subcooling and compressibility had little effect. Conventionally, this behaviour would be interpreted as nucleate boiling and a dimensional expression h=162q{sup 0.44} correlated the data to {+-}20%. However, the heat transfer coefficients were considerably higher than would be expected for pool nucleate boiling and visual observation showed local time-sharing between nucleate boiling and thin-film evaporation without nucleation, with only small temporal changes in the heat transfer coefficient. Eleven correlations for conventional and narrow-channel boiling predicted the data poorly, ranging from 250% average over-prediction to 70% average under-prediction. This suggests that conventional methods of distinguishing between nucleate and convective boiling mechanisms are unreliable and that a better understanding of the mechanisms of boiling in narrow channels is necessary to guide the development of correlations.
Time-averaged local heat transfer coefficients were measured during flow boiling of water at atmospheric pressure in a vertical channel of rectangular cross-section 2 mm by 1 mm for ranges of mass flux 57-211 kg/m2 s, heat flux 27-160 kW/m2, thermodynamic quality 0-0.3 and inlet subcooling 1-12 K. The heat transfer coefficients were found to increase nearly with the square root of the heat flux. There was little effect of mass flux at 107, 134 and 211 kg/m2 s; lower heat transfer coefficients at 57 kg/m2 s were probably due to transient local dryout. Local time-averaged quality and different inlet conditions of subcooling and compressibility had little effect. Conventionally, this behaviour would be interpreted as nucleate boiling and a dimensional expression h=162q0.44 correlated the data to Â±20%. However, the heat transfer coefficients were considerably higher than would be expected for pool nucleate boiling and visual observation showed local time-sharing between nucleate boiling and thin-film evaporation without nucleation, with only small temporal changes in the heat transfer coefficient. Eleven correlations for conventional and narrow-channel boiling predicted the data poorly, ranging from 250% average over-prediction to 70% average under-prediction. This suggests that conventional methods of distinguishing between nucleate and convective boiling mechanisms are unreliable and that a better understanding of the mechanisms of boiling in narrow channels is necessary to guide the development of correlations
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.
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...
Grass to cow milk transfer coefficient (Fm) of iodine for equilibrium and emergency situations
Radioiodine (131I) is one of the radionuclides likely to get released into the atmosphere in case of a reactor accident, though chances of such an accident are very remote due to stringent engineering safety features. If released to the environment during an accident, 131I may enter the grassâ†’cowâ†’cow milk pathway, leading to increased thyroid dose to those consuming milk, especially infants and children. The estimation of site-specific grass to milk transfer coefficient (Fm) for iodine is essential for an accurate assessment of the radiological hazard to the population in the region surrounding a nuclear power plant. In this study, a method based on the chemical separation of iodine present in grass and cow milk, and subsequent neutron activation analysis (NAA) has been optimized for the determination of stable iodine concentration in grass and cow milk. The method involves preconcentration of iodine from the sample matrix, and determination of iodine by NAA. The detection limit of stable iodine in milk was found to be 1 ng/mL. For the validation of the result, iodine concentration in NIST reference materials was determined simultaneously. The present study has yielded a Fm value of 5.6 x 10-3 d/L for dairy farm cows and 6.3 x 10-3 d/L for local breed cows under equilibrium conditions. These results are similar to the values given in International Atomic Energy Agency report (TRS-472). To simulate a rapid deposition of iodine on grass and for the estimation of Fm value for an emergency situation, grass grown in the experimental field was sprayed with stable potassium iodide solution and fed to the adopted cows, and the milk samples were collected regularly and analyzed. The Fm value for the simulated accidental situation was found to be 3.9 x 10-3 d/L. (author)
Data Qualification Report For DTN: MO0012RIB00065.002, Parameter Values For Transfer Coefficients
A data-qualification evaluation was conducted on Reference Information Base (RIB) data set MOO0 12RIB00065.002, ''Parameter Values for Transfer Coefficients''. The corroborating data method was used to evaluate the data. This method was selected because it closely matches the literature-review method followed to select parameter values. Five criteria were considered when the corroborating method was used: adequacy of the corroborative literature, sufficiency of value-selection criteria, implementation of the selection criteria, documentation of the process, and whether the analysis was conducted in accordance with applicable quality assurance (QA) procedures. Three criteria were used when a literature review was not conducted: appropriate logic used to select parameters, documentation of the process, and whether the analysis was conducted in accordance with applicable QA procedures. The RIB data item, the associated Analysis and Model Report (AMR), the corroborative literature, and the results of an audit revision O/ICN--0 of the AMR were examined. All calculations and the selection process for all values were repeated and confirmed. The qualification team concluded: (1) A sufficient quantity of corroborative literature was reviewed and no additional literature was identified that should have been considered. (2) The selection criteria were sufficient and resulted in valid parameter values. (3) The process was well defined, adequately documented in the AMR, and correctly followed. (4) The analysis was developed in accordance with applicable QA procedures. No negative findings were documented that resulted in questions about the quality of the data. The qualification team therefore recommends that the qualification status of RIB data set MO0012RIB00065.002 be changed to qualified
The goat milk transfer coefficient of Tc administered as TcO4- was found to be 20 to 40 times that of Tc administered in a reduced form. The fraction of Tc, as TcO4-, transferred from gut to blood was approximately 6 to 10 times that of reduced Tc. The milk transfer coefficient of Tc administered as TcO4- was 6 to 8 times greater for goats than cows. The fraction of Tc, as TcO4-, absorbed from the gut by cows, however, was approximately twice that absorbed by goats. The mean time for loss of Tc in cows' milk based on the average values plotted in Figure 2 was approximately 10 hours. The fraction of Tc, administered as TcO4-, absorbed from blood to mammary gland by cows was estimated to be approximately 2% that of goats. 4 refs., 15 tabs
Takahashi, Yasushi; Gokan, Yoshitsugu; Inayoshi, Makoto; Ishima, Tsuneaki; Obokata, Tomio
Cooling performance is a significant issue for air-cooled motorcycle engines, because its performance depends on the vehicle motion. Commonly, a heat transfer coefficient is calculated by heat flux and temperature difference, which are solved by energy equation under conjugated condition between a solid and a fluid. However, this method is complicated. Therefore, Karman's analogy based on a relation between the fluid friction and the heat transportation was used to obtain a heat transfer coefficient without solving an energy equation. Partial Cells in Cartesian coordinate method was employed as a CFD (Computational Fluid Dynamics) method for an efficient calculation around complex obstacles. Characteristics of heat transfer in a straight pipe were confirmed by a comparison with the Colburn's empirical formula. The results showed good agreement within Â±10% differences under Pr=0.7 and 104motorcycle engine was shown. From the above, a new approach of heat analysis by a CFD was proposed.
Although detailed thermodynamic analyses of the 2-pK diffuse layer surface complexation model generally specify bound site activity coefficients for the purpose of accounting for those non-ideal excess free energies contributing to bound site electrochemical potentials, in applic...
Coefficient of friction between carbon steel and perlite concrete surfaces. Test report
The results of coefficient of friction, Î¼, tests conducted on perlite blocks and carbon steel plates under various conditions are discussed. Variables included in the test entailed the use of lubricants (i.e. water and simulated radioactive waste solution) abrasives (120 grit, 60 grit, 40 grit sand paper) applied to the surfaces of the perlite block and carbon steel plates
Rajesh Joshi
2014-02-01
Full Text Available The performance of a domestic refrigerator is affected by the Surface roughness of condenser, evaporator and associated piping. The heat transfer in a domestic refrigerator is a complex phenomenon as it involves two phase flow inside the condenser, evaporator and the tubing. Various equations had been developed in the past by different Researchers to calculate the heat transfer for fluid flow inside tubes. In the present study Boyko and Kurzhillin equation is being used to determine the heat transfer coefficient for two phase flow in the condenser of a domestic refrigerator using R134a as refrigerant. For this an experimental setup has also been developed containing different condensers having different inside tube diameters varying in the range of 6.25mm to 12mm and the mass flow rate of refrigerant is varied in the range of 0.002kg/s to 0.02 kg/s.
Condensation Heat Transfer Performance of Nano- Engineered Cu Surfaces
We investigated condensate mobility and resulting heat transfer performance on Cu based water repellent surfaces including hydrophobic, superhydrophobic and oil-infused surfaces. We observed the transient microscale condensation behaviours up to 3 hours with controlling the supersaturation level at 1.64. We experimentally characterized the nucleation density, droplet size distribution and growth rate, and then incorporated them into the developed condensation heat transfer model to compare the condensation heat transfer performance of each surface. Due to the spontaneous coalescence induced jumping, superhydrophobic surface can maintain the high heat transfer performance while other surfaces show a gradual decrease in heat transfer performance due to the increase in the thermal resistance across the growing droplets. We also quantified each thermal resistance values from the vapor to the surface through the droplets to find out the relative importance of each thermal resistance term
Condensation Heat Transfer Performance of Nano- Engineered Cu Surfaces
Kim, Hyunsik; Nam, Youngsuk
2014-11-01
We investigated condensate mobility and resulting heat transfer performance on Cu based water repellent surfaces including hydrophobic, superhydrophobic and oil-infused surfaces. We observed the transient microscale condensation behaviours up to 3 hours with controlling the supersaturation level at 1.64. We experimentally characterized the nucleation density, droplet size distribution and growth rate, and then incorporated them into the developed condensation heat transfer model to compare the condensation heat transfer performance of each surface. Due to the spontaneous coalescence induced jumping, superhydrophobic surface can maintain the high heat transfer performance while other surfaces show a gradual decrease in heat transfer performance due to the increase in the thermal resistance across the growing droplets. We also quantified each thermal resistance values from the vapor to the surface through the droplets to find out the relative importance of each thermal resistance term.
Full text of publication follows: Models or correlations for phase interface are needed to analyze the multi-phase flow. Interfacial heat transfer coefficients are important to constitute energy equation of multi-phase flow, specially. In subcooled boiling flow, bubble condensation at the bubble-liquid interface is a major mechanism of heat transfer within bulk subcooled liquid. Bubble collapse rates and temperatures of each phase are needed to determine the interfacial heat transfer coefficient for bubble condensation. Bubble collapse rates were calculated through image processing in single direction, generally. And in case of liquid bulk temperature, which has been obtained by general temperature sensor such as thermocouple, was used. However, multi-directional images are needed to analyze images due to limitations of single directional image processing. Also, temperature sensor, which has a fast response time, must be used to obtain more accurate interfacial heat transfer coefficient. Low pressure subcooled water flow experiments using micro-thermocouple and double directional image processing with mirrors were conducted to investigate bubble condensation phenomena and to modify interfacial heat transfer correlation. Experiments were performed in a vertical subcooled boiling flow of a rectangular channel. Bubble condensing traces with respect to time were recorded by high speed camera in double direction and bubble collapse rates were calculated by processing recorded digital images. Temperatures were measured by micro-thermocouple, which is a K-type with a 12.7 ?m diameter. The liquid temperature was estimated by the developed algorithm to discriminate phases and find each phase temperature in the measured temperature including both liquid and bubble temperature. The interfacial heat transfer coefficient for bubble condensation was calculated from the bubble collapse rates and the estimated liquid temperature, and its correlation was modified. The modified correlation has been compared with other correlations. (authors)
Heat and mass transfer to flowing bodies of surface water
The most important limiting quantities for heat transfer from a river to its environment are the thermal radiation, the free convection and the forced convection due to wind. For a sure preliminary calculation of the heat emission of a flowing body of water it is necessary to know exactly the decisive heat- and mass transfer coefficients and their dependence on wind velocity. Measurements have been effected at a power plant channel in Pleidelsheim/Neckar. The measuring technique, arrangement of the measuring points and measuring devices are shown in detail as well as the theoretical basis for the analysis of the measurements. Balancing calculations lead to relations representing, in the form of extended exponential functions, the dependence of the transfer coefficients on wind velocity. As against the transfer coefficients so far used for calculating the thermal load plans, much higher values have been obtained. This is of considerable practical importance insofar as a flowing water obviously emits the received foreign heat quicker than assumed until now. Because of the importance of the radiation a new intermittent measuring method has been developed enabling the determination of the different radiation fluxes as well as the heat- and mass transfer coefficients. (orig.)
Study of local heat transfer on the face surface of a nozzle ring model
Khalatov, A.A.; Kapitanchuk, K.I.; Kovalenko, A.S.; Trufanov, A.N.
1986-01-01
Results of an experimental study of local heat transfer on the face surface of a model of the nozzle ring of a gas turbine are reported. A method for generalizing experimental data is proposed which makes it possible to obtain a unified similarity equation allowing for the effect of the curvature of flow lines, for the three-dimensional nature of the flow, for flow acceleration along the channel, and for the laminar transition of the flow. The equation can be used for calculating local heat transfer coefficients at arbitrary points of the face surface. 9 references.
Kukreja, R. T.; Park, C. W.; Lau, S C
1998-01-01
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 i...
Heat and mass transfer on turbulent liquid flow near a roughness surface
Process of heat and mass transfer at turbulent flow of the fluids in the vicinity of a rough surface is analized. For description of turbulent viscosity variation at the cross section of the flow, the latter is represented by a simple ''two-layer'' pattern. The relations calculated are given showing dependence of the Stenton number and friction coefficient on Re for the fluid flow in the rough tubes at various Pr. It is established that at Pr 1 surface roughness considerably intensifies the heat and mass transfer processes. There exists a region of the Re values wherein the effect of surface roughness on heat and mass transfer exceeds its effect on friction. The expressions which are derived make it possible to calculate the heat exchange characteristics for various types of the rough surfaces
Theory of the kinetic coefficients of the atomically rough surface of 4He crystals
Bowley, R.M.; Edwards, D. O.
1983-01-01
The growth coefficient K (the velocity of growth per unit chemical potential difference) and the Onsager cross-coefficients b1 and b2, coupling growth and heat flow, are calculated for atomically rough surfaces of hcp 4He crystals. The calculation is based on the premise, suggested by Andreev and Parshin, that growth is limited by the collision of phonons and rotons with the interface. The calculated K is compared with that obtained by Keshiskev et al. from the damping of melting-freezing wav...
Ozawa, S.; Suzuki, S.; Hibiya, T.; Fukuyama, H.
2011-01-01
Influences of oxygen partial pressure, PO2, of ambient atmosphere and temperature on surface tension and its temperature coefficient for molten iron were experimentally investigated by an oscillating droplet method using an electromagnetic levitation furnace. We successfully measured the surface tension of molten iron over a very wide temperature range of 780 K including undercooling condition in a well controlled PO2 atmosphere. When PO2 is fixed at 10-2 Pa at the inlet of the chamber, a "boomerang shape" temperature dependence of surface tension was experimentally observed; surface tension increased and then decreased with increasing temperature. The pure surface tension of molten iron was deduced from the negative temperature coefficient in the boomerang shape temperature dependence. When the surface tension was measured under the H2-containing gas atmosphere, surface tension did not show a linear relationship against temperature. The temperature dependence of the surface tension shows anomalous kink at around 1850 K due to competition between the temperature dependence of PO2 and that of the equilibrium constant of oxygen adsorption.
Sørum, Mikkel
2014-01-01
High heat transfer rates at reasonably low temperature differences can be obtained by utilizing a boiling fluid. The use of boiling heat transfer is often limited by onset of a heat transfer crisis named the Critical Heat Flux (CHF). The CHF is accompanied by an inordinate increase in temperature with the most severe consequence being related to the physical burnout of the heated surface. Two-phase boiling flows in channels are sometimes prone to flow instabilities. Density Wave Oscillations ...
Transfer coefficients of energy in mass for X radiation-air: the kV relation and effective energy
The objective was to determine, through specific software, the mass-energy transfer coefficients by X-ray beams in air between 30-150 kV. Were generated by the Spectrum Processor program, the spectra and calculated their mass coefficients. The results behaved numerically decreasing order, ranging between 0.3733 and 0.0439 cm2/g, inversely proportional to the voltage used and differing behavior of mono-energetic beams above 100 keV. Values align with literal definitions of the interaction of radiation with matter, being useful for dosimetry in diagnostic radiology, including for systems not using an ionization chamber. (author)
Monte Carlo calculations have been carried out for the sputtering energy reflection coefficient (YE) of plasma ions incident on a carbon surface. The calculations incorporate a simulation of the velocity distribution of plasma ions incident on a surface with a floating potential. The average energy of an ion can increase by more than a factor of three as a result of this potential and the effect on YE can be significant. An analytic form for YE is constructed expressed in terms of the ion plasma temperature and the surface floating potential. The new model provides a fast and accurate means to calculate YE. (author)
Rong, Li; Nielsen, Peter V.; Zhang, Guoqiang
2010-01-01
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 trans...
The fuel to clad heat transfer coefficient in advanced MX-type fuel pins
Advanced fuels (mixed carbides, nitrides and carbonitrides) are characterised by a high thermal conductivity compared to that of oxide fuels (5 times greater) and their behaviour under irradiation (amount of swelling, fracture behaviour, restructuring) is far more sensitive to the design parameters and to the operating temperature than that of oxide fuels. The use of advanced fuels is therefore conditioned by the possibility of mastering the above phenomena, and the full exploitation of their favorable neutron characteristics depends upon a good understanding of the mutual relationships of the various parameters, which eventually affect the mechanical stability of the pin. By far the most important parameter is the radial temperature profile which controls the swelling of the fuel and the build-up of stress fields within the pin. Since the rate of fission gas swelling of these fuels is relatively large, a sufficient amount of free space has to be provided within the pin. This space originally appears as fabrication porosity and as fuel-to-clad clearance. Due to the large initial gap width and to the high fuel thermal conductivity, the range of the fuel operating temperatures is mainly determined by the fuel-to-clad heat transfer coefficient h, whose correct determination becomes one of the central points in modelling. During the many years of modelling activity in the field of oxide fuels, several theoretical models have been developed to calculate h, and a large amount of experimental data has been produced for the empirical adjustment of the parameters involved, so that the situation may be regarded as rather satisfactory. The analysis lead to the following conclusions. A quantitative comparison of experimental h-values with existing models for h requires rather sophisticated instrumented irradiation capsules, which permit the measurement of mechanical data (concerning fuel and clad) together with heat rating and temperatures. More and better well-instrumented irradiation experiments are necessary in order to make progress on this problem. The h-values are sensitive to changes in the linear heat rating and/or clad temperature. A quantitative comparison of experimental values of h with existing models requires capsule irradiations, in which temperatures, rating and also mechanical parameters are all recorded during irradiation
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 original technique, inspired from tensor signal processing tools. Our aim is to improve the simulation results and to obtain a faster algorithm runtime. We consider multiway array called tensor data T CC. Then, in order to compute an aerial image, we develop a lower-rank tensor approximation algorithm based on the signal subspaces. For this purpose, we propose to replace SVD by the Higher Order SVD to compute the eigenvectors associated with the different modes of TCC. Finally, we propose a new criterion to estimate the optimal number of leading eigenvectors required to obtain a good approximation while ensuring a low information loss. Numerical results we present show that our proposed approach is a fast and accurate for computing aerial images.
Methamphetamine residue dermal transfer efficiencies from household surfaces.
Van Dyke, Mike; Martyny, John W; Serrano, Kate A
2014-01-01
Methamphetamine contamination from illegal production operations poses a potential health concern for emergency responders, child protective services, law enforcement, and children living in contaminated structures. The objective of this study was to evaluate dermal transfer efficiencies of methamphetamine from contaminated household surfaces. These transfer efficiencies are lacking for methamphetamine, and would be beneficial for use in exposure models. Surfaces were contaminated using a simulated smoking method in a stainless steel chamber. Household surfaces were carpet, painted drywall, and linoleum. Dermal transfer efficiencies were obtained using cotton gloves for two hand conditions, dry or saliva moistened (wet). In addition, three contact scenarios were evaluated for both hand conditions: one, two, or three contacts with contaminated surfaces. Dermal transfer efficiencies were calculated for both hand conditions and used as inputs in a Stochastic Human Exposure and Dose Simulation model (SHEDS-Multimedia, Office of Research and Development, United States Environmental Protection Agency, Research Triangle Park, N.C.). Results of this study showed that average dermal transfer efficiencies of methamphetamine ranged from 11% for dry hands to 26% for wet hands. There was a significantly higher wet transfer as compared to dry transfer for all surfaces. For wet hands, dermal transfer depended on surface type with higher transfer from carpet and linoleum as compared to drywall. Based on our estimates of dermal transfer efficiency, a surface contamination clearance level of 1.5Â Î¼g/100Â cm(2) may not ensure absorbed doses remain below the level associated with adverse health effects in all cases. Additional dermal transfer studies should be performed using skin surrogates that may better predict actual skin transfer. PMID:24579754
Coupled heat and mass transfer in porous media has many important applications in engineering. These include the migration of moisture in fibrous insulation, the spreading of chemical pollutants in saturated soil, underground disposal of nuclear wastes and the extraction of geothermal energy. Here, similarity solutions are reported for coupled heat and mass transfer by free, forced, and mixed convection from a horizontal surface in a saturated porous medium. The present analysis shows that similarity solutions are possible for a surface maintained at a constant heat flux and mass flux condition. The governing parameters for the problem under consideration are the Lewis number Le, the buoyancy ratio N and mixed convection parameter Ra/Pe3/2. Depending on the values of N and Le, the heat and mass transfer results may range from the asymptotic free convection limit to that of the forced convection limit. The results are presented in terms of the relation between the transfer coefficients and the governing parameters
Meso-scale wrinkled coatings to improve heat transfers of surfaces facing ambient air
Meso-scale (micrometer-to submillimeter-scale) wrinkled surfaces coated on steel sheets used in outdoor storage and transport facilities for industrial low-temperature liquids were discovered to efficiently increase convective heat transfer between ambient air and the surface. The radiative and convective heat transfer coefficients of various wrinkled surfaces, which were formed by coating steel sheets with several types of shrinkable paints, were examined. The convective heat transfer coefficient of a surface colder than ambient air monotonically changed with average height difference and interval distance of the wrinkle undulation, where the proportions were 0.0254 and 0.0054Â W/m2/K/Î¼m, respectively. With this wrinkled coating, users can lower the possibility of condensation and reduce rust and maintenance cost of facilities for industrial low-temperature liquids. From the point of view of manufacturers, this coating method can be easily adapted to conventional manufacturing processes. - Highlights: â€¢ Various wrinkled surfaces were fabricated by a practical process. â€¢ Topographical effect on convection was parameterized separately from radiation. â€¢ Meso-scale wrinkled coatings increased convective heat transfer with ambient air. â€¢ Maintenance cost of outdoor steel sheets due to condensation can be reduced
The local heat transfer coefficient is experimentally investigated for the reflux condensation in a countercurrent flow between the steam-air mixture and the condensate. A single vertical tube has a geometry which is a length of 2.4m, inner diameter of 16.56mm and outer diameter of 19.05mm and is made of stainless steel. Air is used as a noncondensible gas. The secondary side is installed in the form of coolant block around vertical tube and the heat by primary condensation is transferred to the coolant water. The local temperatures are measured at 15 locations in the vertical direction and each location has 3 measurement points in the radial direction, which are installed at the tube center, at the outer wall and at the coolant side. In three different pressures, the 27 sets of data are obtained in the range of inlet steam flow rate 1.348âˆ¼3.282kg/hr, of inlet air mass fraction 11.8âˆ¼55.0%. The local heat transfer coefficient increases as the increase of inlet steam flow rate and decreases as the decrease of inlet air mass fraction. As an increase of the system pressure, the active condensing region is contracted and the heat transfer capability in this region is magnified. The empirical correlation is developed represented with the 165 sets of local heat transfer data. As a result, the Jacob number and film Reynolds number are dominant parameters to govern the local heat transfer coefficient. The rms error is 17.7% between the results by the experiment and by the correlation
The local heat transfer coefficient is experimentally investigated for the reflux condensation in a countercurrent flow between the steam-air mixture and the condensate. A single vertical tube has a geometry which is a length of 2.4 m, inner diameter of 16.56 mm and outer diameter of 19.05 mm and is made of stainless steel. Air is used as a noncondensable gas. The secondary side has a shape of annulus around vertical tube and the lost heat by primary condensation is transferred to the coolant water. The local temperatures are measured at 11 locations in the vertical direction and each location has 3 measurement points in the radial direction, which are installed at the tube center, at the outer wall and at the coolant side. In three different pressures, the 27 sets of data are obtained in the range of inlet steam flow rate 1.348âˆ¼3.282 kg/hr, of inlet air mass fraction 11.8âˆ¼55.0 percent. The investigation of the flooding is preceded to find the upper limit of the reflux condensation. Onset of flooding is lower than that of Wallis' correlation. The local heat transfer coefficient increases as the increase of inlet steam flow rate and decreases as the increase of inlet air mass fraction. As an increase of the system pressure, the active condensing region is contracted and the heat transfer capability in this region is magnified. The empirical correlation is developed by 165 data of the local heat transfer. As a result, the Jacob number and film Reynolds number are dominant parameters to govern the local heat transfer coefficient. The rms error is 17.7 percent between the results by the experiment and by the correlation. (author)
Niu Hai-jun
2012-03-01
Full Text Available Abstract Background Early diagnosis of Osteoarthritis (OA is essential for preventing further cartilage destruction and decreasing severe complications. The aims of this study are to explore the relationship between OA pathological grades and quantitative acoustic parameters and to provide more objective criteria for ultrasonic microscopic evaluation of the OA cartilage. Methods Articular cartilage samples were prepared from rabbit knees and scanned using ultrasound biomicroscopy (UBM. Three quantitative parameters, including the roughness index of the cartilage surface (URI, the reflection coefficients from the cartilage surface (R and from the cartilage-bone interface (Rbone were extracted. The osteoarthritis grades of these cartilage samples were qualitatively assessed by histology according to the grading standards of International Osteoarthritis Institute (OARSI. The relationship between these quantitative parameters and the osteoarthritis grades was explored. Results The results showed that URI increased with the OA grade. URI of the normal cartilage samples was significantly lower than the one of the OA cartilage samples. There was no significant difference in URI between the grade 1 cartilage samples and the grade 2 cartilage samples. The reflection coefficient of the cartilage surface reduced significantly with the development of OA (p Conclusion High frequency ultrasound measurements can reflect the changes in the surface roughness index and the ultrasound reflection coefficients of the cartilage samples with different OA grades. This study may provide useful information for the quantitative ultrasonic diagnosis of early OA.
Cushing, G. W.; Navin, J. K.; Valadez, L.; JohÃ¡nek, V.; Harrison, I.
2011-04-01
An effusive molecular beam technique is described to measure alkane dissociative sticking coefficients, S(Tg, Ts; Ï‘), on metal surfaces for which the impinging gas temperature, Tg, and surface temperature, Ts, can be independently varied, along with the angle of incidence, Ï‘, of the impinging gas. Effusive beam experiments with Tg = Ts = T allow for determination of angle-resolved dissociative sticking coefficients, S(T; Ï‘), which when averaged over the cos (Ï‘)/Ï€ angular distribution appropriate to the impinging flux from a thermal ambient gas yield the thermal dissociative sticking coefficient, S(T). Nonequilibrium S(Tg, Ts; Ï‘) measurements for which Tg â‰ Ts provide additional opportunities to characterize the transition state and gas-surface energy transfer at reactive energies. A resistively heated effusive molecular beam doser controls the Tg of the impinging gas striking the surface. The flux of molecules striking the surface from the effusive beam is determined from knowledge of the dosing geometry, chamber pressure, and pumping speed. Separate experiments with a calibrated leak serve to fix the chamber pumping speed. Postdosing Auger electron spectroscopy is used to measure the carbon of the alkyl radical reaction product that is deposited on the surface as a result of alkane dissociative sticking. As implemented in a typical ultrahigh vacuum chamber for surface analysis, the technique has provided access to a dynamic range of roughly 6 orders of magnitude in the initial dissociative sticking coefficient for small alkanes on Pt(111).
Transfer coefficients of 137Cs via the forage-cow-milk pathway in Aomori Prefecture of Japan
The transfer of radiocesium to foodstuff of cattle is very serious, because it contributes significantly to internal exposure resulting from the intake of 137Cs through the feed-cow-milk pathway. The transfer coefficient from feed to milk (Fm) is widely used to predict the dose to man from the radioactivity released to the biosphere. A commercial fuel reprocessing plant is under construction in Rokkasho-mura/Aomori Prefecture, the northeastern district of Japan. To figure out Fm under conventional farming conditions, therefore, transfer of 137Cs deposited in the environment in cooperation with two daily farms in this region. Transfer factors for 137Cs from feed to cow's milk have been obtained from data acquired from biweekly routine monitoring program under the two dissimilar farming conditions. The one dairy farm condition is mainly composed of high hay ration and the other is high concentrate ration. As a result of the experiments, 137Cs activity of milk correlated significantly with that of feed. The mean transfer coefficients of 137Cs to milk were calculated to be 0.0037 and 0.0063 (d/l), respectively. (author)
A mathematical model is presented to study the Soret and Dufour effects on the convective heat and mass transfer in stagnation-point flow of viscous incompressible fluid towards a shrinking surface. Suitable similarity transformations are used to convert the governing partial differential equations into self-similarity ordinary differential equations that are then numerically solved by shooting method. Dual solutions for temperature and concentration are obtained in the presence of Soret and Dufour effects. Graphical representations of the heat and mass transfer coefficients, the dimensionless thermal and solute profiles for various values of Prandtl number, Lewis number, Soret number and Dufour number are demonstrated. With Soret number the mass transfer coefficient which is related to mass transfer rate increases for both solutions and the heat transfer coefficient (related to heat transfer rate) for both solutions becomes larger with Dufour number. The Prandtl number causes reduction in heat and the mass transfer coefficients and similarly with the Lewis number mass transfer coefficient decreases. Also, double crossing over is found in dual dimensionless temperature profiles for increasing Soret number and in dual dimensionless concentration profiles for the increase in Dufour number. Due to the larger values of Dufour number the thermal boundary layer increases and for Prandtl number increment it decreases; whereas, the solute boundary layer thickness reduces with increasing values of Prandtl number and Lewis number. (paper)
Bozzoli, F.; Cattani, L.; Pagliarini, G.; Rainieri, S.
2015-03-01
This paper presents and assesses an inverse heat conduction problem (IHCP) solution procedure which was developed to determine the local convective heat transfer coefficient along the circumferential coordinate at the inner wall of a coiled pipe by applying the filtering technique approach to infrared temperature maps acquired on the outer tube's wall. The data-processing procedure filters out the unwanted noise from the raw temperature data to enable the direct calculation of its Laplacian which is embedded in the formulation of the inverse heat conduction problem. The presented technique is experimentally verified using data that were acquired in the laminar flow regime that is frequently found in coiled-tube heat-exchanger applications. The estimated convective heat transfer coefficient distributions are substantially consistent with the available numerical results in the scientific literature.
The computation and analysis of the heat transfer coefficient correction factor the shell and tube type of the Kartini reactor's heat exchanger (HE) has been carried out. The computation of the correction factor was done by measuring of the actual dimension of HE. As known that the shell and tube type of the Kartini reactor's has been opera-ted for more than 15 years. Due to the scraping and rusting occur at the buffle, the total heat transfer coefficient correction factor Ft was decrease. At the later computation, it is found that it's value is 0,4669 or differ of 0,1331 compared to the prediction standard value. So far, if the rusting and scraping of the secondary water coolant to the buffle is linear to the earlier HE's operation time, it is predicted that the function of the buffle will crisis approximately in the year of 2002/2003 or 7,5 years again
Experimental Investigation on the Heat Transfer Coefficient of the Thermosyphon Cross Section Shape
Mohammed M. I. Hammad,; Jasem H. ALsuwaidi
2015-01-01
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 ...
Effect of pressure on heat transfer coefficient at the metal/mold interface of A356 aluminum alloy
Fardi Ilkhchy, A.; Jabbari, Masoud; P. Davami
2012-01-01
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 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 differenc...
Impact of External Pressure on the Heat Transfer Coefficient during Solidification of Al-A356 Alloy
Jabbari, Masoud; Ilkhchy, A.Fardi; Moumani, E.
2012-01-01
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 ...
D. SÅ‚ota
2011-10-01
Full Text Available In the paper, solution of the inverse problem is presented, which consists in determination of the heat transfer coefficient during the process of binary alloy solidification for the known temperature measurements in the selected points of the cast. In the considered model distribution of temperature is described with the aid of Stefan problem with the varying liquidus temperature depending on the concentration of alloy component. Whereas, for description of the concentration the broken line model is used.
D. SÅ‚ota; E. Hetmaniok; R. WituÅ‚a
2011-01-01
In the paper, solution of the inverse problem is presented, which consists in determination of the heat transfer coefficient during the process of binary alloy solidification for the known temperature measurements in the selected points of the cast. In the considered model distribution of temperature is described with the aid of Stefan problem with the varying liquidus temperature depending on the concentration of alloy component. Whereas, for description of the concentration the broken line ...
Oleksandr I. Brunetkin; Anna V. Gusak
2015-01-01
The article highlights the reason of complication of usage of alternative fuel gases on the installed equipment — the organization of effective process of their combustion. As one of the parameters affecting the dynamic characteristics of the control object, the coefficient of convective heat transfer is considered. The effect of changes of physical characteristics of heat and rate of combustion products arising from the use of various combustible gases on it is determined. It is found that t...
P. Raveendiran; SIVARAMAN B
2015-01-01
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 bot...
Zhang, Zhiqiang; Gao, Peng; Liu, Chaoyang; Li, Xiangji
2015-12-01
An optimization-based numerical procedure was developed to determine the pressure-dependent heat transfer coefficient (HTC) between the blank and tools during the hot stamping of boron steel. During the quenching period, HTC increased with the contact pressure between blank and lower tool. There is no obvious linear relationship between them. The maximum value of 1500 W/m2 K was achieved at contact pressure 18 MPa.
Sticking coefficient and SIMS of hydrocarbons on fusion relevant plasma-sprayed tungsten surfaces
In this work we concentrate on the quantification of the sticking coefficient of CD3+ on fusion relevant plasma-sprayed tungsten (PSW) surfaces in the collision energy range from about 0 up to 100eV. PSW samples were cut from ASDEX Upgrade tiles and both untreated and electropolished surfaces are investigated. A collision energy, Ecoll, selected CD3+ ion beam deposits hydrocarbon layers onto the target surfaces which are ex-situ analyzed by nuclear reaction analysis (NRA) via D(3He,p)4He at 800kV and 2.5MeV, respectively. The sticking coefficient, S, for deuterium has been found to be collision energy dependent, decreasing with increasing energy. It is in the order of Sâˆ¼0.4 for PSW and Sâˆ¼0.1 for electro polished PSW at Ecoll=10eV. Secondary ion mass spectra of charged particles are recorded after ion-surface collisions with the polished PSW surface for collision energies up to 100eV. While at very low collision energies below about 10eV only simple reflection of CD3+ is observed, at higher collision energies both fragmentation of the projectile and fragmentation of ion-surface reaction products are observed. Concerning the stability of the layers we prove that hydrogen exchange plays a role on the time scale of weeks
TrumiÄ‡ B.; StankoviÄ‡ D.; TrujiÄ‡ V.
2009-01-01
In order to increase the active surface of platinum catalysts for ammonia oxidation and on the basis of theoretic considerations and tests in industrial environment, we have finally decided on their specific design. Efficiency on the newly designed catalyst was checked in industrial circumstances. A comparative analysis of the total ammonia recovery coefficient between the mentioned new catalysts and previously applied platinum catalysts was carried out. All advantages of catalysts with incre...
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 Ã— 3.2 mm thin film resistive temperature detector (RTD sensor. We used a circulation system to simulate different flow rates at 39Â°C for in vitro experiments using distilled water, tap water and saline. We heated the sensor approximately 5Â°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/(m2Â·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.
Alfandi, Ashraf; Yoon, Juhyeon; Abusaleem, Khalifeh; Albati, Mohammad; Khafaji, Salih
2015-11-01
In this study, the effect on a shell-side heat transfer coefficient is investigated using the CFD code FLUENT with a variation in longitudinal pitch to diameter ratio, SL, in the range of 1.15 to 2.6 with a fixed transverse pitch to diameter ratio. For the benchmark purposes with the available empirical correlation, typical thermal-hydraulic conditions for the Zukauskas correlation are assumed. Many sensitivity calculations for different mesh sizes and turbulent models are performed to check the accuracy of the numerical solution. A realizable Îº- É› turbulence model was found to be in good agreement with results of the Zukauskas correlation among the other turbulence models, at least for the staggered tube bank. It was found that the average heat transfer coefficient of a crossflow over a staggered tube bank calculated using FLUENT is in good agreement with the Zukauskas correlation-calculated heat transfer coefficient in the range of 1.15 - 2.6. For a staggered tube bank, using the Zukauskas correlation seems to be valid down to SL = 1.15.
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 Ïˆ = 45o.
A physical model for analyzing the radiative and convective heat transfer in a fog cooled, naturally ventilated greenhouse was developed for estimating the overall heat transmission coefficient based on the conduction, convection and thermal radiation heat transfer coefficients and for predicting the soil heat flux. The contribution of the water vapor of the inside air to the emission and absorption of thermal radiation was determined. Measurements of the outside and inside greenhouse environments to be used in the analysis were conducted around solar noon (12:19-13:00) on a hot sunny day to provide the maximum solar radiation transmission into the greenhouse. The net solar radiation flux measured at the greenhouse floor showed a reasonable agreement with the predicted value. The net fluxes were estimated around noon. The average net radiation (solar and thermal) at the soil surface was 220.0 W m-2, the average soil heat flux was 155.0 W m-2 and the average contribution of the water vapor of the inside air to the thermal radiation was 22.0 W m-2. The average overall heat transmission coefficient was 4.0 W m-2 C-1 and was in the range between 3.0 W m-2 C-1 and 6.0 W m-2 C-1 under the different hot summer conditions between the inside and outside of the naturally ventilated, fog cooled greenhouse
Boissieux, X.; Heikal, M.R.; Johns, R.A. [University of Brighton (United Kingdom). Engineering Research Centre
2000-06-01
This paper presents experimental heat transfer results obtained during the evaporation of Isceon 59, R407C and R404A in a horizontal tube. The results have been compared with existing correlations which characterise the evaporative heat transfer coefficient to assess the validity of these models for refrigerant mixtures. The results compared well with the (Gungor K.E., Winterton, R.H.S. Simplified general correlation for saturated flow boiling and comparisons of correlations with data. The Canadian Journal of Chemical Engineering, Chemical Engineering Research and Design 1987;65(2):148-156 and Shah M.M. Chart correlation for saturated boiling heat transfer: equations and further study. ASHRAE Transactions 1982;88(1):185-196) correlations over a 0.2 to 0.8 vapour quality range. These correlations, however, did not accurately predict the results obtained during the dry-out at high vapour quality. A model, developed by (Kattan N., Thome J.R., Favrat D., 1998. Flow boiling in horizontal tubes: part 1 - development of a diabatic two-phase flow pattern map. Journal of Heat Transfer, Transactions of ASME, Vol. 120, pp. 140-147; Kattan N., Thome J.R., Favrat D., 1998. Flow boiling in horizontal tubes: part 2 - new heat transfer data for five refrigerants. Journal of Heat Transfer, Transactions of ASME, Vol. 120, pp. 148-155; Kattan N., Thome JR., Favrat D., 1998. Flow boiling in horizontal tubes: part 3 - development of a new heat transfer model based on flow pattern. Journal of Heat Transfer, Transactions of ASME, Vol. 120, pp. 156-165), was found to express the local variations in heat transfer during the whole evaporation process. This model was modified to fit the three new refrigerants. The modified Kattan model offers a good prediction of the heat transfer results, with a standard deviation of 6.1%. (author)
A new measurement method for measuring the mean fuel temperature as well as the fuel-to-coolant heat transfer coefficient of fast breeder reactor subassemblies (SA) is reported. The method is based on the individual heat balance of fuel SA's after fast reactor shut-downs and uses only the plants normal SA outlet temperature and neutron power signals. The method was used successfully at the french breeder prototype Super Phenix 1. The mean SA fuel temperature as well as the heat transfer coefficient of all SPX SA's have been determined at power levels between 15 and 90% of nominal power and increasing fuel burn-up from 3 to 83 EFPD (Equivalent of Full Power-Days). The measurements also provided fuel and whole SA time constants. The estimated accuracy of measured fuel parameters is in the order of 10%. Fuel temperatures and SA outlet temperature transients were also calculated with the SPX1 systems code DYN2 for exactly the same fuel and reactor operating parameters as in the experiments. Measured fuel temperatures were higher than calculated ones in all cases. The difference between measured and calculated core mean values increases from 50 K at low power to 180 K at 90% n.p. This is about the double of the experimental error margins. Measured SA heat transfer coefficients are by nearly 20% lower than corresponding heat transfer parameters used in the calculations. Discrepancies found between measured and calculated results also indicate that either the transient heat transfer in the gap between fuel and cladding (gap conductance) might not be exactly reproduced in the computer code or that the gap in the fresh fuel was larger than assumed in the calculations. (orig.)
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 (Î±, 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 |Î±0 - 0.5|, where Î±0 is the transfer ratio in the quasi-static regime, and Î±0 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 Î± for a fast transfer system.
TrumiÄ‡ B.
2009-01-01
Full Text Available In order to increase the active surface of platinum catalysts for ammonia oxidation and on the basis of theoretic considerations and tests in industrial environment, we have finally decided on their specific design. Efficiency on the newly designed catalyst was checked in industrial circumstances. A comparative analysis of the total ammonia recovery coefficient between the mentioned new catalysts and previously applied platinum catalysts was carried out. All advantages of catalysts with increased active surfaces were confirmed and a new method of their manufacturing process was selected.
Haddag, B.; Atlati, S.; Nouari, M.; Zenasni, M.
2015-10-01
This paper deals with the modelling and identification of the heat exchange at the tool-workpiece interface in machining. A thermomechanical modelling has been established including heat balance equations of the tool-workpiece interface which take into account the heat generated by friction and the heat transfer by conduction due to the thermal contact resistance. The interface heat balance equations involve two coefficients: heat generation coefficient (HGC) of the frictional heat and heat transfer coefficient (HTC) of the heat conduction (inverse of the thermal contact resistance coefficient). Using experimental average heat flux in the tool, estimated for several cutting speeds, an identification procedure of the HGC-HTC couple, involved in the established thermomechanical FE-based modelling of the cutting process, has been proposed, which gives the numerical heat flux equal the measured one for each cutting speed. Using identified values of the HGC-HTC couple, evolution laws are proposed for the HGC as function of cutting speed, and then as function of sliding velocity at the tool-workpiece interface. Such laws can be implemented for instance in a Finite Element code for machining simulations.
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
Role of nuclear surface tension coefficient in alpha decay process of the superheavy nuclei
The present paper role of nuclear surface tension in alpha decay resulted from the need to improve the Isospin Cluster Model, where the excess of neutron and proton numbers are taken in account effectively of a nucleus in decay calculations. The appropriate value of nuclear surface tension coefficient in proximity potential which plays an important role to estimate the nuclear attraction between two nuclear surfaces is reviewed, in this model. The nuclear proximity force is proportional to the surface tension and its contribution necessarily should be appropriate. The synthesis of super heavy elements, formed by either of cold fusion or hot fusion process, is primarily decay through alpha-particle emission. The successive emission of alpha particles from a superheavy element ends at spontaneous fission
Chang, Wen-Ruey; Matz, Simon; Chang, Chien-Chi
2014-05-01
The maximum coefficient of friction that can be supported at the shoe and floor interface without a slip is usually called the available coefficient of friction (ACOF) for human locomotion. The probability of a slip could be estimated using a statistical model by comparing the ACOF with the required coefficient of friction (RCOF), assuming that both coefficients have stochastic distributions. An investigation of the stochastic distributions of the ACOF of five different floor surfaces under dry, water and glycerol conditions is presented in this paper. One hundred friction measurements were performed on each floor surface under each surface condition. The Kolmogorov-Smirnov goodness-of-fit test was used to determine if the distribution of the ACOF was a good fit with the normal, log-normal and Weibull distributions. The results indicated that the ACOF distributions had a slightly better match with the normal and log-normal distributions than with the Weibull in only three out of 15 cases with a statistical significance. The results are far more complex than what had heretofore been published and different scenarios could emerge. Since the ACOF is compared with the RCOF for the estimate of slip probability, the distribution of the ACOF in seven cases could be considered a constant for this purpose when the ACOF is much lower or higher than the RCOF. A few cases could be represented by a normal distribution for practical reasons based on their skewness and kurtosis values without a statistical significance. No representation could be found in three cases out of 15. PMID:24268803
Surface-Phonon Polariton Contribution to Nanoscale Radiative Heat Transfer.
Rousseau, Emmanuel; Laroche, Marine; Greffet, Jean-Jacques
2009-01-01
Heat transfer between two plates of polar materials at nanoscale distance is known to be enhanced by several orders of magnitude as compared with its far-field value. In this article, we show that nanoscale heat transfer is dominated by the coupling between surface phonon-polaritons located on each interface. Furthermore, we derive an asymptotic closed-form expression of the radiative heat transfer between two polar materials in the near-field regime. We study the temperature dependence of th...
Theory of the kinetic coefficients of the atomically rough surface of 4He crystals
The growth coefficient K (the velocity of growth per unit chemical potential difference) and the Onsager cross-coefficients b1 and b2, coupling growth and heat flow, are calculated for atomically rough surfaces of hcp 4He crystals. The calculation is based on the premise, suggested by Andreev and Parshin, that growth is limited by the collision of phonons and rotons with the interface. The calculated K is compared with that obtained by Keshiskev et al. from the damping of melting-freezing waves. The theory assumes that the excitations are in the ballistic regime where their mean free path is large compared to the wavelength of the melting-freezing waves. In the experiment only the phonons satisfy this condition, yet the theory agrees with the data even when roton scattering is important. Irreversible thermodynamics requires that the cross coefficients b1 and b2 be equal. This is shown by direct calculation. The value of b1 and b2 depends on the ratio of two integrals over the phonon transmission coefficient and it is evaluated for two models of the transmission. The theory agrees fairly well with a recent measurement of b1. A calculation of the dissipation in the hydrodynamic regime, where the free path is short, shows that the damping of melting-freezing waves should have a different dependence on frequency compared to the ballistic regime
It is proposed the model of potential field near solid surface, which allows to get the analytical solution of Schroedinger equations and calculate the coefficient of beams reflection by solid surface. It is obtained the oscillations of the reflection coefficient when changing the field characteristics
Highlights: â€¢ Infra-red thermographic study of Taylor bubble train flow in square mini-channel. â€¢ Design of experiments for measurement of local streamwise Nusselt number. â€¢ Minimizing conjugate heat transfer effects and resulting errors in data reduction. â€¢ Benchmarking against single-phase flow and three-dimensional computations. â€¢ Local heat transfer enhancement up to two times due to Taylor bubble train flow. -- Abstract: In mini/micro confined internal flow systems, Taylor bubble train flow takes place within specific range of respective volume flow ratios, wherein the liquid slugs get separated by elongated Taylor bubbles, resulting in an intermittent flow situation. This unique flow characteristic requires understanding of transport phenomena on global, as well as on local spatio-temporal scales. In this context, an experimental design methodology and its validation are presented in this work, with an aim of measuring the local heat transfer coefficient by employing high-resolution InfraRed Thermography. The effect of conjugate heat transfer on the true estimate of local transport coefficients, and subsequent data reduction technique, is discerned. Local heat transfer coefficient for (i) hydrodynamically fully developed and thermally developing single-phase flow in three-side heated channel and, (ii) non-boiling, airâ€“water Taylor bubble train flow is measured and compared in a mini-channel of square cross-section (5 mm Ã— 5 mm; Dh = 5 mm, Bo â‰ˆ 3.4) machined on a stainless steel substrate (300 mm Ã— 25 mm Ã— 11 mm). The design of the setup ensures near uniform heat flux condition at the solidâ€“fluid interface; the conjugate effects arising from the axial back conduction in the substrate are thus minimized. For benchmarking, the data from single-phase flow is also compared with three-dimensional computational simulations. Depending on the employed volume flow ratio, it is concluded that enhancement of nearly 1.2â€“2.0 times in time-averaged local streamwise Nusselt number can be obtained by Taylor bubble train flow, as compared to fully developed single-phase flow. This enhancement is attributed to the intermittent intrusion of Taylor bubbles in the liquid flow which drastically changes the local fluid temperature profiles. It is important to maintain proper boundary conditions during the experiment while estimating local heat transfer coefficient, especially in mini-micro systems
SAFARI 2000 Surface Atmospheric Radiative Transfer (SMART), Dry Season 2000
National Aeronautics and Space Administration â€” Surface-sensing Measurements for Radiative Transfer (SMART) and Chemical, Optical, and Microphysical Measurements of In-situ Troposphere (COMMIT) consist of a suite...
SAFARI 2000 Surface Atmospheric Radiative Transfer (SMART), Dry Season 2000
National Aeronautics and Space Administration — Surface-sensing Measurements for Radiative Transfer (SMART) and Chemical, Optical, and Microphysical Measurements of In-situ Troposphere (COMMIT) consist of a suite...
Heat transfer characteristics of large superconductors with different surface conditions
For the development of large current, high current density superconductors, steady-state boiling helium heat transfer characteristics of the model conductors having different cooling surfaces were measured. This reports describes example conditions, experimental conditions, measurement means and results. (author)
Filtering Non-Linear Transfer Functions on Surfaces
Heitz, Eric; Nowrouzezahrai, Derek; Poulin, Pierre; Neyret, Fabrice
2014-01-01
Applying non-linear transfer functions and look-up tables to procedural functions (such as noise), surface attributes, or even surface geometry are common strategies used to enhance visual detail. Their simplicity and ability to mimic a wide range of realistic appearances have led to their adoption in many rendering problems. As with any textured or geometric detail, proper filtering is needed to reduce aliasing when viewed across a range of distances, but accurate and efficient transfer func...
Experimental study on augmentation of nucleate boiling heat transfer on nano porous surfaces
Park, Young Jae; Kim, Hyung Dae [Kyung Hee Univ., Seoul (Korea, Republic of)
2012-10-15
Nucleate boiling broadly occurs in thermal hydraulic and safety systems of nuclear power plant (NPP). Heat transfer performance of nucleate boiling is closely related to efficiency and safety of NPPs. Hence, there have been numerous researches to effectively enhance nucleate boiling heat transfer performance. A number of recent studies have reported significant enhancements in nucleate boiling heat transfer coefficient (NBHTC) and critical heat flux (CHF) by fabricating nano/microscale structures on a boiling surface. Wei et al. showed that both NBHTC and CHF can be significantly enhanced with micro pin finned structures. They explained enhancement of NBHTC and CHF that occurred by increase in effective heat transfer area due to micro pin finned structures. Ahn et al. reported 100% enhancement in CHF on a boiling surface with nano/micro hybrid structures. They analyzed CHF enhancement that was caused by improvement of surface wettability on Nano/micro hybrid structures. In this study, an ordered nano porous surface was prepared using anodized aluminum oxide (AAO) technique and nucleate boiling heat transfer performance was examined in a pool with FC 72. Furthermore, the pool boiling result on the nano porous surface was interpreted based on heterogeneous bubble nucleation theory from a cavity.
Heat transfer enhancement of free surface MHD-flow by a protrusion wall
Due to the magnetohydrodynamic (MHD) effect on the flow, which degrades heat transfer coefficients by pulsation suppression of external magnetic field on the flow, a hemispherical protrusion wall is applied to free surface MHD-flow system as a heat transfer enhancement, because the hemispherical protrusion wall has some excellent characteristics including high heat transfer coefficients, low friction factors and high overall thermal performances. So, the characteristics of the fluid flow and heat transfer of the free surface MHD-flow with hemispherical protrusion wall are simulated numerically and the influence of some parameters, such as protrusion height ?/D, and Hartmann number, are also discussed in this paper. It is found that, in the range of Hartmann number 30 ? Ha ? 70, the protrusion wall assemblies can achieve heat transfer enhancements (Nu/Nu0) of about 1.3-2.3 relative to the smooth channel, while the friction loss (f/f0) increases by about 1.34-1.45. Thus, the high Nusselt number can be obtained when the protrusion wall with a radically lower friction loss increase, which may help get much higher overall thermal performances.
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)
Effect of transverse surface curvature on turbulent heat transfer in nuclear fuel assemblies
Reported here is an analytical study on the effect of the transverse convex curvature on the fluid flow and heat transfer in concentric annuli. The study showed that (1) while the effect of the transverse surface concave on fluid flow is negligible, that of transverse convex curvature is significant, and (2) both the friction coefficient and heat transfer increase with decreasing value of the inner core radius and that their values are always greater than those for the flows in parallel planes for the ranges of parameter studied. It is deduced from the study that since there is no workable theoretical model exists nor the experimental results to quantify the effect of the convex curvature on fluid flow, heat transfer and especially on CHF, any experimental verification of the turbulent fluid flow and heat transfer, including CHF, of nuclear fuel bundles must come from the fuel-bundle simulators of 1:1 bundle lattice geometry. (author)
On the parameterization of surface momentum transport via drag coefficient in low-wind conditions
Zhu, Ping; Furst, Jonathan
2013-06-01
The subgrid-scale surface momentum transport, which plays an important role in determining the exchange between the atmosphere and the underlying surface, is often parameterized in terms of the surface mean wind speed via drag coefficient (CD), a parameter that needs to be determined externally often through the Monin-Obukhov Similarity (MOS) Theory. However, some characteristics of CD derived from observations for overland conditions, particularly the substantial increase of CD with a decrease in wind speed in low-wind conditions, cannot be explained by MOS. This issue is investigated using data collected by a portable meteorological tower. By analyzing the turbulent kinetic energy budget, a novel parameterization framework for momentum fluxes is proposed. The new parameterization not only appropriately describes the observed variation of CD but also can be simplified to MOS with certain assumptions. Moreover, the effect of stability, which traditionally has to be determined empirically, can now be determined internally within the new framework.
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.
An improved method is presented for the prediction of heat transfer coefficients in turbulent falling liquid films with or without interfacial shear for both heating or condensation. A modified Mudawwar and El-Masri's semiempirical turbulence model, particularly to extend its use for the turbulent falling film with high interfacial shear, is used to replace the eddy viscosity model incorporated in the unified approach proposed by Yih and Liu. The liquid film thickness and asymptotic heat transfer coefficients against the film Reynolds number for wide range of interfacial shear predicted by both present and existing methods are compared with experimental data. The results show that, in general, predictions of the modified model agree more closely with experimental data than that of existing models. Comparisons of the predictions of the present model with that of existing models and the experimental data show that agreement is fairly good and consistent. A brief summary of the results are as follows: (1) As opposed to the previous model, present model utilizes a continuous linear variation of eddy viscosity near the interfacial surface. For freely falling liquid film, the present model reduce to the Mudawwar and El-Masri's model. (2) The curves of the present model for the heat transfer coefficients with liquid film Reynolds number have positive slopes in turbulent regime while the curves obtained by other models have negative slopes particularly for condensation. (3) The two criteria for transition from laminar to turbulent film flow, one for low interfacial shear and the other for high interfacial shear, respectively are shown to give the best agreement with the data for the present method
Momentum transfer in a Brillouin surface scattering
The theory of acoustic excitation scattering in the surface of Brilloiun of opaque materials, is related to the question of momentum transfexed from radiation fields to the material when the incident eight is scattered in a measurable spectrum. (A.C.A.S.)
IzÃ¡k, Pavel; KÃ¡rÃ¡szovÃ¡, Magda; Å imÄÃk, Miroslav; Friess, K.; SedlÃ¡kovÃ¡, Zuzana; RÅ¯Å¾iÄka, Marek; Å olcovÃ¡, Olga
Bratislava : AXIMA Graphics Design & Printing Services , 2014, s. 91 ISBN 978-80-89475-13-1. [International Conference of Slovak Society of Chemical Engineering /41./. TatranskÃ© Matliare (SK), 26.05.2014-30.05.2014] R&D Projects: GA TA ÄŒR TE01020080; GA ÄŒR GA14-12695S Institutional support: RVO:67985858 Keywords : ionic liquid membrane * transport properties * trafer coefficients Subject RIV: CI - Industrial Chemistry, Chemical Engineering
IzÃ¡k, Pavel; KÃ¡rÃ¡szovÃ¡, Magda; Å imÄÃk, Miroslav; Friess, K.; SedlÃ¡kovÃ¡, Zuzana; RÅ¯Å¾iÄka, Marek; Å olcovÃ¡, Olga
Bratislava : AXIMA Graphics Design & Printing Services, 2014, s. 91 ISBN 978-80-89475-13-1. [International Conference of Slovak Society of Chemical Engineering /41./. TatranskÃ© Matliare (SK), 26.05.2014-30.05.2014] R&D Projects: GA TA ÄŒR TE01020080; GA ÄŒR GA14-12695S Institutional support: RVO:67985858 Keywords : ionic liquid membrane * transport properties * trafer coefficients Subject RIV: CI - Industrial Chemistry, Chemical Engineering
Volumetric mass transfer coefficients characterising VOC absorption in water/silicone oil mixtures
Dumont, Eric; Darracq, Guillaume; Couvert, Annabelle; Couriol, Catherine; Amrane, Abdeltif; Thomas, Diane; Andres, Yves; Le Cloirec, Pierre
2013-01-01
The physical absorption of three Volatile Organic Compounds (dimethyldisulphide (DMDS), dimethylsulphide (DMS) and toluene) in "water/silicone oil" systems at a constant flow rate for mixtures of different compositions (f = 0, 5, 10, 15, 20 and 100%) was investigated using a dynamic absorption method. The results indicate that silicone oil addition leads to a dramatic decrease in KLa which can be related to the change in the partition coefficient (Hmix). They confirm the results obtained for ...
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 ?-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 diffusion coefficient is considerably higher for the solutionized Inconel 718 than for either the cold rolled or precipitation hardened specimens. Microstructural studies indicate that the reduced hydrogen diffusion coefficients in the latter specimens arise from hydrogen trapping at dislocations and precipitates that are present at much lower concentrations in the solutionized specimens. Repeated permeation transients provide evidence for irreversible hydrogen trapping in the cold rolled and precipitation hardened specimens, but such effects are insignificant in the solutionized specimens. The effect of trapping in determining the hydrogen diffusion coefficients was also studied in alloy 686 and 59 specimens. Microstructural studies indicate the presence of bcc-Mo rich inclusions concentrated along the grain boundaries in alloy 686 specimens, but randomly distributed in alloy 59 specimens. Multiple permeation transients show an increase in diffusion coefficient values for the decay transients compared to rise transients in alloy 686 specimens. On the other hand, the first rise transient had a lower diffusion coefficient compared to successive rise and decay transients in alloy 59 specimens. Effective diffusion coefficient (Deff) values of hydrogen in multiple permeation transients suggest that hydrogen trapping sites are predominantly reversible in alloy 686, but mixed reversible and irreversible in alloy 59.
Piping systems of nuclear power plants include connections of branches conveying fluids at different temperatures. Thermal-hydraulic fluctuations arising from the turbulent mixing of the flows can affect the inner wall of the pipes and can lead to fatigue damage. In order to assess the high-cycle thermal fatigue damages risks of the NPP mixing zones, the knowledge of the temperature fluctuations transfer from fluid to structure is necessary. Some tests were performed in order to evaluate the unsteady heat transfer coefficient in a mixing zone, and especially during the FATHER experiment, which was initiated by AREVA NP, CEA and EDF to study thermal fatigue phenomena. More precisely, a specific sensor called 'coefh' was used during the experiments. This sensor records simultaneously local temperature fluctuations in the fluid and in the structure thanks to thermocouples incorporated in the body of the sensor, which is specifically designed to capture the rapid unsteady temperature fluctuations. This paper describes and compares different approaches that could be used to evaluate a heat transfer coefficient from the 'coefh' fluid and structure unsteady temperature measurements. A specific attention is paid to the impact of the phase difference between the fluid and the structure temperature measurements. (author)
Uthen Kuntha
2002-04-01
Full Text Available Boiling heat transfer coefficients and pressure drop of R-22 and its alternatives, which are R32/R125a/ R134 (23%/25%/52% and R32/R125a (50%/50%, flowing inside smooth and grooved tubes have been determined with the conditions similar to those in small refrigerators. The range of mass flow rates examined is between 0.0025 and 0.0125 kg/s. The data have been taken at the evaporator temperatures of -35 to -4 oC and at the condenser temperatures of 40 to 50 oC. The boiling heat transfer coefficients of the refrigerants in the grooved tubes are higher than those in the smooth tubes and R-22 shows the best performance for both tubes. The heat transfer correlations have also been developed. In case of the pressure drop, the twophase friction multiplier Ï†G 2 increases with Martinelli parameter and there is no effect of the tube roughness and the types of the refrigerants.
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.
A technique for measuring the heat transfer coefficient inside a Bridgman furnace
Rosch, W.; Jesser, W.; Debnam, W.; Fripp, A.; Woodell, G.; Pendergrass, T. K.
1993-01-01
Knowledge of the amount of heat that is conducted, advected and radiated between an ampoule and the furnace is important for understanding vertical Bridgman crystal growth. This heat transfer depends on the temperature, emissivities and geometries of both the furnace and ampoule, as well as the choice of ambient gas inside the furnace. This paper presents a method which directly measures this heat transfer without the need to know any physical properties of the furnace, the ampoule, or the gaseous environment. Data are given for one specific furnace in which this method was used.
Uptake Coefficients of NO3 Radicals on Solid Surfaces of Sea-Salts
Gratpanche, F.; Sawerysyn, J.-P.
1999-02-01
Uptake coefficients of nitrate radicals (? NO_3) have been measured by a technique involving a coated-wall flow tube with radical detection by E.P.R. spectrometry. The variation of NO3 concentration in the gas phase was followed indirectly by monitoring OH radicals produced by the titration reaction H + NO_3. The mean initial value of ? NO3 measured on solid NaCl surfaces was (1.7± 1.2)× 10-2) in the temperature range 258-301 K, while for solid NaBr surfaces the value was (0.11 ± 0.06) at 293 K. In each case, errors limits correspond to one standard deviation. For NaBr, a slight negative temperature dependence was observed over the investigated range, 243-293 K, which can be represented by ?_NO_3^NaBr = 1.6 ?ft(begin{array}{l}+1.8 -0.9) × 10-3exp [(1210± 200)/T]. An analysis of the results shows that under some conditions the heterogeneous loss of nitrate radicals on sea-salt aerosol particles at ambient temperature could be competitive with their loss by homogeneous reaction in the marine troposphere at night. Les coefficients de capture des radicaux nitrate (? NO_3) sur des surfaces de sels marins (NaCl et NaBr) ont été mesurés aux températures troposphériques en utilisant la technique du réacteur à écoulement à paroi recouverte couplée à un spectromètre de résonance paramagnétique électronique (R.P.E). La variation de la concentration en phase gazeuse des radicaux nitrate en présence des surfaces étudiées est suivie en mesurant le signal R.P.E des radicaux OH produits par la réaction de titrage H + NO3. Pour des températures comprises entre 258 et 301 K, la valeur moyenne du coefficient de capture initial (? NO_3) sur des surfaces solides de NaCl est égal à (1.7± 1.2)× 10-2). Sur des surfaces solides de NaBr, (? NO_3) est égal à (0.11 ± 0.06) à 293 K. L'incertitude correspond à une déviation standard. Par ailleurs, pour ce type de surfaces, une légère dépendance négative avec la température est observée dans la gamme de température examinée (243-293 K) : ?_NO_3^NaBr = 1.6 ?ft(begin{array}{l}+1.8 -0.9) × 10-3exp [(1210± 200)/T]. A température ambiante, la disparition hétérogène des radicaux nitrate sur des particules d'aérosols marins pourrait être compétitive avec leur disparition en phase gazeuse durant la nuit.
Discussion on the measurement of the surface tension coefficient by the pull-off method
Tang, Lei; Liu, Guan-nan; Qian, Jun; Sun, Qian; Zhang, Chun-ling
2016-03-01
A simple experiment for measuring the surface tension coefficient is proposed, which is well suited for teaching and learning the behavior of liquids in typical student laboratories. It is based on the pull-off method and the dynamometer used is the Jolly balance. The experiment requires inexpensive equipment but the methods allow for serious analysis of possible systematic errors, such as the impact of the state of the spring and wire on the experimental results, and the unusual movement of the engraved line on the mirror when pulling up the water film.
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
Improvement of dropwise condensation heat transfer using hydrophobic nano porous surfaces
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
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.
Zhihui Wang
2013-01-01
Full Text Available This study investigates the frequency bifurcation phenomena of a typical voltage-fed resonant converter based on mutual induction model. It is found that the Zero Current Switching (ZCS operating frequency has the bifurcation region as the coupling coefficient varies due to the distance. The expression for the bifurcation boundary is derived and analyzed. Such results are very useful for guiding the design of practical Inductively Coupled Power Transfer (ICPT systems especially in applications which have the requirement of the position flexibility. Analytical results are verified both via MATLAB simulations and experimental prototype.
The present work is devoted to an estimation of the transfer coefficient between reared oyster mushrooms and their support die, which was injected with known activity of Am-241 and Pu-242. After 2 months when we get the reared mushrooms of cane oyster mushrooms were dried and prepared by liquid extraction with Aliquat 336. The samples were measured by ?-spectrometry. The results of activity Am-241 and Pu-242 in the mushrooms body and residual activity in the support were detected and calculated. (authors)
Feyissa, Aberham Hailu; Christensen, Martin Gram; Pedersen, SÃ¸ren Juhl; Hickman, Minka; Adler-Nissen, Jens
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...... demonstrates that the method is rather precise at relevant values of hfp in vessel cooking (100â€“300 [W/m2K]), allowing a prediction of the centre temperature within Â±0.6Â°C....
Heat transfer between a nano-tip and a surface
Chapuis, Pierre-Olivier [Laboratoire d' Energetique Moleculaire et Macroscopique, Combustion, CNRS UPR 288, Ecole Centrale Paris, Grande Voie des Vignes, F-92295 Chatenay-Malabry cedex (France); Greffet, Jean-Jacques [Laboratoire d' Energetique Moleculaire et Macroscopique, Combustion, CNRS UPR 288, Ecole Centrale Paris, Grande Voie des Vignes, F-92295 Chatenay-Malabry cedex (France); Joulain, Karl [Laboratoire d' Etudes Thermiques, CNRS UMR 6608 and ENSMA, BP 40109, Futuroscope, F-86961 Chasseneuil cedex (France); Volz, Sebastian [Laboratoire d' Energetique Moleculaire et Macroscopique, Combustion, CNRS UPR 288, Ecole Centrale Paris, Grande Voie des Vignes, F-92295 Chatenay-Malabry cedex (France)
2006-06-28
We study quasi-ballistic heat transfer through air between a hot nanometre-scale tip and a sample. The hot tip/surface configuration is widely used to perform non-intrusive confined heating. Using a Monte Carlo simulation, we find that the thermal conductance reaches 0.8 MW m{sup -2} K{sup -1} on the surface under the tip and show the shape of the heat flux density distribution (nanometre-scale thermal spot). These results show that a surface can be efficiently heated locally without contact. The temporal resolution of the heat transfer is a few tens of picoseconds.
Noroviruses on surfaces: Detection, transfer and inactivation
RÃƒÂ¶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...
The diffusion transfer of sputtered atoms in plasma spraying on the internal cylindrical surface
The sputtering of the surface of the solid by the glow discharge plasma is used widely in the electronics for the deposition of thin films. The sputtered atoms (SA), leaving the surface, clash with the gas atoms and the granules the energy. It is interesting to examine the effect of the condensation coefficient of the SA on the concentration of the SA in the cylindrical discharge volume and the fluxes of the SA to different areas of the wall. The solution of this problem for the case of the diffusion transfer of the SA is the subject of this work
The effect of the liquid-solid system properties on the interline heat transfer coefficient
Wayner, P. C., Jr.
1977-01-01
A theoretical procedure to determine the heat transfer characteristics of the interline region of an evaporating meniscus using the macroscopic optical and thermophysical properties of the system is outlined. The analysis is based on the premise that the interline transport processes are controlled by the London-van der Waals forces between condensed phases (solid and liquid). The procedure is used to compare the relative size of the interline heat sink of various systems using a constant heat flux model. This solution demonstrates the importance of the interline heat flow number which is evaluated for various systems. The heat transfer characteristics of the decane-steel system are numerically compared with those of the carbon tetrachloride-quartz system.
The Effect of Position of Heated Rod in Tube Banks on the Heat Transfer Coefficient
Ehsan Fadhil Abbas
2015-01-01
Heat transfer in flow across a bank of tubes is of a particular importance in the design of heat exchangers. Heat exchangers are used in numerous services and industrial applications. Experimental studies were performed, carried out in cross-flow tube banks. They contain copper heated rod and 17 Aluminum rods arranged in the form of staggered and at arrange of Reynolds number 2700 to 21530. The experimental results indicated that the location of the heated rod in the work section affects the ...
Evaluation of Heat and Mass Transfer Coefficients for R134a/DMF Bubble Absorber
Suresh, M; Mani, A
2011-01-01
The Vapour Absorption Refrigeration System (VARS) has generated renewed interest and is being viewed as one of the alternatives for vapour compression refrigeration due to its potential for waste heat utilization. To improve the efficiency of these systems, it is necessary to study heat and mass transfer processes in absorption system components. The absorber, one of the crucial components in VARS is considered for study. Experimental investigation is carried out to study heat and mass transf...
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.
Frequency comb transferred by surface plasmon resonance
Geng, Xiao Tao; Chun, Byung Jae; Seo, Ji Hoon; Seo, Kwanyong; Yoon, Hana; Kim, Dong-Eon; Kim, Young-Jin; Kim, Seungchul
2016-01-01
Frequency combs, millions of narrow-linewidth optical modes referenced to an atomic clock, have shown remarkable potential in time/frequency metrology, atomic/molecular spectroscopy and precision LIDARs. Applications have extended to coherent nonlinear Raman spectroscopy of molecules and quantum metrology for entangled atomic qubits. Frequency combs will create novel possibilities in nano-photonics and plasmonics; however, its interrelation with surface plasmons is unexplored despite the important role that plasmonics plays in nonlinear spectroscopy and quantum optics through the manipulation of light on a subwavelength scale. Here, we demonstrate that a frequency comb can be transformed to a plasmonic comb in plasmonic nanostructures and reverted to the original frequency comb without noticeable degradation of quantum metrology and subwavelength photonic circuits. PMID:26898307
The effect of ambient temperature on the shoe-surface interface release coefficient.
Torg, J S; Stilwell, G; Rogers, K
1996-01-01
Previous studies of the shoe-surface interface correlated foot fixation with cleat length, configuration, and material composition as well as turf type and surface conditions. Our study examined the effect of temperature on the rotational torsion resistance of artificial turf football shoes. Five football shoe models, a flat-soled basketball-style turf shoe, a natural grass soccer-style shoe, and three multistudded turf shoes, were studied on dry Astro Turf at five temperatures (range, 52 degrees F to 110 degrees F). An assay device, a prosthetic foot mounted on a loaded stainless steel shaft, was used to determine the force necessary to release a shoe from the turf's surface. We used a torque wrench to apply a rotational force so that each shoe was pivoted counterclockwise through an arc of 60 degrees. Our results indicated that release coefficients differ within and among the shoe models at various turf temperatures. We also found that an increase in turf temperature, in combination with cleat characteristics, affects shoe-surface interface friction and potentially places the athlete's knee and ankle at risk of injury. Based on an established risk criterion, which correlated shoe-surface interface combinations in the laboratory with documented clinical occurrences, only the flat-soled basketball-style turf shoe could be designated "safe" or "probably safe" at all five temperatures. PMID:8638758
A problem of particular interest in pressure vessel technology is the calculation of accurate stress-intensity factors for semielliptical surface cracks in cylinders. Computing costs for direct solution techniques can be prohibitive when applied to three-dimensional (3-D) geometries with time-varying boundary conditions such as those associated with pressurized thermal shock. An alternative superposition technique requires the calculation of a set of influence coefficients for a given 3-D crack model that can be superimposed to obtain mode-I stress-intensity factors. This paper presents stress-intensity-factor influence coefficients (SIFICs) for axially and circumferentially oriented finite-length semielliptical inner-surface flaws with aspect ratios (total crack length (2c) to crack depth (a)) of 2, 6, and 10 for clad cylinders having an internal radius to wall thickness (t) ratio of 10. SIFICs are computed for flaw depths in the range of 0.01 â‰¤ a/t â‰¤ 0.5 and two cladding thicknesses. The incorporate of this SIFIC data base in fracture mechanics codes will facilitate the generation of fracture mechanics solutions for a wide range of flaw geometries as may be required in structural integrity assessments of pressurized-water and boiling-water reactors
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.
Investigation into the heat transfer performance of helically ribbed surfaces
The first part of an investigation into flow and heat transfer in annular channels and seven pin clusters is described. One of the main aims of the project is to improve cluster heat transfer prediction codes for helically ribbed surfaces. A study is made of the heat transfer and flow characteristics of a helically ribbed pin in an annular channel. It is shown that the swirling flow, which is induced by the helical ribs, gives rise to substantially enhanced diffusivity levels. This phenomenon had not been taken into account by previous analysis techniques. The methods for analysing heat transfer and pressure drop data from annular channels which were originally developed for non-swirling flow are generalised to accommodate swirling flow. The new methods are shown to be consistent with empirical data. Roughness parameter data is presented for helically ribbed surfaces with an axial rib pitch into height ratio of about 7. (author)
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 measurements. To evaluate the obtained diffusion profiles we adapted the isolated grain boundary model, first proposed by Fisher (1951) to match several observations: (i) Anisotropic diffusion in forsterite, (ii) fast diffusion along the grain boundary, (iii) fast diffusion on the surface of the sample. The latter process is needed to explain an additional flux of material from the surface into the grain boundary. Surface and grain boundary diffusion coefficients are on the order of 10000 times faster than diffusion in the lattice. Another observation was that in some regions the diffusion profiles in the lattice were greatly extended. TEM observations suggest here that surface defects (nano-cracks, ect.) have been present, which apparently enhanced the diffusion through the bulk lattice. Dohmen, R., & Milke, R. (2010). Diffusion in Polycrystalline Materials: Grain Boundaries, Mathematical Models, and Experimental Data. Reviews in Mineralogy and Geochemistry, 72(1), 921-970. Fisher, J. C. (1951). Calculations of Diffusion Penetration Curves for Surface and Grain Boundary Diffusion. Journal of Applied Physics, 22(1), 74-77. Le Claire, A. D. (1951). Grain boundary diffusion in metals. Philosophical Magazine A, 42(328), 468-474.
Frequency comb transferred by surface plasmon resonance.
Geng, Xiao Tao; Chun, Byung Jae; Seo, Ji Hoon; Seo, Kwanyong; Yoon, Hana; Kim, Dong-Eon; Kim, Young-Jin; Kim, Seungchul
2016-01-01
Frequency combs, millions of narrow-linewidth optical modes referenced to an atomic clock, have shown remarkable potential in time/frequency metrology, atomic/molecular spectroscopy and precision LIDARs. Applications have extended to coherent nonlinear Raman spectroscopy of molecules and quantum metrology for entangled atomic qubits. Frequency combs will create novel possibilities in nano-photonics and plasmonics; however, its interrelation with surface plasmons is unexplored despite the important role that plasmonics plays in nonlinear spectroscopy and quantum optics through the manipulation of light on a subwavelength scale. Here, we demonstrate that a frequency comb can be transformed to a plasmonic comb in plasmonic nanostructures and reverted to the original frequency comb without noticeable degradation of <6.51 × 10(-19) in absolute position, 2.92 × 10(-19) in stability and 1?Hz in linewidth. The results indicate that the superior performance of a well-defined frequency comb can be applied to nanoplasmonic spectroscopy, quantum metrology and subwavelength photonic circuits. PMID:26898307
Reactions involving electron transfer at semiconductor surfaces
Comparisons are made between the changes in isotopic composition of isotopically pre-equilibrated (i.p.eq.) and isotopically non-equilibrated (i.n.eq.) gaseous oxygen in contact with prereduced or preoxidised samples of ZnO and TiO2 at room temperature. In the absence of illumination a place exchange (p.x.) process predominated in the oxygen isotope exchange (o.i.e.) detectable at low pressures, ca. 8 x 10-3 Torr, of i.p.eq. O2 upon contact with preoxidised samples, whereas a homophase, R0-type o.i.e. process predominated for i.n.eq. (16O2 + 18O2) contacted with prereduced samples at pressures of ca. 10-1 Torr. The latter R0 activity was removed by preoxidation but light restored it with quantum efficiency > 6 for pure ZnO and > 30 for lithium-doped ZnO. A mechanism is described to account for the correspondingly high turnover achieved on each site photoactivated by light. For i.p.eq. O2 exposed to intense illumination in contact with prereduced or preoxidised ZnO, a heterophase R1-type process, accompanied by a faster R0-type process, predominated and reasons for this are considered. Residual hydroxyls affect the ratio of o.i.e. processes on TiO2 surfaces. (author)
The diet-milk transfer coefficient, Fm (Bq L-1 output in milk divided by Bq d-1 intake to the animal) was studied for eight radionuclides that previously had been given little attention. The Fm values for cows and goats, respectively, were: 2.3 x 10(-5) and 1.5 x 10(-4) for /sup 99m/Tc, 1.4 x 10(-4) and 8.5 x 10(-4) for /sup 95m/Tc, 1.1 x 10(-2) for 99Tc (goats only); 1.7 x 10(-3) and 9 x 10(-3) for 99Mo; 4.8 x 10(-4) and 4.4 x 10(-3) for /sup 123m/Te; 4.8 x 10(-4) and 4.6 x 10(-3) for 133Ba; 5.5 x 10(-7) and 5.5 x 10(-6) for 95Zr; and 4.1 x 10(-7) and 6.4 x 10(-6) for 95Nb. The goat/cow transfer coefficient ratios for milk were approximately 10, but the goat/cow ratios for meat varied by three orders of magnitude