WorldWideScience
1

Modeling Local Hygrothermal Interaction: Local surface transfer coefficients  

DEFF Research Database (Denmark)

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 predictions of the local surface transfer coefficients are relatively accurate.

Steskens, Paul Wilhelmus Maria Hermanus; Janssen, Hans

2009-01-01

2

Heat transfer from extended surfaces subject to variable heat transfer coefficient  

Science.gov (United States)

The present article investigates the effect of locally variable heat transfer coefficient on the performance of extended surfaces (fins) subject to natural convection. Fins of different profiles have been investigated. The fin profiles presently considered are namely; straight and pin fin with rectangular (constant diameter), convex parabolic, triangular (conical) and concave parabolic profiles and radial fins with constant profile with different radius ratios. The local heat transfer coefficient was considered as function of the local temperature and has been obtained using the available correlations of natural convection for each pertinent extended surface considered. The performance of the fin has been expressed in terms of the fin efficiency. Comparisons between the present results for all fins considered and the results obtained for the corresponding fins subject to constant heat transfer coefficient along the fin are presented. Comparisons, i.e. showed an excellent agreement with the experimental results available in the literature. Results show that there is a considerable deviation between the fin efficiency calculated based on constant heat transfer coefficient and that calculated based on variable heat transfer coefficient and this deviation increases with the dimensionless parameter m.

Mokheimer, Esmail

2002-09-01

3

Influence of the convective surface transfer coefficients on the Heat, Air, and Moisture (HAM) building performance  

DEFF Research Database (Denmark)

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.

Steskens, Paul Wilhelmus Maria Hermanus; Janssen, Hans

2009-01-01

4

The heat transfer coefficients of the heating surface of 300 MWe CFB boiler  

Science.gov (United States)

A study of the heat transfer about the heating surface of three commercial 300 MWe CFB boilers was conducted in this work. The heat transfer coefficients of the platen heating surface, the external heat exchanger (EHE) and cyclone separator were calculated according to the relative operation data at different boiler loads. Moreover, the heat transfer coefficient of the waterwall was calculated by heat balance of the hot circuit of the CFB boiler. With the boiler capacity increasing, the heat transfer coefficients of these heating surface increases, and the heat transfer coefficient of the water wall is higher than that of the platen heating surface. The heat transfer coefficient of the EHE is the highest in high boiler load, the heat transfer coefficient of the cyclone separator is the lowest. Because the fired coal is different from the design coal in No.1 boiler, the ash content of the fired coal is much lower than that of the design coal. The heat transfer coefficients which calculated with the operation data are lower than the previous design value and that is the reason why the bed temperature is rather high during the boiler operation in No.1 boiler.

Wu, Haibo; Zhang, Man; Lu, Qinggang; Sun, Yunkai

2012-08-01

5

Critical thickness of an optimum extended surface characterized by uniform heat transfer coefficient  

CERN Document Server

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...

Leontiou, Theodoros

2015-01-01

6

FLOW VELOCITY AND SURFACE TEMPERATURE EFFECTS ON CONVECTIVE HEAT TRANSFER COEFFICIENT FROM URBAN CANOPY SURFACES BY NUMERICAL SIMULATION  

OpenAIRE

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 can...

Sivaraja Subramania Pillai; Ryuichiro Yoshie

2013-01-01

7

Numerical study on correlation of heat transfer coefficient with void fraction at heat transfer tube surface in sodium water reaction  

International Nuclear Information System (INIS)

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 elation 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)

8

Experiment on nucleate pool boiling in microgravity by using transparent heating surface - Analysis of surface heat transfer coefficients  

Science.gov (United States)

Investigation of mechanisms in nucleate boiling under microgravity conditions is essential for the development of the cooling systems handling a large amount of waste heat. A transparent heating surface with multiple arrays of 88 thin film temperature sensors and mini-heaters was developed for the clarification of boiling heat transfer mechanisms in microgravity. To investigate gravity effects on the microlayer behaviors and corresponding local heat transfer coefficients, images of liquid-vapor behaviors underneath attached bubbles and local heat transfer data were simultaneously obtained in microgravity pool boiling. The present paper reports the analysis of the data measured during the ESA parabolic flight campaign. It was found that the liquid-vapor behaviors were strongly affected by the direction and the level of residual gravity. Various patterns of liquid-vapor behaviours and corresponding enhancement or deterioration of the heat transfer are observed.

Kubota, C.; Kawanami, O.; Asada, Y.; Wada, Y.; Nagayasu, T.; Shinmoto, Y.; Ohta, H.; Kabov, O.; Queeckers, P.; Chikov, S.; Straub, J.

2011-12-01

9

Experiment on nucleate pool boiling in microgravity by using transparent heating surface – Analysis of surface heat transfer coefficients  

International Nuclear Information System (INIS)

Investigation of mechanisms in nucleate boiling under microgravity conditions is essential for the development of the cooling systems handling a large amount of waste heat. A transparent heating surface with multiple arrays of 88 thin film temperature sensors and mini-heaters was developed for the clarification of boiling heat transfer mechanisms in microgravity. To investigate gravity effects on the microlayer behaviors and corresponding local heat transfer coefficients, images of liquid-vapor behaviors underneath attached bubbles and local heat transfer data were simultaneously obtained in microgravity pool boiling. The present paper reports the analysis of the data measured during the ESA parabolic flight campaign. It was found that the liquid-vapor behaviors were strongly affected by the direction and the level of residual gravity. Various patterns of liquid-vapor behaviours and corresponding enhancement or deterioration of the heat transfer are observed.

10

The Effects of Surface Roughness and Metal Temperature on the Heat-Transfer Coefficient at the Metal Mold Interface  

Science.gov (United States)

This article focused on the effects of surface roughness and temperature on the heat-transfer coefficient at the metal mold interface. The experimental work was carried out in a unique and versatile apparatus, which was instrumented with two types of sensors, thermocouples, and linear variable differential transformers (LVDTs). The monitoring of the two types of sensors was carried out simultaneously during solidification. The concurrent use of two independent sensors provided mutually supportive data, thereby strengthening the validity of the interpretations that were made. With this type of instrumentation, it was possible to measure temperature profiles in mold and casting, as well as the air gap at the metal mold interface. Commercial purity aluminum was cast against steel and high carbon iron molds. Each type of mold had a unique surface roughness value. Inverse heat-transfer analysis was used to estimate the heat-transfer coefficient and the heat flux at the metal mold interface. A significant drop in the heat-transfer coefficient was registered, which coincided with the time period of the air gap formation, detected by the LVDT. An equation of the form h = frac{1} {{b^{ast}A + c}} + d was found to provide excellent correlation between the heat-transfer coefficient and air gap size. In general, an increase in mold surface roughness results in a decrease in the heat-transfer coefficient at the metal mold interface. On the other hand, a rise in liquid metal temperature results in a higher heat-transfer coefficient.

Coates, Basil; Argyropoulos, Stavros A.

2007-04-01

11

Remote detection of bare soil moisture using a surface-temperature-based soil evaporation transfer coefficient  

Science.gov (United States)

An approach for estimating soil moisture is presented and tested by using surface-temperature-based soil evaporation transfer coefficient ( ha), a coefficient recently proposed through the equation ha = ( Ts - Ta)/( Tsd - Ta) , where Ts, Tsd, and Ta are land surface temperature (LST), reference soil (dry soil without evaporation) surface temperature, and air temperature respectively. Our analysis and controllable experiment indicated that ha closely related to soil moisture, and therefore, a relationship between field soil moisture and ha could be developed for soil moisture estimation. Field experiments were carried out to test the relationship between ha and soil moisture. Time series Aqua-MODIS images were acquired between 11 Sep. 2006 and 1 Nov. 2007. Then, MODIS derived ha and simultaneous measured soil moisture for different soil depths were used to establish the relations between the two variables. Results showed that there was a logarithmic relationship between soil moisture and ha ( P truth data gathered from 46 meteorological stations in Hebei Province. Good agreement was observed between the measured and estimated soil moisture with RMSE of 0.0374 cm 3/cm 3 and 0.0503 cm 3/cm 3 for surface energy balance method at two soil depths (10 cm and 20 cm), with RMSE of 0.0467 cm 3/cm 3 and 0.0581 cm 3/cm 3 for maximum temperature method at two soil depths. For vegetated surfaces, the ratio of ha and NDVI suggested to be considered. The proposed approach has a great potential for soil moisture and drought evaluation by remote sensing.

Zhao, Shaohua; Yang, Yonghui; Qiu, Guoyu; Qin, Qiming; Yao, Yunjun; Xiong, Yujiu; Li, Chunqiang

2010-10-01

12

FLOW VELOCITY AND SURFACE TEMPERATURE EFFECTS ON CONVECTIVE HEAT TRANSFER COEFFICIENT FROM URBAN CANOPY SURFACES BY NUMERICAL SIMULATION  

Directory of Open Access Journals (Sweden)

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-? model which was used for the evaluation of CHTC from surfaces. The calculated CFD results showed good agreement with experimental results. After this validation, the effects of flow velocity and building surface temperature effects on CHTC from urban building surfaces were investigated. It has been found that the change in velocity remarkably affects the CHTC from urban canopy surfaces and change in surface temperature has almost no effect over the CHTC from urban canopy surfaces.

Sivaraja Subramania Pillai

2013-06-01

13

Heat transfer coefficient distributions for the convective cooling of non-cylindrical geometries in crossflow using extended surfaces  

OpenAIRE

An experimental investigation of the performance of extended fin surfaces for the forced convective cooling of a range of engine component geometries in crossflow is reported. The experiments were undertaken to measure the surface heat transfer coefficient distributions of external finning around non-cylindrical geometries for use in aviation gas turbines in which the cooling performance/mass ratio must be maximized. The geometries examined were a box (square with rounded corners), a flute (r...

Neely, Aj; Ireland, Pt; Harper, Lr

1997-01-01

14

Measuring of heat transfer coefficient  

DEFF Research Database (Denmark)

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 and warm forging operations.

Henningsen, Poul; Lindegren, Maria

2000-01-01

15

CFD simulation of direct contact condensation with ANSYS CFX using surface renewal theory based heat transfer coefficients  

International Nuclear Information System (INIS)

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.)

16

Estimation of internal heat transfer coefficients and detection of rib positions in gas turbine blades from transient surface temperature measurements  

International Nuclear Information System (INIS)

This paper describes a non-invasive, non-destructive, transient inverse measurement technique that allows one to determine internal heat transfer coefficients and rib positions of real gas turbine blades from outer surface temperature measurements after a sudden flow heating. The determination of internal heat transfer coefficients is important during the design process to adjust local heat transfer to spatial thermal load. The detection of rib positions is important during production to fulfill design and quality requirements. For the analysis the one-dimensional transient heat transfer problem inside of the turbine blade's wall was solved. This solution was combined with the Levenberg-Marquardt method to estimate the unknown boundary condition by an inverse technique. The method was tested with artificial data to determine uncertainties with positive results. Then experimental testing with a reference model was carried out. Based on the results, it is concluded that the presented inverse technique could be used to determine internal heat transfer coefficients and to detect rib positions of real turbine blades.

17

Analytical determination of local surface heat-transfer coefficients for cooled turbine blades from measured metal temperatures  

Science.gov (United States)

Analytical methods are presented for the determination of local values of outside and inside heat-transfer coefficients and effective gas temperatures by use of turbine-blade-temperature measurements. The methods are derived for a number of configurations that can be applied to typical cooled-turbine-blade shapes as well as to other types of heat-transfer apparatus.

Brown, W Byron; Esgar, Jack B

1950-01-01

18

Determination of friction factors and heat transfer coefficients for flow past artifically roughened surfaces  

Energy Technology Data Exchange (ETDEWEB)

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

19

Influence of wall emissivity and convective heat transfer coefficient on the adiabatic surface temperature as thermal/structural parameter in fire modeling  

International Nuclear Information System (INIS)

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 “Adiabatic Surface Temperature” or more commonly known as AST, introduced by Wickström, 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, “conjugate heat transfer”, 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 “standalone beam” 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: ? An open problem is to transfer parameters obtained by thermal to structural models. ? The useful concept of “Adiabatic Surface Temperature” (AST) is investigated. ? The AST use is right for properly evaluated convective heat transfer coefficient

20

Inverse determination of local heat transfer coefficient  

International Nuclear Information System (INIS)

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 fon 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)

21

Concentration, Soil-to-Plant Transfer Factor and Soil-Soil Solution Distribution Coefficient of Selenium in the Surface Environment  

International Nuclear Information System (INIS)

Of the major radioactive selenium isotopes, Se-79, a beta emitter with a half-life of about 1.1 million years, is of special interest because it is one of the most important radionuclides for the long-term dose assessment of radioactive waste disposal. This radionuclide can reach human beings through several transfer paths in the environment. To predict Se-79 behavior from the environment to human beings, it would be useful to obtain the following information: stable Se concentration in environmental samples; soil-soil solution distribution coefficient (Kd); and soil-to-plant transfer factor (TF). In the present study, stable Se concentrations in river water, soil and crop samples collected in Japan, Kds and TFs were obtained. The results showed that geometric mean (GM) concentrations of river water, soil and crops were 0.057 ?g/L (range: ds for paddy field soil and upland field soil samples were 116 and 67, respectively, whereas GMs of TFs for brown rice and upland field crops were 0.066 and 0.024, respectively. Probably due to longer growing period and different water management in the paddy fields for brown rice compared to those for upland field crops, the TF would be high in brown rice. (authors)

22

Heat transfer coefficient for boiling carbon dioxide.  

DEFF Research Database (Denmark)

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.

Knudsen, Hans JØrgen HØgaard; Jensen, Per Henrik

1998-01-01

23

Heat transfer coefficient of cryotop during freezing.  

Science.gov (United States)

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

Li, W J; Zhou, X L; Wang, H S; Liu, B L; Dai, J J

2013-01-01

24

Transfer coefficients for turbulent flow between parallel plates  

International Nuclear Information System (INIS)

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)

25

Determination of the heat transfer coefficients in transient heat conduction  

International Nuclear Information System (INIS)

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)

26

Radiative Heat Transfer and Effective Transport Coefficients  

CERN Document Server

The theory of heat transfer by electromagnetic radiation is based on the radiative transfer equation (RTE) for the radiation intensity, or equivalently on the Boltzmann transport equation (BTE) for the photon distribution. We focus in this review article, after a brief overview on different solution methods, on a recently introduced approach based on truncated moment expansion. Due to the linearity of the underlying BTE, the appropriate closure of the system of moment equations is entropy production rate minimization. This closure provides a distribution function and the associated effective transport coefficients, like mean absorption coefficients and the Eddington factor, for an arbitrary number of moments. The moment approach is finally illustrated with an application of the two-moment equations to an electrical arc.

Christen, Thomas; Gati, Rudolf

2010-01-01

27

Transfer coefficients in elliptical tubes and plate fin heat exchangers  

International Nuclear Information System (INIS)

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.)

28

Local Pool Boiling Heat Transfer Coefficients on Near Horizontal Tubes  

Energy Technology Data Exchange (ETDEWEB)

They said that as the liquid is methanol the maximum local heat transfer coefficient (h{sub b,max)} was observed at the tube bottom while the maximum was at the tube sides as the boiling liquid was n-hexane. Cornwell and Einarsson reported that hb,max was observed at the tube bottom, as the boiling liquid was R113. Cornwell and Houston explained the reason of the difference in local heat transfer coefficients along the tube circumference with introducing effects of sliding bubbles on heat transfer. According to Gupta et al., the maximum and the minimum local heat transfer coefficients were observed at the bottom and top regions of the tube circumference, respectively, using a tube bundle and water. Kang also reported the similar results using a single horizontal tube and water. However, the maximum heat transfer coefficient was observed at the angle of 45 .deg. Sateesh et al. studied variations of hb along the tube periphery while controlling the inclination angle (?). They tested five inclination angles (i. e., ? =0 .deg, 30 .deg, 45 .deg, 60 .deg, and 90 .deg). The top wall superheat increases and bottom wall superheat decreases as the inclination is changed 90 .deg to 0 .deg from the horizontal. The cause for the tendency is thought as the bubble sliding length. Recently, Kang et al. studied pool boiling heat transfer on a 3-deg inclined tube for application to the design of the advanced power reactor plus. Since some more data is necessary, the present study is aimed to study variations in local pool boiling heat transfer coefficients on nearly horizontal tubes. Effects of the inclination angle on the changes of local pool boiling heat transfer coefficients on the outside surface of a 50.8 mm diameter tube have been investigated experimentally in the saturated water at atmospheric pressure. The azimuthal angles for the maximum and the minimum local coefficients are dependent on the inclination angle and the heat flux. The major mechanisms changing heat transfer on the surface are liquid agitation and bubble coalescence.

Kang, Myeonggie [Andong National Univ., Andong (Korea, Republic of)

2013-05-15

29

Radionuclide transfer to animal products: revised recommended transfer coefficient values  

International Nuclear Information System (INIS)

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

30

Radionuclide transfer to animal products: revised recommended transfer coefficient values  

Energy Technology Data Exchange (ETDEWEB)

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.

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

31

Modeling satellite drag coefficients with response surfaces  

Science.gov (United States)

Satellite drag coefficients are a major source of uncertainty in predicting the drag force on satellites in low Earth orbit. Among other things, accurately predicting the orbit requires detailed knowledge of the satellite drag coefficient. Computational methods are an important tool in computing the drag coefficient but are too intensive for real-time and predictive applications. Therefore, analytic or empirical models that can accurately predict drag coefficients are desired. This work uses response surfaces to model drag coefficients. The response surface methodology is validated by developing a response surface model for the drag coefficient of a sphere where the closed-form solution is known. The response surface model performs well in predicting the drag coefficient of a sphere with a root mean square percentage error less than 0.3% over the entire parameter space. For more complex geometries, such as the GRACE satellite, the Hubble Space Telescope, and the International Space Station, the model errors are only slightly larger at about 0.9%, 0.6%, and 1.0%, respectively.

Mehta, Piyush M.; Walker, Andrew; Lawrence, Earl; Linares, Richard; Higdon, David; Koller, Josef

2014-10-01

32

Analysis of the heat transfer coefficient during potato frying  

OpenAIRE

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 20–30 s. Another method consisted of direct recording of the temperature within a potato slice, close to the surface. Water loss rate was estimated by imag...

Costa, Rui M.; Oliveira, Fernanda A. R.; Delaneya, Olivia; Gekas, Vassilis

2001-01-01

33

Heat transfer coefficient for F.E analysis in the warm forging process  

Directory of Open Access Journals (Sweden)

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.

S.S. Kang

2007-01-01

34

Measurements of average heat-transfer and friction coefficients for subsonic flow of air in smooth tubes at high surface and fluid temperatures  

Science.gov (United States)

An investigation of forced-convection heat transfer and associated pressure drops was conducted with air flowing through smooth tubes for an over-all range of surface temperature from 535 degrees to 3050 degrees r, inlet-air temperature from 535 degrees to 1500 degrees r, Reynolds number up to 500,000, exit Mach number up to 1, heat flux up to 150,000 btu per hour per square foot, length-diameter ratio from 30 to 120, and three entrance configurations. Most of the data are for heat addition to the air; a few results are included for cooling of the air. The over-all range of surface-to-air temperature ratio was from 0.46 to 3.5.

Humble, Leroy V; Lowdermilk, Warren H; Desmon, Leland G

1951-01-01

35

Spatial dependence of local heat transfer coefficients in liquid metal sub-channel flows  

International Nuclear Information System (INIS)

CFD code, FLUENT was applied to investigate the spatial dependence of local rod surface heat transfer coefficients of liquid sodium and liquid lead flows in a triangular sub-channel. As a result of high thermal conductivities in liquid metals, their thermal boundary layers are thicker than ordinary fluids. Their developments are then dependent on the available void spaces inside the sub-channel. This means that local surface convective heat transfer coefficients are not uniform around the fuel rod, resulting non-uniform surface temperature distributions in the azimuthal direction. Our studies show that higher local heat transfer coefficients are observed at surfaces whose facing channel widths are narrower. The ratios of maximum-to-minimum heat transfer coefficients are 2.66, 1.92, 1.57 for pitch-to-diameter ratios of 1.1, 1.2, 1.375 respectively. Such spatial dependence is quite apparent for low P/D's. (authors)

36

Transfer coefficients for plate fin and elliptical tube heat exchangers  

International Nuclear Information System (INIS)

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)

37

High-resolution heat-transfer-coefficient maps applicable to compound-curve surfaces using liquid crystals in a transient wind tunnel  

International Nuclear Information System (INIS)

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

38

Local heat transfer coefficient for turbulent flow in rod bundles  

International Nuclear Information System (INIS)

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.)

39

Enhancement of pool boiling heat transfer coefficients using carbon nanotubes  

International Nuclear Information System (INIS)

In this study, the effect of carbon nanotubes (CNTs) on nucleate boiling heat transfer is investigated. Three refrigerants of R22, R123, R134a, and water were used as working fluids and 1.0 vol.% of CNTs was added to the working fluids to examine the effect of CNTs. Experimental apparatus was composed of a stainless steel vessel and a plain horizontal tube heated by a cartridge heater. All data were obtained at the pool temperature of 7 .deg. C for all refrigerants and 100 .deg. C for water in the heat flux range of 10?80 kW/m2. Test results showed that CNTs increase nucleate boiling heat transfer coefficients for all fluids. Especially, large enhancement was observed at low heat fluxes of less than 30 kW/m2. With increasing heat flux, however, the enhancement was suppressed due to vigorous bubble generation. Fouling on the heat transfer surface was not observed during the course of this study. Optimum quantity and type of CNTs and their dispersion should be examined for their commercial application to enhance nucleate boiling heat transfer in many applications

40

Determination of the surface drag coefficient  

DEFF Research Database (Denmark)

This study examines the dependence of the surface drag coefficient on stability, wind speed, mesoscale modulation of the turbulent flux and method of calculation of the drag coefficient. Data sets over grassland, sparse grass, heather and two forest sites are analyzed. For significantly unstable conditions, the drag coefficient does not depend systematically on z/L but decreases with wind speed for fixed intervals of z/L, where L is the Obukhov length. Even though the drag coefficient for weak wind conditions is sensitive to the exact method of calculation and choice of averaging time, the decrease of the drag coefficient with wind speed occurs for all of the calculation methods. A classification of flux calculation methods is constructed, which unifies the most common previous approaches. The roughness length corresponding to the usual Monin-Obukhov stability functions decreases with increasing wind speed. This dependence on wind speed cannot be eliminated by adjusting the stability functions. If physical, the decrease of the roughness length with increasing wind speed might be due to the decreasing role of viscous effects and streamlining of the vegetation, although these effects cannot be isolated from existing atmospheric data. For weak winds, both the mean flow and the stress vector often meander significantly in response to mesoscale motions. The relationship between meandering of the stress and wind vectors is examined. For weak winds, the drag coefficient can be sensitive to the method of calculation, partly due to meandering of the stress vector.

Mahrt, L.; Vickers, D.

2001-01-01

41

A New Global Potential Energy Surface for the Hydroperoxyl Radical, HO2: Reaction Coefficients for H + O2 and Vibrational Splittings for H Atom Transfer  

Science.gov (United States)

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.

Dateo, Christopher E.; Arnold, James O. (Technical Monitor)

1994-01-01

42

Fuel-clad heat transfer coefficient of a defected fuel rod. Transfer coefficient fuel-clad in the presence of water steam  

International Nuclear Information System (INIS)

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

43

Calculation of time-dependent heat transfer coefficients during rewetting of highly heated tubes  

International Nuclear Information System (INIS)

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.)

44

Experimental and Numerical Study on Effects of Airflow and Aqueous Ammonium Temperature on Ammonia Mass Transfer Coefficient  

DEFF Research Database (Denmark)

This paper reports the results of an investigation, based on fundamental fluid dynamics and mass transfer theory, carried out to obtain a general understanding of ammonia mass transfer from an emission surface. The effects of airflow and aqueous ammonium solution temperature on ammonia mass transfer are investigated by using computational fluid dynamics (CFD) modeling and by a mechanism modeling using dissociation constant and Henry's constant models based on the parameters measured in the experiments performed in a wind tunnel. The validated CFD model by experimental data is used to investigate the surface concentration distribution and mass transfer coefficient at different temperatures and velocities for which the Reynolds number is from 1.36 × 104 to 5.43 × 104 (based on wind tunnel length). The surface concentration increases as velocity decreases and varies greatly along the airflow direction on the emission surface. The average mass transfer coefficient increases with higher velocity and turbulence intensity. However, the mass transfer coefficient estimated by CFD simulation is consistently larger than the calculated one by the method using dissociation constant and Henry's constant models. In addition, the results show that the liquid-air temperature difference has little impact on the simulated mass transfer coefficient by CFD modeling, whereas the mass transfer coefficient increases with higher liquid temperature using the other method under the conditions that the liquid temperature is lower than the air temperature. Although there are differences of mass transfer coefficients between these two methods, the mass transfer coefficients determined by these two methods are significantly related.

Rong, Li; Nielsen, Peter V.

2010-01-01

45

Heat transfer coefficients of shell and coiled tube heat exchangers  

Energy Technology Data Exchange (ETDEWEB)

In the present study, the heat transfer coefficients of shell and helically coiled tube heat exchangers were investigated experimentally. Three heat exchangers with different coil pitches were selected as test section for both parallel-flow and counter-flow configurations. All the required parameters like inlet and outlet temperatures of tube-side and shell-side fluids, flow rate of fluids, etc. were measured using appropriate instruments. Totally, 75 test runs were performed from which the tube-side and shell-side heat transfer coefficients were calculated. Empirical correlations were proposed for shell-side and tube-side. The calculated heat transfer coefficients of tube-side were also compared to the existing correlations for other boundary conditions and a reasonable agreement was observed. (author)

Salimpour, M.R. [Department of Mechanical Engineering, Isfahan University of Technology, Isfahan 84156-83111 (Iran)

2009-01-15

46

Mass transfer coefficients determination from linear gradient elution experiments.  

Science.gov (United States)

A procedure to estimate mass transfer coefficients in linear gradient elution chromatography is presented and validated by comparison with experimental data. Mass transfer coefficients are traditionally estimated experimentally through the van Deemter plot, which represents the HETP as a function of the fluid velocity. Up to now, the HETP was obtained under isocratic elution conditions. Unfortunately, isocratic elution experiments are often not suitable for large biomolecules which suffer from severe mass transfer hindrances. Yamamoto et al. were the first to propose a semi-empirical equation to relate HETPs measured from linear gradient elution experiments to those obtained under isocratic conditions [7]. Based on his pioneering work, the approach presented in this work aims at providing an experimental procedure supported by simple equations to estimate reliable mass transfer parameters from linear gradient elution chromatographic experiments. From the resolution of the transport model, we derived a rigorous analytical expression for the HETP in linear gradient elution chromatography. PMID:25497582

Pfister, David; Morbidelli, Massimo

2015-01-01

47

3D measurements and numerical computations of heat transfer coefficients on spheres in an array  

International Nuclear Information System (INIS)

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-? low-Re, AKN k-? low-Re, standard k-? two-layer, realizable k-? 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 pth experimental measurements and CFD predictions. (authors)

48

Determination of the wall heat transfer coefficient in pebble beds  

International Nuclear Information System (INIS)

The prediction of the temperature distribution in a packed bed requires the knowledge of the effective thermal conductivity in the core and the wall heat transfer coefficient. Empirical correlations published previously yield strongly differing results varying by a factor of ten at low Reynolds numbers. Very high Reynolds numbers had not yet been investigated. Wall heat transfer coefficients in pebble beds were achieved by applying the analogy between heat and mass transfer on sublimation of napthalene into air. The use of mass transfer instead of heat transfer techniques provides some advantages concerning secondary effects. Two series of tests applying napthalene mass transfer were performed in the ranges of Reynolds number 5x101 ? Re ? 6x103 and 2x103 ? Re ? 2x104. Moreover, the mass transfer in the inlet section was investigated. The results of both test series match well. A good agreement is observed with earlier published data, which were not affected by entrance effects. The data are correlated for the range of Reynolds numbers 5x101 ? Re ? 2x104. The transition effect observed at Re ? 4x103 is explained by a change of the flow structure. A correlation is given for the mass and heat transfer in the entrance section. (orig.)

49

Inverse estimation of the local heat transfer coefficient in curved tubes: a numerical validation  

Science.gov (United States)

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.

Bozzoli, F.; Cattani, L.; Corradi, C.; Mordacci, M.; Rainieri, S.

2014-04-01

50

Estimation of convective heat transfer coefficients in industrial steam turbines  

Energy Technology Data Exchange (ETDEWEB)

Steam turbines are increasingly being used in industries for duties other than base load operations, where fast start-ups, rapid load changes, and frequent shutdowns are involved. Generally, industrial steam turbines operate with constant inlet steam parameters and are partial admission turbines having the first turbine stage as an impulse stage and the subsequent turbine stages as reaction stages on drum-type rotors. During start-up, as control valves open, steam is admitted and passes through impulse blading, wheel chamber, and through the subsequent reaction stages. The turbine outer casing is horizontally split and the parting plane flanges have relatively thick sections. To limit thermal stresses which arise due to temperature differences in outer casings and rotors, the steam flow has to be increased gradually. The rate at which the steam flow is to be increased depends on the efficiency of heat transfer, i.e., the heat transfer coefficient, and hence knowledge of inside heat transfer coefficient is essential. The high heat transfer coefficients, h, at the beginning of cold start are attributable to condensation of steam at initial stages. The value of h decreased with lapse of time, and also its variation reduced considerably over time. Further, the h value varies more with location rather than with lapse of time. The variations observed in h show the complexity of heat transfer process and also bring out the fact that semi-empirical formulas, such as Gazley`s (1958), are not accurate for application in steam turbines. More studies need to be conducted on models of steam turbines to generate adequate data based on which a new correlation for the heat transfer coefficient h for start-up phase of operation could be proposed.

Adinarayana, N. [Bharat Heavy Electricals Ltd., Hyderabad (India); Sastri, V.M.K. [Indian Inst. of Tech., Madras (India). Heat Transfer Lab.

1996-05-01

51

Experimental Investigation on the Heat Transfer Coefficient of the Thermosyphon Cross Section Shape  

Directory of Open Access Journals (Sweden)

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.

Mohammed M. I. Hammad,

2015-03-01

52

The prediction of heat transfer coefficient in circulating fluidized bed combustors  

Energy Technology Data Exchange (ETDEWEB)

The growing interest in circulating fluidized bed boilers can be attributed to its efficient combustion of low-grade fuels. However, in order to design circulating fluidized beds, it is important to know the underlying mechanisms involved in the heat transfer between gas-solid suspensions and immersed cooling surfaces. The heat transfer coefficient in circulating fluidized bed combustors involves particle and gas convective heat transfer and radiative heat transfer, whose contribution becomes significant at elevated bed temperatures. This paper reviewed several studies that have been conducted to evaluate heat transfer coefficient in circulating fluidized bed combustors. It then presented results of a theoretical study that was performed to modify an existing model that was used to predict the heat transfer coefficient. Certain parameters in the existing model were given constant values, which resulted in an error in the obtained value of the heat transfer coefficient. As a first step, that model was thoroughly studied and values for certain parameters were changed. The modified model was tested against previous experimental and theoretical data available in literature. It was concluded that the accuracy of the model improved significantly when the parameters of terminal velocity (Ut), cluster voidage (ec), cluster time (c) and wall emissivity (ew) were not treated as fixed values. 7 refs., 5 figs.

Hamdan, M.A.; Al-Qaq, A.M. [Jordan Univ., Amman (Jordan). Dept. of Mechanical Engineering

2007-07-01

53

Experimental study of heat transfer coefficient in exhaust pipe  

Energy Technology Data Exchange (ETDEWEB)

Exhaust gas from spark-ignition engines are one of the main sources of atmospheric pollution, especially in urban areas where traffic is dense. In order to comply with increasingly restrictive standards, the automobile industry must develop cleaning devices such as catalytic converters and particle filters. This experimental study examined the influence of a flow's intermittent character on the heat transfer coefficient within a bent exhaust pipe. A device was developed to estimate the heat transfer coefficient on the right channel or the bent portion of the exhaust line in a periodic intermittent flowing regime, as well as in a steady regime. The goal was to build a database of coefficient and augmentation factors (CAF) for the simulation of heat transfer in a variety of basic geometries found in spark-ignition engine exhaust lines. Parietal heat flux and wall temperature were estimated from temperature measurements using the Beck inverse algorithm. Estimates of gas temperature were derived by Tagawa's method, using temperature measurements in the intermittent gas flow with a two thermocouples probe. The results showed that intermittency intensifies heat transfer in the straight pipe as well as in the bent pipe. The augmentation factor within the straight pipe depends on the frequency. Peak intensification depends on the mechanical frequency of resonance on the tube. The augmentation factor for the bent pipe was found to be lower than in the straight pipe, and did not depend on the frequency. 22 refs., 7 figs.

Bourouga, B.; Bouloc, F. [Nantes Univ., Nantes (France). LTN/UMR; Anthoine, P. [Renault, Rueil Malmaison (France). Direction de la Mecanique

2010-07-01

54

Mass Transfer Coefficient Studies in Bubble Column Reactor  

Directory of Open Access Journals (Sweden)

Full Text Available Stirred bubble column are widely used in chemical and allied processes industries. Stirred bubble column reactor promotes significant liquid hold-up and long liquid residence time. It is used when a large mass transfer area and high mass transfer coefficient in both phases are desired. These columns can operate continuously with a concurrent and counter current phase flow where high interfacial areas between phases are possible with low investment cost. An experimental work was undertaken to focus the effect of various parameters like Height to Diameter ratio (H/D, Gas flow rate and Speed of the stirrer (N on mass transfer coefficient in stirred bubble column reactor. For this purpose, experiments were conducted in 0.14 m i.d column having 2 m height. The column with ring sparger having 67% active area is used as sparger for dispersing the dispersed phase into the continuous phase. For the optimized sparger plate, the effect of various parameters on mass transfer coefficient was studied based on CO2 –absorption Technique.

D. Devakumar

2010-06-01

55

Transfer coefficients of radionuclides from feed to livestock products  

International Nuclear Information System (INIS)

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.)

56

Heat transfer coefficient for lead matrixing in disposal containers for used reactor fuel  

International Nuclear Information System (INIS)

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

57

MASS TRANSFER COEFFICIENT EVALUATION FOR PILOT SCALE FERMENTER USING SODIUM SULPHITE OXIDATION METHOD  

Directory of Open Access Journals (Sweden)

Full Text Available An adequate supply of oxygen in aqueous solution becomes the focal point of interest when it comes to the growth and maintenance of most aerobic microbial and tissue cultures used for biochemical and pharmaceutical production. Unfortunately, oxygen mass transfer to the growth medium serves as a major growth limiting factor owing to it’s low solubility in aqueous solutions. (Approximately 10 ppm at ambient temperature and pressure. The reaction rate is such that as oxygen enters the liquid phase, it is immediately consumed to oxidize the sulfite so that the rate of oxidation equals that of the oxygen transfer. Oxygen must at first be transferred from gas bulk through a series of steps onto the surfaces of cells before it can be utilized. Therefore the enhancement of gas-liquid mass transfer during aerobic cultures and fermentations is always put into priority. The present study involves using the ‘Central Composite Design’, a statistical technique to determine the parametric conditions for the optimum volumetric mass transfer coefficient in a pilot scale (40L fermenter. The optimum volumetric mass transfer coefficient was found to lie outside the range of parameters studied and analytical expressions was obtained to predict the volumetric mass transfer coefficients for the parameter ranges studied using response surface methodology. The analytical expression was addressed to be significantly valid based on ANOVA results.

Rajesh Ghosh* and Sounak Bhattacherjee

2013-04-01

58

Measurement and modeling of interface heat transfer coefficients  

International Nuclear Information System (INIS)

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

59

Dimensionless analysis of fluid-to-particle heat transfer coefficients  

OpenAIRE

Average fluid-to-particle heat transfer coefficients were experimentally determined for spherical aluminium particles heated in car?ymethylcellulose solutions. Two situations were considered: a still panicle immersed in a moving fluid, and a particle rotating in an otherwise stagnant fluid. Fluid flow rate, rotating particle velocity, particle diameter and fluid rheological properties were varied, covering a large range of the generalized Reynolds (0 to 801) and Prandtl (69 to 5358) numbers...

Baptista, Paulo N.; Oliveira, Fernanda A. R.; Oliveira, Jorge C.; Sastry, Sudhir K.

1997-01-01

60

Automatic optimization of the heat transfer coefficient in boiler setups  

International Nuclear Information System (INIS)

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

61

Improved transfer matrix methods for calculating quantum transmission-coefficient  

OpenAIRE

Methods for calculating the transmission coefficient are proposed, all of which arise from improved non-reflecting WKB boundary conditions at the edge of the computational domain in 1-dimensional geometries. In the first, the Schr\\"{o}dinger equation is solved numerically while the second is a transfer matrix (TM) algorithm where the potential is approximated by steps, but with the first and last matrix modified to reflect the new boundary condition. Both methods give excell...

Biswas, Debabrata; Kumar, Vishal

2014-01-01

62

Water mist effect on heat transfer coefficient in cooling of casting die  

Directory of Open Access Journals (Sweden)

Full Text Available This project is showing investigation results of heat transfer process between cast iron die and environment during cooling of die in the temperature range 600÷100 C with compressed air, spray water and water mist streamed under pressure 0.35 0.45 MPa in air jet0.3 0.4 MPa .At the paper are shown results of cooling die’s flat wall using open cooling system. The temperature gradient was presented at die’s wallthickness and calculated thermal curve for cooling surface. The calculation results of heat transfer coefficient ? were presented between die and researched cooling factors and also mathematical models of ? coefficient depending on surface temperature. Revealed that coefficient ? has the biggest value’s range for die cooling with water mist under pressure 0.3/0.35 MPa.

R. W?adysiak

2008-10-01

63

The Tube Side Heat Transfer Coefficient for Enhanced Double Tube by Wilson Plot Analysis  

Directory of Open Access Journals (Sweden)

Full Text Available The purpose of the investigation presented in this study is to evaluate the tube side single phase heat transfer performance on the EXTEK (Twisted Multi-Head tube. The geometry of the cross-section for a flow passage has an effect on its convective heat transfer capabilities. For concentric annuli in a double tube heat exchanger, the annular surface enhancement and tube profile enhancement play an important role. EXTEK (Twisted Multi-Head uses twisted extrusion of a star shape tube for tube profile enhancement. The study was able to develop individual heat transfer coefficient correlations for this new method of enhancement for the turbulent flow regimes. A plain annulus was also investigated for comparison. The Wilson plot method was used to determine the tube side heat transfer coefficients from which the Nusselt type correlations were developed.

Vijay R. Raghavan

2011-01-01

64

Determination of forced convective heat transfer coefficients for subsonic flows over heated asymmetric NANA 4412 airfoil  

Science.gov (United States)

Forced convection over traditional surfaces such as flat plate, cylinder and sphere have been well researched and documented. Data on forced convection over airfoil surfaces, however, remain very scanty in literature. High altitude vehicles that employ airfoils as lifting surfaces often suffer leading edge ice accretions which have tremendous negative consequences on the lifting capabilities and stability of the vehicle. One of the ways of mitigating the effect of ice accretion involves judicious leading edge convective cooling technique which in turn depends on the accuracy of convective heat transfer coefficient used in the analysis. In this study empirical investigation of convective heat transfer measurements on asymmetric airfoil is presented at different angle of attacks ranging from 0° to 20° under subsonic flow regime. The top and bottom surface temperatures are measured at given points using Senflex hot film sensors (Tao System Inc.) and used to determine heat transfer characteristics of the airfoils. The model surfaces are subjected to constant heat fluxes using KP Kapton flexible heating pads. The monitored temperature data are then utilized to determine the heat convection coefficients modelled empirically as the Nusselt Number on the surface of the airfoil. The experimental work is conducted in an open circuit-Eiffel type wind tunnel, powered by a 37 kW electrical motor that is able to generate subsonic air velocities up to around 41 m/s in the 24 square-inch test section. The heat transfer experiments have been carried out under constant heat flux supply to the asymmetric airfoil. The convective heat transfer coefficients are determined from measured surface temperature and free stream temperature and investigated in the form of Nusselt number. The variation of Nusselt number is shown with Reynolds number at various angles of attacks. It is concluded that Nusselt number increases with increasing Reynolds number and increase in angle of attack from 0° to 20° on the upper and lower surface of the airfoil.

Dag, Yusuf

65

Natural convection heat transfer coefficients in phase change material (PCM) modules with external vertical fins  

Energy Technology Data Exchange (ETDEWEB)

To determine the heat transfer coefficient by natural convection for specific geometries, experimental correlations are used. No correlations were found in the literature for the geometries studied in this work. These geometries consisted of a cylindrical module of 88 mm of diameter and 315 mm height with external vertical fins of 310 mm height and 20 and 40 mm length. To determine the heat transfer coefficient by natural convection, experimental work was done. This module, containing PCM (sodium acetate trihydrate), was situated in the middle upper part of a cylindrical water tank of 440 mm of diameter and 450 mm height. The calculated heat transfer coefficient changed by using external fins, as the heat transfer surface was increased. The temperature variation of the PCM and the water are presented as a function of time, and the heat transfer coefficient for different fins is presented as a function of the temperature difference. Experimental correlations were obtained, presenting the Nusselt number as a function of different dimensionless numbers. Different correlations were analysed to find which one fit better to the experimental data. (author)

Castell, Albert; Sole, Cristian; Medrano, Marc; Roca, Joan; Cabeza, Luisa F. [Departament d' Informatica i Enginyeria Industrial, Universitat de Lleida, Pere de Cabrera s/n, 25001 Lleida (Spain); Garcia, Daniel [Departament Projectes d' Enginyeria, Universitat Politecnica de Catalunya, Colom 11, 08222 Terrassa (Spain)

2008-09-15

66

Resonant charge transfer at dielectric surfaces  

CERN Document Server

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...

Marbach, Johannes; Fehske, Holger

2012-01-01

67

Transfer coefficients of radionuclides secreted in milk of dairy cows  

International Nuclear Information System (INIS)

This study simulated experimentally the transfer of radionuclides to milk of dairy cows on a worst-case situation using various radionuclides known to emanate from nuclear power stations and which have been detected on particulates. Two lactating Holstein cows were administered orally one gelatin capsule containing 10 radionuclides in water-soluble form per day for 14 consecutive days. Milk samples were collected and aliquots analyzed in a germanium lithium-drifted detector coupled to a 2048-multichannel gamma-ray analyzer to measure small amounts of complex mixtures of radionuclides. The transfer coefficients of the radionuclides were calculated when their secretion in milk reached or approached a plateau of concentration. The radionuclides and their transfer coefficients to milk were: chromium51 less than 0.01%; manganese54 0.033 +- 0.005%; cobalt60 0.01 +- 0.002%; iron59 0.0048 +- 0.002%; zinc65 0.31 +- 0.07%; selenium75 0.29 +- 0.1%; antimony125 0.011 +- 0.003%; iodine131 0.88 +- 0.05%; and cesium137 0.79 +- 0.08%

68

Local heat transfer coefficient in a fluidized bed  

International Nuclear Information System (INIS)

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

69

Heat Transfer Coefficient Variations in Nuclear Fuel Rod Bundles  

International Nuclear Information System (INIS)

The single-phase heat transfer performance of a PWR nuclear fuel rod bundle is enhanced by the use of mixing vanes attached to the downstream edges of the support grid straps. This improved single-phase performance will delay the onset of nucleate boiling, thereby reducing corrosion and delaying crud-related issues. This paper presents the variation in measured single-phase heat transfer coefficients (HTC) for several grid designs. Then, this variation is compared with observations of actual in-core crud patterns. While crud deposition is a function of a number of parameters including rod heat flux, the HTC is assumed to be a primary factor in explaining why crud deposition is a local phenomenon on nuclear fuel rods. The data from this study will be used to examine this assumption by providing a comparison between HTC variations and crud deposition patterns. (authors)

70

Torque transfer coefficient in DNA under torsional stress.  

Science.gov (United States)

In recent years, significant progress in understanding the properties of supercoiled DNA has been obtained due to nanotechniques that made stretching and twisting of single molecules possible. Quantitative interpretation of such experiments requires accurate knowledge of torques inside manipulated DNA. This paper argues that it is not possible to transfer the entire magnitudes of external torques to the twisting stress of the double helix, and that a reducing torque transfer coefficient (TTC < 1) should always be assumed. This assertion agrees with simple physical intuition and is supported by the results of all-atom molecular dynamics (MD) simulations. According to MD, the TTCs around 0.8 are observed in nearly optimal conditions. Reaching higher values requires special efforts and it should be difficult in practice. The TTC can be partially responsible for the persistent discrepancies between the twisting rigidity of DNA measured by different methods. PMID:23005459

Mazur, Alexey K

2012-07-01

71

Identification of the capillary transfer coefficient in porous building materials  

Science.gov (United States)

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.

Vala, J.; Jarošová, P.

2013-10-01

72

Improved transfer matrix methods for calculating quantum transmission coefficient  

Science.gov (United States)

Methods for calculating the transmission coefficient are proposed, all of which arise from improved nonreflecting WKB boundary conditions at the edge of the computational domain in one-dimensional geometries. In the first, the Schrödinger equation is solved numerically, while the second is a transfer matrix (TM) algorithm where the potential is approximated by steps, but with the first and last matrix modified to reflect the new boundary condition. Both methods give excellent results with first-order WKB boundary conditions. The third uses the transfer matrix method with third-order WKB boundary conditions. For the parabolic potential, the average error for the modified third-order TM method reduces by factor of 4100 over the unmodified TM method.

Biswas, Debabrata; Kumar, Vishal

2014-07-01

73

Assessment of Mass Transfer Coefficients in Coalescing Slug Flow in Vertical Pipes and Applications to Tubular Airlift Membrane Bioreactors  

DEFF Research Database (Denmark)

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 higher shear stresses near the membrane surface, which generate high mass transfer coefficients from the surface to the bulk region. However, measuring the mass transfer coefficient is difficult in complex heterogeneous mixtures like activated sludge and existing techniques (e.g. electrochemical methods) cannot be applied directly. As an alternative, in this work, a multidisciplinary approach was selected, by exploiting dimensionless analysis using the Sherwood number. Mass transfer coefficients were measured at various superficial velocities of gas and liquid flow in a tubular system. Due to the variability of the mass transfer coefficient obtained for each experimental condition, the results were compiled into, mass transfer coefficient histograms (MTH) for analysis. A bimodal MTH was observed, with one peak corresponding to the mass transfer induced by the liquid flow, and the other peak induced by the gas flow. It was noted that coalescence of bubbles affects the MTH. Coalescence increased the “width” of the peaks (i.e. the estimate of the variability of the mass transfer coefficient) and the height of the peak (i.e. amount of time that a mass transfer coefficient of a given value is maintained). A semi-empirical relationship based on the Lévêque 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 the Sherwood number in the non-Newtonian case is 8% higher than that in the Newtonian case.

Ratkovich, Nicolas Rios; Berube, P.R.

2011-01-01

74

Confirmation of selected milk and meat radionuclide transfer coefficients. Progress report  

International Nuclear Information System (INIS)

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

75

Efficiency analysis of straight fin with variable heat transfer coefficient and thermal conductivity  

Energy Technology Data Exchange (ETDEWEB)

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.

Sadri, Somayyeh; Raveshi, Mohammad Reza; Amiri, Shayan [K.N. Toosi University of Technology, Tehran (Iran, Islamic Republic of)

2012-04-15

76

Heat transfer from rough surfaces  

International Nuclear Information System (INIS)

Artificial roughness is often used in nuclear reactors to improve the thermal performance of the fuel elements. Although these are made up of clusters of rods, the experiments to measure the heat transfer and friction coefficients of roughness are performed with single rods contained in smooth tubes. This work illustrated a new transformation method to obtain data applicable to reactor fuel elements from these annulus experiments. New experimental friction data are presented for ten rods, each with a different artificial roughness made up of two-dimensional rectangular ribs. For each rod four tests have been performed, each in a different outer smooth tube. For two of these rods, each for two different outer tubes, heat transfer data are also given. The friction and heat transfer data, transformed with the present method, are correlated by simple equations. In the paper, these equations are applied to a case typical for a Gas Cooled Fast Reactor fuel element. (orig.)

77

Determining convective heat transfer coefficient using phoenics software package  

Energy Technology Data Exchange (ETDEWEB)

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.

Kostikov, A.; Matsevity, Y. [Institute of Mechanical Engineering Problems of National Academy of Sciences of Ukraine, Kharkov (Ukraine)

1997-12-31

78

Confirmation of selected milk and meat radionuclide-transfer coefficients  

International Nuclear Information System (INIS)

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

79

Prediction of Heat Transfer Coefficient for Refrigerant With Oil Contained in Horizontal Evaporator Tuvbes  

Science.gov (United States)

A method which is generally applicable to predict the axially local (circumferentially averaged) heat transfer coefficient for refrigerant with oil contained flowing in horizontal evaporator tubes was developed by modifying a prediction method for pure refrigerants. The dimensionless correlation for an annular flow regime takes account of the influence of oil on an improvement or a reduction in the heat transfer, in addition to the change of the properties due to the addition of oil. For a separated flow regime, the correlations of the average heat transfer coefficients in the top part and the bottom part and their boundary angle were developed by modifying each correlation for pure refrigerants. The circumferentially averaged heat transfer coefficient for the separated flow regime can be obtained by using the solution of the steady heat conduction equation in the tube wall, to which the values calculated from the above correlations are applied as the boundary conditions at the inside surface of the tube. Which flow regime, annular or separated, prevails can be determined by the correlation of the boundary angle. The present prediction method was confirmed to be applicable to various kinds of refrigerant-oil mixture.

Matsunaga, Takeshi; Yoshida, Suguru

80

Turbulent characteristics and bulk transfer coefficients over the desert in the HEIFE area  

Science.gov (United States)

Observations of surface-layer turbulence and turbulent fluxes were made over a desert in northwestern China as a part of HEIFE (HEIhe river Field Experiment). These show that the normalized variations of the vertical wind component and of the air temperature obey Monin-Obukhov similarity well, especially in free convective conditions. However, the variations of specific humidity do not obey Monin-Obukhov similarity. Mean bulk transfer coefficients of sensible heat and momentum flux are obtained as functions of stability over a wide stability range from the observed data of turbulent fluxes and mast profiles. However, the bulk transfer coefficient for water vapor could not be obtained because of the large scatter of the data. In free convective conditions, the sensible heat flux was found to be approximately proportional to the 1.4 power of temperature difference between the surface and 20m. The bulk transfer coefficient of sensible heat is also obtained as a function of the bulk Richardson number for practical convenience.

Tamagawa, Ichiro

1996-01-01

81

Inverse identification of interfacial heat transfer coefficient between the casting and metal mold using neural network  

International Nuclear Information System (INIS)

The effect of the heat transfer coefficient at the casting-mold interface is of prime importance to improve the casting quality, especially for castings in metal molds. However, it is difficult to determine the values of heat transfer coefficient from experiments due to the influence of various factors, such as contacting pressure, oxides on surfaces, roughness of surfaces, coating material, coating thickness and gap formation caused by the deformation of casting and mold, etc. In the present paper, the interfacial heat transfer coefficient (IHTC) between the casting and metal mold is identified by using the method of inverse analysis based on measured temperatures, neural network with back-propagation algorithm and numerical simulation. Then, by applying the identified IHTC in finite element analysis, the comparison between numerical calculated and experimental results is made to verify the correctness of method. The results show that the numerical calculated temperatures are in good agreement with experimental ones. These demonstrate that the method of inverse analysis is a feasible and effective tool for determination of the casting-mold IHTC. In addition, it is found that the identified IHTC varies with time during the casting solidification and varies in the range of about 100-3200 Wm-2K-1. The characteristics of the time-varying IHTC have also been discussed.

82

Modeling the Effect of Internal Convection Currents on Heat Transfer Coefficient of Liquid Foods  

Directory of Open Access Journals (Sweden)

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 (r¬¬o=0. Then after plotting the graph between ‘h’ and ‘T’ 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.

SAJID ALI

2013-04-01

83

Determining heat transfer coefficients in radial flow through a polyethylene packed  

Directory of Open Access Journals (Sweden)

Full Text Available A numerical-experimental methodology was used for determining interstitial heat transfer coefficients in water flowing through po-rous media where it was not in heat balance with the solid phase. Heat transfer coefficients were obtained through the single blow transient test method, combining experimental test equipment results with a mathematical model’s numerical solution. The partial differential equation system produced by the mathematical model was resolved by a numerical finite volume method-ba-sed methodology. Experimental tests and numerical solutions were satisfactorily carried out for different values from the fluid’s surface speed from the entrance to the bed and for different porosity values, finding that Nusselt numbers increased when Reynolds numbers also increased and that Nusselt numbers increased when porosity decreased. A 650 Reynolds number and 0.375 porosity gave a Nusselt number of up to 2.8.

Luís Patiño

2010-07-01

84

Estimation of heat transfer coefficient and flow characteristics on heat transfer tube in sodium water reaction  

International Nuclear Information System (INIS)

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)

85

Dimethylsulfide gas transfer coefficients from algal blooms in the Southern Ocean  

Science.gov (United States)

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.

Bell, T. G.; De Bruyn, W.; Marandino, C. A.; Miller, S. D.; Law, C. S.; Smith, M. J.; Saltzman, E. S.

2015-02-01

86

DMS gas transfer coefficients from algal blooms in the Southern Ocean  

Directory of Open Access Journals (Sweden)

Full Text Available Air/sea dimethylsulfide (DMS fluxes and bulk air/sea gradients were measured over the Southern Ocean in February/March 2012 during the Surface Ocean Aerosol Production (SOAP study. The cruise encountered three distinct phytoplankton bloom regions, consisting of two blooms with moderate DMS levels, and a high biomass, dinoflagellate-dominated bloom with high seawater DMS levels (>15 nM. Gas transfer coefficients were considerably scattered at wind speeds above 5 m s?1. Bin averaging the data resulted in a linear relationship between wind speed and mean gas transfer velocity consistent with that previously observed. However, the wind speed-binned gas transfer data distribution at all wind speeds is positively skewed. The flux and seawater DMS distributions were also positively skewed, which suggests that eddy covariance-derived gas transfer velocities are consistently influenced by additional, log-normal noise. A~flux footprint analysis was conducted during a transect into the prevailing wind and through elevated DMS levels in the dinoflagellate bloom. Accounting for the temporal/spatial separation between flux and seawater concentration significantly reduces the scatter in computed transfer velocity. The SOAP gas transfer velocity data shows no obvious modification of the gas transfer-wind speed relationship by biological activity or waves. This study highlights the challenges associated with eddy covariance gas transfer measurements in biologically active and heterogeneous bloom environments.

T. G. Bell

2014-11-01

87

Boiling Heat Transfer on Superhydrophilic, Superhydrophobic, and Superbiphilic Surfaces  

CERN Document Server

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 ...

Betz, Amy Rachel; Kim, Chang-Jin 'CJ'; Attinger, Daniel

2012-01-01

88

Heat transfer performance of metal fiber sintered surfaces  

Science.gov (United States)

Boiling heat transfer performance on stainless steel metal fiber sintered surfaces is experimentally investigated with Freon 11 (R11) as the working fluid. The boiling heat transfer coefficient for the optimum surface structure gives a tenfold improvement over a smooth surface. The nondimensional specific parameter including all design parameters is introduced to explain the trend of the performance of various kinds of metal fiber sintered surfaces. Moreover, the metal fiber sintered surface clad with titanium film is suggested to be appropriate to an evaporator for Ocean Thermal Energy Conversion (OTEC) system.

Kajikawa, T.; Takazawa, H.; Mizuki, M.

1983-03-01

89

Calculation and Analysis of Heat Transfer Coefficients in a Circulating Fluidized Bed Boiler Furnace  

Science.gov (United States)

A new way for the circulating fluidized bed (CFB) boiler research is proposed by the supervisory information system (SIS) in power plant level. The heat transfer coefficient in CFB boiler furnace is calculated and analyzed by the SIS calculation analysis in a commercial CFB boiler, the way how to calculate the heat transfer coefficient in SIS is introduced, and the heat transfer coefficient is accurately received by calculating a large amount of data from database. The relation about the heat transfer coefficient to unit load, bed temperature, bed velocity, and suspension density is analyzed; the linear relation could be accepted for the commercial CFB design. A new calculating and simple way for the heat transfer coefficient of CFB boiler is proposed for CFB boiler design. Using this research result, the reheat spray water flux larger than the design value in lots of commercial CFB boilers is analyzed; the main reason is the designed heat transfer coefficient smaller than the actual value.

Wang, Zhiwei; Yang, Jianhua; Li, Qinghai

90

Prediciton of nucleate pool boiling heat transfer coefficients of refrigerant-oil mixtures  

International Nuclear Information System (INIS)

This paper describes an experimental investigation to determine the mechanism governing nucleate pool boiling heat transfer in refrigerant-oil mixtures, the role diffusion plays in this process, and the influence of the fluid mixture properties. Boiling heat transfer date were taken in mixtures of up to 10 per cent oil by weight in R-113. Thermophysical properties of the mixtures (density, viscosity, surface, tension, specific heat, and contact angle) were measured. The decrease in heat transfer coefficient with incresing oil concentration is attributed to diffusion in an oil-enriched region surrounding the growing vapor bubbles. A correlation based on a postulated mechanism is presented which shows fair agreement with the experimental data from this study and with data obtained from the literature

91

Adiabatic Effectiveness and Heat Transfer Coefficient on a Film-Cooled Rotating Blade  

Science.gov (United States)

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.

Garg, Vijay K.

1997-01-01

92

Condensation heat transfer on the tube surface of different materials  

International Nuclear Information System (INIS)

In this paper, two kinds of tube surfaces (bare stainless steel tube and Teflon coated tube) in steam-air mixture flow are experimentally studied to obtain design data for the heat exchanger of the latent heat recovery from flue gas. In the test section, 3-tubes are horizontally installed, and steam-air mixture is flowed vertically from top to bottom. The uncertainty for the heat transfer measurement is surveyed to have the uncertainty within 5%. As experimental results, overall heat transfer coefficient of the Teflon (FEP) coated tube is degraded about 20% compared to bare stainless tube. Nusselt number of Teflon (FEP) coated tube in latent heat transfer is lower than that of bare stainless steel tube, but the Sherwood number is higher. The contact angle of the condensate on Teflon coated surface is higher than bare stainless steel surface about 30%, which will be the reason of higher mass transfer coefficient of Teflon coated tube

93

Study on grey model in the heat transfer coefficient of supercritical water  

International Nuclear Information System (INIS)

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

94

Estimation of grass to cow's milk transfer coefficients for emergency situations  

International Nuclear Information System (INIS)

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 coefficientults of grass to milk transfer coefficients for stable isotope of Cesium (Cs) for emergency situation

95

Effect of design and operation parameters on heat transfer coefficient in condensers  

International Nuclear Information System (INIS)

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 esrs (<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)

96

Estimating the workpiece-backingplate heat transfer coefficient in friction stirwelding  

DEFF Research Database (Denmark)

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 transfer coefficient are the variables in an optimisation problem. The objective is to minimise the difference between experimentally measured temperatures and temperatures obtained using a 3D finite element model. The optimisation problem is solved using a gradient based optimisation method. This approach 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 properties of the welded plate. Accurate modelling of the magnitude and distribution of the heat transfer coefficient is therefore an essential step towards improved models of the process. This is the first study using a gradient based optimisation method and a non-uniform parameterisation of the heat transfer coefficient in an inverse modeling approach to determine the heat transfer coefficient in friction stir welding. © Emerald Group Publishing Limited.

Larsen, Anders; Stolpe, Mathias

2012-01-01

97

Calculating the heat transfer coefficient of frame profiles with internal cavities  

DEFF Research Database (Denmark)

Determining the energy performance of windows requires detailed knowledge of the thermal properties of their different elements. A series of standards and guidelines exist in this area. The thermal properties of the frame can be determined either by detailed two-dimensional numerical methods or by measurements in accordance to European or international standards. Comparing measured and calculated heat transfer coefficients for two typical frame profiles with cavities shows considerable differences. This investigation considers two typical frame profiles in aluminium and PVC with internal cavities. The heat transfer coefficient is determined by two-dimensional numerical calculations and by measurements. Calculations are performed in Therm (LBNL (2001)), which is developed at Lawrence Berkeley National Laboratory, USA. The calculations are performed in accordance with the future European standards and measurements have been performed at two German research institutes. The internal cavities have a large influence on the overall thermal performance of the frame profiles and the investigation shows that the applied method for modelling the heat transfer by radiation exchange in the internal cavities of the profiles is critical. The simple radiation model described in the pre European standard (prEN ISO 10077-2) does not yield valid results compared to measured values. Applying a more detailed, viewfactor based, grey surfaces enclosure model as described in the ISO standard (ISO/DIS 15099) gives a better 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 alternative.

Noyé, Peter Anders; Laustsen, Jacob Birck

2004-01-01

98

Plateau diffusion coefficient for arbitrary flux surface geometry  

International Nuclear Information System (INIS)

A relatively simple but accurate representation has been developed for magnetic flux surfaces; it is valid for finite ? and it describes configurations with both ellipticity and D-shape. This representation has been applied to the computation of the diffusion coefficient in the plateau regime

99

Condensation heat transfer coefficient with noncondensible gases for heat transfer in thermal hydraulic codes  

Energy Technology Data Exchange (ETDEWEB)

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

100

A novel approach to determine the heat transfer coefficient in directional solidification furnaces  

Science.gov (United States)

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.

1990-01-01

101

Importance of the speciation of radionuclides for the calculation of transfer coefficients: Application to soil-fungus transfer  

International Nuclear Information System (INIS)

Full text: Transfer coefficients are commonly used as an approximation to the problem of quantifying the transit of radionuclides between an ecosystem's different characteristic receptor media. These coefficients are traditionally defined as the quotient between the specific activities of the receptor and the donor compartments. In the present study, the receptors were edible mushrooms and the donor, the soil. However, not all the radioactive contents of a soil are in a condition to be transferred. Instead, the fraction that is available will depend intimately on the capacity of the different compounds to which the radionuclides are associated to be taken up by the fungus. To analyse the cited capacity, we carried out a scheme of chemical speciation of the surface layer (0-5 cm) of the soils corresponding to two forest ecosystems (pine woods) that present a high productivity of mushrooms. This scheme consists of the sequential extraction of the available soil fraction (extractable with NH4OAc), that soluble in dilute acid (extractable with HCl 1M), that soluble in strong acid (extractable with HCl 6M), and the residue. We analysed the presence of different man-made (137Cs, 90Sr) and natural (40K, 226Ra) radionuclides in each of the soil fractions enumerated above and in two representative species of mushroom from the aforementioned two ecosystems: Hebeloma cylindrosporum and Lactarius deliciosus. Specifically, mornd Lactarius deliciosus. Specifically, more than 75% of the concentrations of 40K and 137Cs present in the soils studied were found bound to fractions not accessible to exchange reactions (the fraction soluble in strong acid and the residue). This implies that they are not associated to chemical compounds capable of being transferred to the fungi's fruiting bodies. Therefore, it is totally inappropriate to calculate the transfer coefficients in the usual way, since this uses the total activity found in the soil layer being considered. By way of example, for 40K the traditional method underestimates the transfer by approximately two orders of magnitude. We hence propose another approach, considering only the fraction of radionuclides present in the soil that are really in condition to be transferred. (author)

102

Importance of the speciation of radionuclides for the calculation of transfer coefficients: Application to soil-fungus transfer  

International Nuclear Information System (INIS)

Transfer coefficients are commonly used as an approximation to the problem of quantifying the transit of radionuclides between an ecosystem's different characteristic receptor media. These coefficients are traditionally defined as the quotient between the specific activities of the receptor and the donor compartments. In the present study, the receptor were edible mushrooms and the donor the soil. However, not all the radioactive content of a soil is in a condition to be transferred. Instead, the fraction that is available will depend intimately on the capacity of the different compounds to which the radionuclides are associated to be taken up by the fungus. To analyse the cited capacity, we carried out a scheme of chemical speciation of the surface layer (0-5 cm) of the soils corresponding to two forest ecosystems (pine woods) that present a high productivity of mushrooms. This scheme consists of the sequential extraction of the available soil fraction (extractable with NH4OAc), that soluble in dilute acid (extractable with HCl 1M), that soluble in strong acid (extractable with HCl 6M), and the residue. We analysed the presence of different man-made (137Cs, 90Sr) and natural (40K, 226Ra) radionuclides in each of the soil fractions enumerated above and in two representative species of mushroom from the aforementioned two ecosystems: Hebeloma cylindrosporum and Lactarius deliciosus. Specifically, more than 75% of tliciosus. Specifically, more than 75% of the concentrations of 40K and 137Cs present in the soils studied were found bound to fractions not accessible to exchange reactions (the fraction soluble in strong acid and the residue). This implies that they are not associated to chemical compounds capable of being transferred to the fungi's fruiting bodies. Therefore, it is totally inappropriate to calculate the transfer coefficients in the usual way, since this uses the total activity found in the soil layer being considered. By way of example, for 40K the traditional method underestimates the transfer by approximately 2 orders of magnitude. We hence propose another approach, considering only the fraction of radionuclides present in the soil that are really in condition to be transferred. (author)

103

Calculation of heat transfer coefficients for nucleate boiling in binary mixtures of refrigerant-oil  

International Nuclear Information System (INIS)

The heat transfer coefficient for nucleate boiling of pure liquids can be determined in many cases by the simple relation h = C X q /SUP n/ . (In nucleate boiling of mixtures with widely varying properties, the concentration gradient close to the heating surface strongly affects the heat transfer. The composition of the mixture is difficult to obtain there. The authors develop simple relations based on experimental values for four different refrigerant-oil mixtures in concentrations from 0.005 to 0.20) the following relation renders best results: h = 0.085 X (exp X (b1w) + exp X (b2w)) x q For each kind of oil, however, different values of b1, b2 and B have to be used; these are given

104

EXPERIMENTAL INVESTIGATION OF HEAT TRANSFER ENHANCEMENT OVER THE DIMPLED SURFACE  

Directory of Open Access Journals (Sweden)

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.

Dr. Sachin L. Borse

2012-08-01

105

Heat transfer coefficient correlation for convective boiling inside plain and micro fin tubes using genetic algorithms  

International Nuclear Information System (INIS)

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)

106

Determination of heat transfer coefficients at the polymer-mold-interface for injection molding simulation by means of calorimetry  

Science.gov (United States)

Appropriate modeling of heat transfer from the polymer material to the injection mold is essential to achieve accurate simulation results. The heat transfer is commonly modeled using convective heat transfer and applying heat transfer coefficients (HTC) to the polymer-mold-interface. The set HTC has an influence on the results for filling pressure, cooling performance and shrinkage, among others. The current paper, presents a new strategy to measure HTC in injection molding experiments using Newtons law of cooling. The heat flux is calculated out of demolding heat (measured by means of calorimetry), injection heat (measured by means of an IR-sensor), cooling time and part mass. Cavity surface area, average mold surface temperature and average part surface temperature lead to the HTC.

Stricker, M.; Steinbichler, G.

2014-05-01

107

The usage of transfer coefficients to describe radionuclide transport from a cow's diet to its milk  

International Nuclear Information System (INIS)

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)

108

Convective Heat Transfer Coefficients of the Human Body under Forced Convection from Ceiling  

DEFF Research Database (Denmark)

The average convective heat transfer coefficient for a seated human body exposed to downward flow from above was determined. Thermal manikin with complex body shape and size of an average Scandinavian female was used. The surface temperature distribution of the manikin’s body was as the skin temperature distribution of an average person. The measurements were performed in a room with controlled thermal environment. Air temperature was set at 26ºC for cooling and at 20ºC for heating. The radiant temperature asymmetry in horizontal and vertical direction was close to zero, i.e. mean radiant temperature was equal to the air temperature. The air velocity of the isothermal downward flow from the ceiling at height of 1.5 m above the floor (above the top of the head) was set in a range between still air and 0.73 m/s. Based on the analyses of the results relationships for determination of the convective heat transfer coefficient of the whole body (hc [W/(m2•K)]) was proposed: hc=4.088+6.592V1.715 for a seated naked body at 20ºC and hc=2.874+7.427V1.345 for a seated naked body at 26ºC. Differences in the convective heat transfer coefficient of the whole body in low air velocity range, V<0.3 m/s, due to the natural convection were found. The results may be useful during design of air distribution in rooms, e.g. low impulse ventilation, diffuse ventilation, etc.

Kurazumi, Yoshihito; Rezgals, Lauris

2014-01-01

109

Experimental investigation of thermal conductivity coefficient and heat exchange between fluidized bed and inclined exchange surface  

Directory of Open Access Journals (Sweden)

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.

B. Stojanovic

2009-06-01

110

Prediction of mass-transfer coefficient for solute transport in porous media  

Science.gov (United States)

Several previously reported laboratory studies related to transport of solutes through packed columns were utilized to develop predictive relationships for mass-transfer rate coefficient. The data were classified into two groups: those obtained under rate-limited mass transfer between mobile and immobile water regions (physical nonequilibrium conditions), and those derived from rate-limited mass transfer between instantaneous and slow sorption sites (sorption nonequilibrium conditions). The mass-transfer coefficient in all these studies was obtained by fitting breakthrough data to a transport model employing a first-order rate limitations with a "constant" mass-transfer coefficient, independent of flow conditions. This study demonstrated that the mass-transfer coefficient in these models is dependent on system parameters including pore-water velocity, length-scale, retardation coefficient, and particle or aggregate size. Predictive relationships were developed, through regression analysis, relating mass-transfer coefficient to residence time. The developed relationships adequately estimated previously reported field mass-transfer values. Successful simulations of field desorption data reported by Bahr [J. Contam. Hydrol. 4 (1989) 205] further demonstrate the potential applicability of the developed relationships.

Maraqa, Munjed A.

2001-12-01

111

Radioiodine transfer coefficients for the terrestrial environment at Tarapur nuclear site  

International Nuclear Information System (INIS)

Radioiodine is one of the important radionuclides released to the environment in case of major accidents in nuclear reactors. The main pathway of 131I uptake is through air to soil to vegetation to milk to man and also vegetation to man. The 131I activity transfer coefficients from one compartment to the other in this pathway are essential to evaluate the dose from the activity releae data. Radioiodine fallout from the Chernobyl accident provid ed an opportunity to evaluate these transfer coefficients. The papaer gives all the possible transfer coefficients from the measurement data available and compares them with the earlier data obtained from French weapon fallout radioiodine. (author). 2 tabs

112

SIMULTANEOUS MEASUREMENT OF INTERFACIAL AREA DISTRIBUTION AND MASS TRANSFER COEFFICIENTS IN BUBBLE COLUMN  

OpenAIRE

In this study, simultaneous measurement of interfacial area distribution and mass transfer coefficients in a bubble column for two-phase dispersed system of air-water is conducted. The time-averaged interfacial area (a) distribution was measured by using ultrasonic computed tomography (UCT), the volumetric liquid mass transfer coefficient (kLa) is measured by dynamic method, and hence, the liquid side mass transfer coefficient (kL) was calculated from the kLa and a. The UCT results show that ...

MUHAMMAD DANI SUPARDAN

2012-01-01

113

Prediction of gas-liquid mass transfer coefficient in sparged stirred tank bioreactors.  

Science.gov (United States)

Oxygen mass transfer in sparged stirred tank bioreactors has been studied. The rate of oxygen mass transfer into a culture in a bioreactor is affected by operational conditions and geometrical parameters as well as the physicochemical properties of the medium (nutrients, substances excreted by the micro-organism, and surface active agents that are often added to the medium) and the presence of the micro-organism. Thus, oxygen mass transfer coefficient values in fermentation broths often differ substantially from values estimated for simple aqueous solutions. The influence of liquid phase physicochemical properties on kLa must be divided into the influence on k(L) and a, because they are affected in different ways. The presence of micro-organisms (cells, bacteria, or yeasts) can affect the mass transfer rate, and thus kLa values, due to the consumption of oxygen for both cell growth and metabolite production. In this work, theoretical equations for kLa prediction, developed for sparged and stirred tanks, taking into account the possible oxygen mass transfer enhancement due to the consumption by biochemical reactions, are proposed. The estimation of kLa is carried out taking into account a strong increase of viscosity broth, changes in surface tension and different oxygen uptake rates (OURs), and the biological enhancement factor, E, is also estimated. These different operational conditions and changes in several variables are performed using different systems and cultures (xanthan aqueous solutions, xanthan production cultures by Xanthomonas campestris, sophorolipids production by Candida bombicola, etc.). Experimental and theoretical results are presented and compared, with very good results. PMID:16155951

Garcia-Ochoa, Felix; Gomez, Emilio

2005-12-20

114

Experimental study of convective coefficient of mass transfer of avocado (Persia americana Mill.)  

Energy Technology Data Exchange (ETDEWEB)

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)

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

115

Experimental measurement of variation of heat transfer coefficient and temperature gradients in 16'' deep fluidised beds  

International Nuclear Information System (INIS)

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

116

Determination of the Heat Transfer Coefficient at the Metal-Mold Interface During Centrifugal Casting  

Science.gov (United States)

The heat transfer coefficient at the metal-mold interface (h MM) has been determined for the first time during the centrifugal casting of a Fe-C alloy tube using the inverse solution method. To apply this method, a centrifugal casting experiment was carried out to measure cooling curves within the tube wall under a mold rotation speed of 900 rpm, imposing a centrifugal force 106 times as large as the gravity force (106 G). As part of the solution method, a comprehensive heat transfer model of the centrifugal casting was also developed and coupled to an optimization algorithm. Finally, the evolution of h MM with time that gives the minimum squared error between measured and calculated cooling curves was obtained. The determined h MM is approximately 870 W m-2 K-1 immediately after melt pouring, decreasing to about 50 W m-2 K-1 when the average temperature of the tube is ~973 K (700 °C), after the end of solidification. Despite the existence of a centrifugal force that could enhance the metal-mold contact, these values are lower than those generally reported for static molds with or without an insulating coating at the mold inner surface. The implemented model shows that the heat loss by radiation is dominant over that by convection at the tube inner surface, causing the formation of a solidification front that meets another front coming from the outer surface of the tube.

Vacca, Santiago; Martorano, Marcelo A.; Heringer, Romulo; Boccalini, Mário

2015-01-01

117

Experimental investigation of heat transfer performance coefficient in tube bundle of shell and tube heat exchanger in two-phase flow  

Directory of Open Access Journals (Sweden)

Full Text Available This paper presents the results of studies in two phase gasliquid flow around tube bundle in the model of shell tube heat exchanger. Experimental investigations of heat transfer coefficient on the tubes surface were performed with the aid of electrochemical technique. Chilton-Colburn analogy between heat and mass transfer was used. Twelve nickel cathodes were mounted on the outside surface of one of the tubes. Measurement of limiting currents in the cathodic reduction of ferricyanide ions on nickel electrodes in aqueous solution of equimolar quantities of K3Fe(CN6 and K4Fe(CN6 in the presence of NaOH basic solution were applied to determine the mass transfer coefficient. Controlled diffusion from ions at the electrode was observed and limiting current plateau was measured. Measurements were performed with data acquisition equipment controlled by software created for this experiment. Mass transfer coefficient was calculated on the basis of the limiting current measurements. Results of mass transfer experiments (mass transfer coefficient were recalculated to heat transfer coefficient. During the experiments, simultaneously conducted was the the investigation of two-phase flow structures around tubes with the use of digital particle image velocimetry. Average velocity fields around tubes were created with the use of a number of flow images and compared with the results of heat transfer coefficient calculations.

Kara? Marcin

2014-03-01

118

Estimation of heat transfer coefficient and flow characteristics on heat transfer tube in sodium-water reaction  

International Nuclear Information System (INIS)

In the steam generator of a sodium-cooled fast reactor, high-pressure water flows inside heat transfer tubes while liquid sodium flows on the shell side. Heat is exchanged through the tube wall. When the tube fails, water vapor leaks into the sodium stream, and a sodium-water reaction is initiated. This reaction occurs rapidly and generates a high-temperature jet. It then becomes possible for neighboring tubes to experience a secondary failure due to overheating. With regard to the secondary failure, an estimate of heat transfer from fluid to the tube is important for safety evaluation. In the present study, a numerical analysis has been carried out to determine the heat transfer coefficient from temperature data obtained in a sodium-water reaction experiment. By updating the heat transfer coefficient, an inverse problem of heat transfer has been solved in the analysis based on the result of the SWAT-1R experiment. It is found that the heat transfer coefficient fluctuates largely during the reaction. The heat transfer coefficient is affected by the flow characteristics. Hence, we characterize the flow pattern near the heat transfer tube at typical periods in the phenomenon progression. (author)

119

Estimation of near-surface quality factors by constrained inversion of Rayleigh-wave attenuation coefficients  

Science.gov (United States)

Quality factors (Q) of near-surface materials are as important as velocities of the materials in many applications. Only phase information of surface-wave data is utilized when high-frequency (? 2 Hz) surface-wave data are routinely inverted to determine near-surface shear (S)-wave velocities. Amplitude information of high-frequency surface-wave data can be used to determine quality factors of near-surface materials. Given S-wave velocity, compressional (P)-wave velocity, and Rayleigh-wave phase velocities, it is feasible to solve for S-wave quality factor QS and P-wave quality factor QP (for some specific velocity models) down to 30 m below the ground surface in many settings by inverting high-frequency Rayleigh-wave attenuation coefficients in a layered earth model. Amplitude of seismic data is an exponential function of attenuation coefficients. When calculating attenuation coefficients from changes in amplitude, this nonlinear nature would result in that small variations in amplitude cause huge changes in attenuation coefficients. This result suggests data (attenuation coefficients) that normally possess large errors could eventually transfer to a model (quality factors); therefore, constraints (or a priori information) on models are necessary. Because an inversion system to solve this problem is unstable, a regularization parameter must be introduced into an inversion algorithm to stabilize the inversion. These characteristics of the inversion problem allow us to solve the problem as a constrained and regularized linear system. Usually, a set of models that meet the defined constraints can be obtained by solving the system. Based on the linear nature of the inversion system, a smooth model can be selected from the set of models as a solution of the inversion using the L-curve method. This approach is a trade-off solution between data misfit and model length. Several real-world examples demonstrate the importance of constraints in finding acceptable realistic quality factors from empirical data.

Xia, Jianghai; Xu, Yixian; Miller, Richard D.; Ivanov, Julian

2012-07-01

120

SIMULTANEOUS MEASUREMENT OF INTERFACIAL AREA DISTRIBUTION AND MASS TRANSFER COEFFICIENTS IN BUBBLE COLUMN  

Directory of Open Access Journals (Sweden)

Full Text Available In this study, simultaneous measurement of interfacial area distribution and mass transfer coefficients in a bubble column for two-phase dispersed system of air-water is conducted. The time-averaged interfacial area (a distribution was measured by using ultrasonic computed tomography (UCT, the volumetric liquid mass transfer coefficient (kLa is measured by dynamic method, and hence, the liquid side mass transfer coefficient (kL was calculated from the kLa and a. The UCT results show that the higher interfacial area around the center of the column and the lower one near the column wall. The experimental results of interfacial area are in a good agreement with the results obtained by the reported correlation and the results obtained by the physical method. A good agreement is also obtained between the experimental results of liquid side mass transfer coefficient and those by the reported correlation.

MUHAMMAD DANI SUPARDAN

2012-06-01

121

Enhancement of pool boiling heat transfer by surface micro-structuring  

International Nuclear Information System (INIS)

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.

122

Characterization of rock matrix block size distribution, dispersivity, and mass transfer coefficients in fractured porous media  

Science.gov (United States)

Fractured porous media are important structures in petroleum engineering and geohydrology. The accelerating global demand for energy has turned the focus to fractured formations. The fractured porous media are also found in conventional naturally fractured reservoirs and the water supply from karst (carbonate) aquifers. Studying mass transfer processes allows us to explore the complexities and uncertainties encountered with fractured rocks. This dissertation is developing an analytical methodology for the study of mass transfer in fractured reservoirs. The dissertation begins with two cases that demonstrate the importance of the rock matrix block size distribution and dispersivity through a transient mass exchange mechanism between rock matrix blocks and fractures. The first case assumes a medium with no surface adsorption, and the second case includes the surface adsorption variable. One of the main focuses of this work is the characterization of the rock matrix block size distribution in fractured porous media. Seismic surveying, well test analysis, well logging, and geomechanical tools are currently used to characterize this property, based on measurements of different variables. This study explores an innovative method of using solute transport to determine the fracture intensity. This methodology is applied to slab-shaped rock matrix blocks and can easily be extended to other geometries. Another focus of this dissertation is the characterization of dispersivity in field scale studies. Improving our knowledge of dispersivity will enable more accurate mass transfer predictions and advance the study of transport processes. Field tracer tests demonstrated that dispersivity is scale-dependent. Proposed functions for the increasing trend of dispersivity include linear and asymptotic scale-dependence. This study investigated the linear dispersivity trend around the injection wellbore. An analysis of the tracer concentration in a monitoring well was used to characterize the slope of the linear function for different rock geometries. The final part of the study is the development of a lumped mass transfer coefficient between fractures and rock matrix blocks with different geometries. The obtained lumped mass transfer coefficient confirms that the scale of study, dispersivity, and the rate of injection of the fluid into the wellbore are important variables in solute transport in fractured rocks.

Sharifi Haddad, Amin

123

Estimating the workpiece-backingplate heat transfer coefficient in friction stirwelding  

OpenAIRE

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 transfer coefficient are the variables in an optimisation problem. The objective is to minimise the difference between experimentally measured temperatures and temperatures obtained using a 3D fini...

Larsen, Anders; Stolpe, Mathias; Hattel, Jesper Henri

2012-01-01

124

Measurement of heat transfer coefficient in the transition region of tube flow  

International Nuclear Information System (INIS)

Heat transfer coefficient and friction factor were obtained experimentally for a circular tube in the transition region from the laminar to the turbulent flow. The measurements were made for two different kinds of intermittently turbulent regions; i.e., puff and slug. A relation between the heat transfer coefficient and the intermittency was examined. Variation of gas temperature was observed and found to be also intermittent. (author)

125

Measurement of radon diffusion coefficients for Japanese surface soils  

International Nuclear Information System (INIS)

The radon diffusion coefficient for soil, D, is a very important parameter used to estimate radon dose for uranium-bearing waste. Many Ds were measured in the uranium mill tailing remediation action project in the US, and a formula for the estimation of diffusion coefficient, Rogers's formula, was proposed. However, it is uncertain whether Rogers's formula is applicable to Japanese soils because most of them have come from volcanic ash and contain much water. This paper describes the development of a measurement apparatus for D using a lump response transient method and a step response transient method, and presents measured D values for Japanese surface soils. Measured alpha ray count curves are good in agreement with those of theory. This shows that radon transportation in soil can be described using Fick's law. Furthermore, the measured effective D values are good in agreement with those of Rogers's formula. This means that Rogers's formula can be applied to Japanese soils. (author)

126

Local heat transfer coefficients during the evaporation of 1,1,1,2-tetrafluoroethane (R-134a) in a plate heat exchanger  

OpenAIRE

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 ...

EMILA ŽIVKOVI?; STEPHAN KABELAC; SLOBODAN ŠERBANOVI?

2009-01-01

127

Transfer coefficients to terrestrial food products in equilibrium assessment models for nuclear installations  

International Nuclear Information System (INIS)

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)

128

Bayesian parameter estimation of convective heat transfer coefficients of a roof-mounted radiant barrier system  

OpenAIRE

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...

Lauret, Philippe; Miranville, Fre?de?ric; Boyer, Harry; Garde, Francois; Adelard, Laetitia

2006-01-01

129

Numerical modeling of the propagation of hydrogen-air flames with variable transfer coefficients  

Energy Technology Data Exchange (ETDEWEB)

Flame propagation in hydrogen-air mixtures with variable transfer coefficients is modeled numerically. It is shown that a decrease in the heat conductivity coefficient to zero leads to a decrease in the normal combustion rate of a stoichiometric hydrogen-air mixture from 1.85 to 0.66 m/s. With a decrease in the diffusion coefficients of all the reacting components to zero, the normal combustion rate decreases to 1.48 m/s. 15 refs.

Shebeko, IU.N.; Korol' chenko, A.IA.; Baratov, A.N.; Shamonin, V.G.

1989-10-01

130

Pool boiling heat transfer enhancement on porous surface tube  

International Nuclear Information System (INIS)

The passive residual heat removal exchanger (PRHR HX), which is a key equipment of the passive residual heat removal system, is installed in an elevated pool. Its heat transfer performance affects security and economics of the reactor, and boiling heat transfer in the liquid surrounding the exchanger occurs when the liquid saturation temperature exceeded. The smooth tubes, which are widely used as heat transfer tubes in PRHR HX, can be replaced by some enhanced tubes to improve the boiling heat transfer capability. In this paper, the pool boiling heat transfer characteristics of smooth tube and a machined porous surface tube are investigated by using high-pressure steam condensing inside tube as heating source. Compared with smooth tube,the porous surface tube considerably enhances the boiling heat transfer, and shortens the time significantly before reaching the liquid saturation temperature. Its boiling heat transfer coefficient increases from 68% to 75%, and the wall superheat decreases by 1.5 degree C. Combining effect of condensation inside tube with boiling outside tube, the axial wall temperatures of heat transfer tube are neither uniform nor linear distribution. Based on these investigations, enhance mechanism of the porous surface tube is analyzed. (authors)

131

Determining the surface roughness coefficient by 3D Scanner  

Directory of Open Access Journals (Sweden)

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.

Karmen Fifer Bizjak

2010-12-01

132

On the radial heat transfer coefficient in grooved heat pipe  

OpenAIRE

It is well known that microscopic effects are important in the evaluation of the radial heat transfer within a grooved heat pipe evaporator. We develop a multi-scale model which is composed of two parts, macroscopic and microscopic, which cannot be decoupled from each other. In our study, we include various effects such as the disjoining pressure, the influence of the interfacial curvature, the variation of the saturation temperature, the interfacial resistance and the thermal conduction. The...

Rossomme, Se?verine; Goffaux, Ce?cile; Hillewaert, Koen; Colinet, Pierre

2009-01-01

133

MM98.04 Measurement of temperature and determination of heat transfer coefficient in backward can extrusion  

DEFF Research Database (Denmark)

Temperature is measured during backward can extrusion of steel. The process is characterised by large deformations and very high surface pressure. In the experiments, a can in low carbon steel with a lubrication layer of phosphate soap is formed. The temperature is measured by thermocouples in the die insert. The die insert is divided into two halves where the thermocouples are welded to the end of milled grooves in the lower part. The temperature of the workpiece is measured by welding a thermocouple directly onto the free surface.All of the temperature measurements in the tool and the workpiece are compared with a number of FEM simulations computed with different heat transfer coefficients. The current heat transfer coefficient is determined from the simulations.

Henningsen, Poul; Hattel, Jesper Henri

1998-01-01

134

Effect of grid spacer on the heat transfer on element surface  

International Nuclear Information System (INIS)

Experiments are performed to study the effect of grid spacer on the heat transfer on element surface with two methods (heat and mass transfer tests). Axial heat and mass transfer coefficients are measured. Finally a comparison is made between the results obtained by the two different methods

135

Modeling of the substrate and product transfer coefficients for ethanol fermentation  

International Nuclear Information System (INIS)

The transfer phenomena of the substrate and product for ethanol fermentation with immobilized biocatalyst were investigated. Fermentation was carried out with a biocatalyst consisting of Ca-alginate gel in the form of two-layer spherical beads in anaerobic conditions. The determination of kinetic parameters was achieved by fitting bioreaction progress curves to the experimental data. The calculation of the diffusion coefficients was performed by numerical methods for experimental conditions. Finally, the glucose and ethanol transfer coefficients are defined and determined, using the effective diffusion coefficients. (Abstract Copyright [2008], Wiley Periodicals, Inc.)

136

Measuring convective heat transfer coefficient around a heated fine wire in cross flow of nanofluids  

International Nuclear Information System (INIS)

Recent researches on nanofluids have mainly focused on the increase of thermal conductivity of nanofluids under static condition. The ultimate goal of using nanofluids, however, is to enhance the heat transfer performance under fluid flow. So it has been highly necessary to devise a simple and accurate measuring apparatus which effectively compares the heat transfer capability between the base and nanofluids. Though the convective heat transfer coefficient is not the complete index for the heat transfer capability, it might be one of useful indications of heat transfer enhancement. In this article, the working principles of experimental system for convective heat transfer coefficient around a heated fine wire in cross flow of nanofluids and its application example to three samples of nano lubrication oils are explained in detail

137

Transient volumetric heat transfer coefficient prediction of a three-phase direct contact condenser  

Science.gov (United States)

An experimental investigation for the time dependent volumetric heat transfer coefficient of the bubbles type, three-phase direct contact condenser has been carried out utilising a short column (70 cm in total height and 4 cm inner diameter). A 47 cm active height was chosen with five different mass flow rate ratios and three different initial dispersed phase temperatures. Vapour pentane and constant temperature tap water as dispersed and continuous phases were implemented. The results showed that the volumetric heat transfer coefficient decreases with increased time until it almost reaches its steady state conditions. A sharp decrease in the volumetric heat transfer coefficient was found at the beginning of the operation and, diminished over a short time interval. Furthermore, a positive effect of the mass flow rate ratios on the volumetric heat transfer coefficient was noted and this was more pronounced at the beginning of the operation. On the other hand, the volumetric heat transfer coefficient decreased with an increase in the continuous phase mass flow rate and there was no considerable effect of the initial dispersed phase temperatures, which confirms that latent heat transfer is dominant in the process.

Mahood, Hameed B.; Sharif, Adel O.; Thorpe, Rex B.

2015-02-01

138

The use of neural network to estimate mass transfer coefficient from the bottom of agitated vessel  

Science.gov (United States)

In this study, the ability of the artificial neural network ( ANN) to estimate the rate of mass transfer coefficient was compared against the mass transfer correlation obtained by dimensional analysis in terms of Sherwood, Schmidt and Reynolds numbers. The results showed that the ANN is better than the conventional mass transfer correlation in most cases and the best results are obtained at 3-7 neurons in the hidden layer.

ElShazly, Yehia M. S.

2015-04-01

139

Local heat transfer coefficient and adiabatic wall temperature measurement beneath arrays of staggered and inline impinging jets  

OpenAIRE

Recent work, Van Treuren et al. (1993), has shown the transient method of measuring heat transfer under an array of impinging jets allows the determination of local values of adiabatic wall temperature and heat transfer coefficient over the complete surface of the target plate. Using this technique, an inline array of impinging jets has been tested over a range of average jet Reynolds numbers (10,000-40,000) and for three channel height to jet hole diameter ratios (1, 2, and 4). The array is ...

Treuren, Kw; Wang, Z.; Ireland, Pt; Jones, Tv; Kohler, St

1994-01-01

140

Hydrodynamics and mass transfer coefficients for a modified Raschig ring packed column  

Science.gov (United States)

The pressure drop, the liquid holdup, as well as the liquid film mass transfer coefficients (kL) for a modified Raschig packing, with turbulence promoters, used in absorption columns, were determined experimentally. The aim of this work is to verify the improved mass transfer properties of this new packing for the randomly and, particularly, for the arranged packed columns. The experiments were performed at gas velocities ranging from 800 to 2,000 m h-1 and liquid velocities scaling between 2.5 and 8.11 m h-1, ranges that cover most of the absorption column operation conditions. Experimental data and correlations for the pressure drop, the liquid holdup and the gas-liquid mass transfer coefficients (kL) for modified Raschig ring packed columns are presented. The influence of the gas and the liquid velocities on the column hydrodynamics and the mass transfer coefficients have been obtained experimentally and also, have been compared with literature data.

Mamaliga, I.; Sidor, D.; Condurat, C.; Iacob Tudose, E. T.

2014-10-01

141

Prediction of transient heat transfer coefficients in thick-walled pressure components of cylindrical geometry  

International Nuclear Information System (INIS)

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.)

142

The influence of surfactant on mass transfer coefficients in evaporation of volatile organic compound from water basin  

Directory of Open Access Journals (Sweden)

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.

Bunyakan, C.

2002-04-01

143

Determination of heat transfer coefficients in plastic French straws plunged in liquid nitrogen.  

Science.gov (United States)

The knowledge of the thermodynamic process during the cooling of reproductive biological systems is important to assess and optimize the cryopreservation procedures. The time-temperature curve of a sample immersed in liquid nitrogen enables the calculation of cooling rates and helps to determine whether it is vitrified or undergoes phase change transition. When dealing with cryogenic liquids, the temperature difference between the solid and the sample is high enough to cause boiling of the liquid, and the sample can undergo different regimes such as film and/or nucleate pool boiling. In the present work, the surface heat transfer coefficients (h) for plastic French straws plunged in liquid nitrogen were determined using the measurement of time-temperature curves. When straws filled with ice were used the cooling curve showed an abrupt slope change which was attributed to the transition of film into nucleate pool boiling regime. The h value that fitted each stage of the cooling process was calculated using a numerical finite element program that solves the heat transfer partial differential equation under transient conditions. In the cooling process corresponding to film boiling regime, the h that best fitted experimental results was h=148.12±5.4 W/m(2) K and for nucleate-boiling h=1355±51 W/m(2) K. These values were further validated by predicting the time-temperature curve for French straws filled with a biological fluid system (bovine semen-extender) which undergoes freezing. Good agreement was obtained between the experimental and predicted temperature profiles, further confirming the accuracy of the h values previously determined for the ice-filled straw. These coefficients were corroborated using literature correlations. The determination of the boiling regimes that govern the cooling process when plunging straws in liquid nitrogen constitutes an important issue when trying to optimize cryopreservation procedures. Furthermore, this information can lead to improvements in the design of cooling devices in the cryobiology field. PMID:25445573

Santos, M Victoria; Sansinena, M; Chirife, J; Zaritzky, N

2014-12-01

144

Estimation of grass to milk transfer coefficient for Strontium for emergency situations  

International Nuclear Information System (INIS)

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)

145

Heat transfer coefficient testing in nuclear fuel rod bundles with mixing vane grids  

International Nuclear Information System (INIS)

An air heat transfer test facility was developed to test the heat transfer downstream of support grids in simulated PWR nuclear fuel rod bundles. The goal of this testing is to study the single-phase heat transfer coefficients downstream of grids with mixing vanes in a square-pitch rod bundle. The technique developed utilizes fully-heated grid spans and a specially designed thermocouple holder that can be moved axially down the rod bundle and aximuthally within a test rod. From this testing, the axial and aximuthally varying heat transfer coefficient can be determined. Different grid designs are tested and compared to determine the heat transfer enhancement associated with key grid features such as mixing vanes. (author)

146

Prediction of mass transfer coefficients in a pulsed packed extraction column using effective diffusivity  

Scientific Electronic Library Online (English)

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 overal [...] l 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.

M., Torab-Mostaedi; J., Safdari.

2009-12-01

147

Local Mass Transfer Coefficient for Idealized 2D Urban Street Canyon Models  

Science.gov (United States)

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.

Leung, Ka Kit; Liu, Chun-Ho

2011-09-01

148

Transfer coefficient study of Sr-90 in the soil-grass-milk chain for Cuba  

International Nuclear Information System (INIS)

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

149

Experimental determination of the local heat transfer coefficient in a closely packed pin arrangement  

International Nuclear Information System (INIS)

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.)

150

Experimental determination of heat transfer coefficients in uranium zirconium hydride fuel rod  

International Nuclear Information System (INIS)

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)

151

Measurement of the thermal conductivity and heat transfer coefficient of a binary bed of beryllium pebbles  

International Nuclear Information System (INIS)

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)

152

Measurement of the thermal conductivity and heat transfer coefficient of a binary bed of beryllium pebbles  

Energy Technology Data Exchange (ETDEWEB)

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

153

Measuring convective heat transfer coefficients of nanofluids over a circular fine wire maintaining a constant temperature  

Energy Technology Data Exchange (ETDEWEB)

This paper describes a measuring apparatus that can be used to appraise the effectiveness of nanofluids as new heat transfer enhancing fluids. A couple of apparatuses using fine hot wires as sensors have been proposed for this purpose; however, they have a technical weakness related to the uncertain working conditions of the sensor. The present method used the convective heat transfer coefficient from a hot wire as an indication of the heat transfer effectiveness of the nanofluid, where the temperature of the wire remains constant during the experiment. The operating principle and experimental procedure are explained in detail, and the validity of the system is tested with pure base fluids. The effects of particle concentration, velocity, and temperature on the heat transfer coefficients of the nanofluids are discussed comprehensively using the experimental data for graphite nanolubrication oil.

Lee, Shinpyo [Kyonggi Univ., Suwon (Korea, Republic of)

2012-01-15

154

Experimental studies of droplet heat transfer from hot metal surfaces  

International Nuclear Information System (INIS)

The boiling of water droplets on hot metal surfaces is studied experimentally and mathematically in order to establish the conditions necessary for droplets to enter a film boiling mode. The subsurface temperature history within a plate undergoing droplet boiling on the surface is measured. A numerical model of the heat transfer in the plate is then used to deduce from these data the following characteristics of droplet boiling: (1) the effective heat transfer coefficient between water droplet and plate during the initial transient forming the spherical droplet, (2) the apparent time period needed to establish the droplet in the film boiling mode, and (3) the minimum plate surface temperature reached during the initial formation of the boiling droplet. The effective heat transfer coefficient, formation time, and minimum surface temperature are sufficient to develop a calculation method which predicts the minimum initial plate temperature necessary for a water droplet to enter film boiling. This numerical conduction model accounts for the influence of plate material, plate thickness, oxidation of the plate surface, the boundary condition on the plate lower surface, and the size of the droplet. The prediction method is successfully used to estimate the minimum film boiling temperature for brass, graphite, Pyrex, copper, aluminum, stainless steel, and Zircalloy II. The findings of the experiments and numerical studies are applied to the rewetting phase of a loss-of-coola to the rewetting phase of a loss-of-coolant-accident in a light water reactor. This application, in turn, provides explanations for some of the phenomena observed in studies of the prequench heat transfer within rod bundles including the effect of multiple droplet impacts

155

Convective and radiative heat transfer coefficients for individual human body segments  

Science.gov (United States)

Human thermal physiological and comfort models will soon be able to simulate both transient and spatial inhomogeneities in the thermal environment. With this increasing detail comes the need for anatomically specific convective and radiative heat transfer coefficients for the human body. The present study used an articulated thermal manikin with 16 body segments (head, chest, back, upper arms, forearms, hands, pelvis, upper legs, lower legs, feet) to generate radiative heat transfer coefficients as well as natural- and forced-mode convective coefficients. The tests were conducted across a range of wind speeds from still air to 5.0 m/s, representing atmospheric conditions typical of both indoors and outdoors. Both standing and seated postures were investigated, as were eight different wind azimuth angles. The radiative heat transfer coefficient measured for the whole-body was 4.5 W/m2 per K for both the seated and standing cases, closely matching the generally accepted whole-body value of 4.7 W/m2 per K. Similarly, the whole-body natural convection coefficient for the manikin fell within the mid-range of previously published values at 3.4 and 3.3 W/m2 per K when standing and seated respectively. In the forced convective regime, heat transfer coefficients were higher for hands, feet and peripheral limbs compared to the central torso region. Wind direction had little effect on convective heat transfers from individual body segments. A general-purpose forced convection equation suitable for application to both seated and standing postures indoors was hc=10.3v0.6 for the whole-body. Similar equations were generated for individual body segments in both seated and standing postures.

de Dear, R. J.; Arens, Edward; Hui, Zhang; Oguro, Masayuki

156

Experimental study of overall heat transfer coefficient in the application of dilute nanofluids in the car radiator  

International Nuclear Information System (INIS)

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 ?-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 50–1000 and the inlet liquid to the radiator has a constant temperature which is changed at 50, 65 and 80 °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: ? Overall heat transfer coefficient in the car radiator measured experimentally. ? Nanofluids showed greater heat transfer performance comparing with water. ? Increasing liquid and air Re increases the overall heat transfer coefficient. ? Increasing the inlet liquid temperature decreases the overall heat transfer coefficient

157

Lumped mass transfer coefficient for divergent radial solute transport in fractured aquifers  

Science.gov (United States)

Dispersion plays an important role in transport of contaminants and tracers in fractured aquifers. In this work we develop a model for the lumped mass transfer coefficient by including dispersion in the fracture network for slab-, cylindrical- and spherical-shapes of the aggregates for the immobile zone. Coupled transport equations of mobile and immobile zones are solved to develop a first-order lumped mass transfer coefficient. An equivalent fracture aperture, uniform rock matrix block size and constant volumetric water contents (mobile and immobile zones) with no adsorption/desorption are used to represent the aquifer. Results reveal that geometry of the rock matrix blocks and dispersivity have important effects on the upscaled mass transfer coefficient. It is found that field scale simulations of transport processes without including the dispersion in fractures are not valid for the whole range of practical injection rates (104 105). It is confirmed that the upscaled lumped mass transfer coefficient is a function of scale and the rate of injection of the tracer. These findings will find applications in modeling of transport processes of contaminated sites remediation and waste disposal.

Sharifi Haddad, Amin; Hassanzadeh, Hassan; Abedi, Jalal; Chen, Zhangxin

2013-07-01

158

Small thermistors for the measurement of heat transfer coefficients; Kleine Thermistoren zur Messung von Waermeuebergangskoeffizienten  

Energy Technology Data Exchange (ETDEWEB)

The measurement of heat transfer coefficients at rotating machine parts is a difficult measurement task and is particularily challenging for fast rotating parts with good thermal conductivity in combination with gaseous flow. This contribution reports about the test of a setup with small thermistors employed to achieve compatibility with the demands of telemetry. (orig.)

Uffrecht, Wieland; Guenther, Andre [TU Dresden (Germany). Inst. fuer Stroemungsmechanik; Caspary, Volker [MAN Diesel und Turbo SE, Oberhausen (Germany)

2012-07-01

159

Evaluation of convective heat transfer coefficient of various crops in cyclone type dryer  

International Nuclear Information System (INIS)

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

160

Evaluation of convective heat transfer coefficient of various crops in cyclone type dryer  

Energy Technology Data Exchange (ETDEWEB)

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.

Akpinar, E. Kavak [Mechanical Engineering Department, Firat University, 23279 Elazig (Turkey)]. E-mail: eakpinar@firat.edu.tr

2005-09-15

161

Determination of heat transfer coefficient with vapor condensation inside the tubes diesel’s radiator sections  

Directory of Open Access Journals (Sweden)

Full Text Available The article presents the calculation of heat transfer coefficient during condensation of steam, the mathematical model of temperature distribution in the gas and liquid phases of the coolant and the model of the formation of the condensate film on the walls of the tubes.

Y.K.Sklifus

2012-12-01

162

Heat transfer coefficients in two-dimensional Yukawa systems (numerical simulations)  

Energy Technology Data Exchange (ETDEWEB)

New data on heat transfer in two-dimensional Yukawa systems have been obtained. The results of a numerical study of the thermal conductivity for equilibrium systems with parameters close to the conditions of laboratory experiments in dusty plasma are presented. The Green-Kubo relations are used to calculate the heat transfer coefficients. The influence of dissipation (internal friction) on the heat transfer processes in nonideal systems is studied. New approximations are proposed for the thermal conductivity and diffusivity for nonideal dissipative systems. The results obtained are compared with the existing experimental and numerical data.

Khrustalyov, Yu. V., E-mail: yuri.khrustalyov@gmail.com; Vaulina, O. S. [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation)

2013-05-15

163

Effects of surface roughness on the coefficients of friction in model orthodontic systems.  

Science.gov (United States)

Orthodontists, like others (Engel, P.A. (1976) Impact Wear of Materials. Elsevier Scientific, New York.), often equate the smoothness of surfaces with the absence of friction. To investigate whether the surface roughness of opposing materials influence the coefficients of friction and ultimately the movement of teeth, arch wires were slid between contact flats to simulate orthodontic arch wire-bracket appliances. From laser specular reflectance measurements, the RMS surface roughness of these arch wires varied from 0.04 microns for stainless steel to 0.23 microns for nickel titanium. Using the same technique, the roughnesses of the contact flats varied from 0.03 microns for the 1 micron lapped stainless steel, to 0.26 microns for the as-received alumina. After each of the arch wire-contact flat couples was placed in a friction tester, fifteen normal forces were systemically applied at 34 degrees C. From plots of the static and kinetic frictional forces vs the normal forces, dry coefficients of friction was obtained that were greater than those reported in the dental literature. The all-stainless steel couples had lower kinetic coefficients (0.120-0.148) than the stainless steel-polycrystalline alumina couple (0.187). When pressed against the various flats, the beta-titanium arch wire (RMS = 0.14 microns) had the highest coefficients of friction (0.445-0.658), although the nickel titanium arch wire was the roughest (RMS = 0.23 microns). Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) verified that mass transfer of the beta-titanium arch wire occurred by adhesion onto the stainless steel flats or by abrasion from the sharply faceted polycrystalline alumina flats. PMID:2211736

Kusy, R P; Whitley, J Q

1990-01-01

164

Evaluation of the heat transfer coefficient at the metal-mould interface during flow  

Directory of Open Access Journals (Sweden)

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.

Z. Konopka

2007-12-01

165

The prediction of heat transfer coefficient in circulating fluidized bed combustors  

Energy Technology Data Exchange (ETDEWEB)

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. (author)

Hamdan, M.A.; Al-qaq, A.M. [Department of Mechanical Engineering, University of Jordan Amman, Qween Rania Street, Amman, AL Jbeeha 11942 (Jordan)

2008-11-15

166

The prediction of heat transfer coefficient in circulating fluidized bed combustors  

International Nuclear Information System (INIS)

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

167

Measurement of the thermal transfer coefficient predicting efficiency of the heat pipe  

International Nuclear Information System (INIS)

Recently, electronic and electrical products have problems how to reduce heat in trend reducing size and increasing speed. heat pipes worked by latent heats can solve problems for effective and quiet electronic applications. Heat Pipes have to be suitably designed for the external conditions due to showing optimum performance. it has influence on efficiency of heat pipes to the exterior structure changed by length, bending angle, diameter. Designing heat pipes has depended on experience from trial and error. this method wasted too many resources, but can't guarantee efficiency. to prevent those wastes, this study aims at making the thermal transfer coefficient predicting efficiency. In this study, the thermal transfer coefficient has been made from experimental results that used variables - lengths between heat source and radiation, bending angles, diameters of heat pipes. variables become non-dimensional in modeling process for making the coefficient

168

Identification of radon transfer velocity coefficient between liquid and gaseous phases  

International Nuclear Information System (INIS)

Radon transfer between a liquid phase and a gaseous phase is modelled by a Robin's condition (radon flux at the common interface is expressed as function of radon concentrations in the two phases). This condition involves two constants: Ostwald's coefficient (?) and the transfer velocity coefficient (?). Assuming the value of ? is known, a method is proposed to determinate the value of ?, by studying the radon transfer phenomenon at the laboratory scale. Knowing the initial radon concentrations, the experiment consists in measuring how long the radon flux passes through the common interface. In this stabilisation time radon transport is governed in each phase by diffusion and disintegration. Then, determination of ? is equivalent to solving an inverse problem formulated using measured data. A numerical procedure is developed to solve this problem. (authors)

169

An investigative study of the interface heat transfer coefficient for Fe modeling of high speed machining  

International Nuclear Information System (INIS)

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 constronitoring 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)

170

Measurement of Heat Transfer Coefficients in an Agitated Vessel with Tube Baffles  

OpenAIRE

Cooling or heating an agitated liquid is a very common operation in many industrial processes. A classic approach is to transfer the necessary heat through the vessel jacket. Another option, frequently used in the chemical and biochemical industries is to use the heat transfer area of vertical tube baffles. In large equipment, e.g. fermentor, the jacket surface is often not sufficient for large heat transfer requirements and tube baffles can help in such cases. It is then important to know th...

Dosta?l, M.; Petera, K.; Rieger, F.

2010-01-01

171

Heat transfer coefficients and other performance parameters for variously positioned and supported thermal loads in ovens with/without water-filled or empty blockages  

Energy Technology Data Exchange (ETDEWEB)

An in-depth experimental study of heat transfer in ovens has provided basic data that is directly applicable to design. Heat transfer coefficients were measured for thermal loads having either black or highly reflective surface finishes. Approximately 100 different data runs were carried out. These heat transfer coefficients enabled the separation of the heat transfer into convective and radiative components, with radiation being the dominant transfer mechanism for blackened loads. The thermal response of the load to the presence of blockages situated either below or above the load was quantified. This response was only slightly affected by the blockages when they were empty of water, but major effects were observed when the blockages were water filled. Major effects were also encountered when the load was supported from below by cookie sheets. On the other hand, extensive investigation of various positions throughout the oven indicated a very weak effect of load position on the thermal response. (author)

Sparrow, E.M.; Abraham, J.P. [University of Minnesota, Minneapolis (United States). Laboratory of Heat Transfer Practice, Department of Mechanical Engineering

2002-08-01

172

A stability-dependent parametrization of transfer coefficients for momentum and heat over polar sea ice to be used in climate models  

Science.gov (United States)

The interaction between sea ice and atmosphere depends strongly on the near-surface transfer coefficients for momentum and heat. A parametrization of these coefficients is developed on the basis of an existing parametrization of drag coefficients for neutral stratification that accounts for form drag caused by the edges of ice floes and melt ponds. This scheme is extended to better account for the dependence of surface wind on limiting cases of high and low ice concentration and to include near-surface stability effects over open water and ice on form drag. The stability correction is formulated on the basis of stability functions from Monin-Obukhov similarity theory and also using the Louis concept with stability functions depending on the bulk Richardson numbers. Furthermore, a parametrization is proposed that includes the effect of edge-related turbulence also on heat transfer coefficients. The parametrizations are available in different levels of complexity. The lowest level only needs sea ice concentration and surface temperature as input, while the more complex level needs additional sea ice characteristics. An important property of our parametrization is that form drag caused by ice edges depends on the stability over both ice and water which is in contrast to the skin drag over ice. Results of the parametrization show that stability has a large impact on form drag and, thereby, determines the value of sea ice concentration for which the transfer coefficients reach their maxima. Depending on the stratification, these maxima can occur anywhere between ice concentrations of 20 and 80%.

Lüpkes, Christof; Gryanik, Vladimir M.

2015-01-01

173

A novel liquid crystal image processing technique using multiple gas temperature steps to determine heat transfer coefficient distribution and adiabatic wall temperature  

OpenAIRE

This paper presents a novel experimental technique, which combines thermochromic liquid crystals with multiple steps in gas temperature, to determine heat transfer coefficient and adiabatic wall temperature distributions. The transient heat transfer experiments have been conducted on a flat plate using the low-temperature analogue of an ISO standard propane-air burner commonly used in aero-engine fire certification. The technique involves the measurement of the surface temperature response of...

Abu Talib, Ar; Neely, Aj; Ireland, Pt; Mullender, Aj

2004-01-01

174

Condensation heat transfer on superhydrophobic surfaces  

OpenAIRE

Condensation is a phase change phenomenon often encountered in nature, as well as used in industry for applications including power generation, thermal management, desalination, and environmental control. For the past eight decades, researchers have focused on creating surfaces allowing condensed droplets to be easily removed by gravity for enhanced heat transfer performance. Recent advancements in nanofabrication have enabled increased control of surface structuring for the development of su...

Miljkovic, Nenad; Wang, Evelyn N.

2013-01-01

175

Study for transfer coefficient of iodine from grass to cow milk  

International Nuclear Information System (INIS)

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

176

A Study on the Determination of the Seasonal Heat Transfer Coefficient in KURT Under Forced Convection  

International Nuclear Information System (INIS)

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 ? 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

177

Integration Of Heat Transfer Coefficient In Glass Forming Modeling With Special Interface Element  

International Nuclear Information System (INIS)

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

178

The effects of surface roughness on the heat transfer at the metal-mold interface  

International Nuclear Information System (INIS)

Heat transfer coefficient values at the metal-mold interface are an important parameter in the production of sound quality castings. This investigation focused primarily on the effect of surface roughness on heat transfer coefficient values. The paper will describe the development of a versatile apparatus. This apparatus was instrumented with thermocouples, displacement sensors-LVDT (Linear Variable Differential Transformer) and an electrical contact detection circuit. The equipment facilitated the recording of the temperature profile in chill and casting, as well as the detection and measurement of movement at the metal-mold interface including mold expansion and air-gap detection and measurement. Experiments were carried out by casting various aluminum alloys against different chill materials, each of various surface roughness. Inverse heat transfer analysis was used to estimate the heat transfer coefficient at the metal mold interface. This estimation revealed how the heat transfer coefficient changes during the metal solidification. Generally, an increase in surface roughness results in a decrease in the heat transfer coefficient at the metal mold interface. (author)

179

Study of the average heat transfer coefficient at different distances between wind tunnel models  

Science.gov (United States)

The paper presents investigations of physical and climatic factors with regard to design and process variables having effect on heat transfer in the building model system at different distances between them in the airflow direction. The aim of this work is to improve energy efficiency of exterior walls of buildings. A method of physical simulation was used in experiments. Experimental results on the average values of the heat transfer coefficient in the building model system are presented herein. A series of experiments was carried out on a specific aerodynamic test bench including a subsonic wind tunnel, heat models and devices for giving thermal boundary conditions, transducers, and the record system equipment. The paper contains diagrams of the average heat transfer distribution at fixed Reynolds number and the airflow angle of attack; the average values of the heat transfer coefficient for each face and wind tunnel models as a whole at maximum, medium, and large distances between them. Intensification of the average heat transfer was observed on the downstream model faces depending on the distance between models.

Gnyrya, A.; Korobkov, S.; Mokshin, D.; Koshin, A.

2015-01-01

180

Survey of literature on convective heat transfer coefficients and recovery factors for high atmosphere thermometry  

Science.gov (United States)

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.

Chung, S.

1973-01-01

181

The effect of gas dissolved in the water on heat transfer coefficients in nuclear reactors  

International Nuclear Information System (INIS)

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

182

The effect of gas dissolved in the water on heat transfer coefficients in nuclear reactors  

Energy Technology Data Exchange (ETDEWEB)

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.

Asmolov, V.G.; Yelkin, I.V.; Kobzar, L.L. (Kurchatov Nuclear Power Inst., Moscow (SU))

1989-11-01

183

Heat transfer coefficient between the flame and a radioactive material transport cask  

International Nuclear Information System (INIS)

At the time of a full-scale fire experiment on a fire-resisting wooden building, a model radioactive material transport cask was placed within the flame of the fire. By measuring its temperatures and temperatures of the fire flame, the heat transfer coefficient etc. were observed. The specimen model cask is a three-layered structure; the outer steel shell, the inner stainless steel shell and a lead radiation shielding layer in between. (1) When the flame started to surround the cask, the heat flux from the flame into the cask was about 7 x 104 kcal/m2h, in agreement with that measured with a heat flow meter. (2) The total heat transfer coefficient from the flame into the cask, calculated from the temperature measurements in both, was about 150 - 200 kcal/m2h0C. (Mori, K.)

184

Enzyme mass-transfer coefficient in aqueous two-phase systems using static mixer extraction column.  

Science.gov (United States)

Recent technical advances in aqueous two-phase systems (ATPS) have made this a sound technique for the extraction of biomacromolecules. The extraction of alpha-amylase was investigated using aqueous two-phase systems formed by sodium sulphate-polyethylene glycol (PEG) in water in a 47-mm inner diameter spray column packed with three types of static mixers. The effects of dispersed-phase flow rate, phase composition, column height and diameter were studied. The extraction column was operated in a semi-batch manner. It was found that the hold-up and volumetric mass transfer coefficients increased with an increase in dispersed (PEG-rich) phase velocity and decreased with increasing phase composition. Empirical correlations were developed for fractional dispersed-phase hold-up and volumetric mass transfer coefficients. PMID:14508675

Rostami, K; Alamshahi, M

2002-09-01

185

A look-up table for film-boiling heat-transfer coefficients in tubes with vertical upward flow  

International Nuclear Information System (INIS)

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)

186

Condensation heat transfer coefficients of R1234yf on plain, low fin, and Turbo-C tubes  

Energy Technology Data Exchange (ETDEWEB)

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)

Park, Ki-Jung; Kang, Dong Gyu; Jung, Dongsoo [Department of Mechanical Engineering, Inha University, Incheon 402-751 (Korea, Republic of)

2011-01-15

187

Estimation of overall heat transfer coefficient of cooling system in RF capacitive hyperthermia  

OpenAIRE

The study presented in this article involves the estimation of the overall heat transfer coefficient of cooling system in RF capacitive hyperthermia treatment using inverse problem based on the conjugate gradient method to provide improved distribution of temperature. The temperature data computed numerically from the direct problem using the finite difference time domain method are used to simulate the temperature measurements. The effects of the errors and sensor positions upon the precisi...

Mohammad Hasan Zahmatkesh; Seyed Rabii Mahdi Mahdavi; Dariush Sardari; Seyed Ali Aghayan

2013-01-01

188

Experimental measurements of heat transfer from an iced surface during artificial and natural cloud icing conditions  

Science.gov (United States)

The heat transfer behavior of accreting ice surfaces in natural (flight test) and simulated (wind tunnel) cloud icing conditions were studied. Observations of wet and dry ice growth regimes as measured by ultrasonic pulse echo techniques were made. Observed wet and dry ice growth regimes at the stagnation point of a cylinder were compared with those predicted using a quasi steady state heat balance model. A series of heat transfer coefficients were employed by the model to infer the local heat transfer behavior of the actual ice surfaces. The heat transfer in the stagnation region was generally inferred to be higher in wind tunnel icing tests than in natural flight icing conditions.

Kirby, Mark S.; Hansman, R. John, Jr.

1988-01-01

189

MM98.34 Experimental Measurements of Die temperatures and determination of heat transfer coefficient in backward can extrusion  

DEFF Research Database (Denmark)

The large deformations in backward can extrusion result in a rise of temperature of more than 200 degrees Centigrade. In the experiments cans in low carbon steel are formed, with a lubrication layer of phosphate soap. The temperature is measured by thermocouples in the die insert and the punch. The die insert is divided into two halves where the thermocouples are welded to the end of milled grooves in the lower part. The temperature of the workpiece is measured by welding a thermocouple directly onto the free surface.The punch is equipped with three thermocouples mounted at a distance of 0.2 mm from the surface. The thermocouples are welded to the end of grooves milled in a small plug, Which is pressed into a hold in the punch nose. All the temperature measurements in the tool and the workpiece are compared with a number of FEM simulations computed with different heat transfer coefficients. The current heat transfer coefficient is determined as the one resulting in the best agreement between measurements and the simulations.

Henningsen, Poul; Hattel, Jesper Henri

1998-01-01

190

MM98.43 Experimental determination of the heat transfer coefficient Under dynamic process conditions in backward can extrusion  

DEFF Research Database (Denmark)

The large deformations in backward can extrusion result in a rise of temperature of more than 200 oC. In the experiments, cans in low carbon steel are formed with a lubrication layer of phosphate soap. The temperature is measured by thermocouples in the die insert and the punch. The die insert is divided into two halves where the thermocouples are welded to the end of milled grooves in the lower part. The temperature of the workpiece is measured by welding a thermocouple directly onto the free surface. The punch is equipped with three thermocouples mounted at a distance of 0.2 mm from the surface. The thermocouples are welded to the end of grooves milled in a small plug, which is pressed into a hold in the punch nose. All the temperature measurements in the tool and the workpiece are compared with a number of finite element (FE) simulations computed with different heat transfer coefficients. The current heat transfer coefficient (HTC) is then determined by the least square method

Henningsen, Poul; Hattel, Jesper Henri

1998-01-01

191

Fuel-clad heat transfer coefficient of a defected fuel rod  

International Nuclear Information System (INIS)

A special rod has been built with a stack of UO2 pellets inside a thick zircaloy clad. The atmosphere inside the fuel rod can be changed and particularly the introduction of water is possible. The capsule was inserted in the Siloe pool reactor in a special device equipped with a neutron flux monitor. The fuel centerline temperature and the temperature at a certain radius of the clad were recorded by two thermocouples. The temperature profiles in the fuel and in the cladding have been calculated and then the heat transfer coefficient. In order to check the proper functioning of the device, two runs were successively achieved with a helium atmosphere. Then the helium atmosphere inside the fuel rod was removed and replaced by water. The heat transfer coefficients derived from the measurements at low power level are in agreement with the values given by the model based on thermal conductivity. However, for higher power levels, the heat transfer coefficients become higher than those based on the calculated gap

192

Heat transfer coefficient, two-phase flow boiling of HFC134a  

International Nuclear Information System (INIS)

Evaporation of HFC134a inside smooth, horizontal tubes is studied. Tests are made with pure refrigerant and with oil-refrigerant mixtures. Heat flux has varied from 2 kW/m2 to 10 kW/m2. The inner diameter of the tubes are 12 mm. Two evaporators are used, 4 and 10 m long. Oil content is varied from 0 to 2.5 mass percentage (synthetic oil, EXP-0275). Oil free HFC134a is found to have higher heat transfer coefficient than HCF22 at the same heat flux, as well as mass flux. The effect of oil in the refrigerant depends on the flux. At 2 and 4 kW/m2, the heat transfer coefficient has a maximum value for an oil content of around 0.5 mass percentage. No increase at all is registered for a heat flux of 6 kW/m2. Heat transfer coefficients for pure refrigerant are also compared to existing correlations. Pierre's correlation predict values with a reasonable accuracy

193

Effect of Mass on Convective Heat Transfer Coefficient During Onion Flakes Drying  

Directory of Open Access Journals (Sweden)

Full Text Available In this present study an open sun and greenhouse drying of onion flakes has been performed to study the effect of mass on convective heat transfer coefficient. Three sets of experiments with total quantity of onion as 300, 600 and 900 g were done. The onion was continuously dried for 33 h both in open sun and in the roof type even span greenhouse with floor area of 1.2 x 0.78 m2. Experiments were carried out during the months of October to December 2003 at IIT Delhi (28°35`N 72°12`E. Experiments were started at 8 am. The data obtained from experimentation under open sun and greenhouse conditions have been used to determine values of the constant `C` and exponent `n` by regression analysis and consequently, convective heat transfer coefficient. It is observed that there is a significant effect of mass on convective heat transfer coefficient for open as well as greenhouse drying. It is also observed that the rate of moisture evaporation in case of greenhouse drying is more than that in open sun drying during the off sunshine hours due to the stored energy inside the greenhouse. The experimental observations were analyzed in terms of percentage uncertainty also.

G.N. Tiwari

2006-01-01

194

Measurement of condensation heat transfer coefficients in a steam chamber using a variable conductance heat pipe  

International Nuclear Information System (INIS)

Condensation heat transfer coefficients have been measured in a pressurised chamber containing a mixture of saturated steam and air. They were determined as a function of the air-steam ratio in nominally stagnant conditions. The effect of pressure is assessed and preliminary measurements with a forced convective component of velocity are presented. A novel measurement technique was adopted, namely to use a vertical heat pipe whose conductance could easily be varied. It transported heat from an evaporator located inside the chamber to a condenser section outside, at which the heat flow was measured. Heat flux at the evaporator could then be determined and a condensation heat transfer coefficient derived. The range of coefficients covered was from 150 W/m2 0K at high air-steam ratios to 20,000 W/m2 0K in pure steam. Results show that increasing either total pressure or velocity enhances condensation heat transfer over the range of air/steam ratios considered. (author)

195

Evaluation of heat transfer coefficient of tungsten filaments at low pressures and high temperatures  

International Nuclear Information System (INIS)

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.

196

Comparison of boiling heat transfer coefficient and pressure drop correlations for evaporators  

International Nuclear Information System (INIS)

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)

197

The influence of a heat transfer coefficient probe on fluid flow near wall  

Directory of Open Access Journals (Sweden)

Full Text Available Good knowledge of the convective boundary condition is necessary for finite element analysis of thermal deformation behavior in machine tools. There are a number of correlation equations for natural and forced convection and several correlations for mixed convection. Due to a relatively wide range of dimensions, temperatures and speeds, all regimes of convective heat transfer can be observed in machine tools, including the transition region between laminar and turbulent free convection, characterized by Rayleigh number values ranging between Ra = 108 – 109. Since convection in machine tools is highly influenced by external and internal factors, the heat transfer coefficient characterizing convective heat transfer and its changes has to be evaluated experimentally. An experimental technique for evaluating the heat transfer coefficient on the wall and its changes between the wall and the ambient air, based on an active sensor, is being developed. Since the probe dimensions are not negligible, given the fluid motion structures near the wall which are induced by buoyancy or by forced flow, the influence of the probe has to be considered. Paper deals with latest experimental results and summarizes previous work.

Mareš Martin

2012-04-01

198

Sensitivity analysis of dose coefficients for 239Pu to transfer rates  

International Nuclear Information System (INIS)

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)

199

Evaluation of heat transfer coefficient of supercritical water flowing inside a tube using CFD code fluent  

International Nuclear Information System (INIS)

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 k? turbulence model, nonequilibrium wall function,viscous heating, full buoyancy effect and including wall roughness effect.In this paper model constants for standard k? 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 5, 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)

200

Effect of blade tip geometry on heat transfer coefficients on gas turbine blade tips and near tip regions  

International Nuclear Information System (INIS)

Detailed heat transfer coefficient distributions on two types of gas turbine blade tip, plane tip and squealer tip, were measured using a hue-detection base transient liquid crystals technique. The heat transfer coefficients on the shroud and near tip regions of the pressure and suction sides of the blade were also measured. The heat transfer measurements were taken at the three different tip gap clearances of 1.0%, 1.5%, and 2.5% of blade span. Results show the overall heat transfer coefficients on the tip and shroud with squealer tip blade were lower than those with plane tip blade. By using squealer tip, however, the reductions of heat transfer coefficients near the tip regions of the pressure and suction sides were not remarkable

201

Transient liquid-crystal technique used to produce high-resolution convective heat-transfer-coefficient maps  

Science.gov (United States)

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.

1993-01-01

202

Immersion Condensation on Oil-Infused Heterogeneous Surfaces for Enhanced Heat Transfer  

Science.gov (United States)

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.

Xiao, Rong; Miljkovic, Nenad; Enright, Ryan; Wang, Evelyn N.

2013-06-01

203

Neoclassical transport coefficients for tokamaks with bean-shaped flux surfaces  

International Nuclear Information System (INIS)

Simple analytic representations of the neoclassical transport coefficients for indented flux surfaces are presented. It is shown that a transport coefficient for an indented flux surface can be expressed in terms of a linear combination of the previously known transport coefficients for two nonindented flux surfaces. Numerical calculations based on actual equilibria from the PBX-M tokamak indicate that, even for modestly indented flux surfaces, the ion neoclassical thermal transport can be over a factor of two smaller than in a circular plasma with the same midplane radius or with the equivalent areas. 6 refs., 5 figs., 1 tab

204

Effect of pressure on heat transfer coefficient at the metal/mold interface of A356 aluminum alloy  

DEFF Research Database (Denmark)

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.

Fardi Ilkhchy, A.; Jabbari, Masoud

2012-01-01

205

Measurement of convectional heat transfer coefficients in a primary containment vessel with outer pool  

International Nuclear Information System (INIS)

New concepts with passive safety systems that use no active compounds, such as pumps, have been recently developed for next-generation nuclear power plants. In these concepts, several ideas and their combination of passive components were adopted for emergency core cooling and residual heat removal systems. For the residual heat removal system, utilization of natural circulation heat transfer in water pools was proposed as a passive containment cooling system (PCCS), which removes decay heat from the primary containment vessel (PCV) during loss-of-coolant accidents (LOCAs). This system consists of a suppression pool (S/P) and an outer pool (O/P), which are set adjacently inside and outside of the steel PCV wall. The core decay heat during LOCA is released through a break as steam and is led into the S/P. The injected steam condenses there, resulting a pool temperature rise. The adsorbed heat in the S/P is transferred to the O/P by convection in both pools and thermal conduction through the steel PCV wall. The heat transferred to the O/P is finally released to the atmosphere by vaporization of the O/P water. Estimation of the convectional heat transfer coefficients in both pools is necessary to predict the heat removal capability in this system precisely. The heat transfer coefficients measured in this study are useful for the design of the next-generation nuclear reactor as the fundamental thermal-hydraulic data in the primary containment vessel with the outer pool containment vessel with the outer pool

206

Development of a New Correlation for Condensation Heat Transfer Coefficient inside a Vertical Tube in the Presence of Noncondensable Gas  

International Nuclear Information System (INIS)

Even a small amount of noncondensable gas can reduce the condensation heat transfer considerably. In the condenser tube, the condensate flows as an annular liquid film adjacent to the tube wall, while the vapor/noncondensable gas mixture flows in the core region. Consequently, the noncondensable gas layer that forms adjacent to the liquid/gas interface reduces the heat transfer capability. Several correlations were developed to evaluate steam condensation heat transfer with noncondensable gas in a vertical condenser tube. In this study, two empirical correlations proposed by Vierow and Schrock and Kuhn are considered and a new correlation is developed to improve the accuracy of prediction. In these correlations, the local heat transfer coefficient is simply expressed in the form of a 'degradation factor,' defined as the ratio of the experimental heat transfer coefficient to a reference heat transfer coefficient

207

Correlations for heat transfer coefficients in open gaps with respect to mixed convection  

International Nuclear Information System (INIS)

Published results on mixed convection phenomena have been applied to determine the convective heat transfer between the cover gas and the open gaps in the roof of SNR 2. It has been reported in the literature that heat transfer coefficients for forced flow conditions in vertical heated or cooled pipes are modified by buoyancy effects. In the ''aiding'' condition, where buoyancy and flow act in the same direction, heat transfer is enhanced. In the ''opposing'' case heat transfer is reduced. This applies for laminar flow; the reverse is true for turbulent flow. The literature indicates furthermore that: the Reynolds number indicating turbulent flow can be as low as 30 for mixed convection; the criterion for the onset of mixed convection is given by the Richardson number Ri=Gr/Re2 > 0,002. The published results have been modified in consistency with the open gaps in the SNR 2 reactor roof. Several heat transfer correlations have been evaluated and their suitability examined. (author)

208

Instantaneous determination of heat transfer coefficients in a steam generator for an alternative energy upgrade system  

Energy Technology Data Exchange (ETDEWEB)

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.

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

209

Study of oxygen mass transfer coefficient and oxygen uptake rate in a stirred tank reactor for uranium ore bioleaching  

International Nuclear Information System (INIS)

Highlights: ? Mass transfer coefficient does not depend on biomass concentration. ? The pulp density has a negative effect on mass transfer coefficient. ? The pulp density is the unique factor that affects maximum OUR. ? In this work, Neale’s correlation is corrected for prediction of mass transfer coefficient. ? 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

210

Prediction of forced convective boiling heat transfer coefficient of pure refrigerants and binary refrigerant mixtures inside a horizontal tube  

International Nuclear Information System (INIS)

Forced convective boiling heat transfer coefficients were predicted for an annular flow inside a horizontal tube for pure refrigerants and nonazeotropic binary refrigerant mixtures. The heat transfer coefficients were calculated based on the turbulent temperature profile in liquid film and vapor core considering the composition difference in vapor and liquid phases, and the nonlinearity in mixing rules for the calculation of mixture properties. The heat transfer coefficients of pure refrigerants were estimated within a standard deviation of 14% compared with available experimental data. For nonazeotropic binary refrigerant mixtures, prediction of the heat transfer coefficients was made with a standard deviation of 18%. The heat transfer coefficients of refrigerant mixtures were lower than linearly interpolated values calculated from the heat transfer coefficients of pure refrigerants. This degradation was represented by several factors such as the difference between the liquid and the overall compositions, the conductivity ratio and the viscosity ratio of both components in refrigerant mixtures. The temperature change due to the concentration gradient was a major factor for the heat transfer degradation and the mass flux itself at the interface had a minor effect

211

Determination of heat and mass transfer coefficients in a rotary shaker used in fermentation processes  

Directory of Open Access Journals (Sweden)

Full Text Available In this paper the volumetric oxygen transfer (kLa and overall heat transfer (Ua coefficients were determined in flasks which were subjected to rotary shaker action, also provided with a temperature control chamber. Likewise, it was determined the effect over such coefficients of some parameters like surrounding temperature, shaking speed, closure type, liquid volume, capacity and baffles presence or absence in each flask, to determine the optimal work conditions in the rotary shaker. The used liquid in these experiments was distilled water. The kLa and Ua coefficients were also determined in the alcoholic fermentation of glucose by Saccharomyces cerevisiae yeast, in order to establish comparison standards. The maximum and minimum values of referred coefficients to distilled water and the operation conditions were:   kLa of 6.2 x 10-3 s-1, working at 25 ºC, 100 rpm, 50 ml of liquid volume, erlenmeyer of 500 ml with baffles and plastic closure. kLa of 4.107 x 10-3 s-1, working at 45 ºC, 60 rpm, 150 ml of liquid volume, erlenmeyer of 250 ml without baffles and cotton closure. Ua of 31.9963 J/min °C, working at 45 ºC, 150 rpm, 150 ml of liquid volume, erlenmeyer of 500 ml with baffles and cotton closure. Ua of 6.0179 J/min °C, working at 35 ºC, 60 rpm, 50 ml of liquid volume, erlenmeyer of 250 ml without baffles and plastic closure. The kLa and Ua values in the alcoholic fermentation and the operation conditions were: kLa of 2.6 x 10-4 s-1 and Ua of 12.8907 J/min °C, working at 35 °C, 150 rpm, 150 ml of liquid volume, Erlenmeyer of 250 ml, with baffles and cotton closure.  

Mario Arias Zabala

2011-12-01

212

Determining the surface roughness coefficient by 3D Scanner  

OpenAIRE

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 curren...

Karmen Fifer Bizjak

2010-01-01

213

Effect of Mass on Convective Heat Transfer Coefficient During Onion Flakes Drying  

OpenAIRE

In this present study an open sun and greenhouse drying of onion flakes has been performed to study the effect of mass on convective heat transfer coefficient. Three sets of experiments with total quantity of onion as 300, 600 and 900 g were done. The onion was continuously dried for 33 h both in open sun and in the roof type even span greenhouse with floor area of 1.2 x 0.78 m2. Experiments were carried out during the months of October to December 2003 at IIT Delhi (28°35`N 72°12`E). Exper...

Tiwari, G. N.; Anil Kumar, *

2006-01-01

214

Mass Transfer Coefficient During Cathodic Protectionof Low Carbon Steel in Seawater  

OpenAIRE

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 wi...

Ameel Mohammed Rahman; Anees Abdullah Khadom; Hameed, Khalid W.

2009-01-01

215

Comparison of Theoretical and Experimental Mass Transfer Coefficients of Gases in Supported Ionic Liquid Membranes.  

Czech Academy of Sciences Publication Activity Database

Ro?. 118, 30 OCT (2013), s. 255-263. ISSN 1383-5866 R&D Projects: GA ?R GAP106/10/1194; GA MŠk(CZ) 7C11009 Grant ostatní: RFCS(XE) RFCR-CT-2010-00009; INP (IT) PON01_01840; HA MŠk(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

Kárászová, Magda; Šim?ík, Miroslav; Friess, K.; Randová, A.; Jansen, J. C.; R?ži?ka, Marek; Sedláková, Zuzana; Izák, Pavel

2013-01-01

216

Evaluation of the heat transfer coefficient at the metal-mould interface during flow  

OpenAIRE

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 da...

Konopka, Z.; ?a?giewka, M.; Zyska, A.

2007-01-01

217

Analysis of the transverse heat transfer coefficients in a dual channel ITER-type cable-in-conduit conductor  

CERN Document Server

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.

Marinucci, C; Bruzzone, P; Stepanov, B

2007-01-01

218

On-line analysis of local values of the heat transfer coefficient during a pressurized thermal shock  

International Nuclear Information System (INIS)

This paper investigates the determination of local, non-stationary values of the heat transfer coefficient (h) in the cooling phase of the pressurized thermal shock (PTS) events and in the cooling phase of the large scale PTS experiments

219

Three-fluid plasmas in star formation II. Momentum transfer rate coefficients  

CERN Document Server

The charged component of the insterstellar medium consists of atomic and molecular ions, electrons, and charged dust grains, coupled to the local Galactic magnetic field. Collisions between neutral particles (mostly atomic or molecular hydrogen) and charged species, and between the charged species themselves, affect the magnetohydrodynamical behaviour of the medium and the dissipation of electric currents. The friction force due to elastic collisions between particles of different species in the multi-component interstellar plasma is a nonlinear function of the temperature of each species and the Mach number of the relative drift velocity. The aim of this paper is to provide an accurate and, as far as possible, complete set of momentum transfer rate coefficients for magnetohydrodynamical studies of the interstellar medium. Momentum transfer rates are derived from available experimental data and theoretical calculations of cross sections within the classic approach developed by Boltzmann and Langevin for a wid...

Pinto, Cecilia

2008-01-01

220

A review of measured values of the milk transfer coefficient (fsub(m)) for iodine  

International Nuclear Information System (INIS)

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)

221

Infrared Thermography applied to measurement of Heat transfer coefficient of water in a pipe heated by Joule effect  

OpenAIRE

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...

Leblay, P.; Henry, J. F.; Caron, D.; Leducq, D.; Bontemps, A.; Fournaison, L.

2012-01-01

222

A correlation for free convection heat transfer from vertical wavy surfaces  

Science.gov (United States)

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 ? = 0.05, 0.1, 0.2 and the Rayleigh numbers ranging from Ra l = 2.9 × 105 to 5.8 × 105. A finite-volume based code was developed to verify the experimental study and obtain the results for all the amplitude-wavelength ratios between ? = 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 ? = 0.2 and those surfaces with ? = 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.

Ashjaee, M.; Amiri, M.; Rostami, J.

2007-11-01

223

Measurement and modelling of forced convective heat transfer coefficient and pressure drop of Al2O3- and SiO2-water nanofluids  

International Nuclear Information System (INIS)

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.eat were properly modelled.

224

Measurement and modelling of forced convective heat transfer coefficient and pressure drop of Al2O3- and SiO2-water nanofluids  

Science.gov (United States)

Forced convective heat transfer coefficient and pressure drop of SiO2- and Al2O3-water nanofluids were characterized. The experimental facility was composed of thermal-hydraulic loop with a tank with an immersed heater, a centrifugal pump, a bypass with a globe valve, an electromagnetic flow-meter, a 18 kW in-line pre-heater, a test section with band heaters, a differential pressure transducer and a heat exchanger. The test section consists of a 1000 mm long aluminium pipe with an inner diameter of 31.2 mm. Eighteen band heaters were placed all along the test section in order to provide a uniform heat flux. Heat transfer coefficient was calculated measuring fluid temperature using immersed thermocouples (Pt100) placed at both ends of the test section and surface thermocouples in 10 axial locations along the test section (Pt1000). The measurements have been performed for different nanoparticles (Al2O3 and SiO2 with primary size of 11 nm and 12 nm, respectively), volume concentrations (1% v., 5% v.), and flow rates (3 103Re<105). Maximum heat transfer coefficient enhancement (300%) and pressure drop penalty (1000%) is obtained with 5% v. SiO2 nanofluid. Existing correlations can predict, at least in a first approximation, the heat transfer coefficient and pressure drop of nanofluids if thermal conductivity, viscosity and specific heat were properly modelled.

Julia, J. E.; Hernández, L.; Martínez-Cuenca, R.; Hibiki, T.; Mondragón, R.; Segarra, C.; Jarque, J. C.

2012-11-01

225

The variation of heat transfer coefficient, adiabatic effectiveness and aerodynamic loss with film cooling hole shape.  

Science.gov (United States)

The heat transfer coefficient and adiabatic effectiveness of cylindrical, fan shaped holes and a slot are presented for the region zero to 50 diameters downstream of the holes. Narrow-band liquid crystals were used on a heated flat plate with heated air coolant. These parameters have been measured in a steady state, low speed facility at engine representative Reynolds number based on hole diameter and pressure difference ratio (ideal momentum flux ratio). The aerodynamic loss due to each of the film cooling geometries has been measured using a traverse of the boundary layer far downstream of the film cooling holes. Compared to the cylindrical holes, the fan shaped hole case showed an improvement in the uniformity of cooling downstream of the holes and in the level of laterally averaged film cooling effectiveness. The fan effectiveness approached the slot level and both the fan and cylindrical hole cases show lower heat transfer coefficients than the slot and non film cooled cases based on the laterally averaged results. The drawback to the fan shaped hole was that the aerodynamic loss was significantly higher than both the slot and cylindrical hole values due to inefficient diffusion in the hole exit expansion. PMID:11460648

Sargison, J E; Guo, S M; Oldfield, M L; Rawlinson, A J

2001-05-01

226

Volumetric mass transfer coefficient and hydrodynamic study of a new self-inducing turbine  

International Nuclear Information System (INIS)

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

227

A comparative study of transfer coefficient of Iodine from grass to cow milk under equilibrium and postulated accidental scenario  

International Nuclear Information System (INIS)

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

228

Heat transfer to a thin liquid film with a free surface  

Science.gov (United States)

The numerically computed flow field and heat transfer coefficient are presented for the free surface flow of a thin liquid film in the presence or absence of a gravitational body force. The results of an approximate analysis using the Pohlhausen integral method is also discussed. The flow systems studied here include both plane and radial film flows in the presence or absence of a gravitational body force. The heating conditions include isothermal and uniformly heated surfaces. The transport conditions considered at the free surface are an adiabatic condition and an evaporative free surface maintained at its saturation temperature. The height of the free surface, flow field and heat transfer coefficient, were found to be strongly affected by the gravitational body force. They were also found to depend on the Reynolds number and Froude number of the incoming fluid. In the presence of gravity, a hydraulic jump was found to occur under some flow conditions.

Rahman, M. M.; Faghri, A.; Hankey, W. L.; Swanson, T. D.

1989-01-01

229

Heat and mass transfer rates during flow of dissociated hydrogen gas over graphite surface  

Science.gov (United States)

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.

Nema, V. K.; Sharma, O. P.

1986-01-01

230

The Tube Side Heat Transfer Coefficient for Enhanced Double Tube by Wilson Plot Analysis  

OpenAIRE

The purpose of the investigation presented in this study is to evaluate the tube side single phase heat transfer performance on the EXTEK (Twisted Multi-Head) tube. The geometry of the cross-section for a flow passage has an effect on its convective heat transfer capabilities. For concentric annuli in a double tube heat exchanger, the annular surface enhancement and tube profile enhancement play an important role. EXTEK (Twisted Multi-Head) uses twisted extrusion of a star shape tube for tube...

Raghavan, Vijay R.; Tiruselvam Ramahlingam

2011-01-01

231

Are spectroscopic factors from transfer reactions consistent with asymptotic normalization coefficients?  

International Nuclear Information System (INIS)

It is extremely important to devise a reliable method to extract spectroscopic factors from transfer cross sections. We analyze the standard DWBA procedure and combine it with the asymptotic normalization coefficient, extracted from an independent data set. We find that the single particle parameters used in the past generate inconsistent asymptotic normalization coefficients. In order to obtain a consistent spectroscopic factor, nonstandard parameters for the single particle overlap functions can be used but, as a consequence, often reduced spectroscopic strengths emerge. Different choices of optical potentials and higher order effects in the reaction model are also studied. Our test cases consist of 14C(d,p)15C(g.s.) at Edlab=14 MeV, 16O(d,p)17O(g.s.) at Edlab=15 MeV and 40Ca(d,p)41Ca(g.s.) at Edlab=11 MeV. We underline the importance of performing experiments specifically designed to extract asymptotic normalization coefficients for these systems

232

Calculation of effective diffusion coefficient in even approximations of the surface pseudo source method  

International Nuclear Information System (INIS)

The preference of even approximations of the surface pseudo source method for calculation of the diffusion coefficient is substantiated. The homogenization limit for the G0 approximation in the case of the cell size tending to zero is analytically proved.

233

Evaporation Heat Transfer of HCFC 22 on the Grooved Surfaces Inside a Horizontal Rectangular Channel  

Science.gov (United States)

The evaporation heat transfer performance on six kinds of grooved surface with 0.15 mm to 0.34 mm of the groove pitch was obtained using a rectangular channel. The upper and lower surfaces inside a horizontal rectangular channel, 10 mm in width, 5 mm in height, and 500 mm in length, were heated electrically by Nichrome heaters. HCFC 22 was used as a working fluid. Evaporating pressure was 0.49 MPa, heat flux was 4.65 kW/m2, vapor quality was varied from 0.1 to 0.9, and mass velocity was varied from 86 to 345 kg/(m2s). The empirical correlations to predict the heat transfer coefficients on upper and lower surfaces were proposed. The maximum heat transfer coefficient on upper surface is obtained on the grooved surface with 2 × 10-8 of the modified bond number. Heat transfer coefficient on lower surface isn't influenced by the groove geometries except for lead angle.

Kido, Osao; Uehara, Haruo

234

Analysis of Radome Using Aperture Integration-surface Integration Method with Modified Transmission Coefficient  

Science.gov (United States)

In this paper, the antenna-radome system in millimeter wave band is analyzed by the aperture integration-surface integration (AI-SI) method. When the electromagnetic wave passes through the radome, the transmission coefficient is determined by the transmission line analogy. However, the conventional transmission coefficient always ignores the phase factor of the lateral transmission in the dielectric. In the present work, the modified transmission coefficient is proposed and verified by both the theoretical derivation and the experimental measurement. The measured results of the antenna-radome systems at W-band show that the modified transmission coefficient is more accurate than the conventional one in the antenna-radome analysis.

Meng, Hongfu; Dou, Wenbin; Chen, Tiantian; Yin, Kai

2009-02-01

235

Pool Boiling Heat Transfer on the Inside Surface of an Inclined Tube  

International Nuclear Information System (INIS)

The present study is aimed at the determination of heat transfer characteristics on the inside surface of a tube while changing the inclination angle. Changes in pool boiling heat transfer coefficients on the inside surface of a 16.2 mm internal diameter has been studied experimentally at atmospheric pressure. Experiments were performed at six different inclination angles to investigate variations in the heat transfer coefficients due to the inclination angle change. Results for 30 .deg.???90 .deg. are almost same whereas the result for ? =15 .deg. is different from the other angles. To predict the heat transfer coefficients an empirical correlation has been developed as ?b 1/(A + Blnq). The developed correlation can predict the measured experimental data within ±4% error bound. Pool boiling is closely related with the design of passive type heat exchangers, which have been investigated in nuclear power plants to achieve safety functions in case of no power supply. Since the space for the installation of a heat exchanger is usually limited, developing more efficient heat exchangers is important. Several researchers have published results for the pool boiling on the outside surface. Jung et al. experimented boiling heat transfer in R-11 to investigate heat transfer mechanisms on the inside surface of a circular cylindrical tank. They simulated the surface by a flat plate. Somewhat detailed study on the inclination angle itself was previously done by Nishikawa et al. by using the combination of a plate and water. Jabardo and Filho performed an experimental study of forced convective boiling of refrigerants in a 12.7 mm internal diameter tube to investigate effects of physical parameters over the variations in local surface temperature. However, mechanisms of pool boiling are much different from those of the forced convective boiling. Kang investigated pool boiling heat transfer of water on the inside surface of a horizontal tube at atmospheric pressure. Experiments were performed at four different azimuthal angles to investigate variations in local heat transfer coefficients along the tube periphery. The local coefficient changes much along the tube periphery and the minimum was observed at the tube bottom. Summarizing the previous works, it is identified that the study for pool boiling heat transfer on the inside surface of a tube is very rare

236

Application of a Fuzzy Neural Network for Modeling of the Mass-Transfer Coefficient in a Stirred Tank Bioreactor  

OpenAIRE

A type of a fuzzy neural network for mathematical modeling of the volumetric mass-transfer coefficient is presented in the paper. Performed investigations show that the presented fuzzy neural network can be successfully used for modeling of such a complex process, like mass-transfer.

Mitko Petrov; Tatiana Ilkova; Stoyan Tzonkov; Uldis Viesturs

2005-01-01

237

Thermocouple error correction for measuring the flame temperature with determination of emissivity and heat transfer coefficient.  

Science.gov (United States)

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

Hindasageri, V; Vedula, R P; Prabhu, S V

2013-02-01

238

Thermocouple error correction for measuring the flame temperature with determination of emissivity and heat transfer coefficient  

Science.gov (United States)

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

239

Adhesion energy between mica surfaces: Implications for the frictional coefficient under dry and wet conditions  

Science.gov (United States)

frictional strength of faults is a critical factor that contributes to continuous fault slip and earthquake occurrence. Frictional strength can be reduced by the presence of sheet-structured clay minerals. In this study, two important factors influencing the frictional coefficient of minerals were quantitatively analyzed by a newly developed computational method based on a combination of first-principles study and thermodynamics. One factor that helps reduce the frictional coefficient is the low adhesion energy between the layers under dry conditions. Potassium ions on mica surfaces are easily exchanged with sodium ions when brought into contact with highly concentrated sodium-halide solutions. We found that the surface ion exchange with sodium ions reduces the adhesion energy, indicating that the frictional coefficient can be reduced under dry conditions. Another factor is the lubrication caused by adsorbed water films on mineral surfaces under wet conditions. Potassium and sodium ions on mica surfaces have a strong affinity for water molecules. In order to remove the adsorbed water molecules confined between mica surfaces, a differential compressive stress of the order of tens of gigapascals was necessary at room temperature. These water molecules inhibit direct contact between mineral surfaces and reduce the frictional coefficient. Our results imply that the frictional coefficient can be modified through contact with fluids depending on their salt composition. The low adhesion energy between fault-forming minerals and the presence of an adsorbed water film is a possible reason for the low frictional coefficient observed at continuous fault slip zones.

Sakuma, Hiroshi

2013-12-01

240

Heat transfer coefficient calculation for analysis of ITER shield block using CFX and ANSYS  

International Nuclear Information System (INIS)

Highlights: ? Benchmark HTC modeling in CFX and compare this modeling with empirical formulas. ? Given the error formulas derived from theory. ? 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.

241

Effect of the mass transfer coefficient on the erosion-corrosion rate of specimens tested in the Ciroco loop  

International Nuclear Information System (INIS)

The erosion-corrosion rate of steels should theoretically depend upon the mass transfer coefficient of the outflow. It is shown with 2 examples: 1) Erosion-corrosion after a steam generator orifice used in some nuclear plant. In this case actual thickness of metal erosion are available. Mass transfer is estimated by a polarographic method. 2) Erosion corrosion produced by impact of a jet. A parallel between the mass transfer coefficients obtained by polarography and the measurements of corrosion depths permits a verification of this dependence

242

Determination of the metal/die interfacial heat transfer coefficient of high pressure die cast B390 alloy  

International Nuclear Information System (INIS)

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.

243

Determination of the metal/die interfacial heat transfer coefficient of high pressure die cast B390 alloy  

Science.gov (United States)

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.

Cao, Yongyou; Guo, Zhipeng; Xiong, Shoumei

2012-07-01

244

Computer Simulation of Electron Transfer at Hematite Surfaces  

International Nuclear Information System (INIS)

Molecular dynamics simulations in combination with ab initio calculations were carried out to determine the rate of electron transfer in bulk hematite (?-Fe2O3) and at two low-index surfaces, namely the (012) and (001) surfaces. The electron transfer reactions considered here involve the II/III valence interchange between nearest-neighbor iron atoms. Two electron transfer directions were investigated namely the basal plane and c direction charge transfers. Electron transfer rates obtained in bulk hematite were in good agreement with ab initio electronic structure calculations thus validating the potential model. The surfaces were considered both in vacuum and in contact with an equilibrated aqueous solution. The reorganization energy is found to increase significantly at the first surface layer and this value is little affected by the presence of water. In addition, in the case of the (012) surface, the electronic coupling matrix element for the topmost basal plane transfer was calculated at the Hartree-Fock level and was found to be weak compared to the corresponding charge transfer in the bulk. Therefore, most surfaces show a decrease in the rate of charge transfer at the surface. However, where iron atoms involved in the charge transfer reaction are directly coordinated to water molecules, water lowers the free energy of activation to a great extent and provides a large driving force for electrons to diffuse toward the bulk thus opposing the intrinsic surface effec thus opposing the intrinsic surface effect. The surfaces considered in this work show different charge transfer properties. Hematite has been shown to exhibit anisotropic conductivity and thus different surfaces will show different intra- and inter-layer rates depending on their orientation. Moreover, the calculations of charge transfers at the hydroxyl- and iron-terminated (001) surfaces revealed that surface termination has a significant effect on the charge transfer parameters in the vicinity of the surface. Finally, our findings indicate that undercoordinated terminal iron atoms could act as electron traps at the surface

245

Electron transfer in gas surface collisions  

International Nuclear Information System (INIS)

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.)

246

Dependence of dose coefficients for 239Pu on transfer rates and absorption parameters  

International Nuclear Information System (INIS)

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 fro 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)

247

Low-Flow Film Boiling Heat Transfer on Vertical Surfaces  

DEFF Research Database (Denmark)

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 coefficient versus the film length is obtained. The Helmholtz instability for the steam-liquid interface is analyzed, and it is shown that films beyond a certain length are unstable. Assuming the most unstable wavelength for disturbances at the steam-liquid interface is a reasonable expression for the film length, an average film boiling heat transfer coefficient is obtained.

Munthe Andersen, J. G.; Dix, G. E.

1976-01-01

248

Dependence of the complete set of spin transfer coefficients on effective interaction in nuclear medium  

International Nuclear Information System (INIS)

Multistep direct reactions 40Ca(p, p'x) at 392 MeV and 40Ca(p, nx) at 346 MeV are analyzed including up to three-step process. The double differential inclusive cross sections and the complete set of spin transfer coefficients Dij are calculated by the semiclassical distorted wave model and compared with experimental data. We use single particle wave functions in a Woods-Saxon potential incorporating the Wigner transform of a one-body density matrix and also introduce a phenomenological effective mass m* of a nucleon in the target. Analysis of Dij in terms of an effective interaction in nuclear medium is also done. (author)

249

Condensation heat transfer coefficient in horizontal stratified cocurrent flow of steam and cold water  

International Nuclear Information System (INIS)

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)

250

Microstructure Simulation of Al-Cu Alloy Based on Inverse Identified Interfacial Heat Transfer Coefficient  

Science.gov (United States)

The interfacial heat transfer coefficient (IHTC) is taken as one of the most important factors affecting the accuracy of the simulation. In the present paper, the IHTC variation with temperature was obtained by an inverse heat conduction method. Then, a 3D cellular automaton-finite element method was adopted to predict the microstructure of an Al-Cu alloy based on the identified IHTC. It was found that the IHTC was of prime importance for the precise simulation of solidification microstructure, especially in the grains distribution. In addition, the simulated results using the IHTC variation with temperature were found to exhibit a better agreement with the experimental results than those using the constant value.

Bu, X. B.; Li, L. X.; Zhang, L. Q.; Zhu, B. W.; Xu, R.; Wang, S. P.

2013-09-01

251

Estimation of overall heat transfer coefficient of cooling system in RF capacitive hyperthermia  

Directory of Open Access Journals (Sweden)

Full Text Available The study presented in this article involves the estimation of the overall heat transfer coefficient of cooling system in RF capacitive hyperthermia treatment using inverse problem based on the conjugate gradient method to provide improved distribution of temperature. The temperature data computed numerically from the direct problem using the finite difference time domain method are used to simulate the temperature measurements. The effects of the errors and sensor positions upon the precision of the estimated results are also considered. The results show that a reasonable estimation of the unknown can be obtained. Finally, measurements in a tissue-equivalent phantom are employed to appraise the reliability of the presented method. The comparison of computed data with measurements shows a good agreement between numerical and experimental results.

Mohammad Hasan Zahmatkesh

2013-05-01

252

EXPERIMENTAL INVESTIGATION OF HEAT TRANSFER ENHANCEMENT OVER THE DIMPLED SURFACE  

OpenAIRE

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 dimpl...

Borse, Dr Sachin L.; Patel, Iftikarahamad H.

2012-01-01

253

Experimental measurements of heat transfer coefficient in a partially/fully opened tilted cavity  

Energy Technology Data Exchange (ETDEWEB)

An experimental investigation was carried out to determine the heat transfer coefficient from a rectangular tilted cavity to the ambient due to the buoyancy driven flow in the cavity. The cavity is partially or fully open from one side. All the walls of the cavity are adiabatic except the wall facing the cavity opening which is heated at a constant heat flux. Air was used as the cavity fluid and the experiments were carried out at a flux Grashof number of 5.5 {times} 10{sup 8}. The tilt angle of the cavity, measured from the vertical direction, was changed between {minus}90 deg to +90 deg in 15 deg increments. Also, geometries of aspect ratio (height-to-width of cavity) of 1.0, 0.5, and 0.25 and of opening ratio (opening height to cavity height) of 1.0, 0.5, and 0.25 were considered in the study. The results are presented in terms of the average Nusselt number for different values of the above experimental parameters. Conclusions are derived for the effect of changing the tilt angle, the aspect ratio, or the opening ratio of the cavity on the average heat transfer coefficient between the cavity and the ambient air. Buoyancy-driven flow in rectangular cavities has been widely investigated by many researchers. This geometry is of special interest in many solar applications such as in solar passive heating, solar concentrators, and solar central receivers. The importance of the geometry extends to other engineering applications such as electronic equipment, fire research, and energy conservation in buildings.

Chakroun, W.; Elsayed, M.M.; Al-Fahed, S.F. [Kuwait Univ. (Kuwait). Mechanical and Industrial Engineering Dept.

1997-11-01

254

Numerical study of turbulent fluid flow and heat transfer in lateral perforated extended surfaces  

International Nuclear Information System (INIS)

Numerical study has been performed in this study to investigate the turbulent convection heat transfer on a rectangular plate mounted over a flat surface. Thermal and fluid dynamic performances of extended surfaces having various types of lateral perforations with square, circular, triangular and hexagonal cross sections are investigated. RANS (Reynolds averaged Navier–Stokes) based modified k–? turbulence model is used to calculate the fluid flow and heat transfer parameters. Numerical results are compared with the results of previously published experimental data and obtained results are in reasonable agreement. Flow and heat transfer parameters are presented for Reynolds numbers from 2000 to 5000 based on the fin thickness. - Highlights: • Lateral perforation shape has significant effects on fin thermal performance. • Solid fins have higher skin friction coefficient value than the perforated ones. • Triangular perforated fins have the lowest skin friction coefficient value. • Hexagonal perforated fins show better thermal and fluid dynamic performances

255

Heat/Mass transfer measurement on concave surface in rotating jet impingement  

International Nuclear Information System (INIS)

The objective of this paper is to investigate the heat/mass transfer characteristics on a concave surface for rotating impinging jets. The jet with Reynolds number of 5,000 is applied to the concave surface and the flat surface, respectively. The rotating experiments have been carried out at the rotating speed of 560RPM which is corresponding to Ro number of 0.075. The two jet orientation (front and trailing orientation) are considered. Detailed heat/mass transfer coefficients on the target plate were measured using a naphthalene sublimation method. The result indicates that the rotation leads to change in local heat/mass transfer distributions and the slight increase in the Sh level. The front orientation induces asymmetric Sh distributions, whereas the trailing orientation shows the shifted heat/mass transfer feature due to rotation-induced flow behavior. The crossflow effect on heat/mass transfer is also observed as the stream wise direction increases. Compared to flat surface, the heat/mass transfer on the concave surface is enhanced with increasing the spanwise direction due to the curvature effect, providing the higher averaged Sh value. It is proved that the difference of surface geometry affects somewhat the local and averaged heat/mass transfer regardless of rotation condition

256

Determination of surface tension coefficient of liquids by diffraction of light on capillary waves  

International Nuclear Information System (INIS)

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)

257

A Method for Estimating Mass-Transfer Coefficients in a Biofilter from Membrane Inlet Mass Spectrometer Data  

DEFF Research Database (Denmark)

A membrane inlet mass spectrometer (MIMS) was used in combination with a developed computer model to study and improve management of a biofilter (BF) treating malodorous ventilation air from a meat rendering facility. The MIMS was used to determine percentage removal efficiencies (REs) of selected 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 combination with computer modeling. Udgivelsesdato: February

Nielsen, Anders Michael; Nielsen, Lars Peter

2009-01-01

258

Simulation of Convective Heat-Transfer Coefficient in a Buried Exchanger  

Directory of Open Access Journals (Sweden)

Full Text Available This study presents analytical models allowing to study a forced convection laminar flow in non-established dynamic and thermic regimes. We treated a flow in a bitubular exchanger in permanent thermal contact with a semi-infinite medium, such as the ground. The wall temperature as well as the wall heat flux evolve in the course of time until a quasi-steady mode. The theoretical method is original because it uses Green's functions method to determine the analytical solutions of the heat propagation equation on the wall during the heating phase. These analytical solutions allow to identify the temperature distribution versus time. The complexity of the system geometry as well as the infinity of the medium surrounding the exchanger make the traditional methods of numerical resolution unable to solve the problem. We used, to solve it, the finite volume method coupled with the finite element method at the boundary. We studied the effect of Reynolds number, the fluid entry temperature and the transfer duration on the axial evolution of the heat transfer coefficient. We illustrated also the profile of the temperature field in the fluid medium.

Taoufik Mnasri

2008-01-01

259

Effect of heat transfer coefficient on sheath and fuel centreline temperatures in SCWRS  

International Nuclear Information System (INIS)

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)

260

Heat Transfer Coefficient Distribution in the Furnace of a 300MWe CFB Boiler  

Science.gov (United States)

Properly understanding and calculating the distributions of heat flux and heat transfer coefficient (?) in the furnace is important in designing a circulating fluidized bed (CFB) boiler, especially with supercritical parameters. Experimental study on the heat transfer in a commercial 300MWe CFB boiler was conducted. The ? from the bed to the water wall was measured by the finite element method (FEM), at five different heights. The influence of suspension density and bed temperature on ? was analyzed. It was found that the pressure difference between the inlet and exit of the three cyclones, and the chamber pressure of the corresponding loop seal were not equal. The results indicated the suspension solid density was non-uniform in the cross section at a certain height. Consequently, the distributions of heat flux and ? in the horizontal plane in the furnace was non-uniform. The furnace can divided into three sections according to the arrangement of the platen superheaters hanging in the upper CFB furnace. In each section, the heat flux near the center showed increasing trend.

Zhang, P.; Lu, J. F.; Yang, H. R.; Zhang, J. S.; Zhang, H.; Yue, G. X.

261

Approximate heat transfer coefficients based on variable thermophysical properties for laminar flow over a uniformly heated flat plate  

Energy Technology Data Exchange (ETDEWEB)

New heat transfer coefficient approximations are developed for forced laminar flow over a uniformly heated flat plate at zero incidence angle. The development is based on solving the variable property boundary layer equations using a variable property similarity transform that incorporates an adjustable similarity scaling constant. The scaling constants value is iteratively adjusted until the scaled temperature gradient-at-the-wall value is equal to the small temperature difference value. The resulting scaled profiles are nearly congruent. The congruency scaling constant is then approximated in terms of simple functions of the kinematic viscosity and the Prandlt number evaluated at the plate and free stream temperatures. The approximate scaling constants are used to form new approximations for the heat transfer coefficient. The new approximate coefficients are compared to traditional coefficients for four gases and six liquid flows covering the range 0.5 < Pr < 3,000 with large temperature differences. (orig.)

Weyburne, David W. [AFRL/SNHC, Hanscom AFB, MA (United States)

2008-05-15

262

Concentration Dependence of Pool Nucleate Boiling Heat Transfer Coefficients for R134a and Polyolester Oil System  

Science.gov (United States)

This paper presents experimental results of the concentration dependence of heat transfer coefficients for mixtures of R134a and polyolester (POE) oil under the conditions of pool nuc1eateboiling. The experiments are conducted by means of ah horizontal platinum wire at saturation tel11peraturesof 9, 19, and 29°C and at oil concentrations from 0 to 8 mass%. The present results show that the boiling heat transfer coefficient for the system concerned decreases with increasing oil concentration as a whole but increases slightly at a low oil concentration of about 4 mass%. A correlation equation is also given as a function of heat flux, temperature and oil concentration to reproduce the experimental boiling heat transfer coefficient within an uncertainly of about±15%.

Sato, Tomoaki; Takaishi, Yoshinori; Oguchi, Kosei

263

Rhodium self-powered detectors transfer regime influence on fuel and emitter material depletion correction coefficients in RBMK-1000 reactors  

International Nuclear Information System (INIS)

The influence of the rhodium self-powered detector transition regime in the RBMK-1000 reactor on correction coefficients taking into account fuel and emitter material burnups is considered. It is shown that application of the known correction coefficients dependence on burnup after the detector transfer into another fuel channel is possible only taking into account the channel power generation and time-integrated current produced by the detector for the moment of transition. 4 refs., 3 figs

264

Measurement of subcooled boiling pressure drop and local heat transfer coefficient in horizontal tube under LPLF conditions  

International Nuclear Information System (INIS)

Highlights: ? Measured subcooled boiling pressure drop and local heat transfer coefficient in horizontal tubes. ? Infra-red thermal imaging is used for wall temperature measurement. ? 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 (450–935 kg/m2 s) and inlet subcooling (29 °C, 50 °C and 70 °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)

265

Heat transfer and friction coefficients for air flow in a smooth annulus  

International Nuclear Information System (INIS)

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.)

266

Stress-intensity-factor influence coefficients for surface flaws in pressure vessels  

International Nuclear Information System (INIS)

In the fracture-mechanics analysis of reactor pressure vessels, stress-intensity-factor influence coefficients are used in conjunction with superposition techniques to reduce the cost of calculating stress-intensity factors. The present study uses a finite-element code, together with a virtual crack extension technique, to obtain influence coefficients for semielliptical surface flaws in a cylinder, and particular emphasis was placed on mesh convergence (less than 1% error was sought in the results from any one mesh construction parameter). Comparison of the coefficients with those obtained by other investigators shows good agreement. Furthermore, stress-intensity factors obtained by superposition for a severe thermal-transient loading condition agree within 1% of the values calculated by a direct finite-element method. Influence coefficients were calculated for three specific axially oriented semielliptical surface flaws. The first was a 2-m-long inner-surface flaw in a nuclear reactor pressure vessel with depth-to-wall-thickness ratios between 0.2 and 0.9. The second was an inner-surface flaw in the reactor vessel with a surface-length-to-depth ratio of 6 and with depth-to-wall-thickness ratios between 0.05 and 0.2. The third was a 1-m-long flaw on the outer surface of a test vessel with depth-to-wall-thickness ratios between 0.1 and 0.9. For the reactor vessel, separate coefficients were calculated for the cladding on the inner surface and for the base-material regnner surface and for the base-material region. This allows for an accurate accounting of the effect of thermal stresses in the cladding on the stress-intensity factor for surface flaws that extend through the cladding into the base material

267

Determination of coefficients for the universal laws of friction and heat transfer for CFTL calculations  

International Nuclear Information System (INIS)

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

268

Heat Transfer Enhancement of Water Spray Cooling by the Surface Roughness Effect  

International Nuclear Information System (INIS)

Water spray cooling has been widely used in a variety of industrial applications. The present study concentrated on quantitative measurements of the heat flux and heat transfer coefficient by water spray as it impinges on the rough surface of a hot steel plate at 900 .deg. C. A novel experimental technique was developed for a high temperature heat flux gauge with a test block, cartridge heaters, and thermocouples that was used to measure the surface heat flux information on the hot steel plate for local heat flux measurements. The roles of the surface roughness on heat transfer are presented in this paper for well-characterized four rough surfaces with average rms roughness heights of 40-80 ?m. The results show that the local heat transfer for rough surfaces is higher than that for a smooth surface. Heat transfer can be significantly increased by the presence of surface roughness elements, which can disrupt the thin thermal boundary layer. In addition, the heat transfer enhancement mechanism on a rough surface can be investigated by a different boiling regime

269

Determination of unidirectional heat transfer coefficient during unsteady-state solidification at metal casting-chill interface  

International Nuclear Information System (INIS)

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

270

Determination of unidirectional heat transfer coefficient during unsteady-state solidification at metal casting-chill interface  

Energy Technology Data Exchange (ETDEWEB)

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/m{sup 2} K and 6.5-5 kW/m{sup 2} K, respectively.

Sahin, Haci Mehmet [Gazi Ueniversitesi, Teknik Egitim Fakueltesi, Teknikokullar, Ankara 06503 (Turkey)]. E-mail: mesahin@gazi.edu.tr; Kocatepe, Kadir [Gazi Ueniversitesi, Teknik Egitim Fakueltesi, Teknikokullar, Ankara 06503 (Turkey); Kayikci, Ramazan [Sakarya Ueniversitesi, Teknik Egitim Fakueltesi, Sakarya (Turkey); Akar, Neset [Gazi Ueniversitesi, Teknik Egitim Fakueltesi, Teknikokullar, Ankara 06503 (Turkey)

2006-01-15

271

Evaluation of fission-product gases in program GAPCON series and FREG-3 to estimate the gap heat transfer coefficient  

International Nuclear Information System (INIS)

In safety evaluation of a fuel rod, estimation of the stored energy in the fuel rod is indispensable. For this estimation, the temperature distribution in the fuel rod is calculated. Most important in determination of the temperature distribution is the gap heat transfer coefficient (gap conductance) between pellet surface and cladding inner surface. Under fuel rod operating condition, the mixed gas in the gap is composed of He, Xe and Kr. He is initial seald gas. Xe and Kr are fission-product gases, of which the quantities depend on the fuel burn-up. In program GAPCON series (GAPCON and GAPCON-THERMAL-1 and -2) and FREG-3, these quantities are given as a function of the irradiation time, power rating and neutron flux in estimation of the thermal conductivity of the mixed gas. The methods of calculating the quantities of Xe and Kr in the programs have been examined. Input of the neutron flux which influences F.P. gas production rates is better than the determination from the fuel-rod power rating. (auth.)

272

Impact of External Pressure on the Heat Transfer Coefficient during Solidification of Al-A356 Alloy  

DEFF Research Database (Denmark)

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 and compared with data in literature which shows acceptable agreement.

Jabbari, Masoud; Ilkhchy, A.Fardi

273

Transfer coefficients in a four-cusp duct simulating a typical nuclear reactor channel degraded by accident  

International Nuclear Information System (INIS)

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)

274

Effect of temperature and pressure on the overall heat transfer coefficient in VHTR-based SI process heat exchangers  

Energy Technology Data Exchange (ETDEWEB)

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.

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

275

Surface charge and hydrodynamic coefficient measurements of Bacillus subtilis spore by optical tweezers.  

Science.gov (United States)

In this work we report on the simultaneous measurement of the hydrodynamic coefficient and the electric charge of single Bacillus subtilis spores. The latter has great importance in protein binding to spores and in the adhesion of spores onto surfaces. The charge and the hydrodynamic coefficient were measured by an accurate procedure based on the analysis of the motion of single spores confined by an optical trap. The technique has been validated using charged spherical polystyrene beads. The excellent agreement of our results with the expected values demonstrates the quality of our procedure. We measured the charge of spores of B. subtilis purified from a wild type strain and from two isogenic mutants characterized by an altered spore surface. Our technique is able to discriminate the three spore types used, by their charge and by their hydrodynamic coefficient which is related to the hydrophobic properties of the spore surface. PMID:24583259

Pesce, Giuseppe; Rusciano, Giulia; Sasso, Antonio; Isticato, Rachele; Sirec, Teja; Ricca, Ezio

2014-04-01

276

Experimental study on the influence of SO2 gas injection to pure liquids on pool boiling heat transfer coefficients  

Science.gov (United States)

SO2 gas is injected into the different pure liquids using new innovative method via meshed tubes. Many experiments have been performed to investigate the influence of gas injection process on the pool boiling heat transfer coefficient of pure liquids around the horizontal cylinder at different heat fluxes up to 114 kW m-2. Results demonstrate that presence of SO2 gas into the vapor inside the bubbles creates a mass transfer driving force between the vapor phase inside the formed bubbles and liquid phase and also between the gas/liquid interfaces. Local turbulences and agitations due to the gas injection process around the nucleation sites leads the pool boiling heat transfer coefficient to be dramatically enhanced. Besides, some of earlier well-known correlations were unable to obtain the reasonable values for the pool boiling heat transfer coefficients in this particular case. Therefore, the most accurate correlation among the examined correlations was modified to estimate the pool boiling heat transfer coefficient of pure liquids. Experimental data were in a good agreement with those of obtained by the new modified correlation with absolute average deviation of 10 %.

Sarafraz, M. M.; Hormozi, F.; Peyghambarzadeh, S. M.; Salari, E.

2014-06-01

277

Measurements of heat transfer coefficients at low contact pressures for actively cooled bolted armour concepts in Tore Supra  

International Nuclear Information System (INIS)

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 limitercalculations (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

278

Effect of surface wettability on carbon nanotube water-based nanofluid droplet impingement heat transfer  

Science.gov (United States)

Recent studies into droplet impingement heat transfer have demonstrated that it has great potential for providing high heat flux cooling in areas such as thermal management of electronics. The wettability of the surface affects the flow dynamics of the impingement process and the resulting heat transfer. In this study, the effect of surface wettability on carbon nanotube water-based nanofluid droplet impingement heat transfer has been studied and compared with water. Superhydrophobic or hydrophilic coatings are applied on one face of monocrystalline silicon wafers (the drop impinges on this face) while the other face is painted matt black to permit infrared thermography. The silicon wafer is preheated to 40 °C and a single droplet impinges normally on the top facing coated surface of the monocrystalline silicon wafer. The inverse heat conduction problem has been solved using the measured black face temperature. For both the water and nanofluid droplets, the convective heat transfer coefficient reduces with the decrease in surface wettability. It is found that the nanofluid produce a significantly higher convective heat transfer coefficient during droplet impingement than water, with the enhancement increasing with increasing wettability.

Jackson, Robert Gordon; Kahani, Mostafa; Karwa, Nitin; Wu, Alex; Lamb, Robert; Taylor, Robert; Rosengarten, Gary

2014-07-01

279

Turbulent bulk transfer coefficients and ozone deposition velocity in the International Consortium for Atmospheric Research into Transport and Transformation  

Science.gov (United States)

In this paper, we examine observations of shallow, stable boundary layers in the cool waters of the Gulf of Maine between Cape Cod, Massachusetts, and Nova Scotia, obtained in the 2004 New England Air Quality Study (NEAQS-04), which was part of the International Consortium for Atmospheric Research into Transport and Transformation (ICARTT). The observations described herein were made from the NOAA Research Vessel Ronald H. Brown. The ship was instrumented for measurements of meteorological, gas-phase and aerosol atmospheric chemistry variables. Meteorological instrumentation included a Doppler lidar, a radar wind profiler, rawinsonde equipment, and a surface flux package. In this study, we focus on direct comparisons of the NEAQS-04 flux observations with the COARE bulk flux algorithm to investigate possible coastal influences on air-sea interactions. We found significant suppression of the transfer coefficients for momentum, sensible heat, and latent heat; the suppression was correlated with lighter winds, more stable surface layers, S-SE wind direction, and lower boundary layer heights. Analysis of the details shows the suppression is not a measurement, stability correction, or surface wave effect. The correlation with boundary layer height is consistent with an interpretation that our measurements at 18-m height do not realize the full surface flux in shallow boundary layers. We also find that a bulk Richardson number threshold of 0.1 gives a better estimate of boundary layer height than 0.25 or 0.5. Mean ozone deposition velocity is estimated as 0.44 mm s-1, corresponding to a boundary removal timescale of about 1 day.

Fairall, C. W.; Bariteau, L.; Grachev, A. A.; Hill, R. J.; Wolfe, D. E.; Brewer, W. A.; Tucker, S. C.; Hare, J. E.; Angevine, W. M.

2006-12-01

280

Pseudoparticle approach for charge-transferring molecule-surface collisions  

Science.gov (United States)

Based on a semiempirical generalized Anderson-Newns model, we construct a pseudoparticle description for electron emission due to deexcitation of metastable molecules at surfaces. The pseudoparticle approach allows us to treat resonant charge-transfer and Auger processes on an equal footing, as it is necessary when both channels are open. This is, for instance, the case when a metastable N2(3?u+) molecule hits a diamond surface. Using nonequilibrium Green functions and physically motivated approximations to the self-energies of the Dyson equations, we derive a system of rate equations for the probabilities with which the metastable N2(3?u+) molecule, the molecular ground state N2(1?g+), and the negative ion N2-(2?g) can be found in the course of the scattering event. From the rate equations, we also obtain the spectrum of the emitted electron and the secondary electron emission coefficient. Our numerical results indicate the resonant tunneling process undermining the source of the Auger channel, which therefore contributes only a few percent to the secondary electron emission.

Marbach, Johannes; Bronold, Franz Xaver; Fehske, Holger

2012-09-01

281

Estimation of the friction coefficient between wheel and rail surface using traction motor behaviour  

International Nuclear Information System (INIS)

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.

282

A Comparative Study of the Effect of Variation of Inside Diameter of Condenser and Mass Flow Rate on the Heat Transfer Coefficient in a Domestic Refrigerator.  

Directory of Open Access Journals (Sweden)

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.

Rajesh Joshi

2014-02-01

283

Mass transfer coefficient of tritium from molten lithium-lead alloy (Li17Pb83) to environmental gas under neutron irradiation  

International Nuclear Information System (INIS)

The mass transfer coefficient of tritium from molten Li17Pb83 alloy to environmental gas was determined by in-situ tritium release experiments under neutron irradiation in the temperature range from 400 to 700deg C. The tritium residence time in the sample in Al2O3 crucible was measured and a tritium release model was applied to obtain the mass transfer coefficient. The mass transfer coefficient decreased with increasing H2 partial pressure in He sweep gas up to 104 Pa at 600deg C, and its maximum value was 5.1x10-3[m s-1]. At 103 Pa in H2 pressure, it was expressed as follows: KD=2.5x10-3[m s-1]xexp(-30.7[kJ mol-1]/RT). From the dependence of KD on H2 pressure and the value of the activation energy in KD, it was concluded that the rate-controlling process is a liquid film diffusion above 103 Pa in H2 pressure while, below 102 Pa, some surface reaction was considered to be a rate-controlling process. (orig.)

284

Mean heat transfer coefficients during the evaporation of 1,1,1,2-tetrafluoroethane (R-134a) in a plate heat exchanger  

OpenAIRE

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...

EMILA DJORDJEVIC; STEPHAN KABELAC; SLOBODAN SERBANOVIC

2007-01-01

285

Mass Transfer Coefficient During Cathodic Protectionof Low Carbon Steel in Seawater  

Directory of Open Access Journals (Sweden)

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.

Ameel Mohammed Rahman

2009-01-01

286

Carbon dioxide heat transfer coefficients and pressure drops during flow boiling: Assessment of predictive methods  

Energy Technology Data Exchange (ETDEWEB)

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)

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

287

Transfer coefficient of 226Ra from vegetation to meadow voles, Microtus pennsylvanicus, on U mill tailings  

International Nuclear Information System (INIS)

The 226Ra level in vegetation growing on U mine tailings in Elliot Lake, Ontario, Canada, was 211 + 22 mBq g-1 (dry weight) compared to less than 7 mBq g-1 (dry weight) in material from a control site. Skeletons of meadow voles (Microtus pennsylvanicus) established on the tailings had concentrations of 226Ra of 6083 +/- 673 mBq per animal in winter; 7163 +/- 1077 mBq per animal in spring; 1506 +/- 625 mBq per animal in summer; and 703 +/- 59 mBq per animal in fall, compared to less than 7 mBq per animal in controls. The 226Ra transfer coefficient from vegetation to voles (defined as total millibecquerels of 226Ra in adult vole per total millibecquerels of 226Ra consumed by the vole in its lifetime) was calculated as 4.6 +/- 2.9 X 10(-2) in summer and 2.8 +/- 0.6 X 10(-2) in fall

288

Transfer coefficient of 226Ra from vegetation to meadow voles, Microtus pennsylvanicus, on U mill tailings  

Energy Technology Data Exchange (ETDEWEB)

The 226Ra level in vegetation growing on U mine tailings in Elliot Lake, Ontario, Canada, was 211 + 22 mBq g-1 (dry weight) compared to less than 7 mBq g-1 (dry weight) in material from a control site. Skeletons of meadow voles (Microtus pennsylvanicus) established on the tailings had concentrations of 226Ra of 6083 +/- 673 mBq per animal in winter; 7163 +/- 1077 mBq per animal in spring; 1506 +/- 625 mBq per animal in summer; and 703 +/- 59 mBq per animal in fall, compared to less than 7 mBq per animal in controls. The /sup 226/Ra transfer coefficient from vegetation to voles (defined as total millibecquerels of /sup 226/Ra in adult vole per total millibecquerels of 226Ra consumed by the vole in its lifetime) was calculated as 4.6 +/- 2.9 X 10(-2) in summer and 2.8 +/- 0.6 X 10(-2) in fall.

Cloutier, N.R.; Clulow, F.V.; Lim, T.P.; Dave, N.K.

1986-06-01

289

Influence of coefficient of transfer of regulators on energyconsumption of automated climatic systems ??????? ???????????? ???????? ??????????? ?? ????????????? ? ?????????????????? ????????????? ????????  

Directory of Open Access Journals (Sweden)

Full Text Available The authors argue that efficient energy saving methods installable into civil buildings include energy saving technologies, cost-efficient and fast-payback technologies, improvement of process flowsheets and patterns of microclimate systems, and automation of engineering systems and installations.Processes of unsteady heat exchange inside premises having automated climatic systems are considered in this article. Advanced methods of analysis of thermal modes of premises are provided. Interrelation between separate parameters of thermal stability in a room and automated microclimate control is another subject of research. The formula designated for the calculation of the coefficient of transfer of regulators is derived by the authors.The ultimate result is identified using the methodology of assessment of influenceof dynamic properties of a room produced on the value of K. The proposed methodol-ogy may be used to develop engineering recommendations concerning selection of the optimal operating mode of regulators designated for engineering installations.The conclusion is substantiated by numerical calculations made using specialized software and graphic examples.??????????? ???????? ??????????????? ??????????? ? ?????????, ????????????? ??????????????????? ?????????????? ?????????. ???????? ??????????? ?????? ??????? ????????? ?????? ?????????. ??????????? ??????????? ????? ?????????? ??????????? ????????????????? ????????? ? ?????????????? ?????????????? ?????? ??????????? ????????????. ???????? ????????? ??? ??????? ???????????? ???????? ??????????. ???????? ??????? ???????????? ???????? ?????????? ?? ????????? ????????????????? ????????? ??????????? ????????????. ?????????? ?????????? ??????? ?? ???????? ??????????????? ????????????? ? ????? ????????? ???????????????????. ?????? ????????????????? ?????????? ????????? ? ??????? ????????? ????????? ?? ??? ? ???????????? ?????????.

Samarin Oleg Dmitrievich

2013-03-01

290

Application effect of region temperature coefficients and improvement of heat transfer analysis model in HTGR  

International Nuclear Information System (INIS)

A HTTR (High Temperature Engineering Test Reactor), which has a thermal output of 30 MW, a coolant inlet temperature of 395degC and a coolant outlet temperature of 850degC/950degC, is a first high-temperature gas-cooled reactor (HTGR) in Japan. The HTGR has a high inherent safety potential to accidents. The safety demonstration tests such as the reactivity insertion and the coolant flow reduction tests using the HTTR are underway in order to demonstrate such excellent inherent safety features of HTGRs. These tests demonstrate that the rapid increase or decrease in the reactor power is restrained by only the negative reactivity feedback effect without an operation of the reactor power control system, and the temperature transient of the reactor is slow. A one-point core dynamics approximation with one fuel channel model could not simulate accurately the reactor power behavior. On the other hand, an original new method using region temperature coefficients and a connection between some fuel channel models and whole core component model for calculating radial heat transfer in the core is adopted. It is crucial to evaluate this method precisely to simulate a performance of HTGR with showing excellent inherent safety features under the reactivity incident by gas circulator tripping error. (author)

291

Effect of Lubricant Viscosity and Surface Roughness on Coefficient of Friction in Rolling Contact  

Directory of Open Access Journals (Sweden)

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.

S.G. Ghalme

2013-12-01

292

Effect of variable heat transfer coefficient on tissue temperature next to a large vessel during radiofrequency tumor ablation  

Directory of Open Access Journals (Sweden)

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 1–2 min, the attained coagulation zone obtained with both time-varying h and constant h does not differ significantly. However, for short duration ablation (5–10 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.

Pinheiro Cleber

2008-07-01

293

Determination of condensing heat transfer coefficients and two-phase flow regimes for dichlorotetrafluoroethane refrigerant (R-114)  

International Nuclear Information System (INIS)

Experimental condensing heat transfer coefficients for R-114 flowing in a horizontal tube were compared with those calculated by the classical Nusselt correlation and with a new prediction method of Rohsenow. It was determined that the Rohsenow method provides satisfactory agreement with the experimental data and that the coefficients calculated by the Nusselt correlation were much too low. A concurrent study of flow regimes was also made by observing the flow patterns in a glass section just downstream of the condensing section. The regimes observed agree reasonably well with a Baker map that was previously developed from theoretical considerations. An improved correlation was also developed for estimating the inside heat transfer coefficients for water in an annulus

294

Recombination coefficients of deuterium on metal surfaces evaluated from ion-driven permeation  

International Nuclear Information System (INIS)

The surface recombination coefficients of deuterium for polycrystalline Ni, Fe, Cu, and Ag were evaluated from the flux of ion-driven permeation. These data agreed rather quantitatively with semi-theoretical estimations based on a simple consideration of equilibrium. This demonstrates that the release kinetics is dominated by the activation barrier for adsorption as well as the solubility. (orig.)

295

Partition coefficients and thermodynamics of transfer of novel drug-like spiro-derivatives in model biological solutions  

International Nuclear Information System (INIS)

Highlights: ? Partition coefficients octanol/buffer of new drug-like spiro-derivatives were determined. ? Thermodynamic functions of transfer were calculated. ? 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

296

On development of analytical closure relationships for local wall friction, heat and mass transfer coefficients for sub-channel codes  

International Nuclear Information System (INIS)

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)

297

Evaluation of interfacial mass transfer coefficient as a function of temperature and pressure in carbon dioxide/normal alkane systems  

Science.gov (United States)

CO2 gas injection is known as one of the most popular enhanced oil recovery techniques for light and medium oil reservoirs, therefore providing an acceptable mass transfer mechanism for CO2-oil systems seems necessary. In this study, interfacial mass transfer coefficient has been evaluated for CO2-normal heptane and CO2-normal hexadecane systems using equilibrium and dynamic interfacial tension data, which have been measured using the pendant drop method. Interface mass transfer coefficient has been calculated as a function of temperature and pressure in the range of 313-393 K and 1.7-8.6 MPa, respectively. The results showed that the interfacial resistance is a parameter that can control the mass transfer process for some CO2-normal alkane systems, and cannot be neglected. Additionally, it was found that interface mass transfer coefficient increased with pressure. However, the variation of this parameter with temperature did not show a clear trend and it was strongly dependent on the variation of diffusivity and solubility of CO2 in the liquid phase.

Nikkhou, Fatemeh; Keshavarz, Peyman; Ayatollahi, Shahab; Jahromi, Iman Raoofi; Zolghadr, Ali

2014-09-01

298

Saturated flow boiling of water in a narrow channel: time-averaged heat transfer coefficients and correlations  

International Nuclear Information System (INIS)

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 ±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 iable and that a better understanding of the mechanisms of boiling in narrow channels is necessary to guide the development of correlations

299

Experimental Heat Transfer Coefficients and Friction Factors in a Rib-Roughened Leading-Edge Cooling Cavity of a Gas Turbine Airfoil  

Science.gov (United States)

A gas turbine airfoil contains multiple coolant passageways. These passages usually have rib roughened wall surfaces in order to increase the heat transfer from the blade to the cooling air. Auxiliary power and compressed air is very valuable in a gas turbine, therefore low pumping power requirements are crucial. The thermal performance of three different coolant channel geometries with three different rib sizes was investigated. Heat transfer calculations were performed for Reynolds numbers ranging from 6,000 to 40,000. The performance characteristics were calculated through the use of the convective heat transfer coefficient and the friction factor. In this study, the most desirable characteristics are a high heat transfer coefficient and minimal pumping power requirements. The thermal performance of each case was determined by comparing the average Nusselt numbers to the friction factor ratio. The resulting value was then plotted against the Reynolds number for each case. The trending data indicated thermal efficiency decreases with an increasing Reynolds number for all cases. The picture data shows increased thermal efficiency at larger distances from the nose portion of the cavity. In addition, thermal efficiency was higher at the half distance of the rib pitch while areas close to the ribs saw a lower thermal efficiency. The following experimental data will show that Rig 2 and 3 are the most thermally efficient geometries, with Rig 2 requiring lower pumping power and Rig 3 having a higher average Nusselt number.

Hagan, Peter

300

Confirmation of selected milk and meat radionuclide transfer coefficients. Third technical progress report, September 1984-August 1985  

International Nuclear Information System (INIS)

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

301

Effect of azimuthal variation of heat-transfer coefficient and pellet-cladding gap on fuel-pin cladding deformation  

International Nuclear Information System (INIS)

The importance of azimuthal temperature variation upon the diametral strain of PWR zircaloy cladding at fuel pin failure is discussed and causes of temperature gradients are considered. A correlation between the surface heat-transfer coefficient profile and the pitch-to-diameter ratio of the pin bundle has been incorporated in the ADVICE computer code. This enables the code to calculate the temperature distribution in a segment of the fuel pin and hence to predict the deformation of the fuel cladding, both before and after contact with adjacent rods. The code also predicts the bowing of the cladding and relative movement between the fuel pellet and the cladding. Two postulated loss-of-coolant flow histories have been studied using the ADVICE code, and estimates of the deformation histories and the failure strains are presented. In the first case the cladding failed while in the alpha phase and the failure strain was limited by temperature gradients caused by unstable bowing. In the second, the cladding started to change phase before cladding substantial deformation had occurred and it hardly bowed at all. In this case, the cladding temperature remained relatively uniform and a higher failure strain was predicted. (author)

302

Rough surfaces with enhanced heat transfer for electronics cooling by direct metal laser sintering  

OpenAIRE

Experimental evidences are reported on the potential of direct metal laser sintering (DMLS) in manufacturing flat and finned heat sinks with a remarkably enhanced convective heat transfer coefficient, taking advantage of artificial roughness in fully turbulent regime. To the best of our knowledge, this is the first study where artificial roughness by DMLS is investigated in terms of such thermal performances. On rough flat surfaces, we experience a peak of 73 % for the convective heat transfe...

Calignano, Flaviana; Asinari, Pietro; Chiavazzo, Eliodoro; Manfredi, Diego Giovanni; Ventola, Luigi

2014-01-01

303

Heat transfer enhancement and surface thermostabilization for pool boiling on porous structures  

OpenAIRE

The scope of the article includes the description of the experimental setup, methodology of the experimental studies, the study results for pool boiling heat transfer coefficient encountered on sintered capillary porous coverings. The results of own studies presented here refer to the boiling in a large volume on copper fibrous coverings. Hysteresis type I, II and III were described. Several examples of capillary porous surface coverings applications in purposely chosen complex boiling heat t...

Wojcik Tadeusz Michal

2012-01-01

304

A detailed experimental investigation of a perforated heat transfer surface applied to gas turbine recuperators  

OpenAIRE

An effort is made to explain and improve the understanding of the mechanisms behind the thermo-hydraulic performance of perforated extended surfaces used in compact heat exchangers in the laminar flow regime (Re D = 400-2500). A transient liquid crystal technique, which uses Helium as operating fluid, together with digital image photographic processing have been used to provide measurements of local heat transfer coefficients for this geometry. This work has found that through the use of perf...

Adams, Jc; Ireland, Pt; Oswald, J.

2003-01-01

305

Convective heat transfer from rough surfaces with two-dimensional ribs - transitional and laminar flow  

International Nuclear Information System (INIS)

Measurements of friction factor and heat transfer coefficients for two rods of 18.9 mm 0.D. with two-dimensional roughness, each in two different outer smooth tubes have been performed in turbulent and laminar flow. The turbulent flow results indicate that the flow was not thermally fully established, the isothermal data however agree reasonably well with our previously obtained general correlation. Laminar flow results can be correlated best when the Reynolds and Greatz numbers are evaluated at the temperature average between the temperature of the inner rod surface and of the outer smooth surface of the annulus, the average being weighted over the two surfaces. (orig.)

306

Enhanced heat transfer surface for cast-in-bump-covered cooling surfaces and methods of enhancing heat transfer  

Science.gov (United States)

An annular turbine shroud separates a hot gas path from a cooling plenum containing a cooling medium. Bumps are cast in the surface on the cooling side of the shroud. A surface coating overlies the cooling side surface of the shroud, including the bumps, and contains cooling enhancement material. The surface area ratio of the cooling side of the shroud with the bumps and coating is in excess of a surface area ratio of the cooling side surface with bumps without the coating to afford increased heat transfer across the element relative to the heat transfer across the element without the coating.

Chiu, Rong-Shi Paul (Glenmont, NY); Hasz, Wayne Charles (Pownal, VT); Johnson, Robert Alan (Simpsonville, SC); Lee, Ching-Pang (Cincinnati, OH); Abuaf, Nesim (Lincoln City, OR)

2002-01-01

307

Heating surface material’s effect on subcooled flow boiling heat transfer of R134a  

Energy Technology Data Exchange (ETDEWEB)

In this study, subcooled flow boiling of R134a on copper (Cu) and stainless steel (SS) heating surfaces was experimentally investigated from both macroscopic and microscopic points of view. By utilizing a high-speed digital camera, bubble growth rate, bubble departure size, and nucleation site density, were able to be observed and analyzed from the microscopic point of view. Macroscopic characteristics of the subcooled flow boiling, such as heat transfer coefficient, were able to be measured as well. Experimental results showed that there are no obvious difference between the copper and the stainless surface with respect to bubble dynamics, such as contact angle, growth rate and departure size. On the contrary, the results clearly showed a trend that the copper surface had a better performance than the stainless steel surface in terms of heat transfer coefficient. It was also observed that wall heat fluxes on both surfaces were found highly correlated with nucleation site density, as bubble hydrodynamics are similar on these two surfaces. The difference between these two surfaces was concluded as results of different surface thermal conductivities.

Ling Zou; Barclay G. Jones

2012-11-01

308

Studies on soil to grass transfer factor (Fv) and grass to milk transfer coefficient (Fm) for cesium in Kaiga region  

International Nuclear Information System (INIS)

Detailed studies were carried out to establish site-specific soil to grass transfer factors (Fv) and grass to cow milk transfer coefficients (Fm) for radioactive cesium (137Cs) and stable cesium (Cs) for Kaiga region, where a nuclear power station has been in operation for more than 10 years. The study included adopted cows, cows of local farmers, and cows from the dairy farm. A grass field was developed specifically for the study and 2 local breed cows were adopted and allowed to graze in this grass field. The soil and grass samples were collected regularly from this field and analyzed for the concentrations of 137Cs and stable Cs to evaluate the soil to grass Fv values. The milk samples from the adopted cows were analyzed for the 137Cs and stable Cs concentrations to evaluate Fm values. For comparison, studies were also carried out in dominant grazing areas in different villages around the nuclear power plant and the cows of local farmers which graze in these areas were identified and milk samples were collected and analyzed regularly. The geometric mean values of Fv were found to be 1.1 × 10?1 and 1.8 × 10?1 for 137Cs and stable Cs, respectively. The Fm of 137Cs had geometric mean values of 1.9 × 10?2 d L?1 and 4.6 × 10?2 d L?1, respectively, for adopted Cows 1 and 2; 1.7 × 10?2 d L?1 for the cows of local farmers, and 4.0 × 10?3 d L?1 for the dairy farm cows. The geometric mean values of Fm for stable Cs were similar to those of 137Cs. The Fm value for the dairy farm cows was an order of magnitude lower than those for local breed cows. The Fm values observed for the local breed cows were also an order of magnitude higher when compared to the many values reported in the literature and in the IAEA publication. Possible reasons for this higher Fm values were identified. The correlation between Fv and Fm values for 137Cs and stable Cs and their dependence on the potassium content (40K and stable K) in the soil and grass were also studied. In order to estimate the ingestion dose accurate data of the dietary habits of the population was necessary and this data was collected through a well planned demographic survey. The internal doses to a child due to the ingestion of 137Cs along with the milk of the local cows and from the dairy farm were found to be 0.29 ?Sv y?1 and 0.04 ?Sv y?1,while that to an adult were 0.39 ?Sv y?1 and 0.05 ?Sv y?1, respectively. -- Highlights: • This is a detailed study on Fv and Fm for 137Cs and stable Cs around the Kaiga nuclear power plant, India. • The geometric mean values of Fv were found to be 1.1 × 10?1 and 1.8 × 10?1 for 137Cs and stable Cs, respectively. • The Fm value for 137Cs for the local breed cows was estimated to be 2.4 × 10?2 d L?1. • The Fm value for dairy farm cows (4.0 × 10?3 d L?1) was an order of magnitude lower than those for local breed cows. • The reasons for the higher Fm values for 137Cs for the local breed cows are identified

309

Studies on soil to grass transfer factor (Fv) and grass to milk transfer coefficient (Fm) for cesium in Kaiga region.  

Science.gov (United States)

Detailed studies were carried out to establish site-specific soil to grass transfer factors (Fv) and grass to cow milk transfer coefficients (Fm) for radioactive cesium ((137)Cs) and stable cesium (Cs) for Kaiga region, where a nuclear power station has been in operation for more than 10 years. The study included adopted cows, cows of local farmers, and cows from the dairy farm. A grass field was developed specifically for the study and 2 local breed cows were adopted and allowed to graze in this grass field. The soil and grass samples were collected regularly from this field and analyzed for the concentrations of (137)Cs and stable Cs to evaluate the soil to grass Fv values. The milk samples from the adopted cows were analyzed for the (137)Cs and stable Cs concentrations to evaluate Fm values. For comparison, studies were also carried out in dominant grazing areas in different villages around the nuclear power plant and the cows of local farmers which graze in these areas were identified and milk samples were collected and analyzed regularly. The geometric mean values of Fv were found to be 1.1 × 10(-1) and 1.8 × 10(-1) for (137)Cs and stable Cs, respectively. The Fm of (137)Cs had geometric mean values of 1.9 × 10(-2) d L(-1) and 4.6 × 10(-2) d L(-1), respectively, for adopted Cows 1 and 2; 1.7 × 10(-2) d L(-1) for the cows of local farmers, and 4.0 × 10(-3) d L(-1) for the dairy farm cows. The geometric mean values of Fm for stable Cs were similar to those of (137)Cs. The Fm value for the dairy farm cows was an order of magnitude lower than those for local breed cows. The Fm values observed for the local breed cows were also an order of magnitude higher when compared to the many values reported in the literature and in the IAEA publication. Possible reasons for this higher Fm values were identified. The correlation between Fv and Fm values for (137)Cs and stable Cs and their dependence on the potassium content ((40)K and stable K) in the soil and grass were also studied. In order to estimate the ingestion dose accurate data of the dietary habits of the population was necessary and this data was collected through a well planned demographic survey. The internal doses to a child due to the ingestion of (137)Cs along with the milk of the local cows and from the dairy farm were found to be 0.29 ?Sv y(-1) and 0.04 ?Sv y(-1),while that to an adult were 0.39 ?Sv y(-1) and 0.05 ?Sv y(-1), respectively. PMID:23685702

Karunakara, N; Ujwal, P; Yashodhara, I; Rao, Chetan; Sudeep Kumara, K; Dileep, B N; Ravi, P M

2013-10-01

310

Data Qualification Report For DTN: MO0012RIB00065.002, Parameter Values For Transfer Coefficients  

Energy Technology Data Exchange (ETDEWEB)

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.

C.H. Tung

2001-01-09

311

Data Qualification Report For DTN: MO0012RIB00065.002, Parameter Values For Transfer Coefficients  

International Nuclear Information System (INIS)

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

312

Radiocesium uptake and transfer coefficients in reindeer and lichens in Sub-Arctic Finnmark  

International Nuclear Information System (INIS)

Full text: Nuclear tests in the atmosphere were made by several nations during the period 1945-1962 and individual tests have occurred later, the latest in October 1980. These tests resulted in local and regional deposition of fission products, non-fissioned material and activation products. Additionally, high yield nuclear detonations caused injection of radioactive debris to the stratosphere, resulting in world-wide fallout of radionuclides, continuing even several years after the detonations. Furthermore, the Chernobyl accident in 1986 caused considerable fallout over areas both inside and outside of the former USSR. The weather conditions were such that considerable quantities of the released radioactive material were brought by prevailing winds to different parts of the Saami region. The reindeer herding community is in general considered to be the most vulnerable population in Norway in regard to deposition of airborne radionuclides following a potential foreign nuclear accident. A more comprehensive understanding of radionuclide uptake and transfer coefficients in reindeers is important in an emergency preparedness perspective, and is currently being approached by studying differences in Radiocesium contents between different reindeer herds and forage availability. Finnmark reindeers are grazing lichen predominantly during winter, with a lower intake during the rest of the year. Lichens have a high ability to absorb radionuclides directly from precipitation, they grow slowly and have a long lifespan, resulting in relatively long biological half-life of the absorbed radioactivity. Muscle samples for domestic reindeer (Rangifer tarandus tarandus) have been collected for several different reindeer herding districts in Finnmark in the period 2004-2008. The reindeer herding districts are located north of 69 degrees N and between 20 degrees - 30 degrees E. Lichens and soil samples are collected from the winter grazing pasture for the respective reindeer herds for the same period. (author)

313

Heat transfer enhancement and surface thermostabilization for pool boiling on porous structures  

Directory of Open Access Journals (Sweden)

Full Text Available The scope of the article includes the description of the experimental setup, methodology of the experimental studies, the study results for pool boiling heat transfer coefficient encountered on sintered capillary porous coverings. The results of own studies presented here refer to the boiling in a large volume on copper fibrous coverings. Hysteresis type I, II and III were described. Several examples of capillary porous surface coverings applications in purposely chosen complex boiling heat transfer processes have been presented based on Wojcik and Poniewski patents.

Wojcik Tadeusz Michal

2012-04-01

314

Experimental study on augmentation of nucleate boiling heat transfer on nano porous surfaces  

International Nuclear Information System (INIS)

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

315

Effects of bridge cable surface roughness and cross-sectional distortion on aerodynamic force coefficients  

DEFF Research Database (Denmark)

Theoretical and experimental investigations to date have assumed that bridge cables can be modeled as ideal circular cylinders and the associated aerodynamic coefficients are invariant with the wind angle-of-attack. On the other hand, bridge cables are normally characterized by local alterations of their inherent surface roughness and shape, which might present a significant disturbance for the surrounding wind flow. The present study focuses on the experimental determination, based on static wind tunnel tests, of the aerodynamic coefficients of full-scale bridge cable section models both perpendicular and inclined to the flow, for varying wind angles-of-attack. The wind tunnel test results demonstrate that the aerodynamic coefficients of bridge cables can be significantly affected by the wind angle-of-attack.

Matteoni, G.; Georgakis, C.T.

2012-01-01

316

Heat transfer enhancement of free surface MHD-flow by a protrusion wall  

International Nuclear Information System (INIS)

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.

317

Transfer coefficients of energy in mass for X radiation-air: the kV relation and effective energy  

International Nuclear Information System (INIS)

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)

318

Ultrasonic reflection coefficient and surface roughness index of OA articular cartilage: relation to pathological assessment  

Directory of Open Access Journals (Sweden)

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.

Niu Hai-jun

2012-03-01

319

Heat transfer characteristics of large superconductors with different surface conditions  

International Nuclear Information System (INIS)

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)

320

On the determination of the overall heat transmission coefficient and soil heat flux for a fog cooled, naturally ventilated greenhouse: Analysis of radiation and convection heat transfer  

International Nuclear Information System (INIS)

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

321

Single droplet separations and surface partition coefficient measurements using laser ablation mass spectrometry.  

Science.gov (United States)

Surface activity of analytes plays a significant role in many chemical and physical phenomena. We present here a mass spectrometric method to characterize surface activity and solute partitioning between bulk liquid and the gas-liquid interface in droplets. The approach employs ablation by an infrared (IR) laser from the surface of a microliter droplet deposited on a stainless steel post. The ablated material is ionized for mass spectrometric analysis by either droplet charging or by postionization in an electrospray plume. Three areas of application have been explored using this method (1) separations in a single droplet: continuous ablation by a series of many successive laser pulses results in faster depletion of more surface active analytes, effectively comprising a surface activity-based separation. (2) Partition coefficient measurements: droplet volume is held constant during ablation by continually replenishing lost solvent. This leads to analyte-specific ion signal decay curves that may be fitted to a model based on Langmuir adsorption isotherms and simple analytical expressions, yielding quantitative values for the analyte surface partition coefficients. (3) Studies of the relationship between surface partitioning and high-performance liquid chromatography (HPLC) phase partitioning: comparisons of surface activities measured by laser desorption with retention times in reversed-phase HPLC reveal that the relationship between the two partitioning processes is very sensitive to chemical structure. Poor correlation between the retention time and surface activity is also observed within a subcategory of analytes (peptides). This effect is attributed to multimodal solute-stationary phase interactions. The laser desorption approach presented here provides direct information on analyte surface activities free from the complications encountered in chromatographic methods due to chemical structure variations. PMID:19886638

Jorabchi, Kaveh; Smith, Lloyd M

2009-12-01

322

Formation processes and secondary emission coefficients for H- production on alkali-coated surfaces  

International Nuclear Information System (INIS)

The formation of negative ions by hydrogen collisions on cesium-coated surfaces is discussed in the limiting cases where the resident cesium is either in the purely ionic state or in the purely atomic state. The survival fraction for negative ions moving away from a metal surface is calculated using a method employing complex eigenvalues. The fraction of surviving ions is found to be larger than calculated by previous workers. The secondary emission coefficient for negative ion production by incident atoms with energies of ten to one hundred electron volts is estimated to be in the range thirty to fifty percent. The secondary emission coefficient is found to be a sensitive function of the thickness of the alkali adsorbate coating for ion energies in the range below a few hundred electron volts

323

Transfer coefficients of 137Cs via the forage-cow-milk pathway in Aomori Prefecture of Japan  

International Nuclear Information System (INIS)

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)

324

A comparison of mass transfer coefficients between trickle-bed, hollow fiber membrane and stirred tank reactors.  

Science.gov (United States)

Trickle-bed reactor (TBR), hollow fiber membrane reactor (HFR) and stirred tank reactor (STR) can be used in fermentation of sparingly soluble gasses such as CO and H2 to produce biofuels and bio-based chemicals. Gas fermenting reactors must provide high mass transfer capabilities that match the kinetic requirements of the microorganisms used. The present study compared the volumetric mass transfer coefficient (K(tot)A/V(L)) of three reactor types; the TBR with 3 mm and 6 mm beads, five different modules of HFRs, and the STR. The analysis was performed using O2 as the gaseous mass transfer agent. The non-porous polydimethylsiloxane (PDMS) HFR provided the highest K(tot)A/V(L) (1062 h(-1)), followed by the TBR with 6mm beads (421 h(-1)), and then the STR (114 h(-1)). The mass transfer characteristics in each reactor were affected by agitation speed, and gas and liquid flow rates. Furthermore, issues regarding the comparison of mass transfer coefficients are discussed. PMID:23434811

Orgill, James J; Atiyeh, Hasan K; Devarapalli, Mamatha; Phillips, John R; Lewis, Randy S; Huhnke, Raymond L

2013-04-01

325

Evaluation of a Hue Capturing Based Transient Liquid Crystal Method for High-Resolution Mapping of Convective Heat Transfer on Curved Surfaces  

Science.gov (United States)

Accurate determination of convective heat transfer coefficients on complex curved surfaces is essential in the aerothermal design and analysis of propulsion system components. The heat transfer surfaces are geometrically very complex in most of the propulsion applications. This study focuses on the evaluation of a hue capturing technique for the heat transfer interpretation of liquid crystal images from a complex curved heat transfer surface. Impulsively starting heat transfer experiments in a square to rectangular transition duct are reported. The present technique is different from existing steady-state hue capturing studies. A real-time hue conversion process on a complex curved surface is adopted for a transient heat transfer technique with high spatial resolution. The study also focuses on the use of encapsulated liquid crystals with narrow color band in contrast to previous steady-state hue based techniques using wide band liquid crystals. Using a narrow band crystal improves the accuracy of the heat transfer technique. Estimated uncertainty for the heat transfer coefficient from the technique is about 5.9 percent. A complete heat transfer map of the bottom surface was possible using only seven liquid crystal image frames out of the 97 available frames during the transient experiment. Significant variations of heat transfer coefficients are quantitatively visualized on the curved surfaces of the transition duct.

Camci, C.; Kim, K.; Hippensteele, S. A.; Poinsatte, P. E.

1993-01-01

326

Energy barrier of proton transfer at ice surfaces  

Science.gov (United States)

We estimated the energy barrier of proton transfer on ice film surfaces through the measurement of the H/D exchange kinetics of H2O and D2O molecules. The isotopomeric populations of water molecules and hydronium ions on the surface were monitored by using the techniques of reactive ion scattering and low energy sputtering, respectively, along the progress of the H/D reaction. When hydronium ions were externally added onto an ice film at a temperature of 70 K, a proton was transferred from the hydronium ion mostly to an adjacent water molecule. The proton transfer distance and the H/D exchange rate increased as the temperature increased for 90-110 K. The activation energy of the proton transfer was estimated to be 10±3 kJ mol-1 on a polycrystalline ice film grown at 135 K. The existence of a substantial energy barrier for proton transfer on the ice surface agreed with proton stabilization at the surface. We also examined the H/D exchange reaction on a pure ice film surface at temperatures of 110-130 K. The activation energy of the reaction was estimated to be 17±4 kJ mol-1, which was contributed from the ion pair formation and proton transfer processes on the surface.

Moon, Eui-Seong; Yoon, Jinha; Kang, Heon

2010-07-01

327

The role of surface energy coefficient in heavy ion reactions and improved proximity model  

International Nuclear Information System (INIS)

In this work we have discussed dependence of surface tension coefficient that appears in proximity potential and energy of incident nucleus. The obtained results from study of the fusion barrier heights and positions for 44 reactions with z?8 reveal that this modification on the formalism of proximity model leads to a better agreement between computed fusion barrier heights and positions and experimental data. (author)

328

Experimental research on heat transfer coefficients for cryogenic cross-counter-flow coiled finned-tube heat exchangers  

Energy Technology Data Exchange (ETDEWEB)

The aim of present experimental research is to find out the suitable correlations for designing the coiled finned-tube heat exchangers used in cryogenic applications. In order to conduct above experimental study, cross-counter-flow coiled finned-tube heat exchangers were developed in our lab and used in actual refrigeration cycle. The experiments were conducted in the range of effective Reynolds number 500-1900. The effect of diametrical clearance on the prediction of overall heat transfer coefficient is also investigated experimentally. The results from present study were compared in the form of overall heat transfer coefficient. Results of present experimental research indicate that different correlations selected in the study can be used with reasonable accuracy for designing the coiled finned-tube heat exchangers, if they are applied with suitable method of calculation of free-flow cross-sectional area. A more accurate new correlation has also been proposed that fitted experimental data within {+-}10% error band. (author)

Gupta, Prabhat Kumar; Kush, P.K. [Cryogenics Section, Raja Ramanna Centre for Advanced Technology (RRCAT), Indore 452013, Madhya Pradesh (India); Tiwari, Ashesh [Institute of Engineering and Technology, DAVV, Indore, Madhya Pradesh (India)

2009-08-15

329

Infrared image filtering applied to the restoration of the convective heat transfer coefficient distribution in coiled tubes  

Science.gov (United States)

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.

Bozzoli, F.; Cattani, L.; Pagliarini, G.; Rainieri, S.

2015-03-01

330

The fuel to clad heat transfer coefficient in advanced MX-type fuel pins  

International Nuclear Information System (INIS)

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

331

An efficient method for transfer cross coefficient approximation in model based optical proximity correction  

Science.gov (United States)

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.

Sabatier, Romuald; Fossati, Caroline; Bourennane, Salah; Di Giacomo, Antonio

2008-10-01

332

Sustained frictional instabilities on nanodomed surfaces: Stick-slip amplitude coefficient  

DEFF Research Database (Denmark)

Understanding the frictional properties of nanostructured surfaces is important because of their increasing application in modern miniaturized devices. In this work, lateral force microscopy was used to study the frictional properties between an AFM nanotip and surfaces bearing well-defined nanodomes comprising densely packed prolate spheroids, of diameters ranging from tens to hundreds of nanometers. Our results show that the average lateral force varied linearly with applied load, as described by Amontons' first law of friction, although no direct correlation between the sample topographic properties and their measured friction coefficients was identified. Furthermore, all the nanodomed textures exhibited pronounced oscillations in the shear traces, similar to the classic stick-slip behavior, under all the shear velocities and load regimes studied. That is, the nanotextured topography led to sustained frictional instabilities, effectively with no contact frictional sliding. The amplitude of the stick-slip oscillations, ?f, was found to correlate with the topographic properties of the surfaces and scale linearly with the applied load. In line with the friction coefficient, we define the slope of this linear plot as the stick-slip amplitude coefficient (SSAC). We suggest that such stick-slip behaviors are characteristics of surfaces with nanotextures and that such local frictional instabilities have important implications to surface damage and wear. We thus propose that the shear characteristics of the nanodomed surfaces cannot be fully described by the framework of Amontons' laws of friction and that additional parameters (e.g., ?f and SSAC) are required, when their friction, lubrication, and wear properties are important considerations in related nanodevices. © 2013 American Chemical Society.

Quignon, Benoit; Pilkington, Georgia A.

2013-01-01

333

Chloride ingress prediction : Part 1: Analytical model for time dependent diffusion coefficient and surface concentration  

DEFF Research Database (Denmark)

Prediction of chloride ingress into concrete is an important part of durability design of reinforced concrete structures exposed to chloride containing environment. This paper presents the state-of-the art: an analytical model which describes chloride profiles in concrete as function of depth and time, and where both the surface chloride concentration and the diffusion coefficient are allowed to vary in time; the Mejlbro-Poulsen model is the general solution to Fick’s 2nd law. The paper also presents conversion formulas for the four decisive but rather abstract parameters to parameters, which makes physical sense for the design engineer, i.e. the achieved chloride diffusion coefficients at 1 year and 100 years, D1 and D100 respectively, and the corresponding achieved chloride concentrations at the exposed concrete surface, C1 and C100. Data from field exposure supports the assumption of time dependent surface chloride concentrations and the diffusion coefficients. Model parameters for Portland cement concretes with and without silica fume and fly ash in marine atmospheric and submerged South Scandinavian environment are suggested in a companion paper based on 10 years field exposure data.

Frederiksen, Jens Mejer; Geiker, Mette Rica

2008-01-01

334

The reflection coefficient oscillations of ion and electron beam by the action of the surface potential field  

International Nuclear Information System (INIS)

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

335

Heat Transfer coefficient and film cooling effectiveness measurement in flat plate and cutback trailing edge vane cascade  

OpenAIRE

This Thesis presents a dissertation about an experimental method, and a subsequent numerical data post processing, having as goal the heat transfer coefficient and adiabatic effectiveness measurement in gas turbine film cooling problems. The present work has been developed starting from an aerodynamic characterization of a linear nozzle vane cascade, cooled at the trailing edge by a cutback geometry, mounted in a suction-type wind tunnel at University of Bergamo turbomachinery laboratory. ...

Miranda, Marco

2014-01-01

336

Effect of surface impurities on the hydrogen recombination coefficient of first-wall materials  

International Nuclear Information System (INIS)

The ''hydrogen recombination coefficient'' kR was evaluated for such metals as stainless steel, vanadium and nickel from experimental data of the permeation rate of ion- and gas-driven hydrogen isotopes. The measured values of kR were found to decrease with increasing the surface concentration of certain impurity elements; oxygen for stainless steel, sulfur for vanadium and nickel as was determined by Auger electron spectroscopy. They were also compared to theoretical models and the role of surface impurities on the hydrogen recombination process was discussed with respect to these models. (orig.)

337

Optical measurements laboratory for determining heat transfer coefficients. [For use in Liquid Metal Fast Breeder Reactor Cask Technology Development Program  

Energy Technology Data Exchange (ETDEWEB)

A laboratory to be used for determining heat transfer coefficients using the technique of laser holographic interferometry (holometry) is described in this report. The basic theory upon which the experimental measurements are based is derived from first principles. Using a relationship between temperature and index of refraction, several cases of free convection in enclosures are evaluated. Results are presented for a heated hexagonal cylinder in an isothermal circular enclosure. In addition, a heated hexagonal cylinder in an isothermal box is evaluated. These provide check cases to some numerical code development which is being done in parallel with the optical measurements laboratory effort. Example holometrograms or holometric interferograms are shown to agree with analytical predictions as to number of fringes in the convective field. For the case of hexagonal cylinder in the circular cross-section enclosure, it is shown that convection has a significant influence upon the temperature gradient (heat transfer coefficient) when compared with thermal conduction. The laboratory will be used to determine heat transfer coefficients in enclosures related to the Liquid Metal Fast Breeder Reactor (LMFBR) Cask Technology Development Program.

Schimmel, W.P. Jr.

1976-06-01

338

Prediction of heat transfer coefficients and friction factors for evaporation of R-134a flowing inside corrugated tubes  

Science.gov (United States)

In this study, experimental and simulation studies of the evaporation heat transfer coefficient and pressure drop of R-134a flowing through corrugated tubes are conducted. The test section is a horizontal counter-flow concentric tube-in-tube heat exchanger 2.0 m in length. A smooth tube and corrugated tubes with inner diameters of 8.7 mm are used as the inner tube. The outer tube is made from a smooth copper tube with an inner diameter of 21.2 mm. The corrugation pitches used in this study are 5.08, 6.35, and 8.46 mm. Similarly, the corrugation depths are 1, 1.25, and 1.5 mm, respectively. The results show that the maximum heat transfer coefficient and pressure drop obtained from the corrugated tube are up to 22 and 19 % higher than those obtained from the smooth tube, respectively. In addition, the average difference of the heat transfer coefficient and pressure drop between the simulation model and experimental data are about 10 and 15 %, respectively.

Laohalertdecha, S.; Aroonrat, K.; Dalkilic, A. S.; Mahian, O.; Kaewnai, S.; Wongwises, S.

2014-04-01

339

Heat transfer enhancement of free surface MHD-flow by the wall with non-uniform electrical conductivity  

OpenAIRE

Due to the Magnetohydrodynamic (MHD) effect, which degrades heat transfer coefficients by pulsation suppression of external magnetic field, on the electrically conducting flow, the wall with non-uniform electrical conductivity is employed in a free surface MHD-flow system for heat transfer enhancement. The non-uniform electrical conductivity distribution of the channel wall may create alternate Lorentz forces along spanwise direction, which can effectively produce flow disturbance, promote mi...

H L Huang, B. Li

2010-01-01

340

DETERMINACION COEFICIENTE CONVECTIVO DE MATERIA EN EL SECADO DE SÓLIDOS / MATHEMATICAL CORRELATION TO GET MASS TRANSFER COEFFICIENT IN SOLIDS DRYING  

Scientific Electronic Library Online (English)

Full Text Available SciELO Chile | Language: Spanish Abstract in spanish Una correlación matemática para determinar el coeficiente convectivo de materia durante la evaporación de agua desde la superficie húmeda, fue desarrollada para su aplicación con aire húmedo con bajas diferencias sicrométricas y temperaturas del aire sobre los 60°C. La teoría clásica para determinar [...] coeficientes convectivos de calor y de materia, a través de parámetros adimensionales y de las analogías fenomenológicas difusivas, tienen validez sólo para aire seco. En el secado de sólidos, donde se requiere controlar las tasas de secado para evitar un daño físico en el producto, se impone la necesidad de operar con temperaturas bulbo húmedo por sobre los 40°C o diferencias sicrométricas moderadas. En esos rangos, las expresiones que relacionan los coeficientes convectivos de calor y materia, presentan errores que varían entre 26% y 113% para temperatura de bulbo húmedo entre 30°C y 70°C con diferencia sicrométrica de 10°C. La expresión formulada para esta aplicación, se plantea como una función de: el coeficiente convectivo de transferencia de calor, la temperatura bulbo húmedo y la diferencia sicrométrica. Los resultados obtenidos permiten establecer que, para las condiciones extremas de temperatura de bulbo húmedo y diferencia sicrométrica antes señalada el error se sitúa entre -1.4% a 2.14%, respecto del obtenido a partir de la metodología clásica La correlación obtenida es de forma polinomial, de fácil operación y viable de ser incorporada a cualquier modelo de simulación para la predicción de la dinámica del secado Abstract in english A mathematical correlation to determine the mass coefficient, during the evaporation of water from a wet surface, was developed for their application in wet air with low psychometric differential and with air temperature above 60°C. The classic theory that has been used in order to get heat and mass [...] convective coefficients, through non-dimensional parameters and phenomenological analogies, turns out to be valid only for dry air. In the particular case of solids drying, where operation requires to be performed under controlled drying rates, in order to prevent physical damage from affecting the product, is necessary to operate on a wet bulb temperature above 40ºC or at moderate psychometric differential. When we work under those ranges of temperature, the expressions that relate heat and mass convective coefficients show errors between 26% and 113% for wet temperature between 30°C and 70°C and psychometric difference of 30°C The expression that has been given for this application is stated as a function of the following: heat transfer coefficient, wet bulb temperature, and psychometric differential. The obtained results allow to settle down that, for the extreme conditions of wet bulb temperature and psychometric differences assigned before, the error is located among -1.4% to 2.14%, regarding the obtained through the classic methodology. The obtained correlation has polynomial form, of easy operation and viable of being incorporate to any simulation pattern for the prediction of the dynamics of the drying

Reinaldo, Sanchez Arriagada.

341

IR Thermography measurement of convective heat transfer coefficients with periodic excitation by Joule effect applied to the estimation of compact heat exchanger efficiency  

OpenAIRE

A new methodology has been developed to characterize the loss of efficiency of heat exchangers due to a maldistribution of the two-phase flow. The approach consists to measure the distribution of the local heat transfer coefficients with a non-intrusive and fast measurement method, based on a periodic excitation by Joule effect and infrared thermography measurement. An analytical model of the heat transfer is used to deduce heat transfer coefficients from the amplitude of the outside tube tem...

Leblay, P.; Henry, J. F.; Caron, D.; Leducq, D.; Bontemps, A.; Fournaison, L.

2012-01-01

342

Analysis of the heat transfer at the tool-workpiece interface in machining: determination of heat generation and heat transfer coefficients  

Science.gov (United States)

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.

Haddag, B.; Atlati, S.; Nouari, M.; Zenasni, M.

2015-01-01

343

Determination of interface heat-transfer coefficients for permanent-mold casting of Ti-6Al-4V  

Science.gov (United States)

Interface heat-transfer coefficients ( h 0) for permanent-mold casting (PMC) of Ti-6Al-4V were established as a function of casting surface temperature using a calibration-curve technique. Because mold geometry has a strong effect on h 0, values were determined for both of the two limiting interface types, “shrink-off” and “shrink-on.” For this purpose, casting experiments with instrumented molds were performed for cylinder- and pipe-shaped castings. The measured temperature transients were used in conjunction with two-dimensional (2-D) axisymmetric finite-element method (FEM) simulations to determine h 0( T). For the shrink-off interface type, h 0 was found to decrease linearly from 2000 to 1500 W/m2 K between the liquidus and the solidus, from 1500 to 325 W/m2 K between the solidus and the gap-formation temperature, and at a rate of 0.3 W/m2 K/K thereafter. For the shrink-on interface type, h 0 was found to increase linearly from 2000 to 2500 W/m2 K between the liquidus and the solidus temperatures, from 2500 to 5000 W/m2 K between the solidus and the gap-formation temperature, and to remain constant thereafter. The shrink-on values were up to 100 times the shrink-off values, indicating the importance of accounting for the interface geometry in FEM simulations of this process. The FEM-predicted casting and mold temperatures were found to be insensitive to certain changes in the h 0 values and sensitive to others. A comparison to published h 0 values for PMC of aluminum alloys showed some similarities and some differences.

Kobryn, P. A.; Semiatin, S. L.

2001-08-01

344

Study of energy transfer in helium atom scattering from surfaces  

CERN Document Server

Recently developed quantum mechanical theory of inelastic He atom scattering (HAS) from solid surfaces is employed to analyze the energy transfer between projectile particles (thermal energy He-atoms) and vibrational degrees of freedom (phonons) characteristic of a variety of experimentally studied surfaces. We have first calculated the angular resolved energy transfer which can be directly compared with the values deducible from the HAS time-of-flight spectra and a good agreement with experimental data has been found. This enabled us to calculate the total or angular integrated energy transfer, which is of paramount importance in the studies of gas-surface scattering, but is neither accessible in HAS (which yields only the angular resolved quantities), nor in the wind tunnel measurements for surfaces whose atomic composition and cleanliness must be maintained during the experiment. Here we present the results for prototype collision systems of this kind, viz. He => Cu(001), He => Xe/Cu(111) and He => Xe(111)...

Siber, A; Toennies, J P

1999-01-01

345

Heat transfer from novel target surface structures to a 3 × 3 array of normally impinging water jets  

OpenAIRE

Impinging jet arrays provide a means to achieve high heat transfer coefficients and are used in a wide variety of engineering applications such as electronics cooling. The objective of this paper is to characterize the heat transfer from an array of 3×3 submerged and confined impinging water jets to a range of target surface structures. The target surfaces consisted of a flat surface, nine 90 deg swirl generators, a 6×6 pin fin array, and nine pedestals with turn-down dishes that turned the...

Jeffers, Nmr; Punch, J.; Walsh, Ej; Mclean, M.

2010-01-01

346

Measurement of local heat transfer coefficient during gas–liquid Taylor bubble train flow by infra-red thermography  

International Nuclear Information System (INIS)

Highlights: • Infra-red thermographic study of Taylor bubble train flow in square mini-channel. • Design of experiments for measurement of local streamwise Nusselt number. • Minimizing conjugate heat transfer effects and resulting errors in data reduction. • Benchmarking against single-phase flow and three-dimensional computations. • 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, air–water Taylor bubble train flow is measured and compared in a mini-channel of square cross-section (5 mm × 5 mm; Dh = 5 mm, Bo ? 3.4) machined on a stainless steel substrate (300 mm × 25 mm × 11 mm). The design of the setup ensures near uniform heat flux condition at the solid–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 1.2–2.0 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

347

An investigation of the effects of interfacial shear between the gas and turbulent falling liquid film on the heat transfer coefficient  

International Nuclear Information System (INIS)

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

348

Detailed measurements of local heat transfer coefficient in the entrance to normal and inclined film cooling holes  

OpenAIRE

The local heat transfer inside the entrance to large scale models of film cooling holes has been measured using the transient heat transfer technique. The method employs temperature sensitive liquid crystals to measure the surface temperature of large scale perspex models. Full distributions of local Nusselt number were calculated based on the cooling passage centreline gas temperature ahead of the cooling hole. The circumferentially averaged Nusselt number was also calculated based on the lo...

Gillespie, Drh; Byerley, Ar; Ireland, Pt; Wang, Z.; Jones, Tv; Kohler, St

1994-01-01

349

Fe-Al alloy surface tension and expansion coefficient of the Monte Carlo simulation  

International Nuclear Information System (INIS)

Using the new modified analytical EAM and the Monte Carlo method, and constructing a new system and surface, the liquid surface tension was calculated. According to a given temperature alloy free energy minima, the coefficient of linear expansion of the Fe-Al alloy is simulated. The method and the results discussed, we give the mathematical relationship between the liquid surface tension and the temperature of the three kinds of Fe-Al alloy. The results of the simulation are in good agreement with existing experimental data in the low temperature zone, however, the result is a little lower than the experimental results in the high temperature zone. So the calculation result shows that the Monte Carlo method is very effective in the Fe-Al alloy and the method is right and reliable here. (authors)

350

Numerical Solution of an Inverse Diffusion Problem for the Moisture Transfer Coefficient in a Porous Material  

CERN Document Server

On the basis of the solution of a nonlinear diffusion equation with initial and boundary conditions, a transport coefficient of moisture in a sample of a porous material is found by minimization of a functional, which expresses diversion of the computed profile of moisture concentration in well-defined time moments from their experimental values for the defined moisture transport coefficient. In this case the transport coefficient as opposed to the previous works is found as a sum of the degree and exponential functions of the moisture concentration. The exponent of the power function depends on time. Thus, a more accurate coincidence of the computed profiles of the moisture concentration with their experimental profiles is gained in comparison to previous works performed by other authors. The exponential term provides a good coincidence of the mentioned profiles for big times nearby the boundary of the sample, where evaporation of the moisture to the atmosphere takes place.

Amirkhanov, I V; Pavlus, M; Puzynina, T P; Puzynin, I V; Sarhadov, I

2005-01-01

351

Optimization of heat transfer coefficient correlation at supercritical pressure using genetic algorithms  

International Nuclear Information System (INIS)

The paper presents a new heat transfer correlation of water at supercritical pressure after review on existing heat transfer correlations. The new correlation is optimized by genetic algorithms based on existing test data. Based on current results, we conclude that genetic algorithms are effective to search a global optimized correlation but it is important to carefully select representative and authentic test data to reach an optimized solution and special attention needs to be paid on the deteriorated heat transfer region in the design of supercritical water reactor because it can not be predicted well by any correlations reviewed. (orig.)

352

Investigation into the heat transfer performance of helically ribbed surfaces  

International Nuclear Information System (INIS)

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)

353

A novel method for measuring the diffusion, partition and convective mass transfer coefficients of formaldehyde and VOC in building materials.  

Science.gov (United States)

The diffusion coefficient (D(m)) and material/air partition coefficient (K) are two key parameters characterizing the formaldehyde and volatile organic compounds (VOC) sorption behavior in building materials. By virtue of the sorption process in airtight chamber, this paper proposes a novel method to measure the two key parameters, as well as the convective mass transfer coefficient (h(m)). Compared to traditional methods, it has the following merits: (1) the K, D(m) and h(m) can be simultaneously obtained, thus is convenient to use; (2) it is time-saving, just one sorption process in airtight chamber is required; (3) the determination of h(m) is based on the formaldehyde and VOC concentration data in the test chamber rather than the generally used empirical correlations obtained from the heat and mass transfer analogy, thus is more accurate and can be regarded as a significant improvement. The present method is applied to measure the three parameters by treating the experimental data in the literature, and good results are obtained, which validates the effectiveness of the method. Our new method also provides a potential pathway for measuring h(m) of semi-volatile organic compounds (SVOC) by using that of VOC. PMID:23145156

Xiong, Jianyin; Huang, Shaodan; Zhang, Yinping

2012-01-01

354

Determination of distribution and transfer coefficients of Sr-90 and Cs-137 based on the environmental monitoring data in Japan  

International Nuclear Information System (INIS)

The pathway of farm product intake are very important for evaluating the human health risks caused by the long term global radioactive contamination. The main parameters contained in this pathway : the distribution coefficient(kd), the transfer coefficient by direct foliar absorption(K) and the transfer coefficient by root uptake(TF), were determined using the Sr-90 and Cs-137 environmental monitoring data in Japan. The major finding obtained in this study are as follows : (1) kd can be determined by the monitoring data of radionuclide concentration in soil, K by the concentration in farm products during larger fallout period, 1960's, and TF by the concentration in farm products during smaller fallout period, after 1970's. (2) The ranges of kd were determined as 10-300 for Sr-90 and 10-2,000(ml/g) for Cs-137. These ranges are smaller than the reported ranges, thus the accuracy for estimating kd were improved in this study. K are 0.03-1 for Sr-90 and 0.4-1(cm2·month/g) for Cs-137 ; TF are 0.001-0.06 for Sr-90 and 0.0005-0.001(-) for Cs-137. (author)

355

Transfer coefficients for the prediction of the dose to man via the forage-cow-milk pathway from radionuclides released to the biosphere  

International Nuclear Information System (INIS)

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

356

An effusive molecular beam technique for studies of polyatomic gas-surface reactivity and energy transfer.  

Science.gov (United States)

An effusive molecular beam technique is described to measure alkane dissociative sticking coefficients, S(T(g), T(s); ?), on metal surfaces for which the impinging gas temperature, T(g), and surface temperature, T(s), can be independently varied, along with the angle of incidence, ?, of the impinging gas. Effusive beam experiments with T(g) = T(s) = T allow for determination of angle-resolved dissociative sticking coefficients, S(T; ?), which when averaged over the cos?(?)/? angular distribution appropriate to the impinging flux from a thermal ambient gas yield the thermal dissociative sticking coefficient, S(T). Nonequilibrium S(T(g), T(s); ?) measurements for which T(g) ? T(s) 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 T(g) 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). PMID:21529024

Cushing, G W; Navin, J K; Valadez, L; Johánek, V; Harrison, I

2011-04-01

357

Effect of Contaminants on Mass Transfer Coefficients in Bubble Column and Airlift Contactors.  

Czech Academy of Sciences Publication Activity Database

Ro?. 58, 8 (2003) , s. 1431-1440. ISSN 0009-2509 Institutional research plan: CEZ:AV0Z4072921 Keywords : mass transfer * bubble * surfactant Subject RIV: CI - Industrial Chemistry, Chemical Engineering Impact factor: 1.562, year: 2003

Vasconcelos, J.M.T.; Rodrigues, J.L.M.; Orvalho, Sandra Petronilho; Alves, S. S.; Mendes, R.L.; Reis, A.

2003-01-01

358

A MEASUREMENT OF A SURFACE SELF-DIFFUSION COEFFICIENT BY SCANNING TUNNELING MICROSCOPY  

OpenAIRE

A technique is described to measure a surface self-diffusion coefficient (D) of a metal (gold) by scanning tunneling microscopy. Micro-hills formed on a gold face show a shape evolution by a diffusion transport of kink site atoms. D is determined via a measurement of the hill apex radius as a function of time and includes corrections of image errors. The technique shows that STM can be used to study diffusion and it opens the possibility of measuring diffusion at lower temperatures where D co...

Drechsler, M.; Blackford, B.; Putnam, A.; Jericho, M.

1989-01-01

359

A study of the rates of heat transfer and bubble site density for nucleate boiling on an inclined heating surface  

International Nuclear Information System (INIS)

Nucleate pool boiling of distilled water from an electrically heated surface at atmospheric pressure is studied for varying heating surface inclinations. The constants of the accepted boiling equation phi = K Tsup(B) and the Rohsenow Correlation Coefficient are found to be dependent on surface orientation. Convection cooling is observed to play a major role in pool boiling phenomena and causes large changes in the heat transfer rates for a given excess of temperature of the heated surface. Active nucleation site density is studied and found to be independent of surface inclination. Empirical relations are presented to provide an understanding of the effects of inclination on other boiling parameters. (author)

360

Balance control during lateral load transfers over a slippery surface.  

Science.gov (United States)

Few studies have measured balance control during manual material handling, and even fewer with environmental cofactors. This study examined the effect of different surface frictions during a stationary manual material handling task. Thirty-six healthy participants completed 180° lateral transfer tasks of a load over high- and low-friction surfaces (? = 0.86 and ? = 0.16, respectively). Balance measures, stance kinematics and lower extremity muscle activities were measured. Success during the novel slippery surface dichotomised our population, allowing us to investigate beneficial techniques to lateral load transfers over the slippery surface. Stance width reduction by 8 cm and 15° of additional external foot rotation towards the load were used to counter the imbalance created by the slippery surface. There was no clear alteration to lower extremity muscular control to adapt to a slippery surface. Changes in stance seemed to be used successfully to counter a slippery surface during lateral load transfers. STATEMENT OF RELEVANCE: Industries requiring manual material handling where slippery conditions are potentially present have a noticeable increase in injuries. This study suggests stance configuration, more so than any other measure of balance control, differentiates vulnerability to imbalance during material handling over a slippery surface. PMID:22026949

Catena, Robert D; DiDomenico, Angela; Banks, Jacob J; Dennerlein, Jack T

2011-11-01

361

Boiling heat transfer coefficient of R-22 refrigerant and its alternatives in horizontal tube : small refrigerator scale  

Directory of Open Access Journals (Sweden)

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 ?G 2 increases with Martinelli parameter and there is no effect of the tube roughness and the types of the refrigerants.

Uthen Kuntha

2002-04-01

362

Natural convection heat transfer on surfaces of copper micro-wires  

Science.gov (United States)

The natural convection heat transfer characteristics and mechanism for copper micro-wires in water and air were investigated experimentally and numerically. The wires with diameters of 39.9, 65.8 and 119.1 ?m were placed horizontally in water inside of a sealed tube and in air of a large room, respectively. Using Joule heating, the heat transfer coefficients and Nusselt numbers of natural convection for micro-wires in ultra pure water and air were obtained. A three dimensional incompressible numerical model was used to investigate the natural convection, and the prediction with this model was in reasonable accordance with the experimental results. With the decrease of micro-wire diameter, the heat transfer coefficient of natural convection on the surface of micro-wire becomes larger, while the Nu number of natural convection decreases in water and air. Besides, the change rate of Nu number in water decreases apparently with the increase of heat flux and the decrease of wire diameter, which is larger than that in air. The thickness of boundary layer on the wall of micro-wire becomes thinner with the decrease of diameter in both water and air, but the ratio of boundary layer thickness in water to the diameter increases. However, there is almost no change of this ratio for natural convection in air. As a result, the proportion of conduction in total heat transfer of natural convection in water increases, while the convective heat transfer decreases. The velocity distribution, temperature field and the boundary layer in the natural convection were compared with those of tube with conventional dimension. It was found that the boundary layer around the micro-wire is an oval-shaped film on the surface, which was different from that around the conventional tube. This apparently reduces the convection strength in the natural convection, thus the heat transfer presents a conduction characteristic.

Guan, Ning; Liu, Zhigang; Zhang, Chengwu; Jiang, Guilin

2014-02-01

363

Experimental Study on the Impact of External Geometrical Shape on Free and Forced Convection Time Dependent Average Heat Transfer Coefficient during Cooling Process  

Directory of Open Access Journals (Sweden)

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.

Sundus Hussein Abd

2012-01-01

364

Reconstruction of subdomain boundaries of piecewise constant coefficients of the radiative transfer equation from optical tomography data  

Science.gov (United States)

In this study we consider the reconstruction of the smooth subdomain boundaries of piecewise constant coefficients of the radiative transfer equation (RTE) from optical tomography data. The assumption is that the values of the absorption and scattering coefficients (?a, ?s) of the different subdomains are known a priori but the smooth subdomain boundaries where ?a and ?s are discontinuous are unknown. For the reconstruction of (?a, ?s) it is then sufficient to find the subdomain boundaries separating different values of the coefficients. This results in a nonlinear ill-posed inverse problem. In this study we propose a numerical algorithm for this inverse problem. The approach is based on the finite element discretization of the RTE. We formulate the forward problem as a mapping from a set of shape coefficients representing the shapes of the subdomain boundaries to optical tomography data, and derive the Jacobian of this forward mapping. Then an iterative Newton-type algorithm which seeks a boundary configuration minimizing the residual norm between measured and predicted data is implemented. The performance of the method is tested with simulated frequency domain optical tomography data from diffusive domains containing low-scattering (void) subdomains.

Arridge, S. R.; Dorn, O.; Kaipio, J. P.; Kolehmainen, V.; Schweiger, M.; Tarvainen, T.; Vauhkonen, M.; Zacharopoulos, A.

2006-12-01

365

Heat and mass transfer effect on hydromagnetic flow of a moving permeable vertical surface  

International Nuclear Information System (INIS)

Numerical results are presented for the effects of heat and mass transfer on hydromagnetic flow of a moving permeable vertical surface. The surface is maintained at linear temperature and concentration variations. The nonlinear-coupled boundary layer equations were transformed and the resulting ordinary differential equations were solved by perturbation technique. Numerical results for the dimensionless velocity profiles, the temperature profiles, the local friction coefficient and the local Nusselt number are presented for various values of Prandtl number, suction/blowing parameter, Schrnidt number, buoyancy ratio and Hartmann number. The effects of the different parameters on the velocity and temperature profiles as well as skin friction and wall heat transfer are evaluated. Favorable comparisons with previously published work confirm the correctness of numerical results

366

EPMA-EDS surface measurements of interdiffusion coefficients between miscible metals in thin films  

Energy Technology Data Exchange (ETDEWEB)

A new technique is developed to study interdiffusion between two miscible metals. The technique is applied to the Ni-Pd system. It consists in measuring the change of apparent surface composition of a Pd substrate coated with an 800 nm Ni thin film during annealing at a given temperature. The measurement is carried out in-situ inside the chamber of a SEM (scanning electron microscope) by EPMA-EDS (electron probe microanalysis-energy dispersive X-ray spectroscopy). The experimental data are processed using a model that mixes the Fick's diffusion equations and the electron probe microanalysis equation. This process allows the determination of the mean interdiffusion coefficient at a given annealing temperature. The main advantages of the technique are the possible determination of interdiffusion coefficients in thin films and at very low temperature (down to 430 deg. C, i.e. {approx}0.4 T{sub m}), which is not achievable with other techniques conventionally used for the study of interdiffusion. The Ni-Pd mean interdiffusion coefficient is shown to follow an Arrhenius law (D-tilde{sub c}=6.32x10{sup -3} exp((178.8kJmol{sup -1})/(RT) )cm{sup 2}s{sup -1}) between 430 deg. C and 900 deg. C, in relatively good agreement with previous interdiffusion measurements made on the Ni-Pd system at higher temperature.

Christien, F., E-mail: frederic.christien@univ-nantes.fr [Laboratoire Genie des Materiaux et Procedes Associes, Universite de Nantes, Polytech' Nantes, Rue Christian Pauc, BP 50609, F-44306 Nantes Cedex 3 (France); Pierson, J.F. [Laboratoire de Science et Genie des Surfaces (UMR CNRS 7570), Ecole des Mines, Parc de Saurupt F-54042 NANCY Cedex France (France); Hassini, A. [Laboratoire Genie des Materiaux et Procedes Associes, Universite de Nantes, Polytech' Nantes, Rue Christian Pauc, BP 50609, F-44306 Nantes Cedex 3 (France); Capon, F. [Laboratoire de Science et Genie des Surfaces (UMR CNRS 7570), Ecole des Mines, Parc de Saurupt F-54042 NANCY Cedex France (France); Le Gall, R.; Brousse, T. [Laboratoire Genie des Materiaux et Procedes Associes, Universite de Nantes, Polytech' Nantes, Rue Christian Pauc, BP 50609, F-44306 Nantes Cedex 3 (France)

2010-01-01

367

Effect of Soft Material Hardness and Hard Material Surface Morphology on Friction and Transfer Layer Formation; Dry Condition  

Directory of Open Access Journals (Sweden)

Full Text Available The morphological features of the surface in both micro and macro levels are important factors governing the tribological behavior of the contacting surfaces. Surface hardness is also an important factor which governs the friction and wear behaviors of the contacting surfaces. Surface morphology of a tool is an important factor as it primarily controls the tribological behavior at the interface which in turn controls the surface finish of products. In the present investigation a pin-on-plate sliding tester was used to identify the effect of surface morphology and hardness on co-efficient of friction and transfer layer which characterizes the tribological behavior. The morphology of mild steel (EN8 plate surfaces were modified by employing three different surface modification methods like grinding (silicon carbide wheel polishing, shot blasting and electric discharge machining methods. Surface roughness parameters which characterize the morphology of the steel plates were measured using a three dimensional optical profilometer. Role of hardness is studied by employing lead, copper and Aluminum (Al6082 pins which were slid against steel plates. Experiments were conducted for plate inclination angles of 1, 1.5,2 and 2.5 degrees. Normal load was varied from 1 to 150N during the tests. Experiments were conducted under dry condition in ambient environment. Scanning electron microscope was used to study the formation of transfer layer on plate and pin surfaces. It was observed that the co-efficient of friction and transfer layer formation were found to depend on the surface morphology of the harder surface. The quantum of transfer layer formation on the surfaces is found to increase with increase in surface roughness

Mr.M Basavaraju

2013-09-01

368

Transfer matrix treatment of atomic chemisorption on transition metal surface  

International Nuclear Information System (INIS)

We study the atomic adsorption of hydrogen on paramagnetic nickel 100 surface, using the Green's function formalism and the transfer matrix technique, which allows the treatment of the geometry of the system in a simple manner. We incorporate electronic correlation at the adatom orbital in a self consistent Hartree-Fock approach. The adsorption energy, local density of states and cherge transfer between the solid and the adatom are calculated for different crystal structures (sc and fcc) and adatom positions at the surface. The results are discussed in comparison with other theories and with available experimental data, with satisfactory agreement. (Author)

369

Transfer matrix treatment of atomic chemisorption on transition metal surface  

International Nuclear Information System (INIS)

The atomic adsorption of hydrogen on paramagnetic nickel 100 surface is studied, using the Green's function formalism and the transfer matrix technique, which allows the treatment of the geometry of the system in a simple manner. Electronic correlation at the adatom orbital in a self consistent Hartree-Fock approach is incorporated. The adsorption energy, local density of states and charge transfer between the solid and the adatom are calculated for different crystal structures (sc and fcc) and adatom positions at the surface. The results are discussed in comparison with other theories and with available experimental data, with satisfactory agreement. (Author)

370

Effect of transverse convex surface curvature on turbulent flow and heat transfer in concentric annuli: analysis and experiment  

International Nuclear Information System (INIS)

The effect of the transverse convex surface curvature on the fully developed turbulent flow and heat transfer in concentric annular ducts with smooth surfaces were studied both analytically and experimentally. It is seen from the study that both the friction and heat transfer coefficients increase with decreasing value of the inner core radius of concentric annuli, Ri. It is concluded from the study that, while the effect of the transverse concave curvature on fluid flow and heat transfer is negligible, that of the transverse convex curvature is rather significant. It is further deduced from the present study that the tube-based heat transfer correlations, especially CHF in nuclear fuel channels, should not be applied to flow outside of tube bundles or in a subchannel whose heated surfaces are convex

371

Effect of ?-irradiation on the temperature coefficient of surface resistivity of two-dimensional island platinum films  

International Nuclear Information System (INIS)

Three sets (A, B and C) of two-dimensional island platinum films (2D-I(Pt)Fs) were prepared via the thermal evaporation technique, where the substrates are corning 7059 glass slides. The mass thickness (dm) of the films of different sets is 5, 10 and 20 A, respectively. The Pt films were exposed to ?-rays from 137Cs (0.662 MeV) radiation source of dose rate 0.5 Gy/min. and the different doses are 100, 200, 300, 500 and 700 Gy. The dependence of the surface resistivity (?) on temperature over the range of 100-300 K was undertaken at different dm and doses then the temperature coefficient of surface resistivity (?) was deduced. It was found that; (i) for particular dm and T, the absolute value of ? decreases as the dose increases (ii) for particular dose and T, the absolute value of ? decreases as dm increases (iii) for particular dose and dm, the absolute value of ? decreases as T increases. Qualitative interpretation for the results was offered on the ground that the electrons transfer among islands takes place by the activated tunneling mechanism and the ?-irradiation has changed the shape of islands from spherical to prolate spheroid.

372

Serrating Nozzle Surfaces for Complete Transfer of Droplets  

Science.gov (United States)

A method of ensuring the complete transfer of liquid droplets from nozzles in microfluidic devices to nearby surfaces involves relatively simple geometric modification of the nozzle surfaces. The method is especially applicable to nozzles in print heads and similar devices required to dispense liquid droplets having precise volumes. Examples of such devices include heads for soft printing of ink on paper and heads for depositing droplets of deoxyribonucleic acid (DNA) or protein solutions on glass plates to form microarrays of spots for analysis. The main purpose served by the present method is to ensure that droplets transferred from a nozzle have consistent volume, as needed to ensure accuracy in microarray analysis or consistent appearance of printed text and images. In soft printing, droplets having consistent volume are generated inside a print head, but in the absence of the present method, the consistency is lost in printing because after each printing action (in which a drop is ejected from a nozzle), a small residual volume of liquid remains attached to the nozzle. By providing for complete transfer of droplets (and thus eliminating residual liquid attached to the nozzle) the method ensures consistency of volume of transferred droplets. An additional benefit of elimination of residue is prevention of cross-contamination among different liquids printed through the same nozzle a major consideration in DNA microarray analysis. The method also accelerates the printing process by minimizing the need to clean a printing head to prevent cross-contamination. Soft printing involves a hydrophobic nozzle surface and a hydrophilic print surface. When the two surfaces are brought into proximity such that a droplet in the nozzle makes contact with the print surface, a substantial portion of the droplet becomes transferred to the print surface. Then as the nozzle and the print surface are pulled apart, the droplet is pulled apart and most of the droplet remains on the print surface. The basic principle of the present method is to reduce the liquid-solid surface energy of the nozzle to a level sufficiently below the intrinsic solid-liquid surface energy of the nozzle material so that the droplet is not pulled apart and, instead, the entire droplet volume becomes transferred to the print surface. In this method, the liquid-solid surface energy is reduced by introducing artificial surface roughness in the form of micromachined serrations on the inner nozzle surface (see figure). The method was tested in experiments on soft printing of DNA solutions and of deionized water through 0.5-mm-diameter nozzles, of which some were not serrated, some were partially serrated, and some were fully serrated. In the nozzles without serrations, transfer was incomplete; that is, residual liquids remained in the nozzles after printing. However, in every nozzle in which at least half the inner surface was serrated, complete transfer of droplets to the print surface was achieved.

Kim, Chang-Jin " CJ" Yi, Uichong

2010-01-01

373

Film boiling heat transfer and vapour film collapse on spheres, cylinders and plane surfaces  

International Nuclear Information System (INIS)

An experimental study of transient film boiling was conducted, with different coolant velocities, on two spheres with different diameters, two cylindrical specimens of different lengths in parallel flow, a cylinder in cross flow and two flat plates with different lengths. A frame by frame photographic study on the nature of the vapour/liquid interface and the collapse modes has revealed a new mode for film collapse, in which an explosive liquid-solid contact is followed by film re-formation and the motion of a quench front over the hot surface. Steady state tests were carried out on a plate similar to the short plate used in the transient experiments and the heat transfer, film stability and collapse results are compared with those of the transient investigation. Heat transfer coefficients and heat fluxes during film boiling were found essentially to depend on specimen temperature and water subcooling. In contrast, the influences on heat transfer of specimen size and water velocity were relatively small for the ranges studied. A theoretical model predicted heat transfer coefficients to within 10% of experimental values for water subcoolings above 10 K and within 30% in all cases.

374

Measurement of convective heat-transfer coefficients on a wind tunnel model by passive and stimulated infrared thermography  

Science.gov (United States)

Research conducted at ONERA to make quantitative infrared thermography operational and applicable to any 3D model is discussed. The problems of precise thermometry using this technique are considered, and the methodological and hardware choices made to obtain quantitative thermograms are described. The problem of determining the convective flows once the unsteady temperatures are known is addressed for two kinds of methods: classical passive thermography, in which only the heating due to convection is used, and active, or stimulated, thermography, in which the heat-transfer coefficients are calculated directly from the additional heating of the model by a radiation source, applied for short periods during the test.

Balageas, D. L.; Boscher, D. M.; Deom, A. A.

1990-11-01

375

Description of the Anisotropic Radiation Transfer model ART to determine photodissociation coefficients  

International Nuclear Information System (INIS)

The purpose of the model ART is to determine the photodissociation coefficients for the interpretation of measurements of radicals. Next, the algorithms used to solve the differential equations for the flux and to integrate the scattering functions to determine the phase function are described. A detailed description of the frame program and the subroutines FLUXES and PHOTO follows. The frame program governs the input and output of the model and calls the subprograms. FLUXES is the routine which actually calculates the photon fluxes and then the routine PHOTO is used to determine the rate coefficients or the radiometer signals. In the chapter which follows next the handling of the model is explained. Here, especially the meaning of the different steering parameters and the different possibilities for running the model are described. Typical results of the simulations for different purposes are shown (orig.)

376

A technique for measuring the heat transfer coefficient inside a Bridgman furnace  

Science.gov (United States)

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.

Rosch, W.; Jesser, W.; Debnam, W.; Fripp, A.; Woodell, G.; Pendergrass, T. K.

1993-01-01

377

Molecular Dynamics Calculation of Carbon/Hydrocarbon Reflection Coefficients on a Graphite Surface Employing Distributed Computing  

Science.gov (United States)

Reflection coefficients of carbon and hydrocarbon molecules have been calculated with a molecular dynamics code. The code uses the Brenner hydrocarbon potential, an empirical many-body potential that can model the chemical bonding in small hydrocarbon molecules and graphite surfaces. A variety of incident energies and angles have been studied. Typical results for carbon show reflection coefficients 0.4 at thermal energy, decreasing to a minimum of 0.15 at 10-20 eV, and then increasing again. Distributed computing is used to distribute the work among 10-20 desktop PCs in the laboratory. The system consists of a client application run on all of the PCs and a single server machine that distributes work and compiles the results sent back from the clients. The client-server software is written in Java and requires no commercial software packages. Thus, the MD code benefits from multiprocessor-like speed-up at no additional cost by using the idle CPU cycles that would otherwise be wasted. These calculations represent an important improvement to the WBC code, which has been used to model surface erosion, core plasma contamination, and tritium codeposition in many fusion design studies and experiments.

Alman, D. A.; Ruzic, D. N.; Brooks, J. N.

2001-10-01

378

Calculation procedure to determine average mass transfer coefficients in packed columns from experimental data for ammonia water absorption refrigeration systems  

Science.gov (United States)

The ammonia purification process is critical in ammonia water absorption refrigeration systems. In this paper, a detailed and a simplified analytical model are presented to characterize the performance of the ammonia rectification process in packed columns. The detailed model is based on mass and energy balances and simultaneous heat and mass transfer equations. The simplified model is derived and compared with the detailed model. The range of applicability of the simplified model is determined. A calculation procedure based on the simplified model is developed to determine the volumetric mass transfer coefficients in the vapour phase from experimental data. Finally, the proposed model and other simple calculation methods found in the general literature are compared.

Sieres, Jaime; Fernández-Seara, José

2008-08-01

379

Forced axial and torsional vibrations of a shaft line using the transfer matrix method related to solution coefficients  

Science.gov (United States)

This present paper deals with a mathematical description of linear axial and torsional vibrations. The normal and tangential stress tensor components produced by axial-torsional deformations and vibrations in the propeller and intermediate shafts, under the influence of propeller-induced static and variable hydrodynamic excitations are also studied. The transfer matrix method related to the constant coefficients of differential equation solutions is used. The advantage of the latter as compared with a well-known method of transfer matrix associated with state vector is the possibility of reducing the number of multiplied matrices when adjacent shaft segments have the same material properties and diameters. The results show that there is no risk of buckling and confirm that the strength of the shaft line depends on the value of the static tangential stresses which is the most important component of the stress tensor.

Chahr-Eddine, Kandouci; Yassine, Adjal

2014-06-01

380

Characterization of transfer layers on steel surfaces sliding against diamondlike carbon in dry nitrogen  

Energy Technology Data Exchange (ETDEWEB)

Transfer layers on sliding steel surfaces play important roles in tribological performance of diamondlike carbon films. This study investigated the nature of transfer layers formed on M50 balls during sliding against diamondlike carbon (DLC) films (1.5 {mu}m thick) prepared by ion-beam deposition. Long-duration sliding tests were performed with steel balls sliding against the DLC coatings in dry nitrogen at room temperature and zero humidity. Test results indicated that the friction coefficients of test pairs were initially 0.12 but decreased steadily with sliding distance to 0.02-0.03 and remained constant throughout the tests, which lasted for more than 250,000 sliding cycles (30 km). This low-friction regime appeared to coincide with the formation of a carbon-rich transfer layer on the sliding surfaces of M50 balls. Micro-laser-Raman spectroscopy and electron microscopy were used to elucidate the structure and chemistry of these transfer layers and to reveal their possible role in the wear and friction behavior of DLC-coated surfaces.

Erdemir, A.; Bindal, C.; Pagan, J. [Argonne National Lab., IL (United States); Wilbur, P. [Colorado State Univ., Fort Collins, CO (United States). Dept. of Mechanical Engineering

1995-03-01

381

Combined measurement of surface, grain boundary and lattice diffusion coefficients on olivine bi-crystals  

Science.gov (United States)

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.

Marquardt, Katharina; Dohmen, Ralf; Wagner, Johannes

2014-05-01

382

Near-field radiative heat transfer for structured surfaces  

OpenAIRE

We apply an analytical approach for determining the near-field radiative heat transfer between a metallic nanosphere and a planar semi-infinite medium with some given surface structure. This approach is based on a perturbative expansion, and evaluated to first order in the surface profile. With the help of numerical results obtained for some simple model geometries we discuss typical signatures that should be obtainable with a near-field scanning thermal microscope operated ...

Biehs, Svend-age; Huth, Oliver; Ru?ting, Felix

2011-01-01

383

Study of Heat Transfer in a Kapok Material from the Convective Heat Transfer Coefficient and the Excitation Pulse of Solicitations External Climatic  

Directory of Open Access Journals (Sweden)

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.

M. Dieng

2013-02-01

384

Exploring the potential energy surface for proton transfer in acetylacetone  

Energy Technology Data Exchange (ETDEWEB)

The portion of the potential energy surface (PES) of acetylacetone relevant for the intramolecular proton transfer reaction is studied using ab initio and DFT methods. The best estimate of the barrier governing proton transfer was found to be 3.4 kcal mol{sup -1} at the MP4(FC)/6-311 + G(2d,2p)//MP2(FC)/6-311 + G(2d,2p) level of theory. Six stationary points on the PES were characterized as well as the reaction paths connecting these points. Special attention paid to the pathway of intramolecular proton transfer reveals that the internal rotation of the methyl group adjacent to the carbonyl group and the proton transfer reaction are consecutive processes.

Matanovic, Ivana [Department of Physical Chemistry, R. Boskovic Institute, Bijenicka 54, 10000 Zagreb (Croatia); Doslic, Nadja [Department of Physical Chemistry, R. Boskovic Institute, Bijenicka 54, 10000 Zagreb (Croatia)]. E-mail: nadja.doslic@irb.hr; Mihalic, Zlatko [Faculty of Science, University of Zagreb, Strossmayerov trg 14, HR-10000 Zagreb (Croatia)

2004-11-15

385

Electron transfer in ion interactions with chlorine covered silver surfaces  

International Nuclear Information System (INIS)

The effect of chemical environment on the neutralisation of ions with adsorbate covered surfaces was investigated on the example of H+ and rare gas ion scattering on chlorine covered Ag. Changes in coverage from the submonolayer chemisorption to chloride nucleation stage, strongly affect electron transfer. In the case of H+, Ne+ and Ar+ these changes induce an ''unusual'' non-linear, oscillating, coverage dependence of electron transfer probabilities, due to modifications in the surface electronic structure. In case of the more highly bound He, we assign the observed changes to modifications in quasi-resonant charge transfer rates involving the Cl 3s core level, because of the core level shifts induced by changes in chemical environment

386

Turbulent temperature fluctuation and heat transfer to a metal surface resulting from the mixing of cold and hot water  

International Nuclear Information System (INIS)

Turbulent temperature fluctuation resulting from the mixing of cold and hot water was studied at 6.9*10/sup 6/ pascal (68 atm) around a simulated Boiling Water Reactor feedwater nozzle blend radius. The resulting heat transfer to the nozzle surface was investigated. This study shows that the instantaneous heat transfer coefficient varies from 30 percent of the steady-state value to five times the steady-state value. A discussion is given for the application of the above findings to a steady-state, two-dimensional turbulent boundary layer. The application of this information to metal surface fatigue life estimation is briefly explained. 11 refs

387

Assessment of surface area normalisation for interpreting distribution coefficients (Kd) for uranium sorption  

International Nuclear Information System (INIS)

Adsorption of radionuclides on soils and sediments is commonly quantified by distribution coefficients (Kd values). This paper examines the relationship between Kd values for uranium(VI) adsorption and the specific surface area (SSA) of geologic materials. We then investigate the potential applicability of normalising uranium (U) Kd measurements using the SSA, to produce 'Ka values' as a generic expression of the affinity of U for the surface. The data for U provide a reasonably coherent set of Ka values on various solid phases, both with and without ligands. The Ka representation provides a way of harmonising datasets obtained for materials having different specific surface areas, and accounting for the effects of ligands in different systems. In addition, this representation may assist in developing U sorption models for complex materials. However, a significant limitation of the Ka concept is that sorption of radionuclides at trace levels can be dominated by interactions with specific surface sites, whose abundances are not reflected by the SSA. Therefore, calculated Ka values should be interpreted cautiously.

388

Arrangement of an experiment for the measurement of the polarization-transfer coefficient Dt in the neutron-proton scattering  

International Nuclear Information System (INIS)

The present thesis describes an apparative arrangement for the measurement of the n-p polarization-transfer coefficient Dt at a mean neutron energy of 25.5 MeV and the possibility for the determination of the 3S1-3D1 mixing parameter. Extensive Monte Carlo programs were developed for the optimization of the experimental arrangement and for the determination of the polarimeter properties. An unpolarized test measurement is presented as well as the course of the data evaluation discussed. A first polarized measurement yielded because of a cup current of only 30 nA as well as some technical problems at the isochronous cyclotron yet no evident result concerning Dt. At a polarized beam current of 500 nA to be expected and a mean neutron polarization of Pn=0.45 the n-p polarization-transfer coefficient Dt can be determined in a four-week beam-time to +-0.025 from which a fixation of the 3S1-3D1 mixing parameter to +-1.0 degrees results. (orig.)

389

Transfer coefficients of selected radionuclides to animal products. I. Comparison of milk and meat from dairy cows and goats  

International Nuclear Information System (INIS)

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

390

Selection of Initial Mold-Metal Interface Heat Transfer Coefficient Values in Casting Simulations—a Sensitivity Analysis  

Science.gov (United States)

Mold-metal interface heat transfer coefficient values need to be determined precisely to accurately predict thermal histories at different locations in automotive castings. Thermomechanical simulations were carried out for Al-Si alloy casting processes using a commercial code. The cooling curve results were validated with experimental data from the literature for a cylindrical-shaped casting. Our analysis indicates that the interface heat transfer coefficient (IHTC) initial value choice between chill-metal and the sand mold-metal interfaces has a marked effect on the cooling curves. In addition, after choosing an IHTC initial value, the solidification rates of the alloy near the chill-metal interfaces varied during subsequent cooling when the gap began to form. However, the gap formation, which results in an IHTC change from the initial value, does not affect the cooling curves within the vicinity of the sand-metal interface. Optimized initial IHTC values of 3000 and 7000 W m-2-K-1 were determined for a sand-metal interface and a chill (steel or copper)-metal interfaces, respectively. The initial IHTC had a significant effect on the prediction of secondary dendrite arm spacing (SDAS) (varying between approximately 15 microns and 70 microns) and ultimate tensile strength (UTS) (varying between approximately 250 MPa and 370 MPa) for initial IHTC values that were less than the optimized value of 7000 W m-2 K-1 for the chill-metal interfaces.

Nayak, Ramesh K.; Sundarraj, Suresh

2010-02-01

391

Influence of Operating Conditions and Physical Properties of Liquid Medium on Volumetric Oxygen Transfer Coefficient in a Dual Impeller Bioreactor  

Directory of Open Access Journals (Sweden)

Full Text Available The objective of this research was to study the effects of process variables on the volumetric mass transfer coefficient of oxygen, KLa, in a stirred bioreactor using the static gassing-out method. In this study, various process conditions were chosen, including 3 parameters, namely, concentration of glucose in medium (10, 15 and 20 g/l, air flow rate (1, 1.25, 1.5 and 1.75 vvm, and agitation rate (300, 400, 500 and 600 rpm. From the results, it was found that the KLa increased with increasing air flow rate and/or speed of agitation, but decreased with increasing concentration of glucose in medium. The maximum KLa occurred when the concentration of glucose in medium was the least (10 g/l, with an air flow rate of 1.75 vvm, and an agitation rate of 600 rpm. Correlations have been developed for the estimation of volumetric mass transfer coefficients at various process conditions for medium with different glucose concentrations. The exponent values representing dependence of KLa on the process conditions were then compared with literature values.

Kongdej LIMPAIBOON

2013-12-01

392

Transverse heat transfer coefficient in the dual channel ITER TF CICCs. Part I: Analysis of steady state temperature profiles resulting from annular heating  

Science.gov (United States)

Two ITER TF dual channel Cable-in-Conduit Conductors (CICCs) have been tested in the SULTAN test facility. The samples were heated either by foil heaters mounted on the outside of the conductor jacket or by induced AC losses. The steady-state temperature response of several thermometers installed on the jacket surface as well as inside the cable were analyzed using the two-channel analytical model proposed by Renard et al. to obtain the equivalent transverse heat transfer coefficient between the bundle and central channel as a function of the mass flow rate. In addition, on the basis of the measured pressure drop and helium flow velocities, the friction factors for helium flow in the bundle and in the central channel were determined. The obtained results may serve as a reference for these cables.

Lewandowska, Monika; Herzog, Robert

2011-10-01

393

Determination of the nuclear vertex constants (asymptotic coefficients) from charged particle transfer reactions  

International Nuclear Information System (INIS)

A new method is suggested for calculating nuclear vertex constants (NVC) from charged-particle transfer reactions taking Coulomb effects into account. Experimental differential cross sections of the D(d, n)3He and T(d, n)4He reactions are analyzed for different energies of the incident deuterons. The NVC square for the virtual processes 3He ? d+p and ? ? t+p are obtained

394

Determination of nuclear vertex constants (asymptotic coefficients) from charged-particle-transfer reactions  

International Nuclear Information System (INIS)

We propose a new method of determination of nuclear vertex constants (NVC) from charged-particle-transfer reactions taking into account Coulomb effects. We analyze experimental differential cross sections for the D(d,n)3He and T(d,n)4He reactions at different energies of incident deuterons and extract squares of NVC for the virtual processes 3He?d+p and ??t+p

395

Evaluation of Heat and Mass Transfer Coefficients for R134a/DMF Bubble Absorber  

OpenAIRE

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...

Suresh, M.; Mani, A.

2011-01-01

396

Experimental Study on States of Liquid Film on Heat Transfer Surface Inside a Horizontal Spirally Grooved Tube during Evaporation  

Science.gov (United States)

This paper presents a prediction method of flow regimes during evaporation of pure refrigerants in a horizontal spirally grooved steel tube with 12mm in average inner diameter. Circumferential temperature distributions on the external surface of the tube and boiling heat transfer coefficients were obtained through the experiments on the flow boiling heat transfer using two kinds of fluorocarbon refrigerants, HCFC123 and HCFC22. Based on the temperature distributions and the characteristics of heat transfer coefficient against vapor quality, we discussed the conditions of liquid film formed on the heat transfer surface. The experimental data were classified into four kinds of flow regimes according to the viewpoint on the liquid film conditions and heat transfer characteristics: annular flow, annular flow with liquid meniscus, separated flow with liquid meniscus and separated flow with dry surface. In order to predict the transition quality from separated flow to annular flow, we developed the correlation for border angle of well-wetted perimeter for the present grooved tube based on the Mori et al. correlation proposed for smooth tubes. The correlation for the transitional quality between separated flow with dry surface and separated flow with liquid meniscus was developed empirically as well as the correlation for the transient transitional quality between annular flow and annular flow with liquid meniscus.

Higashiiue, Shinya; Momoki, Satoru; Shigechi, Toru; Mori, Hideo; Yamaguchi, Tomohiko

397

Analytic approach to charge transfer during atom-surface scattering  

International Nuclear Information System (INIS)

We present an analytic approach to the solution of the time-dependent Newns-Anderson model of charge transfer during atom-surface scattering. For sufficiently slow atomic velocities we show, using a WKB technique, that the time evolution of the electronic state of the atom is determined by the instantaneous quasiparticle energies of the coupled atom plus surface system. Surface electronic structure and level-crossing effects are thus incorporated into the theory in a natural way. The results of the analysis compare quite favorably with numerical solutions and recently discovered exact solutions

398

Development of evaluation method on flow-induced vibration and corrosion of components in two-phase flow by coupled analysis. 4. The evaluation of the mass transfer coefficient induced by a turbulence flow  

International Nuclear Information System (INIS)

The pipe thinning phenomenon which is due to flow accelerated corrosion (FAC) is one of the major causes of unexpected troubles at current nuclear power plants. In order to prevent these troubles in the future, it is highly important to understand and analyze FAC mechanism. So, we calculated three dimensional flow to evaluate a turbulence energy and a mass transfer coefficient at pipe surface which is one of the key parameters of corrosion model. (author)

399

Ion-driven permeation and surface recombination coefficients of deuterium for silver  

International Nuclear Information System (INIS)

The steady-state flux of ion-driven permeation of deuterium through a silver membrane was measured in the range of 160-700deg C. The permeation flux increased with temperature above ? 400deg C, whereas it was roughly constant below ? 300deg C. This temperature dependence is essentially the same as those observed for nickel, iron, and copper, indicating that the transport regime is RD above ? 400deg C and DD below ? 300deg C. The surface recombination coefficient of deuterium was evaluated from the permeation flux density and compared with a semitheoretical calculation. The result is consistent with the small sticking probability of hydrogen on silver, or the high activation barrier for hydrogen adsorption on silver. (orig.)

400

Ion-driven permeation and surface recombination coefficient of deuterium for iron  

International Nuclear Information System (INIS)

The steady-state flux of deuterium permeation through an iron membrane (99.99+% purity, 0.14 mm thickness) driven by a deuterium ion beam (5 keV D3+, 1.0x1015 D-atoms cm-2 s-1) was measured in the range of 30-1050 C. The permeation flux increased with increasing temperature above 200 C whereas it was roughly constant below 150 C. Such temperature dependence was observed for nickel and copper as well, and has been ascribed to the transition in the rate-limiting processes of the deuterium transport in the membrane. The recombination coefficient of deuterium on iron surface was evaluated from the permeation flux density. In the case of ?-iron, the evaluated value agreed with a semitheoretical one estimated using literature data of adsorption probability and solubility. This agreement indicates that the release kinetics reflects the activation barrier for hydrogen (deuterium) absorption. (orig.)

401

Mathematical simulation of stationary surface concentration and sputtering coefficients for multicomponent vacuum coatings  

International Nuclear Information System (INIS)

The paper presents the calculated sputtering coefficients of five-component Ni-Co-Cr-Al-Y coating irradiated with five-component ion beam of the same atoms as well as the steady-state element concentrations at surface region of NbC and Co-Cr-Al coatings bombarded, respetively, with two- and three-component ion beams of the same atoms of kinetic energies in the range 100 eV...1.5 keV. The computation results for both latter coatings are compared with the experimental data obtained by the authors of this work. It is shown that the computation results are not contrary to the experimental data. Discussed is a possibility to obtain in the multicomponent coating the prescribed component concentrations at the subsurface region. Computations wre performed by using a problem program PERST

402

Local pool boiling heat transfer on a 3 Degree inclined tube surface  

Energy Technology Data Exchange (ETDEWEB)

Mechanisms of pool boiling heat transfer have been studied for a long time. Recently, it has been widely investigated in nuclear power plants for the purpose of acquiring inherent safety functions in case of no power supply. To design more efficient heat exchangers, effects of several parameters on heat transfer must be studied in detail. One of the major issues is variation in local heat transfer coefficients on a tube. Lance and Myers reported that the type of boiling liquid can change the trend of local heat transfer coefficients along the tube periphery. Lance and Myers said that as the liquid is methanol the maximum local heat transfer coefficient was observed at the tube bottom while the maximum was at the tube sides as the boiling liquid was n hexane. Corn well and Einarsson reported that the maximum local heat transfer coefficient was observed at the tube bottom, as the boiling liquid was R113. Corn well and Houston explained the reason of the difference in local heat transfer coefficients along the tube circumference with introducing effects of sliding bubbles on heat transfer. According to Gu pta et al., the maximum and the minimum local heat transfer coefficients were observed at the bottom and top regions of the tube circumference, respectively, using a tube bundle and water. Kang also reported the similar results using a single horizontal tube and water. However, the maximum heat transfer coefficient was observed at the angle of 45 deg. Sateesh et al. investigated variations in local heat transfer coefficients along a tube periphery as the inclination angle was changed. Summarizing the published results, some parts are still remaining to be investigated in detail. Although pool boiling analysis on a nearly horizontal tube is necessary for the design of the advanced power reactor plus, no previous results are published yet. Therefore, the present study is aimed to study variations in local pool boiling heat transfer coefficients for a 3 degree inclined tube submerged in subcooled or saturated water.

Kang, Myeong Gie [Andong National Univ., Kyungbuk (Korea, Republic of)

2012-10-15

403

Photoinduced Charge Transfer from Titania to Surface Doping Site  

OpenAIRE

We evaluate a theoretical model in which Ru is substituting for Ti at the (100) surface of anatase TiO2. Charge transfer from the photo-excited TiO2 substrate to the catalytic site triggers the photo-catalytic event (such as water oxidation or reduction half-reaction). We perform ab-initio computational modeling of the charge transfer dynamics on the interface of TiO2 nanorod and catalytic site. A slab of TiO2 represents a fragment of TiO2 nanorod in the anatase phase. Titanium to ruthenium r...

Inerbaev, Talgat; Hoefelmeyer, James D.; Kilin, Dmitri S.

2013-01-01

404

Three-dimensional MHD flow and heat transfer through porous medium bounded by a porous vertical surface with heat source and variable permeability  

International Nuclear Information System (INIS)

In the present paper we study the effect of magnetic field on three-dimensional flow and heat transfer through a porous medium bounded by a porous vertical surface in the presence of heat source and periodic permeability of the medium. Using perturbation technique, the velocity distributions, temperature distributions, skin-friction coefficient and the rate of heat transfer in terms of the Nusselt number at the surface are derived, discussed numerically and shown graphically. (author)

405

Experimental Investigation of Convective Heat Transfer during Night Cooling with Different Ventilation Systems and Surface Emissivities  

DEFF Research Database (Denmark)

Night-time ventilation is a promising approach to reduce the energy needed for cooling buildings without reducing thermal comfort. Nevertheless actual building simulation tools have showed their limits in predicting accurately the efficiency of night-time ventilation, mainly due to inappropriate models for convection. In a full-scale test room, the heat transfer was investigated during 12 h of discharge by night-time ventilation. A total of 34 experiments have been performed, with different ventilation types (mixing and displacement), air change rates, temperature differences between the inlet air and the room, and floor emissivities. This extensive experimental study enabled a detailed analysis of the convective and radiative flow at the different surfaces of the room. The experimentally derived convective heat transfer coefficients (CHTC) have been compared to existing correlations. For mixing ventilation, existing correlations did not predict accurately the convective heat transfer at the ceiling due to differences in the experimental conditions. But the use of local parameters of the air flow showed interesting results to obtain more adaptive CHTC correlations. For displacement ventilation, the convective heat transfer was well predicted by existing correlations. Nevertheless the change of floor emissivity influenced the CHTC at the surface of interest.

Le Dreau, Jerome; Heiselberg, Per

2013-01-01

406

Determination of blade-to-coolant heat-transfer coefficients on a forced-convection, water-cooled, single-stage turbine  

Science.gov (United States)

Blade-to-coolant convective heat-transfer coefficients were obtained on a forced-convection water-cooled single-stage turbine over a large laminar flow range and over a portion of the transition range between laminar and turbulent flow. The convective coefficients were correlated by the general relation for forced-convection heat transfer with laminar flow. Natural-convection heat transfer was negligible for this turbine over the Grashof number range investigated. Comparison of turbine data with stationary tube data for the laminar flow of heated liquids showed good agreement. Calculat