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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

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

3

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

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

4

This study attempts to examine the significance of recent research that has focused on efforts to estimate values for global and surface heat transfer coefficients under forced convection heating induced by end-over-end rotation in retorting of canned peas in brine. The study confirms the accuracy of regression analysis used to predict values for heat transfer coefficients as a function of rotating speed and headspace, and uses them to predict values over a range of process conditions, which make up the search domain for process optimization. These coefficients were used in a convective heat transfer model to establish a range of lethality-equivalent retort temperature-time processes for various conditions of retort temperature, rotating speed, and headspace. Then, they were coupled with quality factor kinetics to predict the final volume average and surface quality retention resulting from each process and to find the optimal thermal process conditions for canned fresh green peas. Results showed that maximum quality retention (surface and volume average retention) was achieved with the shortest possible process time (made possible with highest retort temperature), and reached the similar level in all cases with small difference between surface and volume average quality retention. The highest heat transfer coefficients (associated with maximum rotating speed and headspace) showed a 10% reduction in process time over that required with minimum rotating speed and headspace. The study concludes with a discussion of the significance of these findings and degree to which they were expected. PMID:19019110

Simpson, R; Abakarov, A; Almonacid, S; Teixeira, A

2008-10-01

5

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 coefficient and the flow characteristics has been evaluated so as to investigate the flow characteristics in the SWAT-1R experiment. (author)

6

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.

7

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

8

International Nuclear Information System (INIS)

Convective heat transfer at exterior building surfaces has an impact on the design and performance of building components such as double-skin facades, solar collectors, solar chimneys and ventilated photovoltaic arrays, and also affects the thermal climate and cooling load in urban areas. In this study, an overview is given of existing correlations of the exterior convective heat transfer coefficient (CHTC) with the wind speed, indicating significant differences between these correlations. As an alternative to using existing correlations, the applicability of CFD to obtain forced CHTC correlations is evaluated, by considering a cubic building in an atmospheric boundary layer. Steady Reynolds-averaged Navier-Stokes simulations are performed and, instead of the commonly used wall functions, low-Reynolds number modelling (LRNM) is used to model the boundary-layer region for reasons of improved accuracy. The flow field is found to become quasi independent of the Reynolds number at Reynolds numbers of about 105. This allows limiting the wind speed at which the CHTC is evaluated and thus the grid resolution in the near-wall region, which significantly reduces the computational expense. The distribution of the power-law CHTC-U10 correlation over the windward and leeward surfaces is presented (U10 = reference wind speed at 10 m height). It is shown that these correlations can be accurately determined by simulations with relatively low wind spey simulations with relatively low wind speed values, which avoids the use of excessively fine grids for LRNM, and by using only two or three discrete wind speed values, which limits the required number of CFD simulations.

9

In this paper, the local convective heat transfer coefficient (h) is measured along the surface of an electrically heated vertical wire using digital holographic interferometry (DHI). Experiments are conducted on wires of different diameters. The experimentally measured values are within the range as given in the literature. DHI is expected to provide a more accurate local convective heat transfer coefficient (h) as the value of the temperature gradient required for the calculation of "h" can be obtained more accurately than by other existing optical interferometric techniques without the use of a phase shifting technique. This is because in digital holography phase measurement accuracy is expected to be higher. PMID:25322139

Kumar, Varun; Kumar, Manoj; Shakher, Chandra

2014-09-20

10

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

11

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.)

12

Energy Technology Data Exchange (ETDEWEB)

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.)

Wanninger, Andreas; Ceuca, Sabin Cristian; Macian-Juan, Rafael [Technische Univ. Muenchen, Garching (Germany). Dept. of Nuclear Engineering

2013-07-01

13

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.

14

Effect of surface roughness on local film cooling effectiveness and heat transfer coefficients

In high temperature gas turbine engines, the life cycle of the hot section is extremely dependent on accurate design prediction of component temperature distribution. Particular attention must be paid to the film cooling performance of the first stage turbine stator vanes where the highest heat loads are encountered. Recent investigations have determined during operation the smooth surface of high pressure turbine vanes become rough due to corrosion, oxidation and particulate impact. A transient experimental method has been developed to obtain both local heat transfer and cooling effectiveness information downstream of a row of film cooling holes on a rough flat plate. This investigation provides information on the effects of roughness on film cooling heat transfer for a Reynolds number and dimensionless boundary layer momentum thickness which match conditions applicable to the pressure side of the first stage turbine vane of the Pratt and Whitney F-100-PW229 engine. Data for film cooling on rough surfaces are extremely limited in the literature. However, comparison with the available data is made.

Barlow, Douglas N.

1994-08-01

15

International Nuclear Information System (INIS)

HTPGB1 calculates from experimental data the variation in heat transfer coefficient round a cyclindrical surface. The structure within the cylindrical surface is assumed to consist of a series of concentric annuli for any one of which the physical properties and volume generation of heat remain constant, but may vary from one annulus to another. Conduction of heat along the cylinder is assumed negligible. However, an adjustment for the localised longitudinal conduction effects associated with ribbed surfaces may be included. The information provided by the program can be used in the prediction of round pin temperature variations in a reactor from out-of-pile tests. It is essential for obtaining the correct interpretation of experimental data when the reduction of temperature differences by thermal conduction within the surface is different in the reactor and the experiment. (author)

16

For mammalian cell culture, getting a continuous supply of oxygen and extracting carbon dioxide are primary challenges even in the most modern biopharmaceutical manufacturing plants, due to the low oxygen solubility and excessive carbon dioxide accumulation. In addition, various independent flow and mass transfer characteristics in the culture tanks vessel make scale-up extremely difficult. One method for overcoming these and providing rational optimization is solving the fluid and mass transport equations by numerical simulation. To develop a simulation program, it is decisively important to know mass transfer coefficients of gaseous species in the culture tank. In this study, oxygen mass transfer coefficients are measured using a beaker with a sparger and impellers. In order to investigate the formulation of the mass transfer coefficients, the turbulent flow statistics is calculated by a CFD code for all cases, and the expressions of the mass transfer coefficients are established as functions of the statistics. Until now, the expression by Kawase is known in this field. This expression becomes a function only of energy dissipation rate epsilon. It does not coincide with the conventional experimental fact that mass transfer coefficient is proportional power 0.5 of impeller rotation speed. The new mass transfer coefficient is dependent on both of energy dissipation rate epsilon and turbulent flow energy k. It satisfies the relation of power of 0.5 of impeller rotation speed. PMID:18347829

Amano, Ken; Haga, Ryoichi; Murakami, Sei

2008-06-01

17

International Nuclear Information System (INIS)

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

18

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

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)

20

Inverse determination of local heat transfer coefficient

International Nuclear Information System (INIS)

on the heated tube with two longitudinal fins in cross flow demonstrates the accuracy of the developed method. The actual experimental data were used. Experiments were performed with an array of vertical tubes arranged in staggered pattern. The experimental results reported herein are among the first that show the variation of the local heat transfer coefficients over the circumference of the finned tube. Most data reported previously were acquired for smooth tubes at low temperatures. The main advantage of the method is that it does not require any knowledge, or solution to, the complex fluid flow field. It should be noted that determining unknown steady distribution of heat transfer coefficients by using the developed method is inexpensive, since it requires only one fluid temperature probe and a few thermocouples for temperature measurements inside the solid. Refs. 4 (author)

21

Local Pool Boiling Heat Transfer Coefficients on Near Horizontal Tubes

International Nuclear Information System (INIS)

They said that as the liquid is methanol the maximum local heat transfer coefficient (hb,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

22

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

23

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

24

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

25

Condensation heat transfer coefficients of flammable refrigerants

Energy Technology Data Exchange (ETDEWEB)

In this study, external condensation heat transfer coefficients (HTCs) of six flammable refrigerants of propylene (R1270), propane (R290), isobutane (R600a), butane (R600), dimethylether (RE170), and HFC32 were measured at the vapor temperature of 39 {sup o}C on a plain tube of 19.0 mm outside diameter with a wall subcooling of 3-8 {sup o}C under a heat flux of 7-23 kW m{sup -2}. Test results showed a typical trend that external condensation HTCs decrease with the wall subcooling. No unusual behavior or phenomenon was observed for these flammable refrigerants during experiments. HFC32 and DME showed 28-44% higher HTCs than those of HCFC22 due to their excellent thermophysical properties. Propylene and butane showed the similar HTCs as those of HCFC22 while propane and isobutane showed 9% lower HTCs than those of HCFC22. Finally, a general correlation was made by modifying Nusselt's equation based upon the measured data of eleven fluids of various vapor pressures including halogenated refrigerants. The general equation showed an excellent agreement with all data exhibiting a deviation of less than 3%. (author)

Dongsoo Jung; Soonam Chae; Dongsoo Bae [Inha University, Incheon (Korea). Department of Mechanical Engineering; Sukjae Oho [TechnoChem Co. Ltd., Kyunggi-Do (Korea)

2004-05-01

26

Modeling satellite drag coefficients with response surfaces

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

27

Local heat transfer coefficients during condensation of R-22 and R-32/R-125 mixtures

Energy Technology Data Exchange (ETDEWEB)

In this paper local and average heat transfer coefficients during condensation of refrigerants R-22 and two mixtures of R-32/R-125 (45%/55% and 25%/75%) are presented. The local heat transfer coefficients were determined using a specially instrumented test section that measured local energy flow and surface temperatures during condensation. The local test section used an 8.0 mm (0.32 in) inner diameter smooth tube that was 1.93 m (6.3 ft) long. Average heat transfer coefficients were determined using the Log-Mean-Temperature-Difference equations. The local method yielded useful information on the variation of heat transfer coefficients with refrigerant quality and mass flux. Typically, heat transfer coefficients were found to double from low to high quality at a particular mass flux, while smaller increases occurred with mass flux. Evaluation of local heat transfer coefficients confirmed that the method yields reasonable results. Specifically, comparison of the average of local heat transfer coefficients with measured average heat transfer coefficients showed excellent agreement. The results also indicated that the R-32 (45%)/R-125 (55%) mixture had slightly better heat transfer performance than R-22, while the R-32 (25%)/R-125 (75%) mixture had significantly lower heat transfer performance than R-22.

Eckels, S.J.; Unruh, B.J.

1999-07-01

28

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

29

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

30

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)

31

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)

32

Tests were performed in a transient heat transfer tunnel in which the model under test was preheated prior to allowing room temperature air to be suddenly drawn over the model. The resulting movement of isothermal contours on the model is revealed using a surface coating of thermochromic liquid crystals that display distinctive colors at particular temperatures. A video record is obtained of a temperature and time data pair for all points on the model during a single test. Experiments on a duct model are reported in which the model was preheated using a hot air stream. A manner in which initial model temperature nonuniformities could be taken into account was investigated. The duct model was also tested with a steady-state measurement technique and results were compared with the transient measurements, but recognizing that differences existed between the upstream thermal boundary conditions. The steady-state and transient measurements were shown to be consistent with predicted values. The main advantage of this transient heat transfer technique using liquid crystals is that since the test model need not be actively heated, high-resolution measurements on surfaces with complex shapes may be obtained.

Jones, Terry V.; Hippensteele, Steven A.

1988-01-01

33

Estimation of Volumetric Mass Transfer Coefficient in Bioreactor

Directory of Open Access Journals (Sweden)

Full Text Available This study is concentrated to investigate the effects of aeration and stirring speed on the volumetric mass transfer coefficient (KLa. A dynamic technique was used in estimating KLa values in order to achieve the aim of this study.This study was done in 10L bioreactor by using two medias:-1. Dionized water2. Xanthan solution (1 g /LMoreover, the research covered a comparison between the obtained values of KLa.The Xanthan solution was used because of its higher viscosity in comparison with water. It behaves similarly to the cultivation medium when organisms are cultivated in a bioreactor. Growth of organisms in the reactor leads to a change in the viscosity of the medium which affects the mass transfer.Two variables, the effect of air flow rate (3-20 L/min and the effect of stirring speed (250-700rpm on KLa value were studied. Other parameters such as temperature, liquid volume, and stirrer shape and stirrer position were held constant; the results demonstrated an increase in KLa ? value and mass transfer with increasing stirrer speed. Thus at higher speed, better dispersion of the bubbles was obtained. Therefore, that increased the surface / volume ratio which increased the mass transfer area i.e. KLa value.

Zainab Yaquob Atiya

2012-01-01

34

International Nuclear Information System (INIS)

In this study, we aimed to realize a parametric determination of the convective heat transfer coefficient of a gasoline engine on both the in-cylinder and jacket sides. The combustion products have been determined as a function of excess air coefficient. Cylinder temperature and pressure have been calculated with a simplistic model based on the First Law of Thermodynamics. The in-cylinder heat transfer coefficient is evaluated by using two different expressions; one a specific form of Annand's equation and the other the Woschni equation. Newton's convective heat transfer equation has been utilized to obtain the heat transfer coefficient between the engine block and the cooling water. This process is based on some temperature measurements at various locations in the cooling space, as the distance between the tip of the temperature sensor and the inner cylinder surface is varied for each location. We determined values of both coefficients for various engine parameters

35

Measurement of heat transfer coefficients by nuclear magnetic resonance.

We demonstrate an experimental method for the measurement of heat transfer coefficient for a fluid system by magnetic resonance imaging. In this method, the temporal variation of thermally induced nuclear shielding is monitored and the average heat transfer coefficient is measured as a function of fluid velocity. We examine the cases of natural convection and forced convection at fluid velocity up to 0.8 m s(-1). These cases correspond to low dimensionless Biot (Bi) number where the heat transfer is limited by thermal convection. We demonstrate the NMR method for two simple geometries, a cylinder and a sphere, to experimentally determine the heat transfer coefficient (h) in two NMR imaging and spectroscopy systems through measuring three NMR parameters, the chemical shift, magnetization and spin self diffusion coefficient. PMID:18524523

Gultekin, David H; Gore, John C

2008-11-01

36

Surfaces with adaptive radar reflection coefficients

Conventional (passive) radar-absorbing materials (RAM) have been in use now for over half a century, but it is only with recent advances in conducting polymer composite materials that large-area surfaces having controllable reflection coefficients at radar frequencies have become practicable. Techniques for utilizing these new materials in re-configurable electromagnetic, or `smart', surfaces are reviewed, with due emphasis given to the problem of system integration. The discussion is complemented by modelled and measured performance data on several smart surface configurations.

Chambers, Barry

1997-10-01

37

Measurement of heat transfer coefficient using termoanemometry methods

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This work deals with a measurement of heat transfer from a heated flat plate on which a synthetic jet impacts perpendicularly. Measurement of a heat transfer coefficient (HTC) is carried out using the hot wire anemometry method with glue film probe Dantec 55M47. The paper brings also results of velocity profiles measurements and turbulence intensity calculations.

Dan?ová P.; Sitek P; Vít T.

2014-01-01

38

Measurement of heat transfer coefficient using termoanemometry methods

This work deals with a measurement of heat transfer from a heated flat plate on which a synthetic jet impacts perpendicularly. Measurement of a heat transfer coefficient (HTC) is carried out using the hot wire anemometry method with glue film probe Dantec 55M47. The paper brings also results of velocity profiles measurements and turbulence intensity calculations.

Dan?ová, P.; Sitek, P.; Vít, T.

2014-03-01

39

Subcooled boiling heat transfer on a finned surface

International Nuclear Information System (INIS)

Experimental and numerical studies have been performed to determine the heat transfer coefficients from a finned cylindrical surface to subcooled boiling water. The heat transfer rates were measured in an annular test section consisting of an electrically heated fuel element simulator (FES) with eight longitudinal, rectangular fins enclosed in a glass tube. A two-dimensional finite-element heat transfer model using the Galerkin method was employed to determine the heat transfer coefficients along the periphery of the FES surface. An empirical correlation was developed to predict the heat transfer coefficients during subcooled boiling. The correlation agrees well with the measured data. (6 figures) (Author)

40

Digital Repository Infrastructure Vision for European Research (DRIVER)

A new data reduction technique for measuring the convective heat transfer coefficient is reported. The technique is based on the evaluation of the Fourier transform of simultaneously measured free stream temperature and surface wall temperature or heating power. Any wave shape can be used to heat-up the stream or the wall and the method yields information redundancy on the local heat transfer coefficient. Effects of various uncertainties on the accuracy of the heat transfer coefficient evalua...

Cossali, Gianpietro

2004-01-01

41

Overall Heat and Mass Transfer Coefficient of Water Vapor Adsorption

A fundamental investigation was performed to develop a compact and simple desiccant ventilation unit which is one of the main components of a novel energy saving air-conditioning system. Water vapor in the air is adsorbed and/or desorbed to be controlled the humidity of supply air through a unit of an adsorbent rotor. A numerical simulation helps to understand the phenomena of heat and mass transfer in the rotor block. Overall transfer coefficients were estimated by performing both experiment and calculation. It was examined that the transient overall equivalent heat and mass transfer coefficient was not constant. It seems that both film fluid and diffusion resistance govern the coefficients in the block, and the influence of air flow on the time averaged coefficients is estimated by a considering the laminar forced convection from a flat plate. There is little difference of the coefficient between adsorption and desorption process. The correlation and fitting parameters are presented for prediction of the overall heat and mass transfer coefficients. The estimation accuracy was improved.

Hamamoto, Yoshinori; Mori, Hideo; Godo, Masazumi; Miura, Kunio; Watanabe, Yutaka; Ishizawa, Toshihiko; Takatsuka, Takeshi

42

Heat transfer coefficient in serpentine coolant passage for CCDTL

International Nuclear Information System (INIS)

A series of heat transfer experiments were conducted to refine the cooling passage design in the drift tubes of a coupled cavity drift tube linac (CCDTL). The experimental data were then compared to numerical models to derive relationships between heat transfer rates, Reynold's number, and Prandtl number, over a range of flow rates. Data reduction consisted of axisymmetric finite element modeling where the heat transfer coefficients were modified to match the experimental data. Unfortunately, the derived relationship is valid only for this specific geometry of the test drift tube. Fortunately, the heat transfer rates were much better (approximately 2.5 times) than expected

43

Heat transfer coefficient in serpentine coolant passage for CCDTL

Energy Technology Data Exchange (ETDEWEB)

A series of heat transfer experiments were conducted to refine the cooling passage design in the drift tubes of a coupled cavity drift tube linac (CCDTL). The experimental data were then compared to numerical models to derive relationships between heat transfer rates, Reynold`s number, and Prandtl number, over a range of flow rates. Data reduction consisted of axisymmetric finite element modeling where the heat transfer coefficients were modified to match the experimental data. Unfortunately, the derived relationship is valid only for this specific geometry of the test drift tube. Fortunately, the heat transfer rates were much better (approximately 2.5 times) than expected.

Leslie, P.; Wood, R.; Sigler, F.; Shapiro, A.; Rendon, A.

1998-12-31

44

Experimental evaluation of heat transfer coefficients between radiant ceiling and room

Energy Technology Data Exchange (ETDEWEB)

The heat transfer coefficients between radiant surfaces and room are influenced by several parameters: surfaces temperature distributions, internal gains, air movements. The aim of this paper is to evaluate the heat transfer coefficients between radiant ceiling and room in typical conditions of occupancy of an office or residential building. Internal gains were therefore simulated using heated cylinders and heat losses using cooled surfaces. Evaluations were developed by means of experimental tests in an environmental chamber. Heat transfer coefficient may be expressed separately for radiation and convection or as one total parameter, but this choice may lead to different considerations about thermal performance of the system. In order to perform correct evaluations, it is therefore extremely important to use the proper reference temperature. The obtained values confirm tendencies found in the literature, indicating limitations and possibilities of radiant ceiling systems improvement. (author)

Causone, Francesco; Corgnati, Stefano P.; Filippi, Marco [TEBE Research Group, Department of Energetics, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino (Italy); Olesen, Bjarne W. [ICIEE, Department of Civil Engineering, Technical University of Denmark, Nils Koppels Alle Building 402, 2800 Kgs. Lyngby (Denmark)

2009-06-15

45

Energy Technology Data Exchange (ETDEWEB)

The efficiency of energy utilization within coal-liquefaction process is of major significance to the commercialization of the process. Heat exchange equipment is also one of the major economic investments in new plants. Consequently, reliable heat transfer data are required for the economical design of heat exchange equipment. Since accurate heat transfer coefficients of coal slurries, especially with a gas phase present, cannot be accurately calculated from known physical data for the operational conditions found in the coal-liquefaction process, experimentally determined heat transfer coefficients under actual process conditions are needed. A liquefaction heat-transfer-coefficient measurement test unit for a nominal one-half-ton-per-day coal slurry was constructed, calibrated, and operated at ANL. This test unit was built to determine heat transfer coefficients needed for design of feed-heat and effluent-heat exchangers used in coal-liquefaction processes. The heat-transfer test module was substituted for the preheater and reactor used in the normal coal-liquefaction process. The heat transfer coefficient can be evaluated for the heat transfer between the three-phase feed and effluent fluids in turbulent flow and a heated or cooled stainless steel surface. A description is presented of the unit and its capabilities, calibration procedures and results, and preliminary operation and data analysis. Recommendations are made that should improve accuracy and ease of operation and data analysis of the test unit.

Mulcahey, T.P.; Lo, R.N.K.; Bump, T.R.; Mulcahey, M.E.; Fischer, J.; Cannon, T.F.; Brock, R.E.; Wilson, W.I.; Bowyer, D.

1979-06-01

46

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

47

Boiling heat transfer intensity on small-size surface

Digital Repository Infrastructure Vision for European Research (DRIVER)

Dependence of heat-release surface of heat carrier (water and ethanol) characteristic size, boundary conditions and thermophysical properties on boiling heat transfer intensity on small-size surface was investigated. Criterion equation for boiling heat transfer coefficients on small-size surface was obtained.

Alekseik O. S.; Yu, Kravets V.; Kopchevskaya I. A.

2012-01-01

48

Boiling heat transfer intensity on small-size surface

Directory of Open Access Journals (Sweden)

Full Text Available Dependence of heat-release surface of heat carrier (water and ethanol characteristic size, boundary conditions and thermophysical properties on boiling heat transfer intensity on small-size surface was investigated. Criterion equation for boiling heat transfer coefficients on small-size surface was obtained.

Alekseik O. S.

2012-02-01

49

International Nuclear Information System (INIS)

Sodium-water reaction (SWR) in a steam generator of sodium-cooled fast reactor (SFR) is a significant phenomenon for safety assessment of the system. One of the top concerns in the SWR is an overheating rupture phenomenon in which a neighbor heat transfer tube fails instantaneously because of a deterioration of structural integrity under a high temperature condition. Hence, the heat transfer coefficient on the tube surface is of importance. Since hydrogen gas is generated in the SWR and liquid water will evaporate quickly due to depressurization, the reaction region is covered with a multi-phase flow structure, and thus the value of the heat transfer coefficient will vary widely. In the present paper, a correlation diagram has been developed between the heat transfer coefficient and the void fraction based on one dimensional homogeneous flow simulation. Furthermore, the transient of void fraction in SWAT-1R experiment is investigated using the diagram. (author)

50

The inverse heat transfer problem is one of considerable practical interest in the analysis and design of experimental heat transfer investigations. The analytical and experimental investigation of the inverse heat transfer coefficients in multi-dimensional convective heat transfer applications is examined. An application considered is the sudden quenching of a hot solid in a cold liquid. Other applications include thermal analysis of forced convection over impulsively started solid bodies and investigation of short duration wind tunnel experiments. The primary aim is to describe methods and algorithms for the solution of the ill-posed inverse heat transfer coefficient problem. The solution method used is an extension of the sequential future-information method of Beck. Numerical experiments are conducted for a systematic investigation of the developed algorithms on selected heat transfer coefficient test cases. The overall objective of the experimental work is to investigate the early transients in the heat transfer coefficients from spheres in one- and two-dimensional quenching experiments. Several experiments were performed by plunging hollow spheres in either ethylene glycol or water. The developed methods are used for the analysis of the quenching experiments for the estimation of the transient heat transfer coefficients. Analysis of the results indicate that the transient inverse technique has the capability of estimating early transients and subsequent quasi-steady state values of the heat transfer coefficients in a single transient experiment.

Osman, Arafa Mohamed

1987-05-01

51

Microscale surface modifications for heat transfer enhancement.

In this experimental study, two surface modification techniques were investigated for their effect on heat transfer enhancement. One of the methods employed the particle (grit) blasting to create microscale indentations, while the other used plasma spray coating to create microscale protrusions on Al 6061 (aluminum alloy 6061) samples. The test surfaces were characterized using scanning electron microscopy (SEM) and confocal scanning laser microscopy. Because of the surface modifications, the actual surface area was increased up to 2.8× compared to the projected base area, and the arithmetic mean roughness value (Ra) was determined to vary from 0.3 ?m for the reference smooth surface to 19.5 ?m for the modified surfaces. Selected samples with modified surfaces along with the reference smooth surface were then evaluated for their heat transfer performance in spray cooling tests. The cooling system had vapor-atomizing nozzles and used anhydrous ammonia as the coolant in order to achieve heat fluxes up to 500 W/cm(2) representing a thermal management setting for high power systems. Experimental results showed that the microscale surface modifications enhanced heat transfer coefficients up to 76% at 500 W/cm(2) compared to the smooth surface and demonstrated the benefits of these practical surface modification techniques to enhance two-phase heat transfer process. PMID:24003985

Bostanci, Huseyin; Singh, Virendra; Kizito, John P; Rini, Daniel P; Seal, Sudipta; Chow, Louis C

2013-10-01

52

Energy Technology Data Exchange (ETDEWEB)

The growth rate of a crystal in a supersaturated solution is limited by both reaction kinetics and the local concentration of solute. If the local mass transfer coefficient is too low, concentration of solute at the crystal-solution interface will drop below saturation, leading to a defect in the growing crystal. Here, mass transfer coefficients are calculated for a rotating crystal growing in a supersaturated solution of potassium diphosphate (KDP) in water. Since mass transfer is difficult to measure directly, the heat transfer coefficient of a scale model crystal in water is measured using temperature-sensitive paint (TSP). To the authors' knowledge this is the first use of TSP to measure temperatures in water. The corresponding mass transfer coefficient is then calculated using the Chilton- Colburn analogy. Measurements were made for three crystal sizes at two running conditions each. Running conditions include periodic reversals of rotation direction. Heat transfer coefficients were found to vary significantly both across the crystal faces and over the course of a rotation cycle, but not from one face to another. Mean heat transfer coefficients increased with both crystal size and rotation rate. Computed mass transfer coefficients were broadly in line with expectations from the full-scale crystal growth experiments. Additional experiments show that continuous rotation of the crystal results in about a 30% lower heat transfer compared to rotation with periodic reversals. The continuous rotation case also shows a periodic variation in heat transfer coefficient of about 15%, with a period about 1/20th of the rotation rate.

Bell, J H; Hand, L A

2005-04-21

53

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.)

54

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

55

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

56

Digital Repository Infrastructure Vision for European Research (DRIVER)

The heat transfer coefficient over the surface of a pedestal with fillet radii has been measured using thermochromic liquid crystals and the transient heat transfer method. The tests were performed at engine representative Reynolds numbers for a geometry typical of those used in turbine blade cooling systems. The heat conduction process that occurs in the engine was subsequently modeled numerically with a finite element discretization of the solid pedestal. The measured heat transfer coeffici...

Wang, Z.; Ireland, Pt; Jones, Tv

1995-01-01

57

Uncertainty of evaluations of flow film boiling heat transfer coefficient

International Nuclear Information System (INIS)

The results of evaluations of the heat transfer coefficient (?s) for the flow film boiling (FFB) region received by two approaches, which are complemented each other are discussed here. In particular, they are as follows: 1) using empirical or semiempirical correlations, 2) developing the look-up tables (LUT). There is a need to distinguish two FFB heat transfer regime, such as 1) the post-dryout (PDO) heat transfer and 2) before critical heat flux (CHF) heat transfer. A new version of the LUT for ?s is presented at forced water flow in long tubes uniformly heated. It covers the following range of parameters: pressure 0.1/20 MPa; mass flux 250/3000 kg/m2·s; quality (-0.2)/2.2; heat flux 0.2/1.0 MW/m2; tube diameter 10 mm. The values of the FFB heat transfer coefficient in the LUT are marked by different methods depending on the used calculation method. Four methods were applied to develop the LUT for ?s, namely: 1) averaging experimental data, 2) calculations on the base of the Sergeev model, 3) using data from the LUT developed by Leung L. et al. (1997), 4) using both interpolation and extrapolation beyond the range of experimental data and theoretical evaluations. The calculated errors of the ?s values were obtained by comparison the LUT data with the experimental data stored in the database of the IPPE Thermophysical Data Center. (author)

58

Measurement and modeling of interface heat transfer coefficients

The results of preliminary work on the modeling and measurement of the heat transfer coefficients of metal/mold interfaces is reported. The system investigated is the casting of uranium in graphite molds. The motivation for the work is primarily to improve the accuracy of process modeling of prototype mold designs at the Los Alamos Foundry. The evolution in design of a suitable mold for unidirectional solidification is described, illustrating the value of simulating mold designs prior to use. Experimentation indicated a heat transfer coefficient of 2 kW/sq m /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.

Rollett, A. D.; Lewis, H. D.; Dunn, P. S.

59

Rewetting of a finite rod an arbitrary space-dependent heat transfer coefficient

International Nuclear Information System (INIS)

Two-dimensional rewetting models usually assume two or three regions, with different boundary conditions specified at the solid surface. The more advanced analytical solutions by eigenfunction expansions obtain a formed expression of the temperature distribution in each sub region with a constant heat transfer coefficient. This expression contains some, yet, unknown constants which are determined by matching the temperatures and their axial gradients at the interface between adjacent sub domains. As far as we know, to date there does not exist an analytical solution of a rewetting model with an arbitrary space-dependent heat transfer coefficient. Moreover, eigenfunction expansions solutions of models with a discontinuous heat transfer coefficient have been shown to impede convergence of the series and to decrease the solution accuracy. In the present study, we solve by eigenfunction expansions a two-dimensional model of rewetting of a finite length slab or cylindrical rod, with an arbitrary space-dependent heat transfer coefficient. The unique features of the present approach are the simplicity of the solution, which does not necessitates a tedious splitting of the solution domain into sub domains, and avoiding the convergence problem associated with cases of discontinuous heat transfer coefficients. (authors); 5 refs

60

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

61

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

62

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

63

In vivo measurement of swine endocardial convective heat transfer coefficient.

We measured the endocardial convective heat transfer coefficient h at 22 locations in the cardiac chambers of 15 pigs in vivo. A thin-film Pt catheter tip sensor in a Wheatstone-bridge circuit, similar to a hot wire/film anemometer, measured h. Using fluoroscopy, we could precisely locate the steerable catheter sensor tip and sensor orientation in pigs' cardiac chambers. With flows, h varies from 2500 to 9500 W/m2 x K. With zero flow, h is approximately 2400 W/m2 x K. These values of h can be used for the finite element method modeling of radiofrequency cardiac catheter ablation. PMID:15311835

Tangwongsan, Chanchana; Will, James A; Webster, John G; Meredith, Kenneth L; Mahvi, David M

2004-08-01

64

This paper presents a numerical method for determining heat transfer coefficients in cross-flow heat exchangers with extended heat exchange surfaces. Coefficients in the correlations defining heat transfer on the liquid- and air-side were determined using a nonlinear regression method. Correlation coefficients were determined from the condition that the sum of squared liquid and air temperature differences at the heat exchanger outlet, obtained by measurements and those calculated, achieved minimum. Minimum of the sum of the squares was found using the Levenberg-Marquardt method. The uncertainty in estimated parameters was determined using the error propagation rule by Gauss. The outlet temperature of the liquid and air leaving the heat exchanger was calculated using the analytical model of the heat exchanger.

Taler, Dawid

2012-09-01

65

Modeling the Gas Transfer Coefficient and Gas Fluxes in Stratified Lakes

Lakes and reservoirs are now recognized as significant sources of climatically-active trace gases to the atmosphere. Estimates will be improved if fluxes are computed using gas transfer coefficients which take into account the turbulence at the air-water interface which moderates the transport rather than the wind-only based values which are typically used. Here, in an analysis of eddy covariance results from a weakly stratified lake, we demonstrate how buoyancy flux, that is, heat loss or heat gain, moderates changes in the magnitude of the gas transfer coefficient, k600, during low to moderate winds. Our analysis shows that i) k600 depends on wind speed and buoyancy flux ?, ii) higher values of k600 occur during windy periods with surface cooling than with surface heating, iii) under overnight low wind conditions k600 is more dependent on ? than wind speed, iv) not only the meteorological conditions at the time of measurement but also the inertia within the lake determine k600. Eddy covariance estimates of k600 compare well with predictions of k600 using a surface renewal model for which the inputs are wind speed and ?. Modeling of green house gas emissions will be improved via inclusion of buoyancy flux and wind shear in the gas transfer coefficient as well as consideration of controls on the frequency of events which transport waters with higher gas concentrations to surface waters. Regional and global fluxes of greenhouse gases from lakes may be considerably larger than current estimates.

MacIntyre, S.; Jonsson, A.; Jansson, M.; Aberg, J.; Turney, D. E.; Emery, B. M.; Simons, R. D.; Miller, S. D.

2010-12-01

66

Pool boiling heat transfer coefficients for binary mixtures of acetone, isopropanol, and water

Energy Technology Data Exchange (ETDEWEB)

Pool boiling heat transfer coefficients, bubble departure diameters, and nucleation site densities have been measured for binary mixtures of acetone, isopropanol,and water. The measured heat transfer coefficients are compared to the predictions of a correlation developed by Schluender. Different approaches to determine the ideal heat transfer coefficient required for this correlation are evaluated.

Wenzel, U.; Balzer, F. [Univ. of Auckland (New Zealand). Dept. of Chemical and Materials Engineering; Jamialahmadi, M. [Univ. of Petroleum Industry, Ahwaz (Iran, Islamic Republic of)] Mueller-Steinhagen, H. [Univ. of Surrey, Guildford (United Kingdom). Dept. of Chemical and Process Engineering

1995-01-01

67

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

68

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

International Nuclear Information System (INIS)

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

69

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

70

Measurement of Dynamic Friction Coefficient on the Irregular Free Surface

International Nuclear Information System (INIS)

A spent fuel storage cask must be estimated for a structural integrity when an earthquake occurs because it freely stands on ground surface without a restriction condition. Usually the integrity estimation for a seismic load is performed by a FEM analysis, the friction coefficient for a standing surface is an important parameter in seismic analysis when a sliding happens. When a storage cask is placed on an irregular ground surface, measuring a friction coefficient of an irregular surface is very difficult because the friction coefficient is affected by the surface condition. In this research, dynamic friction coefficients on the irregular surfaces between a concrete cylinder block and a flat concrete slab are measured with two methods by one direction actuator

71

Directory of Open Access Journals (Sweden)

Full Text Available In this paper, the research progress of the interfacial heat transfer in high pressure die casting (HPDC is reviewed. Results including determination of the interfacial heat transfer coefficient (IHTC, influence of casting thickness, process parameters and casting alloys on the IHTC are summarized and discussed. A thermal boundary condition model was developed based on the two correlations: (a IHTC and casting solid fraction and (b IHTC peak value and initial die surface temperature. The boundary model was then applied during the determination of the temperature field in HPDC and excellent agreement was found.

Cao Yongyou

2014-07-01

72

The present study compares measured and computed heat transfer coefficients for high-speed boundary layer nozzle flows under engine Reynolds number conditions (U(sub INF) = 230 divided by 880 m/s, Re(sup *) = 0.37 divided by 1.07 x 10(sup 6)). Experimental data have been obtained by heat transfer measurements in a two-dimensional, nonsymmetric, convergent-divergent nozzle. The nozzle wall is convectively cooled using water passages. The coolant heat transfer data and nozzle surface temperatures are used as boundary conditions for a three-dimensional finite-element code, which is employed to calculate the temperature distribution inside the nozzle wall. Heat transfer coefficients along the hot gas nozzle wall are derived from the temperature gradients normal to the surface. The results are compared with numerical heat transfer predictions using the low-Reynolds-number k-epsilon turbulence model by Lam and Bremhorst. Influence of compressibility in the transport equations for the turbulence properties is taken into account by using the local averaged density. The results confirm that this simplification leads to good results for transonic and low supersonic flows.

Hurst, C.; Schulz, A.; Wittig, S.

1995-04-01

73

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

74

Digital Repository Infrastructure Vision for European Research (DRIVER)

The heat transfer coefficient over the surface of a pedestal with fillet radii has been measured using thermochromic liquid crystals and the transient heat transfer method. The tests were performed at engine representative Reynolds numbers for a geometry typical of those used in turbine blade cooling systems. The heat conduction process that occurs in the engine was subsequently modelled numerically with a finite element discretization of the solid pedestal. The measured heat transfer coeffic...

Wang, Z.; Ireland, Pt; Jones, Tv

1993-01-01

75

International Nuclear Information System (INIS)

The heat-transfer coefficients around a workpiece immersed in an electrically heated heat treatment fluidised bed were studied. A suspension probe designed to simulate a workpiece of complex geometry was developed to measure local total and radiative heat-transfer coefficients at a high bed temperature. The probe consisted of an energy-storage region separated by insulation from the fluidised bed, except for the measuring surface, and a multi-thermocouple measurement system. Experiments in the fluidised bed were performed for a fluidising medium of 120-mesh alumina, a wide temperature range of 110-1050 deg. C and a fluidising number range of 1.18-4.24. It was found that the workpiece surface temperature has a more significant effect on heat transfer than the bed temperature. The total heat-transfer coefficient at the upper surface of the workpiece sharply decreased at the start of heating, and then steadily increased as heating progressed, while a sharp decrease became a rapid increase and then a slow increase for the radiative heat-transfer coefficient. A great difference in the heat-transfer coefficients around the workpiece was observed

76

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.

77

Energy Technology Data Exchange (ETDEWEB)

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{sup -2}K{sup -1}. The characteristics of the time-varying IHTC have also been discussed.

Zhang Liqiang [State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, Hunan University, Changsha, 410082 Hunan (China); College of Materials Science Engineering, Hunan University, Changsha, 410082 Hunan (China); Li Luoxing, E-mail: llxly2000@163.co [State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, Hunan University, Changsha, 410082 Hunan (China) and College of Materials Science Engineering, Hunan University, Changsha, 410082 Hunan (China); Ju Hui; Zhu Biwu [College of Materials Science Engineering, Hunan University, Changsha, 410082 Hunan (China)

2010-10-15

78

Evaluation of heat-transfer coefficient at direct-contact condensation of cold water and steam

International Nuclear Information System (INIS)

The estimation of the heat transfer coefficient at the direct-contact condensation of cold water and steam is a very hard task since the phenoma are essentially undsteady and the interface motion is so complicated that an exact estimation of its araea is almost impossible. The present study shows the heat transfer coefficient evaluated experimentally by assuming simple interface shapes for complicated surfaces and estimated those through comparison of the numerical analyses to the data of experiments related to the loss of coolant accidents of light water reactors. At chugging, the heat transfer coefficient reached up to 2 x 106 W/(m2 K). At condensation oscillation, it ranged between 105-106 W/(m2K). At a jet region of cold water injected into the steam flow in a pipe or the stationary steam in a vessel, the value was around 2 x 105 W/(m2 K), and at the surface of stratified flow, it was between 3 x 103-3x104 W/(m2 K). (orig.)

79

A numerical method for determining heat transfer coefficients in crossflow compact heat exchangers

International Nuclear Information System (INIS)

An essential, and often the most uncertain, part of any two-fluid heat exchanger analysis is the determination of heat transfer coefficients on both fluid sides. Heat transfer coefficients for exchanger surfaces are usually obtained experimentally using the (modified) Wilson plot technique for the test data analysis. Fluid side heat transfer coefficients are determined from an overall heat transfer coefficient, which is known from energy the balance of a heat exchanger. The original and modified Wilson plot techniques are based on the linear regression and their applications are limited to the power-law relationships between Nusselt (Nu) and Reynolds (Re) and Prandtl (Pr) numbers. In this paper a numerical method for obtaining correlations for both fluid sides is presented. The primary measurements consist of the flow rates of each fluid streams (35 % aqueous ethylene glycol solution and air), their inlet and outlet temperatures and pressure drops in both streams between the inlet and outlet of the heat exchanger. The problem of determining non-dimensional average heat transfer coefficients is formulated as a parameter estimation problem by selecting the functional form for the Nusselt number Nu=f(Re, Pr). There are n parameters x=(x1,...,xn)T to be determined such that computed outlet tube side fluid temperatures Ti agree in the least-squares sense with the experimentally acquired temperatures fi. The non-linear emperatures fi. The non-linear least-squares problem was solved using the Levenberg-Marquardt method. The uncertainties in the estimated parameters are determined for temperature measurements with unknown standard deviations. In order to calculate the outlet fluid temperature Ti as the function of searched parameters a mathematical model of the heat exchanger using the control-volume method was developed. The results of the experimental investigation of the plate-fin-tube automotive radiator are presented. The tested two-pass radiator consists of two inline rows of oval tubes with smooth plate fins. The air and coolant mass flows, the total pressure drops through the radiator and inlet and outlet temperatures were measured in eighteen measurement points. The new correlations for the heat transfer coefficients on the air and coolant sides were developed using presented technique. The 95 % confidence intervals for the determined parameters are also given. The main advantage of the presented method is that it does not require any knowledge, or solution of the complex fluid flow field. It can be used for determining heat transfer characteristics of different type heat exchangers. Refs. 3 (author)

80

Boiling Heat Transfer on Superhydrophilic, Superhydrophobic, and Superbiphilic Surfaces

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

81

Energy Technology Data Exchange (ETDEWEB)

Mercury vapor up to 500 psia was condensed outside a cylindrical tube in both horizontal and vertical positions. Results show consistently low heat transfer coefficients compared to Nusselt's theory. Two auxiliary mercury vapor condensers downstream of the boiler vent were used to control and safeguard the system. Constantan wires were spot welded on the surface inside the test condenser tube. The heat flux ranged from 20,000 to 45,000 Btu/h-ft/sup 2/ and the temperature differences between vapor and condensing wall from 6 to 50/sup 0/F. The condensation heat transfer coefficients, ranging from 850 to 3,500 Btu/h-/sup 0/F-ft/sup 2/, are only about 3 to 9 percent of those predicted by Nusselt's theory. Due to the positive pressure in the system for most test runs, the chance of any in-leakage of noncondensable gases into the boiler is extremely small. Since no substantial change of heat transfer rate resulted from wide variations in the heat load on the reflux condenser at some specific heat flux on the test condenser tube, the low heat transfer rate of mercury vapor condensation was not due to the presence of any non-condensable gas. The test data for high vapor pressure up to 500 psia reveal that the heat transfer coefficient is independent of the vapor pressure level. The condensation coefficients calculated based on kinetic theory are much smaller than unity and decreasewith vapor pressure. It is hypothesized that dimer content in the metal vapor phase might behave as non-condensable or semi-condensable gas and create a diffusional barrier at the vapor-liquid interface near the condensate film. This dimer vapor could be the main cause of interfacial resistance during metal vapor condensation process. 41 figures, 7 tables, 58 references. (DLC)

Hsieh, S.; Bonilla, C.F.

1975-01-01

82

Heat transfer performance of metal fiber sintered surfaces

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

83

Mass transfer coefficients in a hanson mixer-settler extraction column

Directory of Open Access Journals (Sweden)

Full Text Available The volumetric overall mass transfer coefficients in a pilot plant Hanson mixer-settler extraction column of seven stages have been measured using toluene-acetone-water system. The effects of agitation speed and dispersed and continuous phases flow rates on volumetric overall mass transfer coefficients have been investigated. The results show that the volumetric overall mass transfer coefficient increases with increase in agitation speed and reaches a maximum. After having reached its maximum, it falls with further increase in agitation speed. It was found that the volumetric overall mass transfer coefficient increases with increase in dispersed phase flow rate, while it decreases with increase in continuous phase flow rate. By using interfacial area, the overall mass transfer coefficients for continuous and dispersed phases are determined from volumetric coefficients. An empirical correlation for prediction of the continuous phase overall mass transfer coefficient is proposed in terms of Sherwood and Reynolds numbers. Also the experimental data of the column investigated are compared with data for various extraction columns. Comparison between theoretical models and experimental results for the dispersed phase mass transfer coefficient shows that these models do not have enough accuracy for column design. Using effective diffusivity in the Gröber equation results in more accurate prediction of overall mass transfer coefficient. The prediction of overall mass transfer coefficients from the presented equations is in good agreement with experimental results.

M. Torab-Mostaedi

2008-09-01

84

Mass transfer coefficients in a hanson mixer-settler extraction column

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english The volumetric overall mass transfer coefficients in a pilot plant Hanson mixer-settler extraction column of seven stages have been measured using toluene-acetone-water system. The effects of agitation speed and dispersed and continuous phases flow rates on volumetric overall mass transfer coefficie [...] nts have been investigated. The results show that the volumetric overall mass transfer coefficient increases with increase in agitation speed and reaches a maximum. After having reached its maximum, it falls with further increase in agitation speed. It was found that the volumetric overall mass transfer coefficient increases with increase in dispersed phase flow rate, while it decreases with increase in continuous phase flow rate. By using interfacial area, the overall mass transfer coefficients for continuous and dispersed phases are determined from volumetric coefficients. An empirical correlation for prediction of the continuous phase overall mass transfer coefficient is proposed in terms of Sherwood and Reynolds numbers. Also the experimental data of the column investigated are compared with data for various extraction columns. Comparison between theoretical models and experimental results for the dispersed phase mass transfer coefficient shows that these models do not have enough accuracy for column design. Using effective diffusivity in the Gröber equation results in more accurate prediction of overall mass transfer coefficient. The prediction of overall mass transfer coefficients from the presented equations is in good agreement with experimental results.

M., Torab-Mostaedi; S. J., Safdari; M. A., Moosavian; M. Ghannadi, Maragheh.

85

International Nuclear Information System (INIS)

A computer tomography based methodology is applied to determine the transport properties of fluid flow across porous media. A 3D digital representation of a 10-ppi reticulate porous ceramic (RPC) sample was generated by X-ray tomographic scans. Structural properties such as the porosity, specific interfacial surface area, pore-size distribution, mean survival time, two-point correlation function s2, and local geometry distribution of the RPC sample are directly extracted from the tomographic data. Reference solutions of the fluid flow governing equations are obtained for Re = 0.2-200 by applying finite volume direct pore-level numerical simulation (DPLS) using unstructured, body-fitted, tetrahedral mesh discretization. The permeability and the Dupuit-Forchheimer coefficient are determined from the reference solutions by DPLS, and compared to the values predicted by selected porous media flow models, namely: conduit-flow, hydraulic radius theory, drag models, mean survival time bound, s2-bound, fibrous bed correlations, and local porosity theory-based models. DPLS is further employed to determine the interfacial heat transfer coefficient and to derive a corresponding Nu-correlation, which is compared to empirical correlations

86

Design of experiments for measuring heat-transfer coefficients with a lumped-parameter calorimeter

A theoretical investigation was conducted to determine optimum experimental conditions for using a lumped-parameter calorimeter to measure heat-transfer coefficients and heating rates. A mathematical model of the transient temperature response of the calorimeter was used with the measured temperature response to predict the heat-transfer coefficient and the rate of heating. A sensitivity analysis was used to determine the optimum transient experiment for simultaneously measuring the heat addition during heating and the convective heat-transfer coefficient during heating and cooling of a lumped-parameter calorimeter. Optimum experiments were also designed for measuring the convective heat-transfer coefficient during both heating and cooling and cooling only.

Vanfossen, G. J., Jr.

1975-01-01

87

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

88

International Nuclear Information System (INIS)

Condensation in the presence of noncondensible gases play an important role in the nuclear industry. The RELAP5/MOD3 thermal hydraulic code was used to study the ability of the code to predict this phenomenon. Two separate effects experiments were simulated using this code. These were the Massachusetts Institute of Technology's (MIT) Pressurizer Experiment, the MIT Single Tube Experiment. A new iterative approach to calculate the interface temperature and the degraded heat transfer coefficient was developed and implemented in the RELAP5/MOD3 thermal hydraulic code. This model employs the heat and mass transfer analogy since it considers the sensible and condensation heat transfer simultaneously. This model was found to perform much better than the reduction factor approach. The calculation using the new model was found to be in much better agreement with the experimental values. (author)

89

Enhancement of Volumetric Mass Transfer Coefficient for Oxygen Transfer Using Fe2O3-Water Nanofluids

Directory of Open Access Journals (Sweden)

Full Text Available Experiments were carried out with Fe2O3-water nanofluids to study possible enhancement in volumetric mass transfer coefficient for transfer of oxygen from air bubble to nanofluid, in an agitated, aerated bioreactor. The nanoparticles concentration was varied in the range of 0.022 to 0.065 wt.%, while the reactor was operated at three operating conditions viz. 200 rpm and 1.5 L min-1 of air flow, 100 rpm and 1.5 L min-1 of air flow and 200 rpm and 0.75 L min-1 of air flow. Nanoparticles were found to contribute to enhance oxygen transfer through ‘grazing effect’. An enhancement of 63% was observed for 0.065 wt.% Fe2O3-water operated at 200 rpm and 0.75 L min-1 air flow.

K.S. Suganthi

2012-01-01

90

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

91

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 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)

92

International Nuclear Information System (INIS)

In the scope of the Megawatt Pilot Experiment (MEGAPIE), i.e. a liquid metal target for a spallation neutron source, an experimental investigation (KILOPIE) of the target window cooling has to be performed. A reason to perform the KILOPIE experiment is that, in the area of the proton beam entry window, the values and distribution of the local convection heat transfer coefficient 'a' for MEGAPIE conditions are unknown. The liquid metal, in this case lead-bismuth eutectic (LBE), is simultaneously used as target material and coolant. A hemispherical flow geometry made of T91 steel is used for the mockup of the proton beam entry window in an experimental set-up for a determination of the local convection heat transfer coefficient 'a'. In KILOPIE two complementary methods are used for a determination of the local convection heat transfer coefficient 'a', the first one is the two dimensional Heat Emitting Temperature Sensitive Surface (2D-HETSS) method develop at PSI (Platnieks et al.) and the second is an improved two-dimensional and dynamic infrared thermography (2DD-IRT) method, also developed at PSI (Patorski et al.). In this paper only the methodology of improved 2DD-IRT will be presented. The experimental activities will be performed at the beginning of 2004 at Forschungszentrum Karlsruhe (FZK) using the THEADES loop of the KALLA laboratory and will be continued at Paul Scherrer Institute (PSI) using the new, consisting of two independent pumped circuits, PSI-LBE-Doub independent pumped circuits, PSI-LBE-Double-Loop. A specially tailored 0.053 mm thick Aluchrom YHf heating foil is used, which allows to apply a uniform and constant heat flux deposition on the outer surface of the hemispherical mockup-specimen of the target window. The optical non-contact IRT equipment measures the outer surface temperature of the mockup-specimen dish with a high space and time resolution, e.g. 1.25 mrad and 20 Hz. The 100 mm diameter of the mockup-specimen dish with approximately 5000 pixels, i.e. temperature measurement points, area of 1.6 mm2 is covering the area of interest, corresponding to the approx. 60 mm diameter of the proton beam footprint and results in temperature contour plots with good resolution. The dynamic capability of 2DD-IRT is essential for the investigation of the change of the local convection heat transfer coefficient 'a' especially during transient load cases, i.e. during changes of the flow rate of the coolant. The accuracy of the temperature measurement is ±1%. The knowledge of constant heat flux and temperature differences between inner surface and coolant allow a two-dimensional dynamic determination and visualization of the local convection heat transfer coefficient 'a'. In other words, the determination of the local convection heat transfer coefficient 'a' is a result of ratio of the known local heat flux from the Aluchrom YHf heating foil to the difference between the local inner surface temperature and the bulk temperature of the LBE coolant. (author)

93

Investigation of Natural Convection Heat Transfer Coefficient on Extended Vertical Base Plates

Directory of Open Access Journals (Sweden)

Full Text Available In this research, Computational analysis of the laminar natural convection on vertical surfaces has been in-vestigated. Natural convection is observed when density gradients are present in a fluid acted upon by a gravitational field. Our example of this phenomenon is the heated vertical plate exposed to air, which, far from the plate, is motionless. The CFD simulations are carried out using fluent software. Governing equa-tions are solved using a finite volume approach. Coupling between the velocity and pressure is made with SIMPLE algorithm. The resultant system of discretized linear algebraic equations is solved with an alternat-ing direction implicit scheme. Then a configuration of rectangular fins is put in different ways on the surface and natural convection heat transfer coefficient on these no slope surfaces is studied and finally optimization is done.

D. Majidian

2011-05-01

94

Directory of Open Access Journals (Sweden)

Full Text Available The article deals with determination of energy transfer coefficient dependence from primary coil to secondary matching device coil on inductive load value. In the course of researches, the discharge pulses oscillograms have been registred, and the inductance of research inductors and the energy transfer coefficient from the primary matching device coil to the inductor– processing tool have been experimentally determined.

Gnatov, A.

2012-06-01

95

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

96

International Nuclear Information System (INIS)

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

97

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

98

Impact of bubble and free surface oxygen transfer on diffused aeration systems.

The primary location of oxygen transfer in a diffused aeration system is examined by separately determining the surface air-water and bubble-water mass transfer coefficients. The mass transfer model developed to determine the mass transfer coefficients advances the McWhirter and Hutter (A.I.Ch.E. J. 35(9) (1989) 1527) model by tracking oxygen and nitrogen transfer into and out of the bubbles as they rise to the water surface. The resulting vertical profiles of the liquid-phase equilibrium concentration inside the bubble and the gas-phase oxygen composition give insight into how the bubble-water concentration gradient changes over depth. The surface mass transfer coefficient, k(Ls)a(s), is 59-85% of the bubble mass transfer coefficient, k(L)a(b), and the driving concentration difference is smaller for surface transfer. Surface transfer and bubble transfer both contribute significantly to oxygen transfer; however, bubble transfer is the primary mode of oxygen transfer for this system at the air flow rates used. Further experiments demonstrate that most of the surface transfer occurs above the bubble plume. PMID:12697232

DeMoyer, Connie D; Schierholz, Erica L; Gulliver, John S; Wilhelms, Steven C

2003-04-01

99

Investigation of two-phase heat transfer coefficients of argon-freon cryogenic mixed refrigerants

Mixed refrigerant Joule Thomson refrigerators are widely used in various kinds of cryogenic systems these days. Although heat transfer coefficient estimation for a multi-phase and multi-component fluid in the cryogenic temperature range is necessarily required in the heat exchanger design of mixed refrigerant Joule Thomson refrigerators, it has been rarely discussed so far. In this paper, condensation and evaporation heat transfer coefficients of argon-freon mixed refrigerant are measured in a microchannel heat exchanger. A Printed Circuit Heat Exchanger (PCHE) with 340 ?m hydraulic diameter has been developed as a compact microchannel heat exchanger and utilized in the experiment. Several two-phase heat transfer coefficient correlations are examined to discuss the experimental measurement results. The result of this paper shows that cryogenic two-phase mixed refrigerant heat transfer coefficients can be estimated by conventional two-phase heat transfer coefficient correlations.

Baek, Seungwhan; Lee, Cheonkyu; Jeong, Sangkwon

2014-11-01

100

Directory of Open Access Journals (Sweden)

Full Text Available This paper explains the need for a database of cooling intensities for liquid quenchants, in order to predict the quench hardness, microstructure, stresses and distortion, when real engineering components of complex geometry are quenched. The existing laboratory procedures for cooling intensity evaluation, using small test specimens, and Lumped-Heat-Capacity Method for calculation of heat transfer coefficient, are presented. Temperature Gradient Method for heat transfer calculation in workshop conditions, when using the Liscic/Petrofer probe, has been elaborated. Critical heat flux densities and their relation to the initial heat flux density, is explained. Specific facilities for testing quenching intensity in workshop conditions, are shown. The two phase project of the International Federation for Heat Treatment and Surface Engineering (IFHTSE, as recently approved, is mentioned.

Božidar Liš?i?

2012-02-01

101

Directory of Open Access Journals (Sweden)

Full Text Available This paper explains the need for a database of cooling intensities for liquid quenchants, in order to predict the quench hardness, microstructure, stresses and distortion, when real engineering components of complex geometry are quenched. The existing laboratory procedures for cooling intensity evaluation, using small test specimens, and Lumped-Heat-Capacity Method for calculation of heat transfer coefficient, are presented. Temperature Gradient Method for heat transfer calculation in workshop conditions, when using the Liscic/Petrofer probe, has been elaborated. Critical heat flux densities and their relation to the initial heat flux density, is explained. Specific facilities for testing quenching intensity in workshop conditions, are shown.The two phase project of the International Federation for Heat Treatment and Surface Engineering (IFHTSE, as recently approved, is mentioned.

Božidar Liš?i?

2012-02-01

102

The determination of individual mass transfer coefficients in liquid-liquid extraction

Directory of Open Access Journals (Sweden)

Full Text Available An improved Lewis cell has been used as an efficient method to determine the mass transfer coefficient for any ternary multi-component system. In this paper the individual mass transfer coefficients were determined for three ternary systems: water-acetone-carbon tetrachloride water-acetone-chloroform and water-acetone-toluene, using the improved Lewis cell. Criteria! equations were developed to calculate the mass transfer coefficients when one or both (organic and aqueous phases were agitated and when solute transfer occurs in both directions.

Radu Tudose Z.

2003-01-01

103

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

104

Energy Technology Data Exchange (ETDEWEB)

The heat transfer coefficient in a spark ignition engine was examined under various knock conditions, by measuring local surface temperatures, heat fluxes and pressures in a combustion chamber, and by calculating gas temperatures with a two-zone model. The heat flux around a knock zone sharply increased with the pressure in knocking. The heat transfer coefficient increased during a compression stroke and before flame arrival, and after it decreased temporarily at flame arrival, increased again to its maximum value. While the maximum values of the heat flux and heat transfer coefficient in the knock zone were slightly affected by knock intensities within 0.3MPa, they increased with the knock intensities of 0.3MPa or more up to the values 2-26 times as high as those under non-knock conditions at 0.6MPa. The heat transfer coefficient also increased throughout the combustion chamber during a expansion stroke. No these heat transfer coefficients could be estimated by existing equations. 18 refs., 9 figs., 2 tabs.

Harigaya, Yasuo; Toda, Fujio; Oyagi, Shigeharu; Tsuji, Hiroshi (Saitama Univ., Saitama, (Japan))

1990-02-01

105

Unsteady radiative-convective heat transfer on a radiating surface

Research of radiation-convective heat exchange on radiating surfaces at natural and forced convection is complex mathematical task and here we obtain approximate analytical formulations for this process. We consider two dimensional unsteady heat transfer between solid surface and fluid under the natural laminar convection within optically transparent grey media. Also we assume constant thermo-physical properties except density which is decreasing linearly with temperature. Complex radiative-convective unsteady heat transfer approximately can be considered as a multi-stage process. At the beginning heat transfer coefficient is time dependent but almost independent on longitudinal coordinate. Afterwards heat transfer coefficient becomes dependent on longitudinal coordinate but does not change over time. Analytic formulations obtained for those two stages could be merged along the "time-space" characteristic basing on the equality of heat flows and temperatures there. Solutions are constructed using asymptotic expansions. Theoretical analysis of the solutions revealed the following: effect of radiation leads to a change in the heat transfer coefficient from the values that are characteristic to the second order boundary conditions to the values that are characteristic for the first order boundary conditions. The rate of this transition depends on ß radiation coefficient. Experimental research confirmed correctness of the simplifications introduced.

Salomatov, Vasily; Puzyrev, Evgeniy; Salomatov, Vladimir

2012-11-01

106

Fouling of heat transfer surfaces

International Nuclear Information System (INIS)

There are many parameters affecting the fouling deposit on the heat transfer surface. These parameters include flow velocity, surface temperature, fluid bulk temperature, fluid characteristics, surface material and structure. The flow velocity is one of the most important parameters affecting the fouling rate and there is a rarity in literature covering this effect. Therefore, the purpose of the present work is to study the effect of flow velocity on the fouling rate. To carry out this study, an experimental test rig has been designed and constructed. The experimental loop has three 97% Cu-Ni test tubes of 2400 mm length and 16 mm inner diameter. Water with a solid particle concentration of 19 m/lit is used as a test fluid. The test fluid flows through the tubes which are heated by means of steam. The cooling water is arranged in a closed loop to keep constant solid particle concentration. The experiments are carried out under constant surface temperature by using the steam as a heating medium. These experiments have been carried out under different flow velocities (from 0.2 to 1.42 m/s). The experimental loop is a differential one and the runs have been operated for long time (about 200 hrs.) to attain the asymptotic fouling resistance. The obtained experimental results are analyzed, and the effect of flow velocity on the fouling rate and the asymptotic fouling resistance is plotted. From the discussion of these results, it is concluded that; both the fouling resistance and the asymptotic fouling resistance decrease with increasing the flow velocity. The delay time is very small and is seen to approach zero in all the experimental work. The saw tooth effect has been obtained in all runs. Results have shown also essential.10 tabs.,4-8 figs.,71 refs

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 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

110

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english 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 perfo [...] rmed 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; J., Janevski; M., Stojiljkovic.

2009-06-01

111

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

112

International Nuclear Information System (INIS)

The mass transfer rates of U(VI), U(IV), Pu(IV) and Pu(III) nitrates across aqueous/organic interfaces have been measured by a single drop method in solvent extraction. The overall mass transfer coefficients for rising, falling and jetting drops were related to the individual mass transfer coefficients in the dispersed and continuous phases. The Sherwood numbers in the dispersed and continuous phases, which contain the individual mass transfer coefficients, were correlated with the Peclet numbers in the corresponding phases, on the basis of the boundary layer theory, Handlos-Baron's theory and the penetration theory. This paper presents the experimental results of the mass transfer rates that were analyzed in terms of these theoretical findings. The mass transfers of U and Pu were confirmed to be controlled by molecular diffusion through the organic film layer for the rising or falling drops and the aqueous film layer for the jetting drops. (author)

113

Condensation heat transfer on two-tier superhydrophobic surfaces

We investigated water vapor condensation on a two-tier superhydrophobic surface in an environmental scanning electron microscope (ESEM) and in a customer-designed vapor chamber. We have observed continuous dropwise condensation (DWC) on the textured surface in ESEM. However, a film layer of condensate was formed on the multiscale texture in the vapor chamber. Due to the filmwise condensation, the condensation heat transfer coefficient of the superhydrophobic surface is lower than that of a flat hydrophobic surface especially under high heat flux situations. Our studies indicate that adaptive and prompt condensate droplet purging is the dominant factor for sustaining long-term DWC.

Cheng, Jiangtao; Vandadi, Aref; Chen, Chung-Lung

2012-09-01

114

Study of Oxygen Mass Transfer Coefficient in Microbial Leaching of Uranium

International Nuclear Information System (INIS)

Oxygen mass transfer coefficient is one of the most important parameters in the design of aerobic process bioreactor, which is represented by the overall volumetric oxygen mass transfer. The purpose of this article was the investigation of the mass transfer coefficient in the vast range of operational parameters in a stirred tank reactor. The effects of cell concentration, stirred power consumption and apparent air velocity on the mass transfer coefficient show that oxygen mass transfer in microbial leaching of uranium and in this range of parameter is not limited in these experiments. The overall volumetric oxygen mass transfer was determined in the range of 36-84 hr-1. Agreements of the suggested mathematical correlation for predicting the mass transfer were also evaluated. The results showed that the equation based on the rpm and/or power consumption and apparent air velocity specifies a good agreement with the experimental results with the coefficient of determination of R2=94.2 and 93.4. It was concluded that the introduced models are suitable for evaluation of the mass transfer coefficient in the microbial leaching of uranium.

115

Measurement of the Convective Heat-Transfer Coefficient

We propose an experiment for investigating how objects cool down toward the thermal equilibrium with their surroundings. We describe the time dependence of the temperature difference of the cooling objects and the environment with an exponential decay function. By measuring the thermal constant t, we determine the convective heat-transfer…

Conti, Rosaria; Gallitto, Aurelio Agliolo; Fiordilino, Emilio

2014-01-01

116

Estimating the workpiece-backingplate heat transfer coefficient in friction stirwelding

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

117

International Nuclear Information System (INIS)

The acoustic coefficients of reflection, transmission, and transformation of first-, second-, and gas sound waves incident normally on the free surface of liquid helium have been determined. The experimental results are compared with the theory developed in Part I of this paper. It is shown that equilibrium theories of boundary conditions disagree with the experiments. Nonequilibrium theories, however, which take into account that mass and energy transport processes occur at the liquid-vapor interface of helium II, lead to a very good description of the experimental data below 2 K. Within experimental accuracy the measurements fully confirm several kinetic models of evaporation and energy transport processes. Near the lambda point, deviations from the theory have been found which might be attributed to influences of critical phenomena. The surface absorption coefficients of first-, second-, and gas sound waves could be deduced from the experimental data on the acoustic coefficients, and it is shown that, in agreement with the theory, appreciable energy dissipation occurs at the free surface of helium II when a second-sound or a gas sound wave is incident

118

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

119

Measurement and Prediction of the Average Heat Transfer Coefficient on a Tube

International Nuclear Information System (INIS)

Most results are for horizontal tubes of diameter ranging 7.6?51 mm. Only Seethes et al. studied variations in local heat transfer coefficients along the tube periphery while controlling the inclination angle. The main result of the previous investigations is that there is a considerable difference among the local heat transfer coefficients along a tube periphery. This has been the major cause of the discrepancy among the results. It is very important to predict the exact heat transfer coefficient on a tube for the thermal design of tubular type heat exchangers. No results have been reported about the way to predict the average value on a tube except Kang who suggested a method for the horizontal tube. The present study is aimed to find out a way of predicting the average heat transfer coefficient with considering the degree of subcooling and the inclination angle. The average heat transfer coefficient was observed at ? =90 .deg in the saturated water regardless of the tube inclination angle. However, as the water was subcooled the location for the average heat transfer coefficient moves to the lower region of the tube

120

Investigation of heat transfer coefficient during quenching in various cooling agents

International Nuclear Information System (INIS)

Highlights: • The highest HTC during quenching in mineral oils occur in temperature 520–550 °C. • The peaks of HTC for polymers exist at lower temperature compared to mineral oils. • Temperature and utilization time of coolant affect the heat transfer coefficient. • Ageing of mineral oils affects their severities; a direction of change is equivocal. -- Abstract: Heat transfer coefficients, HTCs, at the surface of a metal sample during immersion quenching were measured and evaluated using numerical procedures. The boundary inverse heat conduction problem has been defined and solved. A FEM self-developed computer code has been used to obtain a solution to the direct problem. The sensitivity of the method enabled us to examine the effect of various quenching parameters on the heat transfer for two mineral oils and a polymer quenchant. At 800 °C the HTC values were equal to ?0.5 kW/(m2 K) and ?3.2 kW/(m2 K), for mineral oils and a polymer coolant, respectively. They increased to ?4.7 kW/(m2 K) – oil A, ?6.0 kW/(m2 K) – oil B and ?7.4 kW/(m2 K) – polymer, respectively. The peak of HTC was sharp and occurred at a narrow temperature interval between 520 and 550 °C for the oils, whereas for the polymer, the peak was lower by approx. 100 K and flat over 100–120 K interval. Subsequently HTC decreased, and at ?150 °C the values were ?0.5 kW/(m2 K) and ?2.0 kW/(m2 K), for mineral oils and a water polymer coolant, respectively

121

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

122

International Nuclear Information System (INIS)

The validity of thermoelastic thin shell theory for the prediction of localized thermal stress due to thermal perturbations at the outer can coolant interface has been demonstrated by comparison with the exact thermoelastic analysis of a free-standing symmetric can subjected to a highly localized heat transfer coefficient variation. Numerical results also demonstrate the role of internal heat conduction in the can on the nature of the axial distribution of surface temperature, heat flux and stress. (Auth.)

123

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.)

124

Pool boiling heat transfer from enhanced surfaces to dielectric fluids

International Nuclear Information System (INIS)

Pool boiling heat-transfer measurements were made using a 15.8 mm o.d. plain copper tube and three copper enhanced surfaces: a Union Carbide High Flux surface, a Hitachi Thermoexcell-E surface and a Wieland Gewa-T surface. The dielectric fluids were Freon-113 and Fluorinert FC-72, a perfluorinated organic compound manufactured to cool electronic equipment. Data were taken at atmospheric pressure, and at heat fluxes from 100 W/m2 to 200,000 W/m2. Prior to operation, each test surface was subjected to one of three aging procedures to observe the effect of surface past history upon boiling incipience. For Freon-113 the enhanced surfaces showed a two to tenfold increase in the heat-transfer coefficient when compared to a plain tube, whereas for FC-72 an increase of two to five was measured. The High Flux surface gave the best performance over the range of heat fluxes. The Gewa-T surface did not show as much of an enhancement at low fluxes as the other two surfaces, but at high fluxes its performance improved. In fact, it was the only surface tested which delayed the onset of film boiling with FC-72. The degree of superheat required to activate the enhanced surfaces was sensitive to both past history of the surface and to fluid properties

125

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

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.

2014-09-01

126

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

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.

2014-07-01

127

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

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

128

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

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.

2014-04-01

129

Heat transfer on ribbed surfaces

International Nuclear Information System (INIS)

The Local Nusselt numbers of Ribbed surfaces were measured. From the measured data, average Nusselt numbers were evaluated in the sub-regions of ribbed surface, such as front, top and back surfaces of rib, and downstream and upstream regions of base surface. In the present paper were discussed the relationships between the average Nusselt number in each sub-region and Reynolds number, the pitch and height of rib, and heat flux ratio. (author)

130

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

131

The transferability of surface states on tungsten

International Nuclear Information System (INIS)

Surface states associated with a bulk band edge may be transferable from one crystal face to another, corresponding to the band edge being viewed from different directions in k-space: both the W(001) and (011) surfaces show significant surface states near the Fermi energy associated with the fourth band edge. The W(011) surface states have been completely mapped using UV photoemission, and are in good agreement with calculation. The W(011) states consist mainly of 5d orbitals with lobes in the and directions, and the corresponding states on the (001) surface, which lie near the edge of the surface Brillouin zone have dsub(z2) character, with a lobe in the direction. This reflects the d orbital character of the fourth band edge from which these states are derived. Conditions for surface state transferability are discussed, and the reason for the energy shift in going from the (011) to the (001) surface. (Auth.)

132

In the present study, we consider the effect of remotely sensed COT on surface UV irradiance and photolysis rate coefficients. These coefficients and the effect of cloud there on, play a crucial role in atmospheric chemistry, in particular the formation of ozone. The COT for this study is retrieved from the Spinning Enhanced Visible infrared Imager (SEVIRI) by implementing semi-analytical cloud retrieval algorithm for the month of June 2006. A simple parameterization of the effect of cloud on surface UV-A and UV-B irradiance, based on a series of simulations performed with the Tropospheric Ultraviolet and Visible (TUV) radiative transfer model, is developed. The required columnar ozone concentration is set to 335 DU that is obtained from multi sensor Re-analysis data set for June 2006 near the centre of our study domain (Belgium) and the surface albedo is set to 5% for the radiative transfer calculations. For the purpose of validation, measurements of UV-A and UV-B irradiance from two Belgian stations, Ostend and Redu, are used. The time series of the modeled UV-A and UV-B irradiance against the measurements shows a good agreement. This is apparent from the model versus measurement error statistics. The mean absolute error, correlation coefficient and index of agreement for UV-A irradiance for both stations are found to be ~5.6 W/m2, ~0.92 and ~0.93 respectively; whereas, for the UV-B irradiance they are ~0.58 W/m2, ~0.93 and ~0.86, respectively. The effect of COT on photolysis rate coefficients of different photolytic reactions is also presented along with simple parameterizations to account for the effect of cloud. The maximum error associated with the parameterization is found to be of the order of few percent or less, with the highest error of 9%.

Pandey, P.; De Ridder, K.; Gillotay, D.

2011-12-01

133

International Nuclear Information System (INIS)

The temperature and coverage dependences of surface diffusion coefficients is investigated for atomic carbon on graphite (0001) and diamond (111). With the use of quantum-chemical calculations it is shown that the surface diffusion on graphite can be observed only at temperatures above 2000 K due to high activation barriers. The diffusion processes at a diamond surface can play the important role for kinetics of growth. Diffusion coefficients for diamond (111) reach 2.3 x 10-5 cm2c-1 in the range of temperatures (1000-1400 K) used in particle

134

Directory of Open Access Journals (Sweden)

Full Text Available The volumetric overall mass transfer coefficients have been measured in a pulsed packed extraction column using diffusion model for two different liquid-liquid systems. The effects of operational variables such as pulsation intensity and dispersed and continuous phase flow rates on volumetric overall mass transfer coefficients have been investigated. Effective diffusivity is substituted for molecular diffusivity in the Gröber equation for prediction of dispersed phase overall mass transfer coefficients. The enhancement factor is determined experimentally and therefrom an empirical correlation is derived for prediction of effective diffusivity as a function of Reynolds number, Schmidt number and viscosity ratio. Good agreement between prediction and experiments was found for all operating conditions that were investigated.

M. Torab-Mostaedi

2009-12-01

135

Fluoroptic measurements of the local heat transfer coefficient inside the rotating cone reactor

Digital Repository Infrastructure Vision for European Research (DRIVER)

The rotating cone reactor is a novel reactor type for rapid thermal processing of solids. This paper focuses on the experimental determination of the gas-to-particle heat transfer coefficient. This quantity has been measured for several particle diameters (average size of 150, 280 and 425 ¿m) and cone rotational frequencies (11.3 and 28.3 Hz). The gas-to-particle heat transfer coefficient obtained from these experiments varied between 280 and 1030 W m¿2 W¿1. Experimental parameters which w...

Wagenaar, B. M.; Kuipers, J. A. M.; Versteeg, G. F.; Swaaij, W. P. M.

1994-01-01

136

International Nuclear Information System (INIS)

In many investigations concerning transport/exchange of matter in a natural system, e.g. functional studies in nuclear medicine, it is advantageous to relate experimental results to a model of the system. A new computer program is presented for the determination of linear transfer coefficients in a compartment model from experimentally observed time-compartment content curves. The program performs a least-square fit with the specified precision of the observed values as weight factors. The resulting uncertainty in the calculated transfer coefficients may also be assessed. The application of the program in nuclear medicine is demonstrated and discussed. (author)

137

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.)

138

Convective heat transfer coefficients in a full-scale room with and without furniture

Energy Technology Data Exchange (ETDEWEB)

The convective heat transfer coefficient at an outer ambient wall with a window exposed to natural climate was measured in a room with and without furniture. The method used was to estimate the heat flow from measured temperatures and solar radiation. The convective heat transfer was calculated as the difference between the heat flow through the building element and the calculated long-wave radiation. Even though the accuracy was at best {+-} 15%, the effect of different heating and ventilation strategies could clearly be detected. Local coefficients may be more than 10 times the expected, due to ventilation or position of the radiator. (author)

Wallenten, P. [Lund Institute of Technology (Sweden). Dept. of Building Science

2001-07-01

139

Sticking coefficient of small hydrocarbons on fusion relevant surfaces

International Nuclear Information System (INIS)

Full text: Ion-surface interaction is a crucial issue in fusion research, because of its impact on plasma contamination, the lifetime of plasma facing components and tritium inventories of fusion experiments. Deuterium and tritium, that escapes the magnetic confinement of the core plasma, hits the inner wall of the vacuum vessel with a kinetic energy that is large enough to erode wall material. In Tokamak experiments the erosion mainly takes place in the divertor region, which is covered with tungsten and carbon fiber composite (CFC) tiles. The collision of graphite originating from the CFC tiles with deuterium and tritium of the outer plasma column leads to the formation of small hydrocarbon molecule ions. The ionized molecules are guided back to the divertor by the magnetic field lines where they form layers of hydrocarbons. During this process large quantities of radioactive tritium are incorporated leading to a high tritium inventory regarded as a safety hazard in case of a vacuum loss accident. Therefore the probability of the adsorption of these small hydrocarbons on fusion relevant materials like tungsten and CFC plays an important role for the quantification of the tritium retention in fusion experiments. It is essential for the simulation of a fusion reactor at power plant conditions to know the dependence of this so-called sticking coefficient on the kinetic energy of the impacting hydrocarbon molecules. A collaboration of IPP Garching and our group of the Institut fuer Ionenphysik und Angewandte Physik was started in order to gain more knowledge about the energy dependence of the sticking coefficient. Deuterated hydrocarbon gas is ionized in a Nier-type ion source and mass selected by a double focusing mass spectrometer. The surface samples provided by IPP Garching are exposed to this beam of hyperthermal ions, which have a narrow kinetic energy spread with a FWHM smaller than 1 eV. After exposure the samples are transported to Garching for the measurement of the amount of deposited deuterium by Nuclear Reaction Analysis (NRA) in the SAK apparatus. Further Rutherford Backscattering analysis leads to the quantification of the sticking coefficient. (author)

140

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-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

141

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)

142

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

143

Measurements of pressure drop, heat transfer coefficient and critical energy of a bundle conductor

International Nuclear Information System (INIS)

Friction factor, saturation temperature, heat transfer coefficient and critical energy of an eight strand bundle conductor were measured in the test facility SULTAN at SIN in Switzerland. The measured values of the critical energy are in good agreement with those calculated by the computer code LONSA. 10 refs

144

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

145

Simulation Study of Mass Transfer Coefficient in Slurry Bubble Column Reactor Using Neural Network

Directory of Open Access Journals (Sweden)

Full Text Available The objective of this study was to develop neural network algorithm, (Multilayer Perceptron, based correlations for the prediction overall volumetric mass-transfer coefficient (kLa, in slurry bubble column for gas-liquid-solid systems. The Multilayer Perceptron is a novel technique based on the feature generation approach using back propagation neural network. Measurements of overall volumetric mass transfer coefficient were made with the air - Water, air - Glycerin and air - Alcohol systems as the liquid phase in bubble column of 0.15 m diameter. For operation with gas velocity in the range 0-20 cm/sec, the overall volumetric mass transfer coefficient was found to decrease with increasing solid concentration. From the experimental work 1575 data points for three systems, were collected and used to predicate kLa. Using SPSS 17 software, predicting of overall volumetric mass-transfer coefficient (kLa was carried out and an output of 0.05264 sum of square error was obtained for trained data and 0.01064 for test data.

Safa A. Al-Naimi

2013-01-01

146

Digital Repository Infrastructure Vision for European Research (DRIVER)

The influence of glass coating thickness on the interfacial heat transfer coefficient has been examined using numerical modeling. Temperature and heat flux during working of a Inconel 718 work-piece and colder H13 dies have been simulated. The thickness of the glass coating is found to have a significant influence on the forming characteristic. © (2013) Trans Tech Publications, Switzerland.

Busuttil, M.; Lin, Yp; Gebelin, Jc; Reed, Rc

2013-01-01

147

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

148

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

149

Condensation heat transfer coefficients of flammable refrigerants on various enhanced tubes

Energy Technology Data Exchange (ETDEWEB)

In this study, external condensation Heat Transfer Coefficients (HTCs) of six flammable refrigerants of propylene (R1270), propane (R290), isobutane (R600a), butane (R600), dimethylether (RE170), and HFC32 were measured at the vapor temperature of 39 .deg. C on a 1023 fpm low fin and turbo-C tubes. All data were taken under the heat flux of 32{approx}116 and 42{approx}142 kW/m{sup 2} for the low fin and turbo-C tubes respectively. Flammable refrigerants' data obtained on enhanced tubes showed a typical trend that external condensation HTCs decrease with increasing wall subcooling. HFC32 and DME showed up to 30% higher HTCs than those of HCFC22 due to their excellent thermophysical properties. Propylene, propane, isobutane, and butane showed similar or lower HTCs than those of HCFC22. Beatty and Katz' correlation predicted the HTCs of the flammable refrigerants obtained on a low fin tube within a mean deviation of 7.3%. Turbo-C tube showed the best performance due to its 3 dimensional surface geometry for fast removal of condensate.

Park, Ki Jung; Jung, Dong Soo [Inha Univ., Incheon (Korea, Republic of)

2005-10-15

150

The volumetric oxygen transfer coefficient (k(L)a) was tested with mature aerobic granules in the same aeration measurement device and under the same aeration conditions. The k(L)a (min(-1)) was 0.586 1 +/- 0.009 5, 0.586 1 +/- 0.0272, 0.555 6 +/- 0.016 8, 0.5338 +/- 0.0268 for floc sludge, and 0.645 5 +/- 0.027 6, 0.632 0 +/- 0.0755, 0.618 5 +/- 0.062 5, 0.640 6 +/- 0.055 5 for aerobic granules, when the sludge concentration MLSS (mg x L(-1)) was controlled at 2 000, 4 000, 6 000, 8 000, respectively. This indicated that granular sludge exhibited higher k(L)a values than the flocs, and the k(L)a value of floc sludge decreased with the increase of the sludge concentration; however, insignificant decease was found for granular sludge. After screening of granules with different diameter, the k(L)a values of the aerobic granular sludge with different sizes which had the same MLSS, volume, surface area and particle number were compared, and insignificant difference was found, suggesting that the effects of these factors on the k(L)a of granular sludge were negligible. The findings of this work may have significance for the energy-saving operation of wastewater treatment plants. PMID:23947050

Li, Zhi-Hua; Fan, Chang-Qing; Wang, Xiao-Chang

2013-06-01

151

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 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)

152

Energy Technology Data Exchange (ETDEWEB)

In this work, the response of a double volume transmission ionisation chamber, developed at the Instituto de Pesquisas Energeticas e Nucleares, was compared to that of a commercial transmission chamber. Both ionisation chambers were tested in different X-ray beam qualities using secondary standard ionisation chambers as reference dosimeters. These standard ionisation chambers were a parallel-plate and a cylindrical ionisation chambers, used for diagnostic radiology and mammography beam qualities, respectively. The response of both transmission chambers was compared to that of the secondary standard chambers to obtain coefficients of equivalence. These coefficients allow the transmission chambers to be used as reference equipment. - Highlights: Black-Right-Pointing-Pointer Calibration coefficients of standard ionisation chambers were transferred to transmission chambers. Black-Right-Pointing-Pointer Coefficients of equivalence were obtained. Black-Right-Pointing-Pointer Transmission chambers presented good response stability. Black-Right-Pointing-Pointer Transmission chambers can be used as reference equipment considering their response variation.

Yoshizumi, Maira T., E-mail: mairaty@ipen.br [Instituto de Pesquisas Energeticas e Nucleares IPEN - CNEN/SP, Av. Prof. Lineu Prestes 2242, 05508-000 Sao Paulo, SP (Brazil); Caldas, Linda V.E., E-mail: lcaldas@ipen.br [Instituto de Pesquisas Energeticas e Nucleares IPEN - CNEN/SP, Av. Prof. Lineu Prestes 2242, 05508-000 Sao Paulo, SP (Brazil)

2012-07-15

153

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

154

Heat transfer in the fuel-clad gap in a nuclear reactor impacts the overall temperature distribution, stored energy and the mechanical properties of a nuclear fuel rod. Therefore, an accurate estimation of the gap conductance between the UO2 fuel and the clad is critically important for reactor design and operations. To obtain the requisite accuracy in the gap conductance estimation, the thermal accommodation coefficients of the various gases present on the fuel outer surface and the cladding inner surface are very important. In present work, we studied the stainless steel that is the most favored cladding material for advanced gas-cooled reactors. Our goal was to obtain the thermal accommodation coefficients of select inert gases and mixtures of the same on this stainless steel. It has been found for pure helium, pure argon and select He-Ar mixtures that the thermal accommodation coefficient values with stainless steel are very close to constant over the range of pressures studied. The values obtained in this work are in good agreement with similar values reported previously in the literature. As far as we aware, these measurements are the first made of the thermal accommodation coefficients of inert gas mixtures on stainless steel. To aid in the verification of the kinetic theory, additional experiments were done using a two-sphere system and were analyzed using the equivalent sphere approximation. It is found that this theory can be applicable to spherical geometry problems and can be used for a wide range of values of the Knudsen number (Kn). Some sensitivity studies were performed to delineate some key parameter effect in terms of cooling rate, DeltaT difference, and Knudsen number.

Jun, Byung Soon

155

Heat transfer with freezing in a scraped surface heat exchanger

Energy Technology Data Exchange (ETDEWEB)

An experimental study was carried out on a scraped surface heat exchanger used for freezing of water-ethanol mixture and aqueous sucrose solution. The influence of various parameters on heat transfer intensity was established: product type and composition, flow rate, blade rotation speed, distance between blades and wall. During starting (transient period) the solution is first supercooled, then ice crystals appear on the scraped surface (heterogeneous nucleation) and no more supercooling is observed. It seems that, when blades are 3 mm far from the surface, a constant ice layer is formed having this thickness and acting as a thermal resistance. But when the blades rotate at 1 mm from the surface, periodically all the ice layer is removed despite the surface is not really scraped. This could simplify ice generator technology. An internal heat transfer coefficient was defined; it depends mainly on rotation speed. Correlations were proposed for its prediction, which could be applied, at least as a first approach, for the most common freezing applications of scraped surface heat exchanger i.e. ice creams (which are derived from sucrose solutions) and two-phase secondary refrigerants (which are principally ethanol solutions). (author)

Lakhdar, M.B. [LGL France Refrigerating Division, Genas (France); Cerecero, R.; Alvarez, G.; Guilpart, J. [Cemagref, Antony cedex (France). Food Process Engineering; Flick, D. [Institut National Agronomique, Paris (France); Lallemand, A. [Institut National des Sciences Appliquees de Lyon (France). Centre de Thermique

2005-01-01

156

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)

157

Air-ground interface: Surface waves, surface impedance and acoustic-to-seismic coupling coefficient

In atmospheric acoustics, the subject of surface waves has been an area of discussion for many years. The existence of an acoustic surface wave is now well established theoretically. The mathematical solution for spherical wave propagation above an impedance boundary includes the possibility of a contribution that possesses all the standard properties for a surface wave. Surface waves exist when the surface is sufficiently porous, relative to its acoustical resistance, that it can influence the airborne particle velocity near the surface and reduce the phase velocity of sound waves in air at the surface. This traps some of the sound energy in the air to remain near the surface as it propagates. Above porous grounds, the existence of surface waves has eluded direct experimental confirmation (pulse experiments have failed to show a separate arrival expected from the reduced phase speed) and indirect evidence for its existence has appeared contradictory. The experimental evidence for the existence of an acoustical surface wave above porous boundaries is reviewed. Recent measurements including pulse experiments are also described. A few years ago the acoustic impedance of a grass-covered surface was measured in the frequency range 30 to 300 Hz. Here, further measurements on the same site are discussed. These measurements include core samples, a shallow refractive survey to determine the seismic velocities, and measurements of the acoustic-to-seismic coupling coefficient.

Daigle, Gilles; Embleton, Tony

1990-01-01

158

International Nuclear Information System (INIS)

Predicting heat transfer coefficients and friction factors for hydrogen systems operating near and above the thermodynamic critical pressure is at best difficult. Yet most hydrogen land-based and aerospace systems of significant power density operate within this regime. In this paper the authors discuss a modification of the Patankar-Spalding method to include density fluctuations in predicting heat and mass transfer. The essence of this method is then empirically expressed in terms of the volumetric expansion coefficient, the wall to bulk temperature difference, and the reduced Nusselt number. The expression is then applied to hydrogen data. The method is meant to facilitate preliminary design, but for detailed analyses the numerical code is recommended

159

Evaluation of heat transfer surfaces for compact recuperator using a CFD code

Exhaust recovery recuperator is mandatory in order to realize a thermal efficiency of 30% or higher for micro turbines. In this work an attempt is made to select the cross corrugated heat transfer surface with minimum core volume of a recuperator matrix using a CFD code. Analysis is carried out for selected cross corrugated heat transfer surface configurations. The relation between the minimum core volume from design calculation and average skin friction coefficient from CFD analysis has been established.

Ashok Babu, T. P.; Talekala, Mohammad Shekoor

2009-04-01

160

Retrieving the heat transfer coefficient for jet impingement from transient temperature measurements

International Nuclear Information System (INIS)

Highlights: ? Heat transfer coefficient for impinging air jet is retrieved. ? Searched boundary condition approximated by spatial and temporal functions. ? Nonlinearity of problem bypassed by Newton's cooling law. ? Enforced temporal invariability of heat transfer coefficient stabilize solution. ? Results outperforms standard inverse approach. - Abstract: Algorithm of retrieving the heat transfer coefficient (HTC) from transient temperature measurements is presented. The unknown distributions of two types of boundary conditions: the temperature and heat flux are parameterized using a small number of user defined functions. The solutions of the direct heat conduction problems with known boundary temperature and flux are expressed as a superposition of auxiliary temperature fields multiplied by unknown parameters. Inverse problem is formulated as a least squares fit of calculated and measured temperatures and is cast in a form of a sum of two objective functions. The first results originates from an inverse problem for retrieving the boundary temperature the second comes from the inverse problem for reproducing the boundary heat flux. The final form of the objective function is obtained by enforcing constant in time value of the heat transfer coefficient. This approach leads to substantial regularization of the results, when compared with the standard technique, where HTC is calculated from separately reconstructed temperature and heat flux on the boundary. Thnd heat flux on the boundary. The validation of the numerical procedure is carried out by reconstructing a known distribution of the HTC using simulated measurements laden by stochastic error. The proposed approach is also used to reconstruct the distribution of the HTC in a physical experiment of heating a cylindrical sample using an impinging jet.

161

Approximate evaluation method of thermal transient stress under variable heat transfer coefficient

International Nuclear Information System (INIS)

The new approximate evaluation method was proposed for thermal transient stress under variable heat transfer coefficient. The proposed method uses Green functions and convolution integral. The proposed method was applied to the calculations of thermal transient stresses of a skirt-structure and a tube-sheet structure of IHX (intermediate heat exchanger) in commercialized fast reactor. It was verified that the proposed method gave good estimations for thermal transient stresses of those structures. (author)

162

Transfer coefficients of selected radionuclides to animal products. II. Hen eggs and meat

International Nuclear Information System (INIS)

Transfer coefficients to eggs and meat were determined after acute oral doses of /sup 95m/Tc, 99Mo, /sup 123m/Te, 133Ba, 131I, 95Zr and 95Nb to laying hens. The mean values (in units of d kg-1) to eggs and hen meat were, respectively, 3.0 and 0.03 for Tc, 0.87 and 0.18 for Mo, 5.1 and 0.60 for Te, 0.87 and 9.2 x 10(-3) for Ba, 3.2 and 0.01 for I, 2 x 10(-4) and 6 x 10(-5) for Zr, and 1 x 10(-3) and 3 x 10(-4) for Nb. For the same radionuclides administered in the same chemical form, transfer coefficients for eggs are about one to two orders of magnitude higher than for cow's milk, while the transfer coefficients for hen meat are several orders of magnitude higher than for beef

163

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

164

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

165

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

166

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

167

Effects of cooling and internal wave motions on gas transfer coefficients in a boreal lake

Directory of Open Access Journals (Sweden)

Full Text Available Lakes and other inland waters contribute significantly to regional and global carbon budgets. Emissions from lakes are often computed as the product of a gas transfer coefficient, k 600 , and the difference in concentration across the diffusive boundary layer at the air–water interface. Eddy covariance (EC techniques are increasingly being used in lacustrine gas flux studies and tend to report higher values for derived k 600 than other approaches. Using results from an EC study of a small, boreal lake, we modelled k 600 using a boundary-layer approach that included wind shear and cooling. During stratification, fluxes estimated by EC occasionally were higher than those obtained by our models. The high fluxes co-occurred with winds strong enough to induce deflections of the thermocline. We attribute the higher measured fluxes to upwelling-induced spatial variability in surface concentrations of CO2 within the EC footprint. We modelled the increased gas concentrations due to the upwelling and corrected our k 600 values using these higher CO2 concentrations. This approach led to greater congruence between measured and modelled k values during the stratified period. k 600 has a well-resolved and ~cubic relationship with wind speed when the water column is unstratified and the dissolved gases well mixed. During stratification and using the corrected k 600 , the same pattern is evident at higher winds, but k 600 has a median value of ~7 cm h?1 when winds are less than 6 m s?1, similar to observations in recent oceanographic studies. Our models for k 600 provide estimates of gas evasion at least 200% higher than earlier wind-based models. Our improved k 600 estimates emphasize the need for integrating within lake physics into models of greenhouse gas evasion.

Jouni J. Heiskanen

2014-05-01

168

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

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.

Kohút, Peter; Horejš, Otakar; Mareš, Martin

2012-04-01

169

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

Directory of Open Access Journals (Sweden)

Full Text Available The Vapour Absorption Refrigeration System (VARS has generated renewed interest and is being viewed as one of the alternatives for vapour compression refrigeration due to its potential for waste heat utilization. To improve the efficiency of these systems, it is necessary to study heat and mass transfer processes in absorption system components. The absorber, one of the crucial components in VARS is considered for study. Experimental investigation is carried out to study heat and mass transfer characteristics in a glass absorber. A new combination of R134a/DMF is used as the working fluid to overcome the limitations of well known working pairs, ammonia-water and lithium bromide-water. The effects of parameters viz., gas flow rate, solution initial concentration, solution pressure and solution temperature on absorber performance are analyzed. Heat and mass transfer coefficients evaluated from the experiments are compared with the numerical model and it is found that agreement is good. Heat and mass transfer coefficients increase as the gas flow rate, solution initial concentration and solution temperature increase whereas they decrease as the solution pressure increases. Sherwood number and Nusselt number evaluated from the experimental data are compared with those obtained from the numerical correlations developed earlier by the authors.

M. Suresh

2011-01-01

170

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

171

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)

172

Prediction of the heat transfer coefficient for ice slurry flows in a horizontal pipe

International Nuclear Information System (INIS)

In this study, heat transfer for ice slurry flows was investigated. For the experiments, ice slurry was made from 9% ethanol-water solution flow in a 20 mm internal diameter, 1000 mm long horizontal copper tube. The ice slurry was heated by a cylindrical electrical resistance. Experiments of the melting process were conducted with changing the ice slurry mass flux rate and the heat flux. The enthalpy-porosity formulation was used to predict the ice slurry temperature and the local values of heat transfer coefficient in the exchanger. Measurements and data acquisition of ice slurry temperature and mass flow rate at the inlet and outlet are performed. It was found that the heat transfer rates increase with the mass flow rate, the ice fraction and the heat flux density. However, the effect of ice fraction appears not to be significant at high mass flow rates. In addition, the correlation proposed by Christensen and Kauffeld gives good agreement with numerical results.

173

Prediction of the heat transfer coefficient for ice slurry flows in a horizontal pipe

Energy Technology Data Exchange (ETDEWEB)

In this study, heat transfer for ice slurry flows was investigated. For the experiments, ice slurry was made from 9% ethanol-water solution flow in a 20 mm internal diameter, 1000 mm long horizontal copper tube. The ice slurry was heated by a cylindrical electrical resistance. Experiments of the melting process were conducted with changing the ice slurry mass flux rate and the heat flux. The enthalpy-porosity formulation was used to predict the ice slurry temperature and the local values of heat transfer coefficient in the exchanger. Measurements and data acquisition of ice slurry temperature and mass flow rate at the inlet and outlet are performed. It was found that the heat transfer rates increase with the mass flow rate, the ice fraction and the heat flux density. However, the effect of ice fraction appears not to be significant at high mass flow rates. In addition, the correlation proposed by Christensen and Kauffeld gives good agreement with numerical results. (author)

Kousksou, T.; Jamil, A.; Zeraouli, Y. [Laboratoire de Thermique Energetique et Procedes, Avenue de l' Universite, BP 1155, 64013 Pau Cedex (France); El Rhafiki, T. [Laboratoire de Thermique Energetique et Procedes, Avenue de l' Universite, BP 1155, 64013 Pau Cedex (France); Laboratoire d' Energetique, Mecanique des Fluides et Sciences des Materiaux, Universite AbdelMalek Essaidi, 90000 Tetouan (Morocco)

2010-06-15

174

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

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

175

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

176

Tire-to-Surface Friction-Coefficient Measurements with a C-123B Airplane on Various Runway Surfaces

An investigation was conducted to obtain information on the tire-to-surface friction coefficients available in aircraft braking during the landing run. The tests were made with a C-123B airplane on both wet and dry concrete and bituminous pavements and on snow-covered and ice surfaces at speeds from 12 to 115 knots. Measurements were made of the maximum (incipient skidding) friction coefficient, the full-skidding (locked wheel) friction coefficient, and the wheel slip ratio during braking.

Sawyer, Richard H.; Kolnick, Joseph J.

1959-01-01

177

The friction coefficient between surfaces depends not only on their roughness but also on their relative speed. The aim of this work is to show how the friction coefficient would vary with the relative speed of the two rough surfaces provided accounting affects of their reciprocal correlation. The reciprocal spectral density of the two surfaces is studied in addition to their structure function. It is shown that the reciprocal spectral density has important impacts on the friction coefficient of the surfaces, in a sense that a positive or a negative reciprocal correlation would cause a decrease or an increase in the friction coefficient. In addition, the friction is studied in the context of the relaxation time. It is shown that there is a threshold for the relative velocity of the two surfaces, where by exceeding the threshold velocity the friction coefficient would not increase, but decrease.

Nikoofard, H.; Vasheghani Farahani, S.; Jafari, G. R.

2014-11-01

178

Energy Technology Data Exchange (ETDEWEB)

This paper attempts to formulate Overall Thermal Transfer Value (OTTV) coefficients for Composite, Hot-Dry and Warm-Humid climates, the three main tropical climates in India. Four existing air-conditioned office buildings - two mid-rise and two high-rise were modeled as case studies using eQuest v.3.6, which is a DoE2.2, based building energy simulation tool. Based on the study of building envelope, loads, operation and HVAC system characteristics of these case study buildings, a hypothetical high-rise, 16 storey office building, octagonal in plan was created for parametric studies. 98 types of opaque exterior wall constructions and 93 types of glass constructions were varied sequentially in parametric runs to obtain results for hourly wall conduction, glass conduction and glass radiation heat flow in eight orientations for each of the climate type. These hourly results were processed to obtain annual heat gain intensities for each parametric case for all three modes of heat transfer. Regression analysis was used to obtain the OTTV coefficients -TD{sub eq}, DT and SF for the three climates. A new OTTV equation is obtained and presented. The set of coefficients obtained were verified by calculating the OTTV for the four case study buildings, for various parametric runs. The computed OTTV for the four case study buildings exhibits good linear correlation with the annual space cooling plus heating energy use in three climates. (author)

Devgan, Seema; Jain, A.K.; Bhattacharjee, B. [Department of Civil Engineering, Indian Institute of Technology, Hauz khas, New Delhi 110016 (India)

2010-10-15

179

Comparison of the Friction-Loss Coefficient for the Gap of Two Contact Surfaces and a Crack

International Nuclear Information System (INIS)

A leak-detection method has been developed by measuring the pressure variation between the inner and outer heat transfer tubes of a double-wall tube steam generator. An experiment was carried out to measure the leak rate in the gap between two surfaces pressed with a hydraulic press in order to simulate the phenomena, and a correlation was determined for the leak rate in a micro gap. However, in the correlation, the gap width and friction coefficient were coupled with the surface roughness, which affects the two parameters. The two parameters were separated using a surface-contact model to develop a correlation for the friction coefficient. The correlation was compared with the existing correlations used for crack analysis. Although the applied ranges of Reynolds numbers were different, the developed correlation for Reynolds numbers of 0.1.0.35 showed similar tendencies to existing correlations used for higher Reynolds numbers

180

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.

Jabbari, Masoud

2012-01-01

181

Heat transfer at evaporation of falling films of Freon mixture on the smooth and structured surfaces

The paper presents the results of experimental investigation of heat transfer and hydrodynamics of falling films of binary mixtures of R21 and R114 freons on the surfaces with complex configuration. The vertical tubes of 50-mm diameter with the smooth and structured surfaces, made of D16T alloy, were used as the working sections. The range of film Reynolds number at the inlet to the working section was Re =10÷155. The image of wave surface of the falling liquid film was visualized and recorded by a high-speed digital video camera. At evaporation the heat transfer coefficients on the smooth and structured surfaces are determined by the liquid flow rate and weakly depend on the heat flux. At low liquid flows, the heat transfer coefficients on the structured surface decrease in comparison with the smooth surface because of liquid accumulation and enlargement of efficient thickness in microtexture channels. At high liquid flows, a change in the structure of the wave film surface leads to an increase in heat transfer coefficients in comparison with the smooth surface.

Pecherkin, N. I.; Pavlenko, A. N.; Volodin, O. A.

2011-12-01

182

Numerical investigation of heat transfer coefficient in a low speed 1.5-stage turbine

The paper numerically investigated the heat transfer coefficients over the rotating blades in a 1.5-stage turbine. The hexahedral structured grids and k-? turbulence model were applied in the simulation. A film hole with diameter of 0.004 m, angled 36°and 28° tangentially to the suction side and pressure side in streamwise respectively, was set in the middle span of the rotor blade. Simulations are done at three different rotating numbers of 0.0239, 0.0265 and 0.0280 with the blowing ratio varying from 0.5 to 2.0. The effects of mainstream Reynolds number and density ratio are also compared. Results show that increasing blowing ratio can increase the heat transfer coefficient ratio on the pressure side, but the rule is parabola on the suction side. Besides, increasing rotating number and Reynolds number is positive while increasing density ratio is negative to the heat transfer on both the pressure side and the suction side.

Li, Guoqing

2014-08-01

183

International Nuclear Information System (INIS)

The paper reports and analysis of the influence of errors in measuring the temperature and isotopic concentrations in experimental determination of mass and heat transfer coefficient. The calculation model for this coefficient is presented as well as the result obtained from an experimental installation of water distillation. The experimental distillation column of an 108 mm inner diameter was filled with an B ordered packing up to a 14 m height. In such a column temperature, vapor concentrations, pressures and reflux rates were measured in 12 points. A table with measured and calculated values is given. Large errors in this quantities made lead to either sub- or super evaluation of the packing performances. Under-evaluation may lead to investment cost increases while super-evaluation may lead to a production capacity decrease

184

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

185

Assessment of Real Heat Transfer Coefficients through Shell and Tube and Plate Heat Exchangers

Directory of Open Access Journals (Sweden)

Full Text Available The purpose of this paper is to present a procedure used in the assessment of the real heat transfer characteristic of shell and tube and plate heat exchangers. The theoretical fundamentals of the procedure are introduced as well as the measured data collection and processing. The theoretical analysis is focused on the adoption of criterial equations which, subjected to certain verification criteria presented in the paper, provide the most credible value of the convection heat transfer coefficients inside the circular and flat tubes. In the end two case studies are presented, one concerning a shell and tube heat exchanger operational at INCERC Thermal Substation and the other concerning a plate heat exchanger tested on the Laboratory Stand of the Department of Building Services and Efficient Use of Energy in Buildings of INCERC Bucharest.

Dan CONSTANTINESCU

2011-07-01

186

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)

187

Directory of Open Access Journals (Sweden)

Full Text Available In this paper, convective heat transfer coefficient of Indian gooseberry (Emblica officinalis, in three different forms (shreds, slices and pieces, under forced convection mode has been determined. These forms were dried in laboratory drier. Values of constants C and n have been determined using experimental data and regression analysis for calculating values of convective heat transfer coefficient. It was found that the convective heat transfer coefficient varies with form of commodity being dried and decreases as the drying progresses. The value of convective heat transfer coefficient was highest for shredded form (30.39 W/m2oC followed by slices (25.88 W/m2oC and pieces (18.67 W/m2oC when compared at certain final moisture content. The data were also analyzed for per cent uncertainty.

S. I. ANWAR

2012-10-01

188

A correlation for free convection heat transfer from vertical wavy surfaces

Energy Technology Data Exchange (ETDEWEB)

Free convection heat transfer along an isothermal vertical wavy surface was studied experimentally and numerically. A Mach-Zehnder Interferometer was used in the experiment to determine the local heat transfer coefficients. Experiments were done for three different amplitude-wavelength ratios of {alpha} = 0.05, 0.1, 0.2 and the Rayleigh numbers ranging from Ra{sub l} = 2.9 x 10 {sup 5} to 5.8 x 10 {sup 5}. A finite-volume based code was developed to verify the experimental study and obtain the results for all the amplitude-wavelength ratios between {alpha} = 0 to 0.2. It is found that the numerical results agree well with the experimental data. Results indicate that the frequency of the local heat transfer rate is the same as that of the wavy surface. The average heat transfer coefficient decreases as the amplitude-wavelength ratio increases and there is a significant difference between the average heat transfer coefficients of the surface with {alpha} = 0.2 and those surfaces with {alpha} = 0.05 and 0.1. The experimental data are correlated with a single equation which gives the local Nusselt number along the wavy surface as a function of the amplitude-wavelength ratio and the Rayleigh number. (orig.)

Ashjaee, M.; Amiri, M.; Rostami, J. [University of Tehran, Department of Mechanical Engineering, Tehran (Iran)

2007-11-15

189

The role of surface energy coefficients and nuclear surface diffuseness in the fusion of heavy-ions

Digital Repository Infrastructure Vision for European Research (DRIVER)

We discuss the effect of surface energy coefficients as well as nuclear surface diffuseness in the proximity potential and ultimately in the fusion of heavy-ions. Here we employ different versions of surface energy coefficients. Our analysis reveals that these technical parameters can influence the fusion barriers by a significant amount. A best set of these parameters is also given that explains the experimental data nicely.

Dutt, Ishwar; Puri, Rajeev K.

2010-01-01

190

Transfer of tritiated water vapour to and from land surfaces

International Nuclear Information System (INIS)

Deposition of tritiated water vapour may result in contamination of food supplies and reduction of air concentrations, but the process has received little attention. Field and laboratory experiments were undertaken to investigate the mechanisms involved. The exchange between air and ground involves turbulent transfer in the atmosphere near the surface and diffusion within the soil. The exchange velocity for moist soil was limited by atmospheric mixing to about 1 cms-1, and was only a little smaller at dry soil and grass surfaces. For exposure times exceeding a few minutes re-evaporation becomes significant, reducing the net rate of uptake, but the total amount deposited continues to increase as the tritiated water diffuses deeper into the soil. Diffusion in soil was investigated and a simple equation proposed to predict the effective diffusion coefficient. Tritiated water deposited during a brief exposure in the field evaporated from the surface during several weeks, and its behaviour can be described by the diffusion equation with a suitable boundary condition. Rain washes activity into the soil and impedes further evaporation. Most of the vapour will interact with the surface within two or three days of release, and transport over continental distances will be retarded as a result. The effect of surface exchange on the distribution of doses following a release of tritiated water vapour will be complicated by changes in the weather over a period of severales in the weather over a period of several weeks, and will be difficult to foresee. (author)

191

Transfer coefficient of 137Cs from feed to cow milk in tropical region Kaiga (India)

International Nuclear Information System (INIS)

In the transport model for the prediction of the concentration of 137Cs in milk, the transfer coefficient from feed to milk, Fm, is an important parameter. Site-specific transfer coefficient from feed to cow's milk, for 137Cs in the Kaiga environment, a nuclear power station site in India, determined over a period of 10 y is presented in this paper. The value is determined from 137Cs concentration in milk and grass samples of the Kaiga region and the result ranged from 6.43 E-03 to 1.09 E-02 d l-1 with a geometric mean value of 8.0 E-03 d l-1. The result is compared with that for 40K, determined concurrently at the same region and ranged from 3.06 E-03 to 3.48 E-03 d l-1 with a geometric mean value of 3.26 E-03 d l-1. This parameter is quite useful in decision-making for implementing countermeasures during a large area contamination with 137Cs in tropical areas like Kaiga. (authors)

192

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

193

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

194

Energy Technology Data Exchange (ETDEWEB)

Molecular diffusion coefficients of lithium-, sodium-, potassium-, cesium-, calcium-, and strontium nitrate in subcritical water were determined by analysis of Taylor dispersion profiles. Pressures ranged from 300 to 500 bar at temperatures ranging from 25{degrees}C to 300{degrees}C. The reported diffusion values were determined at infinite dilution. Molecular diffusion coefficients were 10 to 20 times faster in near-critical subcritical water than in water at ambient temperature and pressure (ATP). These findings implied that the diffusion rates were more liquid like than they were gas like, hence experimental results were correlated with diffusion models for liquids. The subcritical diffusion data presented in this work, and supercritical diffusion results published elsewhere were correlated with hydrodynamic diffusion equations. Both the Wilke-Chang correlation and the Stokes-Einstein equation yielded predictions within 10% of the experimental results if the structure of the diffusing species could be estimated. The effect of the increased diffusion rates on mass transfer rates in supercritical water oxidation applications was quantified, with emphasis on heterogeneous oxidation processes. This study and results published elsewhere showed that diffusion limited conditions are much more likely to be encountered in SCWO processes than commonly acknowledged.

Goemans, M.G.E.; Gloyna, E.F. [Univ. of Texas, Austin, TX (United States). Dept. of Civil Engineering; Buelow, S.J. [Los Alamos National Lab., NM (United States)

1996-04-01

195

Surface diffusion coefficients by thermodynamic integration: Cu on Cu(100)

Digital Repository Infrastructure Vision for European Research (DRIVER)

The rate of diffusion of a Cu adatom on the Cu(100) surface is calculated using thermodynamic integration within the transition state theory. The results are found to be in excellent agreement with the essentially exact values from molecular-dynamics simulations. The activation energy and related entropy are shown to be effectively independent of temperature, thus establishing the validity of the Arrhenius law over a wide range of temperatures. Our study demonstrates the equ...

Boisvert, Ghyslain; Mousseau, Normand; Lewis, Laurent J.

1998-01-01

196

Directory of Open Access Journals (Sweden)

Full Text Available 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

2005-04-01

197

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.)

198

International Nuclear Information System (INIS)

Several experiments and theoretical researches have been performed to calculate condensation heat transfer and many correlations have been suggested. Generally, correlations are largely divided into two groups: applicable to laminar flow or turbulent flow. That is because, depending on whether flow is laminar or turbulent, flow characteristics and phenomena which play major role in heat transfer process are greatly different. Film Reynolds number is widely used to determine whether flow is laminar or turbulent. MARS code uses two condensation heat transfer coefficient(HTC) correlations: Nusselt's correlation for laminar flow and Shah's for turbulent. Condensation HTCs are calculated by using both correlations and the larger one is taken, that is, Film Reynolds number is not used to determine flow condition and select HTC correlation. This means that a correlation may be able to be incorrectly used just because its HTC is larger, though a correlation is not in an applicable range. In this paper, simulation results of two condensation experiments using MARS code are discussed. It is shown that, though flow condition is similar, different correlation can be used and how much calculated results are differentiated from experimental data

199

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.

200

Flux surface averaging of the diffusion coefficient in electron cyclotron resonance heating

International Nuclear Information System (INIS)

The single particle model has been used to describe electron cyclotron resonance heating. Fielding's (1980) method of calculating the diffusion coefficient has been simplified and extended to include the effect of finite beam width. It is shown how this effect and the effect of the rotational transform lead to a spreading of the resonance over a wider class of particles and how the diffusion coefficient should be averaged over a magnetic surface or surfaces. (author)

201

International Nuclear Information System (INIS)

In the search for a deeper understanding of the factors governing the stability of liquid metal field-ion emitters, the behaviour of a liquid anode with an anomalous surface tension coefficient is studied. The main parameter in this experimental study is the emitter temperature. At the conclusion of the work an important result emerged: apart from the surface tension coefficient, space-charge effects constitute a major factor influencing emitter stability

202

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

203

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

204

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

205

This paper summarizes the properties of the surface backscattering coefficient as a function of roughness, incidence angle, frequency and polarization state. Results are presented in the form of like- and cross-polarized backscattering coefficient curves versus the incidence angle and the polarization state for different values of the surface roughness parameters and frequency. It is seen that there is a gradual transition from the standard small perturbation scattering model into the Kirchhoff scattering model as frequency increases. It is also shown that in the intermediate frequency region neither the small perturbation nor the Kirchhoff model is applicable. The maximum value of the polarized backscattering coefficient occurs at VV polarization and its two minimum values occur at zero ellipticity and orientation angles between 0 deg and 45 deg and between 135 deg and 180 deg. The cross-polarized scattering coefficient has two maximum values which occur in the same polarization state regions as the minima of the polarized coefficients.

Fung, A. K.; Chen, K. S.

1992-01-01

206

Vaporization heat transfer of dielectric liquids on enhanced surfaces covered with screen wicks

Experiments were conducted to investigate the vaporization heat transfer characteristics for the dielectric liquid FC-72 on several wicking surfaces which may be used in flat-plate heat pipes. The wicking materials studied included microstructure enhanced surfaces and coarse surfaces covered with screen meshes. Experimental data for q versus deltaT curves and critical heat fluxes were obtained for the two different operating conditions of a heat pipe, evaporation, and shallow pool boiling. When the liquid level was above the heated surface, the height of the liquid level above the surface was varied from 0 to 10 mm. When the liquid level was below the heated surface, the distance from the liquid level to the edge of the surface was adjusted from 0 to 15 mm. Experimental results revealed that for shallow pool boiling when the heated surface was covered with a wire screen mesh, the heat transfer coefficient increased at lower heat fluxes but the critical heat flux (CHF) decreased for all the surfaces tested. In the case of evaporation, both CHF and the heat transfer coefficient increased as the microstructure surfaces were covered with screen meshes.

Gu, C. B.; Chow, L. C.; Pais, M. R.; Baker, K.

1993-01-01

207

Free-stream turbulence effect on the heat (mass) transfer characteristics on a turbine rotor surface

International Nuclear Information System (INIS)

The heat (mass) transfer characteristics on the blade surface of a first-stage turbine rotor cascade has been investigated by employing the naphthalene sublimation technique. A four-axis profile measurement system is employed for the measurements of the local heat (mass) transfer coefficient on the curved blade surface. The experiments are carried out for two free-stream turbulence intensities of 1.2% and 14.7%. The high free-stream turbulence results in more uniform distributions of heat load on the both pressure and suction surfaces and in an early boundary-layer separation on the suction surface. The heat (mass) transfer enhancement on the suction surface due to the endwall vortices is found to be relatively small under the high free-stream turbulence

208

The effects of a curvilinear surface with ejection holes on the internal heat-transfer coeeficient of arrays of impinging jets have been investigated to simulate impingement-cooled turbine vanes. The experiments show that both the curvature of the surface and the presence of the ejection holes favor the heat-transfer augmentation. It is noted that the internal-impingement heat-transfer coefficient on the suction side of the cooled blade calculated by using the correlation of the coefficient on a flate plate is more or less too conservative.

Li, Liguo; Chang, Haiping

1986-07-01

209

Research on heat transfer characteristics of nano-structured surface

International Nuclear Information System (INIS)

Heat transfer enhancement at nano-structured surfaces on SUS316 substrate is experimentally investigated. In this study, slurry coating and dip-coating of nano-particles on the substrate and ion beam irradiation are applied as the fabrication technique of such surfaces. All of these surfaces shows the heat transfer enhancement with the factor ranging from 1.4 to 2. (author)

210

Heat transfer coefficient between bed and inserted horizontal tube in a three-phase fluidized bed

International Nuclear Information System (INIS)

The heat transfer coefficient between bed and horizontal tube wall was measured in three-phase fluidized beds of 19 and 12 cm i.d. Glass spheres with different diameters (particle diameter=0.052-0.22 cm, particle density = 2.5 g.cm-3) and alumina spheres (particle diameter=0.32 cm, apparent particle density=1.62 g.cm-3) were fluidized by the fluid media of air-water or air-aqueous solution of carboxymethyl cellulose. The superficial velocities of gas and liquid were varied in the range of 2.0-16 cm . s-1 and 0.1-8.0 cm . s-1, respectively

211

Enrichment factors and transfer coefficients from soil to rye plants by INAA

International Nuclear Information System (INIS)

An extensive investigation of elemental levels in cereals and their cultivation soils has been going on across the main production areas of mainland Portugal, with a view to an eventual biofortification of major cultivars through agronomic practices. Cereals are an obvious choice as primary vehicles for food-supplementation programs, especially in countries where they definitely weigh in the dietary intake (like Portugal), and regions whose geographical and/or pedological features may account for nutrient deficiencies in typical diets. Mature rye plants (Secale cereale L.; roots and grains) and local soils were collected in the summer of 2009 from two regions of northern Portugal, and put through k0-standardized, instrumental neutron activation analysis (k0-INAA). Overall, the results (elemental concentrations, enrichment factors, transfer coefficients) seem to confirm an efficient uptake of elements from soil and their translocation to the aerial parts of the plants, notably to the ones that really matter in human nutrition (grains). (author)

212

The heat transfer coefficient (HTC) between the sheet metal and the cold tool is required to predict the final microstructure and mechanical properties of parts manufactured via hot forming die quenching. Temperature data obtained from hot stamping experiments conducted on boron steel blanks were processed using an inverse heat conduction algorithm to calculate heat fluxes and temperatures at the blank/die interface. The effect of the thermocouple response time on the calculated heat flux was compensated by minimizing the heat imbalance between the blank and the die. Peak HTCs obtained at the end of the stamping phase match steady-state model predictions. At higher blank temperatures, the time-dependent deformation of contact asperities is associated with a transient regime in which calculated HTCs are a function of the initial stamping temperature.

Caron, Etienne; Daun, Kyle J.; Wells, Mary A.

2013-04-01

213

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

214

Directory of Open Access Journals (Sweden)

Full Text Available A procedure based on the Artificial Bee Colony algorithm for solving the two-phase axisymmetric one-dimensional inverse Stefanproblem with the third kind boundary condition is presented in this paper. Solving of the considered problem consists in reconstruction of the function describing the heat transfer coefficient appearing in boundary condition of the third kind in such a way that the reconstructed values of temperature would be as closed as possible to the measurements of temperature given in selected points of the solid. A crucial part of the solution method consists in minimizing some functional which will be executed with the aid of one of the swarm intelligence algorithms - the ABC algorithm.

E. Hetmaniok

2012-12-01

215

Reconstruction of the Stefan–Boltzmann coefficients in a heat-transfer process

International Nuclear Information System (INIS)

In this paper, we investigate an inverse problem of determining the coefficients within the framework of Stefan–Boltzmann radiation boundary conditions for the heat-transfer process in a material. A mathematical formulation for the forward and inverse problems is introduced and the uniqueness of the inverse problem is proved. The finite-difference method is utilized for the discretization of the forward problem. Based on our analysis, we propose a fast-reconstruction method for solving the inverse problem, which can be easily realized in practice. Some regularization techniques are implemented to overcome the ill-posedness of the problem. Numerical simulation shows that our reconstruction method is stable and effective. (paper)

216

This paper numerically investigates the hyperbolic thermoelastic problem of an annular fin. The ambient convection heat transfer coefficient of the fin is assumed to be spatially varying. The major difficulty in dealing with such problems is the suppression of numerical oscillations in the vicinity of a jump discontinuity. An efficient numerical scheme involving hybrid application of Laplace transform and control volume method in conjunction with hyperbolic shape functions is used to solve the linear hyperbolic heat conduction equation. The transformed nodal temperatures are inverted to the physical quantities by using numerical inversion of the Laplace transform. Then the stress distributions in the annular fin are calculated subsequently. The results in the illustrated examples show that the application of hyperbolic shape functions can successfully suppress the numerical oscillations in the vicinity of jump discontinuities.

Lee, Haw-Long; Chang, Win-Jin; Chen, Wen-Lih; Yang, Yu-Ching

2012-06-01

217

Effect factors of heat transfer coefficient between hollow glass microsphere and furnace atmosphere

International Nuclear Information System (INIS)

In order to achieve an effective control of the heat transfer coefficient (hq) between microsphere and furnace atmosphere in the fabrication of hollow glass micro-sphere by sol-gel technology, the effects of component percentage, temperature and total pressure of gas mixture on hq are studied. Further, the influences of diameter and wall thickness of hollow glass microsphere on hq are also investigated. The results show that in the range of component percentage, temperature and pressure of gas mixture commonly used in the fabrication of hollow glass microsphere by sol-gel technology, the temperature and total pressure of gas mixture and the wall thickness of hollow glass microsphere have little influence on hq, but hq significantly increases with the volume fraction of helium in the furnace atmosphere and significantly decreases with increasing of microsphere diameter. (authors)

218

International Nuclear Information System (INIS)

A correlation of a heat transfer coefficient was derived for the transition flow region between the quench front and the dispersed flow region during the reflood phase. The correlation was compared with data from a small scale reflood experiment with a 4 x 4 heater-rod bundle and FLECHT experiments and showed fairly good agreement with the experimental data. The predicted errors were nearly within +-30% for all the data of the referred small scale reflood experiment, +-20% for all data except for the data of high flooding rate cases (higher than 7.5 x 10-2 m/s) and the data measured at the location just below the spacer grid, and +-20% for two selected FLECHT tests. (author)

219

Pattern recognition of surface electromyography signal based on wavelet coefficient entropy

Digital Repository Infrastructure Vision for European Research (DRIVER)

This paper introduced a novel, simple and ef-fective method to extract the general feature of two surface EMG (electromyography) signal patterns: forearm supination (FS) surface EMG signal and forearm pronation (FP) surface EMG signal. After surface EMG (SEMG) signal was decomposed to the fourth resolution level with wavelet packet transform (WPT), its whole scaling space (with frequencies in the interval (0Hz, 500Hz]) was divided into16 frequency bands (FB). Then wavelet coefficient entropy ...

Ying Gao; Wai-Xi Liu; Xiao Hu

2009-01-01

220

Heat transfer from the roughened surface of gas cooled fast breeder reactor fuel element

International Nuclear Information System (INIS)

The temperature distributions and the augmentation of heat transfer performance by artificial roughening of a gas cooled fast breeder reactor (GCFR) fuel rod cladding are studied. Numerical solutions are based on the axisymmetric assumption for a two-dimensional model for one rib pitch of axial distance. The local and axial clad temperature distributions are obtained for both the rectangular and ramp rib roughened surface geometries. The transformation of experimentally measured convective heat transfer coefficients, in terms of Stanton number, into GCFR values is studied. In addition, the heat transfer performance of a GCFR fuel rod cladding roughened surface design is evaluated. Approximate analytical solution for correlating an average Stanton number is also obtained and satisfactorily compared with the corresponding numerical result for a GCFR design. The analytical correlation is useful in assessing roughened surface heat transfer performance in scoping studies and conceptual design

221

In this study, the air side heat transfer coefficient of an aluminium mini-channel heat exchanger was investigated for single-phase flow in the mini-channel, with water in the tubes and air on the outside. Research methods included hydraulic tests on a single mini-channel tube, Wilson Plot experiments and experiment validation. Results obtained from the hydraulic test showed that turbulent flow occurred in the tube at a Reynolds number of 830. Wilson Plot experiments were conducted to determine air side heat transfer coefficient of the heat exchanger. The tube side Reynolds number was maintained above 1000 to ensure turbulent flow and tube side heat transfer coefficient was calculated using Gnielinski equation for turbulent flow. The air side heat transfer coefficients obtained from the Wilson Plot experiments were in good agreement with known correlations. The outcome of this study is to use the air side heat transfer coefficient to calculate the performance of refrigerant condensers for different tube pass ratios and flow pass configurations.

Thoo, K. K.; Chin, W. M.; Heikal, M. R.

2013-12-01

222

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

223

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

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.

224

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

225

Directory of Open Access Journals (Sweden)

Full Text Available Pool boiling heat transfer coefficient of monoethylene glycol (MEG, diethylene glycol (DEG and water ternary mixtures has been experimentally measured up to heat flux 114 kW/m2 at various volumetric concentrations of MEG and DEG. As expected, heat transfer coefficient was strongly taken as a direct function of heat flux. Existing well-known correlations are shown to be unable to predict the acceptable values for the tested ternary mixtures, particularly at different concentrations of MEG and DEG. Furthermore, a new modified correlation is developed on the basis of the Stephan - Preußer correlation that predicts the values of heat transfer coefficients with absolute average error of about 7% that is reasonable and acceptable values in compare to other existing correlations.

Sarafraz M.M.

2012-01-01

226

The effect of the oxygen transfer coefficient on the production of xylitol by bioconversion of xylose present in sugarcane bagasse hemicellulosic hydrolysate using the yeast Candida guilliermondii was investigated. Continuous cultivation was carried out in a 1.25-L fermentor at 30 degrees C, pH 5.5, 300 rpm, and a dilution rate of 0.03/h, using oxygen transfer coefficients of 10, 20, and 30/h. The results showed that the microbial xylitol production (11 g/L) increased by 108% with the decrease in the oxygen volumetric transfer coefficient from 30 to 20/h. The maximum values of xylitol productivity (0.7 g/[L.h]) and yield (0.58 g/g) were obtained akLa 20/h. PMID:10849823

Martínez, E A; Silva, S S; Felipe, M G

2000-01-01

227

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.)

228

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)

229

Energy Technology Data Exchange (ETDEWEB)

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/m{sup 2} 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)

Baburajan, P.K. [Atomic Energy Regulatory Board, Mumbai (India); Bisht, G.S. [Indian Institute of Technology, Bombay (India); Gupta, S.K. [Atomic Energy Regulatory Board, Mumbai (India); Prabhu, S.V., E-mail: svprabhu@iitb.ac.in [Indian Institute of Technology, Bombay (India)

2013-02-15

230

Energy Technology Data Exchange (ETDEWEB)

Authors performed post-CHF experiments under wider pressure ranges of 2 MPa - 18 MPa, wider mass flux ranges of 33 kg/m{sup 2}s - 1651 kg/m{sup 2}s and wider superheat of heaters up to 500 K in comparison to experimental ranges at previous post-CHF experiments. Data on boiling transition, critical heat flux and post-CHF heat transfer coefficient were obtained. Used test section was 4x4-rod bundle with heaters, which diameter and length were the same as those of BWR nuclear fuels. As the result of the experiments, it was found that the boiling transition occurred just below several grid spacers, and that the fronts of the boiling transition region proceeded lower with increase of heated power. Heat transfer was due to nucleate boiling above grid spacers, while it was due to film boiling below grid spacers. Consequently, critical heat flux is affected on the distance from the grid spacers. Critical heat flux above the grid spacers was about 15% higher than that below the grid spacers, by comparing them under the same local condition. Heat transfer by steam turbulent flow was dominant to post-CHF heat transfer, when superheat of heaters was sufficiently high. Then, post-CHF heat transfer coefficient was predicted with heat transfer correlations for single-phase flow. On the other hand, when superhead of heaters was not sufficiently high, post-CHF heat transfer coefficient was higher than the prediction with heat transfer correlations for single-phase flow. Mass flux effect on post-CHF heat transfer coefficient was described by standardization of post-CHF heat transfer coefficient with the prediction for single-phase flow. However, pressure effect, superheat effect and effect of position were not described. Authors clarified that those effects could be described with functions of heater temperature and position. Post-CHF heat transfer coefficient was lowest just blow the grid spacers, and it increased with the lower positions. It increased by about 30% in one span of the grid spacers, which length was about 50 cm. (author)

Iguchi, Tadashi; Anoda, Yoshinari [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment; Iwaki, Chikako [Toshiba Corp., Tokyo (Japan)

2002-02-01

231

International Nuclear Information System (INIS)

Authors performed post-CHF experiments under wider pressure ranges of 2 MPa - 18 MPa, wider mass flux ranges of 33 kg/m2s - 1651 kg/m2s and wider superheat of heaters up to 500 K in comparison to experimental ranges at previous post-CHF experiments. Data on boiling transition, critical heat flux and post-CHF heat transfer coefficient were obtained. Used test section was 4x4-rod bundle with heaters, which diameter and length were the same as those of BWR nuclear fuels. As the result of the experiments, it was found that the boiling transition occurred just below several grid spacers, and that the fronts of the boiling transition region proceeded lower with increase of heated power. Heat transfer was due to nucleate boiling above grid spacers, while it was due to film boiling below grid spacers. Consequently, critical heat flux is affected on the distance from the grid spacers. Critical heat flux above the grid spacers was about 15% higher than that below the grid spacers, by comparing them under the same local condition. Heat transfer by steam turbulent flow was dominant to post-CHF heat transfer, when superheat of heaters was sufficiently high. Then, post-CHF heat transfer coefficient was predicted with heat transfer correlations for single-phase flow. On the other hand, when superhead of heaters was not sufficiently high, post-CHF heat transfer coefficient was higher than the prediction with heat transfer correlations for single-phase flow. Mass flux effect on post-CHF heat transfer coefficient was described by standardization of post-CHF heat transfer coefficient with the prediction for single-phase flow. However, pressure effect, superheat effect and effect of position were not described. Authors clarified that those effects could be described with functions of heater temperature and position. Post-CHF heat transfer coefficient was lowest just blow the grid spacers, and it increased with the lower positions. It increased by about 30% in one span of the grid spacers, which length was about 50 cm. (author)

232

International Nuclear Information System (INIS)

A method to determine mutual friction coefficient between normal and superfluid components in superfluid helium-3 has been described. To increase the accuracy of measurement of mutual friction coefficient B the method of oscillation of coasxial cylindric surfaces is realized, in which a multiple intensification of the effect of mutual friction between normal and superfluid components takes place as compared with a hollow cylinder. Results of the experiment carried out for He-2 are presented

233

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

234

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

235

Digital Repository Infrastructure Vision for European Research (DRIVER)

The forced convection heat transfer coefficient and friction factor are determined for the flow of water and nanofluid in a vertical packed bed column. The analysis is undertaken in the laminar and transition Reynolds number range. The column is filled with spherical glass beads as the bed material. The heat transfer coefficients with Al2O3 nanofluid increased by 12% to 15% with the increase of volume concentration from 0.02% to 0.5% compared with water. The experimental values of axial tempe...

Srinivasa Rao, G.; Sharma, K. V.; Chary, S. P.; Rahman, M. M.; Kadirgama, K.; Noor, M. M.

2011-01-01

236

International Nuclear Information System (INIS)

In this paper, a sensitivity analysis on the overall heat transfer coefficient has been carried out as a function of operation temperature and pressure. The sulfur-iodine (SI) cycle and Westinghouse sulfur hybrid cycle, combined with a very high temperature gas-cooled reactor (VHTR), are well-known as feasible technologies for hydrogen production. The SI process consists of a Bunsen reactor; H2SO4, SO3, and HIx decomposers; and a HI pre-heater. The overall heat transfer coefficient of the process heat exchanger (PHE) used in the SI process is a very important factor when sizing the PHE

237

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)

238

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

239

Measurements of absorbed heat flux and water-side heat transfer coefficient in water wall tubes

The tubular type instrument (flux tube) was developed to identify boundary conditions in water wall tubes of steam boilers. The meter is constructed from a short length of eccentric tube containing four thermocouples on the fire side below the inner and outer surfaces of the tube. The fifth thermocouple is located at the rear of the tube on the casing side of the water-wall tube. The boundary conditions on the outer and inner surfaces of the water flux-tube are determined based on temperature measurements at the interior locations. Four K-type sheathed thermocouples of 1 mm in diameter, are inserted into holes, which are parallel to the tube axis. The non-linear least squares problem is solved numerically using the Levenberg-Marquardt method. The heat transfer conditions in adjacent boiler tubes have no impact on the temperature distribution in the flux tubes.

Taler, Jan; Taler, Dawid; Kowal, Andrzej

2011-04-01

240

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

241

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

242

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

243

Directory of Open Access Journals (Sweden)

Full Text Available This work is aimed at modeling the heat transfer mechanism in a fluidized bed of grass seeds (Brachiaria brizantha for supporting further works on simulating the drying of these seeds in such a bed. The three-phase heat transfer model, developed by Vitor et al. (2004, is the one used for this proposal. This model is modified to uncouple one of the four adjusted model parameters from the gas temperature. Using the first set of experiments, carried out in a laboratory scale batch fluidized bed, the four adjusted model parameters are determined, generating the heat transfer coefficient between particles and gas phase, as well as the heat transfer coefficient between the column wall and ambient air. The second set of experiments, performed in the same unit at different conditions, validates the modified model.

A. C. Rizzi Jr.

2009-09-01

244

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english This work is aimed at modeling the heat transfer mechanism in a fluidized bed of grass seeds (Brachiaria brizantha) for supporting further works on simulating the drying of these seeds in such a bed. The three-phase heat transfer model, developed by Vitor et al. (2004), is the one used for this prop [...] osal. This model is modified to uncouple one of the four adjusted model parameters from the gas temperature. Using the first set of experiments, carried out in a laboratory scale batch fluidized bed, the four adjusted model parameters are determined, generating the heat transfer coefficient between particles and gas phase, as well as the heat transfer coefficient between the column wall and ambient air. The second set of experiments, performed in the same unit at different conditions, validates the modified model.

A. C., Rizzi Jr.; M. L., Passos; J. T., Freire.

2009-09-01

245

Surface-mediated gene transfer from nanocomposites of controlled texture

Safe and efficient gene delivery would have great potential in gene therapy and tissue engineering, but synthetic biomaterial surfaces endowed with efficient gene-transferring functions do not yet exist. Inspired by naturally occurring biomineralization processes, we co-precipitated DNA with inorganic minerals onto cell-culture surfaces. The DNA/mineral nanocomposite surfaces obtained not only supported cell growth but also provided high concentrations of DNA in the immediate microenvironment of the cultured cells. Gene transfer from the engineered surfaces was as efficient as an optimized commercial lipid transfection reagent; in addition, the extent of gene transfer was adjustable by varying the mineral composition. DNA/mineral nanocomposite surfaces represent a promising system for enhancing gene transfer and controlling the extent of gene transfer for various biomedical applications, including tissue engineering or gene therapy of bone.

Shen, Hong; Tan, Jian; Saltzman, W. Mark

2004-08-01

246

Directory of Open Access Journals (Sweden)

Full Text Available Two phase heat transfer coefficients and pressure drops of R-404A in a smooth (8.56 mm ID and micro-fin tube (8.96 mm ID are experimentally investigated. Different from previous studies, the present experiments are performed for different condensing temperatures, with superheating and sub cooling and using hermetically sealed compressor. The test runs are done at average saturated condensing temperatures ranging from 35oC to 60oC. The mass fluxes are between 90 and 800 kg m-2s-1 . The experimental results from both smooth and micro-fin tubes show that the average heat transfer coefficient and pressure drop increases with mass flux but decreases with increasing condensing temperature. The average heat transfer coefficient is 30-210% higher for micro-fin tube than that of smooth tube, with moderate increase in pressure drop ranging from 10-55%. New correlations based on the data gathered during the experimentation for predicting condensation heat transfer coefficients are proposed for wide range of practical applications.

DR. S.N. Sapali

2009-11-01

247

Pressure-induced absorption coefficients for radiative transfer calculations in Titan's atmosphere

International Nuclear Information System (INIS)

The semiempirical theory of Birnbaum and Cohen (1976) is used to calculate the FIR pressure-induced absorption (PIA) spectra of N2, CH4, N2 + Ar, N2 + CH4, and N2 + H2 under conditions like those in the Titan troposphere. The results are presented graphically and compared with published data from laboratory measurements of PIA in the same gases and mixtures (Dagg et al., 1986; Dore et al., 1986). Good agreement is obtained, with only a slight underestimation of PIA at 300-400/cm in the case of CH4. The absorption coefficients are presented in tables, and it is suggested that the present findings are of value for evaluating the effects of tropospheric clouds on the Titan FIR spectrum and studying the greenhouse effect near the Titan surface. 24 references

248

International Nuclear Information System (INIS)

Coupled heat and mass transfer in porous media has many important applications in engineering. These include the migration of moisture in fibrous insulation, the spreading of chemical pollutants in saturated soil, underground disposal of nuclear wastes and the extraction of geothermal energy. Here, similarity solutions are reported for coupled heat and mass transfer by free, forced, and mixed convection from a horizontal surface in a saturated porous medium. The present analysis shows that similarity solutions are possible for a surface maintained at a constant heat flux and mass flux condition. The governing parameters for the problem under consideration are the Lewis number Le, the buoyancy ratio N and mixed convection parameter Ra/Pe3/2. Depending on the values of N and Le, the heat and mass transfer results may range from the asymptotic free convection limit to that of the forced convection limit. The results are presented in terms of the relation between the transfer coefficients and the governing parameters

249

Flux surface averaging on the diffusion coefficient in electron cyclotron resonance heating

International Nuclear Information System (INIS)

The single particle model has been used to describe electron cyclotron resonance heating. Fielding's method of calculating the diffusion coefficient has been simplified and extended to include the effect of finite beam width. It is shown how this effect and the effect of the rotational transform lead to a spreading of the resonance over a wider class of particles and how the diffusion coefficient should be average over a magnetic surface or surfaces. The spreading of the resonance due to these effects is expected to increase the threshold for saturation of the heating to occur

250

A mathematical model is presented to study the Soret and Dufour effects on the convective heat and mass transfer in stagnation-point flow of viscous incompressible fluid towards a shrinking surface. Suitable similarity transformations are used to convert the governing partial differential equations into self-similarity ordinary differential equations that are then numerically solved by shooting method. Dual solutions for temperature and concentration are obtained in the presence of Soret and Dufour effects. Graphical representations of the heat and mass transfer coefficients, the dimensionless thermal and solute profiles for various values of Prandtl number, Lewis number, Soret number and Dufour number are demonstrated. With Soret number the mass transfer coefficient which is related to mass transfer rate increases for both solutions and the heat transfer coefficient (related to heat transfer rate) for both solutions becomes larger with Dufour number. The Prandtl number causes reduction in heat and the mass transfer coefficients and similarly with the Lewis number mass transfer coefficient decreases. Also, double crossing over is found in dual dimensionless temperature profiles for increasing Soret number and in dual dimensionless concentration profiles for the increase in Dufour number. Due to the larger values of Dufour number the thermal boundary layer increases and for Prandtl number increment it decreases; whereas, the solute boundary layer thickness reduces with increasing values of Prandtl number and Lewis number.

Bhattacharyya, Krishnendu; Layek, G. C.; Seth, G. S.

2014-09-01

251

Methamphetamine residue dermal transfer efficiencies from household surfaces.

Methamphetamine contamination from illegal production operations poses a potential health concern for emergency responders, child protective services, law enforcement, and children living in contaminated structures. The objective of this study was to evaluate dermal transfer efficiencies of methamphetamine from contaminated household surfaces. These transfer efficiencies are lacking for methamphetamine, and would be beneficial for use in exposure models. Surfaces were contaminated using a simulated smoking method in a stainless steel chamber. Household surfaces were carpet, painted drywall, and linoleum. Dermal transfer efficiencies were obtained using cotton gloves for two hand conditions, dry or saliva moistened (wet). In addition, three contact scenarios were evaluated for both hand conditions: one, two, or three contacts with contaminated surfaces. Dermal transfer efficiencies were calculated for both hand conditions and used as inputs in a Stochastic Human Exposure and Dose Simulation model (SHEDS-Multimedia, Office of Research and Development, United States Environmental Protection Agency, Research Triangle Park, N.C.). Results of this study showed that average dermal transfer efficiencies of methamphetamine ranged from 11% for dry hands to 26% for wet hands. There was a significantly higher wet transfer as compared to dry transfer for all surfaces. For wet hands, dermal transfer depended on surface type with higher transfer from carpet and linoleum as compared to drywall. Based on our estimates of dermal transfer efficiency, a surface contamination clearance level of 1.5 ?g/100 cm(2) may not ensure absorbed doses remain below the level associated with adverse health effects in all cases. Additional dermal transfer studies should be performed using skin surrogates that may better predict actual skin transfer. PMID:24579754

Van Dyke, Mike; Martyny, John W; Serrano, Kate A

2014-01-01

252

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

253

In many engineering applications, heat transfer enhancement techniques are of vital importance in order to ensure reliable thermal designs of convective heat transfer applications. This study examines experimentally the heat transfer characteristics on the base plate around various surface mounted obstacles. Local convection coefficients are evaluated in the vicinity of each individual protruding body with great spatial resolution using the transient liquid crystal technique. Five different obstacles of constant height-to-hydraulic diameter ratio (˜1.3) are considered. These include: a cylinder, a square, a triangle, a diamond and a vortex generator of delta wing shape design. The experiments were carried out over a range of freestream Reynolds numbers, based on the hydraulic diameter of each obstacle, varying from 4,000 to 13,000. The results indicate a negligible effect of the flow speed on the heat transfer topological structure and a considerable effect of the obstacle geometry on the level and distribution of heat transfer enhancement.

Wyssmann, Robert; Ullmer, Dirk; Terzis, Alexandros; Ott, Peter

2014-04-01

254

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 6,083 +/- 673 mBq per animal in winter; 7,163 +/- 1,077 mBq per animal in spring; 1,506 +/- 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. PMID:3519533

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

1986-06-01

255

An Experimental Investigation of Heat Transfer Coefficients for Spiral Plate Heat Exchanger

Directory of Open Access Journals (Sweden)

Full Text Available Spiral plate heat exchangers play a vital role in cooling high density and high viscous fluids. This paper presents an experimental investigation of convective heat transfer co-efficient for electrolytes using spiral plate heat exchanger. The test section consists of a Plate of width 0.3150 m, thickness 0.001 m and mean hydraulic diameter of 0.01 m. The mass flow rate of hot fluid is varying from 0.4 kg sec-1 to 0.8 kg sec-1 and the mass flow rate of cold fluid varies from 0.3 kg sec-1 to 0.8 kg sec-1. Experiments have been conducted by varying the mass flow rate, temperature and pressure of cold fluid, keeping the mass flow rate of hot fluid constant. The effects of relevant parameters on spiral plate heat exchanger are investigated. The data obtained from the experimental study are compared with the theoretical data. Besides, a new correlation for the nusselt number that can be used for practical applications is proposed.

Kaliannan Saravanan

2009-02-01

256

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

257

Parameterization of a surface drag coefficient in conventionally neutral planetary boundary layer

Directory of Open Access Journals (Sweden)

Full Text Available Modern large-scale models (LSMs rely on surface drag coefficients to parameterize turbulent exchange between surface and the first computational level in the atmosphere. A classical parameterization in an Ekman boundary layer is rather simple. It is based on a robust concept of a layer of constant fluxes. In such a layer (log-layer, the mean velocity profile is logarithmic. It results in an universal dependence of the surface drag coefficient on a single internal non-dimensional parameter, namely the ratio of a height within this layer to a surface roughness length scale. A realistic near-neutral planetary boundary layer (PBL is usually much more shallow than the idealized Ekman layer. The reason is that the PBL is developing against a stably stratified free atmosphere. The ambient atmospheric stratification reduces the PBL depth and simultaneously the depth of the log-layer. Therefore, the first computational level in the LSMs may be placed above the log-layer. In such a case, the classical parameterization is unjustified and inaccurate.

The paper proposes several ways to improve the classical parameterization of the surface drag coefficient for momentum. The discussion is focused on a conventionally neutral PBL, i.e. on the neutrally stratified PBL under the stably stratified free atmosphere. The analysis is based on large eddy simulation (LES data. This data reveals that discrepancy between drag coefficients predicted by the classical parameterization and the actual drag coefficients can be very large in the shallow PBL. The improved parameterizations provide a more accurate prediction. The inaccuracy is reduced to one-tenth of the actual values of the coefficients.

I. N. Esau

2004-11-01

258

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

259

International Nuclear Information System (INIS)

The loss of cooling accident (LOCA) in a nuclear reactor is a case where the heat transfer by forced convection is of the same order of magnitude as the heat transfer by natural convection. Two simple theoretical solutions for evaluating the heat transfer coefficient are presented, assuming a combined velocity and temperature profile of natural and forced convection, within the boundary layer. The following mathematical form is proposed: Y= [1+Xsup(n)]sup(1/n) which is a general expression for a combined effect of wo limiting solutions. (author)

260

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

261

This paper describes heat and mass transfer characteristics of organic sorbent coated on heat transfer surface of a fin-tube heat exchanger. The experiments in which the moist air was passed into the heat exchanger coated with sorption material were conducted under various conditions of air flow rate (0.5 1.0 m/s) and the temperature of brine (14 20°C) that was the heat transfer fluid to cool the air flow in the dehumidifying process. It is found that the sorption rate of vapor is affected by the air flow rate and the brine temperature. Meanwhile, the attempt of clarifying the sorption mechanism is also conducted. Finally the average mass transfer coefficient of the organic sorbent coated on heat transfer surface of a fin-tube heat exchanger is non-dimensionalzed as a function of Reynolds number and non-dimensional temperature, and it is found that the effect of non-dimensional temperature on them is larger than Reynolds number .

Inaba, Hideo; Komatsu, Fujio; Horibe, Akihiko; Haruki, Naoto; Machida, Akito

2008-09-01

262

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

263

Absolute measurement of activity implies a determination of effective depths and effective attenuation coefficients. In order to define restoration filters, it is necessary to measure the transfer function, i.e. position a line source at an effective depth for the specific measurement situation. A phantom was designed which can simulate an organ with a certain thickness at a certain depth. The phantom was used to measure transfer functions and a comparison was made with transfer functions from a line source to determine effective depths. Effective attenuation coefficients were calculated for 99mTc, 111In and 201Tl for different organ thicknesses and depths of simulated organs. The effective attenuation coefficient for 99mTc was found to be 0.124 +/- 0.006 cm-1, in good agreement with previously published values. For 111In, the attenuation coefficient decreased with the depth of an organ due to the use of two energy windows in the measurements and a corresponding change in mean photon energy by depth. For 201Tl, the attenuation coefficient decreased with increasing organ thickness due to the increasing fraction of scattered radiation in the 40% energy window used. Using attenuation coefficients of 0.124, 0.184 and 0.11 cm-1 for 99mTc, 201Tl and 111In respectively, the derived equations can be used to calculate the position of a conventional line source for measurements of transfer functions for a specific organ with a certain thickness at a certain depth for definition of different types of restoration filter. PMID:9364591

Starck, S A; Carlsson, S

1997-10-01

264

International Nuclear Information System (INIS)

Absolute measurement of activity implies a determination of effective depths and effective attenuation coefficients. In order to define restoration filters, it is necessary to measure the transfer function, i.e. position a line source at an effective depth for the specific measurement situation. A phantom was designed which can simulate an organ with a certain thickness at a certain depth. The phantom was used to measure transfer functions and a comparison was made with transfer functions from a line source to determine effective depths. Effective attenuation coefficients were calculated for 99mTc, 111In and 201Tl for different organ thicknesses and depths of simulated organs. The effective attenuation coefficient for 99mTc was found to be 0.124±0.006 cm-1, in good agreement with previously published values. For 111In, the attenuation coefficient decreased with the depth of an organ due to the use of two energy windows in the measurements and a corresponding change in mean photon energy by depth. For 201Tl, the attenuation coefficient decreased with increasing organ thickness due to the increasing fraction of scattered radiation in the 40% energy window used. Using attenuation coefficients of 0.124, 0.184 and 0.11 cm-1 for 99mTc, 201Tl and 111In respectively, the derived equations can be used to calculate the position of a conventional line source for measurements of transfer functions for a specific organ with a certain thickness at a certain depth for definition of different types of restoration filter. (author)

265

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

266

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)

267

International Nuclear Information System (INIS)

For a steam generator with straight double-walled heat transfer tubes that will be used in sodium cooled faster breeder reactor, clarification of flow instability in heat transfer tubes is one of the most important research themes. As the first step of the research, thermal hydraulics experiments with water were performed under high pressure condition in JAEA with using a circular tube. Pressure drop, heat transfer coefficients and void fraction data were derived. This paper summarizes the heat transfer characteristics under 15-18 MPa. Saturated boiling heat transfer was discussed with four most famous general heat transfer correlations (Chen, Shah, Steiner-Taborek and Gungor-Winterton) being verified. Under present high pressure condition, it was found that the Shah correlation gave good agreement with data at low mass flow rate and the Chen correlation gave good agreement at high mass flow rate condition. For the nominate flow rate of w=110 g/s, both Chen and Shah correlations can be used. As a result, under present high pressure condition, we recommend that the smaller one of the Chen and Shah correlations be used for the calculation of heat transfer coefficient. (author)

268

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.)

269

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

270

Graphite dust deposition of heat transfer surfaces in the H TGR type reactors

International Nuclear Information System (INIS)

Results of investigation into the intensity of formation of fine-dispersed graphite dust deposits on pipe surfaces and their effect on thermal efficiency of a modular bundle of tubes are presented. Variations in deposit distributions ad local heat-transfer coefficients over tube perimeter in the range of Reynolds numbers of (1-12)x103 at pressure of 0.3-1.2 MPa are shown

271

A series of cold flow heat transfer tests was conducted with a 7.5-percent scale model of the Space Shuttle Rocket Motor (SRM) to measure the heat transfer coefficients in the separated flow region around the nose of the submerged nozzle. Modifications were made to an existing 7.5 percent scale model of the internal geometry of the aft end of the SRM, including the gimballed nozzle in order to accomplish the measurements. The model nozzle nose was fitted with a stainless steel shell with numerous thermocouples welded to the backside of the thin wall. A transient 'thin skin' experimental technique was used to measure the local heat transfer coefficients. The effects of Reynolds number, nozzle gimbal angle, and model location were correlated with a Stanton number versus Reynolds number correlation which may be used to determine the convective heating rates for the full scale Space Shuttle Solid Rocket Motor nozzle.

Whitesides, R. Harold; Majumdar, Alok K.; Jenkins, Susan L.; Bacchus, David L.

1990-01-01

272

Directory of Open Access Journals (Sweden)

Full Text Available The paper presents the FEM method for determination of boiling heat transfer coefficient in cooling liquid flow in a rectangular minichannel with asymmetric heating. Experimental research has focused on the transition from single phase forced convection to nucleate boiling, i.e. the zone of boiling incipience. The “boiling front” location has been determined from the temperature distribution of the heated wall obtained from liquid crystal thermography. The main part of the test section has been a minichannel of pre-set depth from 0.7 to 2.0 mm, of different spatial orientations. Local values of heat transfer coefficient have been determined following the solution of the two-dimensional inverse heat transfer problem. This problem has been solved with the use of Trefftz functions. Trefftz functions have been used to construct base functions in the finite element method (FEMT.

Maciejewska Beata

2012-04-01

273

Cooling performance is a significant issue for air-cooled motorcycle engines, because its performance depends on the vehicle motion. Commonly, a heat transfer coefficient is calculated by heat flux and temperature difference, which are solved by energy equation under conjugated condition between a solid and a fluid. However, this method is complicated. Therefore, Karman's analogy based on a relation between the fluid friction and the heat transportation was used to obtain a heat transfer coefficient without solving an energy equation. Partial Cells in Cartesian coordinate method was employed as a CFD (Computational Fluid Dynamics) method for an efficient calculation around complex obstacles. Characteristics of heat transfer in a straight pipe were confirmed by a comparison with the Colburn's empirical formula. The results showed good agreement within ±10% differences under Pr=0.7 and 104CFD was proposed.

Takahashi, Yasushi; Gokan, Yoshitsugu; Inayoshi, Makoto; Ishima, Tsuneaki; Obokata, Tomio

274

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

275

Coefficient of friction between carbon steel and perlite concrete surfaces. Test report

International Nuclear Information System (INIS)

The results of coefficient of friction, ?, tests conducted on perlite blocks and carbon steel plates under various conditions are discussed. Variables included in the test entailed the use of lubricants (i.e. water and simulated radioactive waste solution) abrasives (120 grit, 60 grit, 40 grit sand paper) applied to the surfaces of the perlite block and carbon steel plates

276

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

277

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)

278

Energy Technology Data Exchange (ETDEWEB)

Measurements of heat transfer coefficient (h) are presented for rows of round holes at streamwise angles of 30{sup o}, 60{sup o} and 90{sup o} with a short but engine representative hole length (L/D=4). The study began with a single row of holes with pitch-to-diameter ratios of 3 and 6, followed by two inline and staggered rows for each hole spacing and streamwise inclination, which amount to 105 different test cases in addition to the 21 test cases presented on the single hole [C.H.N. Yuen, R.F. Martinez-Botas, Film cooling characteristics of a single round hole at various angles in a crossflow: Part I. Effectiveness, Int. J. Heat Mass Transfer, in press; C.H.N. Yuen, R.F. Martinez-Botas, Film cooling characteristics of a single round hole at various angles in a crossflow: Part II. Heat transfer coefficients, Int. J. Heat Mass Transfer, in press]. The present investigation is a continuation of the previous work [Yuen and Martinez-Botas, Parts I and II, in press] with the same test facility, operating conditions (freestream Reynolds number, Re{sub D} of 8563, and blowing ratio, 0.33=

Yuen, C.H.N.; Martinez-Botas, R.F. [Department of Mechanical Engineering, Imperial College of Science, Technology and Medicine, London (United Kingdom)

2005-11-01

279

International Nuclear Information System (INIS)

Full text of publication follows: Models or correlations for phase interface are needed to analyze the multi-phase flow. Interfacial heat transfer coefficients are important to constitute energy equation of multi-phase flow, specially. In subcooled boiling flow, bubble condensation at the bubble-liquid interface is a major mechanism of heat transfer within bulk subcooled liquid. Bubble collapse rates and temperatures of each phase are needed to determine the interfacial heat transfer coefficient for bubble condensation. Bubble collapse rates were calculated through image processing in single direction, generally. And in case of liquid bulk temperature, which has been obtained by general temperature sensor such as thermocouple, was used. However, multi-directional images are needed to analyze images due to limitations of single directional image processing. Also, temperature sensor, which has a fast response time, must be used to obtain more accurate interfacial heat transfer coefficient. Low pressure subcooled water flow experiments using micro-thermocouple and double directional image processing with mirrors were conducted to investigate bubble condensation phenomena and to modify interfacial heat transfer correlation. Experiments were performed in a vertical subcooled boiling flow of a rectangular channel. Bubble condensing traces with respect to time were recorded by high speed camera in double direction and bubble collapse rates were calculated by processing recor rates were calculated by processing recorded digital images. Temperatures were measured by micro-thermocouple, which is a K-type with a 12.7 ?m diameter. The liquid temperature was estimated by the developed algorithm to discriminate phases and find each phase temperature in the measured temperature including both liquid and bubble temperature. The interfacial heat transfer coefficient for bubble condensation was calculated from the bubble collapse rates and the estimated liquid temperature, and its correlation was modified. The modified correlation has been compared with other correlations. (authors)

280

Simultaneous velocity-surface heat transfer behavior of turbulent spots

Energy Technology Data Exchange (ETDEWEB)

The properties of artificially initiated turbulent spots in a heated laminar boundary layer were investigated in a water channel facility. The instantaneous velocity field and surface heat transfer were determined simultaneously over a temporal sequence using a technique that combines traditional particle image velocimetry and thermochromic liquid crystal temperature measurements. The correlated results indicate that the highest surface heat transfer occurs in the trailing region of the spot where only the near-wall fluid is energetic. The results suggest that the ''body'' of the spot entrains, and subsequently recirculates, warm surface fluid within the spot, which reduces the effective heat transfer. (orig.)

Sabatino, D. [United Technologies Research Center, East Hartford, CT (United States); Smith, C.R. [Department of Mechanical Engineering and Mechanics, Lehigh University, Bethlehem, PA 18015 (United States)

2002-07-01

281

Blowdown heat transfer surface in RELAP4/MOD6

International Nuclear Information System (INIS)

New heat transfer correlations for both PWR and BWR blowdowns have been implemented in the RELAP4/MOD6 program. The concept of a multidimensional surface is introduced with the heat flux from a given heat transfer correlation or correlations depicted as a mathematical surface that is dependent upon quality, wall superheat, mass flow and pressure. The heat transfer logic has been modularized to facilitate replacing boiling curves for future correlation data comparisons and investigations. To determine the validity of the blowdown surface, comparison has been performed using data from the Semiscale experimental facility. (author)

282

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

283

Effect of Hydrotropes on Solubility and Mass Transfer Coefficient of Methyl Benzoate

Directory of Open Access Journals (Sweden)

Full Text Available Normal 0 7.8 ? 0 2 false false false EN-US ZH-CN X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:????; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman","serif";} A comprehensive investigation on the solubility and mass transfer coefficient enhancement of methyl benzoate through hydrotropy has been undertaken. The solubility and mass transfer coefficient studies were carried out using hydrotropes such as citric acid, urea and nicotinamide under a wide range of hydrotrope concentrations (0 to 3.0 mol/L and different system temperatures (303 to 333 K. The effectiveness of hydrotropes was measured in terms of Setschnew constant Ks and reported for all hydrotropes used in this study.

Senthil Nathan

2009-02-01

284

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)

285

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

286

Two systems have been developed to study boiling heat transfer on the microscale. The first system utilizes a 32 x 32 array of diodes to measure the local temperature fluctuations during boiling on a silicon wafer heated from below. The second system utilizes an array of 96 microscale heaters each maintained at constant surface temperature using electronic feedback loops. The power required to keep each heater at constant temperature is measured, enabling the local heat transfer coefficient to be determined. Both of these systems as well as some preliminary results are discussed.

Kim, J.; Bae, S. W.; Whitten, M. W.; Mullen, J. D.; Quine, R. W.; Kalkur, T. S.

1999-01-01

287

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

288

MASS TRANSFER COEFFICIENTS FOR A NON-NEWTONIAN FLUID AND WATER WITH AND WITHOUT ANTI-FOAM AGENTS

International Nuclear Information System (INIS)

Mass transfer rates were measured in a large scale system, which consisted of an 8.4 meter tall by 0.76 meter diameter column containing one of three fluids: water with an anti-foam agent, water without an anti-foam agent, and AZ101 simulant, which simulated a non-Newtonian nuclear waste. The testing contributed to the evaluation of large scale mass transfer of hydrogen in nuclear waste tanks. Due to its radioactivity, the waste was chemically simulated, and due to flammability concerns oxygen was used in lieu of hydrogen. Different liquids were used to better understand the mass transfer processes, where each of the fluids was saturated with oxygen, and the oxygen was then removed from solution as air bubbled up, or sparged, through the solution from the bottom of the column. Air sparging was supplied by a single tube which was co-axial to the column, the decrease in oxygen concentration was recorded, and oxygen measurements were then used to determine the mass transfer coefficients to describe the rate of oxygen transfer from solution. Superficial, average, sparging velocities of 2, 5, and 10 mm/second were applied to each of the liquids at three different column fill levels, and mass transfer coefficient test results are presented here for combinations of superficial velocities and fluid levels

289

Energy Technology Data Exchange (ETDEWEB)

In this paper, high performance packing, namely structured packing that has good heat and mass transfer characteristics, is proposed for dehumidification of air using liquid desiccants and for regeneration of liquid desiccants. In order to design a structured packing tower for liquid desiccant -- air contacting operations, heat and mass transfer coefficients for each phase are required. This paper is concerned with the interface of heat and mass when air is brought into contact with the liquid desiccant solution. A theoretical study of evaluating heat and mass coefficients in an air-desiccant contact system employing three liquid desiccants, namely calcium chloride, lithium chloride, and a mixture of 50% calcium chloride and 50% lithium chloride (called cost effective liquid desiccant, CELD) is investigated. Moreover, air phase transfer coefficients are correlated with flow rates of air and liquid and the temperature of air, whereas liquid phase coefficients are correlated with rate of air and liquid flow, and the temperature and concentration of the liquid. The findings for the three liquid desiccants are compared and discussed. (Author)

Al-Farayedhi, Abdulghani A.; Gandhidasan, P.; Al-Mutairi, M.A. [King Fahd Univ. of Petroleum and Minerals, Mechanical Engineering Dept., Dhahran (Saudi Arabia)

2002-05-01

290

The effects of external parameters on the surface heat and vapor fluxes into the marine atmospheric boundary layer (MABL) during cold-air outbreaks are investigated using the numerical model of Stage and Businger (1981a). These fluxes are nondimensionalized using the horizontal heat (g1) and vapor (g2) transfer coefficient method first suggested by Chou and Atlas (1982) and further formulated by Stage (1983a). In order to simplify the problem, the boundary layer is assumed to be well mixed and horizontally homogeneous, and to have linear shoreline soundings of equivalent potential temperature and mixing ratio. Modifications of initial surface flux estimates, time step limitation, and termination conditions are made to the MABL model to obtain accurate computations. The dependence of g1 and g2 in the cloud topped boundary layer on the external parameters (wind speed, divergence, sea surface temperature, radiative sky temperature, cloud top radiation cooling, and initial shoreline soundings of temperature, and mixing ratio) is studied by a sensitivity analysis, which shows that the uncertainties of horizontal transfer coefficients caused by changes in the parameters are reasonably small.

Chang, Y. V.

1986-01-01

291

Temperature dependence of volume and surface symmetry energy coefficients of nuclei

Energy Technology Data Exchange (ETDEWEB)

The thermal evolution of the energies and free energies of a set of spherical and near-spherical nuclei spanning the whole periodic table are calculated in the subtracted finite-temperature Thomas-Fermi framework with the zero-range Skyrme-type KDE0 and the finite-range modified Seyler-Blanchard interaction. The calculated energies are subjected to a global fit in the spirit of the liquid-drop model. The extracted parameters in this model reflect the temperature dependence of the volume symmetry and surface symmetry coefficients of finite nuclei, in addition to that of the volume and surface energy coefficients. The temperature dependence of the surface symmetry energy is found to be very substantial whereas that of the volume symmetry energy turns out to be comparatively mild.

De, J.N., E-mail: jn.de@saha.ac.in [Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064 (India); Samaddar, S.K., E-mail: santosh.samaddar@saha.ac.in [Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064 (India); Agrawal, B.K., E-mail: bijay.agrawal@saha.ac.in [Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064 (India)

2012-09-19

292

Unsteady convection flow and heat transfer over a vertical stretching surface.

This paper investigates the effect of thermal radiation on unsteady convection flow and heat transfer over a vertical permeable stretching surface in porous medium, where the effects of temperature dependent viscosity and thermal conductivity are also considered. By using a similarity transformation, the governing time-dependent boundary layer equations for momentum and thermal energy are first transformed into coupled, non-linear ordinary differential equations with variable coefficients. Numerical solutions to these equations subject to appropriate boundary conditions are obtained by the numerical shooting technique with fourth-fifth order Runge-Kutta scheme. Numerical results show that as viscosity variation parameter increases both the absolute value of the surface friction coefficient and the absolute value of the surface temperature gradient increase whereas the temperature decreases slightly. With the increase of viscosity variation parameter, the velocity decreases near the sheet surface but increases far away from the surface of the sheet in the boundary layer. The increase in permeability parameter leads to the decrease in both the temperature and the absolute value of the surface friction coefficient, and the increase in both the velocity and the absolute value of the surface temperature gradient. PMID:25264737

Cai, Wenli; Su, Ning; Liu, Xiangdong

2014-01-01

293

Unsteady Convection Flow and Heat Transfer over a Vertical Stretching Surface

This paper investigates the effect of thermal radiation on unsteady convection flow and heat transfer over a vertical permeable stretching surface in porous medium, where the effects of temperature dependent viscosity and thermal conductivity are also considered. By using a similarity transformation, the governing time-dependent boundary layer equations for momentum and thermal energy are first transformed into coupled, non-linear ordinary differential equations with variable coefficients. Numerical solutions to these equations subject to appropriate boundary conditions are obtained by the numerical shooting technique with fourth-fifth order Runge-Kutta scheme. Numerical results show that as viscosity variation parameter increases both the absolute value of the surface friction coefficient and the absolute value of the surface temperature gradient increase whereas the temperature decreases slightly. With the increase of viscosity variation parameter, the velocity decreases near the sheet surface but increases far away from the surface of the sheet in the boundary layer. The increase in permeability parameter leads to the decrease in both the temperature and the absolute value of the surface friction coefficient, and the increase in both the velocity and the absolute value of the surface temperature gradient. PMID:25264737

Cai, Wenli; Su, Ning; Liu, Xiangdong

2014-01-01

294

Energy Technology Data Exchange (ETDEWEB)

Floor cooling systems can be designed in the same manner as floor heating systems, except for the different heat transfer coefficient between floor surface and room which is due to the fact that convective heat transfer is lower from a cooled floor than from a heated floor. The heat transfer coefficient and its changes with the reference room temperature must be known both for the design of floor cooling systems and for computer simulation programs. The authors investigated the heat transfer coefficients of floor cooling systems and the effects of the reference room temperature. [German] Fussbodenheizung ist heute weit verbreitet; vor kurzem wurde eine diesbezuegliche internationale Norm, EN1264, fuer Konstruktion und Auslegung veroeffentlicht. Fussbodensysteme werden heute auch zum Kuehlen benutzt (Boerresen, B. (1994), Simmonds, P. (1994), Olesen (1997), Michel, E. (1994)). Fuer Fussbodenkuehlung koennen im wesentlichen die gleichen Konstruktions- und Auslegungsmethoden wie fuer Fussbodenheizung eingesetzt werden mit der Ausnahme, dass der Waermeuebergangskoeffizient zwischen Fussbodenoberflaeche und Raum unterschiedlich ist. Das liegt an der Tatsache, dass die Konvektionswaermeuebergang von einem gekuehlten Fussboden (dessen Oberflaechtemperatur niedriger ist als die Raumtemperatur) erheblich niedriger ist als von einem beheizten Fussboden. Sowohl fuer die Auslegung von Fussbodenkuehlsystemen als auch fuer Computersimulationsprogramme ist es erforderlich, den Waermeuebergangskoeffizienten zu kennen und zu wissen, wie dieser Koeffizient durch die Raumreferenztemperatur beeinflusst wird. Zweck der vorliegenden Abhandlung ist die Untersuchung des Waermeuebergangskoeffizienten fuer Fussbodenkuehlung sowie die Auswirkungen unterschiedlicher Raum-Referenztemperaturen bei der Berechnung des Waermeuebergangs zwischen Fussobdenoberflaeche und Raum. Der Waermeuebergang wird manchmal als Gesamtwaermeuebergang berechnet, d.h. als kombinierter Konvektions- und Strahlungswaermeuebergang; manchmal wird er getrennt nach Strahlung und Konvektion berechnet. Diese Abhandlung ist eine theoretische Eroerterung des Waermeuebergangskoeffizienten. Der Uebergangskoeffizient wird auf der Grundlage von Versuchen aus Messwerten der Oberflaechen- und Lufttemperaturen sowie Messwerten der Waermestromdichte zwischen einem gekuehlten Fussboden und einem Versuchsraum berechnet. Diese Berechnungen werden fuer unterschiedliche Raum-Referenztemperaturen durchgefuehrt, und es werden Berechnungsverfahren empfohlen. (orig.)

Olesen, B.W. [D.F. Liedelt ' ' Velta' ' GmbH, Norderstedt (Germany); Michel, E.; Bonnefoi, F. [Comite Scientifique et Technique des Industries Climatiques (COSTIC), 04 - Digne (France); De Carli, M. [Padua Univ. (Italy). Ist. di Fisica Tecnica

2000-07-01

295

International Nuclear Information System (INIS)

The mass energy absorption, the mass energy transfer and mass absorption coefficients have been widely used for problems and applications involving dose calculations. Direct measurements of the coefficients are difficult, and theoretical computations are usually employed. In this paper, analytical equations are presented for determining the mass energy transfer and mass absorption coefficients for gamma rays with an incident energy range between 0.4 and 10 MeV in nitrogen, silicon, carbon, copper and sodium iodide. The mass absorption and mass energy transfer coefficients for gamma rays were calculated, and the results obtained were compared with the values reported in the literature

296

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

297

Improvement of dropwise condensation heat transfer using hydrophobic nano porous surfaces

International Nuclear Information System (INIS)

Recently interest of passive system in thermal hydraulic safety system of nuclear power plants has been increased. Passive residual heat removal system (PRHRS) is applied to SMART and APR+ for providing the sufficient cooling capacity against accident conditions. PRHRS is a device for removing the decay heat that cools steam through condensation heat transfer in emergency tank. Condensation is one of most important heat transfer methods in almost industry including the PRHRS. Condensation is classified, according to shape of condensate, into drop-wise condensation and film wise condensation. Drop-wise condensation (DWC) exhibits a significantly higher heat transfer coefficient than film wise condensation (FWC). Whether DWC or FWC occurs in a heat transfer surface is strongly affected by wettability of a surface. It is known that DWC is appears on low wettability surfaces while FWC is appears on high wettability one. In this study, nano-porous hydrophobic surfaces were prepared and tested for the improvement of dropwise condensation heat transfer performance

298

Energy Technology Data Exchange (ETDEWEB)

This paper presents experimental heat transfer results that been obtained during the evaporation of R404A in a horizontal tube. These results have been compared with existing correlations characterising the evaporative heat transfer coefficient to assess the suitability of these models with mixtures. The Gungor and Shah correlation predicted the results well over a 0.2 to O.8 vapour quality range, but did not accurately predict the dry-out at high vapour quality. This process is the basis for a correlation development. (authors)

Boissieux, X.; Johns, R.A.; Heikal, M.R. [Heat Transfer Research Unit, Universtiy of Brighton, School of Engineering, Brighton (United Kingdom)

1999-07-01

299

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

Dieng, M.; Diagne, I.; Fleur, B.; Kane, A.; Sow, M. L.; Sissoko, G.

2013-01-01

300

Pool boiling heat transfer on artificial micro-cavity surfaces in dielectric fluid FC-72

The boiling performance and flow mechanism on artificial micro-cavity surfaces with different geometric parameters are presented in the present study. The test surfaces are manufactured on a 625 µm thick, 10 mm × 10 mm square silicon plate. The treated cavities are all cylinders with three diameters (200, 100 and 50 µm) and two depths (200 and 110 µm). The densities of the cavities were designed to be 33 × 33, 25 × 25 and 16 × 16 arrays with 100, 200 and 400 µm spacings, respectively. The characteristics of heat transfer for pool boiling of FC-72 on artificial micro-cavity surfaces were also examined. In this paper, visualization of the flow patterns was conducted to investigate the characteristics of the bubbles in the growth and departure process. The results indicated that boiling incipience and temperature excursion of silicon-based surfaces are more significant than those of metal-based surfaces reported in the literature. The effects of cavity density are stronger in the high heat flux region than in the low heat flux region because of the bubble/vapor coalescence near the heating surface. The heat transfer coefficient increases with heat flux and cavity density but a denser cavity will suppress the value of critical heat flux (CHF). Besides, in moderate and high heat flux regions, a larger cavity diameter surface shows earlier decay and a lower peak value of the heat transfer coefficient. The maximum value of CHF on the base area was 3 × 105 W m-2 (30 W m-2) for the test surface with a 33 × 33 cavity array, which is almost 2.5 times that of the plain silicon surface.

Yu, Chih Kuang; Lu, Ding Chong; Cheng, Tsung Chieh

2006-10-01

301

The coefficient of friction between boron carbide (B4C) surfaces in air and ultrahigh vacuum (UHV)

International Nuclear Information System (INIS)

Friction measurements between two contacting B4C surfaces in air and UHV at room temperature using 0.10-0.13N loads are reported. A pin (radius = 0.005m) on flat device allowing for interchange in UHV is used. The tribological surfaces can be examined using scanning Auger and XPS in the same UHV system. The coefficient of friction for air exposed surfaces is found to vary between air (0.20-0.25) and UHV (1.2-1.8). Stick-slip behavior, indicating strong adhesion, is observed in UHV while only a smooth friction value is measured in air. Air pressures 100Pa are necessary to reduce the friction from the high value in UHV. The friction between the clean surfaces in UHV initially is 0.8-1.3, but following mechanical conditioning at a higher velocity the friction drops to 0.17-0.25. In situ mechanical conditioning is necessary to obtain reproducible friction values for the clean surface. Exposing the clean surfaces to oxygen (10- 3Pa) while conditioning results in an increase in friction (1.0-1.2). Auger line scans through the scar made using the clean surfaces show enhanced B and reduced C. Similar Auger scans for oxygen exposed surfaces indicate that tearing of the oxide layer may be the reason for the high friction. The friction for a clean pin and an in situ nitrogen-implanted flat (10keV, saturation dose) is 0.70-0.80. Film transfer to the pin is observed

302

Energy Technology Data Exchange (ETDEWEB)

A heat transfer (condenser) of a domestic freezer was tested in a vertical channel in order to study the influence of the chimney effect in the optimization of the heat transfer coefficient. The variation of the opening of the channel, position and the heating power of the heat exchanger in the heat transfer coefficient was considered. The influence of the surface emissivity on the heat transfer by thermal radiation was studied with the heat exchanger testes without paint and with black paint. The air velocity entering the channel was measured with a hot wire anemometer. In order to evaluate the chimney effect, the heat exchanger was testes in a open ambient. This situation simulates its operational conditions when installed on the freezer system. The variables collected in the experimental procedures was gathered in the form of dimensionless parameters as Nusselt, Rayleigh, Grashof and Prandtl numbers, and dimensional parameters of the convection. The results showed that the highest heat transfer value occurred when both a specific position and a specific channel opening were used. The experiments pointed out that the radiation contribution must be considered in heat transfer calculations. The conclusions showed that different channel openings can improve the heat transfer coefficient in this heat transfer exchanger. (author)

Rocha, Alan Carlos Bueno da

1997-07-01

303

International Nuclear Information System (INIS)

In the present study, the effect of delta-wing vortex generators(DWVG) on the local heat transfer of the plate fin-oval tube was experimentally analyzed for Reynolds numbers for 2000, 2500 and 3200. The local heat transfer coefficient of the fin surface for four type DWVGs was measured by the naphthalene sublimation technique. As the results, the distribution of the heat transfer coefficient at rear of DWVGs showed longitudinal contours for common flow down DWVGs and wavy contours for common flow up DWVGs. The distribution showed many cell type contours at near wall and downstream for all DWVGs. Compared to case without DWVGs in present experimental tests, all DWVGs showed the best enhancement of heat transfer at Re=2000. Of 4 cases of DWVGs, D type showed the best enhancement of heat transfer

304

Energy Technology Data Exchange (ETDEWEB)

This paper presents experimental heat transfer results obtained during the evaporation of Isceon 59, R407C and R404A in a horizontal tube. The results have been compared with existing correlations which characterise the evaporative heat transfer coefficient to assess the validity of these models for refrigerant mixtures. The results compared well with the (Gungor K.E., Winterton, R.H.S. Simplified general correlation for saturated flow boiling and comparisons of correlations with data. The Canadian Journal of Chemical Engineering, Chemical Engineering Research and Design 1987;65(2):148-156 and Shah M.M. Chart correlation for saturated boiling heat transfer: equations and further study. ASHRAE Transactions 1982;88(1):185-196) correlations over a 0.2 to 0.8 vapour quality range. These correlations, however, did not accurately predict the results obtained during the dry-out at high vapour quality. A model, developed by (Kattan N., Thome J.R., Favrat D., 1998. Flow boiling in horizontal tubes: part 1 - development of a diabatic two-phase flow pattern map. Journal of Heat Transfer, Transactions of ASME, Vol. 120, pp. 140-147; Kattan N., Thome J.R., Favrat D., 1998. Flow boiling in horizontal tubes: part 2 - new heat transfer data for five refrigerants. Journal of Heat Transfer, Transactions of ASME, Vol. 120, pp. 148-155; Kattan N., Thome JR., Favrat D., 1998. Flow boiling in horizontal tubes: part 3 - development of a new heat transfer model based on flow pattern. Journal of Heat Transfer, Transactions of ASME, Vol. 120, pp. 156-165), was found to express the local variations in heat transfer during the whole evaporation process. This model was modified to fit the three new refrigerants. The modified Kattan model offers a good prediction of the heat transfer results, with a standard deviation of 6.1%. (author)

Boissieux, X.; Heikal, M.R.; Johns, R.A. [University of Brighton (United Kingdom). Engineering Research Centre

2000-06-01

305

Sustained frictional instabilities on nanodomed surfaces: stick-slip amplitude coefficient.

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. PMID:24219790

Quignon, Benoit; Pilkington, Georgia A; Thormann, Esben; Claesson, Per M; Ashfold, Michael N R; Mattia, Davide; Leese, Hannah; Davis, Sean A; Briscoe, Wuge H

2013-12-23

306

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.

307

International Nuclear Information System (INIS)

A new measurement method for measuring the mean fuel temperature as well as the fuel-to-coolant heat transfer coefficient of fast breeder reactor subassemblies (SA) is reported. The method is based on the individual heat balance of fuel SA's after fast reactor shut-downs and uses only the plants normal SA outlet temperature and neutron power signals. The method was used successfully at the french breeder prototype Super Phenix 1. The mean SA fuel temperature as well as the heat transfer coefficient of all SPX SA's have been determined at power levels between 15 and 90% of nominal power and increasing fuel burn-up from 3 to 83 EFPD (Equivalent of Full Power-Days). The measurements also provided fuel and whole SA time constants. The estimated accuracy of measured fuel parameters is in the order of 10%. Fuel temperatures and SA outlet temperature transients were also calculated with the SPX1 systems code DYN2 for exactly the same fuel and reactor operating parameters as in the experiments. Measured fuel temperatures were higher than calculated ones in all cases. The difference between measured and calculated core mean values increases from 50 K at low power to 180 K at 90% n.p. This is about the double of the experimental error margins. Measured SA heat transfer coefficients are by nearly 20% lower than corresponding heat transfer parameters used in the calculations. Discrepancies found between measured and calculated results also indicate that either the transient heat transfer in the gap between fuel and cladding (gap conductance) might not be exactly reproduced in the computer code or that the gap in the fresh fuel was larger than assumed in the calculations. (orig.)

308

Directory of Open Access Journals (Sweden)

Full Text Available In order to increase the active surface of platinum catalysts for ammonia oxidation and on the basis of theoretic considerations and tests in industrial environment, we have finally decided on their specific design. Efficiency on the newly designed catalyst was checked in industrial circumstances. A comparative analysis of the total ammonia recovery coefficient between the mentioned new catalysts and previously applied platinum catalysts was carried out. All advantages of catalysts with increased active surfaces were confirmed and a new method of their manufacturing process was selected.

Trumi? B.

2009-01-01

309

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

310

Heat transfer between a nano-tip and a surface

Energy Technology Data Exchange (ETDEWEB)

We study quasi-ballistic heat transfer through air between a hot nanometre-scale tip and a sample. The hot tip/surface configuration is widely used to perform non-intrusive confined heating. Using a Monte Carlo simulation, we find that the thermal conductance reaches 0.8 MW m{sup -2} K{sup -1} on the surface under the tip and show the shape of the heat flux density distribution (nanometre-scale thermal spot). These results show that a surface can be efficiently heated locally without contact. The temporal resolution of the heat transfer is a few tens of picoseconds.

Chapuis, Pierre-Olivier [Laboratoire d' Energetique Moleculaire et Macroscopique, Combustion, CNRS UPR 288, Ecole Centrale Paris, Grande Voie des Vignes, F-92295 Chatenay-Malabry cedex (France); Greffet, Jean-Jacques [Laboratoire d' Energetique Moleculaire et Macroscopique, Combustion, CNRS UPR 288, Ecole Centrale Paris, Grande Voie des Vignes, F-92295 Chatenay-Malabry cedex (France); Joulain, Karl [Laboratoire d' Etudes Thermiques, CNRS UMR 6608 and ENSMA, BP 40109, Futuroscope, F-86961 Chasseneuil cedex (France); Volz, Sebastian [Laboratoire d' Energetique Moleculaire et Macroscopique, Combustion, CNRS UPR 288, Ecole Centrale Paris, Grande Voie des Vignes, F-92295 Chatenay-Malabry cedex (France)

2006-06-28

311

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

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

312

Study of energy transfer in helium atom scattering from surfaces

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

313

Surface diffusion coefficient of Au atoms on single layer graphene grown on Cu

Energy Technology Data Exchange (ETDEWEB)

A 5?nm thick Au film was deposited on single layer graphene sheets grown on Cu. By thermal processes, the dewetting phenomenon of the Au film on the graphene was induced so to form Au nanoparticles. The mean radius, surface-to-surface distance, and surface density evolution of the nanoparticles on the graphene sheets as a function of the annealing temperature were quantified by scanning electron microscopy analyses. These quantitative data were analyzed within the classical mean-field nucleation theory so to obtain the temperature-dependent Au atoms surface diffusion coefficient on graphene: D{sub S}(T)=[(8.2±0.6)×10{sup ?8}]exp[?(0.31±0.02(eV)/(at) )/kT]?cm{sup 2}/s.

Ruffino, F., E-mail: francesco.ruffino@ct.infn.it; Cacciato, G.; Grimaldi, M. G. [Dipartimento di Fisica ed Astronomia-Universitá di Catania, via S. Sofia 64, 95123 Catania, Italy and MATIS IMM-CNR, via S. Sofia 64, 95123 Catania (Italy)

2014-02-28

314

The maximum coefficient of friction that can be supported at the shoe and floor interface without a slip is usually called the available coefficient of friction (ACOF) for human locomotion. The probability of a slip could be estimated using a statistical model by comparing the ACOF with the required coefficient of friction (RCOF), assuming that both coefficients have stochastic distributions. An investigation of the stochastic distributions of the ACOF of five different floor surfaces under dry, water and glycerol conditions is presented in this paper. One hundred friction measurements were performed on each floor surface under each surface condition. The Kolmogorov-Smirnov goodness-of-fit test was used to determine if the distribution of the ACOF was a good fit with the normal, log-normal and Weibull distributions. The results indicated that the ACOF distributions had a slightly better match with the normal and log-normal distributions than with the Weibull in only three out of 15 cases with a statistical significance. The results are far more complex than what had heretofore been published and different scenarios could emerge. Since the ACOF is compared with the RCOF for the estimate of slip probability, the distribution of the ACOF in seven cases could be considered a constant for this purpose when the ACOF is much lower or higher than the RCOF. A few cases could be represented by a normal distribution for practical reasons based on their skewness and kurtosis values without a statistical significance. No representation could be found in three cases out of 15. PMID:24268803

Chang, Wen-Ruey; Matz, Simon; Chang, Chien-Chi

2014-05-01

315

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

316

Surface heat transfer due to sliding bubble motion

Energy Technology Data Exchange (ETDEWEB)

The presence of a rising bubble in a fluid can greatly enhance heat transfer from adjacent heated surfaces such as in shell and tube heat exchangers and chemical reactors. One specific case of this is when a bubble impacts and slides along the surface. The result is heat transfer enhancement by two main mechanisms: first, the bubble itself acting as a bluff body, and second, the wake generated behind the bubble leads to increasing mixing. The current research is concerned with measuring the heat transfer from a submerged heated surface that is subject to a sliding bubble flow. An ohmically heated 25 {mu}m thick stainless steel foil, submerged in a water tank, forms the test surface. An air bubble is injected onto the lower surface of the test plate, it slides along its length and the effects are monitored by two methods. Thermochromic liquid crystals (TLC's) are used in conjunction with a high speed camera to obtain a time varying 2D temperature map of the test surface. A second synchronised camera mounted below the foil records the bubble motion. Tests are performed at angles of 10 deg., 20 deg. and 30 deg. to the horizontal. This paper reports on the enhancement of the heat transfer due to the bubble. It has been found that the angle made between the heated surface and the horizontal influences heat transfer by changing the bubble's motion. In general, a steeper angle leads to a higher bubble velocity, which results in greater heat transfer enhancement.

Donnelly, Brian [Mechanical and Manufacturing Engineering, Trinity College Dublin, College Green Dublin 2 (Ireland)], E-mail: donnelbg@tcd.ie; O' Donovan, Tadhg S. [School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh (United Kingdom); Murray, Darina B. [Mechanical and Manufacturing Engineering, Trinity College Dublin, College Green Dublin 2 (Ireland)

2009-05-15

317

Subcooled flow boiling heat transfer from microporous surfaces in a small channel

International Nuclear Information System (INIS)

The continuously increasing requirement for high heat transfer rate in a compact space can be met by combining the small channel/microchannel and heat transfer enhancement methods during fluid subcooled flow boiling. In this paper, the sintered microporous coating, as an efficient means of enhancing nucleate boiling, was applied to a horizontal, rectangular small channel. Water flow boiling heat transfer characteristics from the small channel with/without the microporous coating were experimentally investigated. The small channel, even without the coating, presented flow boiling heat transfer enhancement at low vapor quality due to size effects of the channel. This enhancement was also verified by under-predictions from macro-scale correlations. In addition to the enhancement from the channel size, all six microporous coatings with various structural parameters were found to further enhance nucleate boiling significantly. Effects of the coating structural parameters, fluid mass flux and inlet subcooling were also investigated to identify the optimum condition for heat transfer enhancement. Under the optimum condition, the microporous coating could produce the heat transfer coefficients 2.7 times the smooth surface value in subcooled flow boiling and 3 times in saturated flow boiling. The combination of the microporous coating and small channel led to excellent heat transfer performance, and therefore was deemed to have promising application prospects in many areas such as air conditioning, chip cooling, refrigeration systems, and many others involving compact heat exchangers. (authors)

318

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.)

319

Reaction surface description of intramolecular hydrogen atom transfer in malonaldehyde

International Nuclear Information System (INIS)

Intramolecular H atom transfer in malonaldehyde is described using a reaction surface Hamiltonian. This model utilizes two large amplitude, reaction-coordinate-like degrees of freedom: i.e., a surface in the 3N--6 dimensional configuration space of an N atom system: with the remaining 3N--8 degrees of freedom being local harmonic motion away from this 2D surface. The two reaction surface degrees of freedom are chosen to be the two OH bond lengths, i.e., the bond being broken and the bond being formed. The present methodology is developed using 3N--6 internal coordinates, in contrast to our earlier reaction surface model [J. Chem. Phys. 81, 3942 (1984)] that utilized the 3N Cartesian coordinates. From our calculations we conclude that the bare barrier (i.e., with no zero point vibrational corrections) for the H atom transfer is between 6 and 7 kcal/mol

320

International Nuclear Information System (INIS)

Physical sputtering yields from the carbon surface irradiated by the boundary plasma are obtained with the use of a Monte Carlo simulation code ACAT. The yields are calculated for many random initial energy and angle values of incident protons or deuterons with a Maxwellian velocity distribution, and then averaged. Here the temperature of the boundary plasma, the sheath potential and the angle ? between the magnetic field line and the surface normal are taken into account. A new fitting formula for an arrangement of the numerical data of sputtering yield is introduced, in which six fitting parameters are determined from the numerical results and listed. These results provide a way to estimate the erosion of carbon materials irradiated by boundary plasma. The particle reflection coefficients for deuterons and their neutrals from a carbon surface are also calculated by the same code and presented together with, for comparison, that for the case of monoenergetic normal incidence. (author)

321

Directory of Open Access Journals (Sweden)

Full Text Available 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 experimental data and literature correlations was made.

EMILA DJORDJEVIC

2007-08-01

322

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

323

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)

324

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

325

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 103Remodelled.

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

2012-11-01

326

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

327

Using structured surfaces to enhance heat transfer in falling film flow

The heat transfer performance of an ordinary roughened (sand-blasted) surface and four commercially available structured surfaces were tested with falling film flow arrangement. The commercial surfaces were: High Flux (Union Carbide), Gewa-T (Wieland) and Thermoexcel-E and -EC (Hitachi). The test evaporator consisted of a jacket and a single, vertical 2 m long test tube. The evaporating liquid flowed down on the outside of the test tube. The tests were conducted with refrigerant R114 at evaporation temperature of 23 deg C. In the fully developed region (greater than 0.4 to 1.0 m), the flow was distorted due to strong nucleation and droplet entrainment. At higher evaporation rates (greater than 35 to 45%), the bottom parts of the test tube were not properly wetted and the heat transfer coefficient decreased although no permanent dry patches were yet seen. Nucleate boiling was dominant at all heat fluxes tested with the commercial surfaces. No boiling hysteresis was observed. They all showed excellent performance, the best one (Thermoexcel-E) having 12 times better heat transfer than the smooth tube. When heat flux was increased they all showed similar trend: the obtained enchancement compared to smooth tube was reduced. The sand-blasted tube could not compete with the structured surfaces. Its behavior was more like smooth tube.

Fagerholm, N. E.; Kivioja, K.; Ghazanfari, A. R.; Jaervinen, E.

1985-12-01

328

Transfer Chamber for DBD Surface Treatment and Analysis

Materials that are hydrophobic, smooth, and have low surface tension lead to poor adhesion for printing and coating. Surface modification using atmospheric pressure dielectric barrier discharge (DBD) improves adhesion by activating the surface, increasing its roughness and functionalizing. We have constructed and tested a DBD discharge system that uses a 15kV, 800-1350Hz pulsed dc source and a mixture of gasses at 300-600Torr. Treated surfaces are studied using X-ray photoelectron spectroscopy, Auger electron spectroscopy, and other methods that require high vacuum environment. We designed a portable transfer chamber to move the sample from the atmospheric pressure treatment chamber to a high vacuum surface analysis chamber with minimal interaction with the environment. The transfer chamber was designed to meet the specific requirements of each system; a bellows drive and sample holder to manually move the sample into the transfer chamber; the ability to fill with pure nitrogen gas to prevent contamination of the sample surface; constructed to withstand a range of pressures from 300 to 10-8Torr; the ability to connect compatibly with each system. Proper surface characterization of the sample is crucial to designing an effective treatment system.

Faust, Jessica; Gershman, Sophia; Daniels, Ryan

2012-10-01

329

Some observations on boiling heat transfer with surface oscillation

International Nuclear Information System (INIS)

The effects of surface oscillation on pool boiling heat transfer are experimentally studied. Experiments were performed in saturated ethanol and distilled water, covering the range from nucleate to film boiling except in the transition region. Two different geometries were employed as the heating surface with the same wetting area, stainless steel pipe and molybdenum ribbon. The results confirm earlier work on the effect of surface oscillation especially in lower heat flux region of nucleate boiling. Interesting boiling behavior during surface oscillation is observed, which was not referred to in previous work. (2 figures) (Author)

330

An investigation of forced-convection heat transfer and associated pressure drops was conducted with air flowing through electrically heated Inconel tubes having various degrees of square-thread-type roughness, an inside diameter of 1/2 inch, and a length of 24 inches. were obtained for tubes having conventional roughness ratios (height of thread/radius of tube) of 0 (smooth tube), 0.016, 0.025, and 0.037 over ranges of bulk Reynolds numbers up to 350,000, average inside-tube-wall temperatures up to 1950deg R, and heat-flux densities up to 115,000 Btu per hour per square foot. Data The experimental data showed that both heat transfer and friction increased with increase in surface roughness, becoming more pronounced with increase in Reynolds number; for a given roughness, both heat transfer and friction were also influenced by the tube wall-to-bulk temperature ratio. Good correlation of the heat-transfer data for all the tubes investigated was obtained by use of a modification of the conventional Nusselt correlation parameters wherein the mass velocity in the Reynolds number was replaced by the product of air density evaluated at the average film temperature and the so-called friction velocity; in addition, the physical properties of air were evaluated at the average film temperature. The isothermal friction data for the rough tubes, when plotted in the conventional manner, resulted in curves similar to those obtained by other investigators; that is, the curve for a given roughness breaks away from the Blasius line (representing turbulent flow in smooth tubes) at some value of Reynolds number, which decreases with increase in surface roughness, and then becomes a horizontal line (friction coefficient independent of Reynolds number). A comparison of the friction data for the rough tubes used herein indicated that the conventional roughness ratio is not an adequate measure of relative roughness for tubes having a square-thread-type element. The present data, as well as those of other investigators, were used to isolate the influence of ratios of thread height to width, thread spacing to width, and the conventional roughness ratio on the friction coefficient. A fair correlation of the friction data was obtained for each tube with heat addition when the friction coefficient and Reynolds number were defined on the basis of film properties; however, the data for each tube retained the curve characteristic of that particular roughness. The friction data for all the rough tubes could be represented by a single line for the complete turbulence region by incorporating a roughness parameter in the film correlation. No correlation was obtained for the region of incomplete turbulence.

Sams, E. W.

1952-01-01

331

Pattern recognition of surface electromyography signal based on wavelet coefficient entropy

Directory of Open Access Journals (Sweden)

Full Text Available This paper introduced a novel, simple and ef-fective method to extract the general feature of two surface EMG (electromyography signal patterns: forearm supination (FS surface EMG signal and forearm pronation (FP surface EMG signal. After surface EMG (SEMG signal was decomposed to the fourth resolution level with wavelet packet transform (WPT, its whole scaling space (with frequencies in the interval (0Hz, 500Hz] was divided into16 frequency bands (FB. Then wavelet coefficient entropy (WCE of every FB was calculated and corre-spondingly marked with WCE(n (from the nth FB, n=1,2,…16. Lastly, some WCE(n were chosen to form WCE feature vector, which was used to distinguish FS surface EMG signals from FP surface EMG signals. The result showed that the WCE feather vector consisted of WCE(7 (187.25Hz, 218.75Hz and WCE(8 (218.75Hz, 250Hz can more effectively recog-nize FS and FP patterns than other WCE feature vector or the WPT feature vector which was gained by the combination of WPT and principal components analysis.

Ying Gao

2009-09-01

332

Reactions involving electron transfer at semiconductor surfaces

International Nuclear Information System (INIS)

Comparisons are made between the changes in isotopic composition of isotopically pre-equilibrated (i.p.eq.) and isotopically non-equilibrated (i.n.eq.) gaseous oxygen in contact with prereduced or preoxidised samples of ZnO and TiO2 at room temperature. In the absence of illumination a place exchange (p.x.) process predominated in the oxygen isotope exchange (o.i.e.) detectable at low pressures, ca. 8 x 10-3 Torr, of i.p.eq. O2 upon contact with preoxidised samples, whereas a homophase, R0-type o.i.e. process predominated for i.n.eq. (16O2 + 18O2) contacted with prereduced samples at pressures of ca. 10-1 Torr. The latter R0 activity was removed by preoxidation but light restored it with quantum efficiency > 6 for pure ZnO and > 30 for lithium-doped ZnO. A mechanism is described to account for the correspondingly high turnover achieved on each site photoactivated by light. For i.p.eq. O2 exposed to intense illumination in contact with prereduced or preoxidised ZnO, a heterophase R1-type process, accompanied by a faster R0-type process, predominated and reasons for this are considered. Residual hydroxyls affect the ratio of o.i.e. processes on TiO2 surfaces. (author)

333

Time Dependent Surface Heat Transfer in Light Weight Aggregate Cement Based Materials

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Full Text Available Surface temperature changes of building materials affect the calculation of heat flow and thus the energy use in heating and cooling. The surface heat transfer coefficient , limiting the heat flow between material surface and ambient air is normally taken as a constant. In this study we propose a time-dependent function . We estimate from unidirectional heat flow experiments with transient and steady-state conditions. Using temperature measurements and the conservation of energy at the surface including convective and irradiative boundary conditions, the value of was obtained both using Finite Difference and Taylor Polynomials methods. Numerical solutions of temperature distribution as function of time were improved with the obtained -functions compared to with constant . There were no clear difference between on different materials, and the final values observed were in the order of magnitude expected from the literature.

Hung T. Nguyen

2010-05-01

334

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.

335

Destruction of magnetic surfaces and the diffusion coefficients of magnetic field lines

International Nuclear Information System (INIS)

In the plasma of tokamaks and RFP in which plasma current exists, there is the instability like tearing. It has been known that this makes the lines of magnetic force stochastic (chaos state), consequently, magnetic surfaces are destructed. This phenomenon is considered as one of the causes of the abnormal transport phenomena due to electrons. In this study, the formula for the diffusion coefficient of the lines of magnetic force which are in stochastic state is to be determined. In this case, by using the method of weak turbulent flow theory being put in, the formula was determined in the form without divergence. The Hamiltonian for the lines of magnetic force and the Liouville equation for this Hamiltonian are determined. By solving the Hamilton equation, the tracks of the lines of magnetic force can be determined. Then, the diffusion coefficient for the lines of magnetic force is obtained. In the vicinity of the threshold value when the lines of magnetic force became stochastic, two cases were taken up, and the diffusion coefficient was evaluated. The results are shown, and the equation of diffusion can be obtained. (K.I.)

336

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

337

Near-field radiative heat transfer for structured surfaces

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

338

International Nuclear Information System (INIS)

Measurements of the polarization transfer coefficients Ksup(y)sup(')sub(y), Ksup(x)sup(')sub(x) and Ksup(x)'sub(z) for the 2 H(p vector,p vector)2 H elastic scattering at Esub(p) =10 MeV are reported in the angular range between THETAsub(c)sub(m) = 300 and 1200. These second order polarization observables are compared with Faddeev calculations. They depend largely on the details of the S-wave interactions and the results are sensitive to the choice of their form factors, i.e. to properties of the off-shell behaviour. (orig.)

339

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

340

Radiation induced surface activation on heat transfer enhancement

International Nuclear Information System (INIS)

Improving the limit of boiling heat transfer or critical heat flux requires that the cooling liquid can contact the heating surface, or a high-wettability, highly hydrophilic heating surface, even if a vapor bubble layer is generated on the surface. From this basis, we investigated surface wettability and heat transfer phenomena using metal oxides irradiated by ?-rays. First, contact angle, an indicator of macroscopic wettability, of a water droplet on metal oxide at room temperature was measured by image processing of the images obtained by a CCD video camera. The results showed that the surface wettability on metal oxide pieces of titanium, zircaloy No. 4 SUS-304, and copper was improved significantly by the Radiation Induced Surface Activation (RISA) phenomenon. Highly hydrophilic conditions of the test pieces were achieved after 500-kGy irradiation by 60Co ?-rays. After the end of irradiation, the contact angle decreased. Second, to delineate the effect of Radiation Induced Surface Activation (RISA) on heat transferring phenomena, the Leidenfrost condition and quenching of metal oxides irradiated by ?-rays were investigated in this study. In the Leidenfrost experiment, when the temperature of the heating surface reached the wetting limit temperature, water-solid contact vanished because a stable vapor film existed between the droplet and the metal surface; i.e., a Leidenfrost condition obtained. The wetting limit temperature increased with integrated irradiation dose. After irradiation, the wet length and the duration of contact increased, and the contact angle decreased. In the quenching test, high surface wettability, or a highly hydrophilic condition, of a simulated fuel rod made of SUS was achieved, and the quenching velocities were increased up to 20 30% after 300 kGy 60Co ?-ray irradiation. (author)

341

Mitigated subsurface transfer line leak resulting in a surface pool

International Nuclear Information System (INIS)

This analysis evaluates the mitigated consequences of a potential waste transfer spill from an underground pipeline. The spill forms a surface pool. One waste composite, a 67% liquid, 33% solid, from a single shell tank is evaluated. Even drain back from a very long pipeline (50,000 ft), does not pose dose consequences to the onsite or offsite individual above guideline values

342

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

343

International Nuclear Information System (INIS)

A problem of particular interest in pressure vessel technology is the calculation of accurate stress-intensity factors for semielliptical surface cracks in cylinders. Computing costs for direct solution techniques can be prohibitive when applied to three-dimensional (3-D) geometries with time-varying boundary conditions such as those associated with pressurized thermal shock. An alternative superposition technique requires the calculation of a set of influence coefficients for a given 3-D crack model that can be superimposed to obtain mode-I stress-intensity factors. This paper presents stress-intensity-factor influence coefficients (SIFICs) for axially and circumferentially oriented finite-length semielliptical inner-surface flaws with aspect ratios (total crack length (2c) to crack depth (a)) of 2, 6, and 10 for clad cylinders having an internal radius to wall thickness (t) ratio of 10. SIFICs are computed for flaw depths in the range of 0.01 ? a/t ? 0.5 and two cladding thicknesses. The incorporate of this SIFIC data base in fracture mechanics codes will facilitate the generation of fracture mechanics solutions for a wide range of flaw geometries as may be required in structural integrity assessments of pressurized-water and boiling-water reactors

344

Scientific Electronic Library Online (English)

Full Text Available SciELO Cuba | Language: Spanish Abstract in spanish La pérdida de eficiencia del proceso de enfriamiento del licor amoniacal, mediante el uso de intercambiadores de calor de placas, está asociada a imprecisiones en la estimación de los coeficientes de transferencia de calor y la acumulación de incrustaciones en la superficie de intercambio. El objeti [...] vo de la investigación es determinar los coeficientes de transferencia de calor y la influencia de las incrustaciones en la pérdida de eficiencia de la instalación. Mediante un procedimiento iterativo se estableció la ecuación del número de Nusselt y su relación con el número de Reynolds y Prandtl. Se utilizó un diseño experimental multifactorial. Los resultados predicen el conocimiento de los coeficientes para el cálculo del número de Nusselt en ambos fluidos. Los valores de los coeficientes del licor amoniacal son inferiores, ello se debe a la presencia de componentes gaseosos. La ecuación obtenida muestra correspondencia con el modelo de Buonapane, el error comparativo es del 3,55 %. Abstract in english The loss of efficiency of the ammonia liquor cooling process, by means of the plate heat exchanger, is associated to the incorrect estimate of the heat transfer coefficients and the accumulation of inlays in the exchange surface. The objective of the investigation is to determine the transfer coeffi [...] cients and the influence of the inlays in the efficiency loss of the installation. By means of an iterative procedure was obtained the Nusselt number equation and the relationship with the Reynolds and Prandtl number, for it was used it a design experimental multifactorial. The results predict the knowledge of the coefficients for the calculation of the Nusselt number for both fluids. The ammonia liquor coefficients values are inferior, due to the presence of gassy components. The obtained equation shows correspondence with the Buonapane pattern, the comparative error is 3,55 %.

Enrique, Torres-Tamayo; Yoalbys, Retirado-Medianeja; Ever, Góngora-Leyva.

345

Scientific Electronic Library Online (English)

Full Text Available SciELO Cuba | Language: Spanish Abstract in spanish La pérdida de eficiencia del proceso de enfriamiento del licor amoniacal, mediante el uso de intercambiadores de calor de placas, está asociada a imprecisiones en la estimación de los coeficientes de transferencia de calor y la acumulación de incrustaciones en la superficie de intercambio. El objeti [...] vo de la investigación es determinar los coeficientes de transferencia de calor y la influencia de las incrustaciones en la pérdida de eficiencia de la instalación. Mediante un procedimiento iterativo se estableció la ecuación del número de Nusselt y su relación con el número de Reynolds y Prandtl. Se utilizó un diseño experimental multifactorial. Los resultados predicen el conocimiento de los coeficientes para el cálculo del número de Nusselt en ambos fluidos. Los valores de los coeficientes del licor amoniacal son inferiores, ello se debe a la presencia de componentes gaseosos. La ecuación obtenida muestra correspondencia con el modelo de Buonapane, el error comparativo es del 3,55 %. Abstract in english The loss of efficiency of the ammonia liquor cooling process, by means of the plate heat exchanger, is associated to the incorrect estimate of the heat transfer coefficients and the accumulation of inlays in the exchange surface. The objective of the investigation is to determine the transfer coeffi [...] cients and the influence of the inlays in the efficiency loss of the installation. By means of an iterative procedure was obtained the Nusselt number equation and the relationship with the Reynolds and Prandtl number, for it was used it a design experimental multifactorial. The results predict the knowledge of the coefficients for the calculation of the Nusselt number for both fluids. The ammonia liquor coefficients values are inferior, due to the presence of gassy components. The obtained equation shows correspondence with the Buonapane pattern, the comparative error is 3,55 %.

Enrique, Torres-Tamayo; Yoalbys, Retirado-Medianeja; Ever, Góngora-Leyva.

2014-04-01

346

Nucleate pool-boiling heat transfer - I. Review of parametric effects of boiling surface

International Nuclear Information System (INIS)

The objective of this paper is to assess the state-of-the-art of heat transfer in nucleate pool-boiling. Therefore, the paper consists of two parts: part I reviews and examines the effects of major boiling surface parameters affecting nucleate-boiling heat transfer, and part II reviews and examines the existing prediction methods to calculate the nucleate pool-boiling heat transfer coefficient (HTC). A literature review of the parametric trends points out that the major parameters affecting the HTC under nucleate pool-boiling conditions are heat flux, saturation pressure, and thermophysical properties of a working fluid. Therefore, these effects on the HTC under nucleate pool-boiling conditions have been the most investigated and are quite well established. On the other hand, the effects of surface characteristics such as thermophysical properties of the material, dimensions, thickness, surface finish, microstructure, etc., still cannot be quantified, and further investigations are needed. Particular attention has to be paid to the characteristics of boiling surfaces. (author)

347

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

348

Heat transfer between a nano-tip and a surface

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study quasi-ballistic heat transfer through air between a hot nanometer-scale tip and a sample. The hot tip/surface configuration is widely used to perform nonintrusive confined heating. Using a Monte-Carlo simulation, we find that the thermal conductance reaches 0.8 MW.m-2K-1 on the surface under the tip and show the shape of the heat flux density distribution (nanometer-scale thermal spot). These results show that a surface can be efficiently heated locally without cont...

Chapuis, Pierre-olivier; Greffet, Jean-jacques; Joulain, Karl; Volz, Sebastian

2008-01-01

349

Heat transfer between a nano-tip and a surface

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study quasi-ballistic heat transfer through air between a hot nanometer-scale tip and a sample. The hot tip/surface configuration is widely used to perform nonintrusive confined heating. Using a Monte-Carlo simulation, we find that the thermal conductance reaches 0.8 MW.m-2K-1 on the surface under the tip and show the shape of the heat flux density distribution (nanometer-scale thermal spot). These results show that a surface can be efficiently heated locally without contact. The temporal ...

Chapuis, Pierre-olivier; Greffet, Jean-jacques; Joulain, Karl; Volz, Sebastian

2006-01-01

350

Heat transfer and pressure drop characteristics in the annulus of concentric helical coils heat exchangers were experimentally investigated. The effects of coil curvature ratio, flow configuration, number of turns and addition of surfactant were investigated. Five test coils were designed and manufactured to study the effect of different parameters on heat transfer and pressure drop. The liquids used in the present study were water and oleyl-dihydroxy-etheyl-amine-oxide (ODEAO, C22H45NO3 = 371) non-ionic aqua surfactant solution flowing through the annulus side. The inner side Reynolds number range 11,000-27,000 and the annulus side range 5,000-19,000. The results showed that the annulus Nusselt number decreases as annulus curvature ratio increases and increases when number of turns decrease. Moreover, the friction factor increases with the curvature ratio and also increases as number of turns decreases. Both Nusselt number and friction factor decrease when ODEAO concentration increases.

Gomaa, Abdalla; Aly, Wael I. A.; Omara, M.; Abdelmagied, Mahmoud

2014-04-01

351

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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, char...

Mareš Martin; Horejš Otakar; Kohút Peter

2012-01-01

352

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

353

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english This work shows the experimental study of a continuous gas-solid fluidized bed with an immersed tube where cold water is heated by fluidized solid particles presenting inlet temperature from 450 to 700°C. Experiments were carried out in order to verify the influence of solid particle flow rate and d [...] istance between baffles immersed in a shallow fluidized bed. The solid material was 254µm diameter silica sand particles, fluidized by air in a 0.90m long and 0.15m wide heat exchanger. The measurements were taken at steady state conditions for solid mass flow rate from 10 to 100 kg/h, in a heat exchanger with the presence of 5 or 8 baffles. Bed temperature measurements along the length of the heat exchanger were experimentally obtained and heat balances for differential control volumes of the heat exchanger were made in order to obtain the axial profile of the bed-to-tube heat transfer coefficient. The results showed that heat transfer coefficient increases with the solid particle mass flow rate and with the presence of baffles, suggesting that these are important factors to be considered in the design of such heat exchanger.

Araí A. Bernárdez, Pécora; Maria Regina, Parise.

2006-09-01

354

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english This work shows the experimental study of a continuous gas-solid fluidized bed with an immersed tube where cold water is heated by fluidized solid particles presenting inlet temperature from 450 to 700°C. Experiments were carried out in order to verify the influence of solid particle flow rate and d [...] istance between baffles immersed in a shallow fluidized bed. The solid material was 254µm diameter silica sand particles, fluidized by air in a 0.90m long and 0.15m wide heat exchanger. The measurements were taken at steady state conditions for solid mass flow rate from 10 to 100 kg/h, in a heat exchanger with the presence of 5 or 8 baffles. Bed temperature measurements along the length of the heat exchanger were experimentally obtained and heat balances for differential control volumes of the heat exchanger were made in order to obtain the axial profile of the bed-to-tube heat transfer coefficient. The results showed that heat transfer coefficient increases with the solid particle mass flow rate and with the presence of baffles, suggesting that these are important factors to be considered in the design of such heat exchanger.

Araí A. Bernárdez, Pécora; Maria Regina, Parise.

355

Directory of Open Access Journals (Sweden)

Full Text Available This work shows the experimental study of a continuous gas-solid fluidized bed with an immersed tube where cold water is heated by fluidized solid particles presenting inlet temperature from 450 to 700degreesC. Experiments were carried out in order to verify the influence of solid particle flow rate and distance between baffles immersed in a shallow fluidized bed. The solid material was 254µm diameter silica sand particles, fluidized by air in a 0.90m long and 0.15m wide heat exchanger. The measurements were taken at steady state conditions for solid mass flow rate from 10 to 100 kg/h, in a heat exchanger with the presence of 5 or 8 baffles. Bed temperature measurements along the length of the heat exchanger were experimentally obtained and heat balances for differential control volumes of the heat exchanger were made in order to obtain the axial profile of the bed-to-tube heat transfer coefficient. The results showed that heat transfer coefficient increases with the solid particle mass flow rate and with the presence of baffles, suggesting that these are important factors to be considered in the design of such heat exchanger.

Pécora Araí A. Bernárdez

2006-01-01

356

Determination of 2p Excitation Transfer Rate Coefficient in Neon Gas Discharges

We will discuss our theoretical modelling and application of an array of four complementary optical diagnostic techniques for low-temperature plasmas. These are cw laser collisionally-induced fluorescence (LCIF), cw optogalvanic effect (OGE), optical emission spectroscopy (OES) and optical absorption spectroscopy (OAS). We will briefly present an overview of our investigation of neon positive column plasmas for reduced axial electric fields ranging from 3x10-17 Vcm2 to 2x10-16 Vcm2 (3-20 Td), detailing our determination of five sets of important collisional rate coefficients involving the fifteen lowest levels, the 1S0 ground state and the 1s and 2p excited states (in Paschen notation), hence information on several energy regions of the electron distribution function (EDF). The discussion will be extended to show the new results obtained from analysis of the argon positive column over similar reduced fields. Future work includes application of our multi-diagnostic technique to more complex systems, including the addition of molecules for EDF determination. array of four complementary optical diagnostic techniques OGE LCIF determination of five sets of important collisional rate coefficients

Smith, D. J.; Stewart, R. S.

2001-10-01

357

A Survey of Ballistic Transfers to the Lunar Surface

In this study techniques are developed which allow an analysis of a range of different types of transfer trajectories from the Earth to the lunar surface. Trajectories ranging from those obtained using the invariant manifolds of unstable orbits to those derived from collision orbits are analyzed. These techniques allow the computation of trajectories encompassing low-energy trajectories as well as more direct transfers. The range of possible trajectory options is summarized, and a broad range of trajectories that exist as a result of the Sun's influence are computed and analyzed. The results are then classified by type, and trades between different measures of cost are discussed.

Anderson, Rodney L.; Parker, Jeffrey S.

2011-01-01

358

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

359

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

International Nuclear Information System (INIS)

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

360

Energy Technology Data Exchange (ETDEWEB)

Heat transfer is a crucial aspect for hot stamping process, the fully austenitized boron steel blank with temperature about 900°C is transferred to the tool, then formed rapidly and quenched in the cooled tool. The desired fully martensitic transformation will happen only if the cooling rate exceeds a critical value approximately 27 K/s. During such process, the heat transfer coefficient (abbreviated as HTC) between the tool and blank plays a decisive role for the variation of the blank temperature. In this work, a theoretical formula based on the joint-roughness model is presented to describe the law of HTC, which relies on the roughness, hardness, and other material parameters of the tool and blank. Moreover, a non-contact temperature measuring system based on the infrared thermal camera is built to catch the temperature change course, and then the HTC value is derived through the inverse analysis. Based on the theoretical and experimental results, the change rule of HTC especially its dependence on the process pressure will be discussed in detail.

Han, Xianhong; Hao, Xin; Yang, Kun; Zhong, Yaoyao [Institute of Forming Technology and Equipment, Shanghai Jiao Tong University, 1954 Hua Shan Road, Shanghai, 200030 (China)

2013-12-16

361

International Nuclear Information System (INIS)

Heat transfer is a crucial aspect for hot stamping process, the fully austenitized boron steel blank with temperature about 900°C is transferred to the tool, then formed rapidly and quenched in the cooled tool. The desired fully martensitic transformation will happen only if the cooling rate exceeds a critical value approximately 27 K/s. During such process, the heat transfer coefficient (abbreviated as HTC) between the tool and blank plays a decisive role for the variation of the blank temperature. In this work, a theoretical formula based on the joint-roughness model is presented to describe the law of HTC, which relies on the roughness, hardness, and other material parameters of the tool and blank. Moreover, a non-contact temperature measuring system based on the infrared thermal camera is built to catch the temperature change course, and then the HTC value is derived through the inverse analysis. Based on the theoretical and experimental results, the change rule of HTC especially its dependence on the process pressure will be discussed in detail

362

Heat transfer is a crucial aspect for hot stamping process, the fully austenitized boron steel blank with temperature about 900°C is transferred to the tool, then formed rapidly and quenched in the cooled tool. The desired fully martensitic transformation will happen only if the cooling rate exceeds a critical value approximately 27 K/s. During such process, the heat transfer coefficient (abbreviated as HTC) between the tool and blank plays a decisive role for the variation of the blank temperature. In this work, a theoretical formula based on the joint-roughness model is presented to describe the law of HTC, which relies on the roughness, hardness, and other material parameters of the tool and blank. Moreover, a non-contact temperature measuring system based on the infrared thermal camera is built to catch the temperature change course, and then the HTC value is derived through the inverse analysis. Based on the theoretical and experimental results, the change rule of HTC especially its dependence on the process pressure will be discussed in detail.

Han, Xianhong; Hao, Xin; Yang, Kun; Zhong, Yaoyao

2013-12-01

363

Numerical analysis of heat transfer on a rotating disk surface under confined liquid jet impingement

International Nuclear Information System (INIS)

The objective of this study is to characterize the conjugate heat transfer for a confined liquid jet impinging on a rotating and uniformly heated solid disk of finite thickness and radius. The model covers the entire fluid region (impinging jet and flow spreading out over the rotating surface) and the solid disk as a conjugate problem. Calculations were done for a number of disk materials and working fluids covering a range of Reynolds number (500-1500), under a broad rotational rate range of 0-750 rpm or Ekman number (4.42 x 10-5 to ?), nozzle to target spacing (? = 0.25-5.0), disk thicknesses to nozzle diameter ratio (b/d n = 0.167-1.67), Biot number (3.73 x 10-3-0.118), Prandtl number (1.29-124.44), and solid to fluid thermal conductivity ratio (36.91-2222). It was found that plate materials with higher thermal conductivity maintained a more uniform temperature distribution at the solid-fluid interface. A higher Reynolds number increased the local heat transfer coefficient reducing the wall to fluid temperature difference over the entire interface. The rotational rate also increased local heat transfer coefficient under most conditions. The simulation results compared reasonably well with previous experimental studies

364

Blade-to-coolant convective heat-transfer coefficients were obtained on a forced-convection water-cooled single-stage turbine over a large laminar flow range and over a portion of the transition range between laminar and turbulent flow. The convective coefficients were correlated by the general relation for forced-convection heat transfer with laminar flow. Natural-convection heat transfer was negligible for this turbine over the Grashof number range investigated. Comparison of turbine data with stationary tube data for the laminar flow of heated liquids showed good agreement. Calculated average midspan blade temperatures using theoretical gas-to-blade coefficients and blade-to-coolant coefficients from stationary-tube data resulted in close agreement with experimental data.

Freche, John C; Schum, Eugene F

1951-01-01

365

International Nuclear Information System (INIS)

In general sorption coefficients, Kd, cat ion exchange capacity, CEC, and BET surface areas are measured on crushed rock samples because it is very time consuming to measure Kd and CEC on larger rock pieces as it takes a long time for the sorbing species to penetrate into and equilibrate a large sample. Also conventional sample holders for BET measurements are too small to hold a large sample. We have manufactured large sample holders for BET measurements and modified the equipment so that it is possible to measure BET surface areas on samples with 50 mm diameter and up to 100 mm length. Results are presented for intact pieces and compared to results on crushed material from the same drillcore. For Kd and CEC measurements we have developed a technique and equipment by which ions can be made to rapidly intrude into and equilibrate the internal surfaces of the same size samples as mentioned above. The method is based on electro-migration where the sample is placed between two vessels one with an anode and other with a cathode. The electric potential gradient drives the ions into and through the sample very much faster than molecular diffusion does. With Cs as the sorbing ion a few weeks were sufficient to equilibrate the 50 mm long sample. In previous diffusion experiments it took more than a year to equilibrate a 15 mm thick sample. A special mixing technique eliminates the development of low and high pH in the electrode compartments. Kd results from measurements on an intact drillcore are presented and comparison is made with results obtained on crushed material from the same bore core. The results from the sorption experiments are compared with the results from the BET surface area determinations in an attempt to evaluate the use of the BET surface area as a proxy for sorption behaviour. (orig.)

366

An experimental investigation is conducted using liquid crystals to study the effects of turbulator profile and spacing on heat transfer coefficient. Friction factors are also measured and both friction factor and heat transfer results for fifteen turbulator geometries are compared. All test configurations position the turbulators on two opposite walls of a rectangular test section in a staggered arrangement with an angle of attack to the mainstream flow of 90 degrees. It is concluded that while turbulators with aspect ratios greater than unity produce higher heat transfer coefficients at the expense of higher pressure losses, 'jersey-barrier' shaped turbulators, properly spaced, are very effective in heat removal with moderate pressure losses.

Taslim, M. E.; Spring, S. D.

1991-06-01

367

Surface roughness effects on heat transfer in Couette flow

International Nuclear Information System (INIS)

A cell theory for viscous flow with rough surfaces is applied to two basic illustrative heat transfer problems which occur in Couette flow. Couette flow between one adiabatic surface and one isothermal surface exhibits roughness effects on the adiabatic wall temperature. Two types of rough cell adiabatic surfaces are studied: (1) perfectly insulating (the temperature gradient vanishes at the boundary of each cell); (2) average insulating (each cell may gain or lose heat but the total heat flow at the wall is zero). The results for the roughness on a surface in motion are postulated to occur because of fluid entrainment in the asperities on the moving surface. The symmetry of the roughness effects on thermal-viscous dissipation is discussed in detail. Explicit effects of the roughness on each surface, including combinations of roughness values, are presented to enable the case where the two surfaces may be from different materials to be studied. The fluid bulk temperature rise is also calculated for Couette flow with two ideal adiabatic surfaces. The effect of roughness on thermal-viscous dissipation concurs with the viscous hydrodynamic effect. The results are illustrated by an application to lubrication. (Auth.)

368

A general method for transferring graphene onto soft surfaces

Recent advances in chemical vapour deposition have led to the fabrication of large graphene sheets on metal foils for use in research and development. However, further breakthroughs are required in the way these graphenes are transferred from their growth substrates onto the final substrate. Although various methods have been developed, as yet there is no general way to reliably transfer graphene onto arbitrary surfaces, such as `soft' ones. Here, we report a method that allows the graphene to be transferred with high fidelity at the desired location on almost all surfaces, including fragile polymer thin films and hydrophobic surfaces. The method relies on a sacrificial `self-releasing' polymer layer placed between a conventional polydimethylsiloxane elastomer stamp and the graphene that is to be transferred. This self-releasing layer provides a low work of adhesion on the stamp, which facilitates delamination of the graphene and its placement on the new substrate. To demonstrate the generality and reliability of our method, we fabricate high field-strength polymer capacitors using graphene as the top contact over a polymer dielectric thin film. These capacitors show superior dielectric breakdown characteristics compared with those made with evaporated metal top contacts. Furthermore, we fabricate low-operation-voltage organic field-effect transistors using graphene as the gate electrode placed over a thin polymer gate dielectric layer. We finally demonstrate an artificial graphite intercalation compound by stacking alternate monolayers of graphene and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). This compound, which comprises graphene sheets p-doped by partial hole transfer from the F4TCNQ, shows a high and remarkably stable hole conductivity, even when heated in the presence of moisture.

Song, Jie; Kam, Fong-Yu; Png, Rui-Qi; Seah, Wei-Ling; Zhuo, Jing-Mei; Lim, Geok-Kieng; Ho, Peter K. H.; Chua, Lay-Lay

2013-05-01

369

Improvement of Reactor Fuel Element Heat Transfer by Surface Roughness

International Nuclear Information System (INIS)

In heat exchangers with a limited surface temperature such as reactor fuel elements, rough heat transfer surfaces may give lower pumping power than smooth. To obtain data for choice of the most advantageous roughness for the superheater elements in the Marviken reactor, measurements were made of heat transfer and pressure drop in an annular channel with a smooth or rough test rod in a smooth adiabatic shroud. 24 different roughness geometries were tested. The results were transformed to rod cluster geometry by the method of W B Hall, and correlated by the friction and heat transfer similarity laws as suggested by D F Dipprey and R H Sabersky with RMS errors of 12.5 % in the friction factor and 8.1 % in the Stanton number. The relation between the Stanton number and the friction factor could be described by a relation of the type suggested by W Nunner, with a mean error of 3.1 % and an RMS error of 11.6 %. Application of the results to fuel element calculations is discussed, and the great gains in economy which can be obtained with rough surfaces are demonstrated by two examples

370

Heat transfer to droplets impinging upon superheated surfaces

International Nuclear Information System (INIS)

Transient surface temperature traces were obtained for a block when impinged upon by a water droplet under different experimental conditions. The temperature measurement relied on successful electro-plating over a surface thermal probe. Instantaneous heat flux from the metal block to the impacting droplet was derived through inverse conduction calculation. Four relevant parameters (degree of wall superheat, degree of droplet subcooling, impinging velocity and droplet size) were experimentally tested to study their effects on the droplet quenching process. The experimental data indicates the following: (1) for a dynamic impingement, the occurrence of liquid contact with a solid beyond Leidenfrost temperature was experimentally confirmed. (2) Heat transfer between droplet and wall surface were significantly affected by the degrees of wall superheat and droplet subcooling. The effects of impinging velocity and droplet size were obscure in the test ranges. (3) Boiling curves were established for this special droplet quenching process. It consisted of two regions: a nucleate-boiling-like region and a transition region. In the nucleate-boiling-like region, the heat transfer rate varied with wall superheat only and was close to Miyasaka et al.'s subcooled pool boiling data. In the transition region, heat transfer depended on both wall superheat and droplet subcooling

371

International Nuclear Information System (INIS)

A comparative assessment of five different heat transfer configurations for operation in compact heat exchangers is presented. The configurations under consideration are four standaed heat exchanger surfaces - two plain fin, an offset strip and a louvered fin geometry - and one surface with so called vortex generators for heat transfer augmentation. In the case of the standard surfaces, the basic performance characteristics in the form of heat transfer and friction data versus the Reynolds number have been taken from published experimental results. In the case of the vortex generator surface, the performance characteristics have been derived from a numerical prediction of the flow and temperature field in a closely spaced parallel plate channel with vortex generators in the form of delta wings mounted on the channel walls. In comparison to the plain fin surfaces with a rectangular cross section, the vortex generator surface shows best performance characteristics allowing a reduction in heat transfer surface area of 76%, for fixed heat duty and for fixed pumping power. (Author)

372

International Nuclear Information System (INIS)

The main correlations likely to be suitable for describing heat transfers between the fluid and wall during decompression are analyzed. The most important experimental work on the boiling crisis in the transient regime is presented. Experimental studies are then treated. The test installation (OMEGA experiment), the instumentation used and the experiments realized are described. The purpose of these experiments was to establish heat exchange laws for decompression conditions. Local and instantaneous exchange coefficients were determined in a heated test section together with the thermohydraulic parameters of the flow. The methods used to investigate the measurements made and to analyze their validity are described. Finally, the test results are presented and discussed. It is shown that under certain conditions, the boiling crisis can be determined with a permanent regime correlation. An attempt is made to establish a correlation for the transition boiling zone from these results. A test reconstitution calculation based on a two-fluid model is presented

373

Estimation of site specific transfer coefficient from feed to cow milk for 137Cs at Kaiga region

International Nuclear Information System (INIS)

Site specific transfer coefficient from feed to cow milk (Fm), for 137Cs at Kaiga environment determined over a period of ten years (2000-2009) is presented in this paper. 137Cs concentrations reported in this paper are of fallout origin. Fm values ranged from 3.47E-03 to 1.38E-02 d. L-1 with geometric mean value is 6.4E-03 d. L-1. These values are comparable with IAEA value for 137Cs (4.6E-03). The site-specific parameter is useful in estimation of dose to man due to ingestion of milk in an accidental condition. The ingestion dose from fallout 137Cs through milk intake for adult and child is also estimated. (author)

374

International Nuclear Information System (INIS)

A numerical investigation is conducted to study leading edge film cooling with large eddy simulation (LES). The domain geometry is adopted from an experimental setup of [Ekkad, S.V., Han, J.C., Du, H., 1998. Detailed film cooling measurement on a cylindrical leading edge model: Effect of free-stream turbulence and coolant density. Journal of Turbomachinery 120, 799-807.] where turbine blade leading edge is represented by a semi-cylindrical blunt body with compound angle of injection. At blowing ratio of 0.4 and coolant to mainstream density ratio of unity, a laminar constant velocity and fully-turbulent coolant jet are studied. In both cases, the results show the existence of an asymmetric counter-rotating vortex pair in the immediate wake of the coolant jet. In addition to these primary structures, vortex tubes on the windward side of the jet are convected downstream over and to the aft- and fore-side of the counter-rotating vortex pair. All these structures play a role in the mixing of mainstream fluid with the coolant. The fully-turbulent coolant jet increases mixing with the mainstream in the outer shear layer but does not directly influence the flow dynamics in the turbulent boundary layer which forms within two coolant hole diameters of injection. As a result, the turbulent jet decreases adiabatic effectiveness but does not have a substantial effect on the heat transfer coefficient. The span-wise averaged adiabatic effectiveness agrees well with experiments for tiveness agrees well with experiments for a turbulent coolant jet, without which the calculated effectiveness is over-predicted. On the other hand, the heat transfer coefficient which is only a function of near wall turbulence, shows good agreement with experiments for both coolant jet inlet conditions

375

Mass transfer of CO2 to groundwaters from a near-surface waste disposal site

International Nuclear Information System (INIS)

Gaseous 14CO2 originating from buried low-level radioactive wastes (LLRW) in a near-surface disposal site can be released to the environment via two major paths: gas-phase diffusion through soils to the atmosphere, and dissolution in groundwater, followed by aqueous migration. Aqueous migration would give the highest dose to an individual, especially if C-14 was converted to an organic form and ingested. Gaseous diffusion would give a lower dose, largely because of atmospheric dispersion and dilution. The objective of this study was to develop the capability to estimate which of the two paths will likely be dominant for typical near-surface disposal facilities. The main missing parameter for making this estimate was a mass-transfer coefficient (KL) of 14CO2 to groundwaters, which was determined experimentally using a large sand box. The KL thus determined was approximately 10 to 20 times smaller than for an open liquid surface. This suggests that there is a potential resistance to mass transfer, probably caused by the capillary fringe. The value obtained was incorporated into a simple model of CO2 transport around a typical near-surface disposal site. The model suggests that CO2 transport via both gaseous release and aqueous migration paths are of similar magnitude for a repository located ?2 m above the water table. (author). 11 refs., 2 tabs., 2 figs

376

Scientific Electronic Library Online (English)

Full Text Available SciELO Chile | Language: Spanish Abstract in spanish Se describe un procedimiento de evaluación del coeficiente de transferencia de calor en operaciones industriales. Se presenta un modelo matemático sencillo de determinación del coeficiente convectivo de transferencia de calor usando el software DCAL (Determinación de Coeficiente de Transferencia de [...] Calor durante un Calentamiento). Para validar el modelo se usaron datos experimentales de muestras procesadas por tratamiento térmico, utilizando diferentes temperaturas y tiempos de proceso. Los datos experimentales fueron procesados automáticamente por el software, para la generación de gráficas y determinación de un coeficiente de transferencia de calor optimizado. Se concluye que la metodología descrita sirve para el cálculo del coeficiente convectivo cuando no hay resistencia interna a la transferencia de calor. Abstract in english The evaluation of the heat transfer coefficient for its use in industrial operations is described. A simple mathematical model to determine the heat transfer convective coefficient using the DCAL software (Determination of Heat Transfer Coefficient during a Heating). To valídate the model experiment [...] al data of samples processed by thermal treatment using different temperatures and process time were used. The experimental data was automatically processed by the software, to genérate graphs and to determine an optimum heat transfer coefficient. The main conclusión was that the methodology described is useful to the compute of convective coefficient when there is no inside heat transfer resistance.

Armando, Alvis; Isaac, Caicedo; Pierre, Peña.

377

The heat transfer at the metal-die interface is believed to have great influence on the solidification process and cast structure of the high-pressure die-casting (HPDC) process. The present article focused on the effects of process parameters, casting thickness, and alloys on the metal-die interfacial heat-transfer coefficient (IHTC) in the HPDC process. Experiment was carried out on a cold-chamber die-casting machine with two casting alloys AM50 and ADC12. A special casting, namely, “step-shape” casting, was used and cast against a H13 steel die. The IHTC was determined using an inverse approach based on the temperature measurements inside the die. Results show that the IHTC is different at different steps and changes as the solidification of the casting proceeds. Process parameters only influence the IHTC in its peak value, and for both AM50 and ADC12 alloys, a greater fast shot velocity leads to a greater IHTC peak value at steps 1 and 2. The initial die surface temperature has a more prominent influence on the IHTC peak values at the thicker steps, especially step 5. Results also show that a closer contact between the casting and die could be achieved when the casting alloy is ADC12 instead of AM50, which consequently leads to a higher IHTC.

Guo, Zhi-Peng; Xiong, Shou-Mei; Liu, Bai-Cheng; Li, Mei; Allison, John

2008-12-01

378

International Nuclear Information System (INIS)

Soil-fungus transfer coefficients are usually defined as the ratio between the content of the fruiting bodies and that of the soil. Since, however, the methodology of how to determine the soil content is not firmly established, there exist a variety of definitions in the literature. We analyzed the 137Cs, 90Sr, 40K, and 226Ra content of mushroom and soil samples from two pine-wood ecosystems in Spain. The location of the mycelium in the soil profiles of these ecosystems was determined by means of the ergosterol concentration. The results showed the mycelium to generally be localized in the surface layer of soil (0-5 cm). We also carried out a speciation procedure for this layer of soil to determine the different degrees of association of the radionuclides in the soil. The results led us to propose some variations to the traditional definition used in quantifying radionuclide transfer. With these modifications, we were able to analyze Cs-K competition in several species of mycorrhizal and saprophytic fungi

379

International Nuclear Information System (INIS)

An experimental investigation has been conducted to determine the local condensation heat transfer coefficient (HTC) of steam in the presence of air or helium flowing downward inside a 46-mm-i.d. vertical tube. The gas-steam mixture flow rate was measured with a calibrated vortex flowmeter before it entered the 2.54-m-long test condenser. Cooling water flow rate in an annulus around the tube was measure with a calibrated rotameter. Temperatures of the cooling water, the gas-steam mixture, and the tube inside and outside surfaces were measured at 0.3-m intervals in the test condenser. Inlet and exit pressures and temperatures of the gas-steam mixture and of the cooling water were also measured. The local heat flux was obtained from the slope of the coolant axial temperature profile and the coolant mass flow rate. It was found that for the same mass fraction of the noncondensable gas, compared with air, helium has a more inhibiting effect on the heat transfer, but for the same molar ratio, air was found to be more inhibiting. An application where there is important is the proposed advanced passive boiling water reactor design (Simplified Boiling Water Reactor), which utilizes the isolation condenser as a main component of the passive containment cooling system (PCCS)

380

Adhesive force mapping of friction-transferred PTFE film surface

The adhesive force of a friction-transferred polytetrafluoroethylene (PTFE) film was mapped by using an atomic force microscope (AFM) system driven by custom software. The friction-transferred PTFE film, which was made by sliding a PTFE polymer rod on a heated glass, consisted of many PTFE ridges running parallel to the sliding direction on the glass surface. The adhesive force on the sample was derived from force curve measurement. A triangular wave amplified with a custom high-voltage amplifier was fed into the Z piezo of the AFM head through an AFM controller unit to obtain force curves while the AFM cantilever scanned a single line of the sample. The force curves both of the PTFE ridges and of the bare glass surface could be obtained by scanning the region perpendicular to the sliding direction. The deflection signal of the cantilever was sampled and stored in a computer through an AD converter. The adhesive force on the PTFE region was about half that on the glass surface. This difference was explained by the difference in capillary force of the surface water.

Suzuki, H.; Mashiko, S.

381

Polarization transfer coefficients Cx and Cz in the ??p?K+??(1520,3/2-) reaction process

We investigate the polarization transfer coefficients Cx and Cz for the ??p?K+??(1520,3/2-) reaction process, in which the photon is polarized circularly and the ?(1520,3/2-) along the x or z axis. To this end, we employ the effective Lagrangian method at tree level and the charge-conservation form factor scheme. In addition to the Born terms, (s,u,tK,tK*) channels and contact term, we include a nucleon resonance D13(2080) in the s channel. We compute the Cx and Cz as functions of ?K as well as Ec.m.. It turns out that the K*-exchange and D13 contributions are weak within the available experimental and theoretical inputs for them. In contrast, we observe that the contact-term and K-exchange contributions play a dominant role in determining Cx and Cz. Especially, K exchange enhances polarization transfer to the recoil ?* along the x axis.

Nam, Seung-Il

2010-01-01

382

Polarization transfer coefficients Cx and Cz in the ?-vectorp?K+?-vector(1520,3/2-) reaction process

International Nuclear Information System (INIS)

We investigate the polarization transfer coefficients Cx and Cz for the ?-vectorp?K+?-vector(1520,3/2-) reaction process, in which the photon is polarized circularly and the ?(1520,3/2-) along the x or z axis. To this end, we employ the effective Lagrangian method at tree level and the charge-conservation form factor scheme. In addition to the Born terms, (s,u,tK,tK*) channels and contact term, we include a nucleon resonance D13(2080) in the s channel. We compute the Cx and Cz as functions of ?K as well as Ec.m.. It turns out that the K*-exchange and D13 contributions are weak within the available experimental and theoretical inputs for them. In contrast, we observe that the contact-term and K-exchange contributions play a dominant role in determining Cx and Cz. Especially, K exchange enhances polarization transfer to the recoil ?* along the x axis.

383

Fundamental research on supercooling phenomenon on heat transfer surface

International Nuclear Information System (INIS)

In relation to the problem of supercooling for ice storage devices, experiments on freezing a relatively large volume of supercooled water is carried out. In the experiment, an experimental method to determine a probability of freezing a large volume of supercooled water with a uniform temperature distribution is introduced. It is accomplished by dividing the water into many smaller droplets. In a statistical analysis, a method to improve an accuracy in a case of having a limited number of experiments is introduced, and the probability of freezing is calculated for each degree of supercooling. The average freezing temperature for the experiment is placed just at the extended region of the other researchers results worked on small droplets. By relating the value with the probability of freezing on various kinds of heat transfer surfaces, the probability of freezing which is independent of the surface is calculated. In this paper it is confirmed to be negligible compared with the one on the surface

384

Impinging jet configurations are encountered in numerous industrial and engineering applications. Among these include cooling of a hot surface, turbine blade cooling, and airplane wing leading edge de-icing. In the design and operation of these applications, the knowledge of the heat transfer coefficient distribution along the cooling surface is important. We evaluated the performance of several turbulence models in the prediction of convective heat transfer due to round jet impingement onto convex spherical surfaces against available experimental data. The jet exit Reynolds number, the jet diameter, and the jet exit to the spherical surface distance were varied according to the experimental values. Based on calculated errors, the superiority of one model over the others cannot be established conclusively. However, the realizable k-epsilon model generally predicted the Nusselt number distribution more accurately than the other models for most cases.

Ramirez, Nichole; Sharif, Muhammad

2008-11-01

385

Gas transfer through wetland surface water due to waving vegetation

We investigate the effect of honami motions in a wetland system, where ';honami' refers to the wind-driven movement of vegetation. We hypothesize that this movement stirs the water column and thus contributes to the transfer of dissolved gases across the air-water interface. To understand the magnitude of this effect, a wetland honami was simulated in the laboratory using an array of plastic tubes to represent vegetation. Starting from deoxygenated water, we measured dissolved oxygen at mid-depth in the water column using a YSI ProODO as the water equilibrated with the atmosphere. From this DO time series, we calculated the gas transfer velocity, k, using the thin film gas transport model. We compare the results to other drivers of gas transfer in wetland surface water, including thermal convection and wind shear at the air-water interface. The results can help predict the role that surface-water stirring plays in connecting wetland soils with the atmosphere. This, in turn, can help predict biogeochemical processes and wetlands' impacts on greenhouse gases.

Foster, M. R.; Variano, E. A.

2013-12-01

386

Diagnostic system for plasma/surface energy transfer characterization

The knowledge of the effective energy deposited onto a surface by the reactive particles (ions, electrons, metastables, photons, etc.) in plasma processes such as thin-film deposition, sputtering, etching, etc., is of high interest to understand the basic mechanisms of energy transfer. In this article, a diagnostic is developed to directly measure the global energy transferred to surfaces (reactor walls, substrates, material to be modified, etc.) immerged in low-pressure plasmas. The diagnostic is based on a commercial HFM7-Vattel® microsensor, confined in a temperature-controlled substrate holder. The manufacturer calibration specifications are only given for atmospheric pressure. They cannot be used in low-pressure plasma conditions (typically 0.1-20Pa). Thus, for this particular application, a calibration of the microsensor is required. It is performed at various pressures, between vacuum and the ambient, according to the NIST protocol and using a homemade blackbody (BB). It is shown that only curves obtained in vacuum or pressures below 0.1Pa are valuable for a true calibration of the sensor. The others are perturbed by the heating of the gas in the BB surroundings. Measurements carried out in a typical transformer coupled plasma reactor in argon gas are presented. Typically the values are of the order of tens or hundreds of mW /cm2 in our experimental conditions. They are consistent with an estimation of the energy transferred by charged particles (ions and electrons) performed from Langmuir probe characterization of the plasma.

Thomann, A.-L.; Semmar, N.; Dussart, R.; Mathias, J.; Lang, V.

2006-03-01

387

Influence of the surface drag coefficient (young waves) on the current structure of the Berre lagoon

Due to the shallowness, currents and hydrodynamics of Berre lagoon (South of France) are closely conditioned by the bottom topography, and wind affects the entire water column, as for many other Mediterranean lagoons (Perez-Ruzafa, 2011). Wind stress, which is caused by moving atmospheric disturbance, is known to have a major influence in lagoon water circulation. According to the numerical simulation for the main directions of the wind: N-NW, S-SE and W (wind speed of 80 km/h) it is observed that the current is maximal alongshore in the wind direction; the bottom nearshore current being larger in shallower area. This fact is coherent with fundamental principle of wind-driven flows in closed or partially closed basins which states that in shallow water the dominant force balance is between surface wind stress and bottom friction, yielding a current in the direction of the wind (Mathieu et al, 2002, Hunter and Hearn, 1987; Hearn and Hunter,1990). A uniform wind stress applied at the surface of a basin of variable depth sets up a circulation pattern characterized by relatively strong barotropic coastal currents in the direction of the wind, with return flow occurring over the deeper regions (Csanady, 1967; Csanady, 1971). One of the key parameters characterizing the wind stress formulation is a surface drag coefficient (Cds). Thus, an effect of a surface drag coefficient, in the range 0.0016 - 0.0032, will be analyzed in this work. The value of surface drag coefficient Cds = 0.0016 used in our previous studies (Alekseenko et al., 2012), would correspond to mature waves (open sea). But, in the case of semi-closed lagoonal ecosystem, it would be more appropriate to consider "young waves" mechanism. A dependency of this coefficient in terms of the wind speed is given by Young (1999) in both cases of mature waves and young waves. For "young waves" generated at a wind speed of 80 km/h, Cds = 0.0032. So, the influence of Cds on the vertical profile of the velocity in the water column is analyzed in the range 0.0016 - 0.0032. For the three main wind directions considered in this work, for a wind speed of 80 km