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Heat Transfer Coefficient (heat + transfer_coefficient)
Kinds of Heat Transfer Coefficient Selected AbstractsIMPACT OF BLENDING OF FRYING OILS ON VISCOSITY AND HEAT TRANSFER COEFFICIENT AT ELEVATED TEMPERATURESJOURNAL OF FOOD PROCESS ENGINEERING, Issue 1 2010SUKUMAR DEBNATH ABSTRACT In the present work, the effect of binary blending of five frying oils on kinematic viscosity (,) and convective heat transfer coefficient (h) was studied at elevated temperatures (170, 180 and 190C). A Cannon Ubbelhode calibrated capillary viscometer (Cannon Instrument Company, State College, PA) in a custom-designed and fabricated convective air bath heater and a highly conductive cylindrical metal transducer were used for generating,and h data, respectively. The value of,decreased from 3.617 × 10 - 6 to 2.062 × 10 - 6 m2 s - 1, and h increased from 221.0 to 301.2 Wm - 2 C - 1 by increasing the aforementioned oil temperatures. A good correlation between, (R2 > 0.996) or h (R2 > 0.987) of these frying oils and their selected binary blends with the previously mentioned temperature range was observed. Significant difference (P < 0.05) was found between different levels of parameters when treatments were compared using Tukey's test. PRACTICAL APPLICATIONS In food engineering applications, the physical properties of foods play an important role in the analysis of process parameters and in the design and fabrication of processing equipment. Determination of kinematic viscosity and convective heat transfer coefficients of frying oils and their selected blends at elevated temperatures are useful from an industrial point of view. In the present work, the effect of blending different edible oils on the kinematic viscosity and convective heat transfer coefficients at elevated temperatures was studied. Because selected blended oils provided lower levels of viscosities and higher levels of heat transfer coefficients, these results may be an attractive proposition in improving the quality of fried products and cost-effectiveness in the fried food industry. [source] HEAT TRANSFER COEFFICIENT FOR COOKIE SHAPED OBJECTS IN A HOT AIR JET IMPINGEMENT OVENJOURNAL OF FOOD PROCESS ENGINEERING, Issue 1 2001N. NITIN ABSTRACT Correlations for average heat transfer coefficient for cookie shaped objects in a hot air jet impingement oven were obtained using aluminum cookie models. The study was carried out in a pilot plant scale hot air jet impingement oven. The effects of individual cookie position, presence of surrounding cookies, air velocity, air temperature and rotation of the oven plate on average surface heat transfer coefficient were investigated. The value of the heat transfer coefficient ranged between 100,225 W/m2K and was found to be a strong function of jet air velocity. The impact of surrounding cookies on the heat transfer coefficient was more for smaller cookies, which had larger cookie-to-cookie spacing. [source] Heat transfer coefficient in viscous three-phase inverse fluidized bedsAICHE JOURNAL, Issue 11 2007S. M. Son First page of article [source] Heat transfer on tube bundles embedded horizontally in a liquid-fluidized bed: 2nd report: On tube bundles of fundamental layouts including in-line layoutsHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2009Kenichi Hashizume Abstract Heat transfer coefficients were measured on tube bundles of fundamental layouts including in-line layouts embedded horizontally in a liquid-fluidized bed. Tested tube layouts were single tubes, transverse single tube rows, longitudinal single tube rows, and in-line arranged tube bundles. A total of 7 kinds of particles were used. Comparisons of the experimental data showed a good agreement with the heat transfer correlation developed for staggered layouts, when the average liquid velocity through each tube bundle was used as the reference velocity for the particle Reynolds number. Distribution of the local heat transfer coefficient was also investigated around tubes. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20245 [source] Experimental investigation into cavity-type inertial separators,a novel technique for development of subcompact circulating fluidized bed boilersINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 14 2005Animesh Dutta Abstract Cavity-type inertial separators developed by GRI (Patent no. 2, 159, 949, Canada, 2002) were tested in a semi-industrial size circulating fluidized bed pilot plant operated at room temperature. Three rows of separators were hung from the roof of the pilot plant where one row was kept inside the riser and the others were kept in the primary separation chamber, located between the back-pass and the riser. Parameters measured were axial pressure drops along the height of the riser, vertical solids flux on the separator walls, lateral outwards solids flux in the riser with and without separator and local temperatures on the separator walls. A net downwards solids flux is on the inner wall of the separators; however, no downwards solids flux is on the outer walls of the separators. Heat transfer coefficients on the outer wall are found higher than those on the inner walls of the separator. It is also found that the presence of inertial separators not only provides additional heat transfer surfaces but also indirectly increases the heat transfer coefficients on the riser wall. Copyright © 2005 John Wiley & Sons, Ltd. [source] Heat transfer behavior of melting polymers in laminar flow fieldPOLYMER ENGINEERING & SCIENCE, Issue 3 2004Sadao Sato Heat transfer coefficients were investigated by insertion of a probe into melting polymers under laminar flow at 200,240°C and a flow velocity of 0.5,2.7 mm/sec. The average heat transfer coefficients of melting polypropylene (PP) and polystyrene (PS) were found to be 160,220 W/m·°C and 180,270 W/m·°C, respectively. These coefficients show remarkable dependence on flow velocity, and the average heat transfer coefficient of PS is about 13%,23% higher than that of PP. When the flow velocity of flowing melting PP and PS exceeds about 0.078mm/sec, heat transfer by convection becomes dominant, whereas under lower flow velocities, since the equivalent conduction layer thickness ,, in which the quiescent state without flow approaches infinity, heat transfer by conduction becomes dominant. The Prandtl number (Pr) and Nusselt number (Nu) of melting PP are 125,133 × 106 and 38.6,51.4, respectively, and those of melting PS are 63,64 × 106 and 42.3,61.3. In the case of constant flow velocity, the Peclet number (Pe) and Stanton number (St) are dependent on the specific heat of melting polymer. Polym. Eng. Sci. 44:423,432, 2004. © 2004 Society of Plastics Engineers. [source] Estimation of Joule heating effect on temperature and pressure distribution in electrokinetic-driven microchannel flowsELECTROPHORESIS, Issue 3 2006Reiyu Chein Professor Abstract In this study we present simple analytical models that predict the temperature and pressure variations in electrokinetic-driven microchannel flow under the Joule heating effect. For temperature prediction, a simple model shows that the temperature is related to the Joule heating parameter, autothermal Joule heating parameter, external cooling parameter, Peclet number, and the channel length to channel hydraulic diameter ratio. The simple model overpredicted the thermally developed temperature compared with the full numerical simulation, but in good agreement with the experimental measurements. The factors that affect the external cooling parameters, such as the heat transfer coefficient, channel configuration, and channel material are also examined based on this simple model. Based on the mass conservation, a simple model is developed that predicts the pressure variations, including the temperature effect. An adverse pressure gradient is required to satisfy the mass conservation requirement. The temperature effect on the pressure gradient is via the temperature-dependent fluid viscosity and electroosmotic velocity. [source] Numerical Modelling of Flow Boiling Heat Transfer in Horizontal Metal-Foam Tubes,ADVANCED ENGINEERING MATERIALS, Issue 10 2009Wei Lu Abstract The flow boiling heat transfer performance in horizontal metal-foam tubes is numerically investigated based on the flow pattern map retrieved from experimental investigations. The flow pattern and velocity profile are generally governed by vapour quality and mass flow rate of the fluid. The porous media non-equilibrium heat transfer model is employed for modelling both vapour and liquid phase zones. The modelling predictions have been compared with experimental results. The effects of metal-foam morphological parameters, heat flux and mass flux on heat transfer have been examined. The numerical predictions show that the overall heat transfer coefficient of the metal-foam filled tube increases with the relative density (1-porosity), pore density (ppi), mass and heat flux. [source] Closed-form thermal stress intensity factors for an internal circumferential crack in a thick-walled cylinderFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 8 2010R. GHAJAR ABSTRACT In this paper the method of weight functions is employed to calculate the stress intensity factors for an internal circumferential crack in a thick-walled cylinder. The pressurized cylinder is also subjected to convection cooling on the inner surface. Finite element method is used to determine an accurate weight function for the crack and a closed-form thermal stress intensity factor with the aid of the weight function method is extracted. The influence of crack parameter and the heat transfer coefficient on the stress intensity factors are determined. Comparison of the results in the special cases with those cited in the literature and the finite element data shows that the results are in very good agreement. [source] Boiling heat transfer coefficient of R22 and an HFC/HC refrigerant mixture in a fin-and-tube evaporator of a window air conditionerHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 6 2010M. Herbert Raj Abstract The commonly used refrigerant in unitary type air conditioners is R22 and its phase out schedule in developing countries is to commence from 2015. Many alternatives to R22 are found in published literature in which R407C has similar characteristics to those of R22 except for its zeotropic nature. However, R407C which is an HFC is made compatible with the mineral oil lubricant in the system compressor by the addition of 20% of HC. This HFC/HC mixture called the M20 refrigerant mixture is reported to be a retrofit refrigerant for R22. Though its latent heat value is greater than that of R22, its refrigerating capacity is lower when it is used to retrofit R22 window air conditioners. Hence, a heat transfer analysis was conducted in the evaporator of a room air conditioner, for practically realized heat flux conditions during standard performance testing. The tests were conducted as per the BIS and ASHRAE standards. Kattan,Thome,Favrat maps are used to confirm the flow patterns, which prevail inside the fin-and-tube evaporator in the tested operating conditions. It is revealed that the heat transfer coefficient/heat fluxes are poorer for M20 because of the lower mass flow rate and higher vapor fraction at the entry of the evaporator than that of R22 in the prevailing operating conditions. The heat transfer coefficients of the M20 refrigerant mixture under various test conditions are lower in the range of 14% to 56% than those of R22. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/htj.20299 [source] Enhancement of condensation on a vertical plate (2nd report, prediction of condensation on a dispersed finned surface)HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2010Rencai Chu Abstract In this study, a prediction model for condensation heat transfer on a vertical dispersed finned surface was proposed, utilizing the Adamek-Webb model for condensation heat transfer outside a horizontal finned tube. The prediction model was based on two main experimental observation results. One is the phenomena of the condensate retention at the bottom of each row of the dispersed fin. Another is the offset phenomena of the condensate flow between each row of the dispersed fin. Given the results by the present model, it is predicted that the dependence of the condensation heat transfer coefficient for the dispersed finned surface on the fin pitch is controlled mainly by the dispersed fin length, not the total fin length. On the contrary, for a different fin pitch, the effect to the condensation heat transfer by dispersing the fin is different. From comparison with the experiment results, it is confirmed that the present model was able to predict the condensation with extremely good precision when the fin pitch was larger. Further, when the fin pitch was smaller, the predicted values were higher than the experimental values, but the tendency of the condensation heat transfer with dispersing the fin was nearly predicted. In addition, this condensing model can predict the experimental values with an error of 25% at the maximum in a range of fin pitch 0.6 mm to 1 mm. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20288 [source] Heat transfer on tube bundles embedded horizontally in a liquid-fluidized bed: 2nd report: On tube bundles of fundamental layouts including in-line layoutsHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2009Kenichi Hashizume Abstract Heat transfer coefficients were measured on tube bundles of fundamental layouts including in-line layouts embedded horizontally in a liquid-fluidized bed. Tested tube layouts were single tubes, transverse single tube rows, longitudinal single tube rows, and in-line arranged tube bundles. A total of 7 kinds of particles were used. Comparisons of the experimental data showed a good agreement with the heat transfer correlation developed for staggered layouts, when the average liquid velocity through each tube bundle was used as the reference velocity for the particle Reynolds number. Distribution of the local heat transfer coefficient was also investigated around tubes. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20245 [source] The heat transfer and pressure loss characteristics of a heat exchanger for recovering latent heat (the heat transfer and pressure loss characteristics of the heat exchanger with wing fin)HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 4 2007Kiyoshi Kawaguchi Abstract In recent years the requirement for reduction of energy consumption has been increasing to solve the problems of global warming and the shortage of petroleum resources. A latent heat recovery type heat exchanger is one of the effective methods of improving thermal efficiency by recovering latent heat. This paper described the heat transfer and pressure loss characteristics of a latent heat recovery type heat exchanger having a wing fin (fin pitch: 4 mm, fin length: 65 mm). These were clarified by measuring the exchange heat quantity, the pressure loss of heat exchanger, and the heat transfer coefficient between outer fin surface and gas. The effects of condensate behavior in the fins on heat transfer and pressure loss characteristics were clarified. Furthermore, the equations for predicting the heat transfer coefficient and pressure loss which are necessary in the design of the heat exchanger were proposed. ©2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(4): 215,229, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20154 [source] The influences of thermophysical properties of porous media on superadiabatic combustion with reciprocating flowHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 5 2006Liming Du Abstract The influences of thermophysical properties of porous media on superadiabatic combustion with reciprocating flow is numerically studied in order to improve the understanding of the complex heat transfer and optimum design of the combustor. The heat transfer performance of a porous media combustor strongly depends on the thermophysical properties of the porous material. In order to explore how the material properties influence reciprocating superadiabatic combustion of premixed gases in porous media (short for RSCP), a two-dimensional mathematical model of a simplified RSCP combustor is developed based on the hypothesis of local thermal non-equilibrium between the solid and the gas phases by solving separate energy equations for these two phases. The porous media is assumed to emit, absorb, and isotropically scatter radiation. The finite-volume method is used for computing radiation heat transfer processes. The flow and temperature fields are calculated by solving the mass, moment, gas and solid energy, and species conservation equations with a finite difference/control volume approach. Since the mass fraction conservation equations are stiff, an operator splitting method is used to solve them. The results show that the volumetric convective heat transfer coefficient and extinction coefficient of the porous media obviously affect the temperature distributions of the combustion chamber and burning speed of the gases, but thermal conductivity does not have an obvious effect. It indicates that convective heat transfer and heat radiation are the dominating ways of heat transfer, while heat conduction is a little less important. The specific heat of the porous media also has a remarkable impact on temperature distribution of gases and heat release rate. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(5): 336,350, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20120 [source] Effect of fins on forced convection heat transfer around a tube in an aligned-arranged tube bundleHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 8 2005Kenichi Hashizume Abstract The effect of fins on heat transfer around a tube in an aligned-arranged tube bundle was investigated experimentally, and the obtained results were compared for three arrangements, i.e., single tube, single tube row, and staggered-arrangement. It was found from the experiment that the effect of fins begins to appear in an aligned-arrangement with larger fin spacing than in a staggered-arrangement. The degradation in the local heat transfer coefficient due to fins can be recognized not only on the rear region of the tube, as observed in other arrangements, but also on the frontal region. As a result of this phenomenon, the degradation in the average heat transfer coefficient in an aligned-arrangement becomes larger than in other arrangements with the same fin spacing. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(8): 555,563, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20091 [source] Heat transfer and fluid flow characteristics in a swirling impinging jetHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 5 2005Mamoru Senda Abstract An experimental study on heat transfer and fluid flow has been carried out for a swirling round impinging jet. A thermosensitive liquid crystal sheet was used for the heat transfer measurements and the three velocity components were measured with LDV in the stagnation region for cases where the Swirl number Sw = 0.0, 0.22, and 0.45 at the Reynolds number Re = 8100. The formation of recirculation flow due to a swirl near the impinging wall was found to deteriorate the heat transfer coefficient in the stagnation region and results in a more uniform distribution of the Nusselt number with an increasing Swirl number. The heat transfer mechanism of the swirling impinging jet is discussed based on the flow characteristics of the mean velocities and turbulence quantities. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(5): 324,335, 2005; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/htj.20068 [source] Heat transfer on tube bundles embedded horizontally in a liquid-fluidized bedHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 2 2005Kenichi Hashizume Abstract Heat transfer on tube bundles embedded horizontally in a liquid-fluidized bed was investigated experimentally. In the experiment, a total of 5 kinds of tube bundles in an equilateral triangular staggered arrangement, including a single tube, was used. Tested particles were of glass and ceramics, and their diameter range was from 2.1 to 6.0 mm. It was found that the distribution of local heat transfer coefficients around a tube depends not on the kind of particles, but on the tube pitch only, when a good fluidizing condition is maintained. Based on the experimental data, a new method was proposed to predict average heat transfer coefficient, which can be applicable for tube bundles having a tube pitch to diameter ratio of 1.2 to infinity (single tube). © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(2): 85,98, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20048 [source] Research on Marangoni condensation heat transfer for water and ethanol mixture vaporHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 8 2004He Yang-peng Abstract A brass block was constructed as a test block to study the Marangoni condensation in this paper. The maximal temperature difference of the block surface on which pure steam condensed was 11°C when the block was cooled by the normal temperature water. Regulations and modes of Marangoni condensation for mixture vapor with different mass fractions were studied when the speed of vapor was 0.3 m/s. As both temperature gradients and concentration gradients exist on the condensing surface, the experimental results indicate that the maximal heat transfer coefficient of mixture vapor can be 2.8 times that of pure steam when the Marangoni condensation of mixture vapor appears. The heat transfer coefficient of mixture vapor increases with the decrease of surface subcooling, and it appears a steep increase when the surface subcooling is small enough; the heat transfer flux has a maximum value as the surface subcooling rises; and the different modes of condensation are confirmed when the different ethanol concentration and different surface subcooling exist. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(8): 505,514, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20035 [source] Experimental research of pool boiling heat transfer in horizontal narrow spacesHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 5 2004Enshen Long Abstract Much progress has been made in high-performance electronic chips, the miniaturization of electronic circuits and other compact systems recently, which brings about a great demand for developing efficient heat removal techniques to accommodate these high heat fluxes. With this objective in mind, experiments were carried out on five kinds of test elements with distilled water and ethanol as working liquids. The test elements used in these experiments consisted of five parallel discs with diameters varying from 5 mm to 40 mm. The experiments were performed with the discs oriented horizontally and uniform heat fluxes applied at the bottom surfaces. The influence of narrow spacing, space size, working liquid property, and heat flux on boiling heat transfer performance in narrow spaces has been investigated. Experimental results showed that the boiling heat transfer coefficient of a narrow space was 3 to 6 times higher than that of pool boiling when the narrow space size and heat flux combine adequately, but the critical heat flux was lower than that of pool boiling. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(5): 307,315, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20017 [source] Enhancement of pool boiling heat transfer in water and ethanol/water mixtures (effect of surface-active agent)HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 4 2004Toshiaki Inoue Abstract The surface tension of alcohol/water mixtures has been measured over the whole fraction range and then it has been measured when a surface-active agent was added into the mixtures. The effect of the concentration of alcohol and the surface- active agent on surface tension was experimentally clarified, in order to gain base data related to enhancement of the heat transfer coefficient in the mixtures and water. The experiment was also carried out to enhance the boiling heat transfer coefficients of water and alcohol/water mixtures on a horizontal heated fine wire at a pressure of 0.1 MPa by adding a surface-active agent into the tested liquid. The results show, the coefficients were enhanced in lower alcohol concentration (C , 0.5) and low heat flux range which occur just after the onset of boiling. It was also found that the enhancement effect by the surfactant disappears in concentrations over 1000 ppm. Finally, we demonstrated that the surface tension remarkably affects the heat transfer coefficients in nucleate pool boiling. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(4): 229,244, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20010 [source] Method of calculation of heat transfer coefficient of the heater in a circulating fluidized bed furnaceHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 7 2002J.F. Lu Abstract Knowledge of heat transfer coefficients is important in the design and operation of CFB boilers. It is the key to determining the area and the layout of the heat transfer surfaces in a CFB furnace. Local bulk density has a close relationship to the local heat transfer coefficient. Using a heat flux probe and bulk density sampling probe, the local bed to wall heat transfer coefficient in the furnace of a 75 t/h CFB boiler was measured. According to the experimental results and theoretical analysis of the facts that influence the heat transfer, the heat transfer coefficient calculation method for the CFB furnace was developed. The heat transfer surface configuration, heating condition, and the material density are considered in this method. The calculation method has been used in the design of CFB boilers with a capacity from 130 t/h to 420 t/h. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(7): 540,550, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10056 [source] Pool boiling heat transfer in binary mixtures of ammonia/water: Effect of heat of dilution and dissolution on heat transfer coefficientHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 4 2002Toshiaki Inoue Abstract Nucleate boiling heat transfer coefficients were measured on a horizontal heated wire during the pool boiling of non-azeotropic mixtures of ammonia/water. The experiment was carried out at pressures of 0.4 and 0.7 MPa, at heat fluxes below 2.0 × 106 W/m2, and over a range of mass fraction. The heat transfer coefficients in the mixtures were smaller than those in single-component substances. No existing correlation is found to predict boiling heat transfer coefficients over the range of mass fraction of interest. In the mixtures of the ammonia/water, the heats of dilution and dissolution were generated near a liquid surface while vapor with a rich concentration of ammonia was condensed and then was diffused into the bulk liquid; while in most other mixtures, little heat was generated during any dilution and dissolution. In relation to the heat generated, the effect of the heats of dilution and dissolution on pressure and temperature in a system (pressure vessel) is shown herein. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(4): 272,283, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10034 [source] Augmentation of boiling heat transfer from horizontal cylinder to liquid by movable particlesHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 1 2002Yoshihiro Iida Abstract This paper presents a series of experimental results on a passive augmentation technique of boiling heat transfer by supplying solid particles in liquid. A cylindrical heater 0.88 mm in diameter is placed in saturated water, in which a lot of mobile particles exist, and the nucleate and film boiling heat transfer characteristics are measured. Particle materials used were alumina, glass, and porous alumina, and the diameter ranged from 0.3 mm to 2.5 mm. Particles are fluidized by the occurrence of boiling without any additive power, and the heat transfer is augmented. The maximum augmentation ratio obtained in this experiment reaches about ten times the heat transfer coefficient obtained in liquid alone. The augmentation ratio is mainly affected by the particle material, diameter, and the height of the particle bed set at no boiling condition. The augmentation mechanism is discussed on the basis of the experimental results. © 2001 Scripta Technica, Heat Trans Asian Res, 31(1): 28,41, 2002 [source] Forced convective heat transfer for fluid flowing through a porous medium with internal heat generationHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2001Hua Du Abstract Forced convection in channels filled with packed beads with internal heat source was numerically analyzed by using the extended Darcy model for the flow and energy conservation equations with nonthermal equilibrium (NTE). The temperature difference between the matrix and fluid phases was discussed with three dimensionless parameters (Rep, H/dp, and ks/kf). It is concluded that the thermal equilibrium assumption may be adopted for the situation when the solid conduction dominated over the convection or when the heat transfer coefficient between the two phases is large at large Rep. The Nusselt number at the wall with the variation of Rep for different ks/kf was also investigated. © 2001 Scripta Technica, Heat Trans Asian Res, 30(3): 213,221, 2001 [source] An inverse radiation problem of simultaneous estimation of heat transfer coefficient and absorption coefficient in participating mediaINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 6 2003H. M. Park Abstract An inverse radiation problem is investigated where the spatially varying heat transfer coefficient h(z) and the absorption coefficient , in the radiant cooler are estimated simultaneously from temperature measurements. The inverse radiation problem is solved through the minimization of a performance function, which is expressed by the sum of square residuals between calculated and observed temperature, using the conjugate gradient method. The gradient of the performance function is evaluated by means of the improved adjoint variable method that can take care of both the function estimation and the parameter estimation efficiently. The present method is found to estimate h(z) and , with reasonable accuracy even with noisy temperature measurements. Copyright © 2002 John Wiley & Sons, Ltd. [source] Effect of incidence angle with wake passing on a film cooled leading edge: A numerical studyINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2010F. Montomoli Abstract This work presents the numerical study of a film-cooled blade under the influence of wake passing at different incidence angles. The film cooling technology has been proven to be effective to increase the blade life of first turbine stages. However, the leading edge is affected by an high heat transfer rate and cooling this region is difficult. Moreover, separated regions downstream the coolant injection increases the local heat transfer coefficient and can have a detrimental effect in terms of airfoil life. This work analyses how the flow field is affected by the wake passing at different incidence angles (,5, 0, 5) and the impact on heat transfer coefficient. The test case is a linear cascade with two rows of cylindrical holes at the leading edge. Two different holes arrangements are compared in terms of film cooling structures, namely AGTB-B1 and AGTB-B2 with 0 and 45, spanwise inclination. The numerical results show a good agreement with the experiments. A deeper investigation is carried out on AGTB-B1. The results obtained show that the wake passing and the incidence angle have a strong effect on coolant jets. In particular, there is a significative impact on coolant redistribution near the leading edge. The wake passing has a stronger effect on pressure side, mainly at negative incidence. The predictive approach is based on an U-RANS in-house CFD solver using a conventional two-equations closure. In order to avoid extra turbulence production, critical in the leading edge region, the turbulence model incorporates an extra algebraic equation that enforces a realizability constraint. The unsteady formulation is based on a dual time stepping approach with a sliding plane between the moving bars and the cascade. Copyright © 2009 John Wiley & Sons, Ltd. [source] Performance of a modified direct expansion A/C unitINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 13 2010Esmail M. A. Mokheimer Abstract This technical note communicates the thermal performance of a modified ten-Ton Refrigerant Direct Expansion (10-TR DX) air conditioning unit into a chiller under actual operating conditions. The modified unit achieved higher COP and cooling capacity compared with conventional DX. The increase in the unit cooling capacity is basically attributed to the enhanced heat transfer coefficient of the Plate-and-Frame Heat Exchanger evaporator. Copyright © 2009 John Wiley & Sons, Ltd. [source] Two-phase flow convective condensation of refrigerant mixtures under gas/liquid injectionINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 15 2005Samuel M. Sami Abstract The influence of gas/liquid injection on two-phase flow condensation heat transfer characteristics of some refrigerant mixtures in horizontal enhanced surface tubing is presented. Correlations were proposed to predict the impact of the gas/liquid injection on the heat transfer characteristics such as average heat transfer coefficient of R-507, R-404A, R-410A, and R-407C in two-phase flow condensation inside enhanced surface tubing. The data also revealed that gas, liquid and gas/liquid injection is beneficial at certain gas/liquid injection ratios to the heat transfer coefficient depending upon the Reynolds number and the condensation point of the refrigerant mixtures in question. It was also evident that the proposed condensation correlations and the experimental data were applicable to the entire heat and mass flux, investigated in the present study under gas/liquid injection conditions. The deviation between the experimental and predicted under gas/liquid injection were less than ± 10, for the majority of data. Copyright © 2005 John Wiley & Sons, Ltd. [source] Influence of magnetic field on two-phase flow convective boiling of some refrigerant mixturesINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 15 2005Samuel M. Sami Abstract In this paper, an experimental study on the influence of magnetohydrodynamic (MHD) on heat transfer characteristics of two-phase flow boiling of some refrigerant mixtures in air/refrigerant horizontal enhanced surface tubing is presented. Correlations were proposed to predict the impact of MHD on the heat transfer characteristics such as average heat transfer coefficients, and pressure drops of R-507, R-404A, R-410A, and R-407C in two-phase flow boiling inside enhanced surface tubing. In addition, it was found that the refrigerant mixture's pressure drop is a weak function of the mixture's composition. It was also evident that the proposed correlations for predicting the heat transfer characteristics were applicable to the entire heat and mass flux, investigated in the present study. The deviation between the experimental and predicted value using new and improved correlations for the heat transfer coefficient and pressure drop were less than ±20%, for the majority of data. Copyright © 2005 John Wiley & Sons, Ltd. [source] The effect of condenser heat transfer on the energy performance of a plate heat pipe solar collectorINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 10 2005Jorge Facão Abstract For a novel prototype solar collector, using a plate heat pipe, condenser heat transfer was analysed in detail. The condenser has the shape of a rectangular channel. Flow and heat transfer of water in the rectangular channel was modelled and the heat transfer coefficient assessed, using the Fluent code. Under typical operating conditions a mixed convection situation occurs. The channel is inclined and heating is through one wall only (upper channel surface). The range of temperature differences considered was similar to the one verified under real operating conditions, covering a wide range of Grashof numbers. Results showed that the Nusselt number is significantly higher than the one for forced convection in a rectangular channel with fully developed boundary layers. In order to enhance heat transfer, a modification to the rectangular channel was analysed, using baffles to improve flow distribution and increase velocity. The effect of this modification on collector energy performance (efficiency) was assessed. Copyright © 2005 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||