Convection Heat Transfer (convection + heat_transfer)

Distribution by Scientific Domains


Selected Abstracts


Study on heat transfer characteristics of porous metallic heat sink with conductive pipe under bypass effect

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2009
Sheng-Chung Tzeng
Abstract The work investigated the forced convection heat transfer of the heat sink situated in a rectangular channel by considering the bypass effect. The fluid medium was air. The relevant parameters were the Reynolds number (Re), the relative top by-pass gap (C/H), and the relative side by-pass gap (S/L). The size of the heat sink was 60 mm (L)×60 mm(W)×24 mm(H). Two heat sinks were employed as test specimens: (A) the 0.9-porosity aluminum foam heat sink and (B) the 0.9-porosity aluminum foam heat sink with a 20 mm diameter copper cylinder. The copper cylinder was used as a conductive pipe of heat sink. The average Nusselt number was examined under various forced convection conditions. Experimental results demonstrate that increasing by-pass space decreased the Nusselt number. Besides, the average Nusselt number of mode B heat sink was higher than that of mode A heat sink by 30% for the case without by-pass flow. The heat transfer enhancement by the copper cylinder would decline as the by-pass space grew. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20247 [source]


Enhancement of natural convection heat transfer from a vertical heated plate using inclined fins

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 6 2007
Masao Fujii
Abstract An enhancement technique is developed for natural convection heat transfer from a vertical heated plate with inclined fins, attached on the vertical heated plate to isolate a hot air flow from a cold air flow. Experiments are performed in air for inclination angles of the inclined fins in the range of 30° to 90° as measured from a horizontal plane, with a height of 25 to 50 mm, and a fin pitch of 20 to 60 mm. The convective heat transfer rate for the vertical heated plate with inclined fins at an inclination angle of 60° is found to be 19% higher than that for a vertical heated plate with vertical fins. A dimensionless equation on the natural convection heat transfer of a vertical heated plate with inclined fins is presented. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(6): 334,344, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20168 [source]


Effect of fins on forced convection heat transfer around a tube in an aligned-arranged tube bundle

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 8 2005
Kenichi 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]


Reverse computation of forced convection heat transfer for optimal control of thermal boundary conditions

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2004
Kazunari Momose
Abstract A reverse computation based on adjoint formulation of forced convection heat transfer is proposed to obtain the optimal thermal boundary conditions for heat transfer characteristics; for example, a total heat transfer rate or a temperature at a specific location. In the reverse analysis via adjoint formulation, the heat flow is reversed in both time and space. Thus, using the numerical solution of the adjoint problem, we can inversely predict the boundary condition effects on the heat transfer characteristics. As a result, we can obtain the optimal thermal boundary conditions in both time and space to control the heat transfer at any given time. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(3): 161,174, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20002 [source]


Heat transfer research on vapor-gas mixture with condensation in a vertical tube

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 7 2002
L. Jia
Abstract The convection-condensation heat transfer of vapor-gas mixtures in a vertical tube was studied theoretically and experimentally. The effects of the condensation of a small amount of water vapor (8 to 20%) on heat transfer in a vertical tube were discussed. Comparisons show that theoretical solutions obtained through modified film model and experimental results are in good agreement. The results show that the condensation heat transfer of a small amount of water vapor and single-phase convection heat transfer in the vapor-gas mixtures are of the same order of magnitude, and these two modes of heat transfer could not be neglected. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(7): 531,539, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10055 [source]


Numerical simulation of natural convection heat transfer in the open space between two horizontal circular planes

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 6 2001
Hideki Tokanai
Abstract Numerical simulations were conducted for natural convection heat transfer in a narrow gap between two horizontal plates in air. The lower plate is an infinite plate with a circular heating zone. The upper one is the bottom of a vertical cylinder, which is placed right above the circular heated plate and kept at room temperature. A set of Navier,Stokes equations and an energy equation are analyzed for a variety of combinations of gap clearance and Rayleigh number. The calculated average heat transfer values are shown to be in good agreement with the experimentally obtained ones reported in a previous paper. From the obtained isotherms, streamlines, and local Nusselt numbers, it is found that two types of convection appear in the gap space according to the conditions of Rayleigh number and gap clearance: one is a simple convection due to a single renewal flow which replaces heated air with ambient air and the other is a combined convection due to several vortex flows and a renewal flow. Furthermore, the flow rate of each flow controls the rate of heat transfer from the limited area which is covered by each flow. From this fact, the validity of the previously proposed heat transfer correlation is briefly discussed. © 2001 Scripta Technica, Heat Trans Asian Res, 30(6): 485,502, 2001 [source]


Improvement of the basic correlating equations and transition criteria of natural convection heat transfer

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 4 2001
Shi-Ming Yang
Abstract In this paper, improvements in the basic physical laws of natural convection heat transfer were implemented in two major respects by incorporating recent research findings in this field. A preferred transition criterion was adopted in this paper to correlate all of the experimental data. Since transition correlations are primarily flow stability problems, the Grashof number, instead of the Rayleigh number, was found to be the preferred criterion. Furthermore, in the case of natural convection heat transfer from a horizontal cylinder, a series of experimental data in the high-Rayleigh-number regions recently became available. These data made it possible to establish new reliable correlations and also to test the validity of previous correlations. It is concluded that the previous correlation for a horizontal cylinder in high-Rayleigh-number regions was based on unreliable experimental results. The transition correlation for a horizontal cylinder occurred at much higher values of Rayleigh number than the previous recommendation. In the case of natural convection heat transfer from a vertical plate, more accurate property values for air under pressurized conditions are now available. This made it possible to replot the reliable data of Saunders. From this result and the experimental result of Warner and Arpaci, a new set of basic correlations in natural convection heat transfer for laminar, transitional, and turbulent regimes are recommended. These recommendations reflect a better understanding of the basic physical laws in the field of heat convection. © 2001 Scripta Technica, Heat Trans Asian Res, 30(4): 293,300, 2001 [source]


Natural convection heat transfer along a vertical flat plate with a projection in the turbulent region

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2001
Katsuo Komori
Abstract In the present study, the heat transfer coefficients occurring with a projection in the turbulent region of a vertical flat plate were measured experimentally for various projection heights in the range of 0 to 20 mm. The wall temperature and fluid flow fields were also visualized using a liquid crystal sheet and nylon 12 powder, respectively. The average and local Nusselt numbers reach 1.07 to 1.22 and 1.2 to 1.7 times those for pure turbulent natural convection, respectively. The maximum enhancement rates of heat transfer are attained at a position of 2.3 to 3.3 times the projection height from the upper projection surface toward the downstream, and these positions are in good agreement with those of the reattachment of the fluid flow and with centers of dark red regions in the liquid crystal. On the other hand, the heat transfer coefficients in the just upstream and downstream regions of the projection are small compared with those for no projection. By introducing the nondimensional parameter R, the present experimental results are rearranged quantitatively and effectively. © 2001 Scripta Technica, Heat Trans Asian Res, 30(3): 222,233, 2001 [source]


Simulations of flow through fluid/porous layers by a characteristic-based method on unstructured grids

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2001
Baili Zhang
Abstract An upwind characteristic-based finite volume method on unstructured grids is employed for numerical simulation of incompressible laminar flow and forced convection heat transfer in 2D channels containing simultaneously fluid layers and fluid-saturated porous layers. Hydrodynamic and heat transfer results are reported for two configurations: the first one is a backward-facing step channel with a porous block inserted behind the step, and the second one is a partially porous channel with discrete heat sources on the bottom wall. The effects of Darcy numbers on heat transfer augmentation and pressure loss were investigated for low Reynolds laminar flows. The results demonstrate the accuracy and robustness of the numerical scheme proposed, and suggest that partially porous insertion in a channel can significantly improve heat transfer performance with affordable pressure loss. Copyright © 2001 John Wiley & Sons, Ltd. [source]


Effect of pressure and temperature on cluster and particle heat transfer in a pressurized circulating fluidized bed

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 14 2001
B. V. Reddy
Abstract The present work reports the influence of pressure and bed temperature on particle-to-wall heat transfer in a pressurized circulating fluidized bed (PCFB). The particle convection heat transfer plays a dominant role in determining the bed-to-wall heat transfer coefficient. So far, no information is reported on the effect of pressure and bed temperature on particle-to-wall heat transfer in a PCFB in the published literature. The present investigation reports some information in this direction. The effect of system pressure and bed temperature are investigated to study their influence on cluster and particle heat transfer. The particle convection heat transfer coefficient increases with system pressure and bed temperature due to higher cluster thermal conductivity. The increase in particle concentration (suspension density) results in greater cluster solid fraction and also the particle concentration near the wall is enhanced. This results in higher cluster and particle convection heat transfer between the bed and the wall. Higher particle convection heat transfer coefficient results in enhanced heat transfer between the bed and the wall. The results will also help to understand the bed-to-wall heat transfer mechanism in a better way in a PCFB. Copyright © 2001 John Wiley & Sons, Ltd. [source]


DIMENSIONLESS CORRELATIONS FOR CONVECTIVE HEAT TRANSFER IN CANNED PARTICULATE FLUIDS UNDER AXIAL ROTATION PROCESSING

JOURNAL OF FOOD PROCESS ENGINEERING, Issue 2010
MRITUNJAY DWIVEDI
ABSTRACT Dimensionless correlations for estimating heat transfer coefficients (U and hfp) in canned high viscosity Newtonian liquids (with and without particles) were developed using stepwise multiple nonlinear regressions of statistically significant dimensionless groups using tangent as an estimate and Newton as search method. Data on overall heat transfer coefficient U and fluid-to-particle heat transfer coefficients hfpwere obtained for several processing conditions and were analyzed separately for particle and particle-free conditions. In free axial mode, a newly developed form, combining natural and forced convection, provided higher R2 = 0.93. In the absence of particles in end-over-end mode, introducing natural convection term (Gr × Pr), improved R2 from 0.81 to 0.97. Combination of the reel radius, radius of the can and radius of the particles was chosen as characteristics length. PRACTICAL APPLICATIONS Most earlier dimensionless correlations for a canned liquid particulate mixture subjected to free axial mode of agitation are present for either U or hfp individually due to the difficulties in obtaining time,temperature profiles of the liquid and particles simultaneously; however, the time,temperature prediction at the particle center requires appropriate correlations for both U and hfp and cannot be made with only one of these coefficients. Additionally, importance of natural convection in forced convection heat transfer correlations has been demonstrated by developing the U and hfp correlations using the mixed convection approach as the combination of natural and forced convection heat transfer. These developed correlations would help in modeling the time,temperature profiles of a canned particulate mixture and will be helpful in determining the contribution of natural and forced convection heat transfer. These dimensional numbers would give a better understanding of the physical phenomenon and can also be easily used for scale-up purposes. [source]