Begell House
Journal of Enhanced Heat Transfer
Journal of Enhanced Heat Transfer
1065-5131
10
3
2003
Numerical Investigation of Impingement Cooling in Ribbed Ducts Due to Jet Arrays
A numerical investigation of impingement heat transfer and fluid flow in a rectangular two-pass duct was carried out. The impingement wall was smooth or with periodically mounted square ribs. A multiblock parallel CFD code was employed for the calculation. The turbulence modeling was treated by applying a low Reynolds number turbulence eddy viscosity model (LEVM) and a V2F model. First, the calculations were validated against available experimental data in a two-pass duct where the impingement wall was smooth. Then, jets impinging on ribbed walls were simulated. The distance from the nozzle to the impingement wall was fixed at four nozzle diameters (d). The square rib width was set as 0.5 d. The duct inlet Reynolds number was fixed at 10,000. Results show that the presence of ribs was favorable for the heat transfer enhancement on the impingement wall, but not for the side wall.
Masoud
Rokni
Division of Heat Transfer, Lund Institute of Technology, P.O. Box-118, 22100 Lund, Sweden
Rongguang
Jia
Division of Heat Transfer, Lund Institute of Technology, P.O. Box-118, 22100 Lund, Sweden
Bengt
Sunden
Division of Heat Transfer, Department of Energy Sciences, Lund University, Box 118, Lund, SE-22100, Sweden
243-256
Fuel Cell Performance Augmentation: Mass Transfer Enhancement
A comprehensive three-dimentional fuel cell model is used to study proton exchange memberane (PEM) fuel cell performance augmentation resulting from mass transfer enhancement with an interdigitated flow field design. The mass transfer enhancement of the interdigitated flow field is first studied by comparing the oxygen mole fraction distributions at different overpotentials with those of conventional flow field. Comparisons of fuel cell performances with the two types of flow fields are made by comparing the polarization curves as well as the current density distributions under the same operating conditions. Further modeling study is carried out to investigate the effects of gas channel width, gas diffusion layer (GDL) thickness, and GDL porosity of the interdigitated flow field. The modeling results show that the PEM fuel cell with interdigitated flow field outperforms that with conventional flow field, and this is due to the mass transfer enhancement of forced convection through the GDL. This study concentrates on the performance of the fuel cell only, thus the additional pressure-drop penalty of the interdigitated flow field is not considered.
Hongtan
Liu
University of Miami, Department of Mechanical Engineering, Coral Gables, FL 33124
Tianhong
Zhou
University of Miami, Department of Mechanical Engineering, Coral Gables, FL 33124
257-274
Scaling of Heat Transfer Characteristics in an Oscillating Flow
Oscillating-flow heat transfer is an essential factor for the design of stacks, heat exchangers, and regenerators of acoustic refrigerators. Aiming to have a design basis for such components, experimental and analytical investigations have been conducted into the heat transfer characteristics in an incompressible oscillating flow in a tube. The modes of heat transfer are classified into laminar and turbulent flow heat transfers. The boundary between these modes is closely related to the laminar-to-turbulent transition of flow. The space-cycle averaged heat transfer coefficients are well correlated with Nusselt, Reynolds, Prandtl, and Strouhal numbers.
Mamoru
Ozawa
Department of Safety Science, Kansai University, 7-1 Hakubai-cho, Takatsuki-shi, Osaka 569-1098, Japan
Masatoshi
Shinoki
Department of Mechanical Engineering, Kansai University, Yamate-cho 3-3-35, Suita, Osaka 564-8680, Japan
Kenji
Nagoshi
Department of Mechanical Engineering, Kansai University, Yamate-cho 3-3-35, Suita, Osaka 564-8680, Japan
Eriko
Serizawa
Department of Mechanical Engineering, Kansai University, Yamate-cho 3-3-35, Suita, Osaka 564-8680, Japan
275-286
The Effects of Gap Position in Discrete Ribs on Local Heat/Mass Transfer in a Square Duct
Local heat/mass transfer measurements are conducted to investigate the effects of rib arrangements and gap positions on the discrete rib. The combined effects of the gap flows of the discrete ribs and secondary flows are examined in order to promote uniformity of heat/mass transfer distributions, as well as to augment heat/mass transfer. A square channel with rectangular ribs is used for the stationary duct test. The rib-to-rib pitch to the rib height ratio is 8, and the rib attack angle is 60°. The gap width is the same as the rib width, and two gap positions, which are upstream and downstream gaps, are examined with parallel and cross rib arrangements. A naphthalene sublimation method is used to measure local heat/mass transfer coefficients. With the angled discrete ribs, the heat transfer on the surface is enhanced and the uniformity of the heat transfer coefficients is promoted because the gap flow promotes local turbulence and flow mixing near the ribbed surface, while the rib-induced secondary flow is maintained in a duct. The discrete rib arrangements with downstream gaps show better cooling performance than continuous rib or discrete rib arrangements with upstream gaps.
Hyung-Hee
Cho
School of Mechanical Engineering, Yonsei University, Seoul 120 749, South Korea
Y. Y.
Kim
Department of Mechanical Engineering, Yonsei University, Seoul 120-749, Korea
Dong-Ho
Rhee
Korea Aerospace Research Institute Daejeon, 305-333, Korea
S. Y.
Lee
Department of Mechanical Engineering, Yonsei University, Seoul 120-749, Korea
S. J.
Wu
Department of Mechanical Engineering, Yonsei University, Seoul 120-749, Korea
C. K.
Choi
Department of Mechanical Engineering, Seoul National University, Seoul 120-749, Korea
287-300
Heat Transfer Enhancement Using Turbulent Promoters for Drag-Reducing Surfactant Aqueous Solution Flow
Both enhancement of heat transfer and the reduction of pressure loss are important in order to achieve high-performance heat exchangers. In this article, characteristics of fluid flow and heat transfer of a drag-reducing dilute cationic surfactant solution in a channel and a tube are investigated to realize a high heat exchanger. It is attainable for the reduction of the turbulent frictional drag by dilute polymeric and surfactant aqueous solutions. However, many investigations, which are of full drag-reducing flow without disturbance, have shown that heat transfer is reduced simultaneously. In order to recover the reduced heat transfer, the effect of some turbulent promoters and a row of delta-winglets that generate the longitudinal vortices was tested in a two-dimensional channel. Furthermore, an examination of the relation between heat transport and momentum was carried out; it was found that the critical velocity corresponding to the critical Reynolds number at which the drag-reduction effect reaches a maximum value solely depends on the concentration of the surfactant solution.
Kimitoshi
Sato
Department of Mechanical Engineering and Intelligent Systems, University of Electro-Communications, 182-8585 Tokyo, Japan
Rencai
Chu
Komatsu Ltd., 1200 Manda, Hiratsuka, Kanagawa 254-8567, Japan
Masaya
Kumada
Department of Mechanical Engineering, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan
301-310
Numerical Analysis of Laminar Forced Convection Heat Transfer in Microencapsulated Phase Change Material Suspensions
In this article, a new numerical model of laminar forced convection heat transfer in microencapsulated phase change material suspensions is developed. By combining the finite difference method (FDM) with the dual reciprocity boundary element method (DRBEM), a numerical simulation for the process of heat transfer in microencapsulated phase change material suspensions in a circular tube with constant wall heat flux is presented. The effects of the specific heat at constant pressure are examined on the basis of the newly developed formulation. The numerical results are in reasonable agreement with the experimental data by Goel et al. [1994]. Some new understandings of the mechanism of enhanced heat transfer in the suspensions are obtained and are of significance for the design of latent functionally thermal fluids.
Wen-Qiang
Lu
Division of Thermal Science, Department of Physics, The Graduate School of the Chinese Academy of Sciences, Beijing, People's Republic of China
Fengwu
Bai
Division of Thermal Science, Department of Physics, The Graduate School of the Chinese Academy of Sciences, Beijing, People's Republic of China
311-322
Efficiency of Fins Used in a Finned Oval Tube Heat Exchanger
The fin efficiency of a finned oval tube heat exchanger is usually calculated by first converting the oval tube to an equivalent round tube and then using the Schmidt fin efficiency technique. There are two ways of selecting the equivalent round tube: one is to make the perimeter of the equivalent round tube equal to that of the oval tube; and the other is to make the area of the equivalent round tube equal to that of the oval tube. The present research uses the sector method to calculate the fin efficiency of finned oval tube exchangers. The fin efficiencies obtained from the equal-perimeter and equal-area methods were compared with those calculated from the sector method. The equal-perimeter method yields a higher fin efficiency, whereas the equal-area method gives a lower fin efficiency compared to the sector method. To make the Schmidt equation applicable to the oval tube case, correlations for determining the radius of the equivalent round tube were developed based on the results generated by the sector method. Correlations are provided for both staggered and in-line arrays of oval tubes. By combining the radius correlation with the Schmidt equation, one can readily determine the fin efficiency of a finned oval tube exchanger with accuracy comparable to that of the sector method.
Jingchun
Min
Tsinghua University
Tao
Tao
Department of Thermal Engineering, Tsinghua University, Beijing 100084, China
Xiao-Feng
Peng
Laboratory of Phase Change and Interfacial Transport Phenomena, Department of Thermal Engineering, Tsinghua University, Beijing 100084
323-334
Condensation Heat Transfer and Pressure Drop Measurements in Miniature Horizontal Tubes with Low Mass Flux Rates
Both a flow visualization experiment and measurements of heat transfer and pressure drop were conducted for water undergoing complete condensation in a family of horizontal tubes with diameters from 1.7 to 4 mm. The flow visualization experiment reveals a skewed annular liquid film over nearly the entire condensation length. Average heat transfer coefficients were calculated for tubes of 1.7, 2.5, 3.2, and 4.0 mm diameter, over a range of mass fluxes from 10 to 25 kg/m2s, at saturation temperatures of 60, 70, 80, and 90 °C. At a fixed mass flux, results for complete condensation show the average heat transfer coefficient decreases and pressure drop increases with increasing condensation length. For the same mass flux and at comparable condensation lengths, the average heat transfer coefficient and pressure drop increase with decreasing tube diameter. The effects of saturation temperature and mass flux are shown for each of the four tube diameters tested.
E.
Begg
Department of Mechanical Engineering, University of Connecticut, 191 Auditorium Rd., Unit 3139, Storrs CT 06269-3139, USA
Brian M.
Holley
United Technologies Research Center 411 Silver Lane, M/S 129-89 East Hartford, CT 06108, USA
Amir
Faghri
College of Engineering, Department of Mechanical Engineering, University of Connecticut, 191 Auditorium Rd., Unit 3139, Storrs CT 06269-3139, USA
335-354