Begell House Inc.
Journal of Enhanced Heat Transfer
JEH(T)
1065-5131
3
1
1996
Review of Patents in Europe, Japan, and the U.S. (1993-1994)
1-13
10.1615/JEnhHeatTransf.v3.i1.10
Klaus W.
Menze
Air Side Performance of Brazed Aluminum Heat Exchangers
15-28
10.1615/JEnhHeatTransf.v3.i1.20
Yu-Juei
Chang
Energy and Resources Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan
Chi-Chuan
Wang
Nantional Yang Ming Chiao Tung Univ
Extensive experiments on the heat transfer and pressure drop characteristics of brazed aluminum heat exchangers were carried out. In the present study, 27 samples of louvered fin heat exchangers with different geometrical parameters, including tube width, louver length, louver pitch, fin height, and fin pitch were tested in an induced draft open wind tunnel. Results are presented as plots of friction factor, f, and Colburn j factor against Reynolds number based on louver pitch in the range of 100 to 1000. Comparisons between the Sahnoun and Webb model and the present test data are reported and good agreements were found. By introducing “area ratio” parameters, a simpler correlation of the Colburn j factor and friction factor f were obtained. It is shown that 85% of the experimental data of heat transfer and friction data were correlated within ± 10%.
Laminar Mixed Convection Heat Transfer in Externally Finned Pipes
29-42
10.1615/JEnhHeatTransf.v3.i1.30
F.
Moukalled
American University of Beirut, Beirut, Lebanon
M.
Darwish
Faculty of Engineering and Architecture, Mechanical Engineering Department, American University of Beirut, Beirut, Lebanon
Sumanta
Acharya
Mechanical, Materials and Aerospace Engineering Department, Illinois Institute of Technology,
Chicago, IL 60616
The influence of aiding and opposing buoyancy forces on forced convection heat transfer in vertically oriented, externally finned pipes is studied numerically. A periodically varying external heat transfer coefficient is used to model the finned surface. Results are presented in terms of the streamwise variation of the fluid bulk temperature and tube-side Nusselt number, axially-averaged and periodically fully developed Nusselt number values, and axial velocity and temperature profiles. Average Nusselt number correlations for both constant and periodically varying Biot numbers are also presented. Buoyancy induced effects are observed to increase with higher levels of the external heat transfer coefficient (or fin effectiveness) and decrease with increasing inter-fin spacing. A constant spatially averaged Biot number approximation to the periodic variation is found to be satisfactory only in the periodically developed regions of the flow.
An Experimental Study of R-11 and R-12 Film Condensation on Horizontal Integral-Fin Tubes
43-53
10.1615/JEnhHeatTransf.v3.i1.40
I. I.
Gogonin
S. S. Kutateladze Institute of Thermophysics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
Oleg A.
Kabov
Kutateladze Institute of Thermophysics of the Siberian Branch of the Russian Academy of Sciences, 1, Acad. Lavrentyev Ave., Novosibirsk, 630090, Russia; Novosibirsk State University, 2, Pirogova str., Novosibirsk, 630090, Russia; Novosibirsk State Technical University, 20 Prospect K. Marksa, Novosibirsk, 630073, Russia
Experimental results on heat transfer during film condensation of stationary pure vapor refrigerants R-11 and R-12 on a smooth tube and on four tubes with transverse ribs of constant curvature are reported. The tubes were manufactured in such a way that the fins and valleys had circumferences of the same radius. All tubes were made of brass. The effect of surface curvature on heat transfer was studied. The heat transfer coefficient on the finned tubes (based upon the smooth tube surface area having the diameter of the fin root) increased in all cases. The maximum enhancement being obtained with the tube having the smallest fin radius. Experimental data have been compared with the theoretical models of condensation on the curvilinear surfaces. They have also been processed in dimensionless form.
Steam Condensation on Horizontal Integral-Fin Tubes of Low Thermal Conductivity
55-71
10.1615/JEnhHeatTransf.v3.i1.50
M. Hassib
Jaber
UOP, Process Equipment, Tonawanda, NY 14151
Ralph L.
Webb
Department of Mechanical Engineering, The Pennsylvania State University, University Park, PA 16802, USA
This work identifies preferred integral-fin geometries for steam condensation on low conductivity, integral-fin tubes (admiralty, copper-nickel, and titanium). Although much work has been done to measure and predict condensation coefficients for refrigerants on high thermal conductivity copper tubes, very little has been done for the problem of present interest. Because of the low tube thermal conductivity, and condensate retention, it is necessary to solve a conjugate problem with tube side coolant flow. An adaptation of a model previously published by Adamek and Webb is used for the steam side, and the heat transfer to the coolant, accounting for circumferential wall heat conduction is included in the model. The model was validated by predicting 53 data points for steam, R-11 and R-113. Ninety four percent of the data were predicted within ± 15%. A parametric study was performed to determine the effect of fin height, fin spacing, and fin shape on the condensing coefficient for steam condensing at 35°C on the three tube materials. The results show that the enhancement level decreases as the tube thermal conductivity decreases. The predicted enhancement level for admiralty, copper-nickel, and titanium (or stainless steel) increases as the fin height is reduced from 1.0 mm to 0.5 mm. The preferred fin geometry for titanium, copper-nickel, and admiralty tubes is a 0.5 mm fin height, 0.2 mm tip thickness, and 0.9 mm base thickness. A maximum enhancement level is achieved at 512 fins/m (13 fins/m) for admiralty, copper-nickel, and titanium, for 0.5 mm fin height. The economic optimum fins/in is expected to be less than 512 fins/m. This work has resulted in the identification of preferred fin geometries for low thermal conductivity materials, which are different from those commercially available.
Enhancement of Evaporation of a Liquid Droplet using EHD Effect: Criteria for Instability of Gas-Liquid Interface Under Electric Field
73-81
10.1615/JEnhHeatTransf.v3.i1.60
Kiyoshi
Takano
Institute of Industrial Science, University of Tokyo 7-22-1, Roppongi, Minato-ku, Tokyo, 106, JAPAN
Ichiro
Tanasawa
Department of Mechanical Engineering, Nihon University, 1 Tokusada, Tamura-cho, Kooriyama-shi, Fukushima 963-8642, Japan
Shigefumi
Nishio
Key Laboratory of Enhanced Heat Transfe and Energy Conservation, Ministry of Education, School of Chemical and Energy Engineering, South China University of Technology, China; and Institute of Industrial Science and Technology, University of Tokyo, Japan
It was confirmed, in the preceding study, that an evaporation of a liquid droplet on a heated surface was enhanced to a great extent by applying an electric field. Visual observation of the evaporation process indicated that small columns of the liquid were formed underneath the bottom of the droplet, causing direct contact between the liquid and the solid surface. The direct contact underneath the bottom of the droplet was considered to be induced by the interfacial instability due to the electric field. In the present study, an experiment was carried out to clarify the mechanism that an electric field induced the instability of a liquid surface. The static electric voltage was applied between the liquid surface and a horizontal planer electrode placed over the surface. The applied voltage was raised gradually until the liquid surface became unstable. The threshold voltages were measured for different distances between the electrode and the liquid surface and for different liquids. The test liquids used in the experiment were water, ethanol, refrigerant Rl 13, carbon tetrachloride and cyclohexane. The visual observation of the process leading to destabilization of the liquid surfaces was performed using a high-speed video facility. Criteria for the onset of instability were derived analytically using a modified Rayleigh-Taylor instability equation, finding that the theoretical results agreed very well with the experimental data. In addition, the temperature of the heat transfer surface above which the drop evaporation was enhanced was predicted using the result of the instability analysis.