Begell House Inc.
Journal of Enhanced Heat Transfer
JEH(T)
1065-5131
7
5
2000
Flow Condensation in Smooth and Micro-fin Tubes with HCFC-22, HFC-134a and HFC-410A Refrigerants. Part I: Experimental Results
289-310
10.1615/JEnhHeatTransf.v7.i5.10
Liangyou
Tang
Outokumpu Copper Franklin, Inc., 4720 Bowling Green Road, Franklin, KY 42134
Michael M.
Ohadi
Small and Smart Thermal Systems Laboratory, Center for Energy Environmental Engineering, Department of Mechanical Engineering, University of Maryland, College Park, Maryland 20742, USA
Arthur T.
Johnson
Department of Biological Resources Engineering, University of Maryland, College Park, MD 20742
A study of single-phase convection and flow condensation heat transfer in horizontal copper tubes (8.81 mm inside diameter) was conducted using three refrigerants (HCFC-22, HFC-134a and HFC-410A). A smooth tube and three micro-fin tubes (axial, helical and Crosshatch enhancement) were examined. Local-mean flow condensation data were experimentally obtained. Experimental conditions were selected to reflect typical operating conditions encountered in refrigeration and air-conditioning applications. All micro-fin tubes illustrated significant enhancement in single-phase convection and flow condensation. The cross-hatch enhancement performed particularly better in both single-phase convection and flow condensation. For the three refrigerants investigated, the refrigerant type seemed to have little influence on the enhancement mechanism of the micro-fin tubes examined. The experimental results are presented in Part I. Development of design equations is presented in Part II.
Flow Condensation in Smooth and Micro-fin Tubes with HCFC-22, HFC-134a and HFC-410 Refrigerants. Part II: Design Equations
311-325
10.1615/JEnhHeatTransf.v7.i5.20
Liangyou
Tang
Outokumpu Copper Franklin, Inc., 4720 Bowling Green Road, Franklin, KY 42134
Michael M.
Ohadi
Small and Smart Thermal Systems Laboratory, Center for Energy Environmental Engineering, Department of Mechanical Engineering, University of Maryland, College Park, Maryland 20742, USA
Arthur T.
Johnson
Department of Biological Resources Engineering, University of Maryland, College Park, MD 20742
An empirical study of single-phase convection and flow condensation heat transfer in horizontal tubes was conducted. Three refrigerants (HCFC-22, HFC-134a and HFC-410A), a smooth tube, and three micro-fin tubes (axial, helical and Crosshatch enhancement) were examined. Commonly cited correlations were evaluated, utilizing the experimental data obtained in Part I of this study. Although these correlations had fairly good agreement with HCFC-22 and HFC-134 results, all of them failed to predict HFC-410A performance. A modified Shah equation was developed for smooth tube annular flow condensation, which overcomes the shortcomings of the existing correlations. Furthermore, design equations were developed for single-phase heat transfer and two-phase condensation with all three micro-fin tubes investigated, and covering all three refrigerants tested.
Heat Transfer Enhancement and Pressure Drop in the Flow Boiling Field with the Bubble Movement Restricted by a Screen Sheet
327-331
10.1615/JEnhHeatTransf.v7.i5.30
Morifumi
Tashiro
National Institute for Resources and Environment, 16-3 Onogawa, Tsukuba, 305-8569 Ibaraki, Japan
Katsushiko
Kadoguchi
National Institute for Resources and Environment, 16-3 Onogawa, Tsukuba, 305-8569 Ibaraki, Japan
A unique method, which was previously proposed by the authors in the pool boiling case, was experimentally investigated under flow boiling conditions. A screen sheet was used in this method. It was set parallel to the horizontal heated wall with a very small separation. When nucleate boiling occurred on the wall, the vapor bubbles generated were trapped by the screen and became flat. Then they moved downstream along the heated surface in the gap between the screen and the wall. This movement caused the heat transfer augmentation. Although the pressure drop was increased considerably, the results showed that the heat transfer enhancement seen in pool boiling also occurred under the flow boiling situation within the present experimental range.
Technology Review - A Survey of Recent Patents of Fin-and-Tube Heat Exchangers
333-345
10.1615/JEnhHeatTransf.v7.i5.40
Chi-Chuan
Wang
Nantional Yang Ming Chiao Tung Univ
This study presents updated information about patents of the fin-and-tube heat exchangers during 1981 ∼ 1999. A total of 51 patents were examined and compared. Fin patterns like convex-louver, enhanced wavy, enhanced slit, enhanced louver, vortex generators, and several special fin patterns are reported in the present report. It is recommended that further detailed examinations via numerical simulation or experimental investigation be carried out in the future to gain further insight of these fin designs.
Compound Augmentation of Pool Boiling on Three Selected Commercial Tubes
347-360
10.1615/JEnhHeatTransf.v7.i5.50
J.
Darabi
Center for Environmental Energy Engineering, Department of Mechanical Engineering, University of Maryland, College Park, MD 20742-3035, USA
Michael M.
Ohadi
Small and Smart Thermal Systems Laboratory, Center for Energy Environmental Engineering, Department of Mechanical Engineering, University of Maryland, College Park, Maryland 20742, USA
Serguei V.
Dessiatoun
Department of Mechanical Engineering, University of Maryland, College Park, Maryland, USA
This paper will present results of an experimental study in which the Electrohydrodynamic (EHD) technique was utilized to provide compound enhancement of pool boiling heat transfer on three commercially available tubes. The tubes tested were: a low-fin 19 fins per inch, a modified high-fin 52 fins per inch, and a mechanically formed re-entrant cavity type. All tubes tested had a length of 63.5 mm (2.5″) and an outer diameter of 19 mm (3/4″). Five different electrode designs were tested, each over a predetermined heat flux and saturation temperature. The enhanced boiling mechanism in each case and a comparison of results for the three tubes are described. It was found that for the electrodes and heat fluxes tested, the specially designed (modified) high-fin tube yielded the highest enhancement amongst the three, with a nearly three-fold increase in the heat transfer coefficient. In the worst case, the EHD power consumption was less than 0.4% of the total heat transfer rate in the test section.