Begell House Inc.
Journal of Enhanced Heat Transfer
JEH(T)
1065-5131
9
1
2002
An Experimental Study of Convective Boiling in a Compact Serrated Plate-Fin Heat Exchanger
1-15
Barbara
Watel
CEA-Grenoble/DTP/GRETH, Grenoble, France
Bernard
Thonon
GRETh/CEA-Grenoble 17 rue des Martyrs 38054 Grenoble Cedex 9 France
The experimental apparatus used to study boiling of a pure refrigerant (propane) during a vertical upflow inside a compact serrated plate-fin exchanger is presented in this paper. The experimental conditions perfectly reflect those occurring in industrial applications. The maximal heat rate exchanged between both fluids is equal to 70 kW. The propane evaporates in the exchanger and the outlet vapour quality is between 0.15 and 0.9. Tests are carried out with propane mass fluxes between 12 and 71 kg m−2s−1 for pressures between 0.46 and 1.17 MPa. From the measurements carried out on the loop, the data processing allows us to deduce the propane local boiling heat transfer coefficients. An analysis of the measured convective boiling heat transfer coefficients, without nucleate boiling, shows the separate effects of quality, mass flux, and pressure. The trends observed have been identified as characteristic of slug flow. They are very different from those of the annular flow regime.
Heat Transfer and Pressure Drop During Evaporation and Condensation of HCFC22 in Horizontal Copper Tubes with Many Inner Fins
25-37
Seiichi
Ishikawa
Research and Development Center, Mitsubishi Shindoh Co., Ltd., Fukushima, Japan
Kotaro
Nagahara
Research and Development Center, Mitsubishi Shindoh Co., Ltd., Fukushima, Japan
Shunroku
Sukumoda
Research and Development Center, Mitsubishi Shindoh Co., Ltd., Fukushima, Japan
Experimental tests using R22 were conducted to measure the condensation coefficient and the vaporization coefficient inside a given microfin tube (Wolverine DX-75). Data were also taken for nucleate pool boiling on a plain surface and on the microfin surface. A key objective of the present work is to define the contribution made by nucleate boiling to the microfin tube evaporation performance. An asymptotic model is used to combine the nucleate boiling and convective terms to account for both contributions. This was done using the experimental condensation and nucleate boiling curves. The convective contribution for vaporization is the same as for convective condensation below 70% and also below the dryout point. The tests show that nucleate boiling makes a significant contribution to vaporization for vaporization of R22 in a microfin tube.
Heat Transfer Mechanisms for Condensation and Vaporization Inside a Microfin Tube
25-37
Davide
Del Col
University of Padova, Department of Industrial Engineering, Via Venezia 1, 35131 Padova, Italy
Ralph L.
Webb
Department of Mechanical Engineering The Pennsylvania State University, University Park, PA 16802, USA
Ram
Narayanamurthy
Wolverine Tube Inc., Decatur, Alabama, USA
Experimental tests using R22 were conducted to measure the condensation coefficient and the vaporization coefficient inside a given microfin tube (Wolverine DX-75). Data were also taken for nucleate pool boiling on a plain surface and on the microfin surface. A key objective of the present work is to define the contribution made by nucleate boiling to the microfin tube evaporation performance. An asymptotic model is used to combine the nucleate boiling and convective terms to account for both contributions. This was done using the experimental condensation and nucleate boiling curves. The convective contribution for vaporization is the same as for convective condensation below 70% and also below the dryout point. The tests show that nucleate boiling makes a significant contribution to vaporization for vaporization of R22 in a microfin tube.
The Specific Heat at Constant Pressure in the Latent Functional Fluid with Microencapsulated Phase-Change Materials
39-46
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
The specific heat at constant pressure is an important thermo-physical parameter in the latent functional fluid with microencapsulated phase-change materials. It expresses the special function of the functional fluid. However, a uniform and correct formula to calculate the specific heat has been lacking. In this paper, on the basis of the theorem of thermodynamics and two-phase flow, the relation between the specific heat of the mixture and every phase, and the latent heat, the volume fraction, the mass fraction of every phase, and other thermophysical parameters is theoretically deduced by a thermodynamic derivative method. The effect of different physical parameters on the specific heat of the mixture is further discussed.
Heat Transfer Enhancement by Turbulent Impinging Jets Using a Universal Function Method
47-55
M.
Kumagai
Department of Mechanical Engineering, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, USA
Michael K.
Jensen
Center for Multiphase Flow, Rensselaer Polytechnic Institute, Troy, NY, USA; University of Wisconsin-Milwaukee, Mechanical Engineering Department Milwaukee, Wisconsin 53201
A numerical and experimental investigation on cooling of a solid surface was performed by studying the behavior of an impinging jet onto a fixed flat target. The local heat transfer coefficient distributions on a plate with a constant heat flux were computationally investigated with a normally impinging axisymmetric jet for nozzle diameter of 4.6 mm at H/d = 4 and 10, with the Reynolds numbers of 10,000 and 40,000. The two-dimensional cylindrical Navier-Stokes equations were solved using a two-equation k-ε turbulence model. The finite-volume differencing scheme was used to solve the thermal and flow fields. The predicted heat transfer coefficients were compared with experimental measurements. A universal function based on the wave equation was developed and applied to the heat transfer model to improve calculated local heat transfer coefficients for short nozzle-to-plate distance (H/d = 4). The differences between H/d = 4 and 10 due to the correlation among heat transfer coefficient, kinetic energy, and pressure were investigated for the impingement region. Predictions by the present model show good agreement with the experimental data.