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Abstract: The electrohydrodynamic effect to natural convection inside the vertical channels is numerically investigated by computational fluid dynamics technique. The range of parameters considered are 104 = Ra =107, 7.5= V 0 =17.5 kV, and 2=aspect ratio=10. Flow and temperature distributions are affected with supplied voltage at the wire electrodes, and the heat transfer enhancement is significantly influenced at low Rayleigh number. The augmented volume flow rate of fluid is indicated in relation with the number of electrodes. Moreover, heat transfer enhancement also depended on the electrode arrangement while the number of electrodes is initially fixed. The relation between channel aspect ratio and number of electrodes that performs the maximum heat transfer is expressed incorporating with the optimum concerning parameters. [Copyright &y& Elsevier]

Abstract: This study is to experimentally investigate the heat transfer enhancement by delta winglet vortex generators in air cooling of a staggered array of rectangular electronic modules. The winglet vortex generators are placed in front of 3×5 modules with 20° attack angle. Each module has dimensions of 1.8×5.4×0.6mm and each one generates heat at 2.5W. The adiabatic heat transfer coefficients, the thermal wake functions including their correlations for the modules with and without the vortex generators are considered at different values of Reynolds number and the module density. It could be seen that the vortex generators could enhance the adiabatic heat transfer coefficients, reduce the thermal wake functions and the module temperatures significantly. The module temperatures predicted by the superposition of the convective effect due to the module heat generations and the module thermal wakes are fitted very well with the measured data. [Copyright &y& Elsevier]

Abstract: Heat transfer enhancement with electrohydrodynamic (EHD) technique in laminar forced convection inside a wavy channel with different wire electrode arrangements is numerically investigated. The electric field is generated by the wire electrodes charged with DC high voltage. The mathematical modeling includes the interactions among electric field, flow field, and temperature field. The simulation is firstly conducted with the experimental data in case of rectangular flat channel and the results agree very well. Then the modeling is carried out in the case of wavy channel. It is found that the heat transfer coefficient with the presence of electric field increases with the supplied voltage but decreases when the Reynolds number and the distance between the wire electrodes and the wall surface are augmented. The heat transfer enhancement is also dependent on the number of the wire electrodes, the number of wave per length, and the wave aspect ratio. [Copyright &y& Elsevier]

Abstract: A total of 23 cross-flow heat exchangers having crimped spiral configurations is studied. The effect of tube diameter, fin spacing, transverse tube pitch, and tube arrangements are examined. For the inline arrangement, the pressure drop increases with the rise of tube diameter but the associated heat transfer coefficient decreases with it. The increase of fin height also gives rise to considerable increase of pressure drop and decrease of heat transfer coefficients for the inline arrangement. However, for the staggered arrangement, the effect of the fin height on the pressure drop is much smaller than that of the inline arrangement due to the major contribution to the total pressure drops from the blockage of the airflow from staggered arrangement. Effect of the fin spacing on the air side performance is strongly related to the transverse tube pitch for both inline and staggered arrangements. Correlations of the present crimped spiral fins in both staggered and inline arrangements are developed. The proposed correlations give fairly good predictive ability against the present test data. [Copyright &y& Elsevier]

Abstract: This research studies the heat transfer characteristic during ice formation of a direct contact heat transfer between carbon dioxide and water mixture. This research is divided into two parts. For the first part, the low temperature carbon dioxide, between −15 and −60 °C, is injected into water initially at 28 °C and exchanges heat directly. The flow rate of carbon dioxide is varied between 0.003 and 0.017 kg/s while the volume of water is between 1 and 3 L. From the experiment, it is found that the effectiveness of the direct contact heat transfer between the carbon dioxide and the water is closed to 100%. Moreover, the lumped model is found to be used for predicting the temperature of water and the mass of ice formation quite well. However, for this technique, the blockage of ice around the injector always occurs. To avoid this problem, slurry ice is considered instead of pure ice. In the second part of this work, the thermal behavior of the slurry ice by direct contact heat transfer technique between carbon dioxide and water mixture is investigated. Compressor oil and Tween 60 are mixed with water for making slurry ice and it is found that the suitable composition is water/oil/Tween 60 at 100/6/1 by volume. Again, the lumped model can be used for predicting the temperature of water mixture and the mass of slurry ice quite well. [Copyright &y& Elsevier]