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Abstract: The heat transfer performances of the fin array with shield in the bypass had been experimentally investigated. The variations of the mean Nusselt number and friction factor were obtained under varied parameters, such as the heated power input, the Reynolds number, the position and height of the shield. The optimum position and height of shield were analyzed under the identical pressure drop and the identical pumping power criteria. Experimental results indicated that the heat transfer and flow performances of fin array were marginally influenced by the power input. As the presence of the shield, the heat transfer of fin array was enhanced and the flow resistance increased. The heat transfer coefficient increased as the dimensionless shield position decreased and the shield height increased. The friction factor increased with the dimensionless position and height of shield. Evaluated under the identical pressure drop and the identical pumping power criteria, the optimum position of shield was the position where the dimensionless shield position equaled 0, and the optimum shield height was half of the fin height. Finally, the correlations of mean Nusselt number and friction factor were fitted considering the influences of Reynolds number, the shield position and the shield height. The predicted values fitted the experimental data with the deviations less than ±15.0%. [Copyright &y& Elsevier]

· Shield is a feasible way to improve the bypass effect and enhance the heat transfer of heat sink. · Experimental and numerical studies of fin array with wedge shield installed in the top bypass are proposed. · Shield inclination angle has a significant effect on the thermal and hydraulic performance. · The maximum enhancement of heat transfer is about 12% and 16% under identical pressure drop and pumping power. In this study, the thermal and hydraulic performances of fin array with a wedge shield installed in the bypass to alter the flow were experimentally and numerically investigated. The effect of the wedge shield inclination angle was explored at Reynolds numbers ranging from 2753 to 20,825. The mean Nusselt number and friction factor were measured in a wind tunnel with the varying volume rate of inlet air flow. The comprehensive performance evaluation criteria under identical pressure drop and identical pumping power were adopted to evaluate the effect of the wedge shield. The velocity, temperature and pressure fields, and the local Nusselt number were characterized using ANSYS Fluent. The results indicated that the heat transfer enhanced and the flow resistance increased by the wedge shield effect. At a same Reynolds number, the mean Nusselt number and friction factor reach their maximum values at θ S = 10 ∘ and θ S = 60 ∘ , respectively. According to the comprehensive performance evaluation, the applicable condition of wedge shield to enhance fin array performance was the inclination angle θ S = 135 ∘ at Reynolds number Re =3286, in which the enhancement was approximately 9% under identical pressure drop and 14% under identical pumping power. The numerical results showed that the velocity increase in fin channel and recirculation zone, caused by the blockage of the wedge shield, was the fundamental mechanism of wedge shield to enhance the heat transfer and increase the flow resistance. The velocity increase and recirculation zone, along with the low temperature region and high pressure in the entrance region of the fin channel caused by them, were all affected by the wedge shield inclination angle. [ABSTRACT FROM AUTHOR]

Abstract: Condensation heat transfer of sonic steam jet in subcooled water was investigated experimentally over a wide range of steam mass flux and water temperature. Four different steam plume shapes were observed in present test conditions, and condensation regime map was given based on steam mass flux and water temperature. Maximum expansion ratio and dimensionless penetration length of the steam jet were also obtained in the ranges of 1.04–2.20 and 2.86–14.60, respectively. Then the semi-empirical correlations were given to predict the expansion ratio and penetration length, the results showed good agreement between the predictions and experiments. Moreover, temperature fields in the steam plume and surrounding water were measured. Axial temperature distributions represented the four typical steam plumes, and variation of the axial temperature confirmed existence of expansion and compression waves. Finally, surface renewal model was adopted to predict condensation heat transfer coefficients, which were in the range of 0.98–1.45MW/m2 K and mainly dependent on the physical property and steam plume shape, including expansion angle, expansion ratio and penetration length. [Copyright &y& Elsevier]