Experimental investigation of flow condensation characteristics in a mini channel with micro pin fin

Abstract

A flow condensation experiment was performed in a 300 mm long mini channel with a diamond pin fin array. The working fluid is R134a and four pin fin arrays were tested, including different channel widths of 1.0, 1.2, and 1.4 mm, as well as fin angles of 60°and 90°. The experimental system used in previous studies was adopted to obtain the local heat transfer coefficient. The measurements were done within the saturation pressure range of 600–1500 kPa with mass flux ranging from 160 to 450 kg/m²s. The experimental results indicated that the local heat transfer coefficient increases with an increase in vapor quality, mass flux, and heat flux whereas it decreases with an increase in saturation pressure. The influence of heat flux and pin fin array structure on heat transfer coefficient was more significant in the high vapor quality region relative to that of the low vapor quality region. Higher fin density and larger fin angles contribute to improved condensation. With a diamond fin angle of 60°, the heat transfer coefficient of the pin fin array with a fin density of 0.22 is 24 %∼56 % higher than that of the pin fin array with a fin density of 0.16. For the pin fin array with the same fin density, the heat transfer coefficient at fin angle 90° is 1.1–1.4 times that at fin angle 60°.Additionally, the performance evaluation criteria named Penalty Factor was applied to evaluate the performance of the pin fin array, and SG60_3 outperforms the other channel, corresponding to a fin angle of 60° and channel widths of 1.4 mm. The Penalty Factor value of SG60_3 is 70 %∼80 % of that of the other three pin fin array. The existing correlations fail to give a reasonable prediction for the heat transfer coefficient of the present experimental data. Therefore, a new correlation accounting for the effects of geometric sizes of pin fin array and heat flux was developed with the maximum mean absolute deviation of 7.48 % on four test channels. The present study can provide valuable knowledge on the design optimization of mini channel condensers with pin fin array.