Effect of fin pitch on the filmwise condensation of steam on three-dimensional conical pin fin arrays: A comparative study

Abstract

An experimental investigation on the use of three-dimensional conical pin fins to enhance filmwise condensation of steam on vertical plates was carried out. Nine surfaces with conical pin fin arrays were fabricated by Selective Laser Melting and tested in a condensation chamber. The conical pin fin arrays have the same fin base diameter but are of different fin heights and fin pitches. The effects of fin pitch on the condensation heat transfer performance of the conical pin fin arrays were examined. A detailed comparative study was also carried out to evaluate the thermal performances of the conical, sinusoidal and cylindrical pin fin arrays fabricated by Selective Laser Melting. Based on our investigation, it was determined that the condensation heat flux and heat transfer coefficient of the conical pin fin specimens increase as the fin pitch increases from 1.25 mm to 1.67 mm. However, with a further increase in the fin pitch from 1.67 mm to 2.50 mm, reductions in the heat flux and heat transfer coefficient were recorded. The highest thermal enhancement factor of 2.46 was achieved with the conical pin fin specimen of 1.28 mm fin height and 1.67 mm fin pitch. Visualization studies of the static condensate retention height show that the change in fin pitch has more significant effect on the condensation retention height as compared to the change in fin height. A fin analysis was performed to determine the average heat transfer coefficients of the conical pin fins. In addition, a thermal enhancement-to-area enhancement ratio was also proposed to evaluate the condensation performances of conical pin fin arrays. Our results show that significantly higher average heat transfer coefficients and thermal enhancement-to-area enhancement ratios were obtained by the conical pin fin surfaces as compared to the sinusoidal and cylindrical pin fins. Due to the significant surface tension effect and reduced condensate flooding, the conical pin fin structure is shown to be the best geometry for enhancing natural convection condensation heat transfer as compared to the sinusoidal and cylindrical pin fins.