Effect of Pin Density on Heat-Mass Transfer and Fluid Flow at Low Reynolds Numbers in Minichannels

Previous investigations on the performance of straight pins, pins with tip clearance, and profiled fins showed that closely packed cylindrical pin fins are very competitive with the modified pins. Therefore, the objective of this paper is to investigate the effect of pin density on performance. Steady/time-dependent calculations are performed to investigate the effect of pin density on friction and heat transfer. Pins packed at distances of $SD=1.1$⁠, 1.2, 1.3, 1.4, 1.5, 2.0, 2.5, and 3 pin diameters $(D)$ are investigated for $10≤ReD≤600$⁠. Two performance measures are used to compare the different pin fin densities. The first measure is to maximize heat transfer capacity for a given pumping power compared with a plane channel. The second measure used is based on entropy generation minimization (EGM), where the objective is to reduce the total irreversibility of the pin fin array to obtain an optimal spacing. Based on the performance measure of maximizing heat capacity, it is shown that for plain channels operating in the laminar range using denser pin packing has distinct advantages with $SD=1.1$ providing the best augmentation. However, the augmentation in heat capacity becomes relatively independent of the pin density for a channel operating in the turbulent regime. Based on the EGM method, at $ReD>200$⁠, $SD=1.3$⁠, 1.4, and 1.5 are the most suitable, with the least entropy generation observed at $SD=1.4$⁠. At $ReD<200$⁠, $SD=1.1$⁠, 1.2, and 1.3 are also suitable for keeping entropy generation low.