Heat-Mass Transfer and Friction Characteristics of Profiled Pins at Low Reynolds Numbers in Minichannels

Abstract

Three pin fin array geometries (T60, T90, and T120) are investigated at low Reynolds numbers, Re _D  < 350, in a channel. The number in T60, T90, and T120 denotes the angle made by the pin surface with the end wall. Results show that the T120 pin is the most effective in facilitating momentum transport along the height of the pin and mitigates the undesired effect of low momentum and recirculating wakes. Additionally, pin T120 causes localized flow acceleration between pins near the end wall, which results in high heat transfer coefficients at the end wall. Overall, T120 has the highest heat transfer (augmentation ratio 2.9 at Re _D  = 325), without any increase in friction factor (augmentation ratio 8.3 at Re _D  = 325) from the baseline configuration of T90. However, T120 results in a large reduction in end-wall surface area, which reduces overall conductance, and in this respect T60 is superior in the range Re _D  < 150. A performance study of conductance under the constraint of the same pumping power in an equivalent plane channel shows that the profiled geometries T60 and T120 augment conductance between 40% and 250% over an equivalent channel.

Notes

¹As an example, for air as the working fluid, the Richardson number (Ri) = Gr/Re _D ² < 0.1. Similarly, the Boltzmann number (B_o), which is the ratio of heat carried by forced convection to radiative transfer, is of O(100).

²The notation is used to denote the ith component of vector .

³It is noted that 1/(θ _w  − θ _ref) is indicative of the local Nusselt number.