UNSTEADY FLOW AND HEAT TRANSFER IN PARALLEL-PLATE HEAT EXCHANGERS WITH IN-LINE AND STAGGERED ARRAYS OF POSTS

Abstract

A numerical study has been carried out to analyze the unsteady three-dimensional flow and conjugate heat transfer in a channel with in-line and staggered arrays of periodically mounted square posts. The simulations have been carried out for Reynolds numbers in the range 150–600 (based on the post width and the average velocity), and a Prandtl number of 6.99 (corresponding to water). The flow is found to be unsteady at a critical Reynolds number around 400 for the in-line case, while it is unsteady at Re = 150 (the lowest Reynolds number studied) for the staggered case. The unsteady flow shows quasi-periodic behavior with multiple frequencies (having different dominant shedding frequencies). For the in-line configuration, the heat transfer enhancement is small when the flow is steady (2.28–2.88 relative to a plane channel flow for Re ≤ 250), but it is significant when the flow is unsteady (17 times that for a plane channel flow for Re = 600). The staggered case shows significant enhancement at all Reynolds number (19–66), but with an associated pressure loss penalty (54–150 times the value for the plane channel flow). However, the thermal performance factor for the in-line configuration has lower values than the staggered configuration at all Reynolds numbers.

This work was supported by a grant from Defense Advanced Research Projects Agency (DARPA). Their support is gratefully acknowledged.