Influences of a Baffle on Mixed Convection Characteristics of Backward-Facing Step Flow in Vertical Channels

摘要

Aiming to enhance the heat transfer characteristics of mixed convection in abruptly expanding channels, the present study proposes a method to install a baffle onto the channel wall. The effects of the dimensionless baffle height H{sub}b, baffle thickness W{sub}b, and distance between the backward-facing step and baffle D on the flow structure, temperature distribution and Nusselt number variation for the system at various Re and Gr/Re{sup}2 are numerically investigated. Results show that even a short baffle with H{sub}b= 0.2 could substantially compress the recirculation cell behind the backward-facing step and pack the isotherms, which then would effectively promote the heat transfer performance. The variation of baffle width causes insignificant influences, the difference in the average Nusselt number is within 3% as W{sub}b varies from 0.2 to 0.5. The effects of D on the heat transfer coefficient for heating channel plate are more substantial than that for heating step. Comparing the results of the cases with or without the installation of baffle, the maximum augmentation on average Nusselt number is about 190% for the heating step and 150% for the heating section of channel plate when Pr = 0.7, H{sub}s = 0.5, L = 5, H{sub}b ≤ 0.3, W{sub}b ≤ 0.5, 50 ≤ Re ≤ 500 and 0≤Gr/Re{sup}2 ≤ 1.