Low Reynolds numbers convective heat transfer in single/two-phase roughened microchannels. (5th November 2021)

• Record Type: Journal Article
• Authors: Hsieh, Shou-Shing; Huang, Ching-Feng; Pan, Jian-Siang
• Is Part Of: Applied thermal engineering. Volume 198(2021)
• Publication Date: 2021-11-05
• Subjects: Transverse-ribs roughened microchannel -- Convective boiling -- Low Reynolds number -- Heat transfer enhancement -- Axial heat conduction; Heat engineering -- Periodicals; Heating -- Equipment and supplies -- Periodicals; Periodicals; 621.40205
• DOI: 10.1016/j.applthermaleng.2021.117468
• Languages: English
• ISSNs: 1359-4311

Abstract

Highlights: Low Reynolds numbers Flow boiling with roughened surfaces enhancement was studied. Axial heat conduction on roughened/smooth microchannels flow boiling was examined. Heat transfer enhancement in roughened microchannels flow boiling can be up to 38%. Flow boiling decreases axial heat conduction significantly for roughened surfaces. Abstract: Convective heat transfer coefficient and friction factor (only for single phase) in single/two-phase roughened rectangular (60 µm × 200 µm; cross-section) microchannels with a length of 25 mm were experimentally studied at low Reynolds numbers of 7 ≤ Re ≤ 22 with deionized water as the cooling fluid. Transverse-rib (100 µm × 200 µm; length × width) roughened surface was applied with three different rib heights of 12 µm, 15 µm and 20 µm at a definite pitch of 150 µm. A constant heat flux of 150 W/cm 2 was mounted on the bottom wall of the channel through the copper surface. Flow velocity distribution was measured via micro particle image velocimetry along the downstream of the single-phase flow for both smooth and roughened plexiglass microchannels. Temperature measurements were conducted via a thermocouple for both single- and two-phase roughened microchannels. The heat transfer coefficient, as well as heat transfer enhancement due to the effect of roughened ribs for single phase and flow boiling are presented and discussed herein. The subcooled flow boiling experiments were only conducted for G = 200 kg/m 2 s with the corresponding inlet Reynolds number of 20. The results indicate that the increase in the critical heat flux can reach up to about 20% and reduce the onset of nucleate boiling by 2 °C as compared to those of smooth channels. Under the same operating conditions, the heat transfer enhancement effect seems greater (38%) due to phase change than that of the single-phase roughened channels, in which there is only about a 16% heat transfer increase as compared to those of smooth channels. In addition, axial heat conduction in the microchannel was found to be so small that the effect on convective heat transfer could neglected especially for flow boiling in roughened microchannels.