Experimental and Visualization Study of Flow Boiling in Open Rectangular Microchannel with Large Aspect Ratio
Year: 2026
Type: article
Abstract: Large aspect ratio microchannels provide a larger solid-liquid contact area for the same base contact area, resulting in superior heat dissipation performance. The top gap structure of open microchannels effectively reduces pressure drop and suppresses flow instability. However, comparative experiments between large aspect ratio open rectangular microchannels and closed rectangular microchannels are still limited. This study designed a copper-based open rectangular microchannels (ORM) with an aspect ratio of 4, and a corresponding closed rectangular microchannels (CRM) with the same structure. A fully transparent cover window was also designed to facilitate the investigation of flow boiling characteristics in the microchannels. Flow boiling experiments were conducted using R245fa as the refrigerant, with mass fluxes ranging from 89 to 545 kg/m²·s, heat fluxes from 6.3 to 218.5 W/cm², and an inlet temperature of 14°C. Visualization results indicated that, in ORM, the flow regime transitions more rapidly from bubbly flow to slug flow and churn flow compared to CRM. Additionally, a unique stratified flow pattern was observed. The heat transfer coefficient in ORM increased by 4.2%-14.1%, and the pressure drop decreased by 11.5%-58.6% within the low mass flux range (89-269 kg/m²·s). However, at a high mass flux of 545 kg/m²·s, the pressure drops increased by 29.9%-246.8%, with additional two-phase pressure drop introduced by the top-gap structure being significant. As heat flux increased, inertial forces gradually dominated over gravitational forces, and the heat transfer contribution from flow boiling surpassed that from nucleate boiling. The figure of merit (FOM) suggests that, at low mass fluxes, the performance of the ORM is superior to that of the CRM.
Source: Energies
DOI: 10.3390/en19020561
Institution: Dalian University of Technology
Language: English
Subfield: Mechanical Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $3,137
OpenAlex ID: W7125481789