Conjugate heat transfer effects on flow boiling in microchannels

• Main Authors: Municchi, F, Mellas, I. El, Matar, O. K, Magnini, M
• Format: Journal Article
• Language: English
• Published: 17-03-2022
• Subjects: Physics - Fluid Dynamics
• DOI: 10.48550/arxiv.2203.09305

This article presents a computational study of saturated flow boiling in
non-circular microchannels. The unit channel of a multi-microchannel
evaporator, consisting of the fluidic channel and surrounding evaporator walls,
is emulated and the conjugate heat transfer problem is solved. Simulations are
performed using OpenFOAM v2106 and the built-in geometric Volume Of Fluid
method, augmented with self-developed libraries to include liquid-vapour
phase-change and improve the surface tension force calculation. A systematic
study is conducted by employing water at atmospheric pressure, a channel
hydraulic diameter of Dh = 229 um, a uniform base heat flux of qb = 100kW/m2,
and by varying the channel width-to-height aspect-ratio and channel fin
thickness in the range AR = 0.25-4 and Wf = Dh/8-Dh, respectively. The effects
of conjugate heat transfer and channel aspect-ratio on the bubble and
evaporative film dynamics, heat transfer, and evaporator temperature are
investigated in detail. This study reveals that, when the flow is single-phase,
higher Nusselt numbers and lower evaporator temperatures are achieved for AR <
1. In the two-phase flow regime, the trends of the Nusselt number versus the
aspect-ratio are mixed, although for smaller channel fins an ascending trend of
Nu for increasing aspect-ratios is apparent. Nonetheless, due to conjugate heat
transfer, Nusselt numbers and evaporator base temperatures follow different
trends when varying the aspect-ratio, and channels with AR < 1 seem to promote
lower evaporator temperatures than higher aspect-ratio conduits, despite
exhibiting slightly worse two-phase convective heat transfer performances.