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Conjugate heat transfer effects on flow boiling in microchannels

Municchi, F.; El Mellas, I.; Matar, O. K.; Magnini, M.

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Authors

F. Municchi

I. El Mellas

O. K. Matar



Abstract

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 simulated 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 µm, a uniform base heat flux of qb=100 kW/m2, and by varying the channel width-to-height aspect-ratio and channel fin thickness in the range ϵ=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 base temperatures are achieved for smaller channel aspect-ratios, from Nu≃4 and Tb−Tsat≃9K when ϵ=4, to Nu≃6 and Tb−Tsat≃2K when ϵ=0.25, for same fin thickness Wf=Dh/8. In the two-phase flow regime, Nusselt numbers in the range Nu=12−36 are achieved. The trends of the Nusselt number versus the aspect-ratio are non-monotonic and exhibit a marked dependence on the channel fin thickness. For small fin thicknesses, Wf=Dh/8 and Wf=Dh/4, an overall ascending trend of Nu for increasing aspect-ratios is apparent, although in the narrower range ϵ=0.5–2 the Nusselt number appears weakly dependent on ϵ. For thicker fins, Wf=Dh/2 and Wf=Dh, the Nusselt number decreases slightly when increasing the aspect-ratio in the range ϵ=0.5–2, although this trend is not monotonic when considering the entire range of aspect-ratios investigated. Nonetheless, due to conjugate heat transfer, Nusselt numbers and evaporator base temperatures follow different trends when varying the aspect-ratio, and channels with ϵ<1 seem to promote lower evaporator temperatures than higher aspect-ratio conduits.

Citation

Municchi, F., El Mellas, I., Matar, O. K., & Magnini, M. (2022). Conjugate heat transfer effects on flow boiling in microchannels. International Journal of Heat and Mass Transfer, 195, Article 123166. https://doi.org/10.1016/j.ijheatmasstransfer.2022.123166

Journal Article Type Article
Acceptance Date Jun 16, 2022
Online Publication Date Jun 27, 2022
Publication Date Oct 1, 2022
Deposit Date Apr 23, 2023
Publicly Available Date Apr 28, 2023
Journal International Journal of Heat and Mass Transfer
Print ISSN 0017-9310
Electronic ISSN 0017-9310
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 195
Article Number 123166
DOI https://doi.org/10.1016/j.ijheatmasstransfer.2022.123166
Public URL https://nottingham-repository.worktribe.com/output/8956316
Publisher URL https://www.sciencedirect.com/science/article/pii/S0017931022006366?via%3Dihub

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