Conjugate heat transfer effects on flow boiling in microchannels
Conjugate heat transfer effects on flow boiling in microchannels
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DOI：
10.1016/j.ijheatmasstransfer.2022.123166
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发表时间：
2022-03
影响因子：
5.2
通讯作者：
Federico Municchi;I. Mellas;O. Matar;M. Magnini
中科院分区：
文献类型：
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作者：
Federico Municchi;I. Mellas;O. Matar;M. Magnini
本文对非圆形微通道内的饱和流动沸腾进行了计算研究。对多微通道蒸发器的单元通道进行了数值模拟，求解了单元通道内的耦合传热问题。使用OpenFOAM v2106和内置的几何流体体积方法进行模拟，并使用自行开发的库进行扩展，以包括液体-蒸汽相变并改进表面张力计算。采用大气压下的水，通道水力直径D h= 229 µm，均匀基底热流B= 100 kW/m2，通道宽高比和通道翅片厚度分别在φ = 0.25-4和W f= D h/8− D h范围内变化，进行了系统的研究。研究了共轭传热和通道长径比对汽泡和蒸发膜动力学、传热和蒸发器温度的影响。该研究表明，当流动为单相时，对于较小的通道纵横比，获得较高的努塞尔数和较低的蒸发器底部温度，对于相同的翅片厚度W f= D h/8，从当φ = 4时的Nu φ 4和T B− T s a t φ 9 K到当φ = 0.25时的Nu φ 6和T B− T s a t φ 2 K。在两相流状态下，可实现Nu= 12− 36范围内的努塞尔数。的努塞尔数与纵横比的趋势是非单调的，并表现出显着的依赖于沟道鳍厚度。对于小的翅片厚度，W f= D h/8和W f= D h/4，随着展弦比的增加，Nu的总体上升趋势是明显的，尽管在较窄的范围内Nu = 0.5-2，Nu数似乎对Nu的依赖性很弱。对于较厚的翅片，W f= D h/2和W f= D h，当在0.5-2的范围内增加长宽比时，努塞尔数略有减小，尽管当考虑所研究的整个长宽比范围时，这种趋势不是单调的。尽管如此，由于共轭热传递，当改变纵横比时，努塞尔数和蒸发器底部温度遵循不同的趋势，并且具有Nu < 1的通道似乎比更高纵横比的管道促进更低的蒸发器温度。
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 D h= 229 µm, a uniform base heat flux of q b= 100 kW/m 2, and by varying the channel width-to-height aspect-ratio and channel fin thickness in the range ϵ= 0.25–4 and W f= D h/8− D h, 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 T b− T s a t≃ 9 K when ϵ= 4, to Nu≃ 6 and T b− T s a t≃ 2 K when ϵ= 0.25, for same fin thickness W f= D h/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, W f= D h/8 and W f= D h/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, W f= D h/2 and W f= D h, 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.