Critical heat flux characteristics of R1234yf, R1234ze(E) and R134a during saturated flow boiling in narrow high aspect ratio microchannels

Martin Ryhl Kærn,Gennaro Criscuolo,Knud Erik Meyer,Wiebke Brix Markussen

doi:10.1016/j.ijheatmasstransfer.2021.121840

Martin Ryhl Kærn, Gennaro Criscuolo + Show 2 more

Open Access

https://doi.org/10.1016/j.ijheatmasstransfer.2021.121840

Copy DOI

Abstract

This experimental study investigated narrow and high aspect ratio multi-microchannels that were micro-machined in copper with thin separating walls during saturated flow boiling of refrigerants. The hypothesis was that these channels could increase the footprint critical heat flux and support the future development of thermal management systems for power electronics and other electronic packages. The measured footprint critical heat flux was as high as 678.5 W/cm2, which is twice as high as other investigations in the literature concerning saturated flow boiling of refrigerants. Two test samples were fabricated with a footprint area of (10 × 10) mm. The first had 25 rectangular channels (198 μm wide, 1167 μm high). The second had 17 rectangular channels (293 μm wide, 1176 μm high). The experimental investigation covered low-GWP replacement refrigerants (R1234yf, R1234ze(E)) as well as the well-examined R134a serving as a benchmark. A large data bank was obtained with 432 data points covering a wide range of typical inlet subcooling (1.3–14.7) K and mass fluxes (333–1260) kg/m2s as well as two nominal saturation temperatures (30 and 40) °C.The effect of inlet subcooling was found to be consistently significant at the higher mass fluxes. This was contradictory to other investigations that found moderate or insignificant effects. The result is suggested to be attributed to the two-phase stability induced by the upstream throttle valve, inlet orifices, isolated refrigerant in the inlet and outlet plenums as well as the short heated length causing higher importance of orifice to channel pressure drop importance. Finally, a new modified Katto and Ohno correlation including the effect of subcooling was proposed, achieving a 4.0% mean average error and predicting 93.3% of the data points within 10% error.

Highlights

The continuous miniaturization and advancement in the performance of modern microelectronics have resulted in a sustained increase of the cooling demands and the maximum heat flux targets of applications such as high-performance computing and power electronics
The current target for power electronics in electric vehicles is close to 250 W/cm2 at the chip level, while in some niche applications, such as defense power electronics, it can reach up to Abbreviations: CHF, critical heat flux; GWP, global warming potential; mean absolute error (MAE), mean average error; Ozone Depletion Potential (ODP), ozone depletion potential; RTD, resistance thermal detector
The results indicate that the geometry “F” achieves the highest footprint CHF

Summary

Introduction

The continuous miniaturization and advancement in the performance of modern microelectronics have resulted in a sustained increase of the cooling demands and the maximum heat flux targets of applications such as high-performance computing and power electronics. Ible volume instability, excursive instability or parallel channel instability [4,5] These instabilities are generally more pronounced at lower mass fluxes and subcooling and may be suppressed by the use of upstream throttling valve and/or flow restrictions at the microchannel inlets [2,4,5]. The current study strives to achieve a high effective CHF (based on footprint area) using saturated flow boiling of refrigerants in narrow high aspect ratio microchannels with thin separating walls and low pumping power.

Objectives

Results

Discussion

Conclusion