Effect of Subcooling on Pool Boiling of Water from Sintered Copper Microporous Coating at Different Orientations

Seongchul Jun,Seung M You,Jinsub Kim,Hwan Yeol Kim

doi:10.1155/2018/8623985

Abstract

The subcooling effect on pool boiling heat transfer using a copper microporous coating was experimentally studied in water for subcoolings of 10 K, 20 K, and 30 K at atmospheric pressure and compared to that of a plain copper surface. A high-temperature thermally conductive microporous coating (HTCMC) was made by sintering copper powder with an average particle size of 67 μm onto a 1 cm × 1 cm plain copper surface with a coating thickness of ~300 μm. The HTCMC surface showed a two times higher critical heat flux (CHF), ~2,000 kW/m2, and up to seven times higher nucleate boiling heat transfer (NBHT) coefficient, ~350 kW/m2K, when compared with a plain copper surface at saturation. The results of the subcooling effect on pool boiling showed that the NBHT of both the HTCMC and the plain copper surface did not change much with subcooling. On the other hand, the CHF increased linearly with the degree of subcooling for both the HTCMC and the plain copper surface. The increase in the CHF was measured to be ~60 kW/m2for every degree of subcooling for both the HTCMC and the plain surface, so that the difference of the CHF between the HTCMC and the plain copper surface was maintained at ~1,000 kW/m2throughout the tested subcooling range. The CHFs for the HTCMC and the plain copper surface at 30 K subcooling were 3,820 kW/m2and 2,820 kW/m2, respectively. The experimental results were compared with existing CHF correlations and appeared to match well with Zuber’s formula for the plain surface. The combined effect of subcooling and orientation of the HTCMC on pool boiling heat transfer was studied as well.

Highlights

Subcooled boiling is an effective heat transfer mode that utilizes both single-phase and two-phase heat transfer for the cooling of high heat flux devices
According to Jun et al [16], the enhancement of the nucleate boiling heat transfer (NBHT) coefficient of the high-temperature thermally conductive microporous coating (HTCMC) is attributed to its porous structure with micron-scale cavities and reentrant-type cavities which create larger embryonic bubbles
The subcooled pool boiling of both the HTCMC and the plain copper surfaces revealed that the wall superheats at different subcoolings were close at heat fluxes up to ∼ 2,000 kW/m2 and ∼1,000 kW/m2, each being near the critical heat flux (CHF) at saturation

Summary

Introduction

Subcooled boiling is an effective heat transfer mode that utilizes both single-phase and two-phase heat transfer for the cooling of high heat flux devices. Rainey et al [10, 11] investigated the subcooling effects of a plain 10 mm × 10 mm flat copper surface in FC-72 and compared them with an ABM (aluminum particles, Devcon Brushable Ceramic epoxy, and methyl ethyl ketone) coating with a coating thickness of ∼50 μm at a subcooling temperature of 0–50 K They found that nucleate boiling heat transfer was closely maintained regardless of subcooling. The subcooling effect of copper microporous coatings created by sintering, called high-temperature thermally conductive microporous coatings (HTCMCs), was experimentally investigated with subcooled water of 10–30 K and compared with the results of a plain surface. Vent to condenser Pressure transducer Electric wire and thermocouple for heater assembly

Pool Boiling Experiments

Results and Discussion

Conclusions