Experimental investigations were performed to understand the fundamentals of pool boiling heat transfer in nanofluids. The pool boiling curves of water and nanofluids at the pressure of 2.89 psia (Tsat = 60°C) were obtained and compared using a flat square (1 × 1 cm) heater. The tested nanofluids contain aluminum oxide (Al2O3) nanoparticles dispersed in distilled-deionized water. The concentrations of nanofluids range from 0 gram/liter to 0.05 gram/liter. The results show that the boiling heat transfer coefficient is independent of concentrations of nanofluids. Remarkable enhancement (~200%) of CHF was achieved for low concentrations of nanofluids (above 0.01 gram/liter). The boiling parameters, such as bubble size and departure frequency, were measured and analyzed using a 390-μm-diameter platinum wire. The measurement reveals that the size of bubbles increases and the bubble frequency decreases significantly in saturated nanofluids as compared to those in pure saturated water. The surface orientation effects on boiling heat transfer in nanofluids are also investigated. The results show that CHF enhancement of nanofluids is more effective as the boiling surface faces downward.

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