Pool-boiling enhancement using multilevel modulated wick
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Nasersharifi, Yahya; Kaviany, Massoud; Hwang, Gisuk. 2018. Pool-boiling enhancement using multilevel modulated wick. Applied Thermal Engineering, vol. 137:pp 268-276
Main challenges in saturated pool-boiling heat transfer are limited Critical Heat Flux (CHF) and Heat Transfer Coefficient (HTC), caused by the counterflow of liquid and vapor over the heated surface. Using multilevel modulated wicks, i.e., monolayer, columnar, and mushroom post wicks, we control the liquid and vapor flow for efficient phase separation, thereby improving the CHF and HTC. The wicks are fabricated using multi-step sintering process using 200 mu m copper particles, and the pool boiling uses n-pentane at ambient pressure. The monolayer wicks without and with the mushroom post structure provide 20% and 87% CHF enhancements, respectively, compared to the plain surface. It is found that the CHF enhancement of the mushroom wick is attributed to its pitch distance, 3.5 mm, which effectively reduce the hydrodynamic instability (Rayleigh-Taylor) wavelength. The further reduction of the pitch distance, 1 mm, results in the 250% CHF improvement in agreement with the theory. The columnar and mushroom posts with monolayer increase HTC by tenfold, compared to the plain surface, due to the reduced conduction path through the thin monolayer wick under the controlled vapor region using the columnar and mushroom post wick (vapor chamber-like environment in pool boiling). The multilevel wick design provides fundamental insights into simultaneous CHF and HTC enhancements with potential use in advanced thermal management systems.
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