High-Pressure Pool-Boiling Heat Transfer Enhancement Mechanism on Sintered-Particle Wick Surface

Abstract

We experimentally study high-pressure pool-boiling heat transfer enhancement using a copper sintered-particle wick structure in water. The wicks are fabricated using the multi-step sintering process using 200 µm sintered copper powder. Thermophysical properties of water change at elevated pressure, therefore changing the bubble dynamics. For the single-layer wick, Critical Heat Fluxes (CHF) of 179.63, 182.42, and 198.16 W/cm 2 are found at 0, 103.4, and 206.8 kPa, respectively. The maximum CHF is found at 206.8 kPa with the wick superheat of 9.9 K. A 110% enhancement is found in the CHF for 206.8 kPa, compared to 0 kPa. We observed a CHF 1.8 times higher compared to the plain surface at 0 kPa. The maximum Heat Transfer Coefficient (HTC) of 252.46 W/cm 2 K is found at a heat flux of 100 W/cm 2 and a pressure of 206.8 kPa. The high-pressure pool-boiling result for the single-layer wick shows that the heat transfer coefficient is enhanced by 100% compared to 0 kPa. We suggest the reasons for enhancement of the pool-boiling performance is primarily due to high rate of bubble generation, high bubble release frequency, and reduced thermal-hydraulic length modulation, and enhanced thermal conductivity due to the sintered wick layer. Our analysis suggests that the Rayleigh-critical wavelength decreases by 4.67% with varying pressure, which may cause the bubble pinning between the sintered particles and prevents bubble coalescence. Similarly, the role of pressure in enhancing heat transfer compared to the effect of the wicking layer is also analyzed and found that the critical flow length, λ u reduces by three times for 200 µm diameter particles. We suggest that the porous wick layer provides a capillary-assist to liquid flow effect, and delays the surface dry out. The pressure and surface modification amplify the boiling heat transfer performance. All these reasons may contribute to the CHF and HTC enhancement in the wicking layer at high-pressure.

Advances in micro and nanoengineered surfaces for enhancing boiling and condensation heat transfer: a review

“…43 In this regard, surface micro/nanoengineering has the potential to the generate suitable surface cavities to increase nucleation size density for pool boiling enhancements and have received increasing attention in the last few decades. [44][45][46][47] Furthermore, the wall superheat required for onset of nucleate boiling (ONB) has been shown to decrease with engineered nucleation sites, 48 thus expanding the region of nucleate pool boiling and increasing HTC.…”

Experimental and Analytical Study on the Influence of Saturation Pressure and Surface Roughness on Pool Boiling CHF of HFE-7100

“…Most models and correlations used parameter K de ned by Kutateladze [43] to predict CHF. In the proposed equation (7), CHF parameter K re ected the e ect of experimental conditions, such as wettability, surface roughness, saturation pressure, surface orientation, liquid properties, etc., while other items illustrated the impact of thermophysical properties of the working uid. As shown in Table 2, parameter K was usually expressed as dimensionless parameters or constants.…”

“…More attempts have been made to investigate the impact of pressure on pool boiling process at a critical state. Dahariya and Betz [6,7] conducted pool boiling experiments for water on horizontal smoothed and sintered-particle wick copper surfaces at pressures ranging from 0 to 413.7 kPa, and the results showed that higher pressure would result in the enhancement of CHF due to the formation of a thermal boundary layer, merging of vapor trains into neighboring trains and modulation of wavelength. Sakashita [8] measured CHF in saturated pool boiling for water and TiO 2 nano uid on a vertical copper surface at pressures of 0.1∼0.8 MPa, and they indicated that CHF of water and a nano uid increased with the increase of pressure, while CHF enhancement of a nano uid would decrease with the increasing pressure.…”