Boiling of saturated water on grooved surface

Bubble formation in liquids is frequently observed in nature and applied in various industrial processes. These include pool and flow boiling for thermal management systems, where bubbles may form asymmetrically at narrow slits and in convective flows. While previous studies have focused on symmetric bubble formation at circular orifices, the dynamics of asymmetric bubble formation remains poorly understood. Here, we experimentally investigate bubble formation at rectangular orifices and examine the effects of the orifice size and aspect ratio and the gas flow rate on the bubble size. The asymmetric bubble shape evolution at the rectangular orifice is analyzed, and we find that the size of the bubble neck is controlled either by the orifice size or by the capillary length. Based on these findings, we develop a static force balance model to predict the bubble size in the quasi-static regime, where the roles of Bond number and aspect ratio are identified. The bubble size evolution in the dynamic regime is further understood by introducing a Weber number that evaluates the effect of the virtual mass force induced by gas flow. Our study provides physical understanding of the dynamics of asymmetric bubble formation and guidance to predict the bubble size at asymmetric orifices.

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Influence of surface roughness and Wettability of novel surface on nucleate boiling performance in deionised water at atmospheric pressure

Nithyanandam¹,

Duraisamy²,

Sridharan³

et al. 2022

THERM SCI

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Pool boiling is one of the very suitable techniques for an efficient thermal management system dealing with two phases. The present work deals with the experimental exploration of critical heat flux for safety concern and heat transfer coefficient related to the performance point of view in nucleate boiling regime of pool boiling system. The copper substrate was coated with porous copper nano particles by sputtering technique to the thicknesses of 250 nm, 500 nm and 750 nm. The surface characteristics of the copper nano coated surfaces have been analysed as a result of wettability, surface roughness and microstructure. The contact angle goniometer, stylus profilometer, X-ray diffractometer and scanning electron microscope have been employed to analyze the surface structure. The maximum augmentation of critical heat flux was 59% for the thickness of 750 nm as compared to plain copper substrate. A 99% increase in the heat transfer coefficient was achieved for 750 nm thickness surface in comparison with the plain copper surface. The tremendous augmentation in critical heat flux and heat transfer coefficient was achieved due to wetting and rewetting properties of the deionized water on the copper nano coated surfaces. The capillary action on the copper nano structure improves the fluid supply to the test surface and removes the heat at low wall superheat than the plain copper surface. The average roughness of the copper nano coated surface augments the heat transfer area which tends to enhance the performance factor significantly.

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Boiling of saturated water on grooved surface

Cited by 3 publications

References 23 publications

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Asymmetric Bubble Formation at Rectangular Orifices

Influence of surface roughness and Wettability of novel surface on nucleate boiling performance in deionised water at atmospheric pressure

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