Active biphasic heat transfer enhancement in vertical natural convection

TL;DR

This study introduces a novel biphasic approach to vertical natural convection, significantly enhancing heat transfer efficiency by inducing pseudo-turbulence through bubble dynamics and phase change processes.

Contribution

The paper presents a new method of augmenting vertical natural convection heat transfer using biphasic bubbles and a gas-liquid layer, achieving substantial efficiency improvements.

Findings

Achieved 246% heat transfer enhancement at constant superheat.

Validated bubble-induced agitation improves heat flux and temperature distribution.

Demonstrated self-sustained pseudo-turbulence in the system.

Abstract

Vertical natural convection (VC), often cannot meet the high heat transfer demands due to the inherent misalignment of the direction of buoyancy (vertical) with the direction of the heat transfer (horizontal). Here we applied a novel strategy on a water based VC system to enhance the heat transfer. By adding 2% of the total volume with a low-boiling-temperature liquid (HFE-7000) and introducing a gas-liquid layer on top of the VC cell, we create a self-sustained state of pseudo-turbulence with evaporating, circulating and condensing biphasic bubbles. The system achieves 246% heat transfer enhancement at constant superheat $T_{sup}\approx6.4 \text{K}$ when the liquid in the full nucleate boiling state. Using shadowgraphy and Laser Doppler Anemometry (LDA) methods, we validate that the bubbles and biphasic particles induced agitation enhances the heat flux and modifies the temperature field of the heat transfer.