Experimental Study on Flow Boiling of Fluorocarbon Medium in the Pin-Ribbed Mini-Channel with Rigid Tails

Abstract

Facing the requirements and challenges of efficient heat dissipation for electronic devices, flow boiling cooling technology is more promising than single-phase cooling technology. Moreover, the structural optimization of heat sinks has been the focus of research for a long time. In this work, a novel type of pin-ribbed mini-channel with rigid tails is designed based on the conventional pin-ribbed mini-channel. And a comparative experimental study of them is carried out by using fluorocarbon medium Novec649. The flow boiling heat transfer and pressure drop characteristics are investigated under vertical and horizontal placement with inlet subcooling temperature of 25 °C, inlet mass flow rate of 0.012 ~ 0.042 kg·s-1 and heat flux of 50 ~ 500 kW·m-2. The results show that: When the mass flow rate is the same, at medium and high heat flux of 300 ~ 500 kW·m-2, the vertical pin-ribbed mini-channel with rigid tails has the lowest average wall temperature, the largest average heat transfer coefficient, and the smallest total pressure drop, therefore it has the largest j-factor. With the aid of a high-speed camera, the localized boiling phenomenon and bubble movement phenomena in horizontally or vertically placed mini-channel with rigid tails was mainly shot at a mass flow rate of 0.012 kg·s-1 and a heat flux of 100 kW·m-2. It is clearly shown that the rigid tails in the mini-channel mainly act in the ways of "impact" and "shear", and the vertical placement is more helpful for the rigid tails to play a role in the breakup and detachment of bubbles. The experimental results confirm the advantages of attaching rigid tails structure on the square-rib backflow surface for enhancing the comprehensive heat transfer performance of flow boiling, and their related conclusions can provide a reference basis for the structural optimization of two-phase miniature heat sinks.

Keywords: Rigid tail structure, Flow boiling, two-phase heat transfer, Bubble dynamics