Ultrasonic heat transfer enhancement on different structural tubes in LiBr solution

Abstract

A LiBr absorption refrigeration system that uses solar energy is a promising alternative to traditional air-conditioning systems. However, its overall efficiency is low due to the poor boiling heat transfer of the LiBr solution. This paper investigates the ultrasonic heat transfer enhancement on three different structural tubes (smooth, screwed and finned) in LiBr solution in the sub-cooled boiling regime. The pool boiling heat transfer performance of the LiBr solution is investigated, and the characteristics of the boiling heat transfer, which are driven by the ultrasonic field, are described using bubble dynamics, which are numerically determined by the Rayleigh–Plesset (R–P) equation. The effects of ultrasonic parameters (e.g., frequency, power) on the boiling heat transfer of the three different structural tubes are investigated, and the sound pressure distribution around the tested tubes that is calculated by a two-dimensional numerical model is used to describe the mechanism of the ultrasonic heat transfer enhancement. Additionally, a high-speed camera is used to take images of the bubbles in the structural tubes to help analyze the mechanism.