Experimental investigations and an updated correlation of flow boiling heat transfer coefficients for ammonia/lithium nitrate mixture in horizontal tubes

Abstract

In this work, experiments have been performed to investigate the flow boiling heat transfer coefficients (HTC) of ammonia/lithium nitrate mixture in horizontal smooth tubes with different internal diameters (4mm, 6mm). According to the practical working conditions of absorption refrigeration system, the ammonia concentration for the tested ammonia/lithium nitrate mixture was selected as 45.0 wt%, and the boiling temperature of tests were in the range of 78–90°C. The effects of boiling temperature, heat flux, mass flux and tube size on the flow boiling HTCs were investigated in this article. Results show that higher heat and mass fluxes as well as heat transfer tube with larger diameter tend to exert positive influence on flow boiling HTCs of the present study cases. Based on more than 600 groups of experimental data, a new correlation was proposed to predict the effects of mass flux, heat flux, and tube size on flow boiling HTCs for NH3/LiNO3 mixture under investigated conditions, with a mean deviation less than ±10%. The new correlation will be of great significance to the design and optimization of generators in the practical absorption refrigeration units using ammonia/lithium nitrate mixture.