Flow boiling heat transfer characteristics and pressure drop of ammonia-lithium nitrate solution in a smooth horizontal tube

Abstract

This paper presents experimental results of flow boiling heat transfer coefficient of ammonia/lithium nitrate solution in a smooth horizontal tube with diameter of 10mm. The test conditions are selected based on practical working conditions of absorption refrigeration system with ammonia/lithium nitrate solution. The ammonia concentration of the solution at the inlet of test section is around 45.5wt%. The mass flow rate and boiling temperature of the solution are in the ranges of 20–55kg/h and 76.7–93.2°C, respectively. The effects of the heat flux, mass flux and exit vapor quality has been investigated. The maximum flow boiling heat transfer coefficient reaches 2100W·m-2K-1. Results show that heat fluxes have significant influence on boiling heat transfer coefficients (HTCs). Nucleate boiling is found to be predominant during the tests. The experimental results are also compared with the available flow boiling heat transfer coefficients of NH3/LiNO3 solution and predicting correlations in literature. Kandlikar’s correlation is appropriate to characterize the experimental boiling heat transfer coefficients with a mean deviation of ±12.56%. Pressure drops in the solution side are also measured under different working conditions. The results of the present study will be of great significance to the design and optimization of generators in the absorption refrigeration units using ammonia/lithium nitrate solution.