Shell side direct expansion evaporation of ammonia on a plain tube bundle with exit superheat effect

•Direct expansion of ammonia on shell side of a shell and tube evaporator•Reduced charge compared to conventional flooded or spray evaporator•Correlation developed with superheat effect There are no data available on the direct expansion evaporation of refrigerant on the outside of a tube bundle. With the current ozone depletion and global warming issues it is critical to develop systems with low charge refrigerants especially with natural refrigerants such as ammonia which has zero ozone depletion potential (ODP) and zero global warming potential (GWP). This study presents results of an extensive experimental work on direct expansion of ammonia on a triangular pitch plain tube bundle with saturation temperature range −1.7 to −20 °C, heat flux range 5 to 45 kW m−2 and exit superheat range 2 to 10 °C. The test matrix falls well within the practical operating conditions of industrial refrigeration systems. A typical increase in heat transfer coefficient was observed with saturation temperature and heat flux. The effect of exit super heat on the overall performance of the bundle was also reported. A correlation for outside boiling on a tube bundle in direct expansion mode was developed and compared with existing single tube pool, flooded bundle boiling and spray evaporation studies.