Liquid entrainment reduces the amount of liquid that could otherwise be evaporated for refrigeration and reduces the cooling capacity. Liquid entrainment/carryover is a common phenomenon for the shell-and-tube flooded or falling film evaporators of a water-cooled centrifugal chiller and has an important impact on the performance and safety of the chiller and compressor. Based on the analysis of the experimental results, it is recommended that the maximum entrainment factor for efficient operation of the centrifugal chiller should be controlled within 1%. For the chiller tested, when the entrainment factor reaches 0.89% and 1.02%, respectively, at 700 ton and 800 ton, the rapid increase of the entrainment factor leads to a significant decrease in the coefficient of performance (COP) during the charging process. At 700 and 800 refrigeration ton (RT), the entrainment factor of the test evaporator increases with the increase of refrigerant charge and the growth rate gradually accelerates.
The experimental results show that the variation of the evaporator entrainment factor with refrigerant charge amount is different for different cooling capacity. The uncertainty propagation analysis shows that for Method 2, the inlet and outlet water temperatures of the evaporator and condenser, motor input power, motor efficiency, transmission power loss and compressor suction and discharge temperatures are important factors. Method 2 was found to have slightly higher measurement accuracy, compared to Method 1. Experimental measurements on the flooded evaporator of a single-stage water-cooled centrifugal chiller with refrigerant R134a show that, for a system with good thermal balance, there is little difference in the entrainment factor values obtained by the two methods. The applicable conditions of the methods are discussed. Method 1 involves only the heat exchange capacity of the evaporator and Method 2 involves both evaporator and condenser.
In this paper, two methods for measuring the liquid entrainment factor in the evaporator of a centrifugal chiller based on energy balance are proposed. Liquid entrainment in a flooded evaporator has an important impact on the performance and safety of a water-cooled centrifugal chiller.
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