Measurement Method and Experimental Analysis of Liquid Entrainment for a Flooded Evaporator of a Water-Cooled Centrifugal Chiller Based on Energy Balance

Liquid entrainment in a flooded evaporator has an important impact on the performance and safety of a water-cooled centrifugal chiller. In this paper, two methods for measuring the liquid entrainment factor in the evaporator of a centrifugal chiller based on energy balance are proposed. Method 1 involves only the heat exchange capacity of the evaporator and Method 2 involves both evaporator and condenser. The applicable conditions of the methods are discussed. 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. Method 2 was found to have slightly higher measurement accuracy, compared to Method 1. The uncertainty propagation analysis shows that for method two, 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. The experimental results show that the variation of the evaporator entrainment factor with refrigerant charge amount is different for different cooling capacity. 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. 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. 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%.

A Study on Onset of Liquid Entrainment in Low Pressure Depressurization System of Advanced Passive Pressurized Water Reactors

The low-pressure depressurization system (LPDS) of advanced passive pressurized water reactors (PWRs) is designed to provide depressurization of the reactor coolant system during a small break loss-of-coolant accident (LOCA). The liquid entrainment to the LPDS is important for the safety case of the advanced passive PWRs due to the significant increase of the pressure loss and the depressurization rate versus mass loss characteristics. The existing experimental researches on the liquid entrainment at LPDS have been reviewed, and the intermittent entrainment mechanism and the continuous entrainment mechanism are identified. The intermittent entrainment is closely related to the flow regime transition from the horizontal stratified flow to the intermittent flow in the hot leg where the LPDS port is located. The horizontal stratification model previously developed for the FULL SPECTRUM LOCA evaluation model has been assessed against the entrainment onset data in the available LPDS entrainment experiments, i.e., the ATLATS air–water experiment, the ADETEL air–water and steam–water experiments, and the full-scale FATE air–water experiment. The prediction matches the measure data well especially in the full-scale FATE experiments. The comparison results also confirmed the scalability of the horizontal stratification model with the applicability of the horizontal stratification criterion to the full-scale PWR condition. The uncertainty factors that impact the depressurization system entrainment onset are discussed for the future improvements. This work provides the direction to accurately model the entrainment onset for LPDS and improve the simulation of LOCA in advanced passive PWRs.