Performance simulation and optimization calculation of casing CO2 evaporator
In order to optimize the design of casing CO2 evaporator and improve the efficiency of heat exchanger,a simulation model was established by using the steady state lumped parameter and the accuracy of the model was verified by experiments.The influences of internal and external conditions and structural parameters of evaporator on heat transfer performance were analyzed and the relationship between drying phenomenon and pipe length was analyzed.The results show that the evaporation temperature and mass flux have great influence on the heat transfer performance.When the evaporation temperature drops from 4 ℃ to-4 ℃,the cooling capacity decreases by 4 500 W/(m2·K).When the mass flux increases by 100 kg/(m2·s),the heat transfer coefficient increases by about 1 000 W/(m2·K)on average.In the design condition,the length of the pipeline traveled by CO2 fluid first decreases and then increases before drying out and reaches the lowest point at the evaporation temperature 0 ℃.In terms of structural parameters,the evaporator heat transfer effect is better when the diameter of outer tube is 23 mm.When the temperature of chilled water drops from 11℃ to 10 ℃,the pressure drop decreases by 3.5 kPa,which is significantly lower than the pressure drop under other temperature conditions.
casing CO2 evaporatorsteady state lumped parameter methodsimulation calculationheat transfer performance
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