Effect of Vapor Quality and Pressure Drop on the Performance of CO2 Trans-Critical Air Conditioning Cycle with Porous Evaporator

Abstract

Evaporation process is playing a big rule on the performance of trans-critical CO2 cycle. Because of its low performance in air conditioning systems, low ozone depletion, low global warming, CO2 as refrigerant pushed many researchers to study the effect of many thermodynamic parameters on its coefficient of performance. In this experimental study, the effect of pressure -drop and vapor quality on the performance of trans-critical carbon dioxide air conditioning system is studied when using an evaporator partially filled with porous material. A test rig consists of porous evaporator, compressor, gas cooler and expansion valve is used. Small steel balls with porosities of 30%,40%, 50% and 100% are used. Gas cooler pressure is changed from 75-125 bar. Evaporation temperature is changed from 8-18 o C. An increase in pressure-drop of about 157.6% is noticed by decreasing porosity from 100% to 30%. An increase in pressure-drop reached a value of 66.2% by increasing vapor quality from 0.1-0.48 and fixing porosity at 30%. Percentages of decrease in coefficient of performance of about 37% and 49% are recorded by increasing pressure-drop from 24.8 -43.3 kPa and increasing vapor quality from 0.1-0.48, respectively. The decrease of porosity and the increase of pressure drop resulted in an increase in the cycle coefficient of performance. An optimum value of coefficient of performance of 4.9 is found when the gas cooler pressure reached 100 bar at porosity and evaporation temperature of 30% and 14 o C, respectively.