Theoretical Calculation And Experimental Study Of The CO₂ Air-cooler

Today,all of the word are facing the more and more environmental problems,such as ozone hole and greenhouse effect.Refrigeration industry has an unshakable responsibility.From the Montreal Protocol to the present Montreal Protocol-Kigali amendment,are continuing to promote the use of environmentally friendly and efficient refrigerants.CO₂,as the earliest natural refrigerant,accessed by the refrigeration industry after abandoned about hundred years.Although as refrigerant,CO₂ still has some technical problems,but its superior environmental performance,thermal performance and low price makes it has a very large space for development in the modern refrigeration industry.Air-cooler is the most commonly used and most critical components in cold storage and other refrigeration systems.Improving the performance of air-cooler has a significant effect on the optimization and energy saving of refrigeration systems.In this paper,the effect of geometrical parameters,air side parameters and the refrigerant side parameters on the performance of the air-cooler are analyzed by theoretical calculation and experimental study.The concrete research are as follows.?1?According to the geometric structure and size of the CO₂ air-cooler,the steady-state partitioning parameter model is established by referring to the empirical formula in the relevant literature.Before the mathematic model is established,some factors that have little effect on the calculation result are neglected,and the calculation model is more simple and convenient.?2?The heat transfer coefficient and the cooling capacity of the CO₂air-cooler were calculated by the mathematical model under different structural geometrical parameters,different air side parameters and different refrigerant side parameters.The influence of the geometric parameters of the air-cooler on its heat transfer coefficient and cooling capacity is shown below.The heat transfer coefficient is proportional to the fin spacing and is inversely proportional to the tube spacing.On the contrary,the cooling capacity is inversely proportional to the fin spacing and proportional to the tube spacing.The influence of the air side parameters on the chillers is as follows.Heat transfer coefficient and cooling capacity are proportional to the temperature of the calibration tank;there is the best face velocity?3.2-3.4 m/s?to make the performance of air-cooler to best.The influence of the refrigerant side parameters on the air-cooler is as follows,the heat transfer coefficient of the air-cooler is proportional to the circulation rate,and the best circulation rate is about three.In practical application,it should be a comprehensive consideration of these factors,so that the effect of the air-cooler to achieve the best.?3?The influence of the plenum chamber width on the wind speed uniformity of the windward and the influence of the plenum chamber width on the heat transfer coefficient ofthe air-cooler were studied experimentally.The results show that when the plenum chamber width changes from 320 mm to 520 mm,the wind speed uniformity of windward is getting higher and higher.As the plenum chamber width reaching 520 mm,the maximum wind speed and the minimum wind speed difference is only 0.11 m / s.The heat transfer coefficient is proportional to the plenum chamber width.When the plenum chamber width is 520 mm and the calibration tank temperature is-20 ?,the heat transfer coefficient is15.8W / m2· K.?4?The experimental study on the performance of No.1 air-cooler is studied experimentally under different air side parameters and refrigerant side parameters.And the experiment has the same trend with the theoretical calculation,the experimental data show that the heat transfer coefficient and cooling capacity of air-cooler is proportional to the calibration tank temperature.When the temperature of the calibration box is in the range of-40 to-20?,the variation range of the corresponding heat transfer coefficient is 14.9 to16.5 W / m2 · K,the cooling capacity variation range is 30.4-32.6kW,increase of 10.7%and 7.2% respectively.When the circulation rate is changed and reaches 3,the value of the heat transfer coefficient tends to be stable.?5?Comparing the experimental value and the theoretical calculation value of the No.1air-cooler,verify the rationality of the mathematical model.The results show that the trend of the experimental value and the theoretical calculation are consistent basically,the theoretical calculation value is higher than the experimental value.In each comparison,the maximum error value of the theoretical calculation and the experimental are about 25%,the minimum error is 14.8%.