| In the vapor compression refrigeration system, the performance of evaporator which is directly cooling component directly affects the efficiency of the whole system.The liquid refrigerant tranform into gas-liquid two phase refrigerant through the throttle valve. Therefore the distribution uniform of the gas-liquid two phase refrigerant in evaporator coils effect the heat transfer performance of evaporator significantly. The distributor as auxiliary component of evaporator, is the key part to distribute the refrigerant uniformly to the evaproator coils, of which the performance influence the evaporator’s performance inportantly. Through the reading of literature at home and abroad and survey of enterprise product, find that the evaporator distributor has a great variety, but do not a unified standard of classification. Moreover due to the congenital deficiencies of the traditional distributor principle, it can not completely overcome the shortcomings of mal-distribution, leading to the deterioration of the evaporator heat transfer performance. The main contents of this paper studied are as follows:Firstly, according to the process of remixing,flow pattern setting and redistribution of the refrigerant passed from throttle valve into distributor, we reclassified the distributors. Based on the research of the traditional distributors, put forward a new distribution concept: transform the gas-liquid two phase uniform distribution into single phase uniform distribution. Eatablished the design model of gas-liquid separation distributor by applying the matlab software and designed two kinds of structure of gas-liquid separation distributor.Secondly,using the FLUENT software, simulated the phase division respectively of the two kinds of structure of gas-liquid separation distributors, CAL distributor and venturi distributor. The results show that for the split-phase distributor,the feeding pipe with a U-shaped bending or bend has an effect of gas-liquid two pahse separation in advance. The venturi distributor easily appeared uneven phenomenon, the CAL distributor can achieve almost equal quality distribution.The sepatation degree of the NO.2 gas-liquid separation distributor is more thoroughly compared that of the NO.1 gas-liquid separation distributor, which is easier to translate two phase flow distribution into single phase flow distributionThirdly,on the base of the air cooler performance testing laboratory,we built the distributor pressure drop performance test device.Installing the venturi distributor, CAL distributor and the two structure of gas-liquid separation distributors respectively on the same air cooler, test the air cooler performance and the distributor perssure drop performance at the calibrating tank temperature 0℃、-4℃、-8℃、-12℃、-16℃、-20℃. The experimental results are as follows:(1) Under the condition of-18℃ calibrating tank temperature, the cooling capacity and heat transfer coefficient of the evaparator with the installation of the two kinds of gas-liquid seperation distributor first increases and then decreases with the increase of the gas bypass valve opening degree. The two kinds of gas-liquid separation distributor both have a best gas bypass volume. For the NO.1 and NO.2 gas-liquid separation distributors, when the gas bypass walve open degree reach respectively the fourth and second opening degree, the cooling capacity of evaparator reach the max value,respectively 5.015 k W and5.142 k W, while the heat transfer coefficient respectively reach the max value of 30.2 W/(m2·K) and 30.6 W/(m2·K) when the opening degree both reach the third opening degree. Under the same opening degree, the heat transfer coefficient of NO.2 distributor slightly greater than that of the NO.1 distributor.(2) Under the same experimental conditions,with the four kinds of distributors installation respectively, the order of the cooling capacity and heat transfer coefficient of the evaporator are as follows: the NO.2 gas-liquid seperation distributor, NO.1 gas-liquid seperation distributor, the CAL distributor and venturi distributor. According to the installation order of the NO.1 gas-liquid separation distributor with the opening degree of gas bypass valve respectively closed, reached the first opening degree and second opening degree, CAL distributor,venturi distributor and the NO.2 gas-liquid separation distributor with the opening degree of gas bypass valve respectively closed, reached the first opening degree and second opening degree, when the calibrating tank temperature is 0℃,the cooling capacity of the NO.2 gas-liquid seperation distributor with the gas bypass valve reached second opening degree compared others, respectively increased by 15.6%, 9.8%, 9.8%, 8.6%, 12.5%, 1.2% and 0.7%, the heat transfer coefficient respectively increased by 15.5%, 9.7%, 10.2%, 9.7%, 13.5%, 1.2% and 13.5%; while under the condition of-18℃ calibrating tank temperature, the cooling capacity respectively increased by 7.2%, 10.1%, 10.1%, 6.8%, 9.1%, 1.2% and 1.1%, the heat transfer coefficient respectively increased by 15.9%, 9.4%, 9.4%, 2.8%, 6.3%, 2.8% and 6.3%.(3) For the respectively installation of the four kinds of distributors, the pressure drop of the distributor, evaparator and the total pressure drop decreases with the decrease of the calibrating tank temperature. The venturi distributor perssure drop account for high percentage of the evaporator’s total pressure drop, while the the percentage of other distributors is low. Under the same conditions, the venturi distributor pressure drop is greater than that of other three forms of distributors, then is the NO.1 gas-liquid separation distributor, CAL distributor and the NO.2 gas-liquid separation distributor in turn. For two kinds of structure of gas-liquid separation distributors, under the same conditions, their pressure drop decreases with the increase of the gas bypass valve(needle valve)opening degree.Fourthly, based on the flow pattern theory of two phase flow,the orifice type distributor was optimized. The performance of air cooler with optimized distributor and non-optimized distributor are tested out at the calibrating tank tempetature of 0℃,-4℃,-8℃,-12℃,-16℃,-20℃ respectively using heat balance method and enthalpy-difference method simultaneously. The results showed that at the condition of the same calibrating tank temperature, the cooling capacity and heat transfer coefficient of air cooler with the optimized distributor is higher than that of air cooler with the non-optimized distributor. The calibrating tank temperature from 0℃ to-20℃, their cooling capacity respectively decreases from 7.17 k W and 6.02 k W to 5.39 k W and 5.10 k W,while the average heat transfer coefficient is respectively 27.02W/(m2·K) and 32.95W/(m2·K). Thus the optimized distributor can mix the gas and liquid more fully, leading to the improvement of the refregerant uniform distribution. |
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