单工质变流量复叠制冷系统实验研究

发布时间：2018-06-19 22:47

本文选题：变流量 + 复叠式制冷　；参考：《天津商业大学》2017年硕士论文

【摘要】：在制冷系统设计过程中,考虑到压缩比和系统运行效率,单级蒸气压缩制冷循环一般用到蒸发温度-30℃以上的系统,如果压缩比继续升高,单级压缩制冷系统中压缩机的相对余隙容积增加,输气系数会急剧下降,造成系统能效比的显著降低。解决大压缩比工况下的制冷系统运行问题,研究人员给出了两套技术可行的方案,其一是采用双级压缩制冷系统,其二是采用复叠式制冷系统。上述两种方案均可有效解决大压缩比带来的效率下降问题。从目前的研究情况来看,双级压缩制冷系统仍存在其技术应用的缺点,其不能解决单机双级压缩制冷系统的容量问题和配组式双级压缩机的回油问题。复叠式制冷系统由两个单机压缩制冷系统组成,压缩机独立运行,有效解决了双级压缩制冷系统的两个问题。本文以冷库制冷系统用复叠式制冷系统为研究对象,开展级间匹配问题的相关研究。目前国内外制冷系统中,复叠系统大多采用的是定频压缩机,高低温级系统流量比固定,一般根据工况和制冷剂特性选择最佳流量比,在实际环境当中,工况随时处于变换中,蒸发温度根据不同需要也会发生改变,甚至在一些特殊情况下制冷剂也会更换,要保持系统最佳运行状态就需要改变系统流量比;此外,定频压缩制冷系统通常通过开停机来实现温度恒定,造成压缩机频繁启停,耗电量增加,也会降低制冷系统的寿命,另一方面启停式制冷也会造成冷库温度波动较大,会造成食品干耗严重。针对目前冷库储存问题上的不足,本课题提出一种变流量复叠式制冷系统,高低温级均采用转子式变频压缩机,在相同工况条件下,通过调节节流阀开度和压缩机频率,改变高低温级吸气压力,从而找到最佳冷凝蒸发器的压力,减小冷凝蒸发器的换热温差,减小冷库温度波动。最终达到制冷系统高效运行和降低食品干耗的作用。在理论方面,课题以复叠式制冷系统的优化为目标,理论分析R410A单工质复叠式制冷循环在最佳中间温度下高低温级流量比和制冷系数COP的关系。理论分析结果表明:当低温级流量比增大时中间温度增加,COP先增大后减小,存在一个使COP值最大的最佳流量比;工况温度对COP的影响会大于流量比变化的影响,当环境温度上升或需要降低库温时,需要减小低温级流量,当库温需要迅速降温时,则需要增大低温级流量,同时还要调节高温级流量以确保复叠式制冷系统处于最佳的高低温级流量比。在理论分析的基础上,设计和搭建了复叠式制冷实验系统,系统由直流变频转子式R410A压缩机、风冷式冷凝器、钎焊式板式换热器,电子膨胀阀组成,采用热平衡法测试复叠式制冷系统的制冷量。搭建了既能进行单机压缩制冷循环又能切换为复叠压缩制冷循环的变制冷剂流量制冷系统,以满足不同系统的运行测试。本文通过理论建模和实验验证,总结出系统随负荷及工况变化时,高、低温系统制冷剂流量值和冷凝蒸发器最佳温度关系以及不同工况对系统能效的影响。研究表明:蒸发温度越高,冷凝温度越低,复叠换热温差越小,压缩机吸气过热度越小,冷凝过冷度越大系统的COP越大。影响系统性能的主要因素是蒸发温度和低温级系统冷凝过冷度。在提供-30℃以下低温时,R410A复叠式制冷循环系统比R410A双级压缩系统在安全使用,环境保护和能源节约方面更加具有优势。通过实验测量的数据验证了蒸发温度与冷凝温度对复叠制冷系统的影响,R410A的蒸发过热度控制在4~6℃之间,有利于系统性能的提高。
[Abstract]:In the process of the design of the refrigeration system, considering the compression ratio and the operating efficiency of the system, the single stage steam compression refrigeration cycle usually uses the system above the evaporation temperature of -30 centigrade. If the compression ratio continues to rise, the relative clearance volume of the compressor in the single stage compression refrigeration system increases and the gas transmission coefficient will drop sharply, resulting in the significant energy efficiency ratio of the system. To solve the problem of refrigeration system operation under the condition of large compression ratio, the researchers have given two sets of technically feasible schemes, one is using a double stage compression refrigeration system, and the other is a cascade refrigeration system. The above two schemes can effectively solve the problem of reducing the efficiency caused by the large compression ratio. The compression refrigeration system still has its shortcomings. It can not solve the problem of the capacity of the single machine and double stage compression refrigeration system and the problem of oil recovery of the matching double stage compressor. The cascade refrigeration system consists of two single compressor refrigeration systems, and the compressor operates independently, and the two problems of the double stage compression refrigeration system are effectively solved. In this paper, a cascade refrigeration system used in cold storage refrigeration system is taken as the research object, and the related research on the problem of interstage matching is carried out. At present, most of the refrigeration systems in the refrigeration system are fixed frequency compressor, the flow ratio of the high and low temperature level system is fixed, and the optimum flow ratio is chosen according to the working condition and the refrigerant characteristics. When the condition is changing at any time, the evaporation temperature will change according to the different needs, and even in some special circumstances, the refrigerant will be replaced. To keep the optimal operating state of the system, the system flow ratio needs to be changed. In addition, the constant frequency compression refrigeration system usually realizes the constant temperature by opening the machine, causing the compressor to start and stop frequently and consume electricity. As the quantity increases, the life of the refrigeration system will be reduced. On the other hand, the starting and stopping refrigeration will also cause the high fluctuation of the temperature of the cold storage. In view of the shortage of the cold storage problem at present, a variable flow cascade refrigeration system is put forward in this paper, and the rotor type frequency conversion compressor is used in the high and low temperature levels, and the conditions are in the same working condition. By adjusting the opening of the throttle valve and the frequency of the compressor to change the high and low temperature suction pressure, the pressure of the best evaporator is found, the heat transfer temperature difference of the evaporator is reduced and the temperature fluctuation of the cold storage is reduced. Finally, the effect of the efficient operation of the refrigeration system and the reduction of the food consumption is achieved. In theory, the subject is a cascade refrigeration system. The relationship between the high and low temperature level flow ratio and the cooling coefficient COP under the optimum intermediate temperature is theoretically analyzed. The theoretical analysis shows that when the rate of low temperature flow increases, the intermediate temperature increases, and the COP increases first and then decreases, and there is a maximum ratio of the maximum flow rate to the COP value; the temperature of the working condition is COP to COP. The influence of the flow ratio will be greater than the change of the flow ratio. When the temperature of the environment rises or needs to be reduced, the low temperature level flow should be reduced. When the temperature needs to be cooled quickly, the low temperature level flow should be increased. At the same time, the high temperature level flow should be adjusted to ensure the optimal flow ratio of the high and low temperature level at the cascade refrigeration system. On the basis of this, a cascade refrigeration experiment system is designed and built. The system consists of a DC variable frequency rotor R410A compressor, a air-cooled condenser, a brazing plate heat exchanger and an electronic expansion valve. The refrigeration capacity of the cascade refrigeration system is tested by the heat balance method. The variable refrigerant flow refrigeration system of the refrigeration cycle is used to meet the operating test of different systems. Through theoretical modeling and experimental verification, the relationship between the flow value of the refrigerant and the optimum temperature of the condensing evaporator and the effect on the system energy efficiency in different conditions are summarized by theoretical modeling and experimental verification. The higher the temperature, the lower the condensing temperature, the smaller the overlap heat transfer temperature, the smaller the superheat of the compressor, the greater the COP of the system. The main factors that affect the performance of the system are the evaporation temperature and the cryogenic degree of cryogenic system condensation. The R410A cascade refrigeration cycle system is compared with the R410A double stage compression system when providing low temperature below the temperature. The effects of the evaporation temperature and the condensation temperature on the cascade refrigeration system are verified by the experimental data. The evaporation overheat of R410A is controlled at 4~6 C, which is beneficial to the improvement of the system performance.
【学位授予单位】：天津商业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB657

【参考文献】