Research On Characteristics Of Gas-injection Scroll Compressor

In vehicle air conditioning system,scroll compressor has been widely used because of high efficiency,energy saving and simple structure.Although it has many advantages that other compressors don’t have,it’s low efficiency and high exhaust temperature at low temperature limited its further application.To solve this problem,the structure of gas injection scroll compressor was put forward.Gas injection scroll compressor can fill refrigerant with suitable temperature and medium pressure in the compressor chamber during the process of compression by opening the air injection hole on the suitable plate of scroll compressor.By doing this,the efficiency of the system will increase and the exhaust temperature will decrease,the air injection scroll compressor always has good performance.This paper researched on the gas injection scroll compressor.First,the working principle of gas-injection compressor was explained and two quasi-two-stage compression systems and two quasi-three-stage compression systems with gas-injection compressor and their working process were researched as the basic of following studies.The circular involute was used as the scroll line and the mathematical expression of the circular involute was given and the 3d model of the scroll compressor was established.Then the parameters of the conventional scroll compressor such as scroll tooth thickness,scroll pitch and spindle eccentricity were calculated according to the model and mathematical expression.Gas injection scroll compressor needs to be designed by conventional scroll compressor,so the design of the conventional scroll compressor is the basic of the design of the gas injection scroll compressor.Then the calculation procedure of quasi-two-stage compression system was designed based on the joint simulation of MATLAB/SIMULINK and REFPROP to calculate the performance of quasi-two-stage compression system with flash tank and economizer;heating COP,heating capacity,exhaust temperature and compressor power consumption of the system with different injection pressures are calculated.Results show that quasi-two-stage system with flash tank and economizer can improve heating COP by and 4.4% and 3.5% compared with conventional system,and the best injection pressure based on the best heating COP and the best place for air injection hole are determined,the effects of relevant parameters such as injection dryness and mass flow rate on system performance are also analyzed.Then the calculation procedure of quasi-three-stage compression with two flash tank was designed;the above parameters of the system with different first and second injection pressures are calculated.Results show that quasi-three stage system can improve heating COP by 7.5% compared with conventional system,the best injection pressures based on the best heating COP and the best places for gas injection hole are determined,the effects of relevant parameters such as injection dryness and mass flow rate on system performance are also analyzed.Advantages and disadvantage of different injection holes were analyzed.Then by extracting the flow passage based on the model of air injection scroll compressor,the flow passage of gas injection scroll compressor used for CFD simulation was got.In the CFD simulation,the boundary temperature and pressure were got according to the data,the UDF to define the motion of scroll plate was written according to the actual movement of scroll plate.Then the result of refrigerant temperature,pressure,velocity and exhaust mass flow rate and injection mass flow rate in gas-injection scroll compressor with different structures were got.At the same time,the effect of different injection holes on refrigerant flow in the scroll compressor was also studied by simulation.The experimental scheme of gas-injection scroll compressor system was designed,the injection hole was opened on a scroll compressor to get the gas injection scroll compressor.Then the parts in the system such as inner heat exchanger and expansion valve were chosen based on the system performance,the control logic of the system and experimental conditions were also established.