Numerical Investigation On Characteristics Of Scroll Compressor Under Variable Operating Conditions

The scroll compressor has the advantages of high efficiency, energy saving, low noise, small volume, light weight, simple structure and stable operation and other characteristics, it has been widely applied in refrigeration, air conditioning, power engineering, transportation and other fields.With the change of the working environment and the demand of flow regulation, the scroll compressor often operates under variable conditions. In recent years, there are many researches on the flow field distribution in the scroll compressor, but the analysis of the flow field under the condition of variable condition is less. Therefore, in this paper the commercial code PumpLinx has been used to simulate the internal flow field of the scroll compressor under two working conditions of variable pressure ratios and variable speeds. The simulation results of flow changes of scroll compressor are discussed in detail and the effects of pressure ratio and rotational speed on the performance of scroll compressor are obtained.To study the change law under the variable conditions of the scroll compressor internal flow field, the refrigerant in the evaporator temperature is 7.2?, the compressor suction and exhaust pressure were 0.625MPa, 1.6446 MPa, the internal flow field of scroll compressor speed under 2880r/min is analyzed in detail. The results show that: the scroll compressor chamber pressure distribution is quite uniform, but temperature distribution is not uniform; the outlet temperature is fluctuant. At the suction and compression chamber exhaust vortex. The tangential leakage velocity is larger. Import and export quality flow fluctuations, the entrance quality is not 0 when the orbiting scroll at 0 degree.At the speed of 2880r/min, by changing the inlet pressure to control the internal pressure ratio,this paper makes a numerical simulation of the scroll compressor under five pressure ratio conditions. The five conditions are under the compression condition. The numerical results show that under the compression condition, with the decrease of the pressure ratio, scroll compressor chamber pressure to the exhaust pressure angle gradually close to the discharge angle, leakage velocity between the exhaust chamber and the compression chamber decreases as the pressure ratio decreases. The fluctuation of mass flow rate of inlet and outlet is obvious, which increases with the decrease of pressure ratio. The influence of the pressure ratio on input power and volume efficiency are not changed. The cooling capacity and COP,torque of orbiting scroll increase with the decrease of the pressure ratio. The results show that the performance of scroll compressor can be improved by decreasing the pressure ratio.As an important parameter to adjust the displacement of scroll compressor, speed is very important to the performance of scroll compressor. In this paper, the numerical simulation of the variable speed of the scroll compressor with inlet and outlet pressure of 0.625MPa and 1.6446 MPa are carried out. In the 1080 r/min to 4320 r/min speeds range, maximum cavity pressure gradually increased and symmetric cavity pressure imbalance gradually increases with the increase of speed . The angle of the cavity pressure reaches the exhaust pressure increases gradually but still less than the exhaust angle. The results show that the scroll compressor is under compression condition. The maximum leakage velocity, the flow velocity and the mass flow rate increase with the increase of the rotating speed. The cooling capacity and input power also increase with the increase of the rotating speed. When the rotational speed is lower than 2880r/min, with the increase of rotating speed, the exhaust temperature decreases gradually, the volumetric efficiency increases rapidly. When the rotating speed is higher than 2880r/min, with the increase of the rotating speed, the exhaust temperature changes little, the volumetric efficiency increases slowly.Because the exhaust loss increases when the rotating speed increases rapidly and cause power consumption increases, COP increases with the speed increased first and then decreased, there exists an optimum speed.Therefore, in the actual operation of the scroll compressor, the reasonable speed and pressure ratio should be selected, so that the scroll compressor has the highest efficiency.