The 2005 "Special Research Fund for Doctoral Programs in Colleges and Universities" scroll compressor is a new type of high-efficiency positive displacement compressor developed in the late 1970s. It overcomes many defects of previous compressors and has low energy consumption. With the advantages of small vibration, small size and light weight. With the intensification of the energy crisis, it is imperative to research and develop a new generation of energy-efficient scroll compressors. This paper adds liquid to the traditional compressor structure. The refrigerant is injected into this part, and the influence of this process on the thermal behavior of the compressor is analyzed. From the theory and the same, in the compression chamber, there are both refrigerant vapor and refrigerant liquid, and the injected refrigerant liquid According to the pressure in the compression chamber at this time, a part can be vaporized to form steam, and the other part is still in a liquid state. In the control volume, the refrigerant gas is sucked, the refrigerant liquid is injected, the refrigerant is discharged, and the refrigerant and the scroll wall occur. The heat exchange is dynamic, and the heat exchange relationship between them will be explained below.
2.1 The general model of the compressor cylinder for refrigerant injection is the control volume. The analysis model is shown in the figure. In the control volume, the mass of the refrigerant vapor mg and the mass of the refrigerant liquid are simultaneously present. The heat transferred from the agent to the liquid refrigerant is Q, the heat transfer between the scroll wall and the liquid refrigerant is Qw, the heat transfer between the scroll wall and the gas refrigerant is Qw, and the evaporation amount of the liquid refrigerant is. The energy conservation equation and the mass conservation equation are: 730050 Lanzhou Lanzhou University of Technology, School of Petrochemical Engineering, steam ratio; Ggm-injected vapor mass flow rate; hgm-inflow vapour ratio; hg-gas ratio ç„“; vg- The specific volume of the gas.
The volume change equation of the control volume is: U-reflux flow rate, D-intake channel diameter, - thermal conductivity, v-kinetic viscosity, Pr-refrigerant Reynolds number.
During the compression process, the refrigerant absorbs heat from the suction process, the compression process, and the exhaust process. In the compression chamber, the heat transferred from the scroll wall to the refrigerant is represented by the following formula: T-refrigerant temperature, Twt compression The temperature of the chamber wall, the Awt heat transfer area, that is, the sum of the peripheral area of ​​the vortex wall and the upper and lower surface areas of the vortex in the suction chamber and the compression chamber.
Heat transfer coefficient.
The formula derives that the nature of the refrigerant is determined by the average pressure conditions of the inhalation and exhaust processes.
The heat absorbed by the liquid refrigerant from the injection passage to the compression chamber can be expressed by the temperature of the vortex wall of the Tr injection passage; Tin-the refrigerant saturation temperature at the injection passage pressure; and the heat transfer of the AP-injection passage. Area; heat transfer coefficient, which can be expressed by the following formula: D-channel diameter, U-injection speed. : V-volume; specific volume of Vi-liquid; mass flow rate of Glin-injected liquid; mass flow rate of Gio-outflow liquid.
2.2 Description of heat flow In the dynamic process of refrigerant gas suction, refrigerant liquid injection and heat transfer between the scroll wall and the refrigerant, the heat is calculated according to the following formulas. 2.2.1 Intake process The flow of heat from the refrigerant suction passage into the compression chamber can be expressed as As - the heat transfer area from the suction hole to the refrigerant suction hole; the temperature of the Tsuc-suction refrigerant; Ts- The vortex wall temperature from the suction hole to the refrigerant suction hole; as-heat transfer coefficient.
3. Increase the subcooling temperature of the refrigerant by heat exchange. The circulation of the oil is driven by a gear pump and the viscosity of the oil is measured by a viscometer. The refrigerant flow rate through the evaporator is measured by the Coriolis type flow meter. The relationship between the compressor power and the injection rate. Note: Compressor power; LR-injection rate is the compressor power at R%.
4 Relationship between inhalation mass flow rate and injection rate Note: G-inhalation mass flow rate; Gr-injection rate is R%% mass flow rate.
The amount of flow into the refrigerant injection passage is measured by an ellipsometer. The suction and discharge pressure of the compressor is measured by a pressure gauge. The exhaust gas temperature is measured by the thermocouple. As the injection rate increases, the exhaust gas temperature decreases linearly. As shown, this indicates the heat transfer alignment occurred during the refrigerant injection phase. The gas temperature has a large influence, which verifies that the heat transfer model of the injection phase in the theoretical model is correct.
From. At this point, the compression power is increasing, as shown. However, due to the increase in compressor power, the adiabatic efficiency of the compressor is gradually reduced, and this trend is as shown. However, as the injection rate increases, the heat transfer process from the vortex wall to the refrigerant gradually increases, causing the temperature of the vortex wall to decrease, thereby effectively alleviating the tendency of the compression efficiency to decrease.
As the injection rate increases, the temperature of the oil decreases and the solubility of the oil increases as shown. The large amount of oil dissolved causes the viscosity of the oil to be greatly reduced, which, as shown, will increase the mechanical loss of the compressor. It has been observed from experiments that in the range of higher injection rates, foaming occurs in the oil and oil oozes out of the closed container, which reduces the reliability of the compressor.
The technology of injecting liquid refrigerant into the scroll compressor can effectively reduce the exhaust temperature of the compressor, improve the circulation efficiency of the refrigerant and the heat transfer efficiency of the condenser. Therefore, this technology deserves our in-depth study and improvement.
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