Analysis of quasi-secondary compression cycle characteristics of common refrigeration compressors in petrochemical equipment test Xu Shuxue, Ma Guoyuan, Peng Yu (Beijing University of Technology, Beijing 100124) The performance of the cycle. The gas-inductive characteristics and cycle performance of five common types of refrigeration and mining machines, such as piston type, screw type, scroll type, rolling piston type and centrifugal type, are analyzed. The characteristics of the air supply process and system cycle are summarized. The scope of their respective applications.
In recent years, there have been many studies on the quasi-secondary compression cycle of compressors. As a technically feasible and easy to implement technical solution, the compressor with improved fixed volume ratio has a significant effect in reducing the amount of heating (cooling) and reducing the compressor efficiency when deviating from the design working condition. The quasi-secondary compression cycle of the screw compressor was analyzed, and the design method of the air inlet and the calculation method of the compression work were proposed. The quasi-secondary compression cycle of the scroll compressor was studied. It was pointed out that the quasi-secondary compression heat pump cycle can be operated for a long time in a low temperature environment under the premise of ensuring the heat generation and performance coefficient. Researchers in the UK have analyzed the quasi-secondary compression cycle of carbon dioxide as a working fluid rolling piston compressor and built a test rig. 13. Based on changes in ambient temperature and cooling (heating) requirements, For the purpose of cycle characteristics of the unit, it is possible to construct a quasi-secondary compression cycle with different types of compressors, increase or decrease the flow rate of the working fluid in the compressor, change the heating or cooling capacity, improve the operating stability of the compressor, and form different evaporation temperatures, etc. . In this paper, the quasi-secondary compression construction methods of several commonly used refrigeration compressors and the cyclic characteristics of their systems are analyzed.
Introduction to Fund Projects National Natural Science Foundation of China (50776001) 1 quasi-secondary compression cycle type quasi-secondary compression cycle type with subcooler system (a) flash system (b) supercooled liquid storage system (c) As well as the ejector system (d), the gas refrigerant charged by the flasher system is closer to saturation than the subcooler system and the supercooled reservoir system, so the system performance is improved to a better extent, only the design The flashing system requires a higher matching of the two-stage throttling components. The system with the ejector utilizes the pressure energy of the refrigerant in the supplemental gas line to pre-compress the priming fluid, which increases the displacement of the compressor to a greater extent and improves the efficiency of the compressor. Experimental studies have shown that the system with the injector is better than the supercooled reservoir system. 142.2 The quasi-secondary compression cycle of the different type compressors is shown in the quasi-secondary compression cycle of the 2.1 piston compressor piston compressor. The air inlet of the piston compressor can be located at a certain position on the top or inner wall of the piston cylinder, which is determined by the purpose of qi. When the air inlet is installed at the top of the cylinder, the low-temperature low-pressure (liquid or two-phase) refrigerant is injected into the compressor chamber from the top of the piston compressor, which can cool the cylinder, reduce the refrigerant temperature and make up for the compressor. Insufficient inhalation 15. When the purpose of the air supply is to form a plurality of evaporation temperatures, the position of the air supply port may be set at a certain position on the cylinder wall. The working process is as follows. The piston moves from the outer dead center to the inner dead center to suck in the low-pressure refrigerant vapor, during which the air-filling orifice is covered by the piston. When the piston moves to the position close to the inner dead center, the intermediate air supply hole is opened, the intermediate pressure gas enters the cylinder, and the pressure is higher than the original suction pressure in the cylinder. At the moment when the intermediate pressure gas enters the cylinder, the suction valve is closed, and the piston is closed. Continue to the inward stop motion, and after the end dead center, the middle air supply process continues. During the process, the air vent is again covered by the piston, and the middle qi process ends.
Experiments show that the degree of improvement of the refrigeration coefficient COP is different under different refrigerants and different evaporation temperatures. The refrigerants that improve the COP are more pronounced R717 and R115, while R12, R22 and R502 are lower than the normal single-stage compression cycle.
Theoretical and experimental research on double-temperature refrigerator with qi is carried out. (b) The method of intermediate qi is used to make the refrigerator refrigeration system have two kinds of evaporation temperatures, which reduces the temperature difference and the irreversible loss of heat transfer process. Experiments show that at ambient temperature of 25 ° C and 32 ° C, the secondary air compressor for refrigerators has obvious energy-saving effect regardless of R12 or mixed refrigerant R22/R142b. Electric 1 piston compressor 2 condenser 3 reservoir 4 capillary 5 heat exchanger 6. High temperature evaporator 7 low temperature evaporator piston compressor quasi-secondary compression cycle piston compressor maximum air supply problem is on the gas supply line The design and control of the intermittent opening valve, because the suction and exhaust of the piston compressor is periodic, the timing of the qi is not good will seriously affect the normal operation of the compressor.
2.2 Screw Compressor The screw compressor has the working characteristics of one-way suction and exhaust. Therefore, it is convenient to design the system as a quasi-secondary compression system. To this end, a plenum is added to the gap between the tooth groove and the suction port of the screw compressor. The working process is that after the suction is completed, the base volume is closed for a period of time and then connected with the air supply port. The middle air supply hole is gradually opened with the rotation of the screw, the air volume is gradually increased, the pressure inside the cavity is gradually increased, and the pressure difference is reduced. The amount of gas is also reduced until the end of the qi process. By analyzing some of the main losses of the medium pressure aeration process and the mixing pressurization process, we can find the relevant parameters that can obtain the ideal process and the geometrical characteristics of the optimal air inlet channel. The current prevailing optimal intake position is based on the fact that the pressure after mixing the intake air is equal to the pressure in the cycle. It is also believed that the operating heat pump cycle conditions will be affected by the ability of each of the four mixed working fluids Lu 22'R142b better than the ecttodcPublishi random factors g1 ring 5s so-called best qi points should be the best area of ​​Si.
Attention should be paid to the opening of the venting hole: 1 The flow cross section should satisfy the isentropic flow of the medium pressure intake as much as possible. 2 Stop the air supply after the element volume is separated from the medium pressure air supply port. The mixing pressure in the 3 element volume is not greater than the medium pressure. The medium-pressure gas is injected into the element volume of the screw machine according to the isentropic process, and the generated kinetic energy reversibly enters the nip of the screw machine along the tangential direction of the rotation of the screw machine rotor, so as to facilitate the effective conversion of energy.
After the addition of the economizer, a large amount of refrigerant liquid passing through the container is cooled, the degree of subcooling becomes large, and the refrigeration capacity of the system is increased, and the increase of the compression work caused by the intermediate qi process is less than that of the cooling capacity, thereby improving the system. The coefficient of refrigeration. The size of the supercooling benefit is related to the nature of the working fluid and the working conditions. Under the same working conditions, the liquid is smaller than the heat, and the latent heat of vaporization is also relatively small. Compared with R502, R12, R22 and R717, R502 is the best, followed by R12R22 and R717. After the economical device is set, the refrigeration capacity of the refrigerant R717 can be increased by about 22% under the condition of t=-35Ktk=35°C. If the refrigerant R22 is used, the unit cooling capacity of the unit is increased by 7%~30%. 2.3 The scroll compressor of the scroll compressor was patented by the French Creux in 1905, and it began to rapidly after the silence of the early 20th century. Developed. The utility model has the advantages of high efficiency (continuous one-way operation of suction and exhaust gas, volumetric efficiency is more than 95%), small torque variation, small vibration, low noise and simple structure. Most of the current small household air conditioners (1 to 15 kW) use scroll or rolling piston compressors. The structure of the scroll compressor is more complicated, so its qi is involved in more content. See the scrolling disc and the filling hole opening area of ​​the scroll machine.
The three working processes of the suction, compression, and exhaust of the scroll compressor are continuously performed in one direction, and the start and end of the supplemental gas are automatically opened or closed as the scroll rotates. Studies have shown that: (1) to obtain the maximum heating energy, the filling hole is more suitable in the position where the suction chamber is just closed. 2 The power consumption and heating capacity of the compressor increase with the increase of the supplemental pressure, and the maximum heat and the preferred heating coefficient can be obtained under a certain intermediate pressure.
Compared with the ordinary unit, when the evaporation temperature is 25 °C, the quasi-secondary compression system can increase the heating capacity by 20% and the COP by 14%. When the evaporation temperature is 20 °C, the quasi-secondary compression system can increase the heating capacity by 14%. %~20%, COP can be increased by 6%~8%, and the exhaust temperature is controlled below 130 °C to ensure safe operation of the unit.
2.4 Rolling piston compressor The rolling piston compressor is also one of the main models of small air conditioners. Composed of a stator and an eccentrically rotating rotor, the compressor performs a complete inhalation and exhaust process for each revolution. The position of the air inlet and the air supply pressure determine the quality of the refrigerant to be replenished or released. See the air supply position of the rolling piston compressor.
The amount of injection/release of the working fluid is seen as a function of the change in the angle of the compressor. It can be seen that the injection amount decreases as the rotation angle of the rolling piston increases, because the pressure of the gas in the chamber increases as the angle of rotation increases, and the pressure difference between the injected medium and the working medium in the chamber decreases. The release amount increases as the angle of rotation of the rolling piston increases, because as the angle of rotation increases, the pressure of the gas in the chamber increases, increasing the pressure difference between the working medium in the chamber and the working medium. The power consumption of the compressor is closely related to the quality of the cavity. When the outdoor temperature rises to a certain value, the compressor performs deflation and compression, causing the compressor power consumption to drop drastically.
Shrinking the loop, it adjusts the capacity as the environment changes. When the heating cycle is carried out in winter, if the ambient temperature is very low, the insufficient circulation of the working fluid leads to insufficient heating capacity and the isentropic efficiency of the compressor is reduced. The compressor performs the air circulation cycle to ensure that the heating coefficient is not lowered and the system is improved. Heat; when the refrigeration cycle is carried out in summer, if the ambient temperature is low, the indoor cooling load is reduced, and the optimal operating condition of the refrigeration cycle is deviated. The system no longer requires a large working fluid circulation of the compressor, and the compressor releases. Cycle to ensure continuous operation of the compressor under low load conditions.
2.5 Centrifugal Compressor The Freon centrifugal chiller is generally single-stage under normal working conditions. When lower temperature is obtained, two or more impellers are often used. In order to improve the cycle efficiency, a quasi-secondary compression cycle with intermediate gas is used.
The air inlet of the centrifugal compressor should be placed in the middle of the two-stage impeller, so the number of air inlets is less than the number of stages. 1. When the number of stages is greater than or equal to 3, a cycle of multiple economizers can be formed (b). The evaporating temperature can be used at a temperature above 7 °C for a secondary impeller, with a three-stage impeller above 23 °C, and a four-stage impeller at a temperature above 40-45 °C. The flashing of the air supply circuit and the cooling of the air supply circuit are required to be heated. The steam absorbs heat in the closed tank, so that the liquid suction port entering the throttle valve is in the air supply position of the piston compressor. 1 Intake port 2 In addition to the 7% exhaust port of the centrifugal compressor 3, the intermediate air supply cycle can also reduce noise, eliminate low-load surge problems, and extend the life of the unit.
The results of the quasi-secondary compression cycle of five different types of refrigeration compressors, such as piston, screw, scroll, rolling piston and centrifugal, are as follows: 1 The quasi-secondary compression cycle adaptation of various compressors The change of the working environment makes the efficiency of the compressor deviate from the design working condition and the condition of insufficient heating (cooling) is obviously improved. It is only necessary to simply modify the original unit, and the performance after the transformation is stable and easy to implement. 2 According to the structure and working characteristics of different types of compressors, the parameters of the secondary compression cycle air inlet (size, shape, position) should be designed. At the same time, the air supply parameters should be determined according to the system characteristics and work purpose, and a reasonable cycle type should be selected. .
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