Application Research of Frequency Conversion Technology in Single Screw Refrigeration Compressor

:Frequency conversion technology; single-screw refrigeration compressor; application 1 bow singular single-screw refrigeration compressor has the characteristics of simple structure, good force balance, long bearing life, low vibration, low noise, etc., currently in refrigeration and air conditioning conditions There are great applications in it. Due to the application and changes in external climatic conditions, the single-screw refrigeration compressor requires a certain cooling capacity adjustment function in the design process to meet the needs of different load conditions, achieving energy saving and consumption reduction effects.

In the work that has been completed, domestic and foreign scholars have conducted a series of studies on the energy regulation mechanism and its working principle, and proposed many different techniques for adjusting the cooling capacity of the single-screw refrigeration compressor. Japan's Mitsui Seiki machine first used a membrane gas regulator to achieve cooling capacity adjustment. The mechanism can be installed independently on the intake pipe, which has no effect on the mainframe structure, but the structure is more complicated, only the small screw with frequent changes in gas volume. Used in compressors. Subsequently, Jin Guangyu (1983) studied the basic structure and working principle of the rotating ring gas volume adjustment mechanism used in the single-screw refrigeration compressor, and proposed the determination method of each structural parameter in the design process of the rotating ring. B.Zimmern( In 1983, 2000, a method of adjusting the air volume of a single-screw refrigeration compressor through a spool valve was proposed, and the adjustment mechanism of the spool valve was improved. After that, Daikin Corporation of Japan (28 proposed a modification scheme of the spool valve, that is, The groove section of the spool valve is provided with a boss, and the pressure generated by the refrigerant gas on the boss is used to suppress the rotation of the valve body, thereby ensuring the gap between the spool valve and the screw rotor. In the theoretical research of the gas volume adjustment method, Zhou Lei, Lin Qiang, Jin Guangyu, et al. (1998) studied the effects of the rotary ring regulator and the spool regulator on the internal volume ratio, the indicated power and the specific power of the compressor used in the gas volume regulation of single-screw refrigeration compressors. Control of changes in volume ratio to reduce or even avoid additional energy losses, Zhou Lei and Jin Guangyu (1999 proposed a split spool structure, but Due to its complicated adjustment mechanism, its application has not been seen. In 2007, the US VILTER formula proposed a double-slip valve gas volume adjustment mechanism and applied for a patent.

Although the double slide valve adjustment mechanism theoretically eliminates the energy loss caused by over-compression, it needs to separately control the displacement of the slide valve by gears, racks, etc., and the stability is poor, so it is currently used more in the single-screw compressor. Still a single slide valve gas volume adjustment mechanism.

It can be seen that the current single-screw refrigeration compressors use more air volume adjustment methods, such as membrane type, rotating ring type and spool type, and the use of frequency conversion technology in single-screw refrigeration compressors has not been disclosed. the study.

In this paper, the structure and working characteristics of the single-screw refrigeration compressor are studied. The problems that may occur in the application of the frequency conversion technology in the single-screw refrigeration compressor are studied. The strength of each component due to the high pressure in the compression chamber during the compressor startup process is analyzed. The impact and comparison of the energy consumption of the compressor under the two conditions of refrigeration and heating after the use of frequency conversion technology. Through analysis, the technical difficulties of frequency conversion technology in single-screw refrigeration compressor are pointed out, and the basis for developing new technology is provided.

2 Principles of Frequency Conversion Technology With the development of economy, the demand for electric energy in human production and life is increasing. Therefore, the application of green energy-saving inverter technology in the air-conditioning refrigeration industry is also emerging. The frequency conversion speed regulation is to adjust the speed by changing the frequency or voltage of the stator winding of the motor. Current frequency conversion technologies used in refrigeration units include DC frequency conversion and AC frequency conversion.

AC frequency conversion technology is a technology that changes the frequency of the power supply through the frequency converter, thereby changing the speed of the compressor. When the three-phase AC power is connected to the stator winding, the motor speed can be used by the public. http:// swin矣 矣 矣 sw swmm quasi-swmid 矣 矣 矣 s s problem: (3) single-screw refrigeration compressor At shutdown, the pressure within the entire system is balanced, at which point the pressure is the flushing pressure, which is much higher than the inlet pressure during the compressor design process. If it is started directly without unloading, the pressure in the compression chamber will be much higher than normal, which will bring great challenges to the strength of the main components of the compressor.

2 The position of the exhaust port is fixed after the design of the single-screw refrigeration compressor. When the variable frequency technology is used to adjust the gas volume of the compressor to adapt to the load change, the pressure ratio will also change. However, due to the fixed position of the exhaust port, the internal volume ratio is not adjustable, resulting in unequal internal and external pressure ratios, which will bring additional energy loss.

3 Excessive internal pressure during the start-up process will not only affect the structural strength of the internal components of the compressor, but also increase the starting torque of the compressor and increase the starting load of the motor.

4 The speed change has a great influence on the running characteristics of the bearing.

4 Calculation results and analysis For the single-screw refrigeration compressor of a certain model, the influence of the frequency conversion technology on the working process of the single-screw refrigeration compressor is analyzed from the perspective of the first two problems in the previous section. The parameters of this type of compressor are shown in Table 1. The refrigerant used is R134a. The main parameters of the single-screw refrigeration compressor of Table 1 are the diameter of the screw diameter. The center of the star wheel is the width of the star wheel. 4.1 The starting process The high pressure in the compression chamber is due to refrigeration. The demand for the quantity, after the chiller assembly machine is completed, when the compressor is in the shutdown state, the refrigerant in the whole system is in equilibrium, and the internal pressure is much higher than the suction pressure. When the compressor is started, the inhaled gas is an equilibrium refrigerant vapor whose pressure is much higher than the rated suction pressure of the compressor. The traditional mechanical unloading scheme can also perform the unloading during the startup process while adjusting the gas volume. However, the frequency conversion technology realizes the gas volume adjustment by changing the rotation speed, which makes the single-screw refrigeration compressor adopting the adjustment scheme have the characteristics of high starting pressure and large force of each component in the starting process.

Below we analyze the stress of the compressor in the starting state and normal operating state. Due to the special structure of the single-screw compressor, the star-wheel symmetric arrangement and the two ends of the screw are connected by the balance hole, so that the screw rotor is theoretically free of axial force and radial force. Therefore, we focus on the star wheel in the analysis. Force.

During the operation of the compressor, the force of the star wheel is as shown. The gas force Fg is equal to the gas force received by the three star teeth that are simultaneously engaged.

The force of each star tooth is A star wheel indexing angle swin air intake closed angle quasi-swmid star tooth front side biting the cogging when the star wheel angle quasi-swout star tooth back side biting the cogging star wheel Corner (quasi sw.) - pressure in the working chamber at any corner position p suction pressure Si - area of ​​the i-th star tooth bite into the groove b star tooth width Rsr - screw diameter Rsw - star wheel diameter a center The half angle of the S-tooth width is visible, and the gas force acts on the star tooth near the top of the tooth, and the gas force will generate a tipping moment. This overturning moment needs to be balanced by the torque generated by the bearings at both ends of the star wheel bracket.

From the above formula, the gas force and overturning moment on the star wheel of the normal working condition and the starting moment are calculated respectively, and the calculation results are as shown in 3.

From, 3 can be seen, during the start-up process, the force of the star wheel is far away. The working parameters of the compressor are the parameters of the refrigeration condition. The heating condition is the chilled water inlet and outlet temperature fc) 12/7 the source water inlet and outlet temperature (c) 15 /7 Cooling water inlet and outlet temperature (°c) 30/35 hot water inlet and outlet 5 only Peng Peng 4.2 variable working conditions Additional energy loss After the design of the single screw refrigeration compressor, the position of the exhaust orifice is fixed. However, the application and external climatic conditions are constantly changing, and the frequency conversion technology cannot adjust the internal volume ratio, which causes the compressor to operate under different working conditions, resulting in additional energy loss due to unequal internal and external pressure ratios. Shown is the pv diagram of the working process of the compressor under different load conditions.

It can be seen from b and 0 that when the internal and external pressure ratios of the compressor are not equal, there is inevitably an additional loss of power consumption. The power consumption of the compressor during operation under both cooling and heating conditions is now analyzed. Table 2 shows the operating parameters of the compressor operating under both cooling and heating conditions.

The overturning moment of the star wheel angle (deg) star wheel is much higher than the force of the star wheel during normal operation of the compressor, and can reach twice the normal working condition. At the same time, the overturning moment generated by the gas force needs to balance the bearings on both sides of the star wheel bracket, so the load of the bearing increases.

Based on the above analysis, we can find that in the single-screw refrigeration compressor using the frequency conversion technology for gas volume adjustment, if the unloading device is not provided, it is necessary to improve the strength of the component and the bearing capacity of the bearing in the design process.

According to the operating parameters in Table 2, the power consumption of the compressor at different speeds is analyzed. In the existing design method, the refrigeration compressor in the chiller is generally designed according to the refrigeration condition. Therefore, we calculated the additional energy loss due to the change of internal pressure ratio under heating conditions for the compressor designed for refrigeration conditions. The calculation results are shown.

14W "+ additional energy loss â–² compression mechanism The additional energy loss of the thermal condition is compared with the energy consumption of the normal compression work compared with the heating condition. The additional energy loss accounts for 0.58% of the total energy consumption. It is thus seen that the frequency conversion technology is adopted. The compressor that performs the air volume adjustment has a small additional energy loss due to the difference in internal and external volume ratios when the operating conditions are changed, which is negligible.

5 Conclusions This paper analyzes the problems caused by the application of frequency conversion technology in single-screw refrigeration compressors. The following conclusions are drawn through analysis: (3) During the startup process of single-screw refrigeration compressors with variable frequency technology, the star wheel is far-reaching. Under normal working conditions, the star wheel can be forced to double the normal working condition; 2 when the application and external climatic conditions change, the imbalance of internal and external pressure ratio will generate additional energy loss, and the cooling condition is The additional energy loss of the benchmark designed compressor under heating conditions accounts for 0.58% of the total energy consumption. It can be seen from the above analysis that the first problem to be solved is to apply the variable frequency technology to the single-screw refrigeration compressor. The problem of excessive pressure in the compression chamber.

Adsorption Dryer is another type of dryer used to get rid of water in compressed air. It achieves drying effect by "pressure change" (pressure swing adsorption principle). Because the moisture containing capacity of air is inversely proportional to pressure, part of the dried air decompresses to atmospheric pressure, this pressure changes makes the expanded air gets drier.Then let it pass through adsorption tower which need regeneration, the drying regeneration air extract water, then take the water out of adsorption tower. So adsorption dryer normally are of twin tower construction. One tower dries the air from the compressor while the desiccant in the other tower is being regenerated after the pressure in the tower has been reduced to atmospheric pressure.

There are two types of adsorption dryers: heatless adsorption type, no internal or external heaters are used, and heat adsorption dryer, which need a heater. Compared with Refrigerant Dryer, the advantage of adsorption dryer is its drying performance is beter, but its disadvantage is this kind of dryer consumes compressed air, which makes operation power consumption bigger.

Adsorption Dryer

Adsorption Dryer,Adsorption Air Dryer,Adsorption Compressed Air Dryer,Regeneated Adsorption Air Dryer

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