Study On Reciprocating Compressors With Soft Suction Structures And Discharge Structures

Based on the experimental work of a refrigerator compressor with soft suction structures, the new soft suction structures were put forward. The performance of the compressor and the frequency properties of noise were also studied by means of tests. The results showed that these structures could reduce the noise of compressor. The main experiments included refrigeration capacity, COP, vibration, noise and its spectrum. The soft structures of suction and discharge, materials and main assembling requirements were offered in this paper. The testing system, testing process, testing conditions and testing results were also put forward. The testing results were analyzed in the end of this paper. INTRODUCTION Energy economy and environment protections are becoming the two focus problems for us. The reciprocal compressor, being widely used in small refrigeration devices, wanted to be with lower cost, with higher efficiency and at lower noise/vibrate level. It is necessary that analyze the factors that affect the performance and the noise characteristics of compressor, reexamine its structure and materials, redesigned its craft process, so as to raise the energy efficiency [1][2][3] and to subdue the noise/ vibrate level . Adjusting the suction way , for example changing the indirect gas suction to direct suction, using the concave valve plate [1][2][3] are two of the efficient methods, hence being adopted in most of the high-efficiency reciprocal compressors. Raising the gas pressure in the suction is regarded as another way to improve the energy efficiency [10] of reciprocal compressor. Takahide Nagao [5] and Alessio Farason [6] have investigated on noise reduction of high-efficiency compressors. Hyuk Lee's work [7] focuses on how to reduce the noise caused by the discharge valve system. Using a soft structure on the direct suction passage and muffler , the pressure fluctuations at the inlet of the suction valves were decreased, so that the noise and the vibrations can be obviously cut down. On the bases of the work , the new soft suction were put forward. The performance of the compressor and the frequency properties of noise were also studied by means of tests. The results showed that these structures could reduce the noise of compressor. The main experiments included refrigeration capacity, COP, vibration, noise and its spectrum. The soft structures of suction passage, its materials and main assembling requirements were offered in this paper. The testing system, testing process, testing conditions and testing results were also put forward. The testing results were analyzed in the end of this paper. STUCUCTURE OF SUCTION PASSAGE AND MUFFLER The direct suction was adopted in the sample compressors. Piston-cylinder part was under the motor of the compressor as shown in fig. 1. In the suction process, the refrigerant vapor flow through the suction passage, the muffler, and the top of the cylinder, the suction valve in sequence, and finally enter the cylinder. The suction passage was soft structured, made of elastomeric materials, and fixed by connecting spring, as shown in fig. 2. The muffler was also made of elastomeric materials, as shown in fig. 3. In order to decrease the pressure fluctuations caused by the reciprocal motion of the piston, a flow resistance at the inlet of the muffler was increased by means of the circumfluence method, as shown in fig. 4. By this way, the energy efficiency of the compressor can be raised as well. It is necessary that optimize the structure and the properties of the passage and the muffler when they used in different type of compressor. SAMPLE COMPRESSORS Two type compressors were chosen. Using the new suction passage and muffler, each kind of sample includes 30 sets. They adopt R134a as the refrigerant and Ester VG22 as the lubrication oil. The first kind of model is with slide sleeve type and 2.98cc for its sweeping volume of the piston, another is crank rod one and its sweeping volume of the piston is 7.96 cc. The farmer is on the base of QD30 produced by the plant A and the second is on the base of QD80GL produced by the plant B. The difference between the test sample compressors and theirs fathers is the suction passage. The way of gas suction in compressor QD30 is indirect suction and in QD80GL is direct suction. All of them are assembled on the plant lines. EXPERIMENTAL DISCRIPTIONS According to the test conditions formulated by the standard [11], the refrigeration performances of the samples were measured with thermometer. The experimental results show in table 1 and table 2. During the test process, the gas pressure was controlled within rang from 113.7Kpa to 114.8Kpa in the suction end and within rang from 1465Kpa to 1475Kpa in the discharge system. In term of the test conditions and process prescribed by the standard, the noise was tested for the models. The anechoic room and the substitute refrigerating system for the experiment are tallied with the prescription of the standard. In order to eliminate the effect of the substitute refrigerating system, several topical revisions had been made. The pipe in suction side of the system is a very soft pipe what made from nylon. A heat insulation tank was added between the valve and the nylon pipe and placed out of the anechoic room where the air temperature can be adjusted and controlled. The discharge pipe had been handled with fire fade. A specific dryness filter was added in the system as well. At the suction side of the substitute test system, an oil tank was added to keep the suction gas temperature within -20±0.3°C steadily. The distance of the suction pipe from the tank to the compressor shell is about 250 millimeters. The electric source should be put off for about 2 minutes before you start to record the noise data and keep the state to you finish your test. The noise test conditions are shown in table 1. The recorder starts to work while the compressor begins to work, write once every thirty minutes and last for six hours to test the noise of compressor running at a certain test condition. Before the noise test begin in due form, the compressor should be running for a least three hours so as to make sure the moisture in the test system be fully out. When once test ended and let the compressor stop working long enough to make the shell cooled fully. Then another test under a new condition can be start. There are ten points, which tallied with the prescription of the standard, to be tested at the same time. For a specific compressor, a refrigerant is closely related to definite noise characteristics of the compressor while it running at definite conditions. The noise characteristics changed while the conditions changed. The relationship between the main characteristics of the noise and the factors by which the noise caused might be discovered by being compared the main frequency and the frequency distribution of the compressor under different conditions. Generally speaking, some wave crest would remove its main frequency along with the changing condition, and others would always keep theirs main frequency stillness. The latter may usually be caused by the factors about mechanism friction or the factors about electromagnetism of the running motor whereas the former may due to the other factors. Among the former cases, some wave crest would remove its main frequency when a definite gas suction condition changed, and others would still keep theirs main frequency almost stillness. The changed frequency might be corresponding to the factors that changed only. With different suction condition changed only, the noise frequency can be tested and protracted out by the way. Thus, the main characteristics of the noise mainly due to a specific suction factor can be roughly differentiated. Table 1. The test conditions Serial number Refrigerant Lubricant Suction pressure (kpa) Discharge pressure (kpa) 1 9