Air compressor green environmental protection refrigerant

Refrigeration as a science and technology refers to the artificial method of cooling a substance or fluid at a certain time and space to keep its temperature below the ambient temperature and maintain this temperature. Its essence is to transfer the average kinetic energy of molecular thermal motion. Over the past 100 years, with the continuous advancement of science and technology, refrigeration technology has developed rapidly. A series of refrigeration methods have matured and are widely used in business, industry, agriculture, animal husbandry, construction, defense, medicine and people's daily life. In life, therefore, it is especially important for people to learn and master the knowledge of refrigeration.

In 1999, the author developed a thermodynamic refrigeration cycle experimental instrument and obtained a national patent. It not only allows students to understand the principle of liquid evaporative refrigeration cycle of household refrigerators, masters the common fault analysis and operation and maintenance skills of small refrigeration equipment, but also makes the equal pressure, adiabatic, throttling and other basic laws of thermodynamics in thermodynamics qualitative. The semi-quantitative or quantitative visual expression has deepened the students' understanding of the basic theoretical knowledge of thermodynamics and is favored by students. However, in the use of several years, we also found some drawbacks. Therefore, we developed an innovative refrigeration cycle comprehensive experimental instrument in 2005, which overcomes the problems of Freon pollution environment and easy damage of ammeter, and has made some new improvements.

2 The use of a green environmentally friendly refrigerant The liquid evaporative refrigeration unit obtains a cold process, which is an endothermic and exothermic process resulting from a state change of the refrigerant in the system. Therefore, the refrigerant is a heat carrier in the refrigeration device, which is also referred to as a "working fluid".

At present, there are dozens of industrial refrigerants, which can be classified into inorganic compounds (such as ammonia, water), chlorofluorocarbons (collectively referred to as "Freon"), and hydrocarbons (such as ethane, propane, ethylene, etc.). ). Among them, Freon (CFC212) is widely used in refrigerators, freezers, automotive air conditioners and thermodynamic refrigeration cycle testers because of its advantages of non-toxic, odorless, non-flammable, non-explosive, good stability and good lubrication to equipment. However, Freon has its fatal shortcoming, which is a "greenhouse effect gas" that destroys ozone in the atmosphere. In the 1980s, two scholars in California took the lead to point out that CFCs (chlorofluorocarbons) emit chlorine atoms under the action of ultraviolet rays. The chlorine atoms react with the ozone molecules in a free radical chain. One chlorine atom can consume tens of thousands. Ozone molecules, which affect the absorption of ultraviolet light from 250 to 320 nm by ozone molecules, cause excessive ultraviolet rays to reach the surface of the earth, directly affecting the survival of humans and other living things. Therefore, the innovative refrigeration cycle comprehensive experimental instrument uses a green environmentally friendly refrigerant (HFC2134a). In addition to the many advantages of Freon, the new refrigerant solves the problem of damage to the ozone layer. HFC2134a

Refrigerant has entered the practical stage since 1995, and has been widely used as a replacement for Freon (CFC2134a) in the world. The reasons for its wide application are: (1) stable performance and safe and convenient use. HFC2134a is a hydrofluorocarbon-containing compound, and the bond energy of the fluorocarbon bond is very high, so that the general fluorocarbon compound has good thermal stability and chemical stability. In addition, HFC2134a is non-toxic and non-combustible to ensure that the original CFC212 refrigeration equipment is filled and repaired under the same process conditions, without special protective measures.

(2) HFC2134a production technology is improving day by day, and the cost is gradually decreasing.

(3) It has a complete supporting technology. The alternative technology of Freon is a large systematic project. In order to ensure that the newly developed substitutes have a good market prospect, the world's major multinational companies have generally developed the alternative production technology and supporting technologies. For example, the British ICI company built the world's first HFC2134a production plant at the end of 1990. At the same time, the matching compressors, lubricants and refrigerators filled with HFC2 134a have also been put on the market. Due to advances in technology, so far, the refrigeration system of refrigerators and car air conditioners has achieved a good match with the new working fluids, and its energy consumption, cooling speed and other indicators have reached and exceeded the level of the original working fluid.

All in all, HFC2134a is still the replacement of CHC212 refrigerant with the best comprehensive performance, the most complete supporting technology and the most mature application.

3 The improvement of the refrigeration cycle system The liquid evaporative refrigeration cycle system mainly consists of four parts: compressor, condenser, capillary (throttle valve) and evaporator. According to the characteristics of HFC2 134a refrigerant, the following improvements were made to the refrigeration cycle system: (1) The imported R134a compressor was directly used. The compressor is like the heart of the human body in the refrigeration cycle system. Any mechanical operation requires oil for lubrication. Since the R134a refrigerant is compatible with the ester oil, it has poor affinity with the mineral oil or alkylbenzene oil used in the R12 compressor, and the ester oil is not allowed to be mixed with other lubricating oils, and the water absorption is strong. If the original R12 compressor is used, it is necessary to completely remove the oil impurities in the machine and fill the PAG or HAB refrigeration oil. This is not easy for a small fully enclosed compressor and may not achieve the desired result.

(2) Use air forced convection air-cooled condenser. The effect of condensation directly affects the cooling effect. Due to the use of R134a refrigerant and compressor, the exhaust pressure is increased and the exhaust temperature is also increased. If the air convection wire tube condenser is still used, the condensation area must be increased, occupying too much space, otherwise it will not be good. Condensation effect. The use of air forced convection air-cooled condenser can save space and increase the air flow rate, make the condensing temperature more stable, have a lower impact on the cooling capacity, and set the condensing fan power switch, turn off the switch, and also Through the pressure gauge, ammeter, temperature indicator and other instruments, it is observed that the direct effect of the condensation effect on the cooling capacity.

(3) Select a capillary with a suitable aperture and length. Small refrigeration equipment typically uses capillary tubes to throttle and depressurize. The R134a refrigerant receives a large amount of resistance in the pipeline and reduces the flow rate. If the length of the capillary is too long and the pore diameter is too small, the high pressure of the system will be high and the low pressure will be low. If the length of the capillary is too short and the pore diameter is too thick, the desired throttling effect will not be achieved. Both situations directly affect the cooling effect. Choosing a capillary with the right aperture and length is the key to keeping the system running.

(4) A copper coil evaporator is used. The evaporator is installed in the freezer compartment (warm barrel). In order to accurately measure the refrigeration capacity of the compressor, it is usually filled with two-thirds of the height of the aqueous alcohol or car antifreeze in the insulated drum. The copper coil evaporator has good oxidation resistance, corrosion resistance and thermal conductivity, and can increase the heat transfer area.

4 protection circuit design 4. 1 design ideas In a sense, physical experiments are to observe physical phenomena, measurement data, calculation results, and draw conclusions through instrumentation. Measurement of various data must be accurate. Therefore, it is especially important to choose the right measuring instrument and provide the ideal working condition for the meter itself. This is the leading idea of ​​designing protection circuits in the process of developing innovative refrigeration cycle comprehensive experimental instruments.

4. 2 The design process generally selects the measurement value of the pointer type electrical instrument between 1Π2~1Π3 of its full scale value, which is not difficult for the unit circuit of the pure resistive load, but not for the unit circuit of the inductive load. For example, when measuring the working current of a piston compressor, its starting peak current is 4 to 7 times of the rated current, and the duration starts to decline after about 2 s, and then gradually stabilizes to a normal value. The rated current of the compressor of this instrument is 1. 20 A. It is necessary to avoid the impact of the starting peak current on the ammeter and the power factor meter, and to measure the more accurate data. We have selected the ammeter with a range of 2 A and used it. The H3Y22 time delay relay protects the ammeter and power factor meter and designs a feasible protection circuit. As shown.

4. 3 Working principle When the switch Kd is turned on, the time delay relay SJ is in the delay state, that is, the SJ 1 2 1 contact is open, the SJ 2 1 contact is closed and the additional resistor and power factor meter current contact are connected. And the ammeter is shorted, at this time the power factor meter and the ammeter pointer are not deflected, and the compressor starts to start. At this time, the path of the peak current of the compressor is: L→K d→SJ 2 1→delay relay SJ, and the working state is changed after the delay is completed. ↓Overload protector→motor winding→N after several seconds (specific time Depending on the delay action time of the time delay relay set according to the starting peak current duration of the motor), the time delay relay SJ starts to pull in, that is, the SJ 2 1 contact is opened, and the SJ 1 2 1 contact is closed and The additional resistance is short-circuited, the power factor meter and the ammeter are normally indicated, and the compressor gradually enters a stable operating state.

At this time, the working current path of the compressor is: L→Kd→SJ 1 2 1→power factor meter (I a 2 I 3)→current meter A d→time delay relay SJ↓overload protector→motor winding→N 4. 4 additional resistance during the start-up of the compressor, the delay relay SJ 2 1 contact and current meter, power factor meter shunt circuit as shown. It can be seen that the current coil of the power factor meter and the coil of the ammeter can be regarded as a small resistance and inductance, forming a series branch, which is formed in relation to the contact resistance of the time delay relay SJ 2 1 . A parallel circuit. In order to ensure that the i 1 branch shunt is zero, an additional resistor is connected in series in its branch. After the delay is completed, the additional resistor is short-circuited by SJ 1 2 1 to avoid long-term participation in the operation.

5 Conclusion By using HFC2134a refrigerant, the innovative refrigeration cycle comprehensive experimental instrument has played a green and environmental protection role; through the reasonable selection of compressors, condensers, capillaries and other components, the performance of the entire refrigeration cycle system has been greatly improved . The fact that students have completed the experiment in recent years shows that using self-made instruments can make them full of pride; enhancing the applicability can stimulate their interest in learning; introducing the design ideas and improvement process of the instruments can cultivate their innovative consciousness and ideas.