1.Stirling refrigeration technology
Stirling refrigeration technology has a history of 50 years, and is widely used in military. The first is the integral structure, that is, the compression piston and the expansion piston are mechanically connected by a connecting rod. The integral structure is easy to produce heat and vibration, which affects the refrigeration part. In view of the shortcomings of the system, some improvements have been made abroad. First of all, since 1972, there has been a significant development. The split Stirling cooler developed by Hughes Aircraft Company of the United States has separated the compressor from the expander and connected with a hose in the middle. This structure not only overcomes the shortcomings of the early integrated cooler, but also maintains the advantages of the original system, such as compact structure, high efficiency, fast start-up, etc. Therefore, it is highly valued by foreign users and develops rapidly. Secondly, in order to overcome the wear and tear caused by the dynamic structure of the original motor / crankshaft, Philips Research Institute of the Netherlands began to develop a Stirling engine with linear motor driving linear resonant compressor in 1968. So far, the development of linear resonant Stirling machine has gone through three generations: in 1975, the MC-80 micro refrigerator developed by the scientific and industrial division of Philips company in the Netherlands is called the first generation, which belongs to non military type. When the cooling temperature is 80 Kelvin, the output power is 1W (W); in 1976, the Netherlands and the United States designed the second generation at the same time. Philips of the Netherlands militarized MC-80 on the basis of MC-80, initially named mmc-80, and later officially named ua-7011. In 1982, on the basis of ua-7011, Philips developed a series of linear resonant coolers, known as the third generation. They are made up of a standardized compressor and two cold fingers (expander section) and are specially designed for the US $60 and $120 / 180 detector / Dewar units. The cooling power can reach 1 / 4W and 1W respectively, and the mean time between failures is 2500h. The company is now continuing to develop new products.
2. Pulse tube cooling technology
It was invented by American cryogenic experts in 1963, and it was a key step forward to the practical application after professor mikulin of the former Soviet Union made a significant improvement on the basic type of vessel in 1984. In fact, the pulse tube is a variant of Stirling. There is no need for moving parts in the expander. The structure is more simple and reliable, and it is easy to assemble and control vibration. At present, its mechanism is still under exploration, and it will become a strong competitor of Stirling machine in the future, especially in long-life aircraft.
3. Thermoelectric refrigeration technology
Also known as thermoelectric cooler or semiconductor cooler. In the late 1950s, with the rapid development of semiconductor material technology, the problem of low cooling efficiency in the early system was solved. In particular, the United States, Britain, Japan, the Soviet Union and other countries have done a lot of research in this field, and thermoelectric refrigeration has reached the practical stage in the 1960s. The thermoelectric quality factor Z is one of the factors used to evaluate thermoelectric materials. At the end of 1980s, the Z value of thermoelectric materials in the United States and some European countries could reach 3.5 × 10-3 / ° K (the negative cubic power of 10 / Kelvin), and the former Soviet Union could reach 4.7 × 10-3 / ° K. At present, thermoelectric coolers are mainly used for hand-held thermal imagers, such as the an / pas-7 and hphtv of MAGNAVOX company in the United States, and the lt1065 of lethargic company in the United Kingdom. In addition, it can also be used in other observation and aiming systems, such as an / tas-5 "dragon" thermal imaging sight of Texas Instruments, TWS thermal imaging sight of Magna Vaux, etc.
4. Coke soup refrigeration technology
Also known as throttling refrigeration technology, it was invented in the 1950s. In most cases, open-loop coolers are used, but there are still closed throttling coolers with high-pressure compressors. The early system was composed of counter flow heat exchanger, orifice and gas cylinder with high pressure gas. In order to control the gas consumption, some improvements have been made to the throttling cooler abroad, and a self-adjusting cooler has been designed. Now almost all coke soup systems produced abroad are equipped with this kind of self-adjusting mechanism. In foreign countries, the technology is mostly used in infrared guidance, hand-held thermal imager, vehicle borne thermal imager, anti tank missile thermal sight, etc. For example, Texas Instruments' an / tas-4 ceramic anti tank missile night sight, Coleman's thermal imaging long-distance night observer, Marconi's hht-8 and MSDS handheld thermal imager, Sohn Yimei's multi-purpose thermal imager, TRT's Mira infrared thermal imager, etc.
5. Cooling by phase change
There are liquid cooling and solid cooling. Liquid cycle refrigeration is widely used in laboratory measurement and civil infrared system. Solid state refrigeration system is mainly used in aerospace industry. According to the mass and volume of the stored solid coolant, the service time can be 1 to 3 years or longer.
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