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Introduction and detailed explanation of the working principle of ultra-low temperature refrigerator
From the appearance, ultra-low temperature refrigerators can be divided into two types of box forms: three-dimensional and horizontal. The inner box often adopts the design of independent storage layer opening and closing doors, while the outer box is made of cold-rolled steel plates welded together. There are polyurethane thermal foam materials of certain thickness (about 70mm thick) on the inside and outside of the box. The ultra-low temperature refrigerator box contains a temperature sensor, which can automatically adjust the temperature according to the comparison between the actual temperature in the refrigerator and the manually preset temperature. Since it works in a low temperature environment, the temperature sensor uses low temperature resistant rare metal platinum as the manufacturing material, so it can regulate the temperature in the box. Traditional ultra-low temperature refrigerator refrigerants contain fluorocarbons, while modern ultra-low temperature refrigerators have adopted environmentally friendly refrigerants, which can effectively avoid environmental pollution. In addition, the ultra-low temperature refrigerator is also equipped with an automatic power-off alarm and a temperature alarm to promptly sound an alarm when there is a problem with the refrigerator. In response to the occasional occurrence of large voltage fluctuations caused by excessive harmonics in the power grid, ultra-low temperature refrigerators are generally equipped with voltage boosters to ensure the normal operation of the compressor under low voltage conditions.
The working principle of the refrigeration system in ultra-low temperature refrigerators is different from that of general refrigerators. It adopts a cascade refrigeration method, and there are generally two fully enclosed compressors used as high and low temperature compressors in ultra-low temperature refrigerators. The evaporator copper tube of the low-temperature compressor is directly installed in the form of a coil outside the refrigerator box, and filled with thermal conductive adhesive in the gap between the coil and the refrigerator wall to increase the heat exchange effect. The condensing evaporator inside the box is mostly a shell and tube structure, with four threaded copper tubes inside, usually using a countercurrent heat exchange method. In addition, the low-temperature working system of the refrigerator is also equipped with relevant gas heat exchangers, which can exchange cold and heat between the low-pressure gas discharged from the evaporator and the high-pressure gas before entering the condensing evaporator. This design method reduces the heat load during the operation of the condensing evaporator, maximizes the utilization of the heat generated during the operation of the refrigerator, and reduces energy loss. Ultra low temperature refrigerators generally use wax removal filters, which can effectively remove paraffin from the refrigeration oil to reduce the probability of blockage in the entire refrigeration and thermal conductivity system, ensuring the normal operation of ultra-low temperature refrigerators.
Ultra low temperature refrigerators generally use two-stage refrigeration, with the first stage refrigerant being R-12 (23.0oz, 1oz=28.349523g), designed for a high pressure of 400ppsi (1ppsi=6.89476X103Pa) and a low pressure of 90ppsi. The condenser of the second stage refrigeration and the evaporator of the first stage refrigeration are placed together; The second stage refrigerant is a mixture of R-503 (8.5oz) and R-290 (0.7oz), with a designed high and low pressure of 300ppsi. The temperature sensing probe is a thermistor that displays different temperatures on the panel based on the resistance value (i.e. temperature).
When the power is turned on, when the panel displays a temperature higher than the set temperature, the first stage compressor starts first and the first stage refrigeration system starts working
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