Analysis of structure, principle and application of ultra-low temperature refrigerator
Ultra-low temperature refrigerators are also called ultra-low temperature storage boxes, ultra-low temperature freezers, and ultra-low temperature storage boxes. The more common -60 degree low-temperature refrigerator can be used for the preservation of tuna, the low-temperature test of electronic devices, special materials, and the preservation of plasma, biological materials, vaccines, reagents, etc. There are also extreme freezer refrigerators of -40 degrees, -60 degrees, -86 degrees, -120 degrees, -136 degrees, and -160 degrees and -192 degrees.
Ultra-low temperature refrigerators generally have horizontal and vertical cabinets. The inner box is generally divided into multiple bearing layers, and each layer is designed with an inner door that can be opened and closed independently. The outer box is generally formed by direct splicing of five cold-rolled steel plates. There are 60mm and 80mm polyurethane foam materials inside and outside the box. The thermostat is a platinum resistance sensor for precise temperature control. Refrigerants generally use environmentally friendly refrigerants to meet environmental protection requirements.
The refrigeration system of the ultra-low temperature refrigerator basically adopts the working principle of cascade refrigeration, and two fully enclosed compressors are used as high and low temperature compressors. The copper tube of the low-temperature evaporator is directly attached to the outside of the inner box in the form of a coil, and the gap between the coil and the wall of the box is filled with thermally conductive glue to increase the heat exchange effect. The condensing evaporator is a shell-and-tube structure with four threaded copper tubes inside and adopts a counter-current heat exchange method.
The low-temperature system is also equipped with a gas heat exchanger, which allows the low-pressure gas from the evaporator to exchange heat with the high-pressure gas before entering the condensing evaporator, which not only reduces the heat load of the condensing evaporator, but also makes full use of the heat . The filter mostly uses a wax-removing filter, the purpose of which is to effectively remove the paraffin in the refrigerated oil to reduce the possibility of "oil blockage" in the system.
In addition, the ultra-low temperature refrigerator can also be equipped with some accessories according to different uses, such as a temperature recorder, which is convenient for permanent recording of operating parameters; a carbon dioxide backup system, used in special circumstances to ensure that the gas in the storage environment remains in normal state; , Which can ensure that the compressor works normally under low pressure.
When the power is turned on, when the panel shows that the temperature is higher than the set temperature, the first-stage compressor starts first, and the first-stage refrigeration system starts to work, causing the condenser temperature of the second-stage refrigeration system to drop, that is, the second-stage refrigeration system The temperature of the refrigerant drops. After a few minutes of delay, the second-stage refrigeration system also starts to work. Its evaporator is on the inner wall of the refrigerator, which can make the internal temperature of the refrigerator drop a lot. The evaporator of the first-stage refrigeration system absorbs, and the heat released by the first-stage condenser is dissipated into the air.
When the internal temperature of the refrigerator reaches the set temperature, the resistance of the temperature sensing probe transmits the information, the control relay is de-energized and disconnected, and the two-stage refrigeration system stops working. When the temperature in the refrigerator rises again and exceeds the set temperature, the refrigerator repeats the above operation process again, so that the temperature in the refrigerator is always maintained at the set temperature.
In the biochemistry and molecular biology laboratory, different temperature-controlled refrigerators can be purchased according to the freezing conditions, such as -20°C, -40°C, -70°C, -85°C, -152°C, etc. Among them, the latter two are ultra-low temperature freezers, which were developed in the late 20th century for cryopreservation and storage of biological samples or medicines. They are widely used in biological research, clinical, medicine, and industrial fields.
Ultra-low temperature refrigerators can be used to store medicines, vaccines, enzymes, hormones, stem cells, platelets, semen, transplanted skin and specimens drawn from the human body, plant seed germplasm banks, gene cloning banks, and some important biological and chemical reagents.
In molecular cloning experiments, -70℃ ultra-low temperature refrigerators are widely used to store competent E. coli, competent cells and bacteriophage stocks.
Ultra-low temperature refrigerators generally have a relatively complete equipment operation guarantee function. For example, high temperature alarm function, power failure, filter clogging detection function, automatic input assistance function, sample safety alarm system, micro-processing and analog control system, carbon dioxide backup system and recorder system, etc.
Generally, when inspecting the performance of ultra-low temperature refrigerators, the minimum cooling temperature, size, shape characteristics (horizontal or vertical), compressor noise, vibration amplitude, temperature uniformity in the cabinet, failure rate (especially compressor) and The types of optional accessories are fully considered in combination with their own use requirements and the space arrangement of the laboratory.
In the future, the main concern is the reliability of ultra-low temperature refrigerators and the storage conditions that can meet different samples, including temperature and gas composition. In addition, in order to meet the higher requirements of biological materials for temperature uniformity, some companies use metal rings for cooling in refrigerator shelves, or design the shelves as holes to solve the problem of heat dissipation, increase the freezing speed and increase the temperature. sex.
In the future, the design of ultra-low temperature refrigerators must also consider the requirements for energy conservation and environmental protection, and must be equipped with an environmental detection system. At the same time, nanomaterials will also become promising materials in the preparation of ultra-low temperature refrigerators in the future.
The main purpose of the low-temperature refrigerator: for scientific research, preservation of medical supplies (plasma), biological products (storage organs, vaccines, soil samples), ocean products, electronic components, chemical materials and other special materials for low-temperature experiments and storage, etc. It is used more in hospitals, universities, research units and industrial storage.
