The refrigeration system is an important part of the constant temperature and humidity chamber. Generally speaking, the refrigeration method of the constant temperature and humidity chamber is mechanical refrigeration and liquid nitrogen auxiliary refrigeration. Mechanical refrigeration adopts vapor compression refrigeration. It is mainly composed of compressor, condenser, throttling mechanism and evaporator.
The main operating system of the constant temperature and humidity chamber is the low-temperature refrigeration system, and the assembly of the compressor in the entire cooling system is very important.
Since the low temperature we tested must reach -40 ℃, it is difficult for single-stage refrigeration to meet the requirements, so the cabinet refrigeration methods tested are generally cascade refrigeration. The refrigeration system of the constant temperature and humidity chamber is divided into two parts: the high-temperature part and the low-temperature part, which is a relatively independent refrigeration system.
The evaporation of the refrigerant in the high-temperature zone absorbs heat from the refrigerant in the low-temperature zone and evaporates, the evaporation of the refrigerant in the low-temperature zone absorbs heat from the object to be cooled (the air in the test chamber) to obtain coldness. An evaporative condenser is used between the high and low-temperature section and the low-temperature section, which can be used as the condenser of the high-temperature section and the low-temperature section.
The noise of products of a stability test chamber manufacturer is extremely low when the normal compressor starts (less than or equal to 60dB). If the compressor noise exceeds 80dB, and it is louder than the compressor noise of other equipment, if it is not used, it will definitely fail.
If the low-temperature refrigeration is very slow when the constant temperature and humidity chamber is running, if the compressor body is very hot when you touch the compressor body with your hand, it is also likely to cause problems. The machine must be shut down immediately, and the supplier must be notified to repair and inspect the accessories.
In order to lower costs, some unscrupulous merchants buy or recycle some second-hand compressors and sell them to customers at high prices. Although this can reduce costs, the refrigeration systems and compressors used by the equipment in the future have very large potential failures and the problem of reducing service life.
Usually the new compressor has a brighter appearance, bright color, clear label, and the copper pipe welding port is directly welded at one time without traces of old welding. If it is a second-hand compressor, the color of the shell generally looks dim, and the welded joint of the copper pipe has marks of repeated grinding or overlap welding several times.
The refrigeration system of the temperature and humidity chamber complements the compressor. The minimum evaporating temperature of a single-stage vapor compression refrigerator mainly depends on its condensation pressure and compression ratio. For any refrigerant, the lower the evaporation temperature, the lower the evaporation pressure. When the evaporation temperature is too low, some commonly used refrigerants have reached the freezing temperature, and the flow and circulation of the refrigerant cannot be realized. The evaporation pressure decreases, the volume of the refrigerant increases, and the mass flow rate of the refrigerant decreases. At this time, in order to obtain the required refrigeration capacity, it is necessary to increase the suction volume, thereby making the compressor large.