Half of the stability of the constant humidity and constant humidity test box comes from the manufacturer's design, which cannot be changed by the customer during use; the other half is the setting during use, which can be controlled by the customer himself. Whether the machine is good or not depends largely on how you use it. However, most factory users are not professionally trained and can only operate according to a manual. It is difficult to achieve the ideal state.
When it comes to the stability of the constant temperature and humidity test chamber, we must talk about the refrigeration system of the constant temperature and humidity test chamber. The medium-temperature refrigerant used in the single-stage refrigeration cycle in the constant temperature and humidity test chamber is R404A. Its evaporation temperature is -46.5 ° C under one atmospheric pressure, but the heat transfer temperature difference of the air-cooled condenser is usually around 10 ° C, that is to say Only a low temperature of -36.5 ° C can be made in the tank. What should we do if we want to obtain a lower temperature? At this time, the minimum evaporation temperature of the R404A refrigerant can be reduced to-by lowering the evaporation pressure of the compressor 50 ℃, so to get a low temperature of -50 ℃ and below, it is necessary to adopt a cascade refrigeration cycle of medium-temperature refrigerant and low-temperature refrigerant, so as to ensure the refrigeration stability of the constant temperature and humidity test chamber.
The refrigeration system and compressor of the constant temperature and humidity test chamber are complementary to each other. The minimum evaporation temperature of the single-stage vapor compression refrigerator is mainly determined by its condensing pressure and compression ratio. Shanghai Jianhu technical staff summed up such an experience: First, for any refrigerant, the lower the evaporation temperature, the lower the evaporation pressure. 2. When the evaporating temperature is too low, some commonly used refrigerants have reached the freezing temperature, and the refrigerant cannot flow and circulate. 3. 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 cooling capacity, the suction volume must be increased to make the compressor volume too large.
The temperature and humidity of the constant temperature and humidity test chamber are all completed by the refrigeration system, but the same system can make the machine reach two different states, which are operated by people, so the work of accurately setting the constant temperature and humidity test chamber The system is very important, and it can be used properly and properly to achieve the results you want.
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