Constant temperature and humidity machine are composed of refrigeration system, heating system, control system, humidity system, air supply circulation system, and sensor system, which is divided into two major aspects of electrical and mechanical refrigeration. The working principle and working process of several main systems are described below.
Refrigeration system: one of the key parts of constant temperature and humidity machine in general, the refrigeration mode is mechanical refrigeration and auxiliary liquid nitrogen refrigeration, mechanical refrigeration USES steam compression refrigeration, they are mainly composed of compressor, condenser, throttle mechanism, and evaporator.
If the low temperature of our test should reach -55℃, single-stage refrigeration is difficult to meet the requirements, so the refrigeration method of constant temperature and humidity machine generally adopts cascade refrigeration.
The refrigeration system of constant temperature and humidity machine is composed of two parts, respectively called the high-temperature part and the low-temperature part, each part is a relatively independent refrigeration system.
In the high-temperature part, the refrigerant evaporates by absorbing heat from the low-temperature part. Evaporation of the cryogenic part of the refrigerant absorbs heat from the object being cooled (the air in the testing machine) to obtain the cooling capacity.
The high-temperature part and the low-temperature part are connected by an evaporative condenser, which is both the condenser of the high-temperature part and the condenser of the low-temperature part.
Heating system: The relative refrigeration system, relatively simple it mainly consists of high-power resistance wire, because the heating rate required by the test is large, so the heating system power is relatively large, and the bottom plate of the testing machine is also equipped with a heater. Control system: the core control system of the comprehensive test box determines the temperature rise rate, precision and other important indicators of the testing machine.
Humidity system: the two subsystems of humidification and dehumidification are generally humidified by steam humidification, that is, low-pressure steam is directly injected into the test space for humidification. This method has high humidification ability, high speed, and sensitive humidification control.
There are two ways of dehumidification: mechanical refrigeration dehumidification and dry dehumidification. The dehumidification principle of mechanical refrigeration is to cool the air below the dew point temperature, so that more than saturation moisture content condensation precipitation, to reduce the humidity. Dryer dehumidification is to use the air pump to extract the air in the test box, and to inject dry air, at the same time, the wet air into the recyclable drying for drying, drying and then into the text box, so repeated cycle for dehumidification.
Sensor system: mainly temperature and humidity sensor.
Supply air circulation system: provide air circulation.