Nanjing constant temperature and humidity chamberIt consists of a refrigeration system, a heating system, a control system, a humidity system, a supply air circulation system, and a sensor system. The above systems belong to two major aspects: electrical and mechanical refrigeration. The following describes the working principles and processes of several main systems.
1. Refrigeration system: The refrigeration system is one of the key components of a constant temperature and humidity machine. Generally speaking, the refrigeration methods are mechanical refrigeration and auxiliary liquid nitrogen refrigeration. Mechanical refrigeration adopts vapor compression refrigeration, which mainly consists of a compressor, condenser, throttling mechanism, and evaporator. If we want to achieve a low temperature of -55 ℃ in our experiment, single-stage refrigeration is difficult to meet the requirements. Therefore
Nanjing constant temperature and humidity chamberThe refrigeration method generally adopts cascade refrigeration.
Nanjing constant temperature and humidity chamberThe refrigeration system consists of two parts, namely the high temperature part and the low temperature part, each of which is a relatively independent refrigeration system. The evaporation of refrigerant in the high temperature section absorbs heat from the refrigerant in the low temperature section and vaporizes; The evaporation of the low-temperature refrigerant absorbs heat from the object being cooled (the air inside the testing machine) to obtain cooling capacity. A evaporative condenser is used between the high temperature and low temperature sections, serving as both the condenser for the high temperature section and the condenser for the low temperature section.
2. Heating system: Compared to the refrigeration system, the heating system is relatively simple. It mainly consists of high-power resistance wires. Due to the high heating rate required for the test, the heating system has a relatively high power, and a heater is also installed on the bottom plate of the testing machine.
3. Control system: The control system is the core of the comprehensive test chamber, which determines important indicators such as the heating rate and accuracy of the testing machine. Nowadays, most controllers of testing machines use PID control, and a small number of them use a combination of PID and fuzzy control control. Due to the fact that control systems are basically within the scope of software, and this part generally does not encounter any problems during use.
4. Humidity system: The temperature system is divided into two subsystems: humidification and dehumidification.
The humidification method generally adopts steam humidification method, which directly injects low-pressure steam into the test space for humidification. This humidification method has the ability to humidify, fast speed, sensitive humidification control, and is particularly easy to achieve forced humidification during cooling.
There are two types of dehumidification methods: mechanical refrigeration dehumidification and dry dehumidification. The dehumidification principle of mechanical refrigeration is to cool the air below the dew point temperature, causing water vapor with a moisture content greater than saturation to condense and precipitate, thereby reducing humidity. Dehumidification by a dryer is achieved by using an air pump to extract air from the test chamber, injecting dry air, and sending humid air into a recyclable dryer for drying. After drying, the air is then sent back into the test chamber, and this process is repeated for dehumidification. Nowadays, most comprehensive test chambers use the former dehumidification method, while the latter dehumidification method can achieve a dew point temperature below 0 ℃. Suitable for occasions with special requirements, but the cost is relatively high.
5. Sensor system: Sensors are mainly temperature and humidity sensors. The most commonly used temperature sensors are platinum batteries and thermocouples. There are two methods for measuring humidity: dry wet bulb thermometer method and solid-state electronic sensor direct measurement method. Due to the low measurement accuracy of the dry wet bulb method, current constant temperature and humidity chambers are gradually replacing dry wet bulbs with solid-state sensors for humidity measurement.
6. Air circulation system: Air circulation systems generally consist of centrifugal fans and motors that drive their operation. It provides the circulation of air inside the testing machine.
1. The machine is equipped with a test hole on the machine side, which can be used when connecting to the testing circuit inside the box.
If you want to observe the changes inside the box during the test, you can turn on the indoor light switch and learn about the internal changes through the window.
3. If the machine operates below 0 ℃, try to avoid opening the box door as much as possible, because opening the box door at low temperatures can easily cause ice sealing in the internal evaporator and other parts, especially the lower the temperature, the more serious the situation. If it must be opened, try to shorten the opening time as much as possible.
When completing low-temperature operation, it is necessary to set the temperature condition at 60 ℃ and perform drying treatment for about half an hour to avoid affecting the measurement time of the next operating condition or icing phenomenon.
5. The radiator (condenser) of the freezer should be regularly maintained and kept clean.
6. The inlet pipe of the humidification bucket must discharge the remaining air * to prevent water from entering.
Special attention: After the machine completes low-temperature operation, if there is no work listed in point 6 above, it is also necessary to set the room temperature condition (30 ± 5 ℃) so that the temperature inside the box is at room temperature when stopped, in order to avoid affecting the freezing phenomenon caused by the low temperature inside the box and the fogging phenomenon of the window glass.
During operation, please do not open the box door unless necessary, as it may result in the following adverse consequences:
It is very dangerous for high temperature and humidity to rush out of the box.
The inside of the box door is still holding high temperature, causing injury.
High temperature air may trigger a fire alarm and cause misoperation.
8. Please note that this device must be securely grounded to prevent static electricity induction.
9. Avoid shutting down and restarting the freezing unit within three minutes.
10. If a heating sample is placed inside the box, please use an external power supply for the sample power control, and do not directly use the local power supply.
11. Circuit breakers and over temperature protectors are provided for the safety protection of operators during testing, so please check them regularly.
The correct installation of wet ball gauze is necessary to ensure the correct measurement of relative humidity.
13. It is prohibited to test explosive, flammable, and highly corrosive substances.
Nanjing constant temperature and humidity chamberThe operation of the system is through three interrelated systems: refrigerant circulation system, air circulation system, and electrical self-control system; In the refrigerant circulation system, the liquid refrigerant in the evaporator absorbs heat from the air (the air is cooled and dehumidified) and begins to evaporate, creating a certain temperature difference between the refrigerant and the air. The liquid refrigerant also evaporates into a gaseous state, which is then sucked in and compressed by the compressor (increasing pressure and temperature). The gaseous refrigerant absorbs heat through the condenser (air-cooled/water-cooled) and condenses into a liquid. After being throttled by an expansion valve (or capillary tube), it becomes a low-temperature and low-pressure refrigerant that enters the evaporator, completing the refrigerant circulation process.