Working principle of high and low temperature wet heat test chamber
Date: 2014-06-18Read: 0
The high and low temperature wet heat test chamber consists of a refrigeration system, a heating system, a control system, a temperature system, an air circulation system, and a sensor system. The above systems belong to two major aspects: electrical and mechanical refrigeration.
Refrigeration system: The refrigeration system is one of the components of the comprehensive high and low temperature wet heat test chamber. Generally speaking, the refrigeration method of the high and low temperature wet heat test chamber is single (double) mechanism refrigeration, which mainly consists of a compressor, a condenser, and an evaporator. Due to the low temperature of -55 ℃ that we are testing, single-stage refrigeration is difficult to meet the requirements. Therefore, the refrigeration method of the test chamber is generally cascade refrigeration. The refrigeration system of the high and low temperature wet heat test chamber produced by our company consists of two parts, namely the high temperature part and the low temperature part, each part 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 cooled object (air inside the test chamber) 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. The high-temperature part of the high and low-temperature wet heat test chamber uses medium temperature refrigerant, and the low-temperature part uses low-temperature refrigerant. The temperature inside the chamber can reach -70-150 ℃
Heating system: The heater adopts a porcelain frame nickel chromium wire electric heater, which has low thermal inertia and long service life. The instrument outputs a controllable pulse duty cycle PID signal, which is controlled by a solid-state relay for smooth and reliable control.
Control system: The control system is the core of the comprehensive test box, which determines important indicators such as the heating rate and accuracy of the test box. Nowadays, most of the controllers in the test chamber use PID control, and there are also a few that use a combination of PID and fuzzy 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.
Humidity system: The humidity system is divided into two systems: humidification and dehumidification.
There are two dehumidification methods for high and low temperature wet heat test chambers: 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 expensive.
Sensor system: The sensors of the high and low temperature humidity and heat test chamber (constant temperature and humidity test chamber) 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 test chambers are gradually replacing dry wet bulbs with solid-state sensors for humidity measurement.
Air circulation system: The air circulation system of the high and low temperature humid heat test chamber generally consists of a centrifugal fan and a motor that drives its operation. It provides air circulation inside the test chamber.