Definition
The low-temperature environmental test chamber is a closed experimental equipment used to simulate low-temperature atmospheric conditions. It can control the temperature inside the box within a specified range below the ambient temperature, usually as low as minus tens of degrees Celsius. The core function of this equipment is to create a stable and controlled low-temperature environment for cold resistance testing of various materials, electronic components, industrial products and structural components. By exposing the sample to preset low temperature conditions, changes in its physical properties, mechanical strength, electrical properties, and dimensional stability can be evaluated.
How it works:
The cryogenic environmental test chamber is based on the vapor compression refrigeration cycle or thermoelectric refrigeration effect to achieve cooling. In a vapor compression system, the refrigerant circulates under the drive of a compressor, passing through the evaporator, condenser, and expansion valve. The refrigerant absorbs the heat of the air inside the chamber in the evaporator, reducing the temperature inside the chamber. The circulating fan inside the box ensures that the cold air is evenly distributed. The temperature control system collects the real-time temperature through the temperature sensor and compares it with the set value, and then adjusts the start-stop or heating compensation power of the compressor to maintain temperature stability. thermoelectric refrigeration uses the Peltier effect to drive the heat absorption of the cold end of the semiconductor through direct current, which is suitable for small volume test chambers.
Measurement method
The performance measurement of the low-temperature environmental test chamber mainly involves the temperature parameters in the chamber. The usual method is as follows:
(1) In the effective working space of the box, arrange multiple thermocouples or resistance temperature detectors according to the standard. The measurement point is generally located in the center of the space and at each corner, and is not less than a certain distance from the box wall.
(2) In the stable state, record the temperature value of each point and calculate the average temperature. Temperature deviation is defined as the maximum difference between the reading at each point and the set value.
(3) Use the formula for temperature fluctuations Tfluctuations = Tmax – Tmin indicated, among them Tmax With Tmin The highest and lowest temperatures recorded over a period of time after stabilization.
(4) The temperature uniformity is evaluated by the temperature difference of each measurement point, reflecting the consistency of the temperature distribution in the box.
(5) Cooling rate measures the time it takes from the initial temperature to the set low temperature, converted to the value of degrees Celsius per minute.
Influencing factors
The main factors affecting the performance of the low-temperature environmental test chamber include:
(1) Ambient temperature: The laboratory where the test chamber is placed too high or fluctuates will increase the burden on the compressor and reduce the cooling efficiency and stability.
(2) Sample load: The number, volume, and heat capacity of samples placed in the chamber can affect airflow circulation and temperature uniformity. Samples with a large amount or high specific heat capacity will prolong the cooling time.
(3) Number of door openings: Frequent opening of the box door will lead to the loss of cold capacity, the temperature inside the box will rise sharply, and it will take extra time to recover to the set temperature.
(4) Refrigeration system status: Refrigerant leakage, compressor wear or condenser dust accumulation can directly weaken the refrigeration capacity.
(5) Temperature control parameters: Improper parameter settings of the proportional-integral-derivative (PID) controller can cause temperature overshoot or oscillation, affecting accuracy.
Applications:
Cryogenic environmental test chambers are widely used in many industrial and scientific research fields, but exclude medical drug-related scenarios. Typical applications include:
(1) Electronic product industry: test the starting performance, signal integrity and material embrittlement of chips, circuit boards, and connectors at low temperatures.
(2) Automotive industry: Evaluate the reliability of auto parts such as rubber seals, batteries, and sensors in cold environments.
(3) Aerospace: Simulate high-altitude and low-temperature conditions, and assess the cold resistance of material structures, lubricants and electronic components.
(4) Materials science: study the low-temperature mechanical properties of metals, plastics, and composites, such as impact toughness and changes in elongation at break.
(5) Food and cold chain: Test the sealing and crack resistance of packaging materials in low-temperature transportation, as well as the durability of cold storage equipment.
Key points of selection
Choosing a suitable low-temperature environmental test chamber should consider the following aspects:
(1) Temperature range: Determine the minimum temperature required and the maximum temperature achievable according to the test standard or sample requirements. The common ranges include minus 20 degrees Celsius, minus 40 degrees Celsius, minus 70 degrees Celsius, etc.
(2) Chamber volume: Select the internal space of the box according to the size and quantity of the largest test sample. Too small a volume can limit sample placement, while too large can increase energy consumption and cooling time.
(3) Temperature uniformity and fluctuation: According to the corresponding standards, the allowable deviation for the consistency and stability of temperature distribution is clarified. Generally, the uniformity is required to be within plus or minus 2 degrees Celsius.
(4) Cooling rate: If the test item requires rapid temperature change, a model with sufficient compressor power and a rapid cooling mode should be selected.
(5) Control system: It is advisable to choose a controller with programmable functions, data logging and communication interfaces to facilitate remote monitoring and traceability of experimental parameters.
(6) Safety configuration: There must be over-temperature alarm, overheat protection, refrigeration system overload protection and other devices to ensure the safety of long-term operation.