Core principle: Two box method or three box method

At present, the mainstream high-speed temperature shock box adopts the "two box method" or "three box method" to achieve rapid conversion.

• Two box method:Having a high temperature chamber and a low temperature chamber, the test product is quickly switched between the two chambers through a mobile basket (lifting basket).

• Three box method (more common):It has a high temperature zone, a low temperature zone, and a testing zone (also known as a storage zone). By switching the wind direction control valve (damper), high or low temperature airflow is quickly introduced into the testing area to impact the sample. The sample itself remains stationary.

In order to achieve 3-5 minutes of high-speed stability, the following technologies and designs are crucial:

1. Energy storage refrigeration and heating system (core of the core)

A regular thermostat produces as much cold/heat as needed in real-time. And in order to achieve maximum speed, the impact box usesPre store a large amount of cold and hot energy, ready to release at any timeThe energy storage mode.

• High temperature heat storage:

• High power heater:Equipped with heaters that are much higher than conventional requirements (usually above 6kW or even higher), they can quickly heat and maintain the air in the high-temperature chamber at a level much higher than the set point (such as+150 ° C) in standby mode.

• High heat capacity materials:The inner walls of high-temperature chambers and air ducts are filled or filled with materials with high specific heat capacity (such as special ceramics, stainless steel, etc.), which themselves store enormous thermal energy like "thermal batteries".

• Low temperature cold storage:This is a technical challenge and the key to achieving ultra fast cooling.

• Liquid nitrogen assisted refrigeration:This is the most mainstream and efficient way. The box is directly connected to the liquid nitrogen tank and controlled by a precision solenoid valve to instantly spray liquid nitrogen at -196 ° C into the heat exchanger of the low-temperature chamber, or mix it directly with air. This provides instantaneous cooling power.

• Stacked mechanical refrigeration+cold storage:For mechanical shock boxes that do not use liquid nitrogen, a multi-stage cascade refrigeration system will be used, paired with aCold storage deviceThe inside of the cold storage device is usually coiled with copper pipes and filled with special media (such as ethylene glycol solution, metal blocks, etc.). When in standby mode, the refrigeration system runs at full capacity, cooling the accumulator to a temperature far below the set point (such as -80 ° C), storing a huge amount of "cooling capacity". When impact is required, the fan blows air through this super cold accumulator, instantly cooling it.

2. Strong convective heat exchange system

Just having energy is not enough, it must be efficiently transferred to the test sample.

• High power centrifugal fan:Equipped with specially designed high-speed and high flow centrifugal fans, it can generate high wind speeds (possibly exceeding 20m/s), create strong turbulence, break the air boundary layer on the sample surface, and achieve high heat exchange efficiency.

• Optimized air duct design:The air duct is optimized by CFD (Computational Fluid Dynamics) to ensure uniform airflow, cover the entire testing area, and quickly "blow away" and "replace" the original temperature air in the testing area with new high or low temperature air.

3. Quick switching and insulation system

How to instantly change the environment of the testing area while preventing interference between the hot and cold chambers?

• High speed drive mechanism (two box method):By using high-performance servo motors and transmission mechanisms, the movement time of the basket between high and low temperature zones is compressed to within 10 seconds.

• Efficient pneumatic/electric air door (three box method):The opening and closing action of the air door must be extremely fast and tightly sealed. When the high-temperature air door is opened, the low-temperature air door must be tightly closed, and vice versa, to prevent short circuits of cold and hot air flow and affect the recovery speed.

• Efficient insulation:The box adopts high-performance polyurethane foam and other thermal insulation materials for overall foaming filling to minimize the interference of the external environment on the cavity temperature and the loss of internal cold and heat.

4. Advanced control and algorithms

Hardware is the foundation, intelligent control is the brain.

• Adaptive PID Control:The controller uses advanced and self-tuning PID algorithm. It can not only adjust the heating/cooling output based on the difference between real-time temperature and target temperature, but alsopredictThe trend of temperature changes (such as reducing power in advance when the temperature approaches the set point) effectively suppresses overshoot and overshoot, achieving fast and smooth stability.

• Feedforward control:The system will calculate the approximate energy required in advance based on the set target temperature and current temperature, and instruct the heater or liquid nitrogen valve to perform pre action, rather than waiting for errors to occur before reacting.

Implement a stable workflow for 3-5 minute conversion (using the three box method as an example)

1. Preparation stage:

• The high temperature zone is continuously heated and maintained at+150 ° C (e.g. set temperature at+85 ° C).

• The low-temperature zone is continuously cooled and maintained at -70 ° C (e.g. set temperature to -55 ° C) using liquid nitrogen or a cold storage device.

• The testing area is isolated from the two areas and is at room temperature or the previous testing temperature.

2. High temperature shock command:

• The controller sends a command to the low-temperature air doorInstantly close tightlyHigh temperature air doorInstantly open.

• High power centrifugal fans convert+150 ° C high-temperature air and stored thermal energyFierce blowing inTesting area.

• The ambient temperature air in the testing area is rapidly replaced and heated.

3. Stable process:

• The temperature sensor monitors the temperature in the testing area in real-time.

• When the temperature approaches+85 ° C, the intelligent PID controller begins to reduce the heater power and may introduce a small amount of cold air for balance to prevent temperature overshoot.

• Due to sufficient heat storage, large air volume, and precise control, the temperature can be maintained within a certain rangeIn a very short period of time (such as 2-4 minutes)Reaching a stable state of+85 ° C ± 3 ° C (according to standards such as GB/T 2423.22, stability usually refers to entering the tolerance zone).

4. Low temperature shock command:

• The process is opposite to high-temperature shock. Close the high-temperature air door and open the low-temperature air door.

• Ultra low temperature air (-70 ° C) and stored 'cold' flow into the testing area, rapidly displacing and cooling the air in the testing area.

• The controller precisely controls the opening of the liquid nitrogen valve or the heat exchange of the accumulator, ensuring that the temperature quickly and smoothly drops to -55 ° C and stabilizes.