Definition
A high and low temperature constant temperature tank is an experimental equipment that maintains the precise stability of a liquid medium (usually water or special thermal conductive liquid) within a set temperature range in a closed tank through a heating or cooling system. It is widely used in temperature-related testing and process processing in materials, chemicals, electronics, biology and other fields.
Principle
The core working principle of the device is based on closed-loop temperature control. The temperature sensor monitors the temperature of the medium in the tank in real time and feeds the signal back to the controller. The controller compares the set value with the measured value, and outputs the adjustment signal through the proportional-integral-differential algorithm. The heating element or compressor cooling system adjusts the power according to the signal so that the temperature of the medium approaches and stabilizes at the target value. The circulation pump facilitates the flow of the medium, ensuring uniform temperature within the tank. The control process can be simplified to: measurement→ comparison→ correction → stable dynamic balance.
Measurement method
Temperature measurements are usually measured using standard platinum resistance thermometers or high-precision thermistors that meet international temperature standards. Calibration is based on JJF 1030-2010 "Specification for Technical Performance of Thermostatic Chambers" or similar standards, and the main measurement items include temperature stability, uniformity and fluctuation. Stability measurement is to record the maximum deviation of the center point temperature over a period of time at a set temperature point; The uniformity measurement is to measure the temperature difference at different spatial points in the groove at the same time; Fluctuation reflects the magnitude of temperature changes over time. Calibrated sensors and data loggers should be used for measurements, taking into account sensor immersion depth and heat conduction effects.
Influencing factors
Thermostatic performance is affected by a variety of factors. changes in ambient temperature and humidity may interfere with the heat exchange balance; The material and thickness of the tank insulation layer affect the heat loss rate. The heat capacity and viscosity of the medium are related to the heat transfer efficiency. The flow velocity and flow direction design of the circulation system have a direct effect on the temperature uniformity. The sampling frequency and algorithm parameters of the controller determine the response speed of regulation. The power matching of the heating and cooling unit needs to be adapted to the target temperature zone. In addition, variables are introduced by the heat capacity of the load in use, the opening area, and the cleanliness of the media.
Applications
In materials research, it is used for glass transition temperature testing of polymer materials; In the electronics industry, it is used for high and low temperature aging tests of components; In the chemical industry, it is used for thermostatic control of reactors or temperature calibration of viscometers; In food science, it is used for product shelf life acceleration testing; In the metering department, it serves as a thermostatic source for temperature sensor calibration. Different industries have specific requirements for temperature ranges, accuracy, and tank materials.
Selection considerations
When selecting, it is necessary to comprehensively evaluate the technical parameters and usage conditions. The temperature range should cover the required limits of the experiment and leave an appropriate margin; The temperature stability and uniformity indexes need to meet the requirements of measurement uncertainty. The tank volume and opening size should be adapted to the sample size and container. The type of medium needs to consider the boiling point, freezing point, flash point and chemical compatibility. The refrigeration method (mechanical compression, thermoelectric cooling, etc.) affects the minimum temperature and cooling rate. The control interface and communication functions are related to the ease of operation and automation integration. Energy levels, maintenance intervals and safety features should also be evaluated.