Definition
Electric heating and refrigeration thermostatic chamber is a temperature control equipment that combines electric heating and mechanical refrigeration, which can provide a stable and uniform temperature environment for samples or sensors in a wide temperature range. It is usually composed of tanks, temperature control systems, refrigeration systems, heating elements and circulating stirring devices, and is widely used in industrial quality inspection, material testing, measurement and calibration and other fields.
Principle
The thermostatic tank of electric heating and refrigeration is based on the principle of energy balance to achieve temperature control. When the set temperature is higher than the ambient temperature, the equipment starts the electric heating element to heat up the medium in the tank through heat exchange; When the set temperature is lower than ambient temperature, the refrigeration system (usually cooled by a compressor) is activated, removing heat from the tank. The temperature sensor monitors the temperature of the medium in real time and feeds the signal back to the PID controller, which maintains the temperature in the tank near the set value by adjusting the heating or cooling power. The in-tank circulation pump or agitation device promotes the flow of the medium, reduces the temperature gradient, and improves temperature uniformity.
The temperature control process can be simplified into a closed-loop control model, and the relationship between the output of the control quantity and the deviation can be expressed as:
u(t) = K_p e(t) + K_i ∫ e(t)dt + K_d de(t)/dt
where u(t) is the control output, e(t) is the deviation between the set temperature and the actual temperature, and K_p, K_i, and K_d are proportional, integral, and differential coefficients, respectively.
Measurement method
The performance evaluation of thermostatic tanks is usually carried out according to national or international standards (such as JJF 1030-2010, ASTM E77, etc.). Key measurement items include temperature stability, uniformity, and value error. During measurement, calibrated multi-point temperature sensors (such as platinum resistance thermometers) are placed in different positions in the working area of the tank to record temperature changes at each point over a period of time. Temperature stability is evaluated by calculating the maximum fluctuation amplitude of temperature at a certain point in the trough for a certain period of time. The temperature uniformity is characterized by the maximum temperature difference between the measurement points at the same time. The indicated error is determined by comparing the difference between the device's displayed temperature and a standard thermometer measurement.
Influencing factors
The performance of the thermostatic chamber is affected by a variety of factors. Environmental conditions such as ambient temperature fluctuations and ventilation conditions may interfere with the thermal balance of the tank; The structure design of the tank, including the performance of the insulation layer, the stirring method and the flow rate, directly affects the temperature uniformity; The characteristics of the medium, such as specific heat capacity, viscosity, and thermal conductivity, will affect the heat transfer efficiency. The PID parameter setting of the control system and the response speed of the sensor play a key role in the temperature stability. In addition, the heat capacity of the load and its placement can also introduce temperature disturbances.
Applications
Electric heating and refrigeration thermostatic tanks play an important role in several industries. In the field of metrology, it is used for the calibration of temperature sensors, thermometers and temperature transmitters; In the chemical industry, it provides a constant temperature environment for reactors and viscometers; In materials science, it is used for temperature characteristics testing of polymer materials and metal materials; In food testing, it supports constant temperature control of sample preparation equipment; In the electronics industry, it is used for component aging test and performance test. Its wide temperature range and high stability meet the needs of different scenarios for temperature environments.
Selection considerations
When choosing an electric heating and refrigeration thermostatic tank, it is necessary to comprehensively consider the technical parameters and actual needs. The temperature range should cover the minimum and maximum temperatures required for the application, with some margin; The temperature stability and uniformity index should meet the requirements of relevant test standards; The tank volume and opening size should be suitable for the sample or instrument to be tested. The type of media should be selected according to the operating temperature and compatibility (such as silicone oil, water, ethanol, etc.); cooling and heating power need to ensure that the set point can be reached quickly even in extreme ambient temperatures; The control interface and communication function should be easy to operate and record data. In addition, energy efficiency, ease of maintenance and safety protection functions are also aspects to consider.