Definition
The core function of the cryogenic circulation thermostatic bath is to provide and maintain a liquid bath with a uniform and stable temperature below the ambient temperature, and circulate the thermostatic liquid in external equipment or systems through the circulation pump, so as to achieve precise temperature control of the associated experimental equipment or sample. It is also commonly referred to as a cryostatic circulator or cryogenic bath circulator.
Principle
The working principle of the cryogenic circulation thermostatic bath is based on the combination of refrigeration circulation and fluid circulation. The device usually contains a bath to store the thermal conductive medium (e.g., silicone oil, glycol aqueous solution). First, a compressor refrigeration system or thermoelectric refrigeration system absorbs heat from the bath medium, reducing its temperature to a set value. The temperature sensor monitors the temperature of the medium in real time and feeds the signal back to the control system, which realizes the dynamic stability of the temperature by adjusting the refrigeration power or the heater compensation power. Subsequently, the built-in circulation pump pumps out the constant temperature medium and transports it to the user's external equipment (such as reactor, rotary evaporator, spectrometer sample cell, etc.) through the pipeline, and after the heat exchange is completed, the medium flows back to the bath to form a closed loop, thereby extending the constant temperature environment to the external system.
Measurement and calibration methods
The evaluation of the performance of the cryogenic constant temperature bath mainly focuses on temperature accuracy, uniformity and stability. Measurements are usually carried out according to relevant national or international standards.
Temperature accuracy measurement: Insert a calibrated high-precision platinum resistance thermometer or thermocouple into the designated measurement point in the working area of the bath, and compare the deviation between the set temperature value of the device and the measured value of the standard thermometer after the device shows that the temperature is stable.
Temperature uniformity measurement: In the effective working area of the bath, multiple temperature measurement probes are arranged to measure the temperature at different spatial points at the same time, and the maximum difference is the temperature uniformity index.
Temperature stability measurement: At a certain set temperature, within a specified time (such as 30 minutes), monitor the temperature change of a certain point with time, and its maximum fluctuation amplitude is the temperature stability index. Calibration work needs to be performed regularly by a professional metrology organization to ensure the reliability of the measurement data.
Influencing factors
The performance of the cryogenic constant temperature bath is affected by a variety of factors. The choice of thermal conductive medium is key, and its viscosity, specific heat capacity, freezing point and operating temperature range directly affect the heat transfer efficiency and controllable lower temperature limit. Environmental conditions such as high ambient temperature or poor ventilation can increase the load on the refrigeration system, affecting the cooling rate and minimum temperature. The load on the external circulation system, including the length, diameter, and insulation of the connecting lines, as well as the heat capacity and heat exchange efficiency of the external equipment, can have an effect on circulation flow and temperature stability. In addition, the cooling power, heating power, control system algorithm, and internal stirring or circulation design of the bath itself are intrinsic factors that determine its temperature control accuracy. Regular maintenance of equipment, such as cleaning filters and checking media cleanliness and liquid levels, also has an impact on long-term performance stability.
Applications
Cryogenic circulation thermostatic baths play a role in many scientific research and industrial testing fields. In chemistry and chemicals, it provides a cryogenic environment for synthesis reactions, crystallization processes, material aging tests, and viscometers. In the field of biology and life sciences (non-medical drug applications), it can be used for enzyme activity studies, sample preservation, and centrifuge temperature control. In the field of physics and materials science, it is commonly used in semiconductor testing, superconducting materials research, laser cooling, and thermostatic of optical components. In the petrochemical field, it is used for the determination of oil pouring point, freezing point and cold filtration point. In addition, it is also used in the automotive and new energy battery testing and metrology verification departments for sensor calibration and various experimental scenarios that require low-temperature circulation cooling.
Selection considerations
Selecting a suitable low-temperature circulation constant temperature bath requires a comprehensive evaluation of experimental requirements and technical parameters. The temperature range should be considered first, and it is necessary to ensure that the minimum and maximum temperatures of the equipment meet the experimental requirements and leave appropriate margins. Cooling and heating power need to match the experimental load (i.e., the heat that needs to be taken away or compensated), and insufficient power can prevent the temperature from reaching or maintaining the set temperature. The flow and pressure of the circulation pump need to overcome the piping resistance of the external circulation system to ensure sufficient media flow for effective heat exchange. The capacity size of the work tank should be able to accommodate the parts to be immersed or accommodate external circulation flows. The temperature control accuracy and uniformity index should meet the tolerance requirements of the experiment. Other features to consider include media over-temperature protection, low liquid level protection, external communication interfaces, and media compatibility and ease of replacement. Finally, equipment reliability, energy consumption, and operating noise are also factors to weigh in a laboratory environment.