Definition
Low temperature constant temperature magnetic stirrer is a kind of laboratory equipment that integrates temperature control, magnetic stirring and cryogenic cooling. It can rotate the stirrer in the vessel through magnetic drive within a set low temperature range, so as to achieve simultaneous stirring and constant temperature processing of the sample. This device is often used in experimental scenarios where precise control of the reaction temperature is required to accompany the mixing operation.
How it works:
The working principle of the low-temperature constant temperature magnetic stirrer is mainly based on three core parts: magnetic stirring system, temperature control system and refrigeration system. The magnetic stirring system achieves the mixing function by driving the magnetic stirrer placed in the container to rotate by a rotating magnetic field within the base. The temperature control system adjusts the heating power through heating elements integrated into the base or external bath with temperature sensors, and in conjunction with the PID algorithm to maintain the set temperature. The refrigeration system usually uses compressor refrigeration or Peltier thermoelectric refrigeration technology to reduce the system temperature below ambient temperature and transfer the cooling volume to the sample container through the circulating medium to achieve a low-temperature constant temperature environment.
The temperature control process can be simplified to a feedback adjustment process: the sensor measures the actual temperature Ta, with set temperature TsThe controller calculates the control amount according to the deviation, adjusts the power output P of the refrigeration or heating unit, and makes the actual temperature close to the set value. The process can be represented by the following conceptual relationship: P = f(e), where f represents the controller's regulatory function.
Measurement and calibration methods
The evaluation of the performance of low-temperature constant temperature magnetic stirrers usually involves the measurement of parameters such as temperature accuracy, uniformity, stirring stability, and cooling rate. Measurement of temperature accuracy and uniformity involves using a calibrated multi-point temperature probe or data collector that records the temperature values at each point in a steady state by placing the probe in different spatial positions of the operating medium (such as silicone oil or ethanol). The stirring stability can be measured by an optical tachometer and compared to the set value. The cooling rate is measured by recording the time it takes to drop from the starting temperature to the target temperature under no-load or standard load conditions.
Calibration work should be carried out with reference to relevant national or international standards, for example, the part involving temperature measurement can refer to the relevant methods in JJF 1101 "Specification for Calibration of Temperature and Humidity of Environmental Test Equipment". Regular calibration is the basis for ensuring the reliability of experimental data.
Performance Factors
The actual performance of a low-temperature constant temperature magnetic stirrer is affected by a variety of factors. Ambient temperature and humidity can affect the cooling efficiency and risk of condensation in the refrigeration system. The type and volume of the working medium directly affect the heat capacity and heat transfer efficiency, which in turn affects the temperature uniformity and change rate. The material, shape, and bottom flatness of the container affect magnetic coupling efficiency and heat conduction. The shape, size and magnetic strength of the agitator need to match the size of the vessel and the viscosity of the medium, otherwise it may cause stirring failure or insufficient vortex. In addition, the cooling power, heating power, accuracy of control algorithms, and the thermal insulation design of the bath or module are also key internal factors that determine its temperature control range and stability.
Main application areas:
The device is widely used in many scientific and industrial testing processes that require mixing, reaction or storage under low temperature conditions. In the field of chemical synthesis, it is often used in low-temperature organic reactions, crystallization processes, and polymerization. In materials science, it is used in nanomaterial preparation, sol-gel processes. In the field of biotechnology (non-medical drugs), it can be used for sample processing such as enzymatic reactions, cell component extraction, etc., where it is necessary to maintain activity at low temperatures. In the food testing industry, it can be used for analytical pretreatment of certain ingredients. In environmental monitoring, it can be used for water or soil sample preparation processes that require cryogenic storage and mixing.
Key points to consider in selection
Choosing a suitable low-temperature constant temperature magnetic stirrer needs to be comprehensively considered based on specific experimental needs. The first factor is the temperature range, which ensures that the minimum cooling and maximum heating temperatures of the equipment meet the experimental requirements with appropriate margins. The second is capacity and size, and the appropriate working disk size or bath capacity is selected according to the commonly used sample volume. Temperature control accuracy and uniformity are key parameters, and the model with higher accuracy should be selected for temperature-sensitive experiments. The stirring capacity needs to consider whether the maximum mixing viscosity and speed range are sufficient. In terms of refrigeration method, compressor refrigeration usually obtains lower temperatures and larger cooling capacity, while Peltier refrigeration is relatively compact and vibration-free. In addition, it is necessary to pay attention to safety features such as overheating protection, leakage protection and low level alarm. The corrosion resistance of the equipment's material, user-friendly design of the operating interface, and ease of subsequent maintenance should also be included in the evaluation.