Definition
A laboratory thermostatic sink is a device that establishes and maintains a constant temperature environment in a container through a heating and cooling system. Its core function is to provide precise and uniform temperature conditions for samples, reagents, or small experimental equipment, and is widely used in experimental and testing processes in chemistry, biology, materials, food, and environment.
Principle
Thermostatic sinks usually work on the principle of closed-loop temperature control. The system monitors the temperature of the liquid medium (commonly water or oil) in the tank in real time through a temperature sensor and feeds back the signal to the controller. The controller compares the measured value with the set value, outputs a control signal through a proportional-integral-differential algorithm according to the deviation, adjusts the power of the heater or refrigeration unit, and thus maintains temperature stability. Its basic control relationship can be expressed as:
ΔP = Kp·e(t) + Ki·∫e(t)dt + Kd·de(t)/dt
where ΔP is the output power adjustment amount, and e(t) is the temperature deviation, Kp、Ki、KdThey are proportional, integral, and differential coefficients. The tank is often equipped with a circulation pump that facilitates the flow of media to reduce temperature gradients.
Calibration method
Thermostatic sink temperature measurement primarily relies on an immersion platinum resistance thermometer or thermocouple. To ensure measurement accuracy, calibration is required regularly. Common calibration methods include using traceable precision thermometers to measure at multiple locations in the tank to evaluate temperature uniformity and stability. Uniformity refers to the temperature difference at different points in the groove at the same time, and stability refers to the change of temperature at the fixed point with time. The calibration process should refer to relevant standards and record conditions such as ambient temperature, media type and liquid level height.
The main factors affecting temperature performance
The temperature control performance of a thermostatic sink is influenced by various factors. Fluctuations in ambient temperature may lead to changes in heat exchange conditions, affecting temperature control accuracy. The material and thickness of the tank insulation layer directly affect the heat loss rate. The heat capacity, viscosity and liquid level height of the medium affect the heat transfer efficiency and uniformity. The flow velocity and flow direction design of the circulation system have a significant effect on the temperature distribution. In addition, the response speed of the heating and cooling unit, the placement of sensors, and the parameter setting of the control algorithm are also key factors.
Applications
In chemistry, thermostatic tanks are used for reaction kinetics studies, viscosity determination, and thermostatic sample incubation. In biological experiments, it is often used for enzyme activity determination and cell culture related equipment insulation. It can be used in material testing for asphalt softening points, polymer thermal property analysis, etc. It can be used in the food industry for fat melting point and product stability testing. In terms of environmental detection, it can be used for constant temperature maintenance in certain pretreatment processes. Different applications have specific requirements for temperature range, accuracy, and uniformity.
Key points to consider when selecting
When choosing a constant temperature tank, it is necessary to first clarify the temperature range and accuracy requirements, and common tank types cover a wide range from low to high temperature. The tank volume needs to match the number and size of the sample. The temperature uniformity and stability indexes should meet the experimental allowable errors. Depending on the temperature range and media characteristics, consider whether a cooling function is required or an oil sump is selected. The circulation capacity affects the temperature uniformity, and the external circulation function can meet the temperature control needs of external equipment. User-friendliness of the user interface, safety protection functions, energy consumption and maintenance convenience are also aspects that need to be evaluated in the actual selection.