Low temperature constant temperature reaction bath(also known as low-temperature constant temperature bath or low-temperature bath) is a core equipment used in laboratories and industrial production to provide a constant low-temperature environment. It is widely used in chemical reactions, sample refrigeration, material testing, and other scenarios. Its working principle revolves around the three core links of "refrigeration temperature control circulation", and achieves precise and stable low-temperature constant temperature effects through multi system collaboration. The specific details are as follows:

1、 Core Component System

To understand the working principle, first clarify the key components of the equipment, and each system works together to complete the low-temperature constant temperature function:

Refrigeration system: The core is a compression refrigeration circuit (similar to the refrigeration principle of a refrigerator), which includes four core components: compressor, condenser, throttling element (capillary/expansion valve), and evaporator. Some equipment will be equipped with auxiliary refrigeration structures (such as air-cooled/water-cooled cooling devices);

Heating system: usually an electric heating tube (or heating plate), used to fine tune temperature, compensate for temperature deviation caused by excessive cooling, and ensure constant temperature accuracy;

Temperature control system: composed of temperature sensors (such as platinum resistance PT100, thermocouple) and temperature control instruments (PLC or dedicated temperature controller), it is the "brain" of the equipment, responsible for temperature detection and command issuance;

Circulating system: including circulating pump, circulating pipeline, and bath liner, used to ensure uniform flow of heat transfer medium (such as ethanol, ethylene glycol aqueous solution, silicone oil, etc.) in the bath, ensuring consistent temperature in all areas of the bath;

Insulation system: The outer layer of the inner liner is wrapped with insulation materials (such as polyurethane foam, rock wool) to reduce the heat exchange between the low temperature inside the tank and the external environment, reduce energy consumption, and improve constant temperature stability.

2、 Core workflow (refrigeration+temperature control+cycle coordination)

1. Refrigeration process (core cooling stage)

The refrigeration system is the key to achieving "low temperature". Based on the principle of "vapor compression refrigeration cycle", cooling is achieved by absorbing heat through the phase change of refrigerant

Step 1: The compressor compresses low-temperature and low-pressure refrigerant gases (commonly used refrigerants such as R404A and R134a) into high-temperature and high-pressure gases, increasing the energy level of the refrigerant;

Step 2: The high-temperature and high-pressure refrigerant gas enters the condenser (dissipating heat through air or water cooling), releases heat, and condenses into high-pressure liquid refrigerant;

Step 3: After the high-pressure liquid refrigerant passes through the throttling element (capillary tube/expansion valve), the pressure drops sharply and becomes a low-temperature and low-pressure mist refrigerant (phase change process);

Step 4: The low-temperature mist refrigerant enters the evaporator (which is in contact with or embedded in the inner liner of the bath), absorbs the heat of the heat transfer medium in the bath, evaporates into gas, and the temperature of the heat transfer medium continues to decrease;

Step 5: The evaporated refrigerant gas returns to the compressor, completing the cycle and repeatedly achieving continuous cooling.

2. Temperature control process (precise constant temperature core)

The temperature control system ensures stable temperature at the set value through closed-loop control of "detection comparison adjustment":

Temperature detection: Temperature sensors (such as PT100) real-time collect the actual temperature of the thermal conductive medium in the bath, and convert the temperature signal into an electrical signal to transmit to the temperature control instrument;

Signal comparison: The temperature control instrument compares the actual temperature with the target temperature set by the user to determine whether cooling or heating is needed;

When the actual temperature is higher than the set temperature: the temperature control instrument issues a command to start the refrigeration system and reduce the medium temperature;

When the actual temperature is lower than the set temperature: the temperature control instrument issues a command to start the heating system (electric heating tube) and slightly increase the medium temperature (compensating for temperature fluctuations caused by excessive cooling or environmental heat dissipation);

When the actual temperature equals the set temperature: the temperature control instrument shuts down the cooling and heating system, or maintains low-power operation to keep the temperature stable.

Precision control: The temperature control instrument of high-quality equipment adopts PID (proportional integral derivative) adjustment algorithm, which can automatically adjust the cooling/heating power according to the size and change rate of temperature deviation, avoiding temperature "overshoot" (exceeding the set value) or "undershoot", and achieving high-precision constant temperature of ± 0.1 ℃ or even ± 0.01 ℃.

3. Loop process (uniformity guarantee)

The function of the circulation system is to ensure uniform flow of the heat transfer medium in the bath, avoiding local temperature differences:

After the circulation pump is started, it pushes the thermal conductive medium in the bath tank to form a forced circulation (some equipment supports internal circulation, external circulation, or switching between internal and external circulation);

Internal circulation: The medium flows inside the bath to maintain consistent temperature in various areas of the bath (such as the bottom, middle, and near the bath wall), ensuring even heating/cooling of reaction vessels, samples, etc. placed inside the bath;

External circulation: Some devices can transport low-temperature media to external devices (such as reaction vessels and sample tanks) through pipelines, providing a low-temperature and constant temperature environment for external devices. Afterwards, the media flows back to the bath, achieving multi device linkage cooling.

3、 Key auxiliary principles

The function of thermal conductivity medium: Water cannot be directly added to the bath (it will freeze at low temperatures), and specific thermal conductivity medium (such as ethanol or ethanol water mixture commonly used below -50 ℃, ethylene glycol ethanol mixture commonly used below -100 ℃, or special low-temperature silicone oil) needs to be used. Its function is to transfer heat, and it has the characteristics of low freezing point, high thermal conductivity efficiency, and good chemical stability, ensuring that it does not freeze or evaporate at low temperatures and stably transfers refrigeration capacity;

Insulation principle: The insulation material on the outer layer of the inner liner can reduce heat conduction and convection, reduce the heat exchange between the low-temperature medium in the tank and the external environment (avoid external heat entering the tank and causing temperature rise), improve the stability of constant temperature, reduce the workload of the refrigeration system, and save energy consumption;

Safety protection principle: Equipment is usually equipped with multiple safety protection functions, such as overload protection (automatic power-off when the compressor or heating tube is overloaded), low liquid level protection (stopping cooling/heating when the medium is insufficient to prevent dry burning or equipment damage), and over temperature protection (alarm and shutdown when the temperature exceeds the safe range), to ensure the safe operation of the equipment.

summary

　　Low temperature constant temperature reaction bathThe core working logic is to achieve cooling of the thermal medium through a compression refrigeration system, accurately adjust the cooling/heating power through a PID temperature control system, ensure uniform temperature of the medium through a circulation system, and reduce heat loss through an insulation system, ultimately providing a stable, uniform, and high-precision low-temperature constant temperature environment for experiments or production. Its essence is the synergistic effect of "phase change refrigeration+closed-loop temperature control+forced circulation", which solves the problem of precise temperature control in low-temperature environments.