The throttling mechanism is a key component in refrigeration systems, whose main function is to restrict the flow area of refrigerant or change the shape of the flow channel, thereby throttling the flow of refrigerant and achieving pressure drop and flow control from the high-pressure side to the low-pressure side. This process is an indispensable step in the refrigeration cycle, aimed at reducing the pressure and temperature of the high-pressure liquid refrigerant condensed in the condenser, allowing it to evaporate and absorb heat at a lower pressure and appropriate temperature in the evaporator, providing cooling capacity for refrigeration or air conditioning systems.
There are various types of throttling mechanisms, and according to their working principles and structural characteristics, they mainly include the following categories:
1. Manual expansion valve
Manual expansion valve is a manual adjustment device specifically used in refrigeration systems, whose main function is to control the flow of liquid refrigerant through the evaporator. This type of valve precisely adjusts the throttling process of the refrigerant through manual operation to meet the load requirements of the refrigeration system under different working conditions, ensuring stable and efficient operation of the refrigeration system. Commonly used in ammonia refrigeration systems, experimental equipment, bypass backup, etc.
2. Floating ball expansion valve
Float expansion valve is a valve device specifically used in refrigeration systems to automatically regulate the flow rate of liquid refrigerant. It is particularly suitable for full liquid evaporators. By monitoring and responding to changes in the evaporator liquid level, it ensures that the refrigerant supply in the system matches the evaporator load, thereby achieving stable and efficient operation of the refrigeration system. The working principle of a floating ball expansion valve is based on the principle of buoyancy and lever action. Suitable for evaporators with free liquid surfaces, such as:
Full liquid evaporator;
Low pressure circulating liquid storage tank;
Intermediate cooler.
3. Thermal expansion valve
Working principle: The opening of the valve is controlled by the superheat of the gaseous refrigerant at the outlet of the evaporator. Used for: non full liquid evaporator. Type: Internal balance type, external balance type.
The external balance type thermal expansion valve collects the pressure as the outlet pressure of the evaporator; The internal balance type thermal expansion valve collects the pressure as the outlet pressure of the expansion valve.
When selecting a thermal expansion valve, consideration should be given to the type of refrigerant; Evaporation temperature range; The maximum cooling capacity of the evaporator behind the valve; Differential pressure before and after the valve;
4. Electronic expansion valve
Electronic expansion valve is an advanced refrigeration system control component used to precisely regulate the flow rate of liquid refrigerant entering the evaporator. Compared to traditional mechanical expansion valves (such as thermal expansion valves, float valves, etc.), electronic expansion valves adopt an electronic control system that can quickly and accurately adjust the flow rate based on the real-time operation status of the refrigeration system, significantly improving the energy efficiency, stability, and flexibility of the refrigeration system.
Structural composition: mainly including valve body, driving motor (stepper motor or servo motor), control valve port, sensors (such as thermistors, thermocouples, etc.), controller (microprocessor) and other parts.
Working process: The controller receives signals from temperature sensors, pressure sensors, etc., and calculates the optimal refrigerant flow demand based on preset control logic and algorithms. Then, the controller sends instructions to the drive motor, which changes the opening of the control valve through a precise mechanical transmission mechanism to accurately adjust the refrigerant flow rate.
5. Capillary tube
A slender copper tube with a diameter of 0.7~2.5mm and a length of 0.6~6m, widely used in small fully enclosed direct cooling devices. The liquid supply capacity depends on the state of the refrigerant at the inlet of the capillary (pressure, temperature), and the geometric dimensions of the capillary (length, inner diameter).
Characteristics of capillary tubes: simple structure and low price; No moving parts; The system does not require the installation of a liquid storage tank and the refrigerant filling is insufficient; After the compressor stops running, the pressure can quickly reach equilibrium, reducing the starting load of the motor; Poor regulation performance, the liquid supply cannot be adjusted with changes in working conditions; Suitable for situations where the evaporation temperature changes little and the working conditions are relatively stable.
6. Throttling short pipe
Throttling short tube is a throttling element applied in refrigeration systems, mainly used to control the flow and pressure of refrigerant in the system, achieving smooth pressure reduction of refrigerant from high pressure to low pressure side. It is a fixed cross-section throttling device that achieves throttling effect through a thin pipe section with a certain length and inner diameter ratio. Due to its simple structure, low cost, and reliable performance, throttling short pipes are widely used in household air conditioning, automotive air conditioning, heat pump systems, and some refrigeration equipment.
The throttling short tube has the advantages of low price, simple manufacturing, good reliability, and easy installation. It eliminates the added temperature sensing package used to determine the refrigeration load in the thermal expansion valve system, and has good interchangeability and self balancing ability.
