The electronic expansion valve is a throttling element that can enter the refrigerant flow of the refrigeration device according to the preset procedure. In some cases where the load changes dramatically or the operating range is wide, the traditional throttling elements (such as capillary tube, thermal expansion valve, etc.) can not meet the requirements of comfort and energy saving. The electronic expansion valve combined with the variable capacity technology of compressor has been widely used.
Since the working principle of the thermal expansion valve has been mentioned before, here is a direct comparison between the two.
Comparison between electronic expansion valve and traditional thermal expansion valve
The thermal expansion valve takes the outlet temperature of the evaporator as the control signal, which is converted into the pressure of the steam in the temperature sensing package through the temperature sensing package, so as to control the opening degree of the expansion valve needle and achieve the purpose of feedback regulation. Disadvantages of thermal expansion method:
1. The feedback of the signal has a large lag. The high temperature gas at the evaporator first needs to heat the outer shell of the temperature sensing package, which has a large thermal inertia, resulting in further lag caused by the heating of the outer shell of the temperature sensing package to the working medium in the temperature sensing package during the reaction. The delay of signal feedback may lead to periodic oscillation of the parameter being adjusted.
2. The adjustment range is limited, because the deformation of the film is limited, the change range of the opening degree of the valve needle is small, so the flow adjustment range is small. In the range of large flow regulation required, for example, in the use of variable-frequency compressor, the thermal expansion valve can not meet its requirements.
3. The adjustment and control accuracy is low. The working medium in the temperature sensing bag transmits the pressure to the valve needle through the film. Reading and installation will affect and installation will affect its sensitivity to pressure deformation, so it is difficult to achieve high control accuracy.
The application of electronic expansion valve overcomes the above shortcomings of thermal expansion valve and provides conditions for the intelligent refrigeration device. The electronic expansion valve uses the electric signal generated by the adjusted parameters to control the voltage and current applied to the expansion valve so as to achieve the purpose of regulation. But because of the complex control system of electronic expansion valve, the price is higher.
Electronic expansion valve can be divided into electromagnetic type and electric type.
Electromagnetic electronic expansion valve: the adjusted parameters are first converted into voltage and applied to the electronic coil of the expansion valve. Before the solenoid is energized, the valve needle is in the fully open position. After power on, the opening of the valve needle decreases under the action of magnetic force. The degree of opening reduction depends on the control voltage applied to the coil. The higher the voltage, the smaller the opening and the smaller the refrigerant flow through the expansion valve. The electromagnetic electronic magnetic expansion valve has a simple structure and a fast response to the change of signal. But when the refrigerator is working, it needs to be provided with control voltage all the time.
Electric electronic expansion valve: electric electronic expansion valve is widely used in stepping motor driving valve needle. Generally, it can be divided into direct acting type and deceleration type.