Introduction and characteristics of several throttling devices in refrigeration equipment

Introduction and characteristics of several throttling devices in refrigeration equipment

Among the four major components in the refrigeration system, the throttling device is one, and its function makes it have its own role.

First, throttling and depressurizing the high-pressure liquid refrigerant to ensure the pressure difference between the condenser and the evaporator, so that the liquid refrigerant in the evaporator evaporates and absorbs heat at the required low pressure, so as to achieve the purpose of refrigeration and decompression; At the same time, the gaseous refrigerant in the condenser releases heat and condenses at a given high pressure.

　　Secondly, adjust the flow rate of the refrigerant supplied to the evaporator to adapt to the change in the heat load of the evaporator, so that the refrigeration device can operate more effectively.

　　 The throttle mechanism has the function of controlling the mass flow of liquid refrigerant entering the evaporator, so it is sometimes called a flow control mechanism. In addition, it throttles and depressurizes the high-pressure liquid refrigerant, so that the refrigerant boils and expands into wet vapor as soon as it exits the valve hole, so it is also called a throttle or expansion valve.

Commonly used throttling mechanisms include the following types: manual expansion valves, floating ball expansion valves, thermal expansion valves and capillary tubes.

　　 One, manual expansion valve

　　The structure of the manual expansion valve is similar to that of the ordinary globe valve, except that its valve core is a needle-shaped cone or a cone with a V-shaped gap. The valve stem adopts fine thread. When the hand wheel is rotated, the opening degree of the valve can be slowly increased or the alkali is small, ensuring good adjustment performance.

　　 Its distinguishing feature is that it is not easy to break. Managers can manually adjust the opening of the expansion valve according to the change of the heat load of the evaporator and the influence of other factors. Therefore, management is troublesome and requires higher experience. Recently, automatic expansion valves are mostly used, while manual expansion valves Only used on the bypass pipe as an auxiliary function.

　　 2. Floating Ball Expansion Valve

　　 Floating ball expansion valve is mostly used in flooded evaporator. This type of evaporator requires the liquid level to maintain a certain height, which is in line with the characteristics of floating ball expansion valve.

　　According to the different flow conditions of liquid refrigerant, it can be divided into two types: straight-through and non-through-flow, each of which has advantages and disadvantages. The liquid supplied by the straight-through expansion valve to the evaporator first passes through the float chamber, and then enters the evaporator through the liquid balance tube, so it has the characteristics of simple structure, but the liquid level of the float chamber fluctuates greatly, which impacts the valve core The force is also large, and the valve core is easily damaged; in addition to the processing, a larger diameter balance pipe is needed. Non-straight-through floating ball expansion valve, the valve mechanism is outside the floating ball room, and the throttled refrigerant does not pass through the floating ball room, but directly enters the evaporator along the pipeline. Therefore, the liquid level of the floating ball room is stable, but in construction and installation Complicated.

　　 Three, thermal expansion valve

　　 Different from the float type expansion valve, it does not control the liquid level but the superheat of the gaseous refrigerant at the outlet of the evaporator to control the flow of the refrigerant supplied to the evaporator. Because a part of the evaporator area must be used to superheat the gaseous refrigerant, it is widely used in all non-filled evaporators in air-conditioning or low-temperature systems (especially Freon refrigeration systems).

　　 The thermal expansion valve has different balancing methods, or different methods of guiding the evaporation pressure to the cavity under the die. There are two types of internal balancing and external balancing.

　　The capacity is an important characteristic parameter of the thermal expansion valve, so we must understand the main factors that affect the capacity:

1. The pressure difference before and after the expansion valve

　　2, evaporation temperature

　　3, refrigerant subcooling degree

　　The installation position of the thermal expansion valve must be close to the evaporator. The valve body should be placed vertically, not inclined, and not installed upside down. It is mainly for the installation of the temperature sensing bag, usually wrapped around the suction pipe, close to the pipe wall, and wrapped tightly. The contact area should be cleaned of oxide scale to expose the nature of the metal pipe. If necessary, apply a layer of aluminum paint for protection Layer to prevent rust.

　　 Four, capillary

　　The capillary works according to the principle that "liquid is easier to pass through than gas". Its liquid supply capacity mainly depends on the state of the refrigerant at the inlet of the capillary tube and the geometric size of the capillary tube. As the inlet pressure increases, the liquid supply capacity of the capillary tube increases, the length of the capillary tube increases, and the inner diameter shrinks, which correspondingly reduces the liquid supply capacity. The capillary tube has its advantages, simple structure, no moving parts, and low price. When using it, the system does not need to be equipped with an accumulator; the refrigerant charged is also less; and after the compressor stops running, the condenser and evaporator The pressure can quickly reach equilibrium automatically, reducing the load on the motor when starting. Its disadvantage is that its adjustment performance is very poor, and its liquid supply capacity cannot be adjusted with fluctuations in working conditions.

　　Pay attention to the following points when using capillary tubes:

1. There should be no place where the refrigerant is likely to accumulate on the high-pressure side pipeline of the refrigeration cycle.

2. The refrigerant charge in the refrigeration system using capillary tubes must be correct. 　　3. A 200-300 mesh/inch filter (net) should be installed at the entrance of the capillary to prevent dirt from clogging the inner hole.

　　4. When several capillary tubes are used in parallel, in order to make the flow even, a liquid separator is used later.

　　 5. The capillary tube should be wrapped with butyl rubber and other materials for sound insulation and shockproof.