译文：
热力膨胀阀广泛应用于中央空调冷水机组。它既可控制蒸发器供液量，又可节流饱和液态制冷剂。根据热力膨胀阀结构上的不同，分为内平衡式和外平衡式两种。考虑到制冷剂流经蒸发器产生一定的压力损失，为降低开启过热度，提高蒸发器传热面积的利用率，一般自膨胀阀出口至蒸发器出口，制冷剂的压力降所对应的蒸发温度降超过2~3℃，应选用外平衡式热力膨胀阀。　　外平衡式热力膨胀阀的工作原理是建立在力平衡的基础上。工作时，弹xing金属膜片上部受感温包内工质的压力作用，下面受蒸发器出口压力与弹簧力的作用。膜片在三个力的作用下，向上或向下鼓起,从而使阀孔关下或开大，用以调节蒸发器的供液量。当进入蒸发器的液量小于蒸发器热负荷的需要时，则蒸发器出口蒸气的过热度增大，膜片上方的压力大于下方的压力，这样就迫使膜片向下鼓出，通过顶杆压缩弹簧，并把阀针顶开，使阀孔开大，则供液量增大。反之当供液量大于蒸发器热负荷的需要时，则出口处蒸气的过热度减小，感温系统中的压力降低，膜片上方的作用力小于下方的作用力时，使膜片向上鼓出，弹簧伸长，顶杆上移并使阀孔关小，对蒸发器的供液量也就随之减少。热力膨胀阀的过热度由开启过热度和有效过热度组成，开启过热度与弹簧的预紧力有关，有效过热度与弹簧的强度及阀针的行程有关。膨胀阀的弹簧是按标准工况设计的，机组在标准工况下，机组满负荷或变负荷运行均维持较高的COP值。但在大压差工况下，蒸发压力降低，蒸发器负荷需求的液量减少，但实际情况相反，在吸气过热度不变的情况下，由于蒸发压力降低，蒸发器出口压力相应降低，膜片上下的压差变大，使主阀开度增大，供液量增加；但在小压差工况下，蒸发压力上升，蒸发器负荷需求的液量增多，但实际情况是在吸气过热度不变的情况下，由于蒸发压力上升，蒸发器出口压力相应提高，膜片上下的压差变小，使主阀开度减小，供液量减少；在变负荷下亦如此。因此热力膨胀阀在变工况下供液量的调节方面需进一步改进。

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原文：
Thermal expansion valve is widely used in central air-conditioning chillers. It can control the evaporator for the fluid volume, but also cutting saturated liquid refrigerant. Thermal expansion valve according to the structure of the different divided into internal and external balanced balanced the two. Taking into account the refrigerant flows through the evaporator produce a certain pressure loss, in order to reduce overheating open, improve the utilization of evaporator heat transfer area, generally from exports to the evaporator expansion valve exit pressure drop of refrigerant evaporation temperature corresponding to down Chaoguo 2 ~ 3 ℃, should be used outside the balanced thermal expansion valve. External balanced thermal expansion valve works is based on the basis of force balance. Work, flexible metal diaphragm upper thermal bag by the pressure of working fluid, the following subject to the evaporator outlet pressure and spring force. Diaphragm under the action of the three forces, up or down to muster, so that the next closed valve hole or opening big, used to regulate fluid volume for the evaporator. When the amount of fluid into the evaporator, the evaporator heat load is less than required, then the evaporator superheat steam export increases, the pressure is greater than the bottom of the top diaphragm pressure to force the diaphragm down so that bulge through the mandrel compression spring, and the valve pin to open the top, so that valve to open big holes are for fluid volume increase. On the contrary when the fluid volume for the evaporator heat load is greater than the need, then exit vapor superheat decreases, temperature system, pressure has eased, diaphragm at the top of the force when the force is less than the bottom, so that diaphragm bulge upward, spring elongation, ejector valve on the move and make a small hole off of the evaporator for the liquid volume also be reduced. Thermal expansion valve superheat from the opening degree of superheat and the effective composition of overheating, open the superheat and spring preload related to the effective superheat and the spring strength and the valve needle stroke. Expansion valve spring was based on standard conditions designed unit in the standard operating conditions, unit operating at full load or variable load remained relatively high COP values. However, in large differential pressure operating conditions, evaporation pressure has eased, the evaporator load requirements of the fluid volume decreased, but the actual situation the contrary, in the suction superheat unchanged, due to evaporation pressure has eased, the evaporator outlet pressure be reduced accordingly, pressure changes above and below the diaphragm, causing the main valve opening increases for increased fluid; but in a small pressure operating conditions, evaporation pressure rise, evaporator load demand for fluid volume increased, but the reality is that in the suction gas superheat unchanged, due to evaporation pressure rise, a corresponding increase in the evaporator outlet pressure, pressure difference above and below the diaphragm smaller, so that the main valve opening decreased for the reduction of liquid volume; in variable load is all about. Therefore, changing operating conditions thermal expansion valve for the regulation of fluid volume area requiring further improvement.

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