制冷原理与置》讲义 What's it? What is its function? Distributor 同 aporator coll circuit 陈江干 上海交通大学制冷研究所 exeunt of a alut - cTrc evaporator coil. The refrigerant distribution problem in evaporators More T FLOW WTLL BE CCEATESI TO PATH OF LEAST AESISTANCE evaporator surface, see Figure 2. apor moe at different To achieve proper distribution Some Pictures The solt. the two-phase low must be divided equally to each evaporator coil the lquid and vapor portions of the refrigerant flow, tain a homogeneous twophase mixture until equal portions of the flow an divided into each evaporator circuit
1 Distributor 陈江平 上海交通大学制冷研究所 《制冷原理与装置》讲义 What’s it? What is its function? The refrigerant distributor is a device connected to the outlet of a thermostatic expansion valve (TEV). The outlet of the distributor is machined to accept tubing which connects the distributor to each evaporator coil circuit. The refrigerant distributor equally distributes refrigerant flow from the thermostatic expansion valve (TEV) into each circuit of a multi-circuit evaporator coil. The refrigerant distribution problem in evaporators A portion of the liquid refrigerant passing through the thermostatic expansion valve (TEV) normally flashes, resulting in two-phase (liquid and vapor) flow at the valve outlet, see Figure 1. This mixture is predominately liquid by weight, but the vapor occupies most of thevolume. For a typical R-22 application, the percentage, by weight and volume, of liquid and vapor flow entering the evaporator coil are listed below: The above values are based on 110°F liquid refrigerant entering the TEV, and a 45°F evaporating temperature. In this example, liquid represents 77% of the flow by weight, though it only amounts to 7% of the flow volume. An additional problem arises due to the fact that liquid and vapor move at different velocities. More… This is sometimes referred to as slip, since gravity has a greater influence on the liquid portion of the flow. If a simple header is used to divide the flow into each of the evaporator circuits, the circuits will not receive equalamounts of refrigerant. The lower circuits of the evaporator invariably receive the most liquid, possibly causing TEV hunting and floodback problems. The upper circuits are then starved, reducing the effective evaporator surface, see Figure 2. To achieve proper distribution… The liquid portion of the two-phase flow must be divided equally to each evaporator coil circuit. The solution: [1] mix the liquid and vapor portions of the refrigerant flow; [2] maintain a homogeneous two-phase mixture until equal portions of the flow are divided into each evaporator circuit. Some Pictures
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2 Very important External Equalizer TEV is needed if distributor is used, because of its high pressure-drop