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Selection of expansion valve in display cases (2)

author: supermarket refrigerated showcase category: display freezer Views: 992Time: 2016-08-22

Selection of other refrigeration equipment

1. Selection of intercooler Two conditions should be met:

First, the speed of gas passing through the cross section of the intercooler should meet the requirements of gas-liquid separation, and the general flow rate should not exceed 0.5m/s;

Second, the heat transfer area should meet the requirements of liquid refrigerant subcooling And the flow velocity of the liquid in the coil is generally not more than 0.4m/S.

2. Accumulator selection calculation. In small fluorine refrigeration devices, there are often fewer rows of heat transfer tubes at the bottom of the shell and tube condenser, leaving space for liquid storage, and no additional liquid accumulator is needed. In the ammonia refrigeration system, accumulators can be divided into high-pressure accumulators and low-pressure accumulators according to their functions, and their selection methods are somewhat different.

1) High-pressure accumulator The liquid level gauge of the high-pressure accumulator indicates the liquid storage volume, and the liquid level height generally does not exceed 80% of the cylinder diameter. The choice of high-pressure reservoir is mainly to determine its volume. The volume should be such that the maximum liquid storage capacity of the display cases refrigeration system during operation does not exceed 70% of the volume, and the minimum liquid storage volume is not less than 10% of the volume. The volume required for the ammonia system reservoir can be calculated according to the following formula, that is, the number of reservoirs can be determined according to factors such as volume, external dimensions, and location. Generally, one for small systems, and multiple selections in parallel for large systems. However, it should be noted that when multiple units are used in parallel, the same model and specification of liquid reservoirs should be used, and gas and liquid connecting pipes should be arranged between each other to ensure the liquid level balance in each liquid reservoir.

2) Low-pressure accumulator Low-pressure accumulators can be divided into low-pressure accumulators, low-pressure circulating accumulators and drain barrels according to their different roles in the system. The structure of the low-pressure accumulator is basically the same as that of the high-pressure accumulator, but the connecting pipes are different, so the selection and calculation methods are also the same. The maximum liquid storage volume of the low-pressure circulation accumulator is not more than 70% of its own volume; the minimum liquid storage volume is not less than 30% of its own volume, and the ammonia pump should be kept for 15-20 minutes. If it is also used as a defrost drain bucket, its volume should be appropriately increased according to the drain volume. The selection of the low-pressure circulation accumulator should meet two conditions: one is the determination of the diameter, and the speed through the cross section of the low-pressure circulation accumulator should meet the requirements of gas-liquid separation; the second is the volume selection.

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Selection of expansion valve in display cases (2)

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