Chiller expansion valve installation and matching

Expansion valve chiller refrigeration system as the four components of large chiller chiller in a large chiller application, the appropriate choice of expansion valve and the normal installation of a direct impact on the cooling capacity of screw chillers and the stable operation of the refrigeration system .

First, matching

According to R, Q0, t0, tk, the loss of resistance of the liquid lines and valves to carry out the steps:

Determine the pressure difference across the expansion valve;

Determine the form of the valve

Select the valve model and specifications.

1, to determine the pressure difference across the valve:

ΔP = PK-ΣΔPi-Po (KPa)

Where: PK - Condensing pressure, KPa, ΣΔPi - ΔP1 + ΔP2 + ΔP3 + ΔP4 (ΔP1 for the liquid pipeline resistance loss; ΔP2 for the elbow, valves and other resistance loss; ΔP3 for the liquid tube is raised Pressure loss, ΔP3 = ρɡh; ΔP4 for the liquid head and the separation of the capillary resistance loss, usually each 0.5bar); Po-evaporation pressure, KPa.

2, determine the valve form:

Choose internal or external balance, depending on the pressure drop in the evaporator. R22 system, when the pressure drop over the corresponding evaporation temperature 1 ℃, should be used outside the balanced thermal expansion valve.

3, choose the valve model and specifications:

According to Q0 and calculated before and after the expansion valve ΔP and evaporation temperature t0 from the table check the valve model and valve capacity. In order to simplify the matching procedure, the design and technical measures can also be taken. The types and specifications of the currently available thermal expansion valve must be based on the type of refrigerant used, the range of evaporating temperature and the thermal load of the evaporator Conduct, the choice should meet the following requirements:

(1) The capacity of the selected thermal expansion valve is 20-30% larger than the actual thermal load of the evaporator;

(2) For the cooling system with no cooling water regulating valve or low winter cooling water temperature, when selecting the thermal expansion valve, the valve capacity should be 70-80% larger than the evaporator load but not more than 2 Times

(3) When selecting the thermal expansion valve, the pressure drop of the liquid supply pipe should be calculated to get the pressure difference before and after the valve. Then the specification of the thermal expansion valve should be determined according to the capacity table of the expansion valve calculated by the manufacturer.

Second, the installation

1, check whether it is intact before installation, especially the temperature sensing part;

2, the installation location must be near the evaporator, the valve body should be mounted vertically, not tilted or upside down installation;

3, the installation, you should pay attention to the temperature of the liquid within the organization always maintain the temperature in the package, so the temperature package should be installed lower than the valve body;

4, the temperature package as far as possible in the evaporator outlet level return pipe, the general should be away from the compressor suction port above 1.5m;

5, temperature package must not be placed on the pipeline with fluid;

6, if the evaporator outlet with a gas-liquid exchanger, the general temperature of the package at the evaporator outlet, that is, before the heat exchanger;

7, the temperature package is usually placed on the evaporator back to the trachea, and close to the wall tightly packed, the contact should be removed oxide scale clean, revealing the true nature of the metal;

8, when the return pipe diameter is less than 25mm, the temperature sensing package can be tied to the top of the return pipe; when the diameter is greater than 25mm, the lower side of the return pipe can be tied at 45 ° to prevent the bottom of the tube oil and other factors, Wen Bao the correct temperature.

Third, debugging

1, the evaporator outlet set thermometer or the use of suction pressure to check the superheat;

2, the superheat is too small (for the amount of fluid is too large), adjust the lever clockwise half turn or circle (that is, increase the spring force to reduce the valve opening), when the refrigerant flow decreases; Of the number of laps should not be too much (adjust the rod thread rotation, superheat change about 1-2 ℃), after repeated adjustments until the meet the requirements so far;

3, experience adjustment methods: Turn the adjustment rod thread to change the valve opening, the evaporator just back to the trachea can frost or condensation. On the evaporation temperature is below 0 degrees refrigeration device, if the hands after frosting touch, there is a feeling of sticky hand cold, when the appropriate opening; on the evaporation temperature of 0 degrees above, you can view as condensation Judgment of the situation.