The evaporator is a very important component in the four major parts of refrigeration. The low-temperature condensing “liquid” body passes through the evaporator to exchange heat with the outside air, and “gas” absorbs heat to achieve the cooling effect.

(1) Maintenance of the evaporator

1) Frequent leak detection of the evaporator. Leakage is a common failure phenomenon of evaporators, and should be carefully checked for leaks during use.

When the ammonia evaporator leaks, there is a pungent odor, and there is no frost at the leak point. Phenolphthalein test paper can be used for the leak, because ammonia is alkaline, and the phenolphthalein test paper turns red. When you look at it, it is usually the leak point where it is not frosted somewhere in the evaporator. You can also use soapy water to find the leak at the leak.

Fluorescent evaporator leaks can be checked using halogen lamps and halogen leak detectors, or soapy water can be used to find leaks. When inspecting, first check the oil drain on the evaporating tube. Because the freon and the oil can be mutually soluble, when the Freon leaks, the oil will also seep out from the leak point. Therefore, where there is oil trace, it will leak. When detecting a leak with a halogen lamp, if there is a Freon leak somewhere, the flame of the halogen lamp changes from blue to light green, light green, grass green, purple green, purple, etc. The amount of Freon leakage can be judged. If the flame is dark green or purple, the phosgene in the flame is toxic and cannot be checked by this method for a long time. In this case, the leak point can be checked with soapy water. For trace leaks, a halogen leak detector should be used for leak detection.

2) Always check the frosting condition of the evaporator. When the frost layer is too thick, it should be defrosted in time. When the frost is abnormal, it may be caused by clogging, and the cause should be found and eliminated.

3) When the evaporator is deactivated, the refrigerant is sucked into the accumulator or the condenser, so that the pressure of the evaporator is maintained at about 0.05 MPa (gauge pressure). If it is an evaporator in a salt water tank, it needs to be washed with tap water. After flushing, fill the pool with tap water.

4) For the evaporator in the chiller, the water quality of the chilled water should be guaranteed. The treated water should be treated with demineralized water. If tap water is used to form scale, descaling should be carried out.

(2) Repair of the evaporator

1) Inspection of the ammonia evaporator. The main fault of the ammonia evaporator is that the oil inside the pipe and the dirt stick block the pipe together; the outside of the pipe is cracked or pin-shaped by the rust and other factors.

1 blocked. If the evaporator memory oil and mechanical impurities are mixed, the viscosity is larger and the pipeline is blocked. First, hot ammonia flushing should be carried out. If the frosting cannot solve the problem, the ammonia of the evaporator should be pumped out, and then 0.6MPa (gauge pressure) should be used. Compressed air is blown off. If the blowout does not solve the problem. Explain that some obstructions in the pipe, such as cork, abrasive cloth for cleaning pipe fittings, cotton yarn, etc., are left in the pipe fittings. This situation should generally be cut off. But in order to reduce the number of roots. The blockage inside the tube should be found. The obstruction can be found according to the throttling phenomenon of the tube before and after frosting, and the liquid flow sound in the tube. Find the obstruction, cut off the pipe fittings, take out the obstruction, and then weld the pipe fittings. After the pressure test is checked, the use of the evaporator can be resumed.

2 plugging leaks. If there is a leak in the evaporation pipe, such as a needle hole in the smooth wall pipe or the top pipe, weld repair should be carried out. If the production task is busy, it is not possible to weld immediately. The rubber plate is blocked at the leak, and the pipe clamp is used to secure the weld during the off-season.

If the fin tube of the air cooler has a leak, the treatment method should be to close the inlet and return valves of the air cooler, open the hot ammonia flushing liquid return valve and the flushing and returning liquid total valve, and use the circulating barrel or the liquid discharging barrel. Take the time to evacuate and open the frost water to increase the pressure so that it is pumped fast and clean. Do not use the method of opening the air return valve. This method takes a long time to evacuate, and it is difficult to clean the ammonia solution. After the equipment is evacuated, the connection can be disconnected to the atmosphere, and welded or welded for welding.

Some equipments can not be evacuated due to the internal leakage of the valve, but can be pumped to below atmospheric pressure. At this time, the needle-shaped small hole can be punched down with a sharp punch, and when the ammonia is not leaked outward, welding can be performed by electric welding. The service life of the equipment is within s years, and the pipe fittings can be treated in such a way that there is no serious corrosion. The welding must be repaired with gas welding.

2) Repair of the Freon evaporator:

1 too much oil. Freon can dissolve with the lubricating oil. Therefore, when the refrigerant circulates in the system, it will inevitably have lubricating oil attached to the inner surface of the pipe. Especially when the design or installation does not meet the requirements, the evaporation pipe has more lubrication. Oil, therefore, will affect the heat transfer effect and ultimately affect the operation of the refrigeration system. When performing maintenance, the refrigerant in the evaporator should be drained, the joints of the supply and return lines should be disassembled, a nitrogen bottle or an air compressor should be connected, and oil and other impurities should be blown off with nitrogen or compressed air. If there is too much oil blown out, it means that the evaporator is not returning oil. The reason may be that there is no oil return bend at the end of each group of evaporation pipes, the diameter of the return pipe is too thick, the flow rate is not enough, or the horizontal pipe section of the return gas is not in the direction. Tilt the machine direction, etc. Repair according to the specific situation.

1 blocked. The evaporator has oil and mechanical impurities, and even blockage caused by cork, cotton yarn, etc., can be repaired according to the maintenance method of the ammonia evaporator.

2 leaks. When the joint of the system connecting pipe or the evaporating pipe is leaking, it can be tightened with a wrench. If there is no looseness, the nut should be removed to check whether the bell mouth is skewed or damaged, and the thread of the bolt is damaged. If the bell mouth is damaged, the bell mouth should be cut with a pipe cutter and re-expanded. It should be noted that the expander should be placed in a positive position, otherwise the flared bell mouth will be deflected and leaked when installed.

The inspection method for steel pipe leakage is the same as the ammonia evaporator welding method. If the copper tube leaks, it can be done by gas welding. The materials used are borax, copper electrodes or silver electrodes.

After the evaporator is repaired, the sealing test shall be carried out. For example, the R717 evaporator has a pressure requirement of 1.2 MPa (gauge pressure); the R22 evaporator has a pressure of 1.2 MPa (gauge pressure); and the R134a evaporator has a pressure requirement of 1.0. MPa (gauge pressure).