Q: Why is the exhaust temperature of the cold dryer too high?

A: The high exhaust temperature of the cold dryer is sometimes abnormal, the causes are: ① the temperature of the compressed air is too high or the flow is too large; (2) The working condition of the refrigeration system changes, causing the refrigerant evaporation temperature to rise, so that the compressed air can not be cooled enough in the evaporator; ③ The heat dissipation of the outer wall of the precooler pipeline is too large.

Q: What is the reason why the air temperature of the cold dryer is too low?

A: The reasons why the air temperature of the cold dryer is too low are: ① the heat conversion area of the precooler is not enough and the cooling capacity of the evaporator is excess; ② The compressed air inlet temperature is low or the flow rate is too small; ③ The working condition of the refrigeration system changes, so that the refrigerant evaporation pressure is lower than normal.

Drying machine

Q: What is the effect of the rupture of the heat exchange copper tube of the precooler on the cold and dry machine?

A: In the precooler, the hot and wet air flows into the evaporator along the shell, and the cold and dry air from the evaporator is discharged through the precooler tube. The compressed air will produce pressure drop after passing through the precooler and evaporator, and the pressure of the hot and wet air upstream is higher than that of the cold and dry air downstream. If the copper pipe breaks, the hot and humid compressed air with high pressure and large water content will enter the cold and dry air pipe directly from the rupture. And condensation in the tube, the condensate produced will be discharged along the shortcut outside the machine, the exhaust gas with water phenomenon.

Q: Is it necessary to set the precooler separately in the automatic drainer?

A: The saturated hot and humid air in the precooler has condensate precipitation during the cooling process. And because the compressed air temperature into the precooler is higher. There is also a lot of water content, so there is a lot of condensate precipitation in the precooler during the heat exchange process. Therefore, an automatic drainer is set separately on the precooler to allow a part of the condensate to be discharged out of the machine first, which can reduce the heat load of the evaporator, especially in large cold and dry machines.

Cold and dry locomotive room

Q: What role does the evaporator play in the cold and dry machine?

A: The evaporator is the main heat exchange component of the cold and dry machine. The compressed air is forced to cool in the evaporator, and most of the water vapor is cooled and condensed into liquid water discharged out of the machine, so that the compressed air is dried. In the evaporator is the convective heat and mass exchange between the air and the refrigerant low-pressure steam, through the throttling device after the low-pressure refrigerant liquid, in the evaporator phase change into low-pressure refrigerant steam, in the phase change process to absorb the surrounding heat, so as to cool the compressed air.

Q: How to prevent the evaporation temperature from being too low?

A: In order to prevent the evaporation temperature from being too low, the energy bypass protection is set in the cold dryer. When the refrigerant evaporation pressure is low to a certain value, the hot gas bypass valve for heat supplement automatically opens (the opening degree increases), and the high pressure and high temperature refrigerant steam in the condenser is directly injected into the evaporator to raise the evaporation pressure to a normal level.

Cold dryer project site

Q: Why are cold and dry evaporators mostly horizontal?

A: Because the condensing heat transfer of compressed air is carried out in the cold dryer. In the process of condensing water vapor into water droplets, a layer of water film must be formed on the outer wall of the copper pipe first, and the horizontal arrangement can make the water film into beads and droplets quickly update the heat exchange surface. If the vertical arrangement of water droplets will flow along the surface of the copper tube into a curtain, the curtain flow makes the water film thicker and affects the heat transfer, so the evaporator copper tube in the cold and dry machine is mostly horizontal arrangement.

Q: Why should the outer edge of the evaporator copper tube be covered with fins?

A: Due to the convection heat exchange between compressed air and refrigerant steam with completely different thermodynamic properties in the evaporator of the cold and dry machine. The heat transfer coefficient of the two gases is more than ten times different. In order to obtain as high a heat transfer effect as possible, the heat transfer area of the medium side with a small heat release coefficient (here is compressed air) must be increased. Therefore, the outer wall of the evaporator copper tube (that is, the contact side with the compressed air) should be used to increase the area and strengthen the heat transfer measures, and the rolled copper tube or finned tube is an effective way to achieve this.