Evaporator

Evaporators can be used for cooling air or liquid. For jobs below 20 tons, power cooling, air cooling evaporator is used almost all the time. The air is cooled in the evaporator is sent directly to the air conditioned space. Air cooling evaporator is called the direct expansion coil, often abbreviated to D-X coil, or just the evaporator.

Evaporator, which cools liquids called cooler, and is part of the cooling system, called the refrigerator, which is designed to cool liquids, usually water. Liquid-cooled chillers using becomes particularly attractive when the refrigeration system exceeds 100 tons capacity. When the cooler is used, it cools the liquid enters the area where it is then routed through the chilled water fan coils and returned to the cooler.

Direct expansion evaporator, as shown here, finned-tube type commonly used in air conditioning and commercial refrigeration. Ribs are flat, thin sheets of aluminum fixed coil pipes. They provide additional heat exchange surface area for heat removal from the air as it passes through the coil. Some have been removed in this scheme, for easy viewing three pipes inside the coil.

The warm air (about 80F) pumped through the coil using a fan. As it flows on the cool surface of the heat exchanger (about 53F), the heat from the air flow descent with warmer air cooler coil fins and tubes, and then in the refrigerant. The air exiting the coil, much cooler than when she entered; 15F 25F temperature drop is normal for a comfort air conditioning systems. This cold air can now be distributed through space absorbs more heat and return it to the fullest.

The refrigerant is supplied to the coil on the small tubes that connect the liquid metering device in the evaporator. One of these pipes, and circuit is shown. There are many schemes in the coil as a liquid connections of the coil.

Temperature and state of the refrigerant as it passes through the evaporator can be built on the basis of temperature and enthalpy (T-H) chart. For example, bold line shows the real state of the refrigerant, and the dashed line shows the various possible States of the refrigerant in the evaporator pressure.

Here we see that the refrigerant enters the coil, is important. It is the right of the saturated liquid, so liquid and gas mixture. This boiling (boiling) at a constant temperature, as it passes through the coil. Its enthalpy is increasing steadily as more of the refrigerant changes in gas. When he reaches the saturated vapour point, additional heat absorption leads to a rise in temperature of becoming overheated.

Although the temperature changes from the beginning to the end is a small (only 10F), the enthalpy change is significant. It consists of about 42 Btu/lb and leaves about 110 Btu/lb. The change of enthalpy per pound refrigerant circulates in 110 Btu/lb - 42 Btu/lb = 68 Btu/lb. It is the change of enthalpy, which largely determines the cooling capacity of the system.

To summarize: the refrigerant enters the evaporator from the metering device as a low pressure and low temperature, saturated liquid-vapor mixture, which is mainly liquid. He leaves the evaporator as low pressure and low temperature of superheated gas. The refrigerant from the evaporator enters the compressor inlet...