Cooling Cycle

TM 55-1905-223-24-17

Cooling Cycle. The cooling cycle shows what happens to the heat after it is removed from the air

by refrigerant in the cooling coil.

(1)

As cold refrigerant liquid moves through the cooling coil (4, FIGURE 1-3), it picks up heat from

the air passing over the surface of the coil. As it picks up heat, the refrigerant changes to a

vapor.

(2)

The heated refrigerant vapor is then drawn into the compressor (3) where it is put under high

pressure. This causes the temperature of the vapor to increase.

Next, the high pressure, high temperature vapor passes to a seawater cooled condenser (2)

where heat is removed from the refrigerant. As the condenser removes heat, the vapor changes

to a liquid but is still under pressure.

(4)

The liquid refrigerant then flows to the expansion valve (1) (or capillary assembly). As the liquid

flows through the valve (or capillary), pressure is reduced instantaneously. This action lowers the

temperature of the liquid still further so that it is now ready to pick up more heat.

(5)

The cold, low pressure liquid refrigerant then flows into the cooling coil (4). The pressure in the

cooling coil is low enough to allow the refrigerant to vaporize as it again absorbs heat from the air

passing over the coil surface. The cycle begins to repeat itself as the heated refrigerant vapor is

again drawn into the compressor (3).

Cooling Coil. The purpose of the cooling coil is to provide a surface over which air from a

compartment can flow, and at the same time, a passage through which refrigerant can flow. The

combination of warm air flowing over the cold refrigerant tends to cool the air and heat the

refrigerant. Actually the temperature of the refrigerant does not change; but the liquid does

change to a vapor, and in this sense, the refrigerant is heated. So, in effect, heat is transferred

from the air to the refrigerant through the coil (heat transfer) surface.

Compressor. The compressor serves two purposes; first, it draws the refrigerant from the-cooling

coil and forces it into the condenser and secondly, it increases the pressure on the refrigerant.

(1)

Compressor Suction. By drawing or sucking the refrigerant, the compressor reduces the

pressure in the cooling coil and maintains it at a level low enough to permit the refrigerant to

vaporize (boil) and consequently absorb heat in the process. Refrigerant boils at a relatively low

temperature when pressure is reduced.

(2)

Compressor Discharge. By discharging or forcing refrigerant into the condenser, the compressor

increases the pressure of the refrigerant. In doing so, the compressor actually increases the

refrigerant vapor temperature. This makes it easier for the condenser to do its job.

1-16