Sources and Effects of Air leakage into a Condensor

The sources of air in the condenser are due to the following:

1. Leakage through packing glands and joints.
2. Leakage through condenser accessories, such as the atmospheric relief valve, etc.
3. Air associated with exhaust steam may also be liberated at low pressure.
4. In the jet condenser, the dissolved air in the cooling water is liberated at low pressures.

The effect of the presence of air in the condenser is:

1. The pressure in the condenser is increased, which reduces the work done by the engine or turbine.
2. The partial pressure of steam and temperature are reduced. The steam tables tell us that at lower pressure, the latent heat of steam is higher. To remove this greater quantity of heat, more cooling water has been supplied and, thus, undercooling of the condensate is likely to be more severe, resulting in lower overall efficiency.
3. The presence of air reduces the rate of condensation of steam since the abstraction of heat by the circulating cooling water is partly from the steam and partly through the air.
4. The rate of heat transfer from the vapor is reduced due to the poor thermal conductivity of air. Thus, the surface is of the tubes has to be increased for a given condenser duty.
5. An air extraction pump is needed to remove air, although some quantity of steam escapes with the air even after shielding to the air extraction section. This reduces the amount of condensate. Moreover, the condensate is undercooled, with the result that more heat has to be supplied to the feed water in the boiler.