What Are Condensers?

As their name implies, condensers are employed to help condense spent steam into water. In this process they act as heat exchangers, extracting heat from the steam in lowering its temperature and further extracting its heat of vaporization in turning the steam into water.

One other result of this action is to cause a vacuum at the exhaust end that helps the steam to pass through the turbine. When engines exhaust steam to the atmosphere, the exhaust pressure is atmospheric or about 14.7 pounds per square inch.

When they exhaust in a condenser, the action is such that the back pressure is reduced to some value below atmospheric pressure. The difference between atmospheric pressure and the absolute pressure in the condenser is known as a vacuum.

Absolute pressure is the pressure above zero pressure; it is the gauge pressure plus the atmospheric pressure, both expressed in the same units.

The effect of this vacuum is to increase the effective pressure difference between the pressure of the incoming steam and that of the exhaust steam; this results in a considerable saving in the steam requirements to achieve the same results if no condenser was employed.

Types of Condensers
Condensers may be divided into two different classes:

1. Jet condensers, in which condensation of the exhaust steam is affected by direct contact of the vapor and the cooling water.

2. Surface condensers, in which the exhaust steam and the cooling water do not come in direct contact with each other; the heat is extracted from the steam by heat transfer through metal walls or tubes.

The jet condenser cools the incoming exhaust steam by causing it to flow under a fine water spray. The mixture of condensate and cooling water also contains air which is carried along with the mixture and removed from the bottom of the condensing chamber. In one type, referred to as a low-level jet condenser, this residue is removed by means of a pump.

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