BASIC DESCRIPTION OF HEAT EXCHANGE EQUIPMENT

HEAT EXCHANGE EQUIPMENT

A 'heat exchanger' may be defined as equipment that transfers the energy from a hot fluid to a cold fluid. Here, the process of heating or cooling occurs. In heat exchangers the temperature of each fluid changes as it passes through the exchangers.

Examples of heat exchangers
• Intercoolers and heaters
• Condensers and boilers in steam plant
• Evaporators
• Regenerators; refrigeration units
• Automobile radiators
• Oil coolers of heat engine
• Milk chiller of a pasteurizing plant

Applications:
• Power Production
• Process chemical food industries
• Electronics
• Environmental Engineering
• Waste Recovery
• Manufacturing Industry
• Air – conditioning and Refrigeration




CLASSIFICATION
Heat exchangers may be classified according to the following main criteria:

1. Nature of heat exchanger process
2. Flow arrangement
3. Physical state of fluids
4. Geometry and construction

1. Classification based on Nature of heat exchanger process

(i) Direct contact:
Heat transfer will occurs by direct mixing of two fluids. This is preferred when the direct mixing is harmless or desirable.
Ex: cooling towers
(ii) Indirect contact:
Heat transfer will occurs through a separating wall between two fluids
Ex: Regenerators and Recuperators

2. Classification based on Flow arrangement

According to the relative directions of two fluid streams the heat exchangers are classified into the following three categories:
(i) Parallel flow or co-current flow heat exchangers
(ii) Counter-flow heat exchangers
(iii) Cross-flow heat exchangers


(i) In a parallel or co-current flow heat exchanger
As the name suggests, the two fluid streams (hot and cold) travel in the same direction. The two streams enter at one end and leave at the other end. The flow arrangement and variation of temperatures of the fluid streams in case of parallel flow heat exchangers, are shown in the below figure. It is evident from the figure that the temperature difference between the hot and cold fluids goes on decreasing from inlet to outlet.
In parallel flow, it is not possible to bring the outlet temperature of the cold fluid nearly to the inlet temperature of the hot fluid. This type of heat exchanger needs a large heat transfer area, so, it is rarely used in practice.
It is particularly useful when sudden cooling or sudden heating is required.
Examples: Oil coolers, oil heaters, water heaters etc.

(ii) Counter-flow heat exchangers
In a counter-flow heat exchanger, the two fluids flow in opposite direction. The hot and cold fluids enter at the opposite ends. The flow arrangement and temperature distribution for such a heat exchanger are shown schematically in the below figure.
In this flow, it is possible to bring the outlet temperature of the cold fluid nearly to the inlet temperature of the hot fluid. This type of heat exchanger needs a small heat transfer area, so, it is widely used in practice.
Examples: Oil coolers, oil heaters, water heaters etc.

(iii) Cross-flow heat exchangers
In cross-flow heat exchangers, the two fluids (hot and cold) cross one another in space, usually at right angles.