Heat exchangers are predominantly used in both mechanical and petroleum industry. Heat exchanger is a system or equipment used to transfer heat between two or more fluids. It is used for cooling and heating purposes in industrial applications. Heat exchangers are of many types depending on the usage in industries such as direct contact, shell and tube heat exchangers etc. Heat exchangers works based on the principle of heat naturally flows from high temperature to low temperature. In heat exchangers the heat is transferred by the process of convection. A simple example will be a car radiator. It is designed to transfer heat from the hot coolant that flows through it to the air blown through it by the fan.
In mechanical industry, the heat exchanger is deployed in all type of power plant. The heat exchanger finds in use in power plant whether a coal powered power plant or a nuclear power plant. The nuclear power plant the heat from hot coolant from the reactor is used to boil the water into steam for energy generation with the use of heat exchanger.
In petroleum industry, the heat exchanger is used in fractional distillation process. The crude oil is heated with the help of furnace with the use of heat exchanger. The crude oil from the storage area is passed through a series of tube bundle which passes through the furnace. As the number of tubes increases the more the heat is transferred as the contact surface area is increased.
For a simple understanding of convection, let us imagine the phenomenon of melting of ice. During the process, Heat moves to the ice from the air. This causes the melting from a solid to liquid.
The mathematical formula for convection is given by
As it shows, the contact area is directly proportional to the heat flows. Therefore as contact area increases, heat flow increases. Here by the surface area of a heat exchanger is increased by increasing the number of tube bundles.
Heat exchangers are typically classified according to flow arrangement and type of construction. The simplest heat exchanger is one for which the hot and cold fluids move in the same or opposite directions. This heat exchanger consists of two concentric pipes of different diameters.
· Parallel-flow arrangement. In the parallel-flow arrangement, the hot and cold fluids enter at the same end, flow in the same direction, and leave at the same end.
· Counter-flow arrangement. In the counter-flow arrangement, the fluids enter at opposite ends, flow in opposite directions, and leave at opposite ends.
The heat transfer surface in heat exchangers can be arranged in several forms. Heat exchangers are therefore also classified as:
· Double pipe heat exchangers
· Shell and tube heat exchangers
· Plate heat exchangers and etc
Heat exchangers are found to be efficient method of waste heat recovery. The waste heat can be recovered using various types of heat exchangers depending on the nature of environment put in use and can be used for heating and cooling purposes or any other industrial applications.
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