Friday, 8 January 2016

Heat Exchangers – An Overview

Heat Exchangers installed in industries and factories drift fumes outside to make the environment work-friendly. These equipment permit efficient transfer of heat between two or more fluid (liquid, gas or solid substance) as well as save energy. This is one of the reasons behind installing of heat exchangers in factories, engines of cars, ships and planes. In addition, heat exchangers are useful in space heating, power stations, petrochemical plants, processing of natural gas and treatment of sewage. The domestic uses of heat exchangers includes working of air conditioners and refrigerators.

Heat Exchanger

What are Heat Exchangers?

A device that allows transfer of heat from a fluid to pass to another fluid with or without any direct contact. There are many different types of heat exchangers available for industrial applications. Manufactured using aluminium, steel, copper, bronze or cast iron, it is essential to use right type of equipment for the process. Selecting the wrong type of heat exchangers can lead to under-performance of plants or even equipment failure. Following are several criteria to check while selecting a suitable type of heat exchangers:
  • Type of application
  • Operating temperature and pressure
  • Temperature driving forces
  • Layout constraints
  • Available utilities
  • Cleanliness and maintenance
  • Future expansion consideration

The Various Specifications

The basic job of heat exchangers is to pass heat from one fluid to another – but they differ in their working mechanism. The classification of heat exchangers is based on two approaches, first being the flow configuration within heat exchanger and classification of equipment being second. Both of these approaches are considered below.

Classification by Flow Configuration

Heat exchangers can be distinguished on the basis of configuration of their flow within their assembly. Heat exchangers are available in Counter Flow, Cocurrent Flow, Cross Flow and Hybrid Flow.

The counter flow heat exchangers is also refer as parallel-flow heat exchangers. Wherein, the both fluids flow parallel to each other in a same direction – entering and existing the exchangers side by side.

In cross-flow heat exchangers, both fluids flow in opposite direction with each other – the entering point of one fluid becomes the existing point of other and vice versa.

Cocurrent heat exchangers are more effective than other types as the fluid flow at right angles to each other inside this configuration.

Classification by Construction

On the basis of construction, heat exchangers are available in four types of models. They are – Shell and Tube heat exchangers, Plate heat exchangers, Regenerative heat exchanger and Adiabatic Wheel heat exchanger.

Tube Heat Exchanger

Shell & tube heat exchangers have multiple tubes for regulating the flow of fluids. These tubes are divided in two sets, out of which first set contains the liquid to be cooled or heated. Whereas, the second set contains the fluid responsible for triggering heat exchange.

Plate Heat Exchanger
Plate heat exchangers have thin plates that are joined together, separated by a small rubber gaskets, collectively making a large surface area. The fluid flows between these plates, where the corners of plates extracts the heats of flowing fluid.

Regenerative Heat Exchanger
The regenerative heat exchangers combines both shell and plate exchangers technologies. In this construction, the same fluid passes through both sides of heat exchangers. The near constant temperature is maintained by regulating the heat from existing fluid to entering fluid. In this process, a large amount of energy is saved due to the cyclic flow of fluids.

Adiabatic Heat Exchangers
In Adiabatic heat exchangers an intermediate medium (fluid or solid material) is used to hold heat. This intermediate medium is then moved to other side to release the heat. An adiabatic wheel which is connected with threads rotates through both types of fluids – cold and hot to transfer heat between them.

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