15-02-2016, 03:33 PM
Introduction
Heat exchangers have always been an important part to the life-cycle and operations of many systems. A heat exchanger is a device built for efficient heat transfer from one medium to another in order to carry and process energy. Typically one medium is cooled while the other is heated. They are widely used in petroleum refineries, chemical plants, petrochemical plants, natural gas processing, Air conditioning, refrigeration and automotive applications. One common example of a heat exchanger is the radiator in a car, in which it transfers heat from the water (hot engine-cooling fluid) in the radiator to the air passing through the radiator.
There are two main types of heat exchangers:
1.1. Direct contact heat exchanger where both media between which heat is exchanged are in direct contact with each other.
1.2. Indirect contact heat exchanger where both media are separated by a wall, through which heat is transferred so that they never mix.
While constructing heat exchangers, following attributes are considered:
• Improvement of shell side heat transfer.
• Less pressure drop for a given mass flow rate.
• Reducing of bypass effects in shell side.
• Decreasing of fouling in shell side.
• Prevention of bundle vibration.
Desirable Features of Heat Exchangers:
In order to obtain maximum heat exchanger performance at the lowest possible operating and capital costs without comprising the reliability, the following features are required of an exchange.
• Higher heat transfer coefficient and larger heat transfer area:
A high heat transfer coefficient can be obtained by using heat transfer surfaces, which promote local turbulence for single phase flow or have some special features for two phase flow. Heat transfer area can be increased by using larger exchangers, but the more cost effective way is to use a heat exchanger having a large area density per unit exchanger volume.
• Lower pressure drop:
Pumping costs are dependent on pressure drop within an exchanger. Therefore the lower pressure drop means lower operating costs.[