Heat Exchangers and Their Three Basic Types

Heat Exchanger

Heat exchanger is a device which is used to transfer heat from one solid body to any other solid body or transfer heat between fluid and solid body. Heat may transfer through any method of heat transfer (conduction, convection and radiation) and using the second law of thermodynamic the direction of heat transfer can be predicted very easily (J.P. Holman, 2010). There are many different types of heat exchanger that can be used for heat transfer and they are as follow (Frank Kreith, 2011).

1.      Recuperators

2.      Regenerators

3.      Direct Contact Exchanger

Recuperators

According to Frank Kreith (2011) recuperators are those heat exchanger in which cold and hot fluids are in separate tubes. Heat from hot fluid first transfer from fluid to tube walls through convection, then from one side of tube to other side of tube through conduction and then from outer side of tube to the cold fluid through convection.

Recuperators type heat exchanger are very simple in design as they are usually consist of only two parts, one in which hot fluid is moving and one in which cold fluid is moving like shell and tube heat exchanger (Durges J Bhatt 2014). Working efficiency of this type of heat exchanger is usually good but can be made excellent very easily for example in shell and tube working efficiency can be increase just by increasing length of tube or by increasing number of tubes in shell (Asawari Barde, 2016). One of the best thing about this type of heat exchanger is that they are compact in size because of very simple geometry which also made them light weight. Problem which is associated with this type of heat exchanger is that they are very difficult to clean and maintain. They may also induce vibration in tubes during operation because force present in flowing fluid.

Regenerator

Regenerator heat exchanger has different very complicated structure and operation. They have a core and a rotor. Hot and cold fluids are placed in separate chamber of core where rotor rotates between hot and cold region (Frank Kreith, 2011).  Heat from hot fluid is first transfer to the rotor through convection and then from rotor to cold fluid through convection.

Regenerator type heat exchanger are complex in design as they are usually consist of more than four parts, one in which hot fluid is moving, second in which cold fluid is moving, third which transfer heat from hot to cold side and fourth is the seal separating two fluid. Working efficiency of this type of heat exchanger is usually good but cannot be made excellent very easily because it involve upgrading the part which in responsible for heat transferring (Thulukkanam, K. 2013). One of the best things about this type of heat exchanger is that they are compact in size but complex geometry made them heavy weight. Problem which is associated with this type of heat exchanger is that they are very difficult to clean and maintain.

Direct Contact Exchanger

According to Frank Kreith (2011) direct contact heat exchangers are those heat exchangers in which hot and cold fluids are in direct contact of heat other for example cooling tower. Cold fluid runs in one direction and hot fluid runs in other direction, during their contact they exchange heat from hotter fluid to colder fluid through convection.

According to TEMA direct type heat exchanger are very simple in design as they are usually consist of only two parts, one from which hot fluid (steam) moving up and one from which cold fluid moving down. Working efficiency of this type of heat exchanger is usually excellent because of direct contact between fluid have its heat transfer coefficient extremely high. One of the bad thing about this type of heat exchanger is that they are not compact in size because of very simple geometry but this simple geometry made them light weight. One of the bad thing about this type of heat exchanger is that they are very easy to clean and maintain. Problem which is associated with this type of heat exchanger is that there use is limited to only those liquids that are allow to contact each other (Shah, R. K., 2003).