WHAT IS HEAT EXCHANGER 

 Heat exchangers are equipment that transfer heat from one medium to another. E.g. 
  From hot water to cold water,
 From hot steam to cold water, 
 From hot gas to cold water, 
 From hot water or unsaturated steam to cool air
 A heat exchanger is a component that allows the transfer of heat from one fluid (liquid or gas) to another fluid. Reasons for heat transfer include the following:
 1. To heat a cooler fluid by means of a hotter fluid 
 2. To reduce the temperature of a hot fluid by means of a cooler fluid 
 3. To boil a liquid by means of a hotter fluid
4. To condense a gaseous fluid by means of a cooler fluid 
5. To boil a liquid while condensing a hotter gaseous fluid Regardless of the function the heat exchanger fulfils, in order to transfer heat the fluids involved must be at different temperatures and they must come into thermal contact. 
 Heat can flow only from the hotter to the cooler fluid. 
TYPES
  Although heat exchangers come in every shape and size imaginable, the construction of most heat exchangers fall into one of two categories: 
  tube and shell, 
  or plate

TUBE AND SHELL 
 The most basic and the most common type of heat exchanger construction is the tube and shell, as shown in Figure. 
 This type of heat exchanger consists of a set of tubes in a container called a shell. The fluid flowing inside the tubes is called the tube side fluid and the fluid flowing on the outside of the tubes is the shell side fluid. 
 At the ends of the tubes, the tube side fluid is separated from the shell side fluid by the tube sheet(s). The tubes are rolled and press-fitted or welded into the tube sheet to provide a leak tight seal

SHELL AND TUBE HEAT EXCHANGER

TUBE AND SHELL 

 In systems where the two fluids are at vastly different pressures, the higher pressure fluid is typically directed through the tubes and the lower pressure fluid is circulated on the shell side
.  This is due to economy, because the heat exchanger tubes can be made to withstand higher pressures than the shell of the heat exchanger for a much lower cost

plate type heat exchanger 

PLATE TYPE EXCHANGER 

 

Aplate type heat exchanger,  

a plate type hype heat exchanger as illustrated in Figure 
2, consists of plates instead of tubes to separate the hot and cold fluids. 
 The hot and cold fluids alternate between each of the plates. Baffles direct the flow of fluid between plates. 
 Because each of the plates has a very large surface area, the plates provide each of the fluids with an extremely large heat transfer area. 
 Therefore a plate type heat exchanger, as compared to a similar ly sized tube and shell heat exchanger, is capable of transferring much more heat.
  This is due to the larger area the plates provide over tubes.