INTRODUCTION TO SHELL & TUBE HEAT EXCHANGER

First question comes in our mind by hearing this word is that what is heat exchanger?

Answer to this question is that, heat exchanger is a mechanical device that transfer heat from one fluid to another fluid. It utilizes the principle of conduction and convection.

There are three steps in heat transfer in heat exchanger.

  STEP 1 : Heat is transferred from the hot fluid to the inner wall of tube by the means of  convective heat transfer.

   STEP 2 :  Heat is transferred from inner wall of the tube to outer wall of tube by the means of conduction.

   STEP 3 : Heat is transferred from outer wall of tube to the cold fluid by the means of convection.

 

There are many types of heat exchangers are available in chemical industries for the heating or cooling application but among all of that shell & tube heat exchanger are most widely used in chemical process industries.

Shell & Tube heat exchangers are mainly used as heat transfer equipment but in few cases shell & tube heat exchanger is also used as the reactor & falling film absorber. Sizing of various parts of shell & tube heat exchanger like tubes, shell, baffles, pass partition plate & tie rods are standardized. These standards are developed by TEMA (Tubular Exchanger Manufacturers Association) USA and HTRI (Heat Transfer Research Institute) USA. IS:4503 is also equivalent to TEMA and used for the process design of the shell & tube heat exchanger and it also specify the maximum allowable baffle spacing, minimum tube sheet thickness, baffle thickness, numbers of tie rods required, etc.

For mechanical design and fabrication of shell & tube heat exchanger ASME (American Society of Mechanical Engineers) Section VIII div II is used along with IS:2825.

Shell & Tube heat exchanger are divided in three types according to TEMA standard:

1. Class R covers heat exchangers which are used for severe duties in petroleum and related industries. Also, it covers heat exchangers that are going to handle toxic gas, highly flammable fluid or hazardous fluid.

2. Class B covers the heat exchangers which are used in chemical process industries not involving severe duties.

3. Class C covers the heat exchangers which are used in commercial and in less important process applications. Example: Heat exchangers used for recovery of energy from an effluent stream.

Process Design of Shell & Tube Heat Exchanger:

One can easily do the process design of shell & tube heat exchanger manually with the help of books, some books are listed below:

1.  Perry, R. H., and D. Green, Perry’s Chemical Engineers’ Handbook, 6th Ed., McGraw-Hill, USA, 1984.

2.  Sinnott, R. K., Coulson and Richardson’s Chemical Engineering, Vol. 6, Revised 2nd Ed., Asian Publishers Books Pvt. Ltd., New Delhi, 1998.

3.  Kern, D. Q., Process Heat Transfer, McGraw-Hill, USA, 1950.

4.  Ludwig, E. E, Applied Process Design for Chemical and Petrochemical Plants, Vol.3, 3rd Ed. Gulf   Publishing, USA, 2001.

Apart from books listed above there are many more books are available for process design of shell & tube heat exchanger. We can also perform the design calculation of shell & tube heat exchanger in the software.

Most popular and reliable softwares used for the design of shell and tube heat exchangers are as follows:

1.      HTRI: Heat Transfer Research Inc., USA

2.      HTFS: Heat Transfer and Fluid Flow Services, UK

3.      BJAC: USA based company

4.      HEI: Heat Exchange Institute, USA.

5.      Aspen EDR (Exchanger Design & Rating): A software by the Aspen Technology.

Design methods and equations that are used by these softwares are proprietary and are not available in open literature. For the design of shell and tube heat exchanger involving fluid without phase change, methods used by these softwares are based on Tinker’s flow model.