How A Shell and Tube Heat Exchanger is Designed?

Background of heat exchanger

Heat exchangers are found in most chemical or mechanical systems. It’s a device that transfers heat between one medium to another. Some  of  the  more  common  applications of  heat exchangers  are  found  in heating, air conditioning  systems,  radiators  on  internal  combustion engines, boilecondensers, and  as  preheaters  or coolers  in  fluid systems.These equipments are widely used in many fields such as, power plants, petrochemical plants, petroleum refineries, and natural gas processing.Because of heat exchangers come in so many shapes, sizes, makes, and models, they are categorized according to common characteristics.One common characteristic that can be used to categorize them is the direction of flow the two fluids have relative to each other.

The three categories are parallel flow, counter flow and cross flow as the following figure

Three flow arrangements categories.

  • Parallel flow exists when both the tube side fluid and the shell side fluid flow in the same direction
  • Counter flow exists when the two fluids flow in opposite directions. Each of the fluids enters the heat exchanger at opposite ends.

Cross flow exists when one fluid flows perpendicular to the second fluid.

Types of Heat exchangers

There are many types of heat exchangers in the industrial fields and the common types ofheat exchangers are shell & tube heat exchanger and plate heat exchanger.

 Plate heat exchanger 

is uses metal plates to transfer heat between two fluids. This has a major advantage over a conventional heat exchanger in that the fluids are exposed to a much larger surface area because the fluids spread out over the

plates.This facilitates the transfer of heat, and greatly increases the speed of the temperature change.

Shell & tube heat exchange

is the most widespread and commonly used in the process industries. 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.In CO2 capture plant the type of the heat exchanger between absorber and stripper is shell and tube heat exchanger to rise the temperature of rich amine and to reduce lean amine temperature.Before entering lean amine to the absorber, the lean amine needs to be cooled to the appropriate absorption temperature.This heat exchanger will save the energy of the streams lean-rich amines instead of using heating or cooling units.The design of a heat exchanger involves many important considerations such as, Tube and shell side flow calculations, Heat transfer area, Area and number of tubes, Overall heat transfer coefficient (U),Shell diameter, types of material construction …etc.

Selection Criteria:

Function

            To cool the organic liquids from 2450 C to 60 o C.

Design: 

          Three exchangers connected parallel having same specifications.

Flow arrangement

Counter current system

Fluid side selection:

Organic fluids on shell side, organic fluids on tube side.

DESIGN CALCULATIONS OF HEAT EXCHANGER

Heat duty

Mass flow rate of cooling water

LMTD

Assumed Calculations

Heat Transfer Area

TUBE DIMENSIONS

side heat transfer coefficient Shell

Fn, Tube row correction factor

Fw, Window factor

Fb, Bypass correction factor

Fl, Leakage correction factor

Shell side Pressure Drop

F’b, bypass correction factor for pressure drop

F’L, leakage factor for pressure drop

Window zone

End zone

Total pressure drop

Tube side Pressure drop

Tube side Co-efficient

Overall Design Co-efficient

Tube side Pressure drop

Clean Overall Coefficient

Design Overall Coefficient Calculated

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