SHELL AND TUBE HEAT EXCHANGERS, LMTD CORRECTION FACTORS,

EXTENDED SURFACE HEAT EXCHANGERS, FIN EFFICIENCY AND FIN

EFFECTIVENESS.

Prepared by:130420105057 – Vasoya Pritesh130420105058 – Chauhan Vishvaraj130420105059 – Mistry Vivek

BE II, SEM IV

CHEMICAL ENGINEERING, SCET.

Shell And Tube Heat Exchangers

• What is a shell and tube heat exchanger?• How does it work?• Components of shell and tube heat exchanger• Types of shell and tube heat exchanger

What is a Shell and Tube Heat Exchanger??

• Consist of two main things as it’s name implies Shell & Tubes.

• The shell is a large vessel with a number of tubes inside it .

• The principle of operation is simple :

• Two fluids of different temperatures are brought into close contact but they are not mixing with each other.

• One fluid runs through the tubes, and another fluid flows over the tubes (through the shell) to transfer heat between the two fluids.

How does it work??

• The temperature of the two fluids will tend to equalize .

• The heat are simply exchanged from one fluid to the other and vice versa. No energy is added or removed.

Components

• shell; shell cover;

• tubes; tube sheet;

• baffles; and nozzles

• Other components include tie-rods and spacers pass partition plates, impingement plate, longitudinal baffle, sealing strips, supports, and foundation.

Types of Shell and Tube Heat Exchanger

• U-Tube Heat Exchanger

• Straight-Tube ( 1-Pass )

• Straight-Tube ( 2-Pass )

• Floating Head shell and tube heat exchanger

U-Tube Heat Exchanger

Straight-Tube ( 1-Pass )

Straight-Tube ( 2-Pass )

Floating Head Shell and Tube Heat Exchanger

LMTD Correction Factor

• Logarithmic Mean Temperature Difference (LMTD)

• Where:

ΔT1 = the temperature difference between hot and cold fluids at one end of the heat exchanger.

ΔT2 = the temperature difference between hot and cold fluids at the other end of the heat exchanger.

However the LMTD is valid only for heat exchanger with one shell pass and one tube pass.

For multiple number of shell and tube passes the flow pattern in a heat exchanger is neither purely co-current nor purely counter-current. Hence to account for geometric irregularity, Logarithmic Mean Temperature Difference (LMTD) has to be multiplied by a Mean Temperature Difference (MTD) correction factor to obtain the Corrected Mean Temperature Difference (Corrected MTD).

Extended Surface Heat Exchangers

• "Extended surface" is a term that covers many possibilities but the type that we shall be most concerned with is the round tube with round fins essentially transverse to the tube axis

• The low-finned tube commonly used in shell and tube exchangers provides about 3 to 4 times as much outside area as inside; i.e., Ao/Ai is about 3 to 4.

• A medium-fin height tube with 11 fins per inch is also used in shell and tube exchangers, and has an Ao/Ai ratio typically about 5.

• The high-fin tube is used to advantage when gases are to be heated or cooled or when a process stream is to be air-cooled.

• High-fin tubes come in a wide variety of fin heights, thicknesses, and spacings, giving values of Ao/Ai up to 25.

Finned Tubing

Fin Efficiency

• Consideration of the heat flow path from the tube-side fluid through the tube wall, and fins, and into the fin side fluid reveals that the distance which the heat must flow' is longer than in the corresponding plain tube case.

• It is true that the additional distance is through the usually highly conductive fin metal, but there is still an additional resistance to the flow of heat, which partially offsets the advantage of the extended surface.

• “Fin Efficiency, " φ, is the ratio of the total heat transferred from the actual fin to the total heat that would be transferred if the fin were isothermal at its base temperature.

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