Heat Exchanger (Shell and tubes) by sujan kharel..

BY:SUJAN KHAREL

Introduction toHEAT

EXCHANGERS(Shell and tubes)

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TRANSFER OF THERMAL ENERGY BETWEE

TWO OR MORE FLUIDS

between a solid surface and a fluid

between solid particulates and a fluid

Heat exchanger

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Classification of Heat Exchangers

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Based on transfer process

Indirect Contact – Shell & Tube Heat ExchangersDirect Contact – Cooling Towers

Gas-Liquid exchangers

Liquid-Liquid exchangers

Gas-Gas heat exchangers

Based on phase of fluids

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Based on construction

Tubular Double pipe heat exchanger Shell and tube heat exchangers Spiral heat exchangers

Plate-type Plate and frame heat exchangers Spiral plate heat exchangers

Extended Surface Plate-fin exchanger Tube-fin exchanger

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Based on flow arrangementsParallel flow / Co-current flow

Counter flow

Cross flow

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Types of HEDouble-pipe exchangerShell and tube exchangersPlate and frame exchangersPlate-fin exchangers.Spiral heat exchangers.Air cooled heat exchangersAgitated vessels.Fired heaters.

SHELL & TUBE HEAT EXCHANGERS

Shell & Tube Heat Exchangers

C.R: Masood Karim

Shell and Tube Heat exchangerA system with Shell & Tubes used

for heat exchange. A shell (a large pressure vessel)

with a bundle of tubes inside it.

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

The set of tubes is called a tube bundle.

See the Animation………

•Control Volume

Qh

Cross Section Area

HOT

COLD

Thermal Boundary Layer

Basic Structure

Types of shell & tube H.E• Among the several types : given are most

readily used.

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AdvantagesLess expensive as compared to

Plate type coolers Can be used in systems with

higher operating temperatures and pressures

Pressure drop across a tube cooler is less

Tube leaks are easily located and plugged since pressure test is comparatively easy

Disadvantages

Heat transfer efficiency is less compared to plate type cooler

Cleaning and maintenance is difficult since a tube cooler requires enough clearance at one end to remove the tube nest

Requires more space in comparison to plate coolers

Bafels

Device used to restrain the flow of a fluid or to prevent the spreading of fluid in a particular direction.

Flow-directing panel in some vessels such as shell and tube heat exchangers, chemical reactors, or static mixers.

Use of Baffles In Shell And Tube Heat Exchangers

Why are baffles used?

To support the tube

To direct the fluid stream across the tube

To improve the rate of heat transfer Shell

Tubes

Baffle

Heat exchangers problems

Exchanger fouling

Corrosion

Vibration

Fouling

• Fouling occurs when any type of particles both organic or inorganic plug or plate out on heat transfer surfaces creating a resistance to transfer energy

• There are two types of fouling– Macro-fouling– Micro-fouling

Macro Vs Micro Fouling

• Macro-fouling

– Sand– Silt– Scale– Rust– Mineral deposits

Example- CaCO3

• Micro-fouling– Biological

growth– Algae– Bacteria– Mussels

• Micro-fouling is controlled by water treatment

2.Corrosion of heat exchangers

Another series problem in heat exchangers is corrosion

Severe corrosion can and does occur in tubing and very often with common fluids such as water.

To avoid corrosion►Proper material selection based on full analysis of the operating fluids, velocities and temperatures is a must.

►Protection of the heat exchanger from corrosion [e.g. cathodic protection]

►Treatment of the cooling water used and using inhibitors.

3.Heat exchangers vibration

Vibration of the tubes as a result of the flow of the shell side past them is important phenomena specially when the H.X size and flow quantities of flow are increased

Vibration effects

►Vibration has a bad effect on both tubes and shell

►The joints between the tubes and tube sheet can fail due to vibration causing leakage

►It causes leakage in the joints between shell and tubes

►Increase the shut down time to repair the H.X

How to avoid vibration

Using inlet support baffles

Using double segmental baffles [improve tube support]

Inlet support baffles

Double-segmental baffles

Conclusion