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Kerns Description of Shell Side Flow in

SHELL-AND-TUBE HEAT EXCHANGER

P M V SubbaraoProfessor

Mechanical Engineering Department

I I T Delhi

Another Peculiar AveragingMethod..

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Shell-Side Reynolds Number

Reynolds number for the shell-side is based on theequivalent diameter and the velocity based on a

reference flow:

s

e

s

ss

D

A

m

Re

s

es

s

esss DGDU

Re

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Shell Side Fluid Flow

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Classification of Shell Side Flow

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Thermodynamic Similarity of Counter & Cross Flow

Heat Transfer

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Fluid dynamic Similarity of Counter & Cross Flow

Heat Transfer ?!?!?!

http://www.google.co.in/url?sa=i&rct=j&q=floww+through+a+shell&source=images&cd=&cad=rja&docid=sKVeMVPMjQ4xVM&tbnid=gOMTpKPMzj7_tM:&ved=0CAUQjRw&url=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FFile%3AShell_tube_flow.png&ei=SBEwUcjnDMGiigfs_4DIAQ&bvm=bv.43148975,d.bmk&psig=AFQjCNFWQ3fPmyEEgNwhVbGWPkWOdCkQ3g&ust=1362191045742269

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Tube Layout & Flow Structure

A Real Use of Wetted Perimeter !

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Tube Layout

Tube layout is characterized by the included angle between

tubes. Two standard types of tube layouts are the square and the

equilateral triangle.

Triangular pitch (30o layout) is better for heat transfer andsurface area per unit length (greatest tube density.)

Square pitch (45 & 90 layouts) is needed for mechanicalcleaning.

Note that the 30,45 and 60 are staggered, and 90 is inline.

For the identical tube pitch and flow rates, the tube layoutsin decreasing order of shell-side heat transfer coefficientand pressure drop are: 30,45,60, 90.

The 90 layout will have the lowest heat transfercoefficient and the lowest pressure drop.

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The square pitch (90 or 45) is used when jet ormechanical cleaning is necessary on the shell side.

In that case, a minimum cleaning lane of in. (6.35 mm)

is provided. The square pitch is generally not used in the fixed header

sheet design because cleaning is not feasible.

The triangular pitchprovides a more compact

arrangement, usually resulting in smaller shell, and thestrongest header sheet for a specified shell-side flow area.

It is preferred when the operating pressure differencebetween the two fluids is large.

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Tube Pitch The selection of tube pitch is a compromise between a

Close pitch (small values of PT/do) for increased shell-sideheat transfer and surface compactness, and an

Open pitch (large values of PT/ do) for decreased shell-sideplugging and ease in shell-side cleaning.

Tube pitch Pt is chosen so that the pitch ratio is 1.25 < PT/do