DESIGN CONSIDERATIONS FOR

PLATE TYPE HEAT EXCHANGER

Arun S

CHEMICAL ENGINEERING

What is a plate type heat exchanger?It’s a type of Heat Exchanger which consists of many corrugated

stainless-steel sheets separated by polymer gaskets and clamped into

a steel frame

•Plate heat exchangers transfer heat by placing thin, corrugated metal

sheets side by side and connecting them by gaskets.

•Flow of the substances to be heated and cooled takes place between

alternating sheets allowing heat to transfer through the metal sheets.

Assembly Instead of pipe passing through chamber, there are two

alternate chambers separated by a corrugated plate

Plates are usually spaced by rubber gaskets

The plates are pressed to form troughs at right angles to

the direction of flow of liquid which runs through the

channel

Plates produce a large surface area ensuring maximum

heat transfer

The number and size of the plates are determined by the

flow rate, physical properties of the fluids, pressure drop,

and temperature

Mainly two forms of corrugations are seen

◦ Intermating corrugations

◦ Chevron corrugations

Greater heat transfer enhancement is produced from chevrons

The frame and the channel plates have portholes that allow process

fluids to enter altenating flow patterns

These narrow gaps and high number of contact points which

change fluid flow direction combine to create a very high turbulence

between the plates.

For a liquid-liquid heat exchanger whose usual fluid velocity is 0.2 to

1 m/s, the Reynolds No will be< 2100, but due to the presence of

corrugations the turbulent characteristics are achieved even at NRe

say about 400-500.

Evidence of Turbulent characteristics is obtained by measuring heat

transfer coefficient which varies with 0.6 to 0.8 power of flow rate

and pressure which varies with 1.7 to 2 power of the flow rate

General Dimensions of PHE

Why Plate Heat Exchanger?

High heat transfer area

High heat transfer coefficient

Compact and has lower floor space

requirements.

By increasing the number of plates the area of

heat exchange can be increased

Most suitable type heat exchangers for lower

flow rates and heat sensitive substances.

Multiple duties can be performed by a single unit

Design using correlations

From the APV heat transfer handbook- Design and Application of

Paraflow- Plate Heat exchangers there are following correlations for

PHEs:

Where Np is the number of passages

w is the width of the plate

W is the mass flow rate

G is the mass velocity

Design using charts

Only limited design correlations are available for the design of Plate heat exchanger

So the preliminary design is on the basis of certain charts by the manufacturers.

As per designing of plate and frame filter press by Christopher Haslego, they introduced a set of certain charts which form the basis of preliminary design.

The use of the charts were on the basis of following points:

◦ Applicable for liquid-liquid design

◦ Valid for only single pass units

◦ Thermal conductivity of wetted material is same as that of SS

◦ For fluids with viscosity between 100cP to 500 cP , the 100 cP

line in the graph should be used.

A = q/U LMTDF.

the number of plates from, N=A/Ap, where A, is the area of a plate

Plate Fin Type Exchanger

Limitations…..

Cost factor is on the higher side as most of the parts are

made of SS.

Not suitable for liquids with high viscosity and

suspended matters.

Often Fouling in plates, leads to requirement of

intermittent cleaning and this reduces the life of gaskets.

Large difference in fluid flow rates cannot be handled.

Applications

Widely used in diary and food

processing industries

A whole heat exchange network can

be condensed to a plate heat

exchanger

Pasteurisation of milk uses the plate

heat exchanger with three- four

sections

Also used in food and cosmetics

industries.

References

Perry’s Chemical Engineering

Handbook ,8th Edition,Don.W.Green,

Robert.H Perry

Unit Operations of Chemical

Engineering, Seventh Edition,

Warren.L.McCabe, Julian.C.Smith

Designing Plate and Frame Heat

Exchanger, Christopher Haslego and

Graham Polley