## Ap

2fG2L gpDe

To solve these equations for a particular duty it is necessary to know G, L, and De, and it is shown below how these can be eliminated to produce a general equation. For any plate,

where m is the total mass flow rate and At the total flow

That is, the film heat-transfer coefficient is expressed only in terms of the surface area and equivalent diameter. A computer program solves equation A8 using a constant value of De and using an empirical factor Z to account for port pressure loss and other deviations from equations A2-A4. The equation is solved using the HTU approach where

UAS m1c1

That is, the number of heat-transfer units is the temperature rise of fluid 1 divided by the mean temperature difference.

U is defined as

De is defined by APV as four times the flow area in a plate divided by the wetted perimeter. Since the plate gap is small compared with the width, then:

where hr and h2 are calculated from an empirical modification of the constants in equation A8. The powers in equation A8 are not modified.

4 X Af wetted perimeter

but since As = L X wetted perimeter where As is the total surface area:

and it is possible to eliminate L from equation A4.

Similarly, by substituting G using equation A5 in equations A2, A3, and A4 and then by rearranging the equa-

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