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While PHEs became popular for liquid-to-liquid heat transfer duties, their use in phase-

changing applications was not common initially. Concerns included leakage from gasket

materials, pressure limits (especially for condensers), freezing risk, and high pressure drops of

generated, or in the case of a condenser, entering, vapour in both the manifolds and plate

passages.

Plate heat exchanger with change in phase differs from normal two phase heat transfer heat

exchanger on two aspects: a) heat transfer equation and b) pressure drop. Heat transfer for

present case will boiling heat transfer for which we have to make use of different correlation.

Algorithm for interface of PHE with phase change will be similar to interface we have developed

for PHE apart from these above mentioned changes.

Heat transferFlow boiling heat transfer is a complex function of many variables, including surface finish, fluid

properties and flow parameters, primarily the mass flux, heat flux, vapour quality and system

pressure. It is generally accepted that flow boiling heat transfer is the combination of two basicmechanisms: nucleate boiling and forced convection. For circular pipes, these two are usually

treated as additive or asymptotic. The nucleate boiling contribution is often calculated from

pool boiling correlations, while the forced convection contribution is calculated from single-

phase correlations. For other types of channels including that of PHEs, the same two

components are generally considered to be present, however their respective contributions are

not known.

For boiling heat transfer following, the following correlation is proposed

Where Tsat is the saturation temperature in K,

* ( )+

is the bubble departure diameter, in which the contact angle, taken as 35 forhydrocarbon refrigerants,

is the thermal diffusivity, in m2

s-1

.

Equation indicates a nucleate boiling dominated heat transfer process, with the heat flux having

a power of 0.56. The influences of the flow velocity and chevron angle were found to be

insignificant and are therefore omitted.

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Pressure drop

Pressure drop in a plate heat exchanger consists of three parts: 1) pressure drop caused by the

inlet and outlet manifolds and ports; 2) pressure drop in the main core of the plates, which

includes the part due to the friction and the part due to fluid acceleration; 3) pressure drop

owing to the change in elevation. To obtain the frictional pressure drop through the PHEchannel, which was found to be the largest of all these contributions, other pressure drops had

to be evaluated and subtracted from the measured value:

*

+

*

+

G: Mass flux, kgm2s

-1

: Change of vapour qualityx: Vapour quality

Once the frictional pressure drop in the was determined, a two-phase friction factor could

then be calculated:

Where is with mean vapour quality

The vapour quality at the evaporator exit is determined from:

Q: Heat transfer rate

M: Mass flow rate, kgs-1

I: Latent heat of Vaporization

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