The total rate of heat transfer between the hot and cold fluids passing through a plate heat exchanger may be expressed as: Q = UA∆Tm where U is the Overall heat transfer coefficient, A is the total plate area, and ∆Tm is the Log mean temperature difference. Generally the heat transfer correlation for a fluid flow past a solid surface is expressed in a dimensionless form

Nu = Nu (Re, Pr)

where Nu is the non dimensionless Nusselt number expressed as

Nu=hd/k

Overall heat transfer coefficients in common heat exchanger designs - tubular, plate or spiral.

Plate heat exchanger, Overall heat transfer coefficients for liquid to liquid is generally-1000-4000 W(m2 K)

For detail please find attached herewith articles.

And below link

https://www.researchgate.net/publication/342411762_Plate_Heat_Exchanger_Overall_Heat_Transfer_Coefficient

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Heat transfer coefficient quantifies the efficacy of heat transmission between a fluid and a solid surface. The following equation may be used to determine the heat transfer coefficient:The heat

h = q / (A * ∆T)