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Heat Transfer Coefficient

To calculate the coefficient α we need the relative easy accessible values of the temperature and the volume flow:

The transferred heat (Q) in a exchanger:
Q = α x A x (T2 – T1) x Δt
with: α = heat transfer coefficient, A = heat transfer surface, (T2 -T1)= temperature difference, Δt = examined time frame

The transferred heat (Q) of one of the liquids:
Q = cp x dm x (T2 – T1) x Δt
with: cp = heat capacity of the fluid, dm= volume flow of the fluid, (T2 – T1) = temperature difference, Δt = examined time frame

equalizing the both heat transfers as well as the average temperatures ΔTm

HeatTransferCoefficient1
results in the heat transfer coefficient (α):

HeatTransferCoefficient2
For the control (development of heat transfer coefficient) are no absolute values required, so it is possible to set A as constant (=1), and assuming always the same liquid cp and hence the same density ρ and set both as well as constant(=1). Doing like this we will get the „qualitative“ Heat transfer coefficient αm .

HeatTransferCoefficient3


using: T2, T1 the inlet and outlet temperature of the fluids and the volume flow.
The heat loss is also taken as constant.