The heat transfer coefficient is a calculated figure we can use to see indirect, what is happening inside a heat exchanger. In an idle world, the internal surface of a heat exchanger stays clean during its operation. If this is the case the heat transfer will constant as well, all good.
See the picture to the left. After installing Merus the tubes are clean, where is constant flow. Such clean tubes, or with a very thin layer of incrustation the heat transfer is very good.
As we are in most case not in an idle world, there happens fouling in heat exchangers. Means one can find all kind of incrustions. These incrustation are acting as an insulation. Less heat is transferred. We at Merus use the heat transfer coefficient to monitor the efficency of the Merus Rings.
How to calculate the 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= mass flow of the fluid, (T2 – T1) = temperature difference, Δt = examined time frame
equalizing the both heat transfers as well as the average temperatures ΔTm
results in the heat transfer coefficient (α):
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 .
using: T2, T1 the inlet and outlet temperature of the fluids and the volume flow.
The heat loss is also taken as constant.
If you will need help, how to do the calculation or how to analyse / interpret your results from the field, please dont hesitate and write us an Email.