I have more than 10 plate heat exchangers (PHE) in my plant. Usually, we'll monitor the flowrate, inlet and outlet temperature, as well as pressure. Before, I joined the company, I observed that the "cleaning in place" (CIP) using caustic solution was carried out when the PHE could no longer produced desired flow rate and temperature outlet. This is one method of eliminating the fouling and scaling on the plate surface in order to improve the heat transfer. If CIP does not work, we have to dismantle the PHE, clean the plates in hot caustic and attach new gasket on it. This will be a far more expensive option and take longer time.
To avoid massive fouling and scaling from getting worse, we have to conduct CIP regularly. When is the right time to perform CIP? As mentioned above, when the flow rate is low or desired outlet temperature could not be achieved, we shall consider doing CIP.
However, I came out with a formula to calculate the "Overall Heat Transfer Coefficient" (U-value) of the heat exchanger. The U-value will give me some indication on which heat exchanger is providing the worse heat transfer. By simplifying the formula in excel file, I can easily know which heat exchanger needs attention just by inserting the inlet/outlet temperature, mass flow rate, heat capacity of oil, and surface area of the plates. The LMTD (log mean temperature difference) will be obtained from the formula and further applied to get the U-value.
I use and manipulated the following formulas:
Q = mc(theta) = UA(LMTD)
Can you work out the formula?
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