PHE fouling factor

[DocMax]

Hello to all

I would like to recive some information about the design of plate heat exchangers.
Last week I had a meeting with a PHE supplier in order to buy PHE for cooling water pourposis. During the meeting we were discussing about the fouling factor. This supplier told me that in their design the fouling factor is not applicable because for the PHE is a non sense; in their design they consider a shear stress in the water flow trought the plates in order to garantee a cleaning effect in the plates. Is this true? Is it better to consider a fouling factor in order to design a heat transfer coefficient for clean condition and dirty conditions?
Thanks to all.

 

[rmw]

Do a search on this site and this forum. This has been discussed many times.

rmw

 

[Casimo5]

I recently attended a seminar by Tranter where they discussed this very topic. The reason that the fouling factor isn't used with PHEs is because it ends up being a self-fullfilling prophecy. If you consider a fouling factor, and then design your exchanger larger to compensate, your velocity through the exchanger will be lower, leading to more fouling. At least that was the gist of it.

 

[DocMax]

Hi Soapy 73
Thank you for your replay.
My meeting with a PHE supplier was Tranter.
Let me explain if I understood the problem:
In the design of PHE the main equation is Q = Ud*A*DTML, where Ud is the overall termal coefficient. The overall termal coefficient must follow this relationship: 1/Ud - 1/U0 > Rd where Rd, is the overall resistance to heat transfer and U0 is the coefficient in clean condition.
The U0 is a function of fluid film coefficients, this coefficient are function of the Nusselt number (turbolence condition) and so Reynolds and Prandtl. The turbulence in the PHE is higher than in tubolar exchangers and Uo is more bigger. If i consider the fouling factor the Ud will increase and so the surface area, this means more plates, more pressure drop, more costs and also it could happen less turbolence in the PHE and so less cleaning effect. So it's better to consider Ud = Uo. Is this all true? Does the turbolence guarantee the cleanning effect? Is this necessary to guarantee the right performance in the PHE?
Thanks
DocMax