I am not surprised you had hard time to find such data. It is not always the usual procedure to take into account fouling factors when designing a PHE. Because of the high fluid velocities involved in PHE, deposits upon the heat exchange surfaces are less likely to appear. It is not a good choice to apply fouling factors typical of HX with a different morphology, as this could lead to oversizing.
Use those numbers at your own peril. I disagree with the use of fouling factors for PHE's and so do most major manufacturers. I don't know where this author got this unless he got it from a S&T handbook.
PHE's get their extraordinary HTC's from the velocity of the fluid passing between the plates. With fluids that have a tendency to foul, the high velocity deters fouling through the scrubbing action due to the momentum change of the fluid constantly changing direction through the convolutions.
Fouling factors adds area to the Hx which reduces velocities which reduces HTC which increases fouling. The Manufacturers I am familiar with will try their best to discourage the application of a fouling factor.
Another reason why fouling factor is not needed on PHE's is that they are completely cleanable (not welded plate types of course). Unlike a S&T which may have areas that are impossible to reach to clean, PHE's are designed to be able to be taken apart and cleaned, every square inch of them.
I would never allow a fouling factor to be added to a PHE that I had to be responsible for.
