**3.4 Conclusions**

548 Heat Exchangers – Basics Design Applications

The Polyurethane-coated tubes gave the thinnest deposit layer, closely followed by the electropolished tubes. The laboratory cleaning tests showed that under the same hydrodynamic conditions, the cleaning time for test tube A9 is only 20% of that needed for

In a test series LUFA Nord-West in Oldenburg-Germany examined the formation of deposit on test PHE plates which had undergone different treatments. Different coated plates were installed in the heating section of a pasteurizer, with PTFE coated plates next to electropolished and standard stainless steel plates. The anti-fouling coatings were high-molecular polymers with implanted nano-particles which resulted in high hardness and scratch resistance. The pasteurizer was operated with a 10% (by weight) whey protein solution which was heated up to 85°C. Figure 13 shows the amount of residue, in g, for different surfaces in three tests. It is noteworthy that in these test conditions there is significant whey

The coatings A2 and A10 showed reduced deposit buildup (the PTFE coating gave more deposit buildup than the standard stainless steel plate). The plates coated with A10 coating had the lowest adhesion, which was similar to the laboratory test results. The deposit buildup on the electro-polished plates was lower than the standard stainless steel plate and almost comparable to the coated plates. Cleaning studies indicated that the cleaning in place (CIP) time, for all coatings was shorter than that for the standard stainless steel plate: PTFE coated plates down by 90%; coated plates down by 70%; electro polished plates down by

Fig. 13. Amount of deposits formed using whey protein solution, in three tests (m2, m3 and

protein deposition on uncoated, electro-polished and A2-coated stainless steel.

the standard stainless steel tube.

**3.3.2 Pilot plant tests by LUFA** 

36%.

m4).

Nano-composites could be used as anti-fouling coatings to decrease fouling inside gasketed plate heat exchangers for the dairy industry. Industrial tests showed that the coatings A2 and A10 reduced fouling, though the PTFE coating showed higher fouling than the standard stainless steel plate. The deposit buildup on the electro-polished plates was lower than the standard stainless steel plates and almost comparable to the coated plates. A CIP time reduction was observed for all coatings: PTFE coated plates down by 90%; nano-composites coated plates down by 70%; electro polished plates down by 36%. Pilot plant testing indicated the coatings must be further developed so that they can withstand the thermal and mechanical stresses which arise in industrial operation.
