**3.2.1 Coated surfaces**

The anti-adhesion nano-composite coatings, with hydrophobic and oleophobic effectiveness, used in this work were produced from commercially available polymer matrices such as epoxy, polyurethane or Polyamide systems which were reactively cross-linked with perfluorinated monomers (or oligomers) and ceramic reinforcement particles. The coating material application was similar to wet chemical coating by spraying, and the required mechanical properties were obtained through a thermal cross linking step. The epoxy and polyurethane systems were hardened at 130 ° C for 1 hour, while the Polyamide systems were hardened at 200 °C for 2 hours, in order to ensure an optimum layer formation. Table 5 summarizes the plates used and their specifications.


Table 5. Contact angle and surface roughness of the sheets prepared by INM.

#### **3.2.2 Laboratory scale testing**

A laboratory facility was constructed by the Institute of Environmental Process Engineering (IUV), University of Bremen in Germany, for the investigation of milk adhesion. A heat exchanger was designed to enable thermal and hydraulic load measurements with variable designs. Its principal components were a double wall heated receiver tank, controllable pump, electromagnetic flow meter and the test cell (duct). A closed loop recirculation configuration was used to decrease the volume of the test medium required. Furthermore, a fast sample change by simple removal of the test cell (duct) was performed. Figure 9 shows the laboratory apparatus used and the test duct. The test channel employs an annular geometry, where the inner cylinder is engaged with an electric heater. The middle part (with the threaded ends) is made of stainless steel, while the coin section (right) and the fastener (left) are made from a high-performance plastic Polychlorotriflouroethylene (PCTFE). This arrangement allows the middle section, which incorporates the heater, to be heated by thermal conduction without large heat losses. The coating material is applied to a small stainless steel tube which is pushed over the heater.

requirements, and increase product quality and consistency. The work will assess the

The anti-adhesion nano-composite coatings, with hydrophobic and oleophobic effectiveness, used in this work were produced from commercially available polymer matrices such as epoxy, polyurethane or Polyamide systems which were reactively cross-linked with perfluorinated monomers (or oligomers) and ceramic reinforcement particles. The coating material application was similar to wet chemical coating by spraying, and the required mechanical properties were obtained through a thermal cross linking step. The epoxy and polyurethane systems were hardened at 130 ° C for 1 hour, while the Polyamide systems were hardened at 200 °C for 2 hours, in order to ensure an optimum layer formation. Table 5

**Water [°]** 

for one minute 61.7 93.5 0.50

for five minutes 60.3 87.8 0.22

A laboratory facility was constructed by the Institute of Environmental Process Engineering (IUV), University of Bremen in Germany, for the investigation of milk adhesion. A heat exchanger was designed to enable thermal and hydraulic load measurements with variable designs. Its principal components were a double wall heated receiver tank, controllable pump, electromagnetic flow meter and the test cell (duct). A closed loop recirculation configuration was used to decrease the volume of the test medium required. Furthermore, a fast sample change by simple removal of the test cell (duct) was performed. Figure 9 shows the laboratory apparatus used and the test duct. The test channel employs an annular geometry, where the inner cylinder is engaged with an electric heater. The middle part (with the threaded ends) is made of stainless steel, while the coin section (right) and the fastener (left) are made from a high-performance plastic Polychlorotriflouroethylene (PCTFE). This arrangement allows the middle section, which incorporates the heater, to be heated by thermal conduction without large heat losses. The coating material is applied to a small

**U1** Stainless steel 83.8 69.6 0.80

**A1** Epoxy-resin based coating of INM 97.6 94.5 0.92 **A2** Epoxy-resin based coating of INM 91.0 97.6 0.95 **A9** Polyurethane based coating of INM 92.2 88.3 0.23 **A10** Polyurethane based coating of INM 93.4 95.5 0.06 **A17** Epoxy-resin based coating of INM 95.8 95.1 1.14

Table 5. Contact angle and surface roughness of the sheets prepared by INM.

**Contact angle Milk [°]** 

**Surface roughness [µm]** 

deposit buildup during the thermal treatment of milk.

summarizes the plates used and their specifications.

stainless steel tube which is pushed over the heater.

**U1min,e** Electrically-polished stainless steel

**U5min,e** Electrically-polished stainless steel

**3.2.2 Laboratory scale testing** 

**Plate Material Contact angle** 

**3.2 Experimental** 

**3.2.1 Coated surfaces** 

Fig. 9. Flowchart of laboratory heat exchanger apparatus (Institute of Environmental Process Engineering IUV, Universität Bremen).

For the experiments, a 10% (by weight) aqueous whey protein solution was set in the receiver tank. The solution was prepared by solving a whey protein concentrate WPC35 in water until the required concentration was obtained. The pH was adjusted to 6.0 using a 0.1 mol/liter HCl solution. Pre-heating was carried out to about 43 °C. The solution was pumped in the closed cycle of the experimental setup, the electric heater of the test channel was activated and the measuring procedure was started. After each trial, the whey protein solution was replaced to exclude any effect of heating on the ingredients. After each run, the tube was cleaned with 0.1 molar NaOH solution with cross flow velocity of 0.6 m/s. The experimental parameters were:

Volumetric flow rate: 0.036 – 0.37 m3/h Whey protein concentration: 10% (by weight) Average flow velocity in annulus: 0.2 m/s Fluid temperature (measuring section): 45 °C Temperature of the heating element: 230 °C Heat flux: 20 kW/m² Experimental time: 15 to 30 min.

#### **3.2.3 Pilot plant testing**

Industrial tests with milk were carried out on a small plant by the Institute of Food Quality LUFA-Oldenburg-Germany, with the support of the company GEA PHE Systems (Figure 10). The pilot plant can produce almost all dairy products. It is used for training purposes as well as technological support and procedure development to the food industry.

Fouling in Plate Heat Exchangers: Some Practical Experience 547

**Substrate Material Thickness [m]** 

The milk was pumped from the receiver tank through the pasteurizer at a constant flow rate. The process steps of heating, cooling and heat recovery were combined together. After a working time of 4 hours, the test was stopped and the plates of the heater and heat recovery sections were removed in order to measure deposit formation. Visual observations and mass investigations were done. Furthermore, the cleaning effectiveness was assessed.

Technical investigations were carried out by IUV and LUFA on the deposits formed from

Laboratory investigations were carried out by IUV on the deposit of whey protein on the tube surface. Different stainless steel tubes were tested by IUV using the laboratory heat exchanger apparatus described in section 3.2. Figure 12 shows the deposit accumulation

Fig. 12. Deposit accumulation rates for laboratory tests with whey protein on small coated

**SS** Stainless steel - **EP** Electrically-polished stainless steel - **A2** Epoxy-resin based coating of INM 83.7 **A9** Polyurethane based coating of INM 53.0 **A10** Polyurethane based coating of INM 85.2 **A67** Polyurethane based coating of INM 27.6 **PTFE** Teflon 22.5

Table 6. Samples specifications used in the pilot plant experiments by LUFA.

whey protein solution in both the laboratory facility and the pilot plant.

rates of whey protein solution for the different tube surfaces.

cylindrical ducts. Plate characteristics are given in Table 6.

**3.3 Results and discussion** 

**3.3.1 Laboratory tests by IUV** 

Fig. 10. Pilot plant used for practical tests (Institute of Food Quality LUFA-Oldenburg-Germany) with GEA Ecoflex VT04 plate heat exchanger.

The plate heat exchanger, in which coated and uncoated plates can be installed, consists of two cooling sections (deep cooler with 8 plates and pre-cooler with 10 plates), heat recovery section (with 12 plates), heating section (with 7 plates) and hot water section (with 6 plates). Before assembling the heat exchanger, selected plates in the heating and heat recovery sections were coated using the method described in section 3.2.1. As a reference, stainless steel, electro-polished and PTFE coated plates were also installed in the heat exchanger (Figure 11). Table 6 details the samples used and their specifications.

Fig. 11. Plates layout inside GEA Ecoflex VT04 plate heat exchanger.


Table 6. Samples specifications used in the pilot plant experiments by LUFA.

The milk was pumped from the receiver tank through the pasteurizer at a constant flow rate. The process steps of heating, cooling and heat recovery were combined together. After a working time of 4 hours, the test was stopped and the plates of the heater and heat recovery sections were removed in order to measure deposit formation. Visual observations and mass investigations were done. Furthermore, the cleaning effectiveness was assessed.
