An attempt was made to mitigate fouling during milk processing in plate heat exchanger by modifying SS316 surface with the coating of polytetrafluoroethylene (PTFE) and titanium dioxide (TiO₂) nanoparticles. The surface characteristics of PTFE-TiO₂ coated and conventional SS316 plates, and their thermal performance during heating of milk in batches for 8 hr were compared. It was observed that the static contact angles of water on SS316 and PTFE-TiO₂ coated plates were 66.8 ± 6.3° and 112.8 ± 0.8°, while for milk they were 61.0 ± 6.1° and 97.5 ± 1.1°, respectively. The increase in contact angle for coated surface was suggestive of weaker interaction between the fluid and surface, and enhancement in hydrophobicity. Overall heat transfer coefficients for uncoated and coated plates ranged from 354.36 to 952.26 Wm⁻² K⁻¹ and 477.11 to 593.73 Wm⁻² K⁻¹, whereas the fouling factor was 1.723 × 10⁻³ and 0.412 × 10⁻³ m²KW⁻¹, respectively. As deposition of foulants occurred, the overall heat transfer coefficient of SS316 and coated surfaces dropped by 62.15 and 19.40%, respectively, from the initial value, resulting in crossover of the curves at 310 min of heating milk. After 480 min of heating milk, the fouling factor of SS316 plates was at least four times higher than that of PTFE-TiO₂ coated plates. The PTFE-TiO₂ coating mitigated the deposition of milk foulants by 20 times than that of SS316 surface.

Practical Applications

Fouling of plate heat exchangers (PHE) during milk processing is an unsolved problem causing significant loss in heat transfer performance, increased pressure drop in flow between plates, loss of process time due to cleaning and impairment of product quality. The high surface free energy and hydrophilic adhesion of SS316 to milk act as stimulants to fouling. Modification of SS316 plates in PHE with coating of polytetrafluroethylene and titanium dioxide nanoparticles mitigates fouling. Coated plates maintain the heat transfer performance of the plates for extended time and reduce the cleaning requirement. Also, savings in harsh chemicals, water, and pumping costs could be realized.