Fouling dynamics of SMUF on a plate heat exchanger

In this paper, we present our first experimental results related to fouling taking place at heat exchangers during heat treatment of milk. Instead of milk we used simulated milk ultrafiltrate (SMUF), which is an aqueous solution simulating the mineral composition of milk. We did the experiments in a simplified model geometry consisting of one heating plate (dimensions 32 mm by 40 mm) made of stainless steel in a flat flow channel (height 2.0 mm) in a closed flow loop. The 3D deposit structure was measured in real time with Optical Coherence Tomography (OCT) with ca. 4 μm resolution. Fouling was observed in a wide flow rate range 300 - 1500 ml/min (Reynolds number 250 - 1250). The largest amount of deposited layer was 70 g/m2 in 7.5 hours at flow rate 1500 ml/min. The thickness of the deposited layer was ca. 300 μm. The temperature of the heating element had to exceed 85 °C for fouling to happen. In some cases we observed detachment of deposit flocks, which was seen both in OCT images and in temporary decrease of the plate temperature (indicating improved heat transfer). The system seemed to be here in a dynamic equilibrium; reflocculation and floc detachment followed each other the plate temperature fluctuating in a range of a few degrees. The measured heat transfer from the heated plate to water flow was used to validate a CFD model that has been developed for this particular fouling processin a research study parallel to this experimental work. In the future, the model will be validated against experimental data for SMUF as well.