Pilot scale ultrasound enabled plate heat exchanger – Its design and potential to prevent biofouling

• Plate heat exchanger with ultrasound enabled frame plate was built on pilot scale.
• Scanning laser vibrometry data was used to select suitable ultrasound conditions.
• Surface vibrations in the range 500–1200 nm appeared to delay biofouling in a first experiment.
• Ultrasound conditions used did not influence physicochemical properties of the milk.
• Heat exchanger plates appeared to be unharmed by ultrasound conditions applied.

A pilot scale 100–150 L/h plate heat exchanger (PHE) was retrofitted with ultrasound transducers without changing the main PHE design. The ultrasound enabled PHE (UPHE) and parallel split stream reference PHE (RPHE) were used to investigate the potential of ultrasound to prevent biofouling during processing of cheese milk inoculated with 103 CFU/mL Streptococcus thermophilus (TRS). Scanning laser vibrometry measurements showed that, for a 15-plate package, ultrasound conditions of 20 kHz and 70 W produced vibration magnitudes in the range of 500–1200 nm, corresponding to the size of the TRS. In one experiment, application of these ultrasound conditions was found to delay the onset of the increase in product outlet TRS concentration by 3 h compared to the RPHE. Application of conditions where only micro-streaming occurred showed no effect on biofouling. The experimental result is a first indication that surface vibrations of the same order magnitude as the adhering microorganism may be a mechanism by which ultrasound can prevent biofouling in plate heat exchangers.