Simulations of thermal phase changes and bacterial inactivation in a superheated steam dishwasher

The use of superheated steam in dishwashers as a means of reducing water consumption and cleaning time without the use of chemical cleaning agents has great future potential for the restaurants, hotels, and hospitals. In these sectors in particular, hygienic safety is an important concern in addition to the removal of food residues. To evaluate this potential application, the heat transfer and phase change characteristics of superheated steam associated with bacterial inactivation are investigated in an idealized three-dimensional dishwasher with a nozzle and a plate at a temperature of 180 °C and a pressure of 10 bar. Transient OpenFOAM simulations were performed using the interThermalPhaseChangeFoam solver. The k-omega shear stress transport turbulence model was used to capture the turbulent flow conditions. Bacteria inactivation was described using first-order Arrhenius kinetics. The flow pattern of the steam jet, the shape of the steam plume, the steam condensate, and the separation of the boundary layer are affected by the structure of the shock interaction, and vortices occur near the nozzle exit, around the perimeter of the plate, and on the side walls of the dishwasher. Strong steam shocks result in a temperature increase, higher steam condensation rate, and lower bacterial concentration on the plate surface. The bacteria on the plate surface are killed within a short time of 25 s, proving the effectiveness of superheated steam in dishwasher cleaning. This study provides a basis for future development and optimization of next-generation superheated steam dishwashers.