Conventional dishwashers often do not eliminate all the harmful microorganisms left on plates, bowls, or cutlery. Moreover, they require long cycles which use a lot of electricity, while the soap that is pumped in and out is released into water sources, leading to environmental pollution.
According to a new study led by the Technical University of Dortmund and the Technical University of Munich (TUM), superheated steam dishwashers – which kill 99 percent of bacteria on dishes in just about 25 seconds – could be a more effective and environmentally-friendly solution.
The scientists created a simulation of an idealized dishwasher, resembling a box with solid side walls, a top opening, and a nozzle at the bottom. Plates covered with heat-resistant strains of bacteria should be placed directly above the nozzle. Once a certain threshold temperature is reached in the simulation, the microorganisms are deemed inactivated.
“Steam comes out of the nozzle at a very high velocity. We can see shocks, and the turbulent flow that is created has eddies and vortices,” said study co-author Natalie Germann, a professor of Fluid Mechanics at TU Dortmund. “We also include heat transfer, which shows how the heat changes in the simulation box and the condensation on the solid surfaces.”
According to the researchers, besides killing bacteria, the shock waves created by the high velocity of the steam and reflected at surfaces in the dishwasher could also be used to effectively remove food debris.
“Our study helps determine the strength of the shocks, the position of the shocks, and the vortices that are created inside the dishwasher,” explained study co- author Laila Abu-Farah, a postdoctoral fellow at TMU. “These things are very important for arranging the items or objects inside the dishwasher and the placement and orientation of the nozzles.”
Although superheated dishwashers would cost more than the traditional ones, their price would pay off in the long run due to savings on water, electricity, and detergent. Such dishwashers would be ideal for use in hospitals, restaurants, or hotels, which must meet higher standards of hygiene.
“We confirmed that the dishwasher application using superheated steam is promising. This is the first work combining fluid dynamics and heat transfer with phase change and bacterial inactivation. It thus lays the foundation for future computational research and further technical work,” Professor Germann concluded.