A supercharged dishwasher using heated steam could kill bacteria in 25 seconds
German researchers have modeled the workings of a new dishwasher system that uses superheated steam, and it can kill bacteria in just 25 seconds, New Scientist reported.
To many, it may seem strange that researchers in a high-tech laboratory in Germany are trying to figure out the workings of a new type of dishwasher. Although scientists are often interested in discovering new things, such as sub-atomic particles or new celestial bodies in space or treating an incurable disease, some are also keen on solving day-to-day problems.
A heat-resistant bacteria like Geobacillus stearothermophilus, for instance. G.stearothermophilus can survive the cleaning of a regular dishwasher and then attacks the food kept in washed plates and ends up spoiling it. This may not sound like a major issue to you and me, but for the hotel industry that relies on dishwashers to do a thorough job of cleaning the dishes, this is a significant pain point.
Turning to superheated steam
Dishwashers in use today rely on hot water and soap to clean. While this cleans the dishes, the pesky G.stearothermophilus gets away. Researchers Natalie Germann and Laila Abu-Farah turned the heat on further and turned to superheated steam to see how the heat-resistant bacteria would fare.
Superheated steam is formed when you increase the temperature of the steam to such a degree that all water droplets evaporate. The steam is then in a completely gaseous state and is dry rather than moist. In this state, steam can carry much more heat than conventional steam.
The researchers used simulations and created a simple device to test their hypothesis. It consisted of a nozzle capable of shooting out superheated steam into a box containing a single plate with heat-resistant bacteria.
What happened next?
The temperatures inside this box reached 356 Fahrenheit (180oC) while the pressure reached 145 pounds per square inch (10 bar). Just two seconds after the simulation began, the number of heat-resistant bacteria dropped by as much as 50 percent. After 25 seconds, they were gone for good.
The researchers believe that more dishes could be washed at once with a higher number of nozzles in the dishwasher that uses superheated steam. Although the time required to get rid of the heat-resistant bacteria would be relatively higher, it surely wouldn't take as long as the time that conventional dishwashers take. This is the step that they plan to take next.
However, not everybody believes that the concept is viable. Superheated steam is already used as a sterilizing agent in food processing plants and in medical setups. The infrastructure needed to get this done is a bit cumbersome and might not be conducive for restaurants, let alone homes.
There is also another problem. Superheated steam can kill heat-resistant bacteria for sure. But it can't remove bits of food stuck to plates and bowls. For that, another alternate cleaning method may be needed; experts told New Scientist.
The research has been published in the journal Physics of Fluids.
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.
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