Dishwashers and Ultrasonics

Gee Whiz!  I was sure somebody would challenge me on the last blog about washing dishes at home.  But, since there are no comments (or fire bombs) in my inbox, I guess everybody agrees that the most efficient way to wash dishes at home is the “old fashioned” way with a dish rag and dish drainer.  I’m shocked!  Dishwashers, then, must be just an easy way to fill that vacant under-cabinet space or purely decoration.  Maybe I should go into the business of selling an insert that looks like a dishwasher but at a reasonable price.  I think I could make a pretty convincing one for about $10.  They should sell like hotcakes!

Despite the fact that nobody took me to task, I know there will always be dishwashers and people who use them.  Actually, I think we would all agree that where larger volumes of dishes are involved as in a restaurant, a good, efficient dishwasher probably makes sense just as does an automated industrial parts washer in a high volume production situation.

While we’re on the subject of dishwashers, I have been approached 10’s if not 100’s of times over the past 40 years about the possibility of using ultrasonics to wash dishes.  The most notable request was an embarrassing number of years ago from a consultant who had been hired by a major airline to devise a way to wash and re-use dishes in flight on long distance hauls.  This was just as the “Jumbo” jets (at that time the 747) were starting to be built and configured.  In those days they actually used china dishes on most flights that served meals and not just in first class!  This guy was determined that ultrasonics was the answer and approached it as if his job depended on it – – maybe it did.  Anyway, I was in sales at the time and of course was seeing $$$’s as the airlines had lots of money and all wanted to be on top of technology.  Certainly they would buy lots of machines if we could come up with one that worked and was practical.  In the back of my mind, of course, I was thinking that if they will pay $1,000 for a toilet seat they should be equally willing to pay a good price for an in-flight dishwasher.

As it turned out, ultrasonics had lots of problems when it came to washing dishes in flight.  The biggest was that ultrasonic cleaning was (and still is) an immersion process.  In short, this meant that washing dishes would require a “vat” of sufficient size to accommodate a sizable number of dishes.  Well, OK, the 747 is pretty big and surely would have room for such a machine – or did it?  We soon learned that the space allocated to the “in-flight dishwasher” in the blue prints was about the same size as a good-sized microwave oven.  Surely more space could be made available for the latest technology.

Undaunted, the consultant and I continued the project on the assumption that space could be made available for the right machine.  From there, however, we met obstacle after obstacle.  One tough one was the amount of water that a large enough machine would use.  The only thing that seemed to make sense was to store and re-use the washing solution repeatedly (much like the in-flight sanitary system) and follow ultrasonic cleaning with a spray rinse using a smaller amount of “fresh” water.  Frankly, that seemed like a feasible solution to  us but not to the airline!  All the water had to come from the ground and was carried at a premium.  They actually told us how much each gallon of water would cost in terms of added fuel consumption and loss of passenger revenue (I’ve forgotten the number).  Another “toughie” was the amount of handling needed to separate the china dishes from the food waste, stack them in the machine and then, after washing, remove them from the machine and prepare them for the next meal.

In the end, it was determined that storing complete sets of dishes with pre-plated food for each meal required less space, weight and labor than any ultrasonic dish washing system that we could come up with would save.  A second group working on the more conventional concept of a spray-type dishwasher did no better than we did with the ultrasonic concept so in the end I didn’t feel too defeated.  I don’t know if the consultant kept his job or not – I suspect he did – and so did I.


2 comments on “Dishwashers and Ultrasonics

  • I have posted a new blog addressing dishwashing in more detail. Thank you for your question!!! FJF

  • Hi John. Ultrasonic cleaning in a dishwashing application is something that I am currently interested in. Having read some of your other blog posts which mention sequential use of turbulation in the liquid to supplement the ultrasonics, I was wondering whether this is an application where you found or think that this would be necessary? Having experimented on a small scale on this topic, I certainly found that trying to remove a thick layer of contaminant with ultrasonics alone was very difficult or impossible. Kind regards, Paul.

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