Rumford Technical Discussion
Venturis, Carburetors and Rumford Throats

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>3/25/97

>Jim: I am interested in any technical articles relating to the "venturi
>effect" that develops in the Rumford. I wonder, for example, that since
>automobile carburetors have a round venturi, why doesn't the rumford?
>Any references would be appreciated.

Andrew Rose
rosea@mail.nwc.whecn.edu

Andrew,

Good questions. I'm afraid you'll catch me being a little free with the carburetor analogy.

Firstly, I have no technical articles on the subject - other than a brief description in the article on my website featured near the top of the home page.

As I suspect we both know, venturis and carburetors most often make use of the fact that the pressure is reduced as the speed of the fluid increases in order to draw up and spray some liquid like paint or gasoline.

In the case of the Rumford throat, I believe it's two other aspects of the venturi that are useful:

1) the streamlined approach to the nozzle keeps the dilution air flowing along streamlines and not mixing with the smoke and volatile gases until they both are shot or sprayed into the receiving smoke chamber. The significance of this is that we are able to build our fireplaces taller which increases the "residency time" of the smoke (the length of time the smoke is hot and in the fire) so that more of it burns up, with the Result that the fireplace is cleaner-burning and more efficient. And

2) the nozzle that shoots the smoke and excess air into the smoke chamber acts like a partial one way check valve that helps to prevent wind induced downdrafts and ordinary vicissitudes from back drafting down through the throat and causing the fireplace to smoke.

I hope this is helpful. Why do you ask? I'd be interested in your ideas. The whole idea of the Rumford throat being a venturi is virtually unexplored and interesting from an historical point of view as well as from a modern combustion engineering perspective.

By the way, why it isn't round is easy. Round probably would be better. But think of it historically, as Rumford stumbling on the idea from his other objective of making fireboxes more shallow, not having the ready example of carburetors and the fact that "round" is difficult in brick.

Best,

Jim Buckley

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