[modeleng] Question - maybe off topic- certainly academic
- From: peter.chadwick@xxxxxxxxxxx
- To: modeleng@xxxxxxxxxxxxx
- Date: Wed, 13 Oct 2004 16:51:32 +0200
If you look at the Nagaoka curves for the quantity of heat transferred
through a material such as a metal sheet or shape (eg firebox) to a
liquid, you can see that as the liquid boils, a sheath of vapour forms
around the metal surface, which tends to insulate the metal from the
liquid. Thus for a given heat input, the heat transfer goes down and the
temperature of the metal wall goes up. This can go so far as to lead to
melting of the metal.
The Nagaoka curves show this by the temperature v. heat transfer graph
increasing to a point of inflexion and then the gradient goes negative -
it's basically a straight line to that point as I remember.
I can see that items such as plate and rod stays will modify this, but has
anyone any information as to how much heat transfer can be achieved
through a firebox before boiling becomes so intense as to cause trouble?
can it make the inside of the firebox more likely to suffer cinder cutting
or other ills by tending to soften it?
An extension of this, is of course, the effects of the build up scale ,
which is a more extreme case.
Peter Chadwick Stockholm
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