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Re: Birthday Wish



At 14:39 4/12/99 +1000, Brian McInnes wrote:
Brian,
You pose a question

I want to bring up a tank of liquid from 125degF to 140degF using
hot liquid at 190degF. I want to raise its temperature at 4 degrees
a minute. What flow rate should I use?

(This question is ill-posed enough to be 'real-world', don't you
think?
Could it be a dairy-farmer has an application for this answer?
Just for fun, try giving an exact formulation assuming no losses.

An attack on this "real-life" situation requires
understanding of a number of concepts that play a part in a
physicist's model of thermal physics: thermal energy,
thermal contact, thermal equilibrium, temperature, energy
transfer, rate of energy transfer.
A naive application of a derivative of the formulation you
called attention to in your previous posting
mass1 x specific heat1 x rise in temperature =
mass2 x specific heat2 x fall in temperature
does not take into account many of the consequences of these
concepts in the application of the model.
For example, the amount of thermal mixing, the mechanics of
the thermal contact between the hot liquid and the liquid in
the tank, could well be more important in the warming of the
tank liquid than the flow rate of the hot liquid.

Brian McInnes

Please assume perfect, fast mixing as well as no losses.
That should provide sufficient input for either a naive,
an approximate, even an exact flow rate determination,
as you prefer.

Regards
Brian

brian whatcott <inet@intellisys.net>
Altus OK