Nichrome-Wire calculations

This is unlikely to stir anyone’s blood … but it’s informative and quite well presented:

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Edited By Michael Gilligan on 15/08/2023 07:17:22

I watched it. Wish that chap had taught me maths at school; he explains every step.

I wonder if the same approach could be applied to model boiler design. What we have are scaled down versions of full-size boilers tweaked to meet practical construction needs rather than optimised efficiency. LBSC started the coal-fired boiler ball rolling over a century ago by imitating full-size practice. His methods were informal.

Though the Battle of the Boilers was controversial, coal-fired became most popular. Between 1922 and 1970-ish, a few boiler configurations were tried without a clear winner emerging. Since then, I don't think much has been done, probably because boilers are expensive, and failed experiments severely punish the wallet! Also, all a model loco needs to do is work reasonably well - top-rate thermally efficiency isn't essential.

CAD offers a cheap way to experiment with boiler design without needing to physically make a real one. Now it's possible to design a model boiler for thermodynamic performance, and add the mechanical details later. For example, given a ⌀70mm boiler, what's the optimum:

• boiler length
• number of tubes
• tube arrangement
• tube outer diameter
• tune inner diameter
• firebox capacity
• firebox dimensions
• firebox grate design

At present, I think all these factors are decided by rule-of-thumb, and although that might have given us the best of all possible designs already, maybe modern engineering methods would result in worthwhile improvements. Especially at IMLEC.

My CAD experience hasn't taken me much beyond basic mechanical engineering. Thermal design is a step too far at my age. Anyone else up for it?

I like the kind of engineering where the designer meets a requirement to cut polystyrene by calculating how much energy is needed to heat a given wire to the correct temperature rather than guessing and hoping for the best! Especially when the same sums lead to hot-wire anemometers and home-made boilers!

Dave

Thanks for the endorsement, Dave

I was impressed, but it’s good to know that I am not alone in that.

MichaelG.

See articles by Martin Johnson in ME. He covered optimisation of tubes. Modelling the fire accurately is fiendishly difficult.

Hi Folks, a good article and resistivity is easy to measure, then getting to the correct alloy, but beware of second order effects such as surface texture and colour.

That set it is a very good engineering guide

Ed