[Stoves] Heat transfer and in-line water heater

[adkarve]

the question was raised about the merits of bath vs. shower. In India,
people take hot water in a bucket of about 15 litres, and using another
small vessel of about half a litre, pour the hot water on their bodies, pot
by pot. After wetting the entire surface of the body, one applies soap to
one's body. The soap is washed away by using the remaining water. The entire
action is comparable to a shower, with the water not falling continuously on
the body, but pot-by-pot. Generally, 15 litres is all the water that one
uses for the daily bath.
Yours
A.D.Karve
----- Original Message -----
From: andrew <list at sylva.icuklive.co.uk>
To: Discussion of biomass cooking stoves <stoves at listserv.repp.org>
Sent: Sunday, December 02, 2007 10:46 PM
Subject: Re: [Stoves] Heat transfer and in-line water heater


> On Saturday 01 December 2007 18:32, Dean Still wrote:
>
> > The velocity of flue gases has a large impact on heat transfer to
> > the pot (surface to be heated). Higher velocity flue gases get
> > closer to the pot, narrowing the boundary layer of still air close
> > to the pot.
>
> I'm told that pulse combustors are actually able to disrupt this
> boundary layer but in general the boundary layer is the limiting
> factor in convection.
>
> Of course despite Crispin not considering radiant heating being
> significant it is not limited by this boundary layer.
>
> > Higher velocity flue gases get more heat into the pot.
>
> All other things being equal I'm sure you are right but it could lead
> us down the logical path that Frank was pursuing, the idea that
> higher massflow would give a higher flue velocity and thus increase
> heat transfer. The thing is the temperature of the flue gas is
> inversely proportional to the massflow and heat transfer at the pot
> is directly related to the temperature difference.
>
> Intuitively I'd say going for a high combustion temperature (which
> enhances radiative transfer greatly) minimises the massflow and
> velocity and increases heat transfer. So to get the higher
> velocities means narrower passages, as you suggest, longer path in
> contact with pot and probably forced draught to overcome the
> increased drag.
>
> <snip>
>
> >
> > Heating bath water is easy because 30C is a lower target.
>
> It's a cool bath too! 41C suits me better.
>
> > Covering
> > the square top tin is not necessary because steam is not made at
> > 30C which is nice because we don't have to worry about pressure.
>
> I'd still use a lid because a small convection above the pot will
> evaporate from the surface and I would expect the normal practice to
> be to heat a small amount of water to >80C and then add this to a
> larger cool volume of water in the bath. We could of course argue
> the merits of a bath versus a shower.
> >
> > Yes, heat transfer efficiency is the ticket,
>
> It strikes me that after minimising indoor pollution by achieving
> good combustion this heat transfer is the next weak link.
>
>
> > See you at ETHOS?
>
> I'm sure my globetrotting friend will get there!
>
> AJH
>
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