[Stoves] TLUD-Oven!

[ajheggie at gmail.com]

[Default] On Sat, 26 Jul 2014 05:15:26 -0400,Crispin Pemberton-Pigott
<crispinpigott at outlook.com> wrote:

>Bread baking is slightly endothermic. You must also heat the mass of wheat to 94 degrees minimum (in the centre) and evaporate some of the moisture. It takes about 3 kw for 1 hour to bake 16 loaves of 800 g each. That is the performance of a well insulated electric oven. That provides a comparison of what energy is need for the actual baking.
>
>There is a rule-of-thumb for gas ovens (which you have) which is something like 1/3 the electrical efficiency. Maybe Andrew Heggie remembers it. It means it is possible to bake 16 x 800 g loaves with 9 kWh of heat. ?12.8/9= 1.5 kg of product per kilowatt-hour.

Crispin I'm afraid I don't recall a formula but ovens and kilns are a
case where electric heating which has essentially no mass flow (other
than gases being given off by the food being baked)  has a bigger
advantage the higher the temperature needed. All the heat transfer to
the food is via the air in the oven which is a bit limiting compared
with boiling water but crucially the gases lost by the oven are at a
high temperature. On the other hand electricity is generally generated
at around 30% efficiency.

We did have a discussion with a Scandinavian group that had built a
wood fired "white" oven some years back where the calculations on heat
transfer into the oven were discussed.

With a traditional range the flue gases are circulated around a
"white" oven and then pass under a hot plate before being vented
allowing some heat recovery.

I hadn't come across the term Jim Hensel used of black and white
ovens, in terms of heat transfer I would expect the black oven to be
better because of the moving flow of hot gases through the oven.

In UK bread was traditionally backed in a form of masonry stove,
bundles of dry small diameter twigs were fired repeatedly inside the
oven until the stones of the walls, floor and ceiling were hot enough,
a number of loaves, normally belonging to neighbours and baked for the
fee of one loaf in 13 according to folklore, were placed in the bread
oven and the door sealed.

We had such an oven on a farm I worked on in 1974, it shared a space
at the side of an inglenook but it had not been used for years, on the
upper floor there was a smoking chamber  to preserve meats.

AJH