[Stoves] Two Stove System - typos corrected v1.1

Crispin Pemberton-Pigott crispinpigott at outlook.com
Sun Nov 29 02:16:17 CST 2015


>Two more quick questions: 

 

>Is moisture still in the calculations? and 

>is this HHV or LHV?

 

The energy available from the fuel is based on the actual LHV available
considering the fuel moisture content.

 

>Just one more question:

 

>If our only task was making tea then measuring the energy going into the
water would be easy. But the efficiency of cooking our rice would be much
harder. 

 

Actually it is not difficult to determine the efficiency of a stove cooking
rice. The actual cooking of rice can be performed and the stove observed.
Then reproduce the cooking cycle with water in the pot, without rice. If it
is really necessary to work out the energy used for a particular food, there
are tables of energy absorbed by different foods. What food happens to be in
a pot does not affect the ability of a stove to create heat from fuel and
transfer it, fortunately. The stove operates independently of what is in the
pot.

 

>And grilling our meat would be very hard. 

 

There is no real need to get the heat gained by a pot during a particular
meal. People cook more than one meal so a proxy cooking cycle incorporating
various behaviours - average behaviour - can be used. It an investigation is
made into the average behaviour of a family, a community or a region, one
can get various cycles that represent 'average behaviour'. That is the best
we can do. There is no need (or intention) to predict the performance of any
particular meal in the field.  What is good however, is to be able to
reasonably predict performance in a given community or performing a given
task like making sugar or drying fish. A stove can be tuned to that purpose.


 

A variety of proxy cooking tasks can be used in the lab representing various
behaviours. For roasting meat, it comes down to reproducing the fire pit and
duration. You can rate the performance in terms of 'producing cooked meat
mass' but not the heat received by the meat. There is no need to do that. If
you were drying fish you could rate the production per hour or per day. That
is no thermal efficiency number available from that, but you could get an
energy consumption per kg of fish, based on the energy content of the fuel
consumed per day.

 

Therefore I am wondering why you done have energy from the fuel (that can
always easily be normalized to the actual fuel mass used) per specific task
completed? 

 

There is no gain in turning things into a mass of fuel - different fuels
have different energy contents. Stay away from fuel mass! Fuel mass if a
proxy for energy. Just use the energy because all the fuels contain
potential combustion energy so there is a common metric (Joules). Use the
common metric.  Using fuel mass, everyone would have to use the same fuel in
order to compare stoves, which is not realistic or wise. Changing the fuel
type changes the performance so the testing context has to reflect what
people do. 

 

As a result of performing a test in a particular context (to get a
prediction of performance in use) the performance has to be stated together
with the testing conditions. There is no 'clever' way around this, however
much we wish it to be so. An example of this fact can be observed in that
the species of wood affects the rate of char production even if everything
else is the same. So a stove can't have a 'certain' char production rate. A
number has to be attached to a species and its moisture content. A stove
could be optimised to deal with a particular input fuel so generalisations
are not possible.

 

Regards

Crispin

 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/attachments/20151129/7623303e/attachment.html>


More information about the Stoves mailing list