Dear Frank
You are on the right track with this approach. The details are not important but let’s see what you have: Energy available when going in [moisture, LHV, mass of fuel standing by] Energy still available when finished the task (if it is a task-based test) [moisture, LHV or all remaining fuel. That is the way to get the thermal efficiency (heat transfer efficiency). Because many stoves burn stick-fuel the moisture is definitely not gone and as the influence on the final energy number is strongly affected by the moisture remaining, we have to measure it. It is not difficult at all. Weigh everything that is left. Put the char aside from the ash and homogenise it with a blender (take a sample of it). Cut off the obviously undried fuel and weigh the burned bit. Put it in a dryer for 24 hours. That gives you the moisture content of fuel remaining. Get an LDV for the dried wood and the char remaining (LHV). Calculate what heat was available to begin with and what remains. That gives you the energy offered by the fire (not necessarily offered to the pot). Some things are calculated from that energy number, but not the fuel consumption. Energy released is not the same as fuel consumed. (Please note, UNFCCC, this important fact.) Please edit any spreadsheet you have to correct this misunderstanding. You have to decide what to do with the heat in the charcoal first. Regards Crispin Stovers, Unless I’m missing something (probably am) it seems we are approaching the WBT trying to make accurate readings using simple equipment that does not measure the components we need. The components needed are: IN Fuel: total weights of 1) carbon, 2) hydrogen and 3) moisture. OUT Fuel: total weights of 1) Carbon, 2) hydrogen, 3) moisture and 4) heat in the fuel. Following these main energy constituents of the fuel we determine the amount used in the process. The procedure could go like this: Determine the weight of CH and moisture of the fuel added. AFTER Add spent fire mix to water to determine heat within (increase water temperature). Mix then drain water into a container where 100 mls filtered through a glass fiber filter and measure the CH to determine the carbon and hydrogen in the total fines drained. Then dry, grind and subsample for carbon and hydrogen in the solid material left. We still lack a moisture reading in the left over fuel but I think starting with low moisture fuel and timing the last fuel addition to the fuel box there will be none left. As for the Simmer and Boiling part of the test: The microwave oven I have has a setting for baked potatoes. Wash and pat dry. When the oven detects moisture vapor(?) the timer starts for cooking. What is the detector (?) and is this something we could use to standardize the process? Perhaps located above the pot of water? Thanks Frank Frank Shields Control Laboratories, Inc. 42 Hangar Way Watsonville, CA 95076 (831) 724-5422 tel (831) 724-3188 fax www.biocharlab.com
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