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</o:shapelayout></xml><![endif]--></head><body lang=EN-CA link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal>Dear Friends<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>As we are, at the CAU stoves conference, talking about thermal efficiency tomorrow, here is something to think about.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>++++++++<o:p></o:p></p><p class=MsoNormal>Efficiency is a ratio, but of what to what? Let us follow the heat and decide which ‘efficiency’ we want to report. <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><ol style='margin-top:0mm' start=1 type=1><li class=MsoNormal style='mso-list:l1 level1 lfo1'>Heat available in the raw fuel if it was to be burned completely<o:p></o:p></li><li class=MsoNormal style='mso-list:l1 level1 lfo1'>Heat available in the dry portion of the raw fuel<o:p></o:p></li><li class=MsoNormal style='mso-list:l1 level1 lfo1'>Heat available from the fire considering incomplete combustion<o:p></o:p></li><li class=MsoNormal style='mso-list:l1 level1 lfo1'>Heat available to the pot, at the pot in the hot gas stream passing by<o:p></o:p></li></ol><p class=MsoNormal style='margin-left:36.0pt'><o:p> </o:p></p><ol style='margin-top:0mm' start=5 type=1><li class=MsoNormal style='mso-list:l0 level1 lfo2'>Heat transferred to the pot – all of it<o:p></o:p></li><li class=MsoNormal style='mso-list:l0 level1 lfo2'>Heat transferred to the pot and subsequently lost from the pot into the surrounding environment<o:p></o:p></li><li class=MsoNormal style='mso-list:l0 level1 lfo2'>Heat absorbed the pot material changing its temperature<o:p></o:p></li><li class=MsoNormal style='mso-list:l0 level1 lfo2'>Heat absorbed by the water – all of it<o:p></o:p></li><li class=MsoNormal style='mso-list:l0 level1 lfo2'>Heat absorbed by the water changing its temperature <o:p></o:p></li><li class=MsoNormal style='mso-list:l0 level1 lfo2'>Heat absorbed by the water and evaporating water (whether the water is hot or not)<o:p></o:p></li><li class=MsoNormal style='mso-list:l0 level1 lfo2'>Heat absorbed by the water and lost from the water (by radiation, not by evaporation)<o:p></o:p></li><li class=MsoNormal style='mso-list:l0 level1 lfo2'>Heat absorbed into the food and being absorbed chemically (transforming it into cooked food)<o:p></o:p></li></ol><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>System efficiency [Overall thermal efficiency] is (7+9+10+12)/1. [When boiling water only #12=0]<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Heat transfer efficiency is …. ? Which one is the one you were thinking of when asked about ‘thermal efficiency’?<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>+++++++++<o:p></o:p></p><p class=MsoNormal>Regards<o:p></o:p></p><p class=MsoNormal>Crispin<o:p></o:p></p></div></body></html>