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</o:shapelayout></xml><![endif]--></head><body bgcolor=white lang=EN-CA link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal><span style='color:#1F497D'>Dear Alex<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>I have very seriously considered this option and have offered it as a good method of determining the effective heat gain. I am first going to try it using with condenser because there is less to build and I can perform the test as the boiling point.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>One of the guys here in Beijing is going to have a stab at modelling the heat loss from the pot with and without a lid because we don’t have an example of that. I would like to know precisely how much load is placed on a stove when the lid is removed and what the influence of the radiation from the rolling water is compared with a shiny aluminum lid. We know it taxes the stove but it may be in the form of evaporation (100%) rather than an additional undocumented loss. I would like to put that puppy to bed.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>I have been looking at the formulas used for calculating LHV together with two students. This was a very interesting exercise. The EPA method for calculating the LHV of biomass co-fired with other fuels is exactly the same (save for units) as the Chinese National Standard but not like the method used by the WBT (discussed in a footnote in the document). I think that is worth exploring because we should start off our theoretical work using the right fuel heat content.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>(Note to Tom M – we figured it out!)<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>The advantage of using the boiling and condenser is that we can separate fuel mass burned from water evaporated in real time allowing us to plot the change in efficiency with power i.e. a standard engineering performance curve. Using a pressure cooker allows us to push the steam (if necessary) a little into a heat radiator or one of those cool glass curly things you see in the movies. We are trying not to make it look like a still for making Newfie Screech or Witblitz.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Regards<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Crispin having fun with Harold and Lodoysamba and Tseyen-Oidov and Hao and Dong and all the others<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal>Crispin,<br><br>On the heat transfer side there are clearly a lot of variables. Get rid of them like we do with boilers. Use a sealed pot with its contents (water) kept at a constant temperature (example; either high ~90C in-95C out, with no condensation or low ~55C in-60C out, with some condensation or both) and a flow meter to measure the thermal work done. A modern automated three way valve controlling the flow through a heat exchanger can regulate the return temperature precisely.<br><br>The pot can be any pot with a non standards lid disc with in/out plumbing connections, glued with silicone to the top of the pot. It should withstand a few inches of water pressure with a stand pipe open to the atmosphere after the outflow thermocouple. The vapour losses then are outside of the measurement frame. The pot could be filled with water or be part filled and have a vapour/air head space. Flow rates and velocities could be high enough to eliminate biases between pots or to mimic natural convective patterns within the pot.<br><br>All you need is a whole bunch of disc lids from 20 to ??cm in diameter in 1cm increments, or custom make them as the required.<br><br>Or you can see how many different efficiencies you can fit on the head of a pin.<br><br>Heuristically yours,<br>Alex<br><br>On 13/10/2013 11:21 AM, Crispin Pemberton-Pigott wrote:<span style='font-size:12.0pt;mso-fareast-language:EN-CA'><o:p></o:p></span></p></div><blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><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 lfo3'>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 lfo3'>Heat available in the dry portion of the raw fuel<o:p></o:p></li><li class=MsoNormal style='mso-list:l1 level1 lfo3'>Heat available from the fire considering incomplete combustion<o:p></o:p></li><li class=MsoNormal style='mso-list:l1 level1 lfo3'>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 lfo6'>Heat transferred to the pot – all of it<o:p></o:p></li><li class=MsoNormal style='mso-list:l0 level1 lfo6'>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 lfo6'>Heat absorbed the pot material changing its temperature<o:p></o:p></li><li class=MsoNormal style='mso-list:l0 level1 lfo6'>Heat absorbed by the water – all of it<o:p></o:p></li><li class=MsoNormal style='mso-list:l0 level1 lfo6'>Heat absorbed by the water changing its temperature <o:p></o:p></li><li class=MsoNormal style='mso-list:l0 level1 lfo6'>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 lfo6'>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 lfo6'>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></blockquote></div></body></html>