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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='color:#1F497D'>Thanks again for all the help.<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 like the idea of working in the 40 to 70 deg range. <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'><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'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Frank<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'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Frank Shields<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>42 Hangar Way<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Watsonville, CA 95076<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>(831) 724-5244 tel<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>(831) 724-3188 fax<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>frank@bioCharlab.com<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'><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'><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'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> stoves-bounces@lists.bioenergylists.org [mailto:stoves-bounces@lists.bioenergylists.org] <b>On Behalf Of </b>Crispin Pemberton-Pigott<br><b>Sent:</b> Wednesday, January 18, 2012 11:25 AM<br><b>To:</b> 'Discussion of biomass cooking stoves'<br><b>Subject:</b> Re: [Stoves] Calculation help<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span lang=EN-CA style='color:#1F497D'>Dear Frank<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-CA style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>>Not that this has anything to do with stoves, but if water has 0 enthalpy at 0 deg C <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'>It is no so. Water at 0° C has lots of heat in it, all the way down to 0° K. The specific heat of ice is not constant actually because it takes different crystal forms (at least 6). Been a while since I read about that. It is about 2.108 so there is about 580 Joules of heat in a g of water ice. You said it was water at 0° so you have to freeze it first (= 335 J /g). So water at 0° contains 915 Joules per g.<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'>>And is the LHV ever calculated using the temperature of the stack gas? <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'>LHV refers to the heat available from the fuel, arbitrarily calculated. The rating for the fuel will be what it is calculated to be. If you are trying to measure the performance of a stove and the question of condensation arises, you will have to compensate for it. Simple as that. <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'>>It seems it would not be because some water may have condensed on the cold surface meaning the total water would not all be in the gas phase.<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'>It increases the heat transfer efficiency in that heat was gained through condensation). It means you have to use the LHV plus the heat gained from condensing that mass of water. It shows up early in testing with large cold pots and a fuel with high H2 like natural gas or alcohol. You can see water condensing on the pot sides that looks as if it is sweating. As it is usually re-evaporated later, there is no overall difference.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-CA style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-CA style='color:#1F497D'>If you want to check the heat transfer efficiency or the system efficiency it should be done when there is no condensation on the pot, i.e. when the pot surface is hot enough to prevent condensation. I suggest 40-70 degrees. As Jim Jetter pointed out recently, it is difficult to tell what the system efficiency is at low power if the pot is already boiling. At the SeTAR Centre we use a cold pot for all power tests and replace it if it gets hot. The water mass and rate of temperature rise from 40-70 gives you the power absorbed, and the fuel mass burned gives you the power generated. The two give you the efficiency at that power level. Pretty accurately too. Remember that it is not the fire-to-pot heat transfer efficiency, it is the efficiency of the whole system.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-CA style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-CA style='color:#1F497D'>You can thus plot the efficiency curve for any emission change as the power is increased from low to high. Repeat this with several pot sizes and you have characterised the stove well enough to predict the WBT performance, or any other cooking cycle (called a ‘burn cycle’). If you instead start with the WBT numbers, you can’t work out anything at all backwards to produce the curves because the number are mixed together.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-CA style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-CA style='color:#1F497D'>What is most interesting is to see that with some stoves, the pot is an important part of the combustion. Changing the pot only can result in a big change in emissions and thermal efficiency. This matters a lot if the stove is designed for small pots and a large one either can’t be boiled or if it interferes with the combustion.<o:p></o:p></span></p><p class=MsoPlainText><span lang=EN-CA style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoPlainText><span lang=EN-CA style='color:#1F497D'>Regards<o:p></o:p></span></p><p class=MsoPlainText><span lang=EN-CA style='color:#1F497D'>Crispin<o:p></o:p></span></p><p class=MsoPlainText><span lang=EN-CA style='color:#1F497D'><o:p> </o:p></span></p></div></body></html>