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HW4QuestionsAnswersME525SP2011 - 1 ME 525 SP2011 Homework#3...

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1 ME 525 SP2011 Homework #3 Questions and Answers Due Thursday, March 10, 2011 Prof. Lucht (E-mail address: Question: Here is what I have come up with so far. I put my work into excel. I was working question 3 and saw that the fuel was CH3OH and I was wondering if the mass balance equation would look like this CH3OH+1.75(O2+3.76N2)<---->CO2+1.5H2O+OH+6.58N2 or do we need to solve for all the other species that were mentioned in the question? thank you for your help Answer: To calculate the stoichiometric mixture fraction you need to consider the equation CH3OH + a_st(O2+3.76N2)= bCO2 + cH2O+dN2 OH is not a stable product of complete combustion. For part b the hint regarding no differential diffusion is crucial, it implies that the mass originating from the fuel stream always maintains the same ratio of C:H:O, so that the mass fraction of oxygen atoms from the fuel stream Y_O,fuel is always equal to a (constant) (Y_C, fuel) or (another constant) (Y_H, fuel). Question: Example problem 7.5 on page 245 of Turns states that the local mixture fraction can be determined knowing that it must be proportional to the local elemental H mass fraction since the only source of elemental H within the flame is from the fuel. I am a little confused why this is true. Also, can this be assumed then for problem 3b of homework 4? Answer: If there is no differential diffusion then all molecules that come from the fuel stream will diffuse at the same rate, so for any lump of fluid that contains fuel stream fluid the ratios of the mass fractions of H, C, and fuel stream O will remain the same. After the fluid from the fuel

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