HW8 - CHE 633--Combustion Priciples--Winter 2012 Assignment...

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Unformatted text preview: CHE 633--Combustion Priciples--Winter 2012 Assignment 8 Due Friday, March 23 Problem 1: Turns Chp 9 Review Question 1 Problem 2: Turns Chp 9 Review Question 9 Problem 3: Turns 9.10 Consider the exploding can demo. The dimensions of our can are 19 cm high with a can diameter of 16 cm, a top hole diameter of 5 mm, and a bottom hole diameter of 8 mm. Assume a top hole orifice coeffiient of C=0.6 (v=c*sqrt(as in class)). Problem 4: Compute the initial length of the flame. Clearly state your assumptions, and compare the to length observed in class (5-6 inches). Problem 5: Estimate the time to explosion and compare to that found in class (8.5 minues). Use the plug flow assumptions. Discuss. You have seen how we derive the laminar flamelet equation. The flamelet equation is a very good model for non-premixed flames. Unlike premixed flames, there is no flame speed, and there is no characteristic flame thickness. Instead, the flame thickness depends on the strain. In the flamelet model this strain is set through the specification of o. The unsteady version is solved in the provided Matlab code. Put the code in a directory and connect Matlab to that directory (type "cd path_to_your_directory." If you are on a Linux machine, just start Matlab from that directory). Problem 6: Run this code by typing "flmlt_1s" at the Matlab prompt. The code outputs the T(f) profile (f is mixture fraction). You can paste this into your favorite math program (e.g., Excel). Convert the temperature profile to a profile in space. Plot T(x). The attached PDF file gives (f) where o=1907 s-1, and we know that (f) = 2D(df/dx)2. You can use these two expressions to get f(x), and then plot T(x). You will have to estimate D. I recommend you use Gaseq to get the value for a stoichiometric ethylene flame at the peak temperature of the T(f) profile, then get D(f) by adjusting using the dependence of D on T (take a unity Lewis number). Problem 7: The value of o=1907 s-1, is the max value before blowout. This corresponds to a thin flame. For a completely unstrained flame, o=0, and the we get equilibrium compositions. What is the corresponding flame thickness? Does this make sense (recall, is the inverse of a timescale)? ...
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