Combustion Problem, Chapter 21, #8

[JHW 3d]

Working through Ch 21 problems in MERM13, and stuck on 21.8 (a):

The solution makes an assumption of the combustion gas temperature of 1000degF., when selecting the specific heat from Table 21-1. How/Why would they use 1000F... ? I picked a temperature midway through the combustion temperature (results) ~ 4000F, and used that to calculate the specific heat. The solutions correct answer is 4,500F, so wouldn't that indicate the assumption before was bad...

Any ideas here?

 

[P-E]

Is this one of those problems that requires iteration? If so I'd guess 1000 too. I never see a much higher flue gas temp in my line of work.

 

[JHW 3d]

Solution does not iterate. I do not bring much intuition about the result, since this is not my principle line of work, but it's just odd they don't mention anything about a source of their assumption.

In part (b), the result shows an actual temperature of about 900 deg F (from the theoretical calculated in part (a) of 4500 deg F), so the original assumption is validated. I guess that's about as good an answer we can expect.