Audi Driver P.E.
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compressor_problem.pdf
Ok, so I am getting to where calculating required horsepower is not as difficult a task as it was when I started my exam prep. In reviewing the solution to the subject problem I am struck by the methodology used to calculate and convert temperatures. The basic issue is the order they do the operations. When I worked the problem, I chose to calculate T2 and T4 in Degrees F and then convert to Rankine. They convert first and then calculate.
The difference in methodology seems to be:
a) (x*y) + Z
vs.
b) (x+z) * y
Where X is the initial temp (i.e. T1 and T3), Y is the Temperature calculation "factor" (for this problem it is equivalent to 1.51 for T1 to T2, and 1.45 for T3 to T4), and Z is the conversion to Rankine.
Using method "a" yields a T2 of 89 degrees F and 459 R.
Method "b" yields a T2 of 783 R which is 323 F.
I would think that, if the problem were to simply solve for T2 and T4 in degrees F, that the solution would yield T2=89F and T4=145F because conversion to Rankine would never even enter into the equation. Correct?
I chose to solve the problem using methodology "a" because I remembered that Delta T in F is equal to Detal T in R.
Am I nuts? or am I to assume I missed some requirement that the temperature calculation is only valid in absolute temperatures? Obviously, if the given solution is the only correct one, that is what i am assuming at this point.
Ok, so I am getting to where calculating required horsepower is not as difficult a task as it was when I started my exam prep. In reviewing the solution to the subject problem I am struck by the methodology used to calculate and convert temperatures. The basic issue is the order they do the operations. When I worked the problem, I chose to calculate T2 and T4 in Degrees F and then convert to Rankine. They convert first and then calculate.
The difference in methodology seems to be:
a) (x*y) + Z
vs.
b) (x+z) * y
Where X is the initial temp (i.e. T1 and T3), Y is the Temperature calculation "factor" (for this problem it is equivalent to 1.51 for T1 to T2, and 1.45 for T3 to T4), and Z is the conversion to Rankine.
Using method "a" yields a T2 of 89 degrees F and 459 R.
Method "b" yields a T2 of 783 R which is 323 F.
I would think that, if the problem were to simply solve for T2 and T4 in degrees F, that the solution would yield T2=89F and T4=145F because conversion to Rankine would never even enter into the equation. Correct?
I chose to solve the problem using methodology "a" because I remembered that Delta T in F is equal to Detal T in R.
Am I nuts? or am I to assume I missed some requirement that the temperature calculation is only valid in absolute temperatures? Obviously, if the given solution is the only correct one, that is what i am assuming at this point.
