Determine the change in the specific enthalpy of nitrogen (N2), in kJ/kg, as it is heated from 600 to 1500 K, using:
a.) The empirical specific heat equation (Shomate Eqn) from the NIST Website.
b.) "The CoP value at the average temperature. (Use the heat capacity polynomial to determine this CoP value.)
c.) The CoP value at room temperature, 25oC. (Use the heat capacity polynomial to determine this CoP value.)
In your analysis, be sure to include a comparison of these three methods. (4 pts)
HINT: You can get the parameters for the Shomate Equation from the NIST Webbook by searching by "name", then click on "gas phase data", then "gas phase thermochemistry data". Part (a) Integral of CoP with respect to T...just like in class. Parts (b) and (c) are easier. Just evaluate CoP at ONE T and then assume CoP has this value and it is constant.
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I think people are misunderstanding the thought behind this problem. THE CHANGE IN ENTHALPY IS TEMPERATURE DEPENDENT EXCEPT WHEN WE HAVE AN IDEAL GAS ISOTHERMAL PROCESS! We are NOT estimating in (b), for instance, that deltaT is the average temperature.
In part (a), you are solving the equation with keeping the temperature dependence of Cp. So, in other words, you CANNOT take it out of the integral!! (So, deltaH = integral (Cp dT)). Plug in the Antoine equation for Cp and then do the integral.
For parts (b) and (c), we simplify it (i.e., make the integral easier!) by estimating Cp to be at a constant temperature. In (b), you should estimate Cp at the average temperature, then you can take Cp out of the integral, yielding deltaH = Cp deltaT. Plug in what you get for Cp at the average temperature, then your two temperatures for deltaT. Use a similar process for part C.
A similar logic is used in Problem 4, only now you need deltaU instead of deltaH.
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