Maximum_Entropy
New member
I am having trouble figuring out how the authors arrived at a solution on the NCEES Mechanical Thermal and Fluid practice exam (978-1-947801-08-00).
For reference, my review and use of the practice test is in preparation for the CBT exam format where the only reference allowed is the electronic PDF of the NCEES Mechanical Reference Handbook. For this reason, my studying has been heavily relying on learning flow and gems hidden in the reference manual, albeit it is not my preferred source.
Question 48 of the practice exam, shown on the attached picture, is a fairly simple looking problem with just performing a energy and mass balance.
My confusion lies in how the author was able to obtain the enthalpy of the "1MPa, 40 C" attemporator water. The author just throws down the enthalpy, h2, as 167.57 kJ/kg.
When I solve this like I normally would and just use MATLAB Xsteam US to look up the properties or the keen and kean tables I have no problem getting the enthalpy of the water at ~167 kJ/kg. I don't see how they got it from the limited steam tables provided in the NCEES Reference Manual.
Does anyone have recommendation of an alternative from the table method to determine the enthalpy of the attemporator water?
The closest thing I can get it by taking the difference of hv and hfg of table 6.3.4. at the temperature of the water but regardless of the pressure. I excerpted the NCEES reference manual table below. I cannot find justification or explanation of why this would work. Alternatively if some one can help explain why taking the difference of h_v and h_fg at the 40 deg. sat liquid that would help too.
Thanks in advance.
-Connor
For reference, my review and use of the practice test is in preparation for the CBT exam format where the only reference allowed is the electronic PDF of the NCEES Mechanical Reference Handbook. For this reason, my studying has been heavily relying on learning flow and gems hidden in the reference manual, albeit it is not my preferred source.
Question 48 of the practice exam, shown on the attached picture, is a fairly simple looking problem with just performing a energy and mass balance.
My confusion lies in how the author was able to obtain the enthalpy of the "1MPa, 40 C" attemporator water. The author just throws down the enthalpy, h2, as 167.57 kJ/kg.
When I solve this like I normally would and just use MATLAB Xsteam US to look up the properties or the keen and kean tables I have no problem getting the enthalpy of the water at ~167 kJ/kg. I don't see how they got it from the limited steam tables provided in the NCEES Reference Manual.
Does anyone have recommendation of an alternative from the table method to determine the enthalpy of the attemporator water?
The closest thing I can get it by taking the difference of hv and hfg of table 6.3.4. at the temperature of the water but regardless of the pressure. I excerpted the NCEES reference manual table below. I cannot find justification or explanation of why this would work. Alternatively if some one can help explain why taking the difference of h_v and h_fg at the 40 deg. sat liquid that would help too.
Thanks in advance.
-Connor
