Thermodynamics Questions & Answers  


I don't understand... How exactly do you find the enthalpy from Figure A9 (psychrometrics chart)? Please explain better your question, then I can answer it.




The equations should read $\overline{q}_{\rm N}=...$ not $\overline{q}_{\rm n}=...$, and the particule mass should read $m_{\rm N}$ not $m_{\rm N_2}$. Please make these changes in your question..


Yes in class, I mentioned that: $$ \underbrace{\sqrt{\frac{3 k_{\rm B} T_{\rm N}}{m_{\rm N}}}}_\textrm{approximate} \approx \underbrace{\sqrt{\frac{8 k_{\rm B} T_{\rm N}}{\pi m_{\rm N}}}}_\textrm{exact} $$ The approximate solution is easy to find from the definition of the temperature as outlined in the tables. The exact solution is difficult to obtain and its derivation is beyond the scope of this course. Just remember that the approximate solution is a very good approximation to the exact solution (less than 15% error). In the exam, you can use either the approximate or the exact solution. I'll give you 1 point bonus boost for this question.




At steady state, the thermodynamic properties such as $\rho$, $P$, $T$, or the gas/liquid macroscopic velocity vector $\vec{v}$ do not change in time. Therefore, all time derivatives involving the macroscopic properties and thermodynamic properties should be set to zero at steadystate. However, the microscopic properties are not necessarily constant in time. For instance, the speed of one molecule is never zero and varies in time whether the problem is steadystate or not.. I'll give you 1 point bonus boost for this question.




When the problem involves chemical reactions, you have to calculate the entropy for each species similarly to how we calculate the enthalpy. That is: $$ s=\frac{\overline{s}^0}{\cal M} + \Delta s $$ where $\overline{s}^0$ is obtained from Table A24 and $\Delta s$ is the entropy addition calculated using perfect gas relationships if the gas is not at 298 K and 1 atm. That is: $$ \Delta s= C_P \cdot \ln\left(\frac{T}{\rm 298~K}\right)  R \cdot \ln \left( \frac{P}{\rm 1~atm} \right) $$ I'll give you 1 point bonus boost for this question.



$\pi$ 