# Mechanical PE Problem Questions



## Mahil (Nov 18, 2020)

Thanks for your previous help @MikeGlass1969, would you be able to help me on 2 problems below as well.

Why does the turbine efficiency disregarded on the calculation of the top problem below (to get the T5_actual versus given T5_ideal with respect to provided turbine efficiency)?

With the given pressure ratio (P2/P1), what prompt to use gas tables to solve the bottom problem below (ended up using Δh versus constant Cp of air x ΔT)? Why wasn't (P2/P1)^(k-1/k) = (T2/T1) used?


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## MikeGlass1969 (Nov 18, 2020)

Mahil said:


> Why does the turbine efficiency disregarded on the calculation of the top problem below (to get the T5_actual versus given T5_ideal with respect to provided turbine efficiency)?


You are given the *actual* Inlet (T4) and Outlet (T5) Temperatures in the table.  It is simply not needed.

You are given all the temperatures for the Regen. except for T3.  T3 is what you need to find to solve the problem for the thermal efficiency of the cycle.


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## MikeGlass1969 (Nov 18, 2020)

Mahil said:


> With the given pressure ratio (P2/P1), what prompt to use gas tables to solve the bottom problem below (ended up using Δh versus constant Cp of air x ΔT)? Why wasn't (P2/P1)^(k-1/k) = (T2/T1) used?


The air tables are the fastest and most accurate things to use.  That equation is for constant entropy process as well.  Best to stick and get used to the tables.  *TIME SAVER*.


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