Differences between basic definitions for compressors and turbines

[Urmi Roy]

While making a comparative study between turbines and compressors, I noticed some differences between the way they are studied...pleasehelp me understand why these differences exist...

1. Efficiency for a turbine = (actual work/ideal work) whereas for compressors, it is (ideal work/actual work).

2. pressure ratio for turbines: (P1/P2) whereas for compressors, it is (P2/P1).

3. We use total to static efficiency in turbines whereas we use static to static efficiency in compressors.

4. Reheating is carried out for turbines whereas preheating is carried out for compressors.

5. Polytropic efficiency of turbine is ((n-1)/n)*(γ/(γ-1)) whereas it is the reciprocal for compressors.

 

[Urmi Roy]

I received these answers from a friend but they don't seem right...

...especially for the first question,it doesn't make sense as efficiency for both machines are defined in terms of ideal and actual work...

"1. Turbine delivers work, while compresor requires work.

2. Turbine extract energy by decreasing the pressure, while compressor increase fluid pressure.

3. This because turbines deliver works by decreasing total pressure to certain static pressure, without its dynamic velocity. While compressor requires energy to achieved total pressure at the outlet.

4. Reheat for turbine increases effiicency by deliver more works. In compressor usually use intercooler, not preheater to increase efficiency."