Polytropic efficiency vs isentropic efficiency?

In summary, polytropic efficiency and isentropic efficiency are both measures of the efficiency of thermodynamic processes, but they differ in terms of the types of processes they measure. Polytropic efficiency takes into account changes in both pressure and volume, while isentropic efficiency only considers reversible and adiabatic processes. These efficiencies are calculated by comparing the actual work done to the work that would be done in an idealized scenario. Isentropic efficiency is often higher than polytropic efficiency due to the assumption of no losses or inefficiencies. Both efficiencies have a significant impact on the performance of a system, and can be improved through optimization and minimizing losses, although achieving 100% efficiency is not possible.
  • #1
jason.bourne
82
0
been reading in many books that polytropic efficiency is always recommended over isentropic efficiency.

what are the advantages of using polytropic efficiency?

what makes it different from isentropic efficiency?

it is also told that polytropic efficiency is independent of pressure ratio? how is this possible?
 
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  • #2
I always thought that polytropic efficiency was isentropic efficiency but at a incremental stage of a quasi-static process.
 
  • #3
yes you are right.

but when these efficiencies are calculated for the turbine or compressor machines which are multi staged, then they differ a lot.
 

1. What is the difference between polytropic efficiency and isentropic efficiency?

Polytropic efficiency is a measure of the efficiency of a thermodynamic process that involves changes in both pressure and volume. Isentropic efficiency, on the other hand, is a measure of the efficiency of a thermodynamic process that is reversible and adiabatic, meaning there is no heat transfer and the process occurs without any loss of energy.

2. How are polytropic efficiency and isentropic efficiency calculated?

Polytropic efficiency is calculated by taking the ratio of the actual work done to the work that would be done if the process were isentropic. Isentropic efficiency is calculated by taking the ratio of the actual work done to the ideal work that would be done if the process were isentropic.

3. Why is isentropic efficiency often higher than polytropic efficiency?

Isentropic efficiency is often higher than polytropic efficiency because it is an idealized measure that assumes no losses or inefficiencies in the process. In reality, there are always some losses and inefficiencies, leading to a lower polytropic efficiency.

4. How do polytropic efficiency and isentropic efficiency affect the performance of a system?

Polytropic efficiency and isentropic efficiency both have a significant impact on the performance of a system. A higher polytropic efficiency means that the system is able to do more work per unit of energy input, while a higher isentropic efficiency means that the system is able to convert more of its energy input into work.

5. Can polytropic efficiency and isentropic efficiency be improved?

Yes, both polytropic efficiency and isentropic efficiency can be improved through various means such as optimizing the design of the system, using more efficient materials, and reducing the losses and inefficiencies in the process. However, achieving a perfect 100% efficiency is impossible due to the laws of thermodynamics.

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