In view of second law of thermodynamics, to optimize the performance of any thermal system, it is important to analyze the exergy of this system by making exergy balance between the system and the environment. In some researches, I noticed that the pumping power exists within the exergy balance. What is the relationship between the exergy and the pumping power?
Hi
The exergy balance equation consist of many terms, the term on the left side (dE/dt) shows the change of the exergy of the system due to the terms on the right side equation, so, the exergy of any system is effected by : the flow of heat that responsible of transfer exergy to or from the system Q(1-(To/T)). The flow of matter causes transfer of exergy to or from the system (Ein-Eex), The shaft work Pdv and boundary work (W) causes also increasing of decreasing the exergy of the system depending upon the work is produced or consumed. Finally the exergy destruction due to the second law inefficiencies is always positive. Therefore any activities on the system boundary causes change of the system exergy.
Dear Khaoula I didn't see any answer to my question in this document. If it is possible to clarify the answer to the question
Dear Dr. hayder, if we studied the analysis of exergy efficiency and pumping power for a solar system with nanofluids as an example, increasing volume friction of nanofluid led to increasing the viscosity of working fluid which consequently increase the friction resulting in entropy generation. the total entropy generation is the total sum of fluid friction and heat, and as we know the power output of the system can be maximized with the minimization of entropy generation, for most studies of nanofluids researcher found using for example Single walled CNT nanofluid could be reduce the entropy generation and enhanced heat transfer which led to reducing pumping power. what I want to explain that the power output (useful work) is proportional pressure drop (friction). Regards
Dear Dr.Mohammed
I am in agreement with you that the use of nanofluid increases the rate of the entropy generation as a result of increasing the pressure drop, but in the exergy balance, this effect was represented and taken into account with mechanical pressure-based in item of the mechanical exergy.
Kind resgards
Hi
The exergy balance equation consist of many terms, the term on the left side (dE/dt) shows the change of the exergy of the system due to the terms on the right side equation, so, the exergy of any system is effected by : the flow of heat that responsible of transfer exergy to or from the system Q(1-(To/T)). The flow of matter causes transfer of exergy to or from the system (Ein-Eex), The shaft work Pdv and boundary work (W) causes also increasing of decreasing the exergy of the system depending upon the work is produced or consumed. Finally the exergy destruction due to the second law inefficiencies is always positive. Therefore any activities on the system boundary causes change of the system exergy.
Dear Abdul Hadi
Thanks for answering my question. What about mechanical exergy (-To×R×ln(P/Po))?
Kindly regards
Dear Dr. Hayder
The exergy can be divided into three catalogues, namely; thermal exergy that depends on the temperature difference, chemical exergy that depends on the mass transfer, and mechanical exergy that depends on the pressure difference.
Dear Abdul Hadi
Mechanical exergy depends on the pressure difference and pumping power also depends on the pressure difference. In exergy analysis, we must present mechanical exergy or pumping power?
Dear Dr. Hayder
Your answer is absolutely write, the exergy work appears in the exergy balance equation by two terms, the first one is the boundary work (W) and shaft work ( including pumps, turbines, ets..) as pdV
Interesting question !
Mainly in most published studies the pressure change is assumed to be neglected due to small impact to overall results. By following this assumption we neglect the pumping energy consumption.
Probably it is worth to clarify if the pressure drop exergy destruction is happening in compressible or non-compressible, because that creates differences in mathematical expressions.
(see A.Bejan book: Book Advanced Engineering Thermodynamics, Forth Edition
)Simple explaination of relation could be this : we need thermodynamic work or electricity (pure Exergy) to overcome the pressure drop in order to create fluid flow. Without that we are not able to transfer the mass taking the heat. So it is directly related - for ideal pump, the consumption of electricity==Exergy.
Dear Karolis Janusevicius
I would like to thank you for the perfect sentence ( electricity is a pure exergy)
Entropy: A concept that is not a physical quantity
https://www.researchgate.net/publication/230554936_Entropy_A_concept_that_is_not_a_physical_quantity
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