Converging nozzle temperature difference - Steady flow energy equation

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Homework Help Overview

The discussion revolves around a problem in thermodynamics related to a converging nozzle and the application of the steady flow energy equation to determine the exit temperature of air. The scenario involves air flowing through a nozzle, with specified inlet and exit velocities and an initial temperature.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to apply the steady flow energy equation but expresses difficulty in reaching the expected answer. They question their understanding of the control volume analysis and the calculations involved.

Discussion Status

Some participants have offered guidance on using the energy equation and checking unit consistency. The original poster has reported progress in understanding after receiving feedback, indicating a productive direction in the discussion.

Contextual Notes

The original poster has a background in civil engineering and is transitioning to a field requiring thermodynamic knowledge, which may influence their familiarity with the concepts discussed. There is mention of a similar question that may have contributed to confusion regarding unit conversions.

Nuclear_eng
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I come from a civil engineering background and I'm about to start a masters in nuclear energy. I have no experience in thermodynamics and I've been doing a bit of revision before the course commences to get me up to speed. I've been working my way through 15 revision questions and I only have a couple left now. I posted a question on this forum yesterday but I'm stuck again with a different type of question on flow processes. This is meant to be one of the easiest questions in my revision booklet but so far the answer has eluded me.

Homework Statement



A converging nozzle is used to accelerate a flow of air from 50m/s at the inlet to 150m/s at the exit. The air temperature is 25°C at the inlet. Assuming heat transfer to the air is negligible, use the steady flow energy equation to calculate the temperature at the exit.

Homework Equations



Steady flow energy equation:

h1+0.5V12+gZ1=h2+0.5V22+gZ2


The Attempt at a Solution



I've revised control volume analysis and steady flow processes but I'm not getting anywhere with this. I assume it will be a very simple calculation as all the other 'easy' revision questions have taken me about a minute or two.

The correct answer is 15.1°C
 
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Is there no one who can help me? I've been looking at this similar question I found on the forums and I can't get 184°C by using the SFEE. I think I must be making a mistake with the units or something really stupid.

https://www.physicsforums.com/showthread.php?t=249494

Could somebody please just plug the numbers in and show me how he got 184°C? I would imagine it will take less than a minute and it would be a massive help to me.

Thanks
 
Use the energy equation you have above. The enthalpy is Cp*T. Ensure you get the units correct on the V^2/(2g) term.
15.1 C is indeed correct.
 
Thank you very much Lawrence. I was getting my units for Cp messed up but I've now managed to get 15.1°C.
 

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