Thermo 1st Law open system question

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Discussion Overview

The discussion revolves around a homework problem related to the first law of thermodynamics applied to an open system, specifically focusing on an insulated nozzle where air expands isentropically. Participants are attempting to calculate the temperature and velocity of the air exiting the nozzle while addressing a specific equation related to enthalpy and kinetic energy.

Discussion Character

  • Homework-related
  • Technical explanation

Main Points Raised

  • One participant presents a homework problem involving an insulated nozzle and questions the transformation of a term in the energy equation.
  • Another participant points out a potential error in the initial pressure value, suggesting it should be 130 kPa instead of 150 kPa.
  • A clarification is provided regarding the units in the equation, explaining how the factor of 1000 arises to convert units from kg-m²/s² to kJ.
  • A later reply acknowledges the clarification and expresses gratitude for the assistance.

Areas of Agreement / Disagreement

There is a minor disagreement regarding the initial pressure value, but the discussion primarily focuses on understanding the equation rather than reaching a consensus on the problem's solution.

Contextual Notes

The discussion does not resolve the overall problem, and participants have not reached a final answer regarding the temperature and velocity calculations.

Abi_mecheng
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Homework Statement


An insulated nozzle receives are at a negligible velocity at a pressure of 150kpa and temp of 25 degrees C. if the flow passing through the nozzle expands to 100kpa in an isentropic process, calculate the temperature and velocity of the air leaving the nozzle.

The Attempt at a Solution



Solution is attached but I don't understand how 1/2 becomes 1/2000 in the equation m(dot)[h2-h1)+1/2(v2^2 - v1^2)

Thanks
 

Attachments

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Be advised that the solution has P1 = 130 kPa, not 150 kPa.
 
Abi_mecheng said:

The Attempt at a Solution



Solution is attached but I don't understand how 1/2 becomes 1/2000 in the equation m(dot)[h2-h1)+1/2(v2^2 - v1^2)

Thanks

Look at the units of the various parts of this equation. The additional factor of 1000 comes about to convert kg-m^2/s^2 to kJ (1 J = 1 kg-m^2/s^2).
 
Ohh ok totally missed that, thanks for pointing that out much appreciated.
 

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