Thermodynamics on steady state

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SUMMARY

The discussion focuses on calculating the molar and volumetric flow rates of ethylene glycol in a refrigerant mixture that is 50% glycol by mass, mixed with water at steady state. Given a water molar flow rate of 4.2 kmol/min and the density of ethylene glycol as 1.115 times that of water, the calculations involve using mass and energy balance equations. The participant encountered difficulties in determining the mass flow rates and volumetric flow rates, leading to negative results, indicating a need for clarification on the flow rates involved.

PREREQUISITES
  • Understanding of thermodynamic principles, specifically steady state analysis.
  • Familiarity with mass and energy balance equations in chemical engineering.
  • Knowledge of fluid properties, including density and molar mass calculations.
  • Basic skills in performing volumetric flow rate calculations.
NEXT STEPS
  • Study the principles of mass and energy balance in steady state systems.
  • Learn how to calculate flow rates using density and molar mass in chemical processes.
  • Explore the properties of ethylene glycol, including its phase behavior and applications in refrigeration.
  • Review examples of refrigerant mixtures and their thermodynamic calculations.
USEFUL FOR

Chemical engineering students, process engineers, and professionals involved in thermodynamics and fluid flow calculations in refrigeration systems.

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Homework Statement


At steady state, a stream of liquid water at 20C, 1bar is mixed with a stream of ethylene glycol (M=62.07 g/mol) to form a refrigerant mixture that is 50% glycol by mass. The water molar flow rate is 4.2 kmol/min. The density of ethylene glycol is 1.115 times that of water.

Determine

a) the molar flow rate, in kmol/min, and volumetric flow rate, in m3/min, of the entering
ethylene glycol.

Homework Equations



m1 + m2 = m3

m1h1 + m2h2 = m3h3


The Attempt at a Solution



Firstly, I do not know whether is there a leaving flow on the ethylene glycol there that make it to have the m3 flow rate to exist.

If I assume there is a flow rate exit there,

Vf = 0.001002 m^3/kg
Density of water = 1/0.001002
= 998 kg/m^3
Density of ethylene = 1.115 x 998
= 1112.77kg/m^3

Mw = 18.015 kg/kmol
Volume flow rate of water = 18.015(4.2)(0.001002)
= 0.07581 m^3/min

0.07581 + m2 = m3

If I assume that the mass flow rate for the exit one is m3 = 0.5m2

The answer turns out to be negative, which i don't think is correct
 
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questions for you:

what is the mass flow of the water?
therefore, what is the mass flow of the ethylene glycol?
therefore, what is the volumetric flow of ethylene glycol?
and finally the molar flow of the ethylene glycol?
 

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