Thermodynamics on steady state

In summary, the problem involves mixing liquid water and ethylene glycol to form a refrigerant mixture that is 50% glycol by mass. The water molar flow rate is 4.2 kmol/min and the density of ethylene glycol is 1.115 times that of water. To solve for the molar and volumetric flow rates of ethylene glycol, the mass flow rates of water and ethylene glycol must be determined. However, there is a discrepancy in the given information that results in a negative answer.
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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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  • #2
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?
 

1. What is the definition of steady state in thermodynamics?

The steady state in thermodynamics refers to a condition where the temperature, pressure, and other thermodynamic properties of a system remain constant over time. This means that the system is not undergoing any changes or fluctuations.

2. How does steady state differ from equilibrium in thermodynamics?

In thermodynamics, equilibrium refers to a state where all the thermodynamic properties of a system are uniform and unchanging. On the other hand, steady state refers to a condition where the properties of a system remain constant, but there may be some internal changes or processes occurring.

3. What is the significance of steady state in thermodynamics?

In thermodynamics, steady state is important because it allows us to analyze and understand the behavior of a system over time. It helps us make predictions and control the state of a system by maintaining it at a desired steady state.

4. How is steady state achieved in a thermodynamic system?

Steady state can be achieved in a thermodynamic system by continuously supplying or removing energy or material from the system to maintain a balance. This can be done through processes such as heat transfer, work, or mass flow.

5. What are some real-world examples of steady state in thermodynamics?

Some examples of steady state in thermodynamics include a refrigerator maintaining a constant temperature, a power plant running at a constant rate, and a chemical reactor operating at a steady state production rate. In these systems, the properties such as temperature, pressure, and composition remain constant over time due to continuous input and output of energy or material.

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