Question 1st law of Thermodynamics

In summary, the conversation is about a person asking for help with a problem in thermodynamics involving a vertical piston-cylinder device and steam at different pressures and temperatures entering the cylinder. The question is to determine the final temperature of the steam and the amount of mass that has entered the cylinder. The solution involves finding the specific volume, enthalpy, and internal energy of the inlet and state 1, and using them to solve for the unknowns using the given equations. One suggested approach is to consider the additional gas having double pressure and density, and the resulting temperature being the average of the initial and final temperatures.
  • #1
kuwait
Hi
I have a question please can you give me a hint how to solve it. It is in thermodynamics

A vertical piston-cylinder device initially contains 0.01 m^3 of steam at 200 C. The mass of the frictionless piston is such that it maintains a constant pressure of 500 kPa inside. Now steam at 1 MPa and 350 C is allowed to enter the cylinder from a supply line until the volume inside doubles. Neglecting any heat transfer that may have taken place during the process, determine (a)the final temperature of the steam in the cylinder and (b)the amount of mass that has entered.

This is were my solution but i couldn't complete it:

State(1):500 kPa, 200 C, 0.01 m^3
State(2):500 kPa, 0.02 m^3
at the inlet: Pi=1 MPa, Ti=350 C

I've found that state 1 and the steam entered are super-heated and i got specific volume for the inlet and state 1 also the h and u from the table of super-heated water vapor

then got m1=V1/v1

m(inlet) = m2-m1

-W + (m h)inlet = m2 u2 - m1 u1...(1)

m of the inlet, m2 and u2 are unknowns

W=P(V2 - V1) = 500(0.02 - 0.01) = 5kJ

or we can write eq(1) as:

m2 h2 - m1 h1 - (m h)inlet = 0

m2, h2 and m of the inlet are unknowns

since h = Pv + u

please can you help me?
 
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  • #2
My naive approach is:

- since the additional gas has double pressure, it has double density. Thus, the final mass is 3 times the initial mass.

- since temperature is energy per particle, the resulting temperature is (T1 + 2 T2)/2, where everything is in Kelvins.
 
  • #3
thank you

i knew how to solve
 

What is the 1st law of Thermodynamics?

The 1st law of Thermodynamics, also known as the Law of Conservation of Energy, states that energy cannot be created or destroyed, only transferred or converted from one form to another. This means that the total amount of energy in a closed system remains constant.

What does the 1st law of Thermodynamics mean for energy conservation?

The 1st law of Thermodynamics means that energy can neither be created nor destroyed, so it is important to conserve and use energy efficiently. This law also tells us that energy can be converted from one form to another, such as from chemical energy to thermal energy.

How does the 1st law of Thermodynamics relate to the Law of Entropy?

The 1st law of Thermodynamics and the Law of Entropy are closely related. While the 1st law states that energy is conserved, the Law of Entropy states that the total entropy (or disorder) of a closed system will always increase over time. This means that although energy is conserved, it becomes less organized and more dispersed as it is converted and transferred.

What are some real-life examples of the 1st law of Thermodynamics?

The 1st law of Thermodynamics can be seen in various everyday scenarios. For example, when you turn on a light bulb, the electrical energy is converted into light energy. Similarly, when you eat food, the chemical energy is converted into thermal energy to keep your body warm.

How does the 1st law of Thermodynamics apply to biological systems?

In biological systems, the 1st law of Thermodynamics is important for understanding how energy is transferred and transformed within living organisms. It helps explain processes such as metabolism, where food is converted into energy for the body to use. It also plays a role in explaining how organisms maintain homeostasis and regulate their internal environment.

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