Conceptual thermodynamics/physics question.

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In summary, the conversation discusses the concept of mass conservation in relation to an air compressor with constant volume. It is mentioned that according to the ideal gas law, the mass of air should be equal at the inlet and outlet. However, the possibility of leaks in the compressor could cause discrepancies. The main focus of the conversation is finding the change in entropy for the compressor, which requires multiplying the specific entropy by the mass of air. This brings up the question of whether mass is conserved in the compressor, as the masses calculated using the ideal gas law were not equal. The possibility of the volume of air changing due to compression is also mentioned.
  • #1
ampzor
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Hey Guys,

Say you have an air compressor with a constant volume. And were given the temperature and pressure at the inlet. And also, the temperature and pressure at the outlet. Would the mass of the air at the inlet equal the mass at the outlet? When applying the ideal gas law to the inlet and outlet (assuming air behaves as an ideal gas), is it possible get two different masses? It seems as though that would conflict with the conservation of mass principle.
 
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  • #2
Yes, mass in = mass out. Note that air compressors may 'leak' so if you're actually measuring a compressor and finding a discrepency, you may want to look for leaks.
 
  • #3
Actually, I was told to find the change in entropy for the compressor. Ie., S(out) - S(in). So I would have to multiply the specific entropy by the mass of the air. That's why I asked if mass is conserved. That way I could just find the mass of the air at the inlet and multiply that by the specific entropy. Unfortunantly, by using the IG law, both masses were not equal so that is why I asked the question. So maybe I am thinking that the volume of the air at the inlet was not the volume at the outlet? Because it is being compressed, it would have a smaller volume at the outlet.
 

1. What is the difference between heat and temperature?

Heat is a form of energy that is transferred between objects due to a difference in temperature. Temperature, on the other hand, is a measure of the average kinetic energy of the particles in a substance. In simpler terms, heat is the energy being transferred, while temperature is the measure of how hot or cold something is.

2. Can heat flow spontaneously from a colder object to a hotter object?

No, according to the Second Law of Thermodynamics, heat will always flow spontaneously from a hotter object to a colder object. This is due to the fact that heat transfer is driven by a difference in temperature, and objects always seek to reach thermal equilibrium.

3. What is the difference between an isolated system and a closed system?

An isolated system is one in which no energy or matter can be exchanged with the surroundings. This means that the system is completely isolated and no external forces can affect it. A closed system, on the other hand, can exchange energy but not matter with the surroundings.

4. How does the first law of thermodynamics relate to conservation of energy?

The first law of thermodynamics states that energy cannot be created or destroyed, only transferred from one form to another. This is in line with the principle of conservation of energy, which states that energy cannot be created or destroyed, only transformed.

5. What is the significance of entropy in thermodynamics?

Entropy is a measure of the disorder or randomness in a system. It is a key concept in thermodynamics as it helps to explain the direction of natural processes, as systems tend to move towards a state of higher entropy. This is known as the Second Law of Thermodynamics.

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