Conservation of Mass Principle applied to Refrigerators

In summary, in a venturi lab test where the mass flow is conserved, it is possible for there to be a difference in the mass-flow rate between the two sides of the pipe, even if the cross-sections are equal. This could be due to differences in downstream pressure, which would result in a higher downstream velocity. However, this does not affect the steady state conditions of the system and friction losses do not play a role in this.
  • #1
recreated
50
1
Dear all,

Can the conservation of mass principle be applied to the mass flow rate of a refrigerant in an ideal refrigerator system? And what about for an actual refrigeration system?

I'm reading the principle here but can't work it out. Says that it applies for steady flow, but I assume for a refrigerator the flow would not be steady because of the evaporation/condensation processes, but maybe it still applies. If so, how exactly? Can anyone help?

I want to eventually find out if the refrigerant mass flow rate is equal in all parts of the refrigeration process, for ideal and actual systems.

Thank you very much
 
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  • #2
Also, if you have any useful links on this please send them, thanks.
 
  • #3
Most refrigeration systems work on a closed cycle, so yes, conservation of mass of the refrigerant applies, unless there is a leak in the system.
 
  • #4
The term "steady flow" (steady state operation) means that nothing is changing with time at each specific spatial location in the system. As long as the refrigerator is running continuously, nothing is changing with time at each specific spatial location, even though the parcels of refrigerant passing through the system are experiencing changes along their paths. But, if the system is switching on and off intermittently as needed to maintain a certain temperature in the refrigerator, then the system is not operating at steady state, and things will be changing at each location with time. However, eventually, if the system is allowed to stay on long enough, it will again approach steady state operation.
 
  • #5
Excellent, thank you both very much.

I will discuss about both in my report: possible losses in system leaks and also about intermittent operation causing steady state condition to change.

Related Question

I remember doing a venturi lab test when the mass flow is conserved, but i think there was some difference in the mass-flow rate of one side of the pipe to the other, even though the cross-sections were equal. Is this meant to be possible and what can cause this, can friction losses upset the steady state conditions in this case?
 
  • #6
recreated said:
I remember doing a venturi lab test when the mass flow is conserved, but i think there was some difference in the mass-flow rate of one side of the pipe to the other, even though the cross-sections were equal. Is this meant to be possible and what can cause this, can friction losses upset the steady state conditions in this case?
If the upstream and downstream pressures were maintained constant, and the mass flow rate upstream was maintained constant, then you should have achieved steady state conditions. Possibly you are referring to the possibility that the downstream pressure was lower, so the downstream density was lower. Under these conditions, the downstream velocity would be higher than the upstream velocity. But mass would still be conserved, and the system would still be at steady state. Friction losses do not affect whether the system is at steady state.

chet
 
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Related to Conservation of Mass Principle applied to Refrigerators

What is the Conservation of Mass Principle?

The Conservation of Mass Principle, also known as the Law of Conservation of Mass, states that mass can neither be created nor destroyed in a chemical reaction. This means that the total mass of the reactants must be equal to the total mass of the products.

How does the Conservation of Mass Principle apply to refrigerators?

In refrigerators, the Conservation of Mass Principle applies to the refrigerant gas. The refrigerant gas is compressed into a liquid state, which then absorbs heat from the inside of the fridge, causing it to evaporate back into a gas. The amount of refrigerant gas remains the same throughout this process, demonstrating the conservation of mass.

What happens if there is a leak in the refrigerator's refrigerant system?

If there is a leak in the refrigerant system, the amount of refrigerant gas will decrease. This can result in the refrigerator not cooling as effectively, as there is not enough gas to absorb heat. It is important to fix any leaks in the refrigerant system to maintain the proper functioning of the refrigerator and to prevent any negative environmental impacts.

Are there any exceptions to the Conservation of Mass Principle?

While the Conservation of Mass Principle is a fundamental law of chemistry, there are some exceptions to it. In nuclear reactions, there may be a small change in mass due to the conversion of mass into energy. However, this is only observed in extreme conditions and does not apply to everyday situations such as refrigeration.

How does the Conservation of Mass Principle impact the design and use of refrigerators?

The Conservation of Mass Principle is an important consideration in the design and use of refrigerators. It ensures that the refrigerant gas is not wasted and is recycled efficiently to maintain the proper functioning of the refrigerator. It also highlights the importance of properly disposing of refrigerators at the end of their lifespan to prevent any environmental harm from refrigerant leaks.

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