Entropy of a sealed room with an open-door refrigerator

  • Thread starter Thread starter techsingularity2042
  • Start date Start date
  • Tags Tags
    Entropy Refrigerator
AI Thread Summary
In a sealed room with an open-door refrigerator, the entropy of the system increases due to the energy dynamics involved. While the refrigerator cools its interior, it simultaneously releases heat into the room, leading to a net increase in the room's entropy. The processes of compression and expansion within the refrigerator are adiabatic, but the system as a whole is not isolated; work is done to circulate the refrigerant, contributing to the overall energy increase. The discussion highlights that even though the heat exchange seems balanced, the energy input from the refrigerator's operation leads to an increase in entropy. Therefore, the correct answer is that the entropy increases, contrary to the initial assumption.
techsingularity2042
Messages
20
Reaction score
2
Homework Statement
A working refrigerator with the door open is placed in a sealed room.

What change occurs to the entropy of the room?
Relevant Equations
Q= ΔU + W
dS = dQ / T
A working refrigerator with the door open is placed in a sealed room.
The entropy of the room
A. is zero.
B. decreases.
C. remains unchanged.
D. increases.

I chose C.
Here's my thought process:
In a working refrigerator, a compressor compresses a refrigerant (at a gas state) in the coil, and the refrigerant turns into liquid. The latent heat of condensation is rejected into the room, making room hotter. When the refrigerant travels into the refrigerator, an expansion valve expands the refrigerant and converts it into gas. The latent heat of fusion comes from the interior of the refrigerator, which causes the inside to become cooler. However, in this case, the door is open. This means that the net heat exchange is 0 as latent heat of condensation = latent heat of fusion.

In my knoweldge, the compression and expansion processes are adiabatic, so there is no heat transferred to or from the system.

But the mark scheme says the entropy increases. Can you explain which part of my solution is wrong and why?
 
Physics news on Phys.org
Is it plugged in?
 
Reply
  • Like
Likes Chestermiller
it says 'working'
 
techsingularity2042 said:
it says 'working'
Right, so think about the energy.
 
techsingularity2042 said:
it says 'working'
What @haruspex is saying is that you've gotten lost in the details. Take as your system the combination of room (assumed insulated) and refrigerator. Is work being done on that system? Is the internal energy of that system increasing?
 
techsingularity2042 said:
In my knowledge, the compression and expansion processes are adiabatic, so there is no heat transferred to or from the system.

But the mark scheme says the entropy increases. Can you explain which part of my solution is wrong and why?
What energizes the compression process, which must overcome the friction resistance of the tubes-condenser-evaporator to circulate through the system and to go through the expansion orifice or valve?
It seems to me that the "sealed room" is still being penetrated by some kind of external energy.

Fig.-6-6_revised-768x630.png
 

Thread 'Errors and significant figures'

I multiplied the values first without the error limit. Got 19.38. rounded it off to 2 significant figures since the given data has 2 significant figures. So = 19. For error I used the above formula. It comes out about 1.48. Now my question is. Should I write the answer as 19±1.5 (rounding 1.48 to 2 significant figures) OR should I write it as 19±1. So in short, should the error have same number of significant figures as the mean value or should it have the same number of decimal places as...
View full post »
Thread 'Collision of a bullet on a rod-string system: query'

Thread 'Collision of a bullet on a rod-string system: query'

In this question, I have a question. I am NOT trying to solve it, but it is just a conceptual question. Consider the point on the rod, which connects the string and the rod. My question: just before and after the collision, is ANGULAR momentum CONSERVED about this point? Lets call the point which connects the string and rod as P. Why am I asking this? : it is clear from the scenario that the point of concern, which connects the string and the rod, moves in a circular path due to the string...
View full post »
Thread 'A cylinder connected to a hanging mass'

Thread 'A cylinder connected to a hanging mass'

Let's declare that for the cylinder, mass = M = 10 kg Radius = R = 4 m For the wall and the floor, Friction coeff = ##\mu## = 0.5 For the hanging mass, mass = m = 11 kg First, we divide the force according to their respective plane (x and y thing, correct me if I'm wrong) and according to which, cylinder or the hanging mass, they're working on. Force on the hanging mass $$mg - T = ma$$ Force(Cylinder) on y $$N_f + f_w - Mg = 0$$ Force(Cylinder) on x $$T + f_f - N_w = Ma$$ There's also...
View full post »

Similar threads

I Heat pumps: Questions about compressor pump refrigerant gas and evaporator
Replies
30
Views
3K
B Cooling effect of evaporation occurs even if the surroundings are colder?
Replies
10
Views
2K
Opening the refrigerator door to cool a room.
Replies
6
Views
2K
I Do refrigerants passing through a venturi act like steam?
Replies
8
Views
2K
The reservoir of refrigerant between condenser & metering device
Replies
7
Views
2K
Entropy and Carnot refrigerators
Replies
20
Views
3K
Vapor-compression refrigeration cycle
Replies
3
Views
2K
Can you me with this question? about a refrigerator and heat?
Replies
6
Views
7K
True/False: Qualitative Thermodynamics Question
Replies
2
Views
7K
Working out signs of work and heat for entropy change question
Replies
10
Views
3K

Hot Threads

Recent Insights

Back
Top