Physics - Heat Pump - 2nd Law of Thermodynamics

So I just rearranged it to |Q_c| = |Q_h| - W_eng and plugged in the values. It worked out! Thanks though!In summary, a heat pump with a coefficient of performance of 3.70 and a power consumption of 6.91x10^3 W delivers 9.2x10^7 J of energy into a home during 1 hour of continuous operation. To find the energy it extracts from the outside air, we can use the equation |Q_c| = |Q_h| - W_eng, which gives us a result of approximately -3.2x10^7 J.
  • #1
JSGhost
26
0

Homework Statement


A heat pump has a coefficient of performance of 3.70 and operates with a power consumption of 6.91 103 W.
(a) How much energy does it deliver into a home during 1 h of continuous operation?
9.2x10^7 J

(b) How much energy does it extract from the outside air?
? J

Homework Equations


COP(coefficient of performance) = |Q_h|/W
P = W/t
W = P*t

e = W_eng/|Q_h| = (|Q_h|-|Q_c|)/|Q_h| = 1 - |Q_c|/|Q_h|

The Attempt at a Solution



(a) I got this part correct.
COP = |Q_h|/W
P = W/t
W = P*t

|Q_h| = COP*W = COP * P*t = 3.70(6.91x10^3 J/s)(3600s) = 9.2x10^7 J

(b) I need help on part (b). I can't get the correct answer.

I tried using e = 1 - |Q_c|/|Q_h|

|Q_c| = |Q_h|(e-1) = 9.2x10^7 J (3.70-1)

but that answer doesn't work.
 
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  • #2
Use W=H1-H2
arranging equations
H1=H2+W

U have got H2 and W on part a.
Now u need to find H1. Just plus them.
 
Last edited:
  • #3
Thanks for replying. I actually figured it out by looking at a previous problem I did where it was |Q_c| = |Q_h| + W_eng.
 

Related to Physics - Heat Pump - 2nd Law of Thermodynamics

1. What is the 2nd Law of Thermodynamics?

The 2nd Law of Thermodynamics states that in any natural process, the total entropy of the universe always increases. This means that energy tends to disperse or spread out over time, rather than concentrate in one place. It also states that heat flows spontaneously from hotter objects to colder objects, and that it is impossible to convert all heat energy into work.

2. How does a heat pump work?

A heat pump works by using mechanical energy to transfer heat from a colder area to a warmer area. It does this by using a refrigerant, which absorbs heat from the colder area and then releases it in the warmer area through a cycle of compression, condensation, expansion, and evaporation.

3. How does the 2nd Law of Thermodynamics relate to heat pumps?

The 2nd Law of Thermodynamics plays a key role in the operation of heat pumps. It states that heat will always flow from a higher temperature to a lower temperature, which is the principle that allows heat pumps to transfer heat from a colder area to a warmer area. However, the 2nd Law also states that some energy will always be lost in the process, making it impossible for a heat pump to achieve 100% efficiency.

4. What is the coefficient of performance (COP) for a heat pump?

The coefficient of performance (COP) is a measure of the efficiency of a heat pump. It is defined as the ratio of the amount of heat energy delivered to the amount of mechanical energy used to run the heat pump. A higher COP indicates a more efficient heat pump.

5. Can a heat pump violate the 2nd Law of Thermodynamics?

No, a heat pump cannot violate the 2nd Law of Thermodynamics. While it may seem like a heat pump is creating energy or transferring heat from a colder area to a warmer area without any energy input, it is actually using mechanical energy to do so. The 2nd Law of Thermodynamics still applies, as some energy is always lost in the process.

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