Solve Thermodynamics Help: Refrigerator Cost/Month

In summary, the problem involves finding the cost of electricity for a household refrigerator operating for 360 hours, with a coefficient of performance of 2.1 and a rate of 600 Btu/h. The equations for coefficient of performance and work were used, but there was confusion about the value of Q_out. It was also noted that the Q/W value cannot be greater than 1, as that would indicate over 100% efficiency. It was clarified that thermal efficiency and coefficient of performance are different concepts.
  • #1
msteves
7
0

Homework Statement



A household refrigerator with a coefficient of performance of 2.1 removes energy from the refrigerated space at a rate of 600 Btu/h. Evaluating electricity at $ 0.08 per kW · h determine the cost of electricity in a month when the refrigerator operates for 360 hours.

Homework Equations



coefficient of performance = Q_in / W_cycle
W_cycle = Q_out - Q_in

The Attempt at a Solution



I assumed that Q_out was 600 Btu/hr, since it said that was the energy removed. The coefficient of performance is obviously 2.1, and I tried to find Q_in using the above equations but had some trouble. I also know that you need to find the work and then you can just use the given "$0.08 per kW" to find the money needed, which is the answer. But I am really confused with this one.
 
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  • #2
I didn't think Q/W could be greater than 1. Since 1 represents 100% effeciency. If an engine had a Q/W value of 2.1, wouldn't it be working at 210% efficiency??
 
  • #3
thermal efficiency is different than coefficient of performance
 

Related to Solve Thermodynamics Help: Refrigerator Cost/Month

What is thermodynamics?

Thermodynamics is a branch of physics that deals with the relationships between heat, energy, and work.

How do refrigerators work?

Refrigerators work by using a refrigerant, such as Freon, that is compressed and then expanded to create a cooling effect. The refrigerant absorbs heat from the inside of the refrigerator and releases it outside, keeping the inside cool.

What factors affect the cost of running a refrigerator?

The cost of running a refrigerator can be affected by factors such as the size and efficiency of the refrigerator, the temperature setting, and how often the refrigerator is opened. The cost can also vary depending on energy rates in different areas.

What is the average cost of running a refrigerator per month?

The average cost of running a refrigerator can vary depending on the factors mentioned above, but it is typically around $10-$20 per month.

How can I reduce the cost of running my refrigerator?

To reduce the cost of running a refrigerator, you can try setting the temperature to a slightly higher setting, keeping the refrigerator stocked to maintain cool temperatures, and regularly cleaning the coils to improve efficiency. You can also consider purchasing an energy-efficient refrigerator.

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