Harnessing Energy in an Engine: The Secrets of Thermodynamics

[Dreebs]

Homework Statement

You're in Paris, working on your first novel and short on cash. The owner of the cabaret downstairs has offered to take care of your rent if you'll help her design a climate control system for the place. It gets too hot and damp in the summer, and too cold and dry in the winter. You're up to the challenge, so you begin to make plans for the new system. You start by considering the summer, when the cabaret air and the outside air are normally at the same temperature and the air in both places is moist and hot. It's hard to have a good time when you're dripping wet, so your system's first goal is to extract the excess moisture from the cabaret air. It does this by creating a cold surface and passing the cabaret air across that surface. Some of the moisture will then condense and run down a drain as liquid water. Why will producing that cold surface inevitably require electricity (or an equivalent source of ordered energy) and why will something become hotter than the original outside air?
Select one:
a. You will have to extract thermal energy from the cold surface, convert that thermal energy into work, and use electricity to get rid of the work. Friction will eventually convert the work into thermal energy and produce hot surfaces.
b. You will have to pump heat from the cold surface to the hotter surroundings, a process that requires the consumption of ordered energy. The pumped heat, as well as the electrical energy that becomes disordered, must go somewhere and it will raise the temperature of its destination.
c. You will have to extract thermal energy from the cold surface, convert that thermal energy into electrical energy, and convey that electrical energy to the power company. When that electricity arrives at the power company, the power company will convert it into thermal energy again by operating an electric space heater.
d. You will have to extract thermal energy from the cold surface, convert that thermal energy into entropy, and use electricity to get rid of that entropy. The entropy will be converted into heat that will flow into the outside air, increasing the temperature of that air.

Homework Equations

N/A

The Attempt at a Solution

A, because it is a device that converts thermal energy into ordered energy as heat flows from hot object to cold object.

 

[Chestermiller]

A is incorrect. Please describe in more detail how you carry out the process, perhaps using a thermodynamic cycle involving an ideal gas.

 

[Dreebs]

A is incorrect. Please describe in more detail how you carry out the process, perhaps using a thermodynamic cycle involving an ideal gas.

If not A, then D because the device wouldn't turn thermal energy into electrical energy. And I don't believe it's B because the device isn't pumping the cold air through the area, it is merely trying to reduce the moisture in the air. Or am I misunderstanding?

 

[Chestermiller]

If not A, then D because the device wouldn't turn thermal energy into electrical energy. And I don't believe it's B because the device isn't pumping the cold air through the area, it is merely trying to reduce the moisture in the air. Or am I misunderstanding?

Any more guesses?

 

[Dreebs]

Any more guesses?

B? Because in order to pump heat from a cold surface to hotter surroundings electrical energy is required, which in turn will raise the temperature of the surrounding air?

 

[Chestermiller]

B? Because in order to pump heat from a cold surface to hotter surroundings electrical energy is required, which in turn will raise the temperature of the surrounding air?

Correct.