Choosing external heat source for generate power.

[kamil]

There are 3 alternatives of heat source. Thoose external source supplies heat for closed cycle system.

 

* At the 200 C air as an hot source and 20 C air as cold one.

* 200 C steam and 20 C water

* 200 C soduim solution and 20 C solid sodium

 

Which one should be choosed for generate power with higher efficiency. Explain theese theoretically and pratically.

 

 

How can i explain this ? I think it's related with spesific heat but i couldn't explain.

[EdEarl]

What do you know about the efficiency of engines, that is thermal efficiency.

 

What practical effect reduces the efficiency of hot and cold systems. Hint, how do you keep things from loosing or gaining heat energy.

Edited May 27, 2013 by EdEarl

[kamil]

basicly (Qhot - Qcold)/Qhot

 

In my opinion

In theoretically; if we assumed that system are reversible than this formula become 1-(Tc/Th) so all of them have same efficiency at this circumstance. Am i right ?

 

in pratically ; reversible systems are not exist. So efficiencies are different for each source. But all of them are same temperature range.

That's why i'm thinking spesific heat are related with efficiency.

 

İ don't know its right or wrong

[EdEarl]

Good. Now what practical effect reduces the efficiency of hot and cold systems. Hint, how do you keep things from loosing or gaining heat energy.

 

Hint, there are a couple of steps before we get to the importance of specific heat.

Edited May 27, 2013 by EdEarl

[kamil]

friction , heat transfer with enviroment , unstable compression and expansion etc...

 

Heat transfer can be reduced with isolation.

Friction depend on many things. Viscosity , pipes surface , pipes cross section etc...

 

But i don't understand why they are important for choosing external source.

[EdEarl]

Excellent.

How does specific heat relate to volume and amount of heat.

[kamil]

Q= m C (Th-Tc) = p V C .....

 

increase of spesific heat cause increasing of heat transfer.

 

Also it related with volume. It seperated as Cp and Cv. Stable pressure or stable volume.

[EdEarl]

Good. Is it more practical to reduce heat loss for a large or small volume?

Edited May 27, 2013 by EdEarl

[kamil]

We define losses as pV in thermodynamic. So small volume is more pactical.

Edited May 27, 2013 by kamil

[EdEarl]

Great. In a small volume, can you carry more heat in a substance with high or low specific heat?

[kamil]

with high spesific heat it's possible.

[EdEarl]

Are your questions answered? If not, what question remains?

[kamil]

yes. thanks for sparing time to me and your patient

[EdEarl]

My pleasure, yw.

 

I assume you know which of the three substances have the highest specific heat.

Edited May 27, 2013 by EdEarl