# Stirling Engine Theory - Mechanically Driven

1. Jul 14, 2011

### kintreemonkey

Hi,

I have had an idea floating around regarding stirling engines, and was hoping that somone may be able to provide some information.

Supposing a stirling engine is run mechanically, one side heats up, the other cools down.

what would happen if the cool side was heated externally?

afaik the cool side should act like a sink drawing heat from the surroundings, the purpose of the question relates to solar heat collection, supposing the receiver is kept cool, more energy could be collected? (in theory)

2. Jul 14, 2011

### jambaugh

Yes more energy could be collected, but at the cost of some energy. The effect would be that the hot side could be maintained at a higher temperature, or if kept at constant temp the load produced by the sterling heatpump would be reduced. Once you heat the "cold" side above the warm side, of course you're back in engine mode.

Heat pumps heat their targets more efficiently than simply converting the input energy to heat. Of course if you heat the "cool" side you need to input less energy still since you're pumping up a shorter temperature difference.

The collected energy is still heat though and will have higher entropy per unit of energy than the prior external heat plus mechanical energy used to drive the pump.

3. Jul 14, 2011

### 256bits

As usual Wikipedia is your friend.
http://en.wikipedia.org/wiki/Applications_of_the_Stirling_engine#Stirling_cryocoolers

kintreemonkey, the Striling heat pump, as you suggest, has been designed and has several applications and is really nothing new. In your instance the cooling would be better served by a Rankine cycle. At your temperatures, the Stirling engine is less efficient, which is why one does not see a window air conditioner operating on the Stirling cycle. These use the Rankine cycle.