I What thermal cycle would describe the action of a candle carousel?

[jsh111]

TL;DR

Could the Brayton cycle describe a candle carousel ( holiday candle powered trinket that is a simple heat engine) when there is no compression at all?

A candle carousel is a popular holiday time trinket that uses wooden if light metal vanes to rotate and assembly by using the heat created by burning a candle directly underneath. It occurred to me that this is a simple, albeit very inefficient heat engine. It resembles a rudimentary gas turbine in operation. I wondered what thermal cycle would best describe its operation.

Since it resembles a gas turbine, the Brayton thermal cycle would seem to best describe it, however the problem I run into is that for this rudimentary machine, there is obviously no compressor involved, and so how on earth would you even draw the PV diagram..... the area of the curve should theoretically be 0.

Similarly, the efficiency for a brayton cycle ( the thermal cycle of gas turbines) is based on the pressure ratio created by the compressor above ambient pressure. Theoretically, the pressure ratio should be 1 since there is no compression, and the device would then not operate. Obviously this is not the case in the actual device.

My question then is, as a mental exercise, where is my flaw in reasoning? I am sure some thermal cycle would describe this, I just don't know what it would be or how the PV diagram would look like. I have attached a picture of the device below:

 

[256bits]

TL;DR: Could the Brayton cycle describe a candle carousel ( holiday candle powered trinket that is a simple heat engine) when there is no compression at all?

there is obviously no compressor involved

Take into consideration the buoyancy of the air as it is heated or cooled.
Try to draw the PV diagram taking into account gravity to account for the buoyancy.

 

[Chestermiller]

There is no cycle involved. You simply heat the air and gases to cause them to expand and make the propeller above to rotate.

 

[Lnewqban]

You have an endless cold source (the atmosphere) for the cooling-contraction process of the exhausted hot air.
The heat source does all the work of transferring thermal energy into kinetic energy onto the blades via the ascending movement of the heated-expanded air.

 

[256bits]

There is no cycle involved. You simply heat the air and gases to cause them to expand and make the propeller above to rotate.

I was going to state the same thing - that it is just convection. But pondering it over, something has to drive the convection.
The earth's atmosphere can be modelled as a heat engine - a hot source T1 at lower altitudes closer to the surface, the power source being the incoming radiation from the sun, cold heat sink at T2 somewhere be the temperature of space. Heat absorption and rejection isothermally, and adiabatic compression and expansion as the air rises and falls. We then have a natural convection circuit modelled as a simple Carnot thermodynamic cycle to make the winds blow, from which work can be extracted with turbine blades.

https://onlinelibrary.wiley.com/doi...8957?msockid=3be610f03b7a6b5b367b04323a416a02