I’m taking advantage of being snowed in by working on a project. Specifically, I had an idea for a tankless steam engine. Instead of boiling the water in the reservoir, I want to boil the water in the tube on the way out of the tank. The idea is that it would have a faster startup and response to heat changes.
So, I got a 5-gallon bucket, some soft copper tubing, fittings, and a single-burner propane stove intended for camping use. I bent the tube into a coil and plumbed it into the bottom of the bucket via a needle valve for flow control.
What I thought would happen is: the coil gets heated above the boiling point of water. Then, when the water flows, it converts to steam and blows out the other end of the tube.
What actually happens depends on whether the water is flowing when the burner is lit. If the water is flowing, then it never converts to steam no matter what the pipe temperature is. If the water is not flowing, then when I do open the valve, it spits steam but never establishes a solid flow.
Okay, the flow-first problem is probably that residence time isn’t long enough to boil the water. Which means I need a longer tube and/or lower flow.
The no-flow problem must be that the first bit of water flashes to steam and the resulting back-pressure keeps more water from entering. But I would expect a continuous flow of steam even in that event.
Dang, I was hoping I’d figure out how to make it work by the time I got done explaining the trouble.
UPDATE: Gravity plays rather a larger role in the process than I had originally assumed. By orienting the water coil such that the outlet is higher than the inlet, I have been able to generate steam at the outlet, as desired. At this point, I was also able to determine that ambient-pressure steam is less energetic than I had hoped. This must be why pressurized boilers were all the rage in their heyday. Obviously, by allowing the steam to escape to the atmosphere, I am giving up any expansion work I might hope to extract from it. If I could measure the pressure within the outlet tube, I could determine whether this line of inquiry is worthy of further pursuit, or a more standard boiler is in my interest.