Maximizing Steam Turbine Efficiency: Small Scale Design and Measurement Tips

[JamesWatt]

SUMMARY
I’m making a small turbine. I’m looking for suggestions as to how to measure efficiency and maximize the pressure of the steam taken in.

DETAILS
If I understand it correctly, essentially, a turbine is a way to convert steam pressure into electricity via a rotating shaft (with buckets on one side to catch flowing fluid such as steam and magnets on the other to generate electricity). Turbines are widely used in power generation. What spins turbines can range from water at hydro-electric dams, to steam from nuclear fission, to steam from burning goal, to gas combustion.

I want to understand the problems that arise in steam-turbine design. I can’t afford a full scale turbine, so I will make one on a small scale. To measure my success, I want to get at the electrical power that is generated as a percentage of the power available in the steam. Measuring the electrical power out is easy with a multi-meter. I have less of an idea of how to figure out how much wattage is available in the steam. I read about an enthalpy drop method where you measure the temperature and pressure before and after the turbine. ((http://www.google.com/url?sa=t&source=web&cd=1&ved=0CBUQFjAA&url=http%3A%2F%2Fwww.gepower.com%2Fprod_serv%2Fproducts%2Ftech_docs%2Fen%2Fdownloads%2Fger4190.pdf&ei=goylTbWmN4Tp0gGzocX9CA&usg=AFQjCNHphV_sgvEfhsVl6xIoWl7DOKo3Vg&sig2=QyJB89CbSXTmx-l1GwkP5w ))
The math of getting from the pre and post turbine temperatures and pressures to an efficiency number is less obvious to me.

For my first iteration on this project, I used a pot on the stove as a steam source. As a combination turbine and generator, I used a PC fan. To measure power generated, I hooked up a multi-meter to the fan’s leads and multiply the measured voltage by the measured current. To connect the fan to the pot, I used zip-ties:

http://postimage.org/image/13mpym0x0/

The fan blades didn’t spin. I think the reason was that the steam wasn’t of a high enough pressure to spin the fan blades. I tried adding towels to channel the steam into the fan.

http://postimage.org/image/2xa0slt1g/

The fan still didn’t spin. The towels weren’t ideal in that they could still absorb the steam, dissipating some of the pressure. I think the problem is that the steam coming into the fan isn’t pressurized enough.

One way I was thinking about doing this was putting a pipe plug on the stove, threading a pipe into it, putting a flange on the other end of the pipe and bolting a fan to the flange. Another idea is putting a metal sheet with a hole cut out on the pot and putting a fan on the hole. Which of these should I try? Do you have another idea? I work at an industrial parts reseller, so I have access to a wide range of material.

 

[Doug Huffman]

A turbine converts thermal energy into mechanical energy.

Your "buckets" imply a Pelton wheel, a primitive impulse turbine that wastes velocity loss.

Hero's steam engine was a primitive reaction turbine that wasted pressure.

Combine impulse and reactions wheels for efficiency. Conceptually, alternate pressure and velocity. Also look into convergent-divergent nozzles that can exchange pressure and velocity.

 

[Robert Moody]

SUMMARY
I’m making a small turbine. I’m looking for suggestions as to how to measure efficiency and maximize the pressure of the steam taken in.

James,
I suggest you simplify to understand the scope and scale. Your muffin fan is a 12V. Get a second fan and tape together. Run fan A and read output (if it spins) from B. Estimate if your steam pot can generate enough CFM to spin fan.

Maybe re-scale to much smaller motor, close fitting many bladed prop, and a small sealed conduit system? Review a real steam turbine?

 

[JamesWatt]

If you were my neighbor, this morning at 6am you would have heard loud, celebratory swearing through your wall. I read 6V off my multi-meter with this:

I started with an unsuspecting aluminum pressure cooker:

I tapped two ¼” NPT holes in the top—one for a pressure gauge and one for the piping system I made.

When I read 13 PSI on the pressure gauge, I released the steam.

Next up is:
The seal between my piping system and the pressure cooker lid is poor. I had 14 PSI before installing the pipe and 13 PSI afterwards. The lid is only 0.08” thick, so it was easy to strip the thread two or three threads I was able to tap. I used pipe nuts as a stop gap, but I think some gasketing would help. Any advice? You can see steam escaping in this picture:

I would like to encase the fan. I was thinking about something like what I used on my PC (see below). The challenge is that I can’t figure out how to adapt from ¼” NPT to 5” diameter duct.

I bet there are more efficient and steam-resistant generators than a PC fan. What do you recommends as a simple step between a PC fan and this: