More on Nozzles, Experiments by Richard Gideon

May 2003

I am back again with more nozzle experiments. Last fall in the members forum James Morris described a method on how to design a convergent/divergent nozzle for optimum performance. Knowing that my nozzle design was basically a hit or miss approach. (Actually more miss then hit.) I decided to try his advice.

Briefly he stated that the convergent inlet to the throat of the nozzle should have a radius that is at least three times the height of the throat and that the angle of the divergent portion of the nozzle should be determined by adjusting this angle to give the lowest possible temperature reading when measured at the output of the nozzle. (His full description can be read in the members forum archive. 10-12-02)

Armed with his knowledge plus checking my engineering handbook I decided to build a test nozzle that had both an adjustable throat and a divergent output. I placed a thermocouple at the output of the nozzle to measure the temperature and also aimed the nozzle to blow on the top of a small postage scale. With this setup I ran a number of tests with different size throat openings and with different lengths for the divergent portion of the nozzle.

Using a regulated air supply then starting with the nozzle set to zero degrees and slowly increasing its angle the results clearly showed the temperature dropping and at the same time the air pressure on the scale increased. Once the lowest temperature and maximum pressure had been reached further increasing of the angle caused the temperature to rise and the pressure on the scale started to drop.

Originally I planned to try to make a chart that could be used to look up the correct angle. However after making numerous test runs I discovered that having the precise angle is absolutely critical to achieving maximum efficiency and in all my tests this optimum angle only varied from about 1 to 3 degrees. At that point I found it impossible to measure the angle accurately enough to be able to make a useful chart. I then moved onto plan "B" and concluded that the best approach would be to design a new nozzle for my turbine in which the divergent portion would be adjustable.

After constructing a new nozzle I "Tuning it" for best performance by taking its temperature and then mounting it on my original test turbine. I got the following results.

In previous tests with my original nozzle and starting with air at 105-PSI and dropping to 80-PSI the maximum no load speed I was able to obtain was 6780 RPM.

With the new super nozzle the maximum speed is now 20000 RPM! Thus proving beyond any doubt that my original nozzle was a piece of junk.

I reduced the air pressure to a regulated 50-PSI this caused the maximum speed to drop to 18000 RPM. Next I applied a load to the turbine slowing it down to 9240 RPM. At this speed the turbine produced approximately 27 in/oz. of torque or about 3.9 HP.

Recalling the results that I got with my multi-nozzle turbine a couple months ago I obviously had to try the new nozzle design in a multi-nozzle arrangement. To do this I then made two additional nozzles and mounted them on my original turbine. (Total of three nozzles 120 degrees apart.)

Using the same air pressure as before the maximum no load speed stayed essentially the same but the acceleration time was cut in half.

Appling a load to the turbine I slowed it down to 10200 RPM at which point I measured approximately 80 in/oz of torque that calculated out to about 13 HP.

Attached is a drawing with a half sectional view of my nozzle showing its internal configuration and size.

Finally I would like to thank James Morris for his contribution. It is the piece-by-piece gathering together of information like this that will hopefully make the Tesla turbine into a practical engine. (Editor: Read James' 6/1/03 explanation of thermodynamics in the PTBC Forum)

What we need now is for someone to develop a method of say burning waste oil in an ultra-clean manner so as to fire a flash tube boiler.

Richard Gideon
Spotteddogs@iwic.net

This is an excellent piece of engineering work. It clearly unlocks one of the mysteries of the Tesla turbine. Tesla mentioned that the efficiency of his engine was dependant on the design of the inlet and outlet nozzles -- this experiment clearly shows the relationship between maximum gas velocity and maximum turbine speed, horsepower, and efficiency.

Other members may find additional nozzle information at their local libraries under: "steam turbines".

Nice job, Richard!

P.S. Stay tuned in the months ahead for info on waste oil burners. -- Ken Rieli