The following test sheet shows the performance of Axial Turbine 4D and Tangential Turbine 5C running on air I said I was going to show after the 27/03/2023 post that also included the following drawings. I will look at the reasons for this performance in the next posts.
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I took a second look at the way the nozzle velocity coefficients were found
I estimated the nozzle velocity coefficient of Axial Turbine 4D to be approximately 0.69 and 0.73 for Tangential Turbine 5C for the tests shown in the last post. These velocity coefficients were determined by starting with the velocity coefficient of 0.93 for the conical nozzle as explained in the 17/03/2023 post then finding the reduction for the pressure drop due to friction. The reduction due to pressure drop was 0.94 for both turbines since they had the same nozzle throat length. This reduced the nozzle velocity coefficient to 0.87. I then found the reduction for expanding to supersonic velocities with a converging only nozzle shown in the following diagram as line A. In the tests shown in the previous post, the Mach number for Axial Turbine 4D was 1.47 and for Tangential Turbine 5C was 1.43. The reduction for expanding supersonic is approximately 0.97 for both turbines when rounded to two decimal places. This reduces the nozzle velocity coefficient to 0.84 for both turbines. The last reduction was for the distance between the nozzle outlet to the rotor. This was 0.186” for Axial Turbine 4D and 0.113” for Tangential Turbine 5C as shown on the two drawings of the last post. The reduction in nozzle velocity coefficient for this was 0.82 for Axial Turbine 4D and 0.87 for Tangential Turbine 5C. This reduced the nozzle velocity coefficient to 0.69 for Axial Turbine 4D and to .73 for Tangential Turbine 5C as stated at the first of this post. The reduction in rotor velocity coefficient for supersonic velocity was 0.98 for both turbines. The rotor velocity coefficient found from the static torque test explained in the 23/03/2023 post were 0.68 for Axial Turbine 4A and 0.27 for Tangential Turbine 5B. Neither of these turbines had the insert and the discharge velocity of the nozzles were approximately sonic, so using the correction for supersonic velocities reduces the rotor velocity coefficient to 0.67 for Axial Turbine 4D and to 0.26 for Tangential Turbine 5C. I will show in the next post how the test results in the last post compare with the velocity diagrams like shown in the 23/03/2023 post.
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Edited By Turbine Guy on 29/03/2023 21:20:09
I looked at the way I determined the nozzle velocity coefficients in this post and believe the corrections I made for the distance from the nozzle outlet to the rotor are not correct. I believe the methods used for the other corrections are valid and the corrected value for the nozzle velocity coefficient of 0.84 for both turbines should be used. The distance from the nozzle outlet to the rotor is space needed for the gas to expand to supersonic Velocities. I will try to find the distance required for the gas to expand to supersonic velocities and the effect of having too short or too long of a distance.
I tried adding an insert with a throat diameter of 0.025” in the nozzle of Axial Turbine 5 to see if the improvements I made changing from Axial Turbine 4 to Axial Turbine 5 would increase the efficiency using the insert. The views shown in the post I quoted show approximately the dimensions of the insert I added in Axial Turbine 5 and how it fits in the nozzle since the nozzle was the same for both Axial Turbine 4 and Axial Turbine 5. Instead of the performance improving, the maximum speed of the propeller for the pressure of 44.0 psig shown for Axial Turbine 4D in the table decreased from 28,000 rpm to 22,000 rpm. This was a substantial decrease in performance so I tried a test running on steam and got similar results. I removed the insert and had the same performance running on air as shown in the table of the 17 December 2024 post so there wasn’t a problem with any of the parts or the placement of the rotor in the housing. The only reason I could find for this drop in performance using the insert was the air not expanding to supersonic velocity. I estimated the performance with sonic velocity and it was still much higher than found in the test. The last thing I could think of was to estimate the performance based on the velocity that would pass the mass flow at the discharge diameter of 0.042”. In other words, expanding to a lower velocity instead of to a supersonic velocity. The estimated performance based on expanding to a lower velocity was close to what was found in the test so this appears to be what happened. I have got performance with the inserts that could only be obtained with the flow expanding to supersonic velocities like shown in the quoted post so I am not sure why I only had this problem with this last configuration. When I remove an insert, I have to remove all the Loctite that held it in place. When I did the cleanup after removing the insert used in this last test, I noticed that I had to remove more Loctite than normal. If the flow had to pass through this extra Loctite it might have been what caused the flow to go subsonic. If you use Loctite 290 to hold a nozzle or insert in place you must be very careful not to let the clearance get too large or it can block part of the flow. Loctite 290 is designed to work in very tight clearances. When I have kept the clearances small Loctite 290 has worked very well for me running with air or steam.