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Testing Models

Testing of model steam engines and turbines.

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Turbine Guy30/09/2019 23:13:24
128 forum posts
60 photos

I made the following chart to summarize the testing of my turbines. I lowered the estimated powers in this chart slightly from what I have previously given to be more conservative. These values of power are approximately the power I calculate using Dr. Balje’s guidelines. The first test with velocity staging resulted in lower power than with the reversing chamber removed. This is comparing an optimized single stage with the first try of velocity staging. Hopefully by optimizing the reversing chamber I can improve the performance of the velocity staging. The next post gives the updated drawing that is the first revision for turbine 3 with the velocity staging. As you can see there are quite a few changes from the drawing shown in the post of 11/07/2019. Some changes were made to improve the design while others were to repair errors in machining. This drawing shows the dimensions important for setup and analysis and shows the actual part dimensions at the time of this revision. Turbines Test Results

Turbine Guy30/09/2019 23:15:35
128 forum posts
60 photos

The followings is the drawing I described in the last post.

Tangential Turbine 3 VS A

Turbine Guy20/10/2019 23:46:14
128 forum posts
60 photos

I ran several tests with air to find the maximum performance. These tests are described in the Model Turbines thread and summarized in this and the following posts. The improvement in performance running on air was very small. The speed increased by 500 rpm without the reversing chamber and 600 rpm with the reversing chamber with the improvements. The turbine still made slightly more power without the velocity staging running on air. Apparently, the back pressure caused by the second stage was enough to keep the performance from getting better than with a single stage. I ran the velocity staging with steam on 14/10/2019 and added the performance of this test to the table. The extra energy of the steam allowed the velocity staging to work better. The boiler pressure was the same as the test of 11/7/2019 without velocity staging, so the energy supplied should be approximately the same. The velocity staging with steam got a 1.8 watt increase in power. I planned on running on air immediately after running on steam to see if that would keep the ball bearings from gumming up. Even after releasing the hose clamp, the silicon hose I used for steam would not come off. I pressed the hose from my airbrush compressor against the silicon hose and got enough pressure to spin the turbine and blow the water out. I then tried pulling as hard as I could on the silicon hose. The stainless steel (ss) tube that was Loctited to my turbine housing popped out. I had to cut the silicon hose to remove it from the ss tube. I don’t know what caused the silicon hose to bond to the ss tube. I Loctited the ss tube back on my turbine housing and will run the turbine on air after the Loctite cures. Hopefully, the ball bearings will not gum up.

Turbine Guy20/10/2019 23:52:50
128 forum posts
60 photos

I ran Turbine 3 on air after Loctiting the stainless steel inlet tube back on the housing. The speed never got back to the speed the turbine was running with the reversing chamber installed but my airbrush compressor was shutting down periodically. This indicated the turbine nozzle was partially blocked. I cleaned out the nozzle and ran the turbine on air again. The speed of the turbine went back to the same maximum speed it had before with velocity staging. Running the turbine on air immediately after running on steam appears to keep the ball bearing oil from gumming up. I wasn’t sure if the blockage in the nozzle occurred before or after the run on steam so I ran the turbine on steam again. After cleaning out the nozzle, Turbine 3 reached a maximum speed of 32,500 rpm with velocity staging. The resulting power of 12.4 watts was about what I hoped I would be able to achieve with velocity staging. This is an increase in power of approximately 4.5 watts with velocity staging. This increase in power is a little misleading. It should be pointed out that if the turbine was turning a load that could be adjusted, the power without velocity staging of Turbine 3 would be around 11 watts at 32,500 rpm. The power added by the velocity staging would be approximately 1.5 watts compared with the power that could be achieved at this speed without velocity staging. Using a propeller for the load results in the speed being set by the torque required to turn the propeller. The speed was very consistent during the short run on steam. Also, the relief valve on the boiler was constantly releasing steam so the pressure of 50 psig (3.4 bar) was the maximum the boiler could produce. I ran Turbine 3 on air after the run on steam and the maximum speed obtained was 22,600 rpm so the friction of the ball bearings has not changed. I am very pleased with the performance of Turbine 3 running on steam with velocity staging. The following chart is updated to show all the tests.

Turbines Test Results 3

Turbine Guy21/10/2019 00:00:35
128 forum posts
60 photos

The following drawing shows some of the important dimensions of my Turbine 3 after getting the best performance I was able to obtain with velocity staging. Making the outer edge of the reversing chamber as thin as possible made the biggest improvement. This opened up the space for the steam or air exiting the second stage. I was able to meet all my goals with these last tests so I don't plan on any further testing of Turbine 3.

Tangential Turbine 3 VS B

Turbine Guy26/10/2019 19:27:20
128 forum posts
60 photos

Since I was able to achieve the performance I hoped to obtain with my turbines, I decided to work on my Stuart Turner St oscillating steam engines again. The following photo shows the machining done on the cylinder and standard of the parts on the right and the same parts without modification on the left for comparison. I machined the mating faces of the standard and cylinder on the parts on the right. As I suspected, the mating surfaces were worn conical by the tilting back and forth of the cylinder as the engine ran. You can also see in the photo how much larger the cylinder support shaft is on the parts on the right side. The following is the speeds I posted 1/7/2019 after running the APC 8x6 propeller with the enlarged cylinder support shaft. The maximum speeds for 5, 10, 15, and 20 psig were 450, 655, 765, and 851 rpm respectively. After machining the faces, the maximum speeds for 10, 15, 20, and 24 psig were 1,000, 1,125, 1,215, and 1,450 rpm respectively. I was able to maintain a pressure of 24 psig after machining the faces. 20 psig was the maximum I could maintain before machining the faces. After testing I took the cylinder off and tried moving the piston with the ports open and closed. There was only a slight increase in force moving the piston with the port closed so the packing loosened up from the previous tests. For propellers, the power goes up by the cube of the speed so the increase in performance was substantial. In the next post I’ll add a chart similar to the one I used for documenting the testing of turbines.

ST Parts

Turbine Guy26/10/2019 20:47:22
128 forum posts
60 photos

The following chart shows the maximum estimated powers my Stuart Turner ST oscillating steam engine has produced in all the tests I have made so far. The dates in the table are with the month first, day second, and year third as we use in the USA. This chart gives only the maximum estimated powers obtained on the given dates for the changes to the engine shown. Posts in this thread near the dates shown have quite a bit of additional information. I am still trying to find out why the amount of power obtained is so low for this engine. I have tried to be very careful in the changes I've made but maybe I have done something that causes this. The loose packing is allowing more leakage but the power has increased over what was produced with the tight packing due to the mating faces of the cylinder and standard being flat now. I'm going to try using the floating O-ring next.

ST Test Results

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