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Member postings for Turbine Guy

Here is a list of all the postings Turbine Guy has made in our forums. Click on a thread name to jump to the thread.

Thread: Model Turbines
23/09/2021 14:15:56

I started the machining of Housing 3 SD Nylon by centering it in the 4 jaw chuck and reaming the bore for the ball bearings as shown in the following photo. I used the smallest change in drill sizes progressing up to just a little smaller than the reamer size. The jump from a K (0.281) to an L (0.290) drill size caused the housing to move in the 4 jaw chuck. I centered the housing again and tightened the jaws a little tighter and had no further problems. I hope that I didn’t lose much accuracy after needing to re-center the housing. The ball bearing took a light push fit to enter the exposed end. A dowel pin the same OD as the ball bearing had a tight slip fit all the way through the bore. I kept the dowel pin in the bore and tightened the 4 jaw chuck a little more before machining the rotor bore and housing faces. The machining of the rotor bore and housing faces was very easy and the finish quite smooth. The problem of gripping the extension of the housing could be helped by making the OD larger. When the ball bearing bore is machined to full size, the wall thickness of the extension is too small for nylon. I made the housing with minimum wall thickness for casting in bronze to reduce the cost. Extra thickness doesn’t add much cost when printing nylon and would be an improvement. 

Housing 3 SD Nylon 1

Edited By Turbine Guy on 23/09/2021 14:19:26

21/09/2021 18:18:43

I received the printed housings as shown in the following photo. I measured the housings, and the following drawing shows the design dimensions with the actual dimensions below them in parenthesis. The housings appeared to be stiff enough and strong enough to work running on air. The details of the velocity staging in the VS Housing Nylon looked very good and would be very difficult to machine. The printing process leaves a rough finish, and I am hoping the machining needed to make the critical dimensions will leave a smooth surface. I will start the machining on Housing 3 SD Nylon first and give updates as the progress continues.

Nylon Housings 3

Nylon Housings 2

09/09/2021 19:47:31

One of the reports I read mentioned that they made their prototypes from plastic until they found their optimum designs. This cuts the cost down considerably and probably the amount of machining time. I haven’t machined any plastics for a while, so I am only guessing they are easier to machine. Shapeways uses a laser to sinter nylon powder into plastic layer by layer that uses SLS technology to print the PA11 nylon. Since the PA11 nylon is unaffected by the Kryox GPL 102 and 105 oils I use for my turbines, I ordered a couple of housings shown in the following drawing. I decided to try housings for my first plastic parts since they are the most expensive bronze castings. The cost of Housing 3 SD for nylon is approximately $20 and for bronze is approximately $180. The cost of the VS Housing for nylon is approximately $25 and for bronze is approximately $300. The Housing 3 SD is designed to be used with all the other parts of Tangential Turbine 3 SD. The VS Housing has 4 blades that circulate the flow back into and out of the rotor like used by Terry turbines. This is something that I have wanted to try and is beyond my machining capabilities. I picked the PA11 nylon since the minimum thickness was even smaller than for bronze (0.5 mm vs 0.6 mm). If Shapeways printed housings hold the tolerances tight enough and the plastic is strong enough to use these housings for my turbines, it will allow me to try many more options. The dimensions on the following drawing were intended to be used to check if Shapeways had the step files scaled correctly. Shapeways did not mention any shrinkage for the printing so I will check the accuracy of the parts by showing the actual dimensions in parenthesis next to design dimensions after I receive the parts.

Nylon Housings 1

04/09/2021 20:06:32

I ran Drag Turbine 4 and Drag Turbine 5 after adding the sleeve to the inlet tube of Cover 5. The larger diameter and extra length allowed the hose clamp to fully tighten and the pressure to reach it’s maximum without leakage. The following table was updated to show the latest test results. Even with the bearings just oiled, Drag Turbine 4 was able to spin the propeller at a speed of 28,000 rpm with a 20 psig pressure. The speed of the propeller went over 30,000 rpm before the 24 psig the airbrush compressor is capable of continuously was reached. With the right load this turbine could produce over 5 watts with the TC-96T airbrush compressor. Drag Turbine 4 is capable of producing the most power but Drag Turbine 3 is more efficient and better suited to energy sources capable of high mass flows at low pressures.

Turbine Test Results 23

03/09/2021 20:56:57

After seeing the improvement of Drag Turbine 3, I ran Drag Turbine 4 that only the cover is different. After reoiling the bearings, it reached a speed of 28,000 rpm turning the GWS EP 2508 propeller. After several short runs the maximum speed started to go over 30,000 rpm so I reoiled the bearings and the maximum speed was 28,000 rpm. Drag Turbine 4 gave me the best performance of all my turbines running on the TC-96T airbrush compressor. Cover 5 added the nozzle directed in the flow direction that I thought would help, but in previous tests did not work as well as Cover 3. I tried to run Drag Turbine 5 to see if the breaking in helped it. I couldn’t keep the airline from blowing off. The hose clamp was tightened until it bottomed out and the hose would still blow off before a pressure of 20 psig could be reached. I cut off the end of the airline where it had been clamped and the hose clamp still bottomed out and the hose blew off. The inlet tube is too short and has a smaller OD than needed. I used Loctite to add a longer and larger OD extension as shown in the picture below. I will try running the drag turbines again tomorrow after the Loctite has fully cured.

Drag Cover 5 Photo 3

Edited By Turbine Guy on 03/09/2021 21:01:01

02/09/2021 16:22:46

I ran another set of tests with my turbines like those in the last post but finding the power that could be maintained continuously with the TC-96T airbrush compressor. The following table shows the results of these tests. Drag Turbine 3 appeared to be improving each time I ran it, so I kept making short runs with it until it appeared to be completely bedded in. The results for Drag Turbine 3 shown in the table were added after making the multiple short runs and adding new oil like was done for the tests of the other turbines. This turbine outperformed all the other turbines with the TC-96T airbrush compressor so I ran it for several short tests without reoiling the bearings to see what speed the turbine could reach after the oil thinned out. The maximum speed turning the GWS EP 2508 propeller was 29,500 rpm. The power required by the propeller for that speed is approximately 4.9 watts so there was a gain in power of approximately 0.7 watts. This variation in performance with the condition of the oil is why it is so important to have the condition of the oil the same for any comparison tests. Both the following table and the table shown in the last post had all the tests with oil just added so the efficiency will only get better until the oil gets too thin or wears out.

Turbine Test Results 22

26/08/2021 18:53:15

To find the maximum power with each of my turbines using my TC-96T airbrush compressor, I pinched the air hose closed and let the pressure raise to the shut off point of 60 psig in the air tank. I then suddenly opened the air line and measured the air pressure where the turbine ran at a speed of 28,000 rpm if this speed could be reached. If the 28,000 rpm could not be reached, I recorded the speed obtained and the air pressure at that speed. The air tank could only supply this air pressure for a few seconds. The following table shows the test results for each of my turbines. Each turbine type used the same ball bearings which were removed from one turbine reoiled with Krytox GPL 102 oil and put in the turbine tested next. Because the temperature is reduced when the air expands in the turbines the temperature is less than ambient, so the viscosity stays relatively high. The Aero Shell Fluid 12 oil that comes with the ball bearings I use is lower viscosity, but I have not found a source for this oil in small quantities. Since these ball bearings are getting very difficult to purchase, I need to add oil regularly to extend their life and the Krytox GPL 102 oil is the best replacement I have found. To measure the loss in power due to using the higher viscosity oil, I measured the speed of Drag Turbine 3 with a GWS EP 2508 propeller and new ball bearings and then with the new bearings reoiled with Krytox GPL 102 oil. The maximum speed dropped from 15,000 rpm to 10,500 rpm. The power required for the GWS EP 2508 propeller for a speed of 15,000 rpm is 0.6 watts and for a speed of 10,500 rpm is 0.2 watts. A loss of power of approximately 0.4 watts. Tangential Turbine 3 SD + Gap, Drag Turbine 3, Drag Turbine 4, and almost Drag Turbine 5 were able to reach the speed of 28,000 rpm without the maximum available energy. Tangential Turbine 1 and Tangential Turbine 2 were not able to reach 28,000 rpm even with the maximum available energy. The Drag Turbines required the least amount of available energy to reach this speed.

Turbine Test Results 21

23/08/2021 18:51:01

I tried to use the efficiency correction given in the report mentioned in the 20/08/2021 Post but it didn’t appear to work for Drag Turbine 3. The report states the clearance between the rotor face and the cover needs to be less than 0.02 time the flow channel effective depth. The flow channel effective depth of Drag Cover 2 is 0.053” so the clearance needs to be less than 0.001”. I put the maximum number of shim washers that would still leave the rotor free to turn for the tests. When I tried adding one more shim washer the rotor was pressed tight enough against the cover that the pressure was the same as when I pushed the rotor flat against the cover plate. It appears that even though I have the required clearance, the flow leakage is still very high. The stall pressure with the 0.001” clearance necessary for running is approximately 11 psig. The stall pressure with the 0.001” shim added is approximately 15.5 psig. Since the TC-95T airbrush compressor has an air tank, it is capable of a higher mass flow for a few seconds than it can maintain continuously. I found that Drag Turbine 3 was able to run at a pressure of 15.5 psig for a very brief time and it was able to reach a speed of approximately 33,000 rpm turning the GWS EP 2508 propeller. This speed is quite a bit higher than the speeds I have the test results for, so I ran the APC 4 x 3.3 EP propeller. The APC 4 x 3.3 EP propeller reached a maximum speed of 6,750 rpm with a pressure of 15.5 psig for a very brief time. The power required by this propeller for this speed is approximately 1.9 watts. The maximum continuous speed with this propeller was 5,500 rpm with a pressure of 10.0 psig. The power required at this speed is approximately 1.0 watts. The available power for 15.5 psig is approximately 25.0 watts resulting in an efficiency of 7.6%. The available power for 11 psig is approximately 22.6 watts resulting in an efficiency of 4.5%. The efficiency correction for leakage should be approximately the ratio of the efficiencies 4.5/7.5 = 0.6. With this 0.6 correction for leakage and the 0.73 correction for blade thickness, the 33% estimated efficiency given by the Ns Ds Diagram mentioned in the 20/08/2021 post is reduced to 14.5%. The actual efficiency for the test being considered was 16.5% so the correction factors I came up with are too conservative. I am going through all this to show what parts of the design of Drag Turbine 3 are causing its performance to be less than predicted for a design meeting all the requirements. I can’t reduce the thickness for the blades so the correction factor for blade thickness will remain the same. I can’t reduce the clearance between the rotor face and the cover plate so the correction for leakage will also remain the same.

What has been shown by these tests, is that the amount of power I can make using the TC-96T airbrush compressor is larger than my GWS EP 2508 propeller can absorb. I am going to make a series of tests with all my turbines to find the pressure required to spin the GWS EP 2508 propeller to a speed of 28,000 rpm. With these pressures found, I will be able to use the airbrush nozzles test chart shown in the 19/08/2021 post to calculate the efficiency for each design.

21/08/2021 19:12:06

Rotor in Housing

The first item I looked at on Drag Turbine 3 that didn’t meet the requirements of the study mentioned in the last post was the blade thickness. To meet the requirements, the blade thickness must be less than 0.2 times the flow channel effective depth. As shown in the picture above, the outer ends of the blades on Drag Rotor 2 have been wiped wider by the machining of the rotor face. Shapeways mentioned that one of the reasons they give a minimum thickness is to prevent this from happening. The blade thickness of Drag Rotor 2 was 0.009” and the minimum thickness recommended by Shapeways for Bronze is 0.024”. With the ends wiped wider, the flow blockage is worst than if I had made the blades 0.024” thick and used a rounded end like for Drag Rotor 4 shown in the picture below. The flow channel effective depth for Drag Cover 2 is 0.053” so the blade thickness needed to be 0.011” to meet the studies requirements. Assuming the effective blade thickness is 0.024” due to the wider ends, the blade thickness to effective channel depth ratio is 0.45”. The efficiency correction factor given by the study for this ratio is 0.73”. I will describe the efficiency correction for the excess leakage in the next post.

Drag Rotor 4

Edited By Turbine Guy on 21/08/2021 19:13:26

20/08/2021 19:32:18

After running the airbrush nozzle tests shown in the last post, I had enough information to update the table shown below to include the last tests of the drag turbines. This table was originally shown in the 09/04/2021 Post. Cover 5 and Rotor 5 never gave me the gain in performance I hoped I would get running on air with more mass flow. The Specific Speed, Ns, and the Specific Diameter, Ds, for the mass flow, enthalpy drop, turbine speed, and a rotor diameter shown for the 8/17/2021 test of Drag Turbine 3 are 2.4 and 7.1 respectively. For these values of Ns and Ds the efficiency of a optimum drag turbine shown in the Ns Ds Diagram in the 29/07/2021 post is approximately 33%. The actual efficiency as shown in the table below was 16.5%. I will look at the correction factors given by ‘A Study Of High Energy Level, Low Output Turbines’ prepared by Dr. O. E. Balje for the Department of the Navy in December 1957’ for the parts of the design that don’t meet the requirements in the next post.

Turbine Test Results 20

19/08/2021 20:48:31

The first oversize of the Cover 5 nozzle changed the bore from 0.038” to 0.040” and dropped the maximum speed 500 rpm so increasing the nozzle bore size didn’t help. I made a nozzle shown in the following drawing and measured the maximum pressure my TC-95T airbrush compressor was able to supply for each change in bore size as shown in the chart below. I had done this for my airbrush compressor TC-20 and it allowed me to find the maximum energy available energy available. It turned out that the optimum nozzle size of Cover 5 was the size that gave the maximum available energy. When I did this with my TC-95T airbrush compressor it turned out that the nozzle sizes from 0.037” to 0.039” gave the maximum available energy so increasing the nozzle size to 0.040” decreased the available energy slightly. Apparently the 0.039” nozzle size gave the best performance I can get for Drag Turbine 4 using the TC-95T airbrush compressor and didn’t beat the performance of Drag Turbine 3.

Airbrush Nozzle Tests 2

Test Nozzle 2

19/08/2021 16:42:06

I ran tests with Drag Turbine 4 and Drag Turbine 5 using the TC-95T airbrush compressor and the GWS EP 2508 propeller. The maximum speed for Drag Turbine 4 was 25,500 rpm with a corresponding power of 3.2 watts. The maximum speed for Drag Turbine 5 was 22,000 rpm with a corresponding power of 2.0 watts. Neither of these turbines exceeded the 3.4 watts I was able to obtain with Drag Turbine 3. Drag Cover 5 used on Drag Turbine 4 and Drag Turbine 5 with the nozzle intended to increase the power by having the flow enter in the direction of rotation only helped Drag Turbine 5. Maybe opening the nozzle size further might help Drag Turbine 4 since the nozzle throttles the flow and the mass flow might be reduced to a point that it reduces the power more than directing the flow in the right direction increases the power. I hesitate to open nozzles because once the material is removed, the nozzle bore can only get bigger unless a sleeve is used. In this case, there doesn’t appear to be a significant downside to trying a larger bore. I think I will try increasing the bore in tiny steps to see the effect on Drag Turbine 4 and Drag Turbine 5. The following table shown in the 04/07/2021 Post that shows what I tried with the TC-20 airbrush compressor. This table shows that the maximum power was with a nozzle size of 0.032” with Rotor 2 and Cover 5. The combination of Rotor 2 and Cover 5 is what I am calling Drag Turbine 4. I think I will find an optimum nozzle size for the TC-95T airbrush compressor the same way.

Turbine Test Results 17

17/08/2021 18:24:27

I ran Drag Turbine 3 with the TC-96T airbrush compressor similar to the test described in the 12/03/2021 Post using the TC-20 airbrush compressor. The following is copied from that post with the values I measured in this test shown in parenthesis next to the values shown for that test.

“I made the following four pressure measurements. First, I measured the pressure with the cover plate removed and pressed tight against a flat surface. The pressure was approximately 2.5 psig (6.5 psig). That is the pressure required to push all the flow through the existing channel size with smooth walls on all sides. The second measurement was with the cover plate bolted tight to the turbine housing with the rotor supported by the ball bearing but pushed tight against the cover plate. The pressure was approximately 9.5 psig (12.5 psig). That is the pressure required to push all the flow through the existing channel size with blades and without leakage. The 7 psig (6.0 psig) increase in pressure was due to the resistance to flow that the blades cause. The third measurement was with the 0.007” total thickness of shim washers keeping the face of the rotor as close to the face of the cover plate as I was able to do without any contact. The pressure was approximately 5.0 to 6.5 psig (12.0 to 12.5 psig) dependent on the rotor position. That is the pressure required to push all the flow through the existing channel size with blades and with leakage.” “The fourth pressure measurement was with everything the same as the third measurement except with the turbine running at a speed of 18,500 rpm (26,000 rpm). I was able to reach that speed again with the GWS EP 2.5x0.8 propeller. The pressure was approximately 4.0 psig (9.5 psig).”

The power required by the GWS EP 2.5x0.8 propeller at 18,500 rpm is 1.2 watts and at 26,000 rpm is 3.4 watts. The power more than doubled using the TC-96T airbrush compressor, so the extra mass flow was as important as I thought. I will run tests with Drag Turbine 4 and Drag Turbine 5 with this airbrush compressor and post the results.

Edited By Turbine Guy on 17/08/2021 18:27:53

14/08/2021 20:13:47

I tried running my Stuart 504 boiler with two burners to confirm the power I got from Drag Turbine 5 in the test shown in the 09/07/2021 Post. The relief valve opened at around 30 psig so I couldn’t get the pressure up to the 35 psig pressure that resulted in the GWS EP 2508 propeller spinning at 30,500 rpm for a power of 5.4 watts. The relief valve keeps releasing at a lower pressure each time I try another test. The spring must need replacing since the relief valve doesn’t leak until it reaches a certain pressure. This pressure should remain about the same but doesn’t anymore. I prefer to do my testing with an airbrush compressor since it is so consistent and doesn’t require near as much time to setup and run a test. I need higher mass flow with my Drag Turbine 5 since the test I was trying to confirm gave a large jump in power when the mass flow increased. I decided to get a twin cylinder airbrush compressor that has about twice the mass flow of my existing single cylinder airbrush compressor. This will allow me to run tests using air with higher mass flows and the pressure can be maintained more consistently. The airbrush compressor I just ordered (shown below) is a Master TC-96T that is a twin cylinder version of my existing airbrush compressor that I have been very pleased with. This airbrush compressor is scheduled to arrive next Monday so I should be able to check the effect of having more mass flow available with all my turbines.Master TC-96T

30/07/2021 15:20:02

I decided to see what the Ns Ds diagram of the last post with corrections would estimate for the test of Axial Turbine 2 running on air shown in the 19/07/2021 Post. For this test the turbine speed was 23,000 rpm, the rotor diameter was 1.181”, the mass flow was 2.0 lb/hr, the enthalpy drop was 34 btu/lb, and the exhaust specific volume was 13.3 ft^3/lb. For these values, Ns is 0.94 and Ds is 14.6. From the Ns Ds diagram shown in the last post, the maximum efficiency is approximately 20%. The rotor tip speed was 119 ft/sec and the kinematic viscosity was 0.000181 ft^2/sec resulting in a Reynolds number of 81,000. The correction for this Reynolds number is 0.64. Multiplying this correction to the maximum efficiency of 20% yields an efficiency of 13%. The energy available to the turbine for this test was approximately 20 watts and the actual power was 2.3 watts, so the actual efficiency was 11.5%. This confirmed that the low Reynolds number reduces the efficiency substantially and appears that Dr. Balje’s correction is conservative for air as well as steam. This also confirmed how useful his methods and diagrams are for estimating the efficiency if you know all the parameters needed. It also shows why my turbines did better running on air than with wet steam.

29/07/2021 16:28:47

The following Ns Ds Diagram is the one mentioned in the last post. Using the mass flows, enthalpy drops, and turbine speeds given in the 26/07/2021 post and a rotor outside diameter of 1.181”, the values of Ns and Ds can be calculated for my test and Werner’s test. For my test, Ns is 0.50 and Ds is 14.5, and the corresponding maximum efficiency from the following Ns Ds Diagram is approximately 10%. For Werner’s test, Ns is 0.68 and Ds is 14.5, and the corresponding maximum efficiency from the following Ns Ds Diagram is approximately 15%. To obtain these efficiencies, the steam would have to be dry and the Reynolds number greater than 200,000. As shown in the posts of 27/07/2021 and 28/07/2021 the steam was wet and the Reynolds number was lower than 200,000 for both these tests. These posts showed how to correct the efficiency to account for this. The correction for moisture was 0.65 and the correction for Reynolds number was 0.44 for my tests. The correction for moisture was 0.90 and the correction for Reynolds number was 0.62 for Werner’s tests. With these corrections the estimated maximum efficiency for my test is 3% and 8% for Werner’s test. The actual efficiencies were 3% for my test and 9% for Werner’s test so Dr. Balje’s corrections are very conservative since the rotor and nozzles weren’t optimum. The point I am trying to make, is how wet steam and Reynolds number below 200,000 can drastically reduce the efficiencies of tiny turbines.

Ns Ds Diagram 2

29/07/2021 15:14:03
Posted by Turbine Guy on 09/12/2020 18:23:48:

The chart shown below and in some earlier posts is copied from ‘A Study Of High Energy Level, Low Output Turbines’ prepared by Dr. O. E. Balje for the Department of the Navy in December 1957. This chart illustrates the maximum performance he estimated for various types of turbines when optimized. The heavy solid lines in the chart are for axial turbines. The dashed lines are for Terry turbines. The thin solid lines are for Drag turbines. The units for the volume flow are ft3/sec and lb/ft3 for the gas density. Dr. Balje intended this chart be used by determining the volume flow at the turbine exhaust (Q3) and expansion head (Had) of the supply gas.

Ns Ds Diagram

The quote from this post shows the equations and units for finding the specific speed Ns and specific diameter Ds for the Ns Ds Diagrams like the one for axial impulse turbines with small number of blades I will show in the next post.

28/07/2021 21:14:16

In ‘A Study Of High Energy Level, Low Output Turbines’ prepared by Dr. O. E. Balje for the Department of the Navy in December 1957 the turbine Reynolds number is defined as:

Re = Reynolds number = blade tip speed x blade OD/kinematic viscosity.

The rotors used in both tests were the same and the blade OD is 1.181in. Also, the kinematic viscosity of 0.000233 ft^2/sec is the same for the fully expanded steam. The blade tip velocity for my test is approximately 93 ft/sec and the blade tip velocity for Werner’s test is approximately 180 ft/sec. With these values, the Reynolds number for my test is approximately 39,000. The Reynolds number for Werner’s test is approximately 76,000.

The correction in efficiency given in the study is:

Reynolds number efficiency correction = (Reynold Number/200,000)^.5

The Reynolds number efficiency correction for my test is 0.44 and the Reynolds number efficiency correction for Werner’s test is 0.62. Reducing the adjusted power of 2.5 watts shown in the last post by the ratio of the Reynolds number corrections:

New adjusted power = 2.5 x 0.44 / 0.62 = 1.8 watts

The difference in this adjusted power and the 1.1 watts power of my test is only 0.7 watts and is probably the result of Werner being able to run at a higher speed.

The corrections I used in this post and the last post are to adjust the predicted performance of his charts for the amount of moisture and running at a Reynolds number of less than 200,000. The specific speed Ns and specific diameter Ds account for the rotor diameter, energy level, volume flow, and turbine speed. In the next post I will apply these corrections to his chart for axial turbines with small blade numbers.

Edited By Turbine Guy on 28/07/2021 21:20:12

27/07/2021 19:24:52

The first thing I thought I would check for determining why Werner Jeggli got so much more power with the same nozzles size is the available energy for each test. The isentropic enthalpy drop for saturated steam starting at a pressure of 40 psig and ending at atmospheric pressure is approximately 77 btu/lb. For a mass flow of 1.6 lb/hr the available energy to Axial Turbine 2 in my test was approximately 36.5 watts. The isentropic enthalpy drop for saturated steam starting at a pressure of 3.5 bar (51 psig) and ending at atmospheric pressure is approximately 109 btu/lb. For a mass flow of 1.4 lb/hr the available energy to Werner’s turbine in his test was approximately 43.5 watts. Reducing the power Werner got by the ratio of the available energy to the turbine in my test divided by the energy available to the turbine in Werner’s test, the adjusted power is 3.9x36.5/43.5 = 3.3 watts. This is still much larger than the 1.1 watts I was able to obtain.

The next thing I checked is the wetness of the steam for each test. Tim Taylor 2 in the 28/01/2019 post of the Testing Models thread suggested that I look at the Two Phase Flow Link. I thought at that time, the flow from my boilers was superheated enough that moisture in the nozzle wouldn’t be a problem. I found from my testing that not using a throttle valve can lead to very large amounts of moisture in the steam. The advantage of the two phase method is that it can be used to determine the percent moisture if the mass flow and nozzle size are known. Using the two phase method, the estimated amount of moisture in my test was approximately 27% and in Werner’s test was approximately 8%. In my book Steam Turbines by Church, third edition, he suggests reducing the power by 1.3 times the percent moisture for wet steam. Reducing Werner’s adjusted power by the difference in percent moisture, the new adjusted power is 3.3x(1-1.3x.19) = 2.5 watts. The large amount of moisture in my test was one of the most important reasons for the difference in performance. Werner’s Throttling from a boiler pressure of 5 bar to a turbine inlet pressure of 3.5 bar kept his steam much drier. I will get into the effects of Reynolds number in the next post.

26/07/2021 20:14:30

I decided to try running a turbine using the Stuart Twin Drum boiler with a small nozzle to eliminate the need for throttling. I found from past testing that if the nozzle size was less than 0.028”, my turbines could run without too much moisture carryover. Since Werner Jeggli had good results with a 0.6 mm, 0.024", nozzle with the cast rotor I use in Axial Turbine 2, I thought I would try the same combination. Since I had increased the nozzle size to 0.032” in Axial Turbine 2, I thought I would try reducing the size with a sleeve as shown in the following drawing. I ruined one of the nozzles trying to add a sleeve as explained starting with the 07/04/2020 Post, but thought I would try doing it again. This time I was able to insert the sleeve, Loctite it in place, and run a 0.024” drill through to clean it out. I put ½ cup of water into the Stuart Twin Drum boiler and ran a test of Axial Turbine 2 with the 0.024” nozzle size. After a short time, Axial Turbine 2 reached a speed of approximately 18,000 rpm which it maintained until the boiler ran out of water in 9 minutes and 30 secs. The mass flow was approximately 1.6 lb/hr. The pressure was approximately 40 psig and there wasn’t any surging caused by slugs of water. Since there was no throttle valve, the pressure at the inlet of the turbine was almost the same as the boiler. The power required by the GWS EP 2508 propeller at 18,000 rpm is approximately 1.1 watts. This is the same performance I got in the table of the 19/07/2021 with a nozzle size of 0.028” and a pressure of 25 psig so the sleeve appears to be working reasonably well. Werner got approximately 3.9 watts with the same cast rotor in his turbine running at 35,000 rpm with a boiler pressure of 5 bar (73 psig), a turbine inlet pressure of 3.5 bar (51 psig), and a mass flow of 10.3 g/min. (1.4 lb/hr.) I’ll explain in the next post why I think Werner was able to get so much more power in his test than I got in this test.

Cover & Insert

Edited By Turbine Guy on 26/07/2021 20:17:44

Edited By Turbine Guy on 26/07/2021 20:20:03

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