Williams ws. Rankin

Andy
After you build and run boilers and engines most of you life then you can use all the cutoff calculation you want. It doesn’t work in real life. You have piston blow by, packing losses heat losses, valve losses.

Now children, play nice.

I tried to determine the volume from the Steam Tables and got confused, more so than usual.

I am not sure what I am looking at.

I tried using Rolly’s example and got nowhere.

The only source I have here at work is only:

[www.energysolutionscenter.org]

I came up with 6.28 inches of volume from his 1 x 2 inch cylinder. That gives me 11304 inches per minute at 1800 RPM.

I tried to look it up for 585 PSIa and get .02278??? If I multiply that times 11304 I get 257.6???

This is all new to me.

Any help is appreciated.

George
I used a double acting cylinder.
Cylinder volume of 3.1416 total cu / inch. In one hour at
1800 rpm = 339,293
585 PSI gage is 48 cu inch of steam from one cu inch of water.

When you get fully familiar with Dr Frederick G. Keyes work,,you may enjoy the fruits of labor,,,which he saw years before and realized the value,to us all,,, He was also a fine judge of motorcars,,and maintined his car with passion,,,to the extent,,when it needed more than plug and a tune,,,he meerly drove it back into its very own shipping crate,and shiped it back to the factory for servace,,,hows that for being a perfectionist,,,Gentleman of the old school,,,fond memories,,,[P-ll Henley roadster] Cheers Ben

Rolly,

I got it now, although I still cannot find the number for 585 PSIa for steam from the chart I have, but I do have the K&K Steam book at home I bought recently.

I think I got it now: .027xxx Cu-Ft. X 12 X 12 X 12 = ~48 Cu-In

Peter,

I called Judy and ordered the three volumes. I'll PDF them once I get them and have it for reference.

Anyone asked Tom to put this together as a primer?

George

Hi George.

1" bore
2" stroke
Double acting

Displacement = Pi*bore^2*stroke*2/4 = 3.14159265*1^2*2*2/4 = 3.141593 cuin per revoloution

Displacement*RPM*60/(12*12*12) = 3.141593 * 1800 * 60 /(12*12*12) = 196.349541 cuft/hr

Saturated steam specific volume at 585 PSIA and 483.5 F is 0.790108 cuft/lb
Feed warter density at 180 F is 0.016510

196.349541/0.790108 = 248.509755 lb/hr

producing 30 HP

248.509755/30 = 8.283659 lb/HP/hr

This may sound like a silly question, but if you get such a large HP number out of a small cylinder like this, where is the inefficiency occur? Seems to me you could run circles around anything else out there, yet IC is more efficient?

Speed may not be efficient,,,Ben

Rolly, I prefer to use methods explained in many many text books, then your seat of the pants methods.

Calculate therotical values and adjust by specific fudge factors for the engine type size etc.

Rolly, Would your method be low or high if the engine was running 95% cutoff?

The fudge factors I think range from about 15% to 35%. Im sure the minum isn't any less then 15%. Maxum maybegreater then 35% don't have books with me.

95%*15%=109.25%

My text book method at 9.05 lb/HP/hr using minum fudge factor of 15% is 9.25% greater then your calculated steam usage.

Andy

In a steam engine efficiency and power density are inversly related.

To get higher efficiency cutoff is shortened to use more expansive energy.

You get less work out but more work per pound of steam.

Power + work/time

Work = force * distance

Say in one case we admit steam for the full stroke. The work done is at a constant force (pressure*piston area) for the full stroke distance. In a second case we admit steam for 1/2 the stroke and let it expand for the other half. In this case we have work for half the stroke at full pressure and work for the last half at a decaying pressure as the pressure drops during expansion. In the second case the engine uses 1/2 the steam but produces much more then 1/2 the work. The second case is more efficient producing less power.

In the piston or any positive displacment steam engine many things you do to improve thermal efficiency reduces the power of the engine. increasing expansion increases efficiency, reduces power. Compresssion of residual steam in the cylander to fill clearance space at inlet pressure reduces output power by the ampunt used doing that compression. You can reduce leakage around moving parts and probably increase fricion losses.

Andy

Andy
That’s a little engine, Build it and show me 30 HP
You can use any thing you want to do your calculation. But you will never get 30 HP out of an engine that small.
If your using PLAN to figure HP forget it. That is only cylinder HP. You need to take it one step further X 55% for frictional losses. A friend of mine and I figured fifteen running engines and the % ranged was from 53% to 65%. Even the 9 HP I project is in dream world as I don’t think you could build such a small engine to hold up to that kind of HP. Doble uniflow If I remember started around 25% cut off and ran around 12%.
No engine I know of runs at 95% cut off. Most engines with exocentric are set around 127 degrees giving on start up about 65% on the down stroke and 55 % on the up stroke and link up is only about 40 % running. Geometry of exocentric
But with other valve gear any thing is possible ?

I used what your stated as horse power. I thought! I didn't figure horse power my self. Sorry miss read your post. It was 30 gal you said and six HP. Oh well.

As for the 95% and excentric timming. How does any of that apply to this:

[www.survivingworldsteam.com]

I see no excentrics or crank or...




Edited 1 time(s). Last edit at 07/11/2007 06:40PM by Andy.

Hi George,

Right on! It takes time to figure out, so have patience. Having a specific engine in mind is a good motivator. Took me lots of calcs on lots of engine ideas to get to where the numbers agreed. But it is a fascinating and fun challenge.

Kent's _Mechanical Engineer's Handbook_, 11th (or earlier) Edition, Chapter 7, has some extremely cool shortcut charts so you can easily estimate actual efficiency/steam use according to type of engine, cutoff, and other factors. These are the charts the pros used when engineering real products. 20% efficient, btw, is tough to get and pretty rare in small engines. I'm always impressed when I see numbers that big, especially in daily workhorse use instead of bench tests (another important/underemphasized difference). Big reciprocating steam engines are much more efficient than small ones. 10-15% is relatively easy ... which isn't saying much ... above that, rapidly diminishing returns ...

Rolly's right, actual steam use (lbs of steam per hp/hour) is different from theoretical. All the engineering books & operators agree, all of them, no debate. This is very important. Leaks, surface losses, all sorts of stuff happens inside any real engine. That is where the "chart factors" come in, for more accurate estimates. Lots of real-world messy stuff modifies theoretical calculations. Chart factors are based on lots of real measurements of lots of real engines. There are ways to reduce the losses, but they can get very tricky esp when cost/benefit estimates nose in.

IC engines have similar occult messiness, BTW. Notice that crankcase breather hose on any modern engine, not to mention the capacious catalytic converter (wasted-fuel burner, efficiency red flag) or the CDROMfuls of software in the control box. Those are just the more obvious signs.

Anyway, enjoy the basics for now, great stuff. Theory first, then modifications.

Brief comments from longtimers with real equipment are often worth many pages of theoretical discussions. Watch for banana peels, but also for gold nuggets. That's my experience so far, anyway.

Sidebar item, Stan Jakuba noted in the Bulletin that SES got their best efficiency at 3:1 expansion ratio. Their engine could expand a lot more than that. Hm, 3:1 sounds like some steam automobiles I've heard about ... and taken rides in ... tell it to Stan ... no pessimism/Luddism here, note regenerative cycles ...

Hi Ben, Thanks for the story about Mr. Keyes' automobile packing crate. Keep 'em coming. Parcel Post or UPS? Wonder where I put the original carton for my Bug? LOL. With my luck, VW would mix up the crates and send back a Veyron. Bleh, water cooled.

Peter

Peter, I purchased and received the three back issues and I scanned them into PDF's. If anyone wants it, let me know. I don't want to take away from the club selling the back issues, so you will have to ask me and/or e-mail me.

George

Hi all,

Been gone on vacation for about 8 days.

George,

Think of pounds per hour(steam) as equivelent to cubic feet of air(gas) per minute. In this way, volume, is considered for. With steam, british thermal units are really close to volume units, as per the steam tables. With gas(air, nitrogen, co2, or argon) these can be considered non-condensable above 70F. Since there expansion(the gasses) is mostly limited within the 70F temp range(superheated), not-so with water/steam(going thru expansion range).

This disscussion would make an excellent thread under the topic, "expansion ratios, calculated thru working volume"

best to all

Jeremy

Jeremy, mass and volume are not in any way equlivant. Especially for a gas. If you know the temperature and volume (not specific volume), can you calculate the pressure? No! You also need to know the mass. You need temperature and specific volume. If you know the temperature and pressure you can figure specific volume. Then knowing specific volume you can figure the pounds knowing the volume.

At 467.0F 1 pound of 500 PSIA steam occupies 0.92763 ft^3 heat content (enthalpy) of 1204.7
At 500.0F 1 pound of 500 PSIA steam occupies 0.99191 ft^3 heat content (enthalpy) of 1231.2
At 600.0F 1 pound of 500 PSIA steam occupies 1.15843 ft^3 heat content (enthalpy) of 1299.1
At 700.0F 1 pound of 500 PSIA steam occupies 1.30375 ft^3 heat content (enthalpy) of 1357.7
At 800.0F 1 pound of 500 PSIA steam occupies 1.43969 ft^3 heat content (enthalpy) of 1412.7
At 467.0F 1 pound of 150 PSIA steam occupies 3.53275 ft^3 heat content (enthalpy) of 1256.6

Jeremy said: "With steam, british thermal units are really close to volume units, as per the steam tables".
They are?! How do you figure that?

Andy

Hi Andy,

Molier(sp?) diagrams.

I think that for me, it goes back to 'un-evenly' heating water in pressure vessels, weras at average temps of like 450*f, for the unit. I observed static pressure in excess of 2000psi. The average temp was 450*f but there were hotspots to explain the peak pressures. I should remark this is only noticable if the space is enclosed, and there is no transfer of volume. Notice you are using enthalpy, to figure this. Its more an isothermic(sp?) reaction in a closed vessel. I havent got my books out right now.

I will start the new tread if you want["expansion ratios, calculated thru working volume"] , but I think your perspective would be refreshing, to start it out with.

Jeremy

-EDIT-

"Its more an isothermic(sp?) reaction "

I meant to say 'isetropic' instead of isothermic.

Uknow, ive routinely buried(pegged) 10,000psi gauges with some of my experimenting.

Jeremy



Edited 1 time(s). Last edit at 07/20/2007 04:46PM by Jeremy Holmes.

jeremy

I wasn't using heat content(enthalpy). I list some state points. Basicly steam table entries execpt I used IFC formulations that calculate them. What I was showing was that specific volume varies depending on other properties. No state point is dependent on a single other propety. It usually takes two properties to deturm a state point.

A long the saturation line you have a mixture of vapor and liquid. Along the saturation line you can deturmin the temperature from the pressure and vise versa. But for other properties you need to know the quality(percentage of vapor in the mix). Any way if you look at thoes states I posted you can see that the volume is not a function of enthalpy. The following linies illistrate what I am talking about:

At 500F 1 pound of 500 PSIA steam occupies 0.99191 ft^3 heat content (enthalpy) of 1231.2 BTU
At 467F 1 pound of 150 PSIA steam occupies 3.53275 ft^3 heat content (enthalpy) of 1256.6 BTU
At 600F 1 pound of 500 PSIA steam occupies 1.15843 ft^3 heat content (enthalpy) of 1299.1 BTU

You can deturmin the volume knowing the Pressure and enthalpy. Pressure has a big effect on volume.

You said : "With steam, british thermal units are really close to volume units, as per the steam tables"

And that just does not make any sense to me. I figured you were talking about enthalpy mesured in BTU. Enthalpy BTU are no were near clse to volume.

Start the thread "expansion ratios, calculated thru working volume" if you wont. Some of these threads are getting too long. Williams vs Rankine for instance. That one is taking way to long to work with. I have reserted to opening new messages in seperate browser windows so then can be loading while I look at other messages and threads.

"expansion ratios, calculated thru working volume" expansion ratios are volume ratios. but I not sure the what you mean by "calculated thru working volume".

Also explain that criptic post a bit. Volume rate and mass rate or both ways of mesuring flows but not the same really. One can be deturmined from the other only when the density(or specific volume) is known.

Andy

HI. Guys I fort you would like to no iamb going in for open hart surgery on the 24 of September. I will have a valve replace. And a dubl bypass.Howard

BEST WISHES AND SPEEDY RECOVERY,,,BEN

A Valve job and dual bypass. Howard you just have to hop up everything you come across, don't you?

Best of recovery and God bless.

Bill G.

HI. Guys thank for the good wishes. Ily post the phone member for the .C.H.U

Hope every thing goes well. Best wishes.

Andy

Wishing you the best
Harry and Frankie

HI. Andy Harry and Frankie. Hanks for the good words Howard

HI Guys new problem. I have to have a prostate gland an operation is for my hart operation so the hart is on hold for a while

vHI Guys sum of the problems of doing a squeaky clean test on the Williams are finding a testing institute vat do steam car engines. The tow we tried wore incompetent as they frot the green monsters boiler would explode and blow up the building. Only a 200000$ code boiler would do. I can go on. I will say one can have a P.H.D, and be a fool the test is being dun by a group of steam people

HI guys I am back from my ftrerst operation. It didn’t go as it could bin im just able to sit in my computer chare. So vats why I have not don a
Post is for. The first dynode test will be dun Wednesday. Howard

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