Dynamic Viscosity of Saturated Steam Fractions

Hey Guys,

Does anyone know how to calculate the dynamic viscosity of a fluid and vapor mixture? I'm specifically interested in water and steam at saturation -- for instance, how do I calculate the viscosity when the dryness is 80 percent versus 20 percent, and so on. It's easy to find processes to estimate viscosity in liquid mixtures and gaseous mixtures, but a liquid/gas mixture isn't much talked about.

Thanks for any information.



Edited 1 time(s). Last edit at 12/04/2020 12:42PM by frustrated.

I don't but this might help.

Gas turbines second edition 2015

Dynamic Viscosity (VIS) and Reynolds Number (RE) (Formulae F19.9)
Dynamic viscosity is used to calculate the Reynolds number, which reflects the ratio of momentum to viscous forces present in a fluid. The Reynolds number is used in many performance calculations, such as for disc windage, and has a second-order effect on component efficiencies. Dynamic viscosity is a measure of the viscous forces and is a function of gas composition and static temperature. As viscosity has only a second-order effect on an engine cycle, total temperature may be used up to a Mach number of 0.6. The effect of fuel air ratio (gas composition) is negligible for practical purposes.
The units of viscosity of N s/m2 are derived from N/(m/s)/m; force per unit gradient of velocity. Gas velocity varies in a direction perpendicular to the flow in the boundary layers on all gas washed surfaces.

Rolly

Hi Rolly,

I think I found the answer. I did a number of Google searches, without any results, until I found the correct jargon -- then a number of references popped out. That's the problem with internet searches, the systems aren't very smart. Fortunately, I wasn't looking in Google patents -- it used to be that worked pretty good, until they "improved" it by adding patents from other countries. It's not that I am against an international database, it's just that they somehow screwed up the search capabilities. I have actually typed in a paragraph taken from a patent and not gotten any hits.

Anyhow, there's a number of ways to find the viscosity of a mixture -- some appear to be better than others. It doesn't look so much like a single mathematical formula as a process. I was looking for this so that I could calculate the pressure drop in a Lamont coil.

Regards,

Ken

Ken
Good luck with it

A forced circulation coil.

It depends on the pipe ID, pressure, length and feedwater rate and back pressure and BTU applied.
.
We started to get into these calculations when I was studying Jet engines but they had me switch to rockets and a lot of this stuff you never seam to use. You just need to know where and how to find it. In your eighties do I need to know today.

Rolly

Hi Rolly,

You're right on all those parameters -- the only other information you need is viscosity and there was no table or Excel plug-in showing viscosity depending upon steam fraction. As my instructor in boot camp said "Ain't nothin' never simple"!

Regards,

Ken

Ken
try these sites


Viscosity is a measure of a fluid's resistance to flow
That’s going to be variable with steam dependent on temperature.

[wiki.anton-paar.com]

[physics.info]

Rolly

Hi Rolly,

I think I found the answer. I've worked with viscosity for many years, but it was almost always in a fluid, occasionally in a gas. It's simple to determine viscosity for both water and steam, at a variety of pressures and temperatures. The problem was finding the viscosity for a saturated mix of steam and water at various vapor fractions -- the process is a bit more involved than one would assume right off the top of the head.

Regards,

Ken

You know Ken, I had this vary discussion with club and board member Tim N. As you know, he is a PH D in Mechanical Engineering. Our synopsis is that the calculation you are contemplating is a vary difficult one to simulate.

I also had a discussion with George N., who designed a Lamont type of system. He too agrees that the calculation is very difficult. George being a BSME from MIT.

Therefore, I believe a good approach is to compare known systems with what would be a given Square Foot / Boiler HP heat value.

Temperature, Flow Rate and Area are key factors in determining these values. I think you are focusing on the flow rate and I would offer the higher the better. Also would offer that to keep the phase as water, inside the Lamont Coil and nozzle into a separator tube/drum is important. Reason for this is the heating value (Hc) of water is far greater than that of Steam. Steam can and will have an effect to insulate as opposed to conduct heat. This is why tubes blow out.

I'm pretty sure you know all this stuff. Just trying to put some thoughts together for modern boiler design.

Hope this helps,
Rick

Hi Rick,

Mostly, I am trying to put together a spreadsheet capable of estimating pressure drop across the coil. It's not intuitive. Take a 5:1 circulation ratio. At the coil entrance, we can assume the flow is essentially saturated water. At the exit, the flow is about 5/6 by weight, but by volume it is overwhelmingly steam. I've dug up a few research papers that give various mathematical treatments for handling the void fraction and, when I get time, I'll need to do a little calculation for consistency. Fortunately, I have a degree in Business Administration and almost completed another in Accounting -- that sounds like a strange background but they really force you to learn your way around a spreadsheet. If necessary, I'm not afraid to make up my own functions, or to compile a lookup table with interpretation by splines.

Once you can calculate pressure drop, you can start to do "what-if" analysis on various diameter versus length tradeoffs. Likewise, you can start to design circulation pumps intelligently and also calculate probably pumping power requirements. My guess is that most people are trying to go with circulation coils having too small a tube diameter.

The other thing that I feel should be examined in a forced recirculation system is preserving kinetic energy. The velocity leaving the tube is quite high. If you can preserve much of that velocity and direct it through a nozzle at the pump suction, so as to reduce the velocity, you should be able to convert velocity back to pressure and reduce pump load. A drum isn't going to be the best mechanism for this due to turbulence -- drumless boilers appear a more appealing option, not only for reducing pump work but also to keep system volume in check. I'm looking at iterations Baker boilers that were not put into production, these had simplified water and steam reserve coils that might preserve motion and still permit decent steam separation.

Of course, if I ever get the chance, I'd like to test a thermopresser and have a rapidly circulating system with no moving parts...

Regards,

Ken

The Baker boiler is not a very easy boiler to duplicate but looks to be a very good steam generator. The center generating steam coil to the engine is actually two separate coils wound together. Not easy to do. I was thinking of making a model, but it would have to come apart or all you would see is what would appear to be is a coil of pipe.
See attached. I know of one never used and still in the factory crate.
Rolly

Hi Rolly,

I'm currently writing a book on the Baker cars for Tom Kimmel and had to research their patents. They had a number of boiler designs. Actually, the one that was used on the cars takes the basic boiler from one patent and the blow-down valve from another. Some of their boilers didn't have any vertical standpipes on the outer reserve coils, making for much simpler construction. A few of the boilers were a bit crazy, with something like the economizer being closest to the burner and the superheater near the flue. At least one used vertical tubes for reserve instead of coils and another also had firetubes going up through a large central standpipe. It was like part of the work was done when he was sober and the other part when he was stoned. Some of the engine valve gears also looked like their primary mission was to make things unnecessarily complicated -- I ended up doing isometric CAD drawings for one valve gear simply because every written description got confusing.

Regards,

Ken

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