Viscosity of Kerosene and Liquid Ogygen

[Urwumpe]

Thanks for that tblaxland, that makes sense.
Opened a real can of worms with this, I now have values for Lox in centi-Stokes, PascalSeconds, in centi-Poisse? and some odd unit called the SSU. Oh well, back to the calculator! When I was a lad it was in RedwoodSeconds

Use pascal seconds and stay metric if possible... I know it isn't easy if you use imperial historic documentation, but it is simpler getting constants and formulas for SI units.

 

[Notebook]

I'll give it a go, hadn't realised there were two variations on vicosity dynamic and kinematic.

N.

 

[agentgonzo]

And from what I have found quickly, another interesting fact: The density of liquid oxygen at -183°C is lower (1.14 g/L) as the density of the gas at 0°C (1.429 g/L).

Nope, you're out by a factor of 1000. The density of LOX is 1.14kg/L, not g/L.

 

[Urwumpe]

Nope, you're out by a factor of 1000. The density of LOX is 1.14kg/L, not g/L.

Must have been an error on the homepage which had such values in their tables.

 

[Notebook]

Did a bit more looking, and found these two sources.

For Kerosene
http://www.seed.slb.com/qa2/FAQView.cfm?ID=389

This gives Kerosene: 1.1 cP at 60 degree C, 2.4 cP at 20 degree C.

using 1cP = .001 PaS
equals 0.11e-2 PaS at 60 Degree C, 0.24e-2 PaS at 20 degree C.

For Lox.
http://www.iop.org/EJ/article/1367-...quest-id=6409ee7d-e5cb-4c77-933e-1686722abac9
Bottom of page 7.

This gives a straight value in Pascal Seconds of
2.2 × 10−4 Pa s at the boiling point of lox.

Taking the 20'C value of Kerosene, seems reasonable for ambient temperature, and shifting the decimal point to match the lox value gives
24 x 10-4?
So can I take it that Lox has a viscosity about 1/10 that of Kerosene?

N.

 

[Thunder Chicken]

The flow of LOX and kerosene in these turbopumps is highly turbulent, so the effect of the viscosity of the fluids on the flow and pump performance is very weak.

When sizing pumps, there are scaling equations used that generally ignore viscous effects. They technically are only correct when the Reynolds numbers (ratio of flow inertia to viscous forces) are the same for two geometrically similar pumps, but they are still approximately correct when the Reynolds numbers are both very high (turbulent flow) and on the same order of magnitude. So if you are pumping two different fluids with approximately the same density and the viscosities don't vary by more than an order of magnitude, you are probably OK.

However, if you try to pump something like cold maple syrup and want to pump air with the same design, this obviously is not going to work well, and the design would need to account for the radical change in viscosity (which is indicated by a huge difference in Reynolds number).

 

[Notebook]

Thanks for that ThunderChicken.
I think I can see that the difference in the physical size of the the pump part of the turbo-pump(lose the turbo part, the pumps are on the same shaft, and rotate at the same speed) is due to the fact they are designed to move different masses of liquid at the same exit pressures?
By different, I mean the kerosene:lox ratio(2.3:1 in this design).
So, viscosity has little impact on a pump of this design, as tblaxland say above?

N.

 

[Urwumpe]

It has an effect, but not the biggest. More important is the density of the liquid you pump, as well as the ratio of specific heats if you pump gases.

 

[Notebook]

Ok, I think we can agree on these two values?

2.2 × 10−4 Pa s at the boiling point of lox
and 24 x 10-4 Pa s at 20'C for kerosene.

This is still a long way from the ratio 16:1 I have in a reference book. It'll be next week before I have access to it, hopefully I've missed something that can clear up it.
Many thanks for all the help.

N.

 

[Thunder Chicken]

Thanks for that ThunderChicken.
I think I can see that the difference in the physical size of the the pump part of the turbo-pump(lose the turbo part, the pumps are on the same shaft, and rotate at the same speed) is due to the fact they are designed to move different masses of liquid at the same exit pressures?
By different, I mean the kerosene:lox ratio(2.3:1 in this design).
So, viscosity has little impact on a pump of this design, as tblaxland say above?

N.

That's correct. In order to pump these two fluids at different flow rates with the same shaft (and therefore same impeller RPM), the designs must be geometrically different (i.e. the kerosene pump isn't just a scaled down version of the lox pump, it will look different). So the difference in size is partly due to the fact that the flow rates are different, and partly due to the fact that they need to operate at different specific speeds (a non-dimensional parameter that defines the class of pump) so they can utilize the same shaft.

 

[Notebook]

At the risk of repeating stuff and boring folk to death!
This a schematic of the turbo-pump, badlly cropped I'm afraid, the left of diagram shows the lox side, the right the kerosene.

http://s89.photobucket.com/albums/k207/Notebook_04/?action=view&current=img018.jpg

This gives as much data as I can find about the turbo-pumps.
http://s89.photobucket.com/albums/k207/Notebook_04/?action=view&current=img024.jpg

That input impeller? has quite a surface area, if thats the right term, Surprised any lox gets past it.

N.

 

[Urwumpe]

Makes sense, the pump increases the volume flow and static pressure, so it makes sense the cross section of the outlet is lower than the inlet.

 

[Notebook]

As we've wandered off into turbo-pump land, and why not! here's a question thats bothered me before.

At engine cut-off, the fuel valves close and prevent the Kero/lox reaching the combustion chambers. You can see them in this schematic.

http://s89.photobucket.com/albums/k207/Notebook_04/?action=view&current=img012.jpg

At valve closure the turbo-pump is still running at full speed, and high pressure. Does the design just rely on the mechanical strength of the pumps, pipe-work and valves to absorb the hydraulic lock?

I can't see any by-pass, or pressure relief in the schematic.

N.

 

[Urwumpe]

Seems so, they could also close the gas generator valve first. One relief path of the liquid pressure would be the gas generator, if the main valves close.

But I would close Gas generator first, then main LOX valve.

 

[Notebook]

I'm not sure it helps, as I'm having trouble visualising whats going on, but there are films of the testing of this engine on this sitehttp://www.nationalarchives.gov.uk/films/1951to1964/filmpage_rocket.htm
(You have to use the windows media clips, the quicktime are of the EE Lighning, maybe somebody should tell them...)

At 56 seconds in to the item. you can see the engine shutdown. you can see some residual burning from the engine, at this point I assume the fuel valves have shut?
To the right of frame, the vertical pipe is the heat exchanger that carries the gas generator/turbine exhaust.
I think you can still see some gas flow from it? It could be just the turbine running down, as the gas generator fuel supply is also cut off at this time.
If it is, this implies the turbo-pump as still turning, unless the gas is leaking past the turbine blades?

Either way, there must be quite a "bang" inside when those propellant valves shut!

N.

 

[Urwumpe]

Well, what I wonder about - it has non-return valves in the gas generator lines, but not for the main lines. The gas generator seems to be made to cut off without a pressure transient traveling back to the pump.

 

[Notebook]

There is a simpler diagram:-

http://s89.photobucket.com/albums/k207/Notebook_04/?action=view&current=File0175.jpg

I'm not sure this helps. If you read these:-
http://s89.photobucket.com/albums/k207/Notebook_04/?action=view&current=img014-1.jpg
and
http://s89.photobucket.com/albums/k207/Notebook_04/?action=view&current=img015-1.jpg

The pressuriasation of the tanks and the turbo-pumps is quite complex!
That would be expexcted during the launch as the rocket leaves the ground services.

At engine cutt-off all those check valves, and non-return valves are redundant?

Edit:- while looking for more info on what happens to turbo-pumps at engine cut-off, I found this:-
https://www.cia.gov/library/center-for-the-study-of-intelligence/kent-csi/vol8no4/pdf/v08i4a03p.pdf
amazing what you can deduce from telemetry!
Intersting comment from last paragraph p.22 across to top of p.24.
Implies that the turbo-pump just winds down over 4-8 seconds when the propellant valves are closed?

Found some stuff about the RR RZ2 engine shutdown.

Complete shutdown occurs automatically should any of a number
of operating parameters, such as Lox-pump bearing temperature,
go outside specified limits. A predetermined degree of rough
combustion also results in shutdown. Programmed shutdown in
flight is triggered by the vehicle control system, the gas-generator
valve closing some 0.05sec in advance of the main Lox and K
valves. The K valve has a longer closing time, and the K-rich​

cutoff gives more repeatable decay and lower residual impulse.

Reading the last sentence, I take that as meaning the run-down of the turbo-pumps was no big deal, its the engine cut-off profile thats important.

All this makes me think the kero/lox impellers just rotated in the liquids, and came to a rapid, but not near instant stop after the valves were shut? Must have caused some stress on the gearbox?
In Blue Streak's case, all the flight engines were test-fired at Spadeadam, than went back to RR for inspection and rebuild. Then off to Woomera for launches.
N.

 

[Notebook]

Apologies for dredging up an old thread, especially one of my own!
Reason is I'm still looking at viscosity of different propellants, and while I can't get my hands on my copy till next week, Amazon let you do some viewing of their books.

This is the book:-[ame="http://www.amazon.com/gp/reader/0471326429/ref=sib_dp_pt#reader-link"]Amazon.com: Rocket Propulsion Elements, 7th Edition: George P. Sutton, Oscar Biblarz: Books[/ame]

Edit:- Didn't realise the reader works only for Amazon registered folk, so here's a picture

If you search on "viscoity", and look at page 256 Table 7-2 shows some properties.

The thing that surprises me is the viscosity of RP-1, its 10 times that of Kerosene.
I always thought that RP-1 was essentially Kerosene, with stricter QC?

Is this surprising. or should I get out more?



N.

 

[tblaxland]

The thing that surprises me is the viscosity of RP-1, its 10 times that of Kerosene.
I always thought that RP-1 was essentially Kerosene, with stricter QC?

Is this surprising. or should I get out more?

I'm not sure what the temperature dependence on viscosity is like for RP-1 &/or kerosene but you would expect it to get thicker as it cools (the table shows that the value of 16.5 is measured at 239K for RP-1, compared to 289K for the kerosene).

 

[Notebook]

Yes, thats a factor. It's quite difficult getting comparative values for these liquids. I'll have a deeper search, and try and get more data.

N.