Recognise this formula

[stanier]

hi,

Does anyone recognise this formula mu * Cp/k ?

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King

http://waterhammer.hopout.com.au/

 

[VEBill]

Lubrication viscosity? Pr=mu*cp/(k) ?

Not my area, but my google-fu is strong.

 

[BigInch]

http://www.processassociates.com/process/dimen/dn_pra.htm

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[TGS4]

BigInch nailed it - it's the Prandtl number.

 

[IRstuff]

VE1BLL got it first Pr is the symbol for the Prandtl number.

TTFN
faq731-376

 

[TGS4]

IRStuff - you're right. Credit where credit is due. Mea culpa.

 

[VEBill]

I'll take a half credit for mindless googling; I wouldn't know a Prandtl from a penguin.

 

[ivymike]

and the penguin only noticed that 32F water feels colder than 32F air, and the water seems colder yet when he swims fast.

 

[BigInch]

Pr, in conjunction with the Grashoff number are important parameters for helping in determining the heat transfer coefficient across a fluid film boundry, such as pipe wall to a liquid or gas flowing inside. Basically determining if convection or conduction control and then setting the degree that each one affects the whole allowing the individual contributions to the OHTC to be determined and evaluated... if I remember correctly.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[ivymike]

oh, the poor freezing penguin.

 

[BigInch]

Assuming that he's a salt water penguin, at 32F, technically he isn't freezing.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[stanier]

Cheers & apologies. I would have Googled but didnt know how to put in a Greek letter. I did try it after posting using the letters "mu" and it came up instantly.

Lesson to myself: Google before asking a question. Dont be lazy. What a clutz. How often have I expressed that to posters?

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King

http://waterhammer.hopout.com.au/

 

[unclesyd]

Boy! does the mention of Prandtl Number bring back some very memories, 1958 to be exact. I had been working only a couple of months when the company decided to build a distillation column to separate two components by distillation who's boiling point was only 1°C apart. Our group was tasked to use the McCabe-Thiele Diagram approach for the number of theoretical trays needed. To get the diagram below the pinch point we got to use the IBM Mainframe Computer. I don't recall the programming language but it took many thousands of punch cards to generate the data points for the curve. Of the twenty or so punch cards operators I don't remember anyone speaking to use as we hand them the data to enter. We had to have two hard wired boards to help with the speed. The time per run was approximately one hour and output was on rolls of printer paper. The end result was that it would take approximately 202 theoretical trays which would have made the column 220' high, all SS.
We were giving ourselves a hardy congratulations when Dr. Bill Moore dropped by and asked how were things going. We told hive of our accomplishment and as we talked he picked up my slide rule an said don't tell me let me guess. He put down some information and started use th slide rule. After about 5 minutes he said that it would take approximately 200 Theoretical trays and the column would have to be 210' tall.
One column was built in Decatur Al, but the one planned for Florida never got beyond design.
I just recently learn the column project has be resurrected and will be built using 200 theoretical trays in a 220' foot column. I understand that the new calculations took about 1 minute.
There are numerous Distillation+Theoretical+Stages+Calculators on the web

 

[BigInch]

I think I'd try to find Dr. Bill first.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[unclesyd]

Biginch

That had came up but everyone thought the results were to far out to be handled on the slide-rule. I not exactly sure how he worked it out. I do recall there was mention of a series and finding the N^th term that would give a number for the concentration, moles/million moles, desired in our case it was 10.
Another irony is that subsequently we had a non-distillation process where we could reduce the
impurity to zero. We produced 500,000 lbs of zero impurity in the Hexamethylenediamine {HMD}
As the impurity Diaminocyclohexane {DCH} was supposed to cause all manner of problems in the manufacture and physical properties of Nylon, wondrous things were supposed to happen as we ran the material through the process. Absolutely nothing changed in production or physical properties Nylon produced. We went back to the existing purification process where the DCH was allowed to range from 50-150 moles/million moles.

 

[Skogsgurra]

I really, really thought it was about Schwackhoefer's constant, or Planck's. What is a Prandtl? And is it really spelt that way? And why are all these numbers German-sounding?

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[VEBill]

 

[zdas04]

Before about 1940 nearly everything worth reading in Fluid Dynamics was written in German (and the little that was in French or English had been translated to German). Researchers in the UK and the US submitted fluids papers in German for peer review. They did graduate work at the University of Leipzig and the Technical University Munich. Before that time you really couldn't call your self a Fluid Dynamics Engineer if you couldn't speak German.

After WWII that changed and many of the seminal works from before the war were translated to English and to other languages. Before WWII if you wanted to read about fluids you pretty much had to do it in German.

German names dominate, but names like Buckingham (an American), Stokes (a Brit), Navier (French) have a pretty prominent place.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[Skogsgurra]

That is interesting. Thanks for the insight, David.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[BigInch]

Probably due to rounding up all the German scientists at the end of the war and giving them visas if they'd start speaking and writing in English, or ... Russian.

If it ain't broke, don't fix it. If it's not safe ... make it that way.