Can someone check my work, please? 4

[gt5pilot]

This is a bit out of my area:

For air @ 80F:

d = 1.5mm (dia lumen)
L = 15cm (lumen length)
mu = 2.07 Pa.s
rho = 0.9996 kg.m^3
V = 1 m/s

Re = (rho * V * d)/ mu

Re = 0.00072 - is that really right?

Q = (V * pi * d * d)/4

Q = 1.77E-06 cc/min

That would mean a pressure loss of:

delatP = (128 * mu * L * Q)/ Pi * d * d * d * d)

= 4.42E+6 Pa or 640 psi - something seems off...but, I did say this is not my comfort zone.

Thanks for any help you can give me.

Kirk


Kirk B Olson
Senior Principal Engineer
HEII, Inc.

 

[gt5pilot]

[THREAD HIJACK ON...]

It seems as though the question that I asked has resulted in a quasi-political debate on the "best" unit...I wish that is what I had asked originally, then I would have felt I made a contribution to this board...

[THREAD HIJACK OFF...]

Kirk

Kirk B Olson
Senior Principal Engineer
HEII, Inc.

 

[IRstuff]

But that's the point, isn't it. Once the tools have matured enough, it's COMPLETELY irrelevant what system you use.

It's equivalent to arguing about whether you should use "*" or "x" to signify multiplication or arguing about whether a 5-scale or 9-scale sliderule is better. It makes no difference so long as the job is done accurately and in a timely manner.

TTFN

 

[vpl]

I must say I'm a bit surprised with the "let the computer figure out the units" attitude. I've found that fewer errors get made if you write out the units and do a unit analysis, rather than assuming a program will do it for you. A small bit of forethought usually reaps large rewards..

Patricia Lougheed

Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.

 

[IRstuff]

Mathcad does the unit analysis in-situ, for you, so there's no need to do a separate analysis.

It allows you to directly calculate BTU/hr-J, without any secondary conversions or analyses.

It's no different that if you entered a bunch of numbers with different exponents into a calculator. You assume and expect that the calculator will figure out the correct exponents in the final calculation. There's no need to verify the scale, as you would have needed to do with sliderules.

Automatic dimensioning is simply the next step in the evolution of math tools. I never have to worry about the units, because MAthcad treats the units in a similar fashion as calculator would with exponents. I have not used or needed to do any unit conversions manually or with some other program in many years.

The analyses I run are usually based on customer, i.e., the US military, specifications, which are often a mix of metric, English and anything the customer chooses or uses. It's not uncommon to find a requirement containing all of the following units:

m, yd, mi, nmi, um, kt, ft, in.

The only unit that wasn't included in Mathcad was the nautical mile, so that's permanently defined on my worksheet template. Calculate the lookdown angle as atan(alt(in ft)/rng(in nmi), and Mathcad merrily cranks out the angle, as it should. Diffraction blur diameter of 2.44lambda/aperture can be entered with lambda in angstroms and aperture in furlongs just as easily as entering lambda in microns and aperture in inches.

Therefore, it's completely irrelevant what units my customer uses and it makes no difference in the data entry or calculation process.

This is the next step in tool evolution and probably why there may not be any further movement toward SI units, as there no mechanical or calculation advantage to do so.

TTFN

 

[MariusChE]

Hi IRstuff

Now I know why there is a search party on Mars looking for a banged-up rover...

remove.marius@mailbox.co.za

 

[CARF]

WASHINGTON (AP) -- Failure to convert English measures to metric values caused the loss of the Mars Climate Orbiter, a spacecraft that smashed into the planet instead of reaching a safe orbit, a NASA investigation concluded Wednesday.

http://www.cnn.com/TECH/space/9911/10/orbiter.02/

: )

[ HIJACK STOP ]

 

[CARF]

OK OK OK one more from Greece,

- England is getting metric: millimeter by millimeter
- US is getting metric: inch by inch

Cheers,
CARF

[ HIJACK STOP ] ( Unless you wanna discuss football, but this maybe painfull for all of you ; )

 

[cah2oeng]

How 'bout them irish? Maybe touchdowns should be worth 10 points so the math would be easier.

Discuss.

 

[IRstuff]

AND, if you read through the article, you'll see that the units mismatch was only one of NINE contributing causes, ANY of which could have potentially prevented the accident.

FURTHERMORE, the article fails to explain HOW the interface specification was not properly vetted by the design teams and the design reviews.

So, ultimately, the failure was a process failure, NOT because of using any particular units, since obviously, if both teams had used the same English units, the module would have worked correctly. Therefore, the lead sentence of the article was designed for sensationalism, rather than verisimilitude

The Board recognizes that mistakes occur on spacecraft projects. However, sufficient processes are usually in place on projects to catch these mistakes before they become critical to mission success. Unfortunately for MCO, the root cause was not caught by the processes in-place in the MCO project..

from the MCO report:ftp://ftp.hq.nasa.gov/pub/pao/reports/1999/MCO_report.pdf


TTFN

 

[MariusChE]

IRstuff

A colleague of mine told me recently that your people (meaning aerospace) had accellerated a photon beyond c. Perhaps you are aware of this? From what he told me it seems that a photon possesses a certain duality, consisting of two equal parts with opposite spin (I think these are called bosons?). Anyhow, apparently these two particles will, when traveling along any plane, assume station with regard to each other.
Apparently (and please forgive me if this is total hogwash; I do not know any better) it is possible to bend one half of the photon into a detour. The other half continues straight on. Since the two must hold station on the straight line with respect to each other (is this a law?), the detoured particle is accellerated beyond c.

Could you kindly point me to the correct forum for this discussion.

Thanks
M

 

[IRstuff]

M,

That's more in the realm of theoretical physics. Not sure if there is really a forum for that particular subject.



TTFN

 

[CARF]

http://astronomyphysics.com/read.php?f=7&i=60&t=34&v=f

If beyond c is possible we could travel in time, kill Napoleon before introducing the SI system, and I would be drinking a gallon of beer now !

Cheers,
CARF

 

[jmw]

Back on thread, for gas viscosity, go here:

http://www.lmnoeng.com/Flow/GasViscosity.htm

JMW

http://www.viscoanalyser.com

Eng-Tips: Pro bono publico, by engineers, for engineers.

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[25362]

If looking for books with thermophysical info., Holman (Heat Transfer) provides tables for the following gases: He, H₂, O₂, N₂, CO₂, NH₃, water vapor, and air.

The tables provide data on density, viscosity, specific heat, thermal conductivity, diffusivity, and Prandtl number at amospheric pressure and at a wide range of temperatures.

 

[gt5pilot]

jmw & 25362 - thank you for the information, I have already looked at the website and have begun the search for books by Holman.

Ultimately, I will have to model the heat transfer from the selected gas through human tissue and try to calculate the depth of neucrosis for varying temperatures and times.

Kirk

Kirk B Olson
Senior Principal Engineer
HEII, Inc.

 

[IRstuff]

Are you trying to determine burn severity for different gases at different temperatures?

TTFN

 

[gt5pilot]

In the end, yes. The current system we have designed uses water at an elevated temperature to cause neucrosis in the tissue - there is a temperature vs. time. vs. pressure model that we know works for water, based on modeling and testing...we are in the process of trying to redesign the system to use gas.

Gas does not have the heat capacity of water, but, it has some safety advantages...as well, it can be heated to higher temperatures that the current therapy temperatures (~90C) to shporten the therapy time. Helium is the most promising gas to date...

Kirk



Kirk B Olson
Senior Principal Engineer
HEII, Inc.

 

[MariusChE]

Another problem solved by eng-tips.com

remove.marius@mailbox.co.za

 

[IRstuff]

Seems like there would be a large variability in the numbers without some sort of fixture that allows close contact and more controlled impingment.

Maybe something like an upside-down heat sink made from Teflon with an array of holes in the base. The fins would maintain a consistent spacing to the skin and the array of holes would more uniformly heat an area.

TTFN

 

[IRstuff]

Out of curiosity, how are you determining the degree of necrosis?

That used to be a big problem, because, without debridement and/or sectioning, the observational results were very subjective and varied according to the skill and experience of the doctor. One of our abandoned projects was to try and correlate hyperspectral imagery with objective lab measurements.

TTFN