[PSUBS-MAILIST] air flow vs. water flow

[Alec Smyth via Personal_Submersibles]

I studied the math, but have had time to forget some of it. So my proposed
solution is to just pose the question here, and get well informed responses
in no time! Antoine and Cliff's responses agreed nicely -- thanks guys. I'm
looking forward to diving in a sub that dives in 2 seconds, that will be
interesting!

Alec



On Fri, Mar 30, 2018 at 10:53 PM, Alan via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Hank,
> I sit in your camp. It is probably quicker than studying maths for
> several years!
> Alan
>
> Sent from my iPad
>
> On 31/03/2018, at 1:50 PM, hank pronk via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> Cliff, your right, you would figure it out during a commercial watching
> the football game on Sunday. I would drive to the lake, annoy a fisherman,
> lie to a tree hugger and probably be late for supper. But in the end we
> would both have it.
> Hank
>
> On Friday, March 30, 2018, 6:32:59 PM MDT, Cliff Redus via
> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
>
> To get a first order approximation, assume turbulent pressure drop in a
> pipe nipple.  Write two cases, one for air and one for water at same
> temperature and pressure near surface and same pressure drop .  This will
> give you that the Vair is equal to Vwat times the square root of ratio of
> water over density over air  and ratio of  friction factor of water over
> the friction factor of air.  Assume friction factors are the same for first
> order approximation.   Va=Vw*(density_w/densityair * fw/fa)^0.5 At the
> surface this reduces to Va=29*Vw for the same pressure drop.  So if took 60
> sections for water, it would take 2 seconds for air.  This assumes the
> limiting factor is the turbulent pressure drop through the MBT vent valve.
> If the MBT flood valve was to small, then, it would start to impact how
> quickly the MBT would fill with water.  In the real world it is a
> combination of the turbulent frictional resisence through both the MBT vent
> and flood valves.   For better approximation use CFD code to model the MBT
> including the MBT vent and flood ports.
>
> What hank would have already done.  Find a 55 gal oil drum from behind his
> shop.  Remove the 2" cap from the top and turn the drum upside down. Cut
> out a hole to fit the new MBT valve.  Put the drum and attached MBT valve
> in the back of his truck and head to the nearest lake.  Suspend a 20 lb
> weight below the drum so it floats.  Open the MBT and measure how long this
> MBT takes to completely flood.  Prorate this time based on volume of Psub
> MBT compared to 55 gals.
>
> Cliff
>
> On Thu, Mar 29, 2018 at 11:35 AM, Alec Smyth via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> Hi everyone,
>
> I was testing one of my new MBTs yesterday, removed from the sub, by
> turning it upside down and filling it with water, then opening the mushroom
> valve to let the water out. It takes 60 seconds to empty. In actual
> operation it will be air instead of water coming out that valve. The
> pressure will be the same, but because it will be air instead of water the
> tank should empty much faster. The question is, does anyone know more or
> less *how much* faster? One should be able to calculate this with
> Bernoulli's formula, but this is very turbulent flow so not sure if it
> would really hold. Any rules of thumb?
>
>
> Thanks,
> Alec
>
> ______________________________ _________________
> Personal_Submersibles mailing list
> Personal_Submersibles at psubs. org <Personal_Submersibles at psubs.org>
> http://www.psubs.org/mailman/ listinfo.cgi/personal_ submersibles
> <http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles>
>
>
> _______________________________________________
> Personal_Submersibles mailing list
> Personal_Submersibles at psubs.org
> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>
> _______________________________________________
> Personal_Submersibles mailing list
> Personal_Submersibles at psubs.org
> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>
>
> _______________________________________________
> Personal_Submersibles mailing list
> Personal_Submersibles at psubs.org
> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.whoweb.com/pipermail/personal_submersibles/attachments/20180331/cb6227b7/attachment.html>