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Calculation of Vertical Air Velocity

12/19/2013 1:37 AM

If I know the solar heat radiation in watt then how I can calculate the wind speed vertically flowing from the ground?

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#1

Re: calculation of Vertical air velocity

12/19/2013 1:59 AM

It's tiny in comparison with wind speeds. Measure it.

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#2
In reply to #1

Re: calculation of Vertical air velocity

12/19/2013 3:46 AM

Theoritical calculation is required for design calculation.

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#3

Re: calculation of Vertical air velocity

12/19/2013 3:49 AM

May be with an anemometer mounted horizontal, but this wind speed will be so minuscule, the anemometer calibration would have to be extremely accurate. You could play around and build one like this.

Good Luck and have fun

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#4
In reply to #3

Re: calculation of Vertical air velocity

12/19/2013 3:53 AM

You know the relation between solar heat radiation and vertical wind speed ?

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#5
In reply to #4

Re: calculation of Vertical air velocity

12/19/2013 4:01 AM

Virtually none. This has already been explained, but the explanations have unaccountably been voted off-topic.

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#6
In reply to #2

Re: calculation of Vertical air velocity

12/19/2013 7:58 AM

There more than one thing missing in your question.

How about telling us which design needs this calculation?

How about materials and temperatures?

Place on Earth, closed or open system, air pressure and all the little details that are needed to come up with something useful.

I'd install a fan and be done with the calculation.

Are you sure you know what you are doing?

I wonder if you was not needing a VBA script for your calculation. Or is that the next question?

Have fun and yes I also like it here!

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#7

Re: Calculation of Vertical Air Velocity

12/19/2013 8:35 AM

Except for caves with multiple openings, air does not flow from the ground.

It may expand away from the ground when heated.

From Wiki:

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Guru
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#8
In reply to #7

Re: Calculation of Vertical Air Velocity

12/19/2013 9:42 AM

Sound good, but what about circulation? Without any other forces wouldn't the air expand and then stagnate?

Is there a differential equation to account for rising heated air and falling cooled air?

.

On a side note, a classmate of mine in college did a presentation on a project he did for a component that was to be installed in the space station. He had to take thermal pictures of a motherboard to determine the heat values for each component. Then he had to optimize it for an air flow across the surface and calculate what would happen if the fan failed. He said the tough part is that without gravity convection didn't work...hot air doesn't rise or really move at all.

Drew K

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#9
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Re: Calculation of Vertical Air Velocity

12/19/2013 11:46 AM

Only if the land/ocean masses beneath the air were all at the same temperature.

Regarding satellites, most of the stuff I worked on was unmanned. So we had zero air to use for cooling. That meant supplying a thermal path for individual hot components that lead to a heat sink surface. Of course weight is at a premium so management always complained that I was adding too much weight with my thermal compounds.

And staking epoxies, too. I had to fight for an adequate weight budget to keep things from flying off the boards and cool enough.

And how do you tell hardware designers without security clearances that the heat dissipation factors of the component in air don't matter.

Interesting work, though.

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#10
In reply to #9

Re: Calculation of Vertical Air Velocity

12/19/2013 12:41 PM

I bet it was interesting work. Did you do any that were designed for an atmosphere?

What did you use as a heat sink for a vacuum? I have been curious how satellites shed heat (but not enough to google for myself :)

Drew K

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#11
In reply to #10

Re: Calculation of Vertical Air Velocity

12/19/2013 2:01 PM

Conduction in the form of thermally conductive epoxies/silicones and radiation in the form of black paint on the outside of aluminum enclosures. We built internal electronics housed in chem. etched and dip brazed housings. Some were made of copper, not many. Lot's of thought went into emissivity and absorptivity of paints we used.

They'd be bolted to internal bulkheads that then pumped the heat to the outer skin of the bird.

We'd run three legs of glop down the sides of TO5's and the like and use the backplanes and circuitry of the PWB's to get it spread out and then ultimately outside our box.

We never built the entire craft, just parts of it. That was long ago, back in the time of the Ferret and Keyhole.

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#12
In reply to #11

Re: Calculation of Vertical Air Velocity

12/19/2013 4:26 PM

So heat is radiated out as infa-red?

How much heat can you get rid of that way? What if you have a high heat load to remove?

Would you then be required to keep the dark side faced away from the sun? That seems like it would be tough considering the bird's orbital position. If a black painted aluminum panel sits in the sun doesn't it heat up your components?

I wish I could have worked on such projects.

Drew K

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#13
In reply to #12

Re: Calculation of Vertical Air Velocity

12/19/2013 4:56 PM

Well, the good news for us was that our stuff was inside the spacecraft, no solar radiation to deal with. We just had to keep our components from frying.

Our entire package was about a 2x2x3 foot cube. We determined the volume of unused space inside the package but filling it with alcohol and measuring the volume of liquid. Air space was wasted space.

Getting the heat out of the entire bird was the job of the guys an Lockeed and a few others who built the rest of the package.

That employed all sorts of devices. Radiators, louvers, cooling loops, I'd guess.

I never saw the complete package.

This is an earlier, now declassified version.

These were launched in the late '60s.

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#14
In reply to #13

Re: Calculation of Vertical Air Velocity

12/19/2013 6:06 PM

Nice...still wish I coulda been there. : )

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#15
In reply to #14

Re: Calculation of Vertical Air Velocity

12/19/2013 6:28 PM

I was lucky to have worked there. I met some "interesting" NSA spooks during that time.

I (not just by myself) did some really cool stuff while there.

In addition to lots of satellites and ground based spook things, we built some of the first satellite radio locater collars for Polar Bears. And solar powered beacons to track Sea Otters when they were on the ocean's surface.

I spent 23 years there.

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#16

Re: Calculation of Vertical Air Velocity

12/19/2013 11:09 PM

Dear Mr. amitabha0107

The density difference will be the deciding factor for the velocity. How much the air gets heated is to be known to calculate the velocity.

DHAYANANDHAN.S

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#17
In reply to #9

Re: Calculation of Vertical Air Velocity

12/19/2013 11:31 PM

Why would you not be able to explain thermal transfer to someone without a security clearance? My freshman physics teacher did a fine job and as far as I know nobody was cleared for it.

In a passive system the thermal energy would have to be either radiated directly from the component or conducted through a thermal conduction path to a thermal radiator.

The Stefan-Boltzmann Law explains HOW radiation transfer rate is a function of temperature.

Thermal management is a cool subject - the most efficient approach is to generate as little thermal waste heat as possible, from there on my imagination tells me there could be some very cool and unique approaches to taking care of the business.

My first two considerations would be to either pressurize or purge and evacuate the compartment with a thermally conductive gas that has a high transparency to IR and make the compartment out of thin copper or some other material with the highest thermal conductivity as possible. The thinner the distance between the components and the compartment walls the better.

Perhaps mount the electronics package components on or near the compartment wall, reducing or eliminating the need for gas enclosure.

Then let Stefan-Boltzmann work.

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#18
In reply to #17

Re: Calculation of Vertical Air Velocity

12/20/2013 12:06 AM

It surely covered in this thread

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#19
In reply to #17

Re: Calculation of Vertical Air Velocity

12/20/2013 12:07 AM

"Why would you not be able to explain thermal transfer to someone without a security clearance?"

Ever worked on highly classified government projects? Security clearances were very thorough and very expensive. They weren't "cleared". These guys were not allowed to know that the hardware they were working on was going into an orbital spy satellite, where there was no air.

Their job was to design a working system. My job was to keep it alive without air or gravity to cool it.

Passive system: #11

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#20

Re: Calculation of Vertical Air Velocity

12/20/2013 12:08 AM

There is no direct relation between solar heat radiation and vertical wind speed at ground level. The hot ground level air will not flow vertically unless it is replaced by cold air from somewhere. On a large area, therefore, there is no reason for vertical air flow.

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#21

Re: Calculation of Vertical Air Velocity

12/20/2013 12:24 AM

Intuition tells me Solar Insolation Rate is only one of a number of variables required to know the vertical acceleration of an air mass.

Perhaps a good start would be a technical explanation from a Hot Air Balloon Pilot as to what gives his aircraft lift.

I believe the first requirement for understanding atmospheric convection would be to determine if air density varies as a function of both temperature and pressure. The Gas Law.

The process of heating air through solar insolation probably has much to do with the color and texture (albedo) of the ground below the air which, through the process of contact conduction and IR radiation then transfers some of that energy to the air.

I believe air is quite transparent to the wave lengths of solar insolation - not so transparent to IR.

The vertical acceleration of the air near the ground, in absence of a horizontal component, would be a function of the temperature differential with the surrounding air.

If there was a black plowed field surrounded by snow covered grass then that temperature differential could be quite significant. .

By knowing the difference in temperature of the surrounding air, at the same distance above the ground, the difference in density could be determined?

Once that is determined the vertical acceleration at that specific point above the ground could be calculated.

Due to Coriolis Force I believe air has a tendency to form a vortex as the "thermal" rises with the core of that thermal having a higher vertical velocity component than the air surrounding it. (venturi?)

There are a lot variables - solar insolation rate alone is totally inadequate, in and of itself, to define the vertical component of air convection.

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#22
In reply to #21

Re: Calculation of Vertical Air Velocity

12/20/2013 12:45 AM

Not knowing all the details variables of what OP chose to leave out is why I believe in the KISS concept of an anemometer, #3

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#23
In reply to #7

Re: Calculation of Vertical Air Velocity

12/20/2013 4:50 AM

air does not flow from the ground

Sailplane pilots might disagree with this one. How far above the ground does a thermal originate?

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#24
In reply to #11

Re: Calculation of Vertical Air Velocity

12/20/2013 6:23 AM

"back in the time of the Ferret and Keyhole" - thought you were talking about a pub (but then I've got a bit of a one-track mind )

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#25
In reply to #15

Re: Calculation of Vertical Air Velocity

12/20/2013 9:09 AM

Lyn,

I did not know that you are such a big engg. 23 years in NASA - Lucky & not a matter of joke.

I have heard that NASA had sent few experimental animals in space. Did they carry out any experiment over the "fertility & embryo development" of animals in space at zero gravity?

This is just for curiosity. As this off topic & if it is a state secret issue you need not answer.

Thanks.

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#26

Re: Calculation of Vertical Air Velocity

12/20/2013 9:16 AM

You can't. There are other variables involved. The sun heats the ground which heats the air above it, so the air closest to the ground is warmer than air above. This change in temperature with altitude is the temperature gradient. This varies by terrain. For example, air is heated much more over a plowed field than over vegetation with the same amount of solar radiation.

Consider a parcel of air. As it rises, it cools because the pressure drops. This change in temperature is the adiabatic lapse rate. The temperature gradient must be greater than the adiabatic lapse rate for the air to circulate by convection and there is no vertical air speed until this threshold is reached.

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#27
In reply to #24

Re: Calculation of Vertical Air Velocity

12/20/2013 10:14 AM

It does have a certain "ring" to it, I'll agree.

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#28
In reply to #7

Re: Calculation of Vertical Air Velocity

12/20/2013 10:20 AM

Lyn: I am somewhat surprised at your answer! Have you totally forgotten about convection? One need only drive down a highway at noon in the summer to witness the schlieren effect due to differences in refraction of warm air rising off the pavement. Mirages are all of a similar nature. Yes, it has to do with expansion, but that only matters in a closed system, actually in a closed system it would be isochoric, and not isobaric. OP did not specifically state closed system, but where in the world is a truly closed system (and adiabatic)?

Therefore, after further review, the play on the field is overturned.

Updraft winds can be measured, but you need a specialized tool for that. It does not involve blocking the horizontal component of wind velocity. I think it takes Doppler radar, or something like that.

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#29
In reply to #28

Re: Calculation of Vertical Air Velocity

12/20/2013 10:27 AM

James,

To my mind, "flowing from the ground", as the OP states, means emanating from the ground, as water flows from a spring.

The earth does not discharge air into the atmosphere, although it might warm air and cause it to rise.

After further review of the review, the play stands.

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#30
In reply to #24

Re: Calculation of Vertical Air Velocity

12/20/2013 10:27 AM

Did someone say Pub? But then again, if you are not a Green King fan there is always the freehouse...

Drew K

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#31
In reply to #25

Re: Calculation of Vertical Air Velocity

12/20/2013 12:58 PM

SYED MD. ANWAR UL ISLAM,

I'm not a big engineer. I was just a member of many teams over the years that worked on different projects.

Also, while NASA (National Aeronautics and Space Administration) did launch many of the satellites we worked on, NSA (National Security Agency) was the customer for many of the classified (secret) projects.

To the best of my knowledge, I never worked on any spacecraft that carried animal experiments.

Everything I mentioned here is a matter of public record.

Thank you.

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#32
In reply to #20

Re: Calculation of Vertical Air Velocity

12/20/2013 9:34 PM

The hot ground level air will not flow vertically unless it is replaced by cold air from somewhere. On a large area, therefore, there is no reason for vertical air flow.

There is colder air above it. If the thermal gradient exceeds the adiabatic lapse rate, the air will be unstable and convection cells will spontaneously form.

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#33
In reply to #32

Re: Calculation of Vertical Air Velocity

12/20/2013 10:13 PM

...in which case the net down flow will equal the net up flow.

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#34
In reply to #26

Re: Calculation of Vertical Air Velocity

12/22/2013 10:52 PM

How this is calculated? Please guide me.I want to know the process.

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#35
In reply to #34

Re: Calculation of Vertical Air Velocity

12/22/2013 11:56 PM

There are so many variables involed that you can not calculate by any simple formulas.

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#36

Re: Calculation of Vertical Air Velocity

12/25/2013 11:00 AM

In 1963 Edward Lorenz developed a simplified mathematical model for atmospheric convection, where air is heated from below and cooled from above. The model, known as the Lorenz Equations, consist of three very simple, ordinary, second order differential equations in x,y,and z.

dx/dt= s(y-x)

dy/dt= x(p-z)-y

dz/dt=xy-bz

where s,p,and b are parameters of the model.

This system of equations triggered a revolution in Mathematical analysis. Chaos!

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#37

Re: Calculation of Vertical Air Velocity

01/02/2014 9:43 AM

For God's sakes, man, measure it with a neutral bouyancy balloon. At time t=0, release the balloon. From distance d, record the time it takes for the balloon to rise to a 45 degree angle to the observer (at distance d). Height h at time t(45), is such that h=d. Divide h by t(45), and you have the vertical component. If the balloon dirfts off somewhere into the distance or pops, do not blame me, I only devised a thought experiment for you.

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#38

Re: Calculation of Vertical Air Velocity

01/17/2014 11:44 PM

As I have no idea why you pose the question, I'd refer you to a nice little staring point called the Cauchy tensor. Our atmosphere-or our oceans for that matter are vast, and so are any significant calculations regarding large areas. We have no idea of the scope you have in mind. Earth to low Earth orbit? Launching an experimental plane?

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#39
In reply to #33

Re: Calculation of Vertical Air Velocity

01/22/2014 9:50 AM

Yes to that, on a global scale, but not on a local scale. I have never seen engineers less willing to exploit a gift of nature than in this forum, but that's a joke, son.

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