×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

flow performance test

flow performance test

flow performance test

(OP)
At work we have a metal shed that sits in full sun. We cut windows (no glass just open holes about 1 x 1 meter) in it to improve ventilation. However the holes had to have louvers in order to keep the rain out. Vermin was also a problem. wire mesh had to cover the 1x1 meter hole. The louvers also reinforced this mesh from wobbling as it is too frail to span 1 meter.

I think the design of these louvers is an overkill. While they do a wonderful gob keeping the rain out, they reduce the ventilation. I would like to remove every 2nd louver. This would increase ventilation but still be adequate to keep the rain out. I can model it in Inventor or 3d Autocad. How do I test the flow? I'd like a before my proposed modifications and after.

RE: flow performance test

Get a velometer and measure the flow.

RE: flow performance test

There was apparently money to install louvers and mesh. Is there money to install a fan?

Or a roof turbine ventilator?
http://www.empirevent.com/vents_turbine-ventilator...

I misunderstood your post on first reading. I think I now understand that you propose removing every second blade from each louver; not removing every second louver assembly, which would let the rain in half the locations.

Under what conditions would you test this modification? What outside air temperature and wind speed? Do you know how much airflow you had before the louvers were installed; how much there is now; how much you need?

What is the cost of items destroyed by excessive heat until a solution is implemented? What is the cost of engineering and management time to agonize over a solution to this problem? How much would it cost to remove every second blade from each louver?

What size fan would accomplish the needed airflow? How much would it cost to install the fan?

RE: flow performance test

(OP)
Management has not allocated for me do research this. I'm doing this by stealth. I would like to show them on paper how they can greatly improve things without spending any money. (A top priority for them) It cost virtually nothing to drill out the pop rivet heads that keep the louvers in place. The moment that I say that it will cost anything, the answer will be no.

Does such software exist?

RE: flow performance test

Suggestion: Enjoy your weekend; don't worry about this.

Why do you think it is a problem that the louvers "reduce the ventilation?"

If your modified louvers let in any rain, then you will probably hear about it:

We didn't have this problem until Rookie37 cut up the louvers. Actually, he isn't the one who did it. I had to climb over boxes to remove the the blades; which, by the way, made the louvers ugly. I cut myself on the sharp edges of the removed blades, and on the mesh. Now I have to mop up the rain that his modified louvers let in; except where the water landed on boxes and ruined product.

If no one is looking for a solution, they may not welcome one.

RE: flow performance test

(OP)
If your modified louvers let in any rain, then you will probably hear about it

I'll take that risk. The product that risks rain damage is stale bread. We make thousands of loaves of fresh bread each day. We also get back hundreds of loaves that the stores didn't sell that's getting close to it's used by date. We take this stale bread and sell it to a company that adds it to animal food.

RE: flow performance test

Remove every second louver and extend the blade length on the remaining louvers - should fix the rain ingress.
What's the next problem - as any air flow restriction would be the result of the wire mesh - not the louvers.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

RE: flow performance test

For ventilation to occur when the shed door is closed, you'll need two openings, one at the top of one wall and the second opening, on the lower portion of the opposite wall. To detected air flow,but not quantitively, do a smoke test, either with a cigar, cigarette or smoke test tube.

RE: flow performance test

For my 2 cents, ask your bosses for money to add more louvers. You risk more than just damaging stale bread by removing blades of the existing louvers without telling your bosses, you risk your job if they can't sell nearly stale bread to animal feed producers.

Since your stored product is bread, I am a little surprised you're not doing more to control the environment in the shed. I imagine the purpose of the ventilation is to increase the longevity of the bread; would not better temperature and humidity control increase the shelf life of the bread further?

RE: flow performance test

The flow and rain problems all depend on the size of the opening when it comes to the wire mesh - if you are using mesh with a large opening - obviously - more flow gets through the mesh, therefore effecting everything else. If you are using a finer mesh - something like the 40 x 40 wire mesh seen here ( Link )you may have better luck. The 40 x 40 means that there will be 40 wires, and 40 openings, in every inch of material - in other words, if you look at this thing by the foot - which most of us will in this case - you will have 40 x 12 (480) wires per linear foot of wire mesh - this is a lot of wires and will certainly effect the flow rate we previously had mentioned.

RE: flow performance test

(OP)
I guess that I didn't explain it very well. Getting money from management for improvements is like trying to pull their teeth!

A fan, velometer, smoke test, or additional spinner vents on the roof are not an option

As you can see by the picture, the vent is a ridiculous design. The 'keep the rain out' aspect of it is quite an overkill

http://content.screencast.com/users/dchristensen77...

Anyone can see that removing louvers would increase air flow. However I will like to give them numbers, data, or some type of simulated performance test on the computer.

RE: flow performance test

I would suggest if management are too tight (read stupid) to put a bit of money into "their" problem then bad luck, the problem remains and they need to live with it.
As for the louvres restricting flow - very unlikely however if the mesh is fine then it will certainly restrict any flow.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

RE: flow performance test

All this attention for a shed. What do you store in it? a lawn mower and some gasoline perhaps or is it for something more crucial to the plant safety?

RE: flow performance test

Chicopee

Come on now, this is a very serious engineering problem and discussion, with the stored contents far more critical than a lawn mower and a can of fuel, it's stale bread (see earlier post from OP).

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

RE: flow performance test

I asked before: "Why do you think it is a problem that the louvers 'reduce the ventilation?'"

Is the bread getting moldy because moisture can't get away?

Is it losing water weight because higher temperature in the shed is driving moisture out and selling the bread by the pound results in less revenue?

What problem needs to be solved?

RE: flow performance test

(OP)
I'm not concerned for the stale bread, it's just so hot that working in there is torture. I'll just have to get use to the hot house. Anyway, you answered my question. There is no way to calculate the airflow on this without physically doing it with smoke or differential pressure.

I would suggest if management are too tight (read stupid) to put a bit of money into "their" problem then bad luck, the problem remains and they need to live with it.

That's the problem, they don't live with it. They live in an air condition mansion worth 2.3 squillion dollars

RE: flow performance test

I,somehow, missed the stale bread storage; my apologies.

RE: flow performance test

I believe there are methods you can use from ASHRAE that may allow you to calculate approximations for the air flow.

Are these louvers designed in house or are they engineered by a company who specializes in it? Maybe they can provide feedback on increased flow with removing every other blade.

I also think there is a lot of good feedback from the members already given.

RE: flow performance test

remove the louvers, install wiremesh and rain hoods similar to RTU outside air intakes - imagine a gooseneck with just the beak (no neck).
You get 100% free area, no rain intake.

RE: flow performance test

Going back to your concern about the "Keep rain out aspect" of the vent design. The vent's design to keep rain out is not overkill, it is designed to keep rain out up to a certain free area velocity, usually (not always) 500 FPM.
Aside from the free area velocity, the shape of the blades are designed to change the direction of the air and "extract" rain via centrifugal forces.
By removing blades, you reduce the reduce the free velocity needed to keep rain out from 500 FPM to 250 FPM or less. (I'm guessing what the new rain penetration will be, but you get the idea anyway I hope.)
Also the straighter path means easier for rain to get through.
So unless you reduce the amount of air going through the louver (not your stated intent) to keep the free area velocity below the penetration velocity, removing louvers is a bad idea. To add louver area without going below the rain penetration velocity you will need more louvers.

RE: flow performance test

What's the temperature at night? you could just add some thermal capacitance, i.e. a fishtank full of water, that or make it more reflective as its key source of heat is just going to be the sun.

RE: flow performance test

also, you won't be able to check the flow rate, you have natural convection which is being interfered with on a minute by minute basis by heat loss by natural convection... well not won't be able to but it would take at least a month to run a CFD simulation, converge it and then calculate the heat loss, calculate a new flow rate, then calculate the new heat loss, you kindof get the picture.

RE: flow performance test

You may be able to use assumptions to get a range of flows. Find a best and worse case. Did you say earlier that you had louvres at the top and the bottom of the space?


RE: flow performance test

What he said earlier is still on this page. Where do you find the word "top" used?

RE: flow performance test

I guess I could have just a search... anyway, I did one now and the message I was thinking of was not from the OP, who seems to have lost interest already.



RE: flow performance test

(OP)
I didn't really lose interest. I just see that my question has been answered (sort of) I can't conduct a physical test. (smoke, differential pressure....) From the answers that I got I conclude that it cannot be tested as a computer simulation without spending a great deal of money.

It was not made by a manufacturer that I can ask questions from. The 'water keep out' properties is such an overkill that little or no thought was put into the design. I can't even see through the window. I can only see reflected light. I can't see outside at all. However this is no problem. Ventilation is the ONLY reason why the window was put in in the first place. I think they over did it a bit on the rain protection. I would like to propose an alteration that cost little or no money at all.


http://content.screencast.com/users/dchristensen77...

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources