Hi everyone,

A couple of months ago, I put a post up about my intent to build a modelling spray-booth for my A-Level Design and Technology. A couple of days ago, I (finally) finished it, and would be interested to hear your views on what I managed.





As you can see, the white base with tamiya-paint-bottle sized holes rotates by around 120 degrees, with another thin acrylic layer on top of this which is free to rotate as a turntable. The fan (which is a £30 200cfm DC Brushless fan, supposedly safe from explosions) is contained at the rear of an mdf box which can slide in and out of a small rectangular hole at the rear of the main booth, so an airtight 'tunnel' is created between the fan and turntable area.





This is one of my 'testing' photographs, as the smoke is much more visible than paint coming from an airbrush. The suction is relatively even across the whole of the turntable and extends vertically to a decent degree.

My Tech Coursework requires an element of evaluation, so any thoughts/criticisms/improvements would be very welcome.

Thanks

Super work!

So school does come in handy sometimes ! Did you make this at home or with machines at school?

Lars

That's a really cool design. So does the rear shield cover 180 degrees (half the base)?

Sweet!!

Cheers guys,

^ Lars; everything but the mdf and fan bit at the back was made at school; all the plastic was cut using a laser cutter, and then the normal bansaw/filing/polishing for the rest of the structure.

^ Rudi; yep, i thought any further than that and the shield would begin to block all the light out.

really cool work

Nice work there, i think this is a really cool design and the flame test has proven functionality to some extent. If its okay with you, i think i will use some of your ideas to constuct my own spray booth for personal use.
Your hobby has given you a niche in which to study at school. Keep this up and you'll be a great innovator. I hope you do well in your A-Levels, i wrote mine this year too. finished C4 math yesterday

Mark,

congratulations on the completed work. I've been waiting for your finished booth ever since you posted the thread..

For an A-level entry, this is far more better. I hope u did well in your paper. If your teacher didnt give you A++ please ask him to contact me...

Anyway, looking at the arrangement it is neat and well plan. Having bottom draft suction is a good choice. That was a powerfull 200 cfm fan i believed (I was so amazed that the size is small for a 200 cfm...)

Performance wise, i cannot comments more but seing those 'flame' test i can say that the suction is good. Did you this test in various point. Typical way to evaluate the suction qualitatively is to make a virtual grid on the surface of face of the opening - in the case on the surface of the suction surface. You can draw a circle on a paper and estimate a 10 point of testing. Then u may run a series of smoke along at each point and observed the smoke trail. Normally the suction is not distribute evenly.
Quantitatively, if you can access to a laser cutter, i believed your school do have airflow meter (some called it Velocity meter, many known as anemometer) then you can use this meter to measure the performance of the booth.

This is just an example of a mock up booth that i build few months ago. Using cardbox and the heart of the system is the centrifugal 165 cfm fan installed at the rear.


this is how i measured the face velocity using the anemometer ..visible here is the anemometer hot wire censor and the meter (TSI)

I point the hot wire sensor at 16 grid point and get the average velocity. Velocity profile differ from point to point and are much more higher at the center.
To further increase the efectiveness of the suction, i add plenum and baffles to the opening of the 'hood'.


This really increase the perfomance by 10-15% (these are only experimental - slot width are not calculated in this trial)...

Okay, i'm not going to give science class here and make you all bored. If u need further assistance you can PM me.

Anyway, your design is innovative. I'm impressed with the arrangement. Just one thing though, having the face open all the way 240 degree requires more air to be sucked and might reduced the performance. You can enclose some more by enlarging the curved wall. By doing this, the air profile outside will be lesser. Imagine a 3/4 quarter sphere of air vs maybe half sphere of air that needed to be sucked out..

Anyway, like i said i cant comments much on the performance without doing any quantitative assessment.

For an A level entry, this is way to hi-tech...
Good work young man. Hope u score with flying colors (and if u dont, let me speak with your teacher )

Cheers,

Zaidi

wow that looks a lot better than some of the A-Level students at my school have built in the past. Looks like you have much better equipment than i had for my GCSE this year. We could only dream of a laser cutter.
Wth regards to evaluation, it looks like it will meet whatever is in your specification, and i think you could sell this without much hassle. one possible improvement that you could mention is that the fan unit at the back takes up a lot of room. I'm not sure how big this is but that might stop it being placed on a thin desk near a wall for example. Looks A* quality though, good luck.

Iv been on the fence ocillating back and forth about getting a spray booth ever since I used alclad a few months ago and experienced lung pain for about 4 weeks after due to inproper ventilation... I want to say how IMPRESSED I am with both of the units on this thread. Young man,you should indeed be PROUD of what youve built. It is very impressive.
After seeing this thread I think I will renew my efforts..I think what stopped me is finding the appropriate fan ,then sourcing it. I tried going to a computer store,then the autoparts store here in my village and they just looked at me like I had 3 heads..

well maybe i'll have a go at a basic one some time too. i saved a couple of computer fas when i threw out my old mac. would they do?

I looked into computer fans ,and the average one only does something like 50 CFM....I think once you do all the fancy math you need about 250CFM as our young inventor has shown here..
I found some on the internet pretty quickly now that I actually know what im looking for..about 25USD

Thank-you everyone for the support; the contact I had with this forum whilst designing and building the booth really helped make it a whole lot better.

The biggest problem everyone (myself included) seems to have is selecting the correct fan; the most important aspect of the booth is to ensure safety, so the fan needs to be brushless, or a 'squirrel cage' centrifugal motor, ie. there is no chance of the motor generating any sparks which could ingnite the potentially flammable vapour. This is the brushless fan I used, and I think its very good value, although its probably only available in the UK. (Squirrel cage motors seem to be more proliferent in the North America than in Europe). This is a superb tutorial which I followed when calculating stuff.

Thanks again (and no suing if my advice blows up in your face )

Final quick question aimed towards Silantra - those horizontal slats you say improve the performance; I'm intrigued as to how they affect the airflow - do they reduce vortices or something like that?

Cheers,
Mark

So I think I figured this out right,Mark..(Im TERRIBLE at math...always have been..) For a ductwork system of a linear length of about 20 feet @ 4" dia. (this figure includes the 90degree elbow conversions) a fan of about 300CFM output would do it?

Mark,

sorry for the late reply....i was away from home...and just noticed your question

Ok, regarding the fan, the most ideal and standard industrial use is centrifugal type fan. With this type, you wont face any problem with regards to the brush issue. The drawback is this type of fan is normally relatively expensive.





Ok, first let see some basic equation (OMG, the class has started), the generic and simplified equation is Q = vA where ;
Q = volumetric flowrate (CFM)
v = velocity of air (feet per minute, fpm)
A = sectional area, square feet (normally area of duct or face of the suction source)

from this equation, Q is proportionate with v and A.

By putting baffles or flanges, it gives system effects. A flange is just a surface parallel to the 'hood' face that provides a barrier to unwanted airflow from behind the hood. A baffles is a surface that provides a barrier to unwanted airflow from the front or sides of the hood.

If the suction source was located on the plane, the flow area would be reduced thereby decreasing the flowrate required to achieve the same velocity. A flange around the hood opening has the same effect. In practice, flanging can decrease the flowrate (or increase velocity) by approx 25%.
Still with me??When the Q is reduced then the velocity is increases so you dont have to get a high rated fan to do the job.
For example, ACGIH recommended that velocity for spray painting should be from 100-200 fpm. and we had a some cfm rated fan, say 200 cfm. Initial design show that the 200 CFM fan was not enough to suck the air at the given velocity. So we change to 300 CFM (example only)... this increase the cost. A cheap solution is to add baffles or flange to the opening and like i mentioned above, baffles reduced the airflow, Q and by doing this, smaller CFM will do the job if u install baffles. SO we dont have to buy a high rated fan, but simply add baffles or flanges to the opening...
In another layman words, if we installed baffles, the flowrate of the fan is reduced and u wont need a higher rated fan to do the job of the same velocity... i hope u can understand... there are some figures that i would like to show but i'm afraid this will be another boring thread...

feel free to ask me if got anything..................

cheers,

Zaidi

Jim,
from the above equations, Q = vA
assume v =100 fpm

so A = pi D/2 square = pi x ((4/12)^2)/4 = 0.087 ft sq

hence, Q = 100 x 0.087 = 8.7 cfm ..
from the result, 300 cfm is was more than enough! of course othjer losses will be consider such as opening size, duct material and those 90 deg elbow loss....

my 2 cents

many thanks! Im kindof leaning toward using 5" ductwork.. I must admit to barely understanding the mathematics involved...yet when you put things in simple terms I get it ..lol..Iv always been a knucklehead at math..thanks my freindd..