Double check my math please

pwnt by pat · Oct 21, 2004

It's for a shroud. I'm trying to find the degree I need to sweep in from the outside of the rad to the outside of the fan. Everything is in MM 'cause metric rocks for measurements and imperial is total ****.

This is wrong, see below:

105mm depth

core side - 162mm
fan side - 120mm
difference - 38mm
difference/side of core-to-fan - 19mm

tan0 (theta) =o/a
tan0 = depth/difference-per-side
tan0=105/19
tan0=5.526 degrees sweep

correct?

Guderian · Oct 22, 2004

If its a dual fan core, Im going to assume you are going for a semi-venturi design: angled sides with straight edge tops, or vice versa?

If its a single fan core, is the finned area 162mm*162mm? And are you trying to get a full venturi shroud for that?

greenman100 · Oct 22, 2004

look at this cat, bustin out the trig

personally, I look at a 120mm fan, the radiator in question, and make something that works

props to doing it through trig though

Guderian · Oct 22, 2004

Also, unless you have some good equipment, or one seriously steady hand... I find it easier to calculate for the length of the joint, as opposed to the angle. Its a bit easier to get onto a template (IMO)

Of course having the angle helps to get the joint length....

core side - 162mm
fan side - 120mm
difference - 38mm

What is 'difference', cause if your going for subtraction (core-fan) you forgot to carry 4 mm.

pwnt by pat · Oct 22, 2004

Whoops, you are correct G. I'll update in a minute - I'm fixing a comp at work and doing this at an off second.

edit:

I've found trig is MUCH easier than guess and check. Plus, .x of a degree isn't that hard to approximate.

One last edit to this post:
sqrt((105^2) + (21^2)) = 107.07941

sunrunner20 · Oct 22, 2004

what do people mean when the talk about "venturi" shrouds and such?

greenman100 · Oct 22, 2004

a venturi shroud uses the venturi effect to change the charactersits of airflow.

check it out on google or your favorite physics professor

pwnt by pat · Oct 22, 2004

A venturi is a short, tapered tube or nozzle. The effect that a venturi or nozzle has on fluid flow is that it causes an increase in the velocity and a corresponding decrease in pressure and that is used especially in measuring fluid flow or for creating a suction.

http://itll.colorado.edu/modules/templates/dsp_body.cfm?action=indphenomenon&phenomenon=118

Basicly, it's a taperd shroud designed to create negative pressure in the largest end which in turn aids in pulling air through the rad.

pwnt by pat · Oct 22, 2004

^ is half of the problem. The other half is the harder part and will be up shortly.

sunrunner20 · Oct 23, 2004

Whats Shortly?

Guderian · Oct 23, 2004

So are you going for the full venturi, or angled sides with flat tops. Single fan, or dual fan?

I tend to work better when I think of it in terms of two rectangles so please fill in the Blanks and correct as necessary:

length of Finned area: 165mm
Width of Finned area: ???
Height of shroud: ???
Length of fan area: ???
Width of fan area: 120mm

Guderian · Oct 23, 2004

This post is assuming you want a full venturi single fan shroud for a core with a finned area of 162mm*162mm.

If you want a shroud depth of 1"(25mm) then you need a piece of cardboard that is ~186mm*186mm. The length of the angled edge is ~32.6mm, and the length of angled joint is ~38.8mm.

If you want a shroud depth of 1.5"(38mm) then you need a piece of cardboard that is ~207mm*207mm. The length of the angled edge is ~43.4mm, and the length of angled joint is ~48.2mm.

If you want a shroud depth of 2"(50mm) then you need a piece of cardboard that is ~229mm*229mm. The length of the angled edge is ~54.2mm, and the length of angled joint is ~58.1mm.

Guderian · Oct 23, 2004

I just noticed you want a shroud depth of 105mm

If you want a shroud depth of 105mm then you need a piece of cardboard that is ~335mm*335mm. The length of the angled edge is ~107.1mm, and the length of angled joint is ~109.1mm.

EDIT:so...

pwnt by pat said:
sqrt((105^2) + (21^2)) = 107.07941

...is exactly what I got as well. To me, your math is correct.

On a side note.... Are you also using the powertoys calculator?

sunrunner20 · Oct 23, 2004

I've got myself a pretty Ti-89T.....
and Thanks, Ill adapt that to go w/ my setup (2x 120mm fans, 2-302 heatercore)

Guderian · Oct 23, 2004

Sunrunner20 said:
Ill adapt that to go w/ my setup

This thread might be more helpful if you are trying to make a full venturi shroud for a 2-302.

pwnt by pat · Oct 23, 2004

Shortly is when I'm awake and not working... 7 days a week + free time = little time to do short things. I use google and windows calc.

length of Finned area: 234.95 millimeters (can't be right - I distincly remember two 120's easily fitting on a 2-342)
Width of Finned area: 161.92500 millimeters
Height of shroud: 105 millimeters
Length of fan area: 240mm
Width of fan area: 120mm

Giblet Plus!'s rig^

The pencil mark is the outline of the size of the core, notices how they just fit?

Edit: I guess since 120'mm is the outer length of the area, I only have to worry about the first problem since the second half is now n/a.

G, I think I'll just stick to my t-angle and protractor. 5 degrees is REALLY easy to find. How much more effective do you think the V designed vs box designed shroud for axial fans really is?

Guderian · Oct 23, 2004

Is the ease of 5 degrees the reason for the 105mm standoff?

I am thinking the venturi is a slight preformance increase, and even then only in the pull format.

I don't have any evidence on hand; though I do remember reading something about it somewhere.... I'll see if I can find it.

My main reason was to prove I could make one, and in my situation, I needed a gap around the outside of the shroud to run my PSU cables. I will be cutting a hole in the case to allow for easier routing next time.

pwnt by pat · Oct 24, 2004

5 degrees was luck. I am searching for the angle, not the length, as you can see in the first post. I subtracted 4 or 5mm from the total length as I will be using metal L-stock for my box and to make sure air goes through all the outer-edged fins, I'm setting the rad back some.

I am doing pull only as push-pull is stupid and louder.

Knivez · Oct 24, 2004

Im doing trigonemetry in school, NO!!!!!!!!!!!!!!!!!!!!!
My head hurts, ouch.

pwnt by pat · Oct 24, 2004

It's really not that bad. I did it last year. Have fun learning the unit circle.

Double check my math please

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