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| Thread ID: 66196 | 2006-02-14 20:40:00 | Adding cooling | The_End_Of_Reality (334) | Press F1 |
| Post ID | Timestamp | Content | User | ||
| 430373 | 2006-02-20 03:44:00 | let us know when u have done the rear ones. you can only put in what you can get out, so if the fronts made that much improvement then the rears will hopefully be even more. | tweak'e (69) | ||
| 430374 | 2006-02-20 03:47:00 | The area of a circular hole is Pi*R^2. Pi is close enough to 22/7, R is half the diameter. You've got 4 holes at the front. Those are the inlet ones, I see. The rear ones are the exhaust. Looking back, the fans are all 80 mm diameter, and you have 4 at the back, so they have about the same potential total area of hole for exhaust. But if they're as badly obstructed you might have less than half the area at the moment. You also have 2 with further obstruction as they are in the PSU(s). Ideally, the inlet shoulld be a bit smaller than the exhaust, because the air expands as it is heated. |
Graham L (2) | ||
| 430375 | 2006-02-20 03:59:00 | i thought he only has 3 rear 80m fans ?? (2x rear case and 1x rear psu) | tweak'e (69) | ||
| 430376 | 2006-02-20 04:19:00 | I thought it was "2 in PSU", in one of the earlier posts. Either way, with the obstructions, the area's a bit lacking at that end. If there are only 3, it's even worse. :D | Graham L (2) | ||
| 430377 | 2006-02-20 04:28:00 | I was getting the front mixed up with the rear. The rear of the case definitely needs opening up, especially if the fan grills there are just perforations as bad as the front ones. Most perforated plate does not have more than 50% open flow area, and most computer perforated grills are far less than that. My flow rig is now half built, just have to add some pressure tappings to see if the pressure drop across perforated plate can be measured, and knock up a U tube manometer. |
Terry Porritt (14) | ||
| 430378 | 2006-02-20 06:52:00 | This (www.imagef1.net.nz) will be the easiest way to describe it :D Sorry about the size, I forgot to change the setting :o As you can see there is 2 on the case, and 1 in the PSU that is visible, there is another 1 behind this facing into the case. I hope that explains it better :) |
The_End_Of_Reality (334) | ||
| 430379 | 2006-02-20 08:05:00 | Apart from the centre bit of those grills, the percentage flow area is much bigger than were the grills on the front. Neglecting the centre bit I'd guess the open flow area is over 50%. However it would still be a good idea just to have open holes and remove the perforated part. On this suppliers website, there are details for different perforated sheet, and also a calculator for the % open area. www.lockernz.co.nz >Standard perforated products>View Perforation |
Terry Porritt (14) | ||
| 430380 | 2006-02-21 00:27:00 | Well, I'm not too happy with the scientific validity of the flow measurements I've made on perforated plate, so they wont be reported in detail :) The fan I used is an 80mm Toyo, 2700rpm nominal, no longer made, but about equivalent to the Toyo USTF8025MW: . ustoyofan . com/pdfs/USTF8025 . pdf" target="_blank">www . ustoyofan . com I should have read the specs before making a manometer, as the pressure with the fan blanked off was only about 2mm of water, not enough to measure any pressure drop across a perforated plate . So I discarded the spacers I'd made with pressure tappings . I 'roughly' measured the air speed around the annular flow area of the fan using a small pocket anemometer, without, and with a perforated plate attached to the fan . I say roughly because the size and presence of the anemometer will affect the air flow . Anyway, these are the results; Mean air speed without perforated plate = 3 . 2 metres/second . Mean air speed with perforated plate = 1 . 4 metres/second Speed ratio = flow ratio = 1 . 4/3 . 2 = 0 . 43 Perforated plate details, hole diameter = 3 . 7mm, hole spacing =5 . 54mm Percentage open area = 40 . 5% So, the unsurprising result is that when using perforated fan grills, the percentage reduction in flow compared to an open hole, is roughly the same as the percentage of open area of the perforations . In many instances, this means fans will only be delivering half or less of their rated flow capacity, and confirms the idea that perforated grills, on the whole are a bad thing, as tweak'e has said all along :thumbs: Here is a rather poor picture, the manometer, spacers and tube on the left were not used as it turned out:: . imagef1 . net . nz/files/checkfan . jpg" target="_blank">www . imagef1 . net . nz |
Terry Porritt (14) | ||
| 430381 | 2006-02-21 01:19:00 | how did you calculate the fan aera? did you minus the aera the centre takes up? what would be an interesting test would be to put a 4" spacer between fan and grill. the grill will have more area (due to gaining the bit normally blocked by the centre of the fan) hence a different air speed. a flow meter (mechcanics or speed shops often have them for flow testing) would be handy to test actual flow of the different grills, however it dosn't take into account the effect the grill has on the actual fan. might be a good idea to record fan RPM while testing. you will see a bit of difference. |
tweak'e (69) | ||
| 430382 | 2006-02-21 02:02:00 | just a few more test for you.... use the spacers and tube, so the fan is at one end and the anemometer at the other. place the grill on the fan to simulate intake fan. swap the fan around to simulate rear fan. i wonder if there is any difference between the two and compared to no grill. |
tweak'e (69) | ||
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