John Hasler wrote: > Chuck Stickelman writes: > > Having fans inside a computer case (such as those mounted on the CPU's > > heat sink) lower the air pressure inside the case - Bernoulli's > > principle. > > No. Those fans just stir the air around inside the case, transferring heat > from the cpu etc to that air. >
Right. Stirring the air lowers it's static pressure. Moving fluid has less pressure. It's the exact same principle that allows a plane to fly. Try this experiment. put a large fan inside of a box, attach a pressure gauge to the box. Now seal the box up tight. Turn the fan on high. Watch the pressure in the box drop. Physics. > > > Turn the fan around like Joerg has suggested. This will make the case > > positively pressured and will keep air (and junk) from infiltrating those > > nooks and crannies. > > Joerg's fan is mount in his power supply. Turning it around will result in > air being drawn into the power supply, heated by the components there, and > then blown into the computer. This will result in the power supply running > cooler but the computer running hotter. His fan is also > tmeperature-controlled: reversing the flow may screw that up such that the > fan doesn't run at all. > Whether or not this matters much depends on the amount of air flow, the amounts of heat generated by the PS and the CPU. I've not done the math and am not likely to anytime soon. What I do know is that I didn't come up with this scheme. It's used by several manufacturers of commercial/industrial grade PC's. The principle of having the case be positively pressured is sound. Whether or not a specific case/fan/PS/case combination will support it I can't say. from personal experience, this works! None of my wife's computers nor any at our house that I've retrofitted have heat or dust problems. YMMV. > > > The solution to THAT problem is to put a filter in front of the fan. > > A _seperate_ fan. Leave the one in the power supply alone. > > > As for noise, get the quietest fans possible - ones with ball bearings > > seem to be better than those that use brass bushings or sleeves. > > That is only because those that use brass bushings or sleeves are very low > quality. Normally bushings are quieter than ball-bearings. > > Taking the fan apart, removing all the grease, and replacing it with Teflon > lubricant may help. The lubricant the manufacturers use seems to quickly > turn to tar. > I've not ever taken the time to rip one open. Costs less to pitch it and buy a new one. Certainly a warranty issue in opening it up, yes? > -- > John Hasler > [EMAIL PROTECTED] > Dancing Horse Hill > Elmwood, Wisconsin > Chuck
