bad engrish there. it "will be" not "should be" 73
On Fri, May 1, 2020 at 3:08 PM Christopher Hoover <c...@murgatroid.com> wrote: > I think we're getting far off the topic of Elecraft .... > > > The operating point for forced air cooling of a system should be the point > where the fan curve intercepts the system resistance curve. > > The fan curve comes from the fan vendor. > > The system resistance is measured on a flow bench in the lab, or you can > can use computational fluid dynamics. But the lab work is ideal if you > have the real thing or a decent mock up and is < 1 days worth of work). > > The system resistance is not something you will typically have at hand > though unless you are the designer. Probably most amatuer designers never > bother. (It isn't very hard to make your own flow bench.) > > > > You typically want to arrange the airflow within the system to maximize dT > between the hot things in the enclosure and the working fluid as the heat > transferred is proportional to dT (q' = h.dT). That's not always > possible for a variety of reasons. Things are in the wrong "order." > Sometimes certain components need to be kept cooler (e.g. camera sensor > suffers from unacceptable noise with Tj > 60C). > > > For a given fan type, flow rate and pressure drop, there is a fan size > that is maximally efficient and least noise. A smaller or larger fan > cannot be more efficient and hence less noise. I know some are likely to > argue about this. I refer you to [Handbook of Acoustical Measurements and > Noise Control, by C. Harris, 1991] for details. That said, you can't > (without paying a chunk of NRE) order up an arbitrary size fan, so there is > a compromise. > > > Adaptive fan control is another matter .... > > > 73 de Ai6KG > -ch > > > > On Fri, May 1, 2020 at 12:12 AM Edward R Cole <kl...@acsalaska.net> wrote: > >> My comment NOT about Elecraft cooling design, but: >> >> I am finding a lot of amplifier designs place fans to exhaust heated >> air with cool air being drawn into the heat sink by the partial >> vacuum created by the fans. >> >> My 6m converted Harris ch.2 TV linear is set up this way (amp has >> openings in the chassis to circuits on input side as well as the >> final transistors). >> >> My W6PQL 1296 LDMOS 600w amp is cooled in the same fashion. >> >> Only departure is my W6PQL 2m-1500w linear that has four 2-inch >> square fans blowing cool air into the heat sink. But I augmented air >> flow by adding a 4-inch exhaust fan on enclosure top cover. The >> intake fans were separated from the heat sink by a 2-inch gap which >> bothered me,so added sheet metal fairings to channel air to the heat >> sink. Seems to work as heat sink temp remains topped out at 39c >> running 1400w with JT65 (Overtemp trips off 50v supply at 55c). >> >> Even my old 2m-8877 with blower had a 7-inch radial exhaust fan to >> reduce back pressure on the blower. >> >> 73, Ed - KL7UW >> http://www.kl7uw.com >> Dubus-NA Business mail: >> dubus...@gmail.com >> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:Elecraft@mailman.qth.net >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> Message delivered to c...@murgatroid.com >> > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
