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
