Getting heat out of a box
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From: markp on 6 Aug 2010 13:43 "markp" <map.nospam(a)f2s.com> wrote in message news:8c01p4FbrcU1(a)mid.individual.net... > Hi All, > > I'm looking for a company that could help solve some thermal management > issues. Basically I've got a design that dissipates about 30W and need to > encase it in a sealed box (not hermetically, but to all intents and > purposes there can be no airflow through the box). > > Current thoughts are an aluminium extruded box with large heatsinks on the > outside, and a method of thermally bonding or piping any higher powered > components directly to to the box inside. I also need an AC-DC supply > which I think needs to be a baseplate cooled type and bond that directly > to the side of the box that has the heatsink. I'm unsure of size of box > needed or even whether this is a viable solution. > > I know it's a bit vague, but anyone know a company who could help > (preferably one with a vested interest in solving it, like an aluminium > extrusion box manufacturer)? > > Thanks! > Mark. > Well everyone, I've found this site which if I can learn to drive it might be really useful. It's got some seriously interesting stuff in there, including online calculators: http://www.frigprim.com/ Mark.
From: Nunya on 6 Aug 2010 13:44 On Aug 6, 10:13 am, Tim Wescott <t...(a)seemywebsite.com> wrote: > On 08/05/2010 05:17 PM, markp wrote: > > > > > "whit3rd"<whit...(a)gmail.com> wrote in message > >news:db6a66cd-1a00-45f7-a7c3-8a6b80e2d110(a)d17g2000yqb.googlegroups.com.... > > On Aug 5, 7:56 am, "markp"<map.nos...(a)f2s.com> wrote: > > >>> ... I've got a design that dissipates about 30W and need to > >>> encase it in a sealed box (not hermetically, but to all intents and > >>> purposes > >>> there can be no airflow through the box). > > >>> Current thoughts are an aluminium extruded box with large heatsinks > > >> If the box has>30 square inches of external free-air surface, a > >> circulating > >> fan inside the box would do it. Or, does it have to be small? > > > Do you mean and area of the sidewalls of the box externally> 30 square > > inches (that's equavalent to 5.48" x 5.48" for ease of visualisation), with > > an internal fan, will get rid of 30W? What's the max temp rise above ambient > > internally do you think, and would I need to put heatsink fins inside the > > box as well as outside? > > Fins inside would certainly help. Total bullshit. He said no moving air inside. All radiation must be external. Remember the SR-71B? It dropped 50°F when they went from bare skin to matte black IR radiative paint... on the OUTSIDE of the airframe. Even though the skin was the source of the heat. Conduction cooling relies on operating AT elevated temps, and designing to reliably do so within a window of EXTERNALLY radiated energy acceptability. So, it needs to be mounted onto a conduction plate externally, or operate at a temp where it can be free standing and still run. The hardest part is usually trying to comply with the upper end of any claimed thermal operating envelope.
From: Nunya on 6 Aug 2010 13:46 On Aug 6, 10:28 am, Jim Thompson <To-Email-Use-The-Envelope-I...(a)On-My- Web-Site.com> wrote: > On Fri, 06 Aug 2010 10:13:58 -0700, Tim Wescott <t...(a)seemywebsite.com> > wrote: > > > > >On 08/05/2010 05:17 PM, markp wrote: > >> "whit3rd"<whit...(a)gmail.com> wrote in message > >>news:db6a66cd-1a00-45f7-a7c3-8a6b80e2d110(a)d17g2000yqb.googlegroups.com.... > >> On Aug 5, 7:56 am, "markp"<map.nos...(a)f2s.com> wrote: > > >>>> ... I've got a design that dissipates about 30W and need to > >>>> encase it in a sealed box (not hermetically, but to all intents and > >>>> purposes > >>>> there can be no airflow through the box). > > >>>> Current thoughts are an aluminium extruded box with large heatsinks > > >>> If the box has>30 square inches of external free-air surface, a > >>> circulating > >>> fan inside the box would do it. Or, does it have to be small? > > >> Do you mean and area of the sidewalls of the box externally> 30 square > >> inches (that's equavalent to 5.48" x 5.48" for ease of visualisation), with > >> an internal fan, will get rid of 30W? What's the max temp rise above ambient > >> internally do you think, and would I need to put heatsink fins inside the > >> box as well as outside? > > >Fins inside would certainly help. I'm rusty at my thermo, but the way > >you'd calculate this would be to figure out the thermal resistance for > >each metal to air interface (component to air, air to box inside, box > >outside to air) and add them up -- you'll find that the thermal > >resistance of the box's aluminum itself is insignificant, unless you're > >really aggressive about fins. > > [snip] > > Configure a "endless" tunnel (with internal fins), fan driven. Fins > on the outside. And pray a lot ;-) > > ...Jim Thompson > -- > | James E.Thompson, CTO | mens | > | Analog Innovations, Inc. | et | > | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | > | Phoenix, Arizona 85048 Skype: Contacts Only | | > | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | > | E-mail Icon athttp://www.analog-innovations.com| 1962 | > > Spice is like a sports car... > Performance only as good as the person behind the wheel. Sounds like a speaker enclosure I once saw an amazing example of. Klipsch. What an amazing piece of art and engineering.
From: John Larkin on 6 Aug 2010 13:50 Something like this? ftp://jjlarkin.lmi.net/L650_HS_proto.JPG ftp://jjlarkin.lmi.net/L650_HS_pretty.JPG John
From: Tim Wescott on 6 Aug 2010 13:57
On 08/06/2010 10:44 AM, Nunya wrote: > On Aug 6, 10:13 am, Tim Wescott<t...(a)seemywebsite.com> wrote: >> On 08/05/2010 05:17 PM, markp wrote: >> >> >> >>> "whit3rd"<whit...(a)gmail.com> wrote in message >>> news:db6a66cd-1a00-45f7-a7c3-8a6b80e2d110(a)d17g2000yqb.googlegroups.com... >>> On Aug 5, 7:56 am, "markp"<map.nos...(a)f2s.com> wrote: >> >>>>> ... I've got a design that dissipates about 30W and need to >>>>> encase it in a sealed box (not hermetically, but to all intents and >>>>> purposes >>>>> there can be no airflow through the box). >> >>>>> Current thoughts are an aluminium extruded box with large heatsinks >> >>>> If the box has>30 square inches of external free-air surface, a >>>> circulating >>>> fan inside the box would do it. Or, does it have to be small? >> >>> Do you mean and area of the sidewalls of the box externally> 30 square >>> inches (that's equavalent to 5.48" x 5.48" for ease of visualisation), with >>> an internal fan, will get rid of 30W? What's the max temp rise above ambient >>> internally do you think, and would I need to put heatsink fins inside the >>> box as well as outside? >> >> Fins inside would certainly help. > > Total bullshit. He said no moving air inside. Please quote a post. The one I can find said that he'd 'really prefer' no moving _parts_. Which is understandable -- fans wear out. It'd be interesting to do an MTTF calculation for the assembly with electrolytics (and elevated temperatures) but no fans, and with electrolytics and fans (and hence lower temperatures). > All radiation must be external. > > Remember the SR-71B? It dropped 50�F when they went from > bare skin to matte black IR radiative paint... on the OUTSIDE > of the airframe. Even though the skin was the source of the heat. Yes, that's basic thermo. > Conduction cooling relies on operating AT elevated temps, Passive heat flow itself requires a temperature differential. So _any_ cooling "relies" on operating at elevated temperatures. > and designing to reliably do so within a window of > EXTERNALLY radiated energy acceptability. So, it needs to > be mounted onto a conduction plate externally, or operate > at a temp where it can be free standing and still run. Again, you assume radiative or conductive cooling externally, when (unless I missed a post) the OP has not said anything at all about the environment he's putting his electronics into. Should he take a Colman cooler, aluminize the inside, put his electronics into that, and shut the lid, then he won't get good cooling no matter what he does with the _inside_ of the box. > The hardest part is usually trying to comply with the upper > end of any claimed thermal operating envelope. True. Unless you don't pay any attention to the lower end of the envelope, in which case you'll be getting calls from your first Alaskan customer come winter. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html |