Enclosure Query - Page 1
Forum section: electronics / projects

author: dreaquil
author_rank: Regular Contributor
timestamp: February 05, 2016, 09:20:00 am
content: I came across this document from Pentair where they state that a non-metallic enclosure or painted metallic enclosure will create a lower temperature rise than an unfinished aluminium or steel enclosure (unventilated and sealed). These seems a bit counter intuitive to me. Can anyone explain why this is? Shouldn't a non metallic enclosure be a better insulator than unfinished aluminium thus causing a higher temperature rise? If not what is the reason please?http://www.hoffmanonline.com/stream_document.aspx?rRID=233309&pRID=162533

author: m98
author_rank: Frequent Contributor
timestamp: February 05, 2016, 09:41:23 am
content: Maybe because thermal radiation is reflected back inside by the metal surface, and the emissivity of metals is quite low, so heat is slower radiated to the environment.

author: bookaboo
author_rank: Frequent Contributor
timestamp: February 05, 2016, 10:31:17 am
content: Yes a metal enclosure will radiate (or absorb) more heat energy than an unpainted surface. A dull plastic enclosure will have about the same emissivity as a painted metal surfact but I would have thought the losses from conduction would be much greater than that due to radiation.

author: Cerebus
author_rank: Super Contributor
timestamp: February 06, 2016, 03:00:51 am
content: We bought a new mixing bowl the other day; stainless steel, with a nicely polished interior. When we got home I was arseing about and, as you do, put it on my head saying "Look at my nice new hat". (Yes, in Eccles' voice, if you really must know.)I was immediately struck by how much heat I could feel reflected from the bowl onto my forehead. This ostensibly cold metal bowl felt warmer than a fur hat as long as I wasn't in actual contact with the metal. Do not underestimate the thermal insulation offered by a simple shiny piece of metal.

author: HAL-42b
author_rank: Frequent Contributor
timestamp: February 06, 2016, 09:25:03 am
content: Pics or it didn't happen.Also stainless steel has pathetic thermal conductivity.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: February 06, 2016, 09:25:48 am
content: Quote from: Cerebus on February 06, 2016, 03:00:51 amStainless steel is, as far as metals go, a remarkably good insulator. Over twice what steel is and close to 13x what aluminium is. It's not nearly as good a reflector as aluminium, but not terrible either.EDIT: HAL-42b beat me to it.

author: uncle_bob
author_rank: Unknown
timestamp: February 06, 2016, 06:28:00 pm
content: HiStuff that radiates well, rarely reflects well. If you pick your case (radiation vs reflection) you can easily switch the order of "what's best". If you have a third or fourth effect (conduction and/or convection) then the contest gets even more complicated.Bob

author: bookaboo
author_rank: Frequent Contributor
timestamp: February 06, 2016, 06:58:16 pm
content: Quote from: uncle_bob on February 06, 2016, 06:28:00 pmYep, not just rarely it's almost directly inversely proportional.As a proportion of heat energy radiated from a surface:Emissivity + Reflection + Transmission = 1Usually "transmission" (that IR transmission not conduction) is so low that it can be ignored.Also Emissivity = Absorbtion, just depends in which direction the IR energy is going.