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Heat Sinks Are Too Hot to Touch

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Amclaussen
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Platinum
Re: That old 10 degree C- Rule...
Amclaussen   8/7/2014 4:37:30 PM
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Re: PFC Swiitcher Engr, You may not be aware of what is called "The 10°C Rule" that is approximately valid not only in electronic components, but many other things in nature... like the temperature effect on many chemical and biochemical reactions (like enzimatic ones), where increasing temperature about 10 Celsius (every 18°F) doubles the reaction speed.  Amclaussen.

William K.
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Re: Hot Equipment
William K.   2/23/2014 4:25:18 PM
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wbswen, At the school where I got my BSEE I learned to learn, and I have been doing that ever since. Not only electronics, but also mechanical design and the basic mechanical sciences. After all, electronic things need to have shape and form and do something useful, which at the ver least means an enclosure and some way to remove the excess heat. And it gets more complex from there on. 

I agree that while it is a simple principle, the compression ignitor is definitely not likely to be made with primative skills. I have seen some interesting friction fire starting, including a rig that used a fair sized log and six people to pull the rope back and forth. It did work fairly well, but the task required a total of eight people. Flint and steel is a reliable means but it demands dry materials to start things going, although flint and steel coupled with tissue and gasoline is more tolerant of less dry materials. BUT not recommened for young scouts to use.

wbswenberg
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Gold
Re: Hot Equipment
wbswenberg   2/22/2014 9:04:29 PM
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William K. you are a wealth of information.  I guess I missed a few things with a BSEE. Not that I have not learned a few things in the 37 following years.  So on the compression fire starter I was looking for a low tech but easy way to start a fire in the feild.  My back ups are lighters and matches and now flint and steel.  I've come to believe that the compression starter is high tech.  I cant imagine primitive people being able to machine to the tollerances or having sealing capibility.  Fire by friction takes too much effort and dexterity for cold hands.  It requires just the right kind of wood and strong cord for the bow type.  

 

William K.
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Platinum
Re: Hot Equipment
William K.   2/21/2014 4:41:27 PM
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wbs, the hot air from a typical vacuum-cleaner is the result of motor heat, since the motor is working fairly hard and is designed to run with forced air cooling. If the blade ever comes loose and stops spinning the thing will heat up quite rapidly, but not quite so much as anticipated since it won't be doing much work. That is one of the reasons that vacuum cleaner motors were not used for other projects by hobby experimentors. Inadequate cooling without that draft.

And just consider the compression ratio of that "compression igniter device. Probably 20:1 or better. Even Diesel engines have a quite high compression ratio in order to ignite the charge. And the PV=nRT formula is the basis for Charles law and Boyles law, the two that relate pressure, volume, and temperature. 

And the dust and dirt not only insulate but they seriously slow the air flow. The explation of the mechanismm by which they slow the flow is a bit tedious, so I won't go into it here. 

wbswenberg
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Gold
Re: Hot Equipment
wbswenberg   2/20/2014 10:52:13 AM
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TJ McDermott & William K.  its been far too long ago to remember.  But it was like a vacuum intake the suction side was cool and the exhaust side blowing was hot.  I know compression heating I have a fire starter.  I don't know wether the packager ran the numbers or not.  It was more of a trial and error thing.  And Ill say that the air flow was simular to a vacuum as subjestive as that is.

At the E company were I was replacing muffin fans I was concerned about filtering.  I noticed a lot of dirty filters and dirtier still circuit boards.  Boards and components were fuzzy gray.  The boxes that blew air in through a filter stayed cleaner cause the filter caught  the dust.   The ones that pulled the air out had dust around every opening besides the boards and components.  The other problem was that an intake filter had to be kept clean or the electroincs got hot.  So a times a lot of trade-offs

And William K. on frictional heating of the blades I bet they also made more noise from the turbulent air flow.  Another problem we had in F22 lab was the singing power supplies and blowers with loud air flow noise.  The package came up with some hanging bats of insulation the cut down noise.  I think the singing was from loose laminations but switchers should be using Ferite a solid ceramic not laminations.  Perhaps loose coils that should have been potted.  The inductive air flow speakers and fans I'll bet are interesting.

 

wbswenberg
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Gold
Re: Hot Equipment
wbswenberg   2/20/2014 10:52:07 AM
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TJ McDermott & William K.  its been far too long ago to remember.  But it was like a vacuum intake the suction side was cool and the exhaust side blowing was hot.  I know compression heating I have a fire starter.  I don't know wether the packager ran the numbers or not.  It was more of a trial and error thing.  And Ill say that the air flow was simular to a vacuum as subjestive as that is.

At the E company were I was replacing muffin fans I was concerned about filtering.  I noticed a lot of dirty filters and dirtier still circuit boards.  Boards and components were fuzzy gray.  The boxes that blew air in through a filter stayed cleaner cause the filter caught  the dust.   The ones that pulled the air out had dust around every opening besides the boards and components.  The other problem was that an intake filter had to be kept clean or the electroincs got hot.  So a times a lot of trade-offs

And William K. on frictional heating of the blades I bet they also made more noise from the turbulent air flow.  Another problem we had in F22 lab was the singing power supplies and blowers with loud air flow noise.  The package came up with some hanging bats of insulation the cut down noise.  I think the singing was from loose laminations but switchers should be using Ferite a solid ceramic not laminations.  Perhaps loose coils that should have been potted.  The inductive air flow speakers and fans I'll bet are interesting.

 

a.saji
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Silver
Re: Hot Equipment
a.saji   2/20/2014 4:47:42 AM
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@TJ: Surprising indeed but don't you think it's the normal theory behind it ? I think many flows are very much the same.   

TJ McDermott
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Re: Hot Equipment
TJ McDermott   2/19/2014 11:36:40 PM
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William K, I understand the ideal gas law; I was simply surprised to read compression heating was a reason to reverse the fan flow.

William K.
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Platinum
Re: Hot Equipment
William K.   2/19/2014 9:21:31 PM
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TJM, compression heating caused by fans is "not very much". The general formula is PV=nRT, where n is the number of mole of gas and R is the universal gas constant. The easy way to get in trouble using this formula is to forget that temperature and pressure need to be in absolute terms, not relative. So you would use Rankin or Kelvin for the temperatures. What you find is that frictional heating from a typical fan is a lot more than the compression heating.

TJ McDermott
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Blogger
Re: Hot Equipment
TJ McDermott   2/19/2014 8:54:53 PM
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WBSwenberg, just how much pressure would the fans have given to make compression heating a concern?

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