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Jeff Finlayson
science forum Guru Wannabe

Joined: 02 May 2005
Posts: 142

Posted: Sun Nov 27, 2005 1:02 am    Post subject: Re: Concurrent forces have no turning effect??

Brian Whatcott wrote:
 Quote: Jeff Finlayson wrote: [Chris] I thought concurrent forces were those acting along lines that intersect. This is in fact what it says in my textbook, but since the forces in my example fulfil this condition and cause a turning effect, I am certainly missing something! [Jeff] You are missing the other condition for equilibrium, that the vector sum of the forces is zero. CHRIS just won't accept that concurrent forces do not imply a turning moment. [Jeff] These comments are misplaced and as stated are backwards with what I have posted elsewhere in this thread. My sincere apologies to Jeff. I was indeed preaching to the choir.

That's OK Brian. You had me puzzled there.
Take it easy..
brian a m stuckless
science forum Guru

Joined: 31 Aug 2005
Posts: 2024

Posted: Sun Nov 27, 2005 11:24 am    Post subject: Re: Particle Radii

Y.Porat wrote: > > just lets try very simple logic;
 Quote: if we agree that a combination of two particles is longish and another condition - the bond is constant and fixed what is more reasonable to think that we have here two 'balls' side by side?

..Dumb-bell.?!!

 Quote: so what is the point of connection is it one point? if yes why rather that point and not another one. or may be two longish shapes? that has 'poles' and the connection is only at the poles?

..OBLONG, Dumb-bell.?!!

 Quote: moreover: how about the possibility that even that 'basic particle' is actually not 'basic but composed of sub particles ?? so if a conglomerating of sub- particles than again we are in the 'direction of' the longish shape ??!!

..albeit, HEAVY-weight OBlong, Dumb-bell.?!!

 Quote: have you hear ed about the 'string theory'?

ONE HEAVY-weight OBlong Dumb-bell Theory at a time.!!

 Quote: have you hear ed about the 'chain of orbitals' theory??

CHAiNs are descretely CONTiNOUS strings of MOLAR particles.!!

brian a m stuckless
 Quote: have you seen a protein molecule? (not to mention the Genome) have you seen the shape of a lightening (that might as well be a shape of a chain of orbitals or may be based on it ?) if not it is just material for new thinking. ATB Y.Porat -------------------
Don A. Gilmore
science forum beginner

Joined: 24 Mar 2005
Posts: 48

Posted: Tue Dec 13, 2005 11:37 pm    Post subject: Re: Look Pivot, NO string (Bob ticked).!!

"David Wilkinson" <david@wilkinson6337.freeserve.co.uk> wrote in message
news:dnn805\$2uv\$1@news8.svr.pol.co.uk...

It's the KooKY KAPITALS that always indicate a superior intellect!

Don
Kansas City
science forum Guru Wannabe

Joined: 07 Oct 2005
Posts: 107

Posted: Wed Jan 04, 2006 10:09 pm    Post subject: Re: Heatsink cooling

Ignoramus18299 wrote:
 Quote: Let's say that I have a source of about 800-1000 watts (two dual IGBTs inverting 200 amps). They should run relatively cool, to stay safe say under 80 C. I have a heatsink that is about 6x13 inches and weighs perhaps 12 lbs. I am cooling it with a fan mounted right next to the ribs, pushing air along them, the fan is about 20 watts. Ambient temp could be quite hot, say 40 C (inside welding machine). Would you say that this amount of cooling should be enough? I will have a overheat switch mounted on the sink, so, hopefully, worst case would be a inconvenience of having to stop welding, but I would like to have some idea of adequacy of this setup. i

What's the CFM (cubic feet of air) rating of the fan? And what's the
surface area of the heatsink? (Material of construction of the
heatsink?)

1 kW of heat to dissipate... have you considered a water-cooled system?

Is this a system you're building yourself, or is this setup on an
off-the-shelf piece of equipment?

Cross-posting to sci.engr.mech, they should be able to contribute more
ideas.
Pooh Bear

Joined: 17 Apr 2005
Posts: 76

Posted: Wed Jan 04, 2006 11:04 pm    Post subject: Re: Heatsink cooling

 Quote: Ignoramus18299 wrote: Let's say that I have a source of about 800-1000 watts (two dual IGBTs inverting 200 amps). They should run relatively cool, to stay safe say under 80 C. I have a heatsink that is about 6x13 inches and weighs perhaps 12 lbs. I am cooling it with a fan mounted right next to the ribs, pushing air along them, the fan is about 20 watts. Ambient temp could be quite hot, say 40 C (inside welding machine). Would you say that this amount of cooling should be enough? I will have a overheat switch mounted on the sink, so, hopefully, worst case would be a inconvenience of having to stop welding, but I would like to have some idea of adequacy of this setup. i What's the CFM (cubic feet of air) rating of the fan? And what's the surface area of the heatsink? (Material of construction of the heatsink?) 1 kW of heat to dissipate... have you considered a water-cooled system?

1kW is nothing really. My amps can generate about that much ( in 2u of 19"
rackmount ) and I get rid of it with a max heatsink temp of 95C with 2 80mm
'boxer' style fans.

Graham
Ignoramus18299
science forum beginner

Joined: 05 Jan 2006
Posts: 1

Posted: Thu Jan 05, 2006 12:28 am    Post subject: Re: Heatsink cooling

On Wed, 04 Jan 2006 23:04:57 +0000, Pooh Bear <rabbitsfriendsandrelations@hotmail.com> wrote:
 Quote: onehappymadman@yahoo.com wrote: Ignoramus18299 wrote: Let's say that I have a source of about 800-1000 watts (two dual IGBTs inverting 200 amps). They should run relatively cool, to stay safe say under 80 C. I have a heatsink that is about 6x13 inches and weighs perhaps 12 lbs. I am cooling it with a fan mounted right next to the ribs, pushing air along them, the fan is about 20 watts. Ambient temp could be quite hot, say 40 C (inside welding machine). Would you say that this amount of cooling should be enough? I will have a overheat switch mounted on the sink, so, hopefully, worst case would be a inconvenience of having to stop welding, but I would like to have some idea of adequacy of this setup. i What's the CFM (cubic feet of air) rating of the fan? And what's the surface area of the heatsink? (Material of construction of the heatsink?) 1 kW of heat to dissipate... have you considered a water-cooled system? 1kW is nothing really. My amps can generate about that much ( in 2u of 19" rackmount ) and I get rid of it with a max heatsink temp of 95C with 2 80mm 'boxer' style fans.

That's very nice to know PB. 1 kW is a bit of an overestimation. 800
watts would be the maximum (200 amps x 2 volts voltage drop x 2 sides
of the bridge), and welding would not be continuous, as well.

i
Pooh Bear

Joined: 17 Apr 2005
Posts: 76

Posted: Thu Jan 05, 2006 7:53 am    Post subject: Re: Heatsink cooling

Ignoramus18299 wrote:

 Quote: On Wed, 04 Jan 2006 23:04:57 +0000, Pooh Bear wrote: onehappymadman@yahoo.com wrote: Ignoramus18299 wrote: Let's say that I have a source of about 800-1000 watts (two dual IGBTs inverting 200 amps). They should run relatively cool, to stay safe say under 80 C. I have a heatsink that is about 6x13 inches and weighs perhaps 12 lbs. I am cooling it with a fan mounted right next to the ribs, pushing air along them, the fan is about 20 watts. Ambient temp could be quite hot, say 40 C (inside welding machine). Would you say that this amount of cooling should be enough? I will have a overheat switch mounted on the sink, so, hopefully, worst case would be a inconvenience of having to stop welding, but I would like to have some idea of adequacy of this setup. i What's the CFM (cubic feet of air) rating of the fan? And what's the surface area of the heatsink? (Material of construction of the heatsink?) 1 kW of heat to dissipate... have you considered a water-cooled system? 1kW is nothing really. My amps can generate about that much ( in 2u of 19" rackmount ) and I get rid of it with a max heatsink temp of 95C with 2 80mm 'boxer' style fans. That's very nice to know PB. 1 kW is a bit of an overestimation. 800 watts would be the maximum (200 amps x 2 volts voltage drop x 2 sides of the bridge), and welding would not be continuous, as well.

Back in the office I have a neat little equation for temp rise in airflow vs energy absorbed. You
can do it from first principles but it may come in handy. I'll post it later. It shows
importantly that for certain temp rises vs watts you need a given mimimum airflow.

Graham
Ignoramus2491
science forum beginner

Joined: 05 Jan 2006
Posts: 3

Posted: Thu Jan 05, 2006 2:20 pm    Post subject: Re: Heatsink cooling

On Thu, 05 Jan 2006 07:53:15 +0000, Pooh Bear <rabbitsfriendsandrelations@hotmail.com> wrote:
 Quote: Ignoramus18299 wrote: On Wed, 04 Jan 2006 23:04:57 +0000, Pooh Bear wrote: onehappymadman@yahoo.com wrote: Ignoramus18299 wrote: Let's say that I have a source of about 800-1000 watts (two dual IGBTs inverting 200 amps). They should run relatively cool, to stay safe say under 80 C. I have a heatsink that is about 6x13 inches and weighs perhaps 12 lbs. I am cooling it with a fan mounted right next to the ribs, pushing air along them, the fan is about 20 watts. Ambient temp could be quite hot, say 40 C (inside welding machine). Would you say that this amount of cooling should be enough? I will have a overheat switch mounted on the sink, so, hopefully, worst case would be a inconvenience of having to stop welding, but I would like to have some idea of adequacy of this setup. i What's the CFM (cubic feet of air) rating of the fan? And what's the surface area of the heatsink? (Material of construction of the heatsink?) 1 kW of heat to dissipate... have you considered a water-cooled system? 1kW is nothing really. My amps can generate about that much ( in 2u of 19" rackmount ) and I get rid of it with a max heatsink temp of 95C with 2 80mm 'boxer' style fans. That's very nice to know PB. 1 kW is a bit of an overestimation. 800 watts would be the maximum (200 amps x 2 volts voltage drop x 2 sides of the bridge), and welding would not be continuous, as well. Back in the office I have a neat little equation for temp rise in airflow vs energy absorbed. You can do it from first principles but it may come in handy. I'll post it later. It shows importantly that for certain temp rises vs watts you need a given mimimum airflow.

Thanks! Yes, I would like indeed to do some calculations. Now that I
am packaging stuff for real installation inside the welder, I want to
avoid making stupid avoidable mistakes.

I made some pictures last night, of the heatsink assembly with some

i
Ignoramus2491
science forum beginner

Joined: 05 Jan 2006
Posts: 3

Posted: Thu Jan 05, 2006 3:43 pm    Post subject: Re: Heatsink cooling

Found this nice article:

http://sound.westhost.com/heatsinks.htm

Will check it out. Turns out that my heatsink with glued in fins is
the highest performance heatsink.

i

On Thu, 05 Jan 2006 14:20:33 GMT, Ignoramus2491 <ignoramus2491@NOSPAM.2491.invalid> wrote:
 Quote: On Thu, 05 Jan 2006 07:53:15 +0000, Pooh Bear wrote: Ignoramus18299 wrote: On Wed, 04 Jan 2006 23:04:57 +0000, Pooh Bear wrote: onehappymadman@yahoo.com wrote: Ignoramus18299 wrote: Let's say that I have a source of about 800-1000 watts (two dual IGBTs inverting 200 amps). They should run relatively cool, to stay safe say under 80 C. I have a heatsink that is about 6x13 inches and weighs perhaps 12 lbs. I am cooling it with a fan mounted right next to the ribs, pushing air along them, the fan is about 20 watts. Ambient temp could be quite hot, say 40 C (inside welding machine). Would you say that this amount of cooling should be enough? I will have a overheat switch mounted on the sink, so, hopefully, worst case would be a inconvenience of having to stop welding, but I would like to have some idea of adequacy of this setup. i What's the CFM (cubic feet of air) rating of the fan? And what's the surface area of the heatsink? (Material of construction of the heatsink?) 1 kW of heat to dissipate... have you considered a water-cooled system? 1kW is nothing really. My amps can generate about that much ( in 2u of 19" rackmount ) and I get rid of it with a max heatsink temp of 95C with 2 80mm 'boxer' style fans. That's very nice to know PB. 1 kW is a bit of an overestimation. 800 watts would be the maximum (200 amps x 2 volts voltage drop x 2 sides of the bridge), and welding would not be continuous, as well. Back in the office I have a neat little equation for temp rise in airflow vs energy absorbed. You can do it from first principles but it may come in handy. I'll post it later. It shows importantly that for certain temp rises vs watts you need a given mimimum airflow. Thanks! Yes, I would like indeed to do some calculations. Now that I am packaging stuff for real installation inside the welder, I want to avoid making stupid avoidable mistakes. I made some pictures last night, of the heatsink assembly with some comments. http://igor.chudov.com/projects/Homemade-TIG-DC-to-AC-Inverter/06-Heatsink/ i

--
Ignoramus2491
science forum beginner

Joined: 05 Jan 2006
Posts: 3

 Posted: Thu Jan 05, 2006 4:52 pm    Post subject: Re: Heatsink cooling I used this calculator: http://www.novelconceptsinc.com/calculators-forced-convection-heat-sink-thermal-resistance.cgi Volumetric Flow Rate m^3/s 0.06 Number of Fins 13 Fin Width m 0.001 Fin Length m 0.3 Fin Height m 0.13 Sink Width m 0.12 Fin Thermal Conductivity W/mK 237 Result: Thermal Resistance C/W 7.46266e-02 So, for a continuous 800 watt load, the temperature rise would be 56C. That's probably acceptable. In reality, my load would be less than 800 watt (current lower than maximum, non-100% duty cycle in a welder). So, I am not worried about adequacy of my heat sink assembly. i
Pooh Bear

Joined: 17 Apr 2005
Posts: 76

Posted: Fri Jan 06, 2006 1:44 am    Post subject: Re: Heatsink cooling

Ignoramus2491 wrote:

 Quote: Thanks! Yes, I would like indeed to do some calculations. Now that I am packaging stuff for real installation inside the welder, I want to avoid making stupid avoidable mistakes.

Here's the info I had in mind. It conveniently mixes units so as to use the ones that are hopefully
most accessible.

Graham

Heat transfer equation from Sunon ( fan manufacturer )

Q = Cp . W . T

Q = Amount of heat transferred
Cp = specific heat of air
T = temperature rise
W = mass flow

putting in the relevant values I got to this..................

Air flow required ( CFM ) = 1.76 * power / temp rise ( degrees C )

Worked example e.g. 200W and delta T = 50C

gives 1.76 * ( 200 / 50 ) = 7 CFM
Ignoramus20351
science forum beginner

Joined: 06 Jan 2006
Posts: 1

Posted: Fri Jan 06, 2006 5:40 pm    Post subject: Re: Heatsink cooling

On Fri, 06 Jan 2006 01:44:20 +0000, Pooh Bear <rabbitsfriendsandrelations@hotmail.com> wrote:
 Quote: Ignoramus2491 wrote: Thanks! Yes, I would like indeed to do some calculations. Now that I am packaging stuff for real installation inside the welder, I want to avoid making stupid avoidable mistakes. Here's the info I had in mind. It conveniently mixes units so as to use the ones that are hopefully most accessible. Graham Heat transfer equation from Sunon ( fan manufacturer ) Q = Cp . W . T Q = Amount of heat transferred Cp = specific heat of air T = temperature rise W = mass flow putting in the relevant values I got to this.................. Air flow required ( CFM ) = 1.76 * power / temp rise ( degrees C ) Worked example e.g. 200W and delta T = 50C gives 1.76 * ( 200 / 50 ) = 7 CFM

Thanks. I also tried to find some place with a calculator and found
something nice. Below is a copy of ,y text file with a little detail
of these calculations. It looks like my setup is just about adequate
for 100% duty, which it will obviously not see due to application
(welder).

http://sound.westhost.com/heatsinks.htm

Heatsink calculations:

Size 7x12 width, 5" depth, 10 fins.

According to http://www.novelconceptsinc.com/calculators-forced-convection-heat-sink-thermal-resistance.cgi

Volumetric Flow Rate m^3/s 0.06
Number of Fins 13
Fin Width m 0.001
Fin Length m 0.3
Fin Height m 0.13
Sink Width m 0.12
Fin Thermal Conductivity W/mK 237

Result: Thermal Resistance C/W 7.46266e-02

--
John Larkin
science forum beginner

Joined: 30 Jul 2005
Posts: 30

Posted: Sat Jan 07, 2006 2:27 am    Post subject: Re: Heatsink cooling

On Fri, 06 Jan 2006 01:44:20 +0000, Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wrote:

 Quote: Ignoramus2491 wrote: Thanks! Yes, I would like indeed to do some calculations. Now that I am packaging stuff for real installation inside the welder, I want to avoid making stupid avoidable mistakes. Here's the info I had in mind. It conveniently mixes units so as to use the ones that are hopefully most accessible. Graham Heat transfer equation from Sunon ( fan manufacturer ) Q = Cp . W . T Q = Amount of heat transferred Cp = specific heat of air T = temperature rise W = mass flow putting in the relevant values I got to this.................. Air flow required ( CFM ) = 1.76 * power / temp rise ( degrees C ) Worked example e.g. 200W and delta T = 50C gives 1.76 * ( 200 / 50 ) = 7 CFM

That looks about right. But that assumes perfect coupling from the
heatsink to the air stream, which doesn't happen.

This gets complex, and I don't really understand it, but it's
something like...

If the fins on a heatsink are few and far between, the 7cfm will zip
through easily and not pick up much heat. So if the sink is
dissipating the 200 watts, the air exit temperature will certainly be
50K above intake (by conservation of energy) but the heatsink may be a
lot hotter. Imagine half the air being in good contact with fins, half
zipping through unaffected, and the halves mixing at exit, averaging
+50. The heatsink only contacts half the air, so it rises +100.

If the fins are very dense, coupling from sink to air will be good,
but you'll develop a lot of back pressure, and a "7 cfm" fan won't
move 7 cfm, so again the sink temp rise will be above 50.

heatsink restricts the fan to delivering about half its rated cfm. And
the fins should be nearly isothermal (ie, not long and skinny) because
cool fins restrict flow without coupling heat very well.

John
ehsjr
science forum beginner

Joined: 21 Jun 2005
Posts: 22

Posted: Sun Jan 08, 2006 1:05 am    Post subject: Re: Heatsink cooling

Ignoramus2491 wrote:

 Quote: Thanks! Yes, I would like indeed to do some calculations. Now that I am packaging stuff for real installation inside the welder, I want to avoid making stupid avoidable mistakes. I made some pictures last night, of the heatsink assembly with some comments. http://igor.chudov.com/projects/Homemade-TIG-DC-to-AC-Inverter/06-Heatsink/ i

I wish more people would do what you do - post updates
of the progrees in your project. You do a very good job
of keeping interested people informed.
Thanks!

Ed
YouGoFirst
science forum beginner

Joined: 13 Jul 2005
Posts: 47

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"JJSomar" <jjsomar@gmx.de> wrote in message

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