I'm planning on building a pair of monoblock amplifier chassis that can be used for a variety of amplifiers that will likely include some first watt amplifiers. A primary driver for the configuration is the available space for the amplifier, which is limited in height and depth, but not too much in width. Also, I will probably house the power supply separately for a variety of reasons including size reduction of the amplifier chassis.
In order to limit the height of the chassis, I am considering having the heat sinks oriented flat with the fins pointing up. If used horizontally I would configure them so that the transistors mounted on them are mounted as centrally as possible. I am thinking this will make the sinks less efficient in shedding heat than the typical vertical orientation. Any ideas on how much difference a horizontal orientation would make in heat dissipation?
Thanks, Jim
In order to limit the height of the chassis, I am considering having the heat sinks oriented flat with the fins pointing up. If used horizontally I would configure them so that the transistors mounted on them are mounted as centrally as possible. I am thinking this will make the sinks less efficient in shedding heat than the typical vertical orientation. Any ideas on how much difference a horizontal orientation would make in heat dissipation?
Thanks, Jim
Mighty Zen Mod is right, without knowing the size of the heatsink it's not able to be accurately discussed.
However, this has some great info and is worth reading, as it will answer your questions - http://www.thermalsoftware.com/vert_vs_horz_sink.pdf
However, this has some great info and is worth reading, as it will answer your questions - http://www.thermalsoftware.com/vert_vs_horz_sink.pdf
Great article, it answered my basic question. Its about a 3% difference.
However I'm also wondering where I should try to locate the transistors on a horizontal heatsink, centrally or nearer the edges. The paper did not directly address location of heat source on a heat sink. It does appear that the edges perpendicular to the fins cool more due to the influx of air at the edges. I'm wondering if the front edge of the chassis I sketched would be the best location for the transistors to mount on the heatsinks. Previously I had been thinking that the best place would be as centrally located as possible. Too bad the thermal modeling software is pricey, it looks like I could easily model what I need with it.
However I'm also wondering where I should try to locate the transistors on a horizontal heatsink, centrally or nearer the edges. The paper did not directly address location of heat source on a heat sink. It does appear that the edges perpendicular to the fins cool more due to the influx of air at the edges. I'm wondering if the front edge of the chassis I sketched would be the best location for the transistors to mount on the heatsinks. Previously I had been thinking that the best place would be as centrally located as possible. Too bad the thermal modeling software is pricey, it looks like I could easily model what I need with it.
I could believe that 
Lots of info here ESP - Heatsink design and transistor mounting
He wisely doesn't give a %age degradation:
"Conduction (and / or convection) requires that there is a continuous stream of air flowing past the fins of the heatsink, which means that the fins should be vertical if at all possible. Horizontally oriented fins will lose a vast amount of thermal transfer, since the air cannot flow through to the body of the heatsink. A fan solves this problem immediately, since air being blown onto the face of the heatsink has considerable turbulence, ensuring that there is always plenty of cool air at the surface of the heatsink."
Lots of info here ESP - Heatsink design and transistor mounting
He wisely doesn't give a %age degradation:
"Conduction (and / or convection) requires that there is a continuous stream of air flowing past the fins of the heatsink, which means that the fins should be vertical if at all possible. Horizontally oriented fins will lose a vast amount of thermal transfer, since the air cannot flow through to the body of the heatsink. A fan solves this problem immediately, since air being blown onto the face of the heatsink has considerable turbulence, ensuring that there is always plenty of cool air at the surface of the heatsink."
years ago I tried big bada$$ heatsink ;
normally oriented - 350W of heat resulting in 55C on fins
horizontal - hardly 200W
go figure
though - above figure of 70-80W for what is sketched , I based on MF A1 , having 80W of heat thrown in laugh of heatsink , placed horizontally
when in temp. eq. , in summer days , I could manage no more than 3-5secs
normally oriented - 350W of heat resulting in 55C on fins
horizontal - hardly 200W
go figure
though - above figure of 70-80W for what is sketched , I based on MF A1 , having 80W of heat thrown in laugh of heatsink , placed horizontally
when in temp. eq. , in summer days , I could manage no more than 3-5secs
In my opinion DIY amps are hard enough without adding unnecessary complexities and compromises.
The OP also mentioned that he wants to place the heatsinks horizontally because of space limitations. This could mean that the amplifiers would be placed in a tight space with limited air flow, making conditions even worse. Seems to me that air movement by fan is the best way to make this situation work.
I looked back at the Thermal Solutions article to see if I missed a zero, but 3% is their basic conclusion, though that is for a specific heat sink size and fin configuration.
The article Scottjoplin suggested provided a lot of practical information on mounting transistors, and chassis construction but did not address efficiency of horizontal vs vertical as did the thermal solutions paper 6L6 provided. Great article and I have another use for my tiny bicycle torque wrench.
That article points to many mounting and construction considerations that could cause significant changes in heat dissipation. Could there have been changes in the mounting of the transistors between Zen mods measurements of vertical and horizontal heatsink temperatures, or perhaps changes in how the heat sinks transferred heat to the rest of the chassis?
So far this has been a very interesting discussion and I appreciate all your input, I hope we can find a reason why Zen mod's direct experience differs from Thermal solution's predictions. It would be helpful to learn the reason why (or perhaps arrive at the conclusion that thermal solution's 3% conclusion is hot air )
Late, tired and run out of steam, forgive my less than elegant language.
Cheers, Jim
The article Scottjoplin suggested provided a lot of practical information on mounting transistors, and chassis construction but did not address efficiency of horizontal vs vertical as did the thermal solutions paper 6L6 provided. Great article and I have another use for my tiny bicycle torque wrench.
That article points to many mounting and construction considerations that could cause significant changes in heat dissipation. Could there have been changes in the mounting of the transistors between Zen mods measurements of vertical and horizontal heatsink temperatures, or perhaps changes in how the heat sinks transferred heat to the rest of the chassis?
So far this has been a very interesting discussion and I appreciate all your input, I hope we can find a reason why Zen mod's direct experience differs from Thermal solution's predictions. It would be helpful to learn the reason why (or perhaps arrive at the conclusion that thermal solution's 3% conclusion is hot air )
Late, tired and run out of steam, forgive my less than elegant language.
Cheers, Jim
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