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Thread: Horizontal SFF Cases - Better to reverse top-down heatsink airflow?

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    Chozo4's Avatar
    Chozo4 is offline Junior Member
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    Sep 2012

    Lightbulb Horizontal SFF Cases - Better to reverse top-down heatsink airflow?

    Has anyone else had similar experiences whereas reversing the airflow of a CPU heatsink made much of a difference or opinions thereof?

    Experience prompting this query:
    I'm assuming this is often a brought up topic in the form of 'reversing fan flow' and so forth. Normally the recommendation as well as my own has been to keep it blowing down to the heatsink with top-down sinks but I've found after a hunch that sometimes reversing it is better depending on the case such as a Small Form Factor. In my case I have an Ultra Microfly case modded with 2x 92mm intake fans and the stock 4-heatpipe Opteron/Phenom cooler (the old style ones with higher fin count) using AS5 for paste. Cable management is good with very few cables visible, tucked away/hidden, making a minimal impact on airflow.

    Being as it's a small form factor case with the mobo laying flat the airflow is blown directly across the board. Having the CPU fan blow down would cause a flow conflict with the exhaust and intakes. This was causing the 'exhausted air' from the sink to blow out one side toward the intake flow causing it to cool already heated air while fighting with the exhaust for airflow. Running at 3.6ghz would spike to around 55-60c which is already a bit warm to begin with (CPU has 69c TCaseMax) with stock cooling in an already cramped case. After reversing it - it has surprisingly caused a ~10c drop in temps down to 45-50c. Surely this wasn't helping before as it is with the mosfets behind the socket with such warm air blown through. Being the CPU fan is a moderate CFM fan (64cfm) - it should have enough 'pull' in the other direction to pull cooler air over the fets in return than it was when blowing.

    This has been effectively the first time I've experienced a such positive difference in temps in all the systems I've done. My last case was a tower with an older opteron 170 @ 2.71ghz so it ended with worse results using the same exact heatsink if the fan was reversed during another test way back when. Actually makes me want to pick up a 100cfm+ fan such as a delta now.
    Last edited by Chozo4; 01-08-2013 at 11:43 PM.
    PC: 'Scarab' - Model#'s+More
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