Quote:
Originally Posted by rcheshire
............ a previous question about preferred fan airflow direction in one of the cooling posts, the answer is derived quite apart from any cooling consideration - wind velocity.....
The effect is eliminated by drawing air through the heatsink rather than blowing air into the heatsink. I think the latter is marginally more effective, but as I found, a significant problem in the field with any sort of breeze.....
A crude analogy might be compressor blade stalling/surging in a gas turbine engine. This is controlled by the incidence of the airflow presented to the compressor by guide vanes - the airflow through the heatsink onto the fan guided by the fins is probably similar in effect.
|
Just wanted to make a few comments based on my testing and reading on this subject. First in relation to fan design, some fans are better at pushing rather than pulling air, and fan blade design is the determinant.
If your fan is pulling air through a heatsink, with many heatsink designs the path of least resistance is through the side of the heatsink vanes and thus airflow over the total vane area can be significantly reduced. With a pusher fan, with good pressure, I believe better heat extraction is possible, provided the air can flow through and is not blocked. There are a number of CPU heatsink fans on the market that push air down onto the CPU mount area and through the heatsink (the idea being that the air then spreads out across the motherboard and produces a general cooling effect). I am using this sort of architecture on my mono camera.
So how do we orient the fan to the cold finger, is there an optimal orientation? My past field experience would suggest that optimal cooling is derived from airflow which is perpendicular to the sensor cold finger. This keeps any warm air extracted from the heatsink away from the TEC and cold finger. However, on my new mono camera I am doing the opposite, with the warmed air exiting the heatsink and aimed at the TEC/cold finger (due to the folded nature of the heat pipe heatsink to achieve low profile). I believe that insulation of the cold finger and TEC area will prevent loss of cooling due to warm air passing, and I will be using a TEC/cold finger 'deflector shield' made of 2mm carbon fibre sheet, to angle the air flow away from the camera.
Differences in orientation may be hard to determine without actually trying them in operating conditions. Since most imaging does not take place during windy conditions (due to effects on telescope stability), I do not believe wind induced fan harmonics are a major risk.