Convection & Shapes: How Would They Affect Heat Plate?

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The discussion focuses on how different shapes of obstacles, such as a heat plate with nothing, a bundle of tubes, and fins, influence convection in a vertical airflow scenario. It highlights that flow lines downstream of an obstacle become homogenized within a distance comparable to the obstacle's width. Specifically, for cylindrical tubes, this distance is equal to their diameter, while for other shapes like tear-drop, it can be significantly smaller. Understanding these dynamics is crucial for optimizing heat transfer in designs involving convection. The conversation emphasizes the importance of shape in affecting airflow and heat distribution.
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Hi, I was wondering if someone could help explain how the following shapes would affect convection. What it is is a heat plate with nothing, a bundle of tubes, and just fins. It's in a vertical tube and the air flows upwards. I understand convection but I don't get how it would be affected in terms of a physical object such as these in its path.

http://img231.imageshack.us/img231/718/heatplatesf1.jpg
 
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The rule of thumb I use is that flow lines just downstream of an obstacle get very close to their far-away away structure within a distance comparable to the width of the obstacle. So if the tubes have a diameter d, then at a distance d downstream from each tube, the flow-lines are essentially homogenized again. For some shapes (tear-drop, for instance), this distance can be much smaller than the width of the object.
 

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