Thermal transfer improvement from adding fins

[leonhart88]

Hi All,

I'm designing a heater for some cylindrical tubes. In my original design, I simply had a flat plate contacting the bottom of the tube. Since the tubes are only conducting on the bottom, the temperature of the contents in the tube are somewhat off from the actual base temperature. I was curious if adding "fins" would help improve the thermal transfer to the tube contents. Please see the attached picture for the fin idea. Note that the tubes are in a rack and the entire tube/rack assembly sits on top of this plate (the rack is not shown). Therefore, the geometry of the fins cannot be changed, as this is the only way it will fit into the rack. The rack also provides some insulation between tubes. Lastly, I don't need to heat the top-half portion of the tube.

I am not sure how to calculate if the fins will be an improvement. In my experiments with the flat plate, the base temperature is set to 68C and then contents in the tube read 60C. I assume that if I can figure out how much extra heat the fins add to the tube via convection (there is a small clearance between the tube diameter and the fins), I can roughly determine what my steady state temperature would be (since I know that currently, losses are preventing the tube from reaching 68C).

Can anyone provide some advice/suggestions on calculating this out?


Thanks!

 

[CWatters]

They will probably help but it's not easy to calculate how effective they will be. The reason the tubes aren't at the same temperature as the base is because there is an energy flow from the base through the tubes. There is an analogy with electricity... a current flowing through a resistance produces a voltage drop. If you reduce the resistance the voltage drop will be lower but unless you know the current you cannot calculate how much lower the voltage drop will be. Likewise unless you know how much power is flowing from the base through the path of interest you can't calculate the temperature drop.

Using copper fins and insulating the outside of the rack is likely to help. The top of the tubes are likely to conduct a lot of the heat away - can you replace the top of the tubes with a different material that doesn't conduct heat as well?