Convection Time-Constant in Air
Convection Time-Constant in Air
(OP)
My book on heat flow analysis does not help me with respect to the time-constants involved with natural or forced convection in air. My application is just an ordinary electronic circuit bolted to an ordinary finned aluminium heatsink. I could calculate the steady state temperature rise from equations in the book, but not the time constant. Obviously the mass of the heatsink needs to be heated up to the steady state value and additionally the heat is simultaneously being convected away.
I have previously experimented with this subject and it seemed to be the case that the more fan cooling I applied, the shorter the resulting time constant.
In my current application rapid temperature changes of the circuit are very bad, but slow changes are fine. The fan cooled heatsink I am using responds too rapidly to ambient changes and I want to get a feel for the problem.
I have previously experimented with this subject and it seemed to be the case that the more fan cooling I applied, the shorter the resulting time constant.
In my current application rapid temperature changes of the circuit are very bad, but slow changes are fine. The fan cooled heatsink I am using responds too rapidly to ambient changes and I want to get a feel for the problem.





RE: Convection Time-Constant in Air
RE: Convection Time-Constant in Air
I apologizes about my first comment.
Good Luck
Twoballcane
RE: Convection Time-Constant in Air
C = thermal capacitance = specific heat x mass
R = thermal resistance = 1/hA (assumes convection dominates)
h = heat transfer coefficient
A = surface area exposed to fluid
So your previous experiments were correct, logbook. For example, if you improve convection (reduce "h") by a factor of 2, you'll need about twice the mass to maintain the same time constant.
If you change from aluminum to copper, heat transfer will improve but typically only 10-20% for most heat sinks (depends on your geometry) and the mass will triple.
ko (www.ecooling.biz)
RE: Convection Time-Constant in Air
RE: Convection Time-Constant in Air