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Heat dissipation and heat transfer coefficient for natural
convection between parallel isothermal plates.
Related links
Natural convection heat sink on line
Thermal design for electronics
Thermal online tools
Unit conversion
Comments
General
The equations are taken from chapter 8 and 10 of the
theory document.
Some articles that also cover the issues:
A Volumetric Approach to Natural Convection,
Natural Convection Cooled PCBs and Equivalent Velocity,
Maximum Heat Dissipation for Natural Convection Cooled PCBs
and
A Bessel function Solution.
The plate tab is simulates the conditions for isothermal surfaces.
The heat source tab simulates conditions for discrete sources.
Observe that the sources can be moved with the mouse.
Inputs
Plate height. Is the height of the plate that is assumed
to be in vertical position.
Plate width. Is the width of the plate.
Plate thickness. Is the thickness of the plates.
Temp diff. Is the temperature difference between the
plate and the incoming air.
Air temp. Is the inlet air temperature.
Pitch start. Is the start pitch for the calculation.
Pitch end.Is the end pitch for the calculation.
Include radiation. If include radiation is selected it is
assumed that the plate radiate heat though the openings in the slot
to a large room with walls that have the
same temperature as the inlet air. For a free plate it is assumed
that the the angle factor is 1.0. The emissivity of the
plate is set to 0.9.
Free plate. If free plate is selected there are not
disturbance from any near plates.
Save last/Delete last.
Saves or deletes the last curve
in the diagram. Maximum capacity is 5 curves.
Pressure and altitude.
These two inputs are mutually dependent. On cursor exit
from one input the other is updated. The allowed altitude
range is 0 - 11000 m.
Outputs
Heat dissipation. Shows a diagram of the heat dissipation
from one plate as function of the pitch.
Heat diss/pitch. Shows a diagram of the heat dissipation
per length unit as function of the pitch. This function has a
maximum for the optimum pitch.
Heat tr. coefficient.
Shows a diagram of the heat transfer coefficient as
as function of the pitch. The coefficient is defined on the
inlet plate-air temperature difference.
Velocity.
Is the average velocity between the plates.
Equ. velocity.
The equivalent air velocity is defined as the forced
convection velocity that results in the same heat transfer
coefficient as for the natural convection case. The physical
velocity follows the equivalent velocity reasonably well up to
1.2*optimum pitch. The difference can be considerable
for larger pitches. The a more in depth explanation
and be found in the article Natural Convection Cooled PCBs
and Equivalent Velocity.
Note
Clicking in the diagram opens a panel with tabled results
that can be copied and pasted into a spread sheet program.
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