Conrad heatsink showing machined
and linished surface.
The component mounting surfaces on Conrad heatsinks are machined, generally
linished and remain uncoated. This surface preparation maximizes
thermal conductivity between component and heatsink by:
Removing the relatively thick, thermally insulating
surface oxide layer, formed as a result of any hot
forming process with aluminium products.
Providing a flat, smooth surface ensuring maximum surface
area contact between component and heatsink.
Keeping the junction between component and heatsink free of any thermally
insulating coating.
Component Mounting Flange
The flanged mounting feature, as seen on type MF30-1F-75 for example, is
designed to improve thermal conductivity, provide greater ease of assembly
and savings in cost compared to a fabricated heatsink and right angle
bracket arrangement.
By eliminating the thermal junction between heatsink base and bracket
with a single piece heatsink, component temperatures are significantly
reduced. (See diagrams below)
For example, the thermal resistance of the interface between a right angle
bracket with cross-section 40x40x6mm bolted at 50mm. intervals to a
flat backed heatsink (including
thermal grease), has been measured at 3.5 C/W/cm2. The corresponding
figure for Conrad flanged heatsink is virtually zero.
The Conrad flanged single piece
heatsink (left) has more effective heat flow
than a conventional
fabricated heatsink.(right)
As a guide, thermal performance for heatsinks used with natural convection varies:
-
in direct proportion to the width (double the width, double the heat dissipation);
-
in proportion to the square root of the length (double the length, 40-50% increased heat dissipation).
As a result, width is thermally more effective than length. Comparing two heatsinks of similar thermal performance as shown below, the wider heatsink on the right (MF30-50) gives 45% more effective power dissipation per unit volume and weighs 28% less than the heatsink on the left (MF15-151.5). Hence, the inclusion of relatively broad heatsinks into the Conrad range.
For similar performance, the
MF30-50 (right) occupies 30% less volume
and weighs 28% less than
the MF15-151.5 (left).
The heatsink section profiles have been designed to provide an optimum
fin profile for a given fin height, length and convection condition.
Except for type MF18, Conrad heatsinks are suitable for both natural
convection (where plain plate fins have been found to be the most effective)
and forced airflow.
Adequate section thicknesses are provided to maintain conservative temperature
gradients across all heatsink surfaces and ensure ample mechanical strength
which is necessary for mounting components (in order to maintain flatness
and provide sufficient fastener thread depth) and for applications
where the heatsink is used as a structural component (for example, as
part of an enclosure).
Aluminium Alloy
Conrad heatsinks are manufactured using primary specification
CC 601 aluminium alloy, chosen for:
high thermal conductivity,
premium physical properties- strength, ductility, machinability,
corrosion resistance and suitability to the forming process.
To maintain premium material properties, all alloy is strontium modified,
titanium-boron grain refined and hydrogen de-gassed prior to use in manufacture.
Coating Material
Textured black polyester powder coating has been chosen as
the standard finish on all coated Conrad heatsinks and provides:
a quality, durable and attractive finish capable of withstanding
elevated temperatures,
increased thermal dissipation in the order of 5% to 8% (depending
on the heatsink) under natural convection.
Test Conditions
The test conditions for Conrad heatsinks apply to a free standing heatsink
in still air with the power applied by a distributed heat source, except
where otherwise stated. For type MF18, figures for both natural convection
and forced air flow are also given using a distributed heat source.
Thermal Performance and Temperature Rise Above Ambient
Especially for cooling with natural convection, the hotter a heatsink becomes,
the more effectively it dissipates heat. The thermal resistance of a
heatsink decreases with an increase in the heatsinks temperature rise
above ambient.
As a guide to the thermal resistance of a heatsink at a temperature rise
T °C above ambient:
R(T)=K(T) x R(80 °C) (1)
Where R(T) is the heatsink thermal resistance at T°C above ambient,
R(80°C) is the heatsink thermal resistance at 80°C above ambient,
K(T) is a temperature correction factor read from the graph below corresponding
to the temperature rise of T°C
Please note that the thermal performance at different temperature rises,
varies from heatsink to heatsink and that the correction factor K is
useful as an approximate guide only.
As an example, to estimate the power dissipation using a MF30-75 at a
temperature rise of 30°C above ambient:
From the heatsink data, MF30-75 thermal resistance at 80°C
rise
R(80°C)
=0.37 C/W
Reading from the graph above, the temperature correction factor
at 30°C
K(30°C)
=1.33
Using equation 1, the approximate
thermal resistance will be
R(30°C)
=1.33 x 0.37 C/W
=0.492 C/W
and the approximate power dissipation at 30°C rise above ambient
will be
P(30°C)
=30.0/0.492
=61.18 Watts
Dimensional Tolerances
For the heatsink dimensions shown in the following diagrams,
tolerances are given in the table below.
Dimension
Symbol
Tolerance (mm.)
Typically (mm.)
Width
W
+0.5
-0.75
+0.0
-0.5
Height
H
+0.5
-0.0
+0.5
+0.2
Base Thickness (Flat Back Heatsinks)
B
+1.0
-0.0
+0.5
+0.2
Base Thickness (Flanged Heatsinks)
B
+0.75
-0.0
+0.5
-0.0
Fin Position
F
+1.0
-1.0
+0.5
-0.5
Flange Position
P
+1.0
-1.0
+0.5
-0.5
Length
L
+0.25
-0.25
+0.25
-0.25
Handling Conrad Heatsinks
To obtain the best results when handling and machining aluminium products in
general and Conrad heatsinks in particular, we would suggest:
when holding securely, place on or clamp between clean compliant surfaces
(cloth, cardboard etc.) to avoid abrasion and indentation of machined and
coated surfaces.
when machining (drilling, tapping, milling etc.) using cutting fluid and
regularly removing, cleaning and re-lubricating the cutting tool. An
accumulation of swarf, particularly while drilling and tapping, may cause
clogging and result in damage to both the tool and the component.
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