Conductive Silicone to improve performance of fin to tube thermal bond in solar collectors

These are the results of a test comparing the performance of two solar collectors.  Both use alum fins and copper tubes.  Both collectors use silicone in the grooved alum fins to improve the conductivity between the alum fin and the copper tube.  The difference between the two is that one uses a thermally conductive silicone and the other uses ordinary silicone.

The idea is to see if the thermally conductive silicone improves the performance of the collector.

The test was run on 9/19/2010, but I'm just getting around to putting the results up.

For more on these small panel tests go here...



The construction of the collectors as whole  and the idea behind the small panel tests are covered here...
This page just shows the absorbers used for this test (with the two different types of silicone).

The picture just below shows the two absorber plates.  They are meant to be identical except that the top plate uses conductive silicone between the alum fin and the copper tube, and the bottom one uses ordinary silicone.

aborber plates for the test


The fins are 6 inches wide and made from 0.018 aluminum painted flat black.  The 2.75 inch wide alum backing plate is also 0.018 thick aluminum.

The regular silicone is Wall Mart store brand white.


The Conductive Silicone

conductive slicone

This is the data sheet on the Silicone Solutions SS-35 conductive silicone.  Other than being conductive, it has properties that are the same as a regular silicone caulk (which is a good thing).  It has about 3 times the conductivity of regular silicone. 

Click for full size.







collector performance


The green long dash line is the reservoir temperature for the collector with the conductive silicone.

The purpleish short dash line on the bottom is the reservoir temperature for the collector with regular silicone.

The top line is the sort of reference collector made with a copper fin soldered continuously to a copper tube -- just for reference.

Ambient temperature averaged about 45F. 
Sun intensity varied from about 800 w/sm at the start of the test down to about 650 w/sm toward the end. 
Wind was near calm.

Here are the results from the plot above tabulated.

Collector Start Temp F End Temp F Increase F Performance
regular silicone 59.7 155.1 95.4 base
conductive silicone 60.4 156.3 95.9 0.5 %

So, the conductive silicone performed about half a percent better.  This is such a small difference that its hard to say that it might not just be variables in the test process.  I guess its safe to say that any advantage of the conductive silicone is small.

If you see any problems with this test or the conclusions, I'd like to hear from you.

This is a picture of the test in progress -- it shows the new better insulated resevoirs and the stands that make it easier to keep the panels aimed toward the sun.  The water charges are weighed in

Test in progress


Gary November 28, 2011