<div dir="ltr"><font color="#000000" face="Times New Roman" size="3">
</font><p style="margin:0in 0in 10pt"><font face="Calibri"><font size="3"><font color="#000000">Alan, your light looks like it is coming together nicely.<span> </span></font></font><font color="#000000" size="3">Good job. I was looking at the pictures of
the unit both the assembled unit in the sink and the disassembled unit to see
what you could possibly do to reduce the array temperature.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">A couple of observations:</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">Acrylic is a good thermal insulator and off
course aluminum is a great thermal conductor so as you note, the back if the enclosure
has got to do the bulk of the work in conducting the heat away from the
array.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">You could increase the heat transfer
rate away from the array several ways.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">The
first is that you should flip the light in the sink so that the light comes out
horizontally rather than vertically.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">You
want the fins to be oriented vertically.</font><span><font color="#000000" size="3">
</font></span><font color="#000000" size="3">Since the water is essentially static in the sink, you have to rely on natural
convection to pull heat away from the fins.</font><span><font color="#000000" size="3">
</font></span><font color="#000000" size="3">The concept being that as the water around and between the fins heats
up, its density drops and it becomes more buoyant relative to the colder waters
so it wants to go up. This sets up a natural circulation pattern. Having the
fins vertically promote this flow.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">The
second observation is your heat transfer rate would increase if you had more
surface area in the fins. If you look at most of the commercial LED lights, they
have more fins and they are thinner than yours.</font><span><font color="#000000" size="3">
</font></span><font color="#000000" size="3">I am assuming you are using thermal grease between the array and base. IF
not this would be a problem. One other point; Borosilicate glass is about nine
times more thermally conducive than acrylic.</font><span><font color="#000000" size="3">
</font></span><font color="#000000" size="3">This would aid in transferring more heat out the front lens.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">These three changes, testing with light to
optimize natural convection, increasing the number of fins and reducing their
thickness and switching to Borosilicate glass should drop the temperature of
the array significantly.</font></font></p><font color="#000000" face="Times New Roman" size="3">
</font><p style="margin:0in 0in 10pt"><font color="#000000" face="Calibri" size="3"> </font></p><font color="#000000" face="Times New Roman" size="3">
</font><p style="margin:0in 0in 10pt"><font color="#000000" face="Calibri" size="3">Cliff</font></p><font color="#000000" face="Times New Roman" size="3">
</font></div><div class="gmail_extra"><br><div class="gmail_quote">On Sat, Apr 15, 2017 at 11:33 PM, Alan via Personal_Submersibles <span dir="ltr"><<a href="mailto:personal_submersibles@psubs.org" target="_blank">personal_submersibles@psubs.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">I put a temperature probe inside the housing of my 80W LED light.<br>
The probe was up against the acrylic lens, as I was concerned about<br>
what temperature the lens was seeing on the inside. The lens is 10mm<br>
away from the LED.<br>
The LED manufacturer told me that on normal LEDs the temperature<br>
out the front of the LED can be 338F (170C) but my flip chips should<br>
run cooler.<br>
Briefly; when run at 30W in water they stabilised at 257F after 5 minutes.<br>
At 45W they stabilised at 280F after 5 minutes. I stopped upping the amps<br>
at this stage.<br>
Next experiment, I filled the housing with silicone oil.<br>
At 45W it hit 116F in 4 minutes & temperature stabilised.<br>
At 76W it hit 139F in 6 minutes & stabilised.<br>
So oil has massive advantages in lessening temperature on the lens,<br>
maybe because it is a buffer from the radiant heat & also transfers the heat<br>
out through the housing quicker.<br>
Greg your thoughts would be appreciated on this; I am thinking that without the<br>
oil the acrylic lens would see temperatures at which it is formed especially<br>
if I went up to 80W. Although the outside of the lens was cold there would be a<br>
temperature transition across the thickness of the lens & it would be considerably<br>
weakened. I am building to 500ft, so it would potentially see 250 psi in operation.<br>
At this stage I haven't made up my mind whether to go with a borosilicate lens<br>
or oil fill with an acrylic lens. I had a large bubble & it would be hard to eliminate<br>
all bubbles in the oil filling process.<br>
Will try & attach photos.<br>
<span class="HOEnZb"><font color="#888888">Alan</font></span><br><br>
<br>
<br><br>
<br>
<br>
<br>
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