Titanium heat exchanger for DIY aquarium chiller

In my first post about building an aquarium chiller, I used a coiled stainless steel heat exchanger that I bought at a lab surplus sale. It was very likely built from 316 stainless steel, but it eventually corroded. Despite my attempts to repair and passivate the stainless steel, the coil continued to corrode, and I permanently removed it from the aquarium.


Since the weather is starting to heat up, I decided to build a titanium replacement for the chiller heat exchanger. I bought some 1" dia x 0.025" wall titanium tubes on eBay after fruitlessly searching for a coil or something that I could bend into a coil. The surface area is about 16 in^2. The stainless coil had a surface area of about 20 in^2, so the heat transfer should be comparable.


The heat exchanger is built so that the metal tube is pinched between the plastic end caps when they are threaded onto the internal aluminum shaft. There are rubber washers to seal the metal to the end caps.

The device fits into my hang-on filter in the same position as the stainless coil did. I'll let everyone know how it works.

Speaker repair - replacing the foam surround

Etching Acetal (Delrin) plastic in preparation for painting, gluing, etc

It looks like it might be possible to glue delrin with 3M DP-8005 after this chromic acid etching process. I'll do some more testing later.


I mixed:
40g water
25g potassium dichromate
500g concentrated sulfuric acid
http://books.google.com/books?id=Fl57...
I guess this mixture is commonly called chromic acid.

Things that I should have done:
Use a Pyrex beaker

Don't use the magnetic stirrer, just use a teflon stir stick

Use an ice bath at the beginning of the procedure

First test run of 1000W Osram xenon short arc lamp

I have now built this lamp into a searchlight housing.

UPDATE: http://benkrasnow.blogspot.com/2010/10/diy-searchlight-housing-for-1000w-xenon.html



I made a short video showing a test of an Osram 1000W xenon short arc lamp. I plan to build this lamp into a searchlight housing.

Looking closely at CDs

I've always been intrigued by the dividing line between the written and unwritten areas on a CD-R. All CD-R formats begin writing in a spiral track starting at the inner radius of the disc and proceeds to the outer radius, so the inner area is written data, while the outer area is still blank. The inner area usually looks lighter in color.

I first placed the CD-R on the microscope stage, bottom-up. This worked at "medium power" 10x, but I could not focus at 40x because the thickness of the CD itself did not permit focusing the 40x objective. Instead, I scratched off a little of the protective coating on the CD top surface, then inspected it from the top.

This is a very old Memorex CD-R. Green-blue dye with a gold top-layer. I lit the CD-R from below with the microscope's built-in light. The image was pretty dark, but by setting the camera exposure to 3 sec, the final image looks great.

Here's a shot of the dividing line between the data area (upper half) of the disk and the blank unused portion of the disc (lower half). The length scale is approximate.



Here is a %100 crop from my camera. The length scale is approximate and computed by dividing the frame height of my camera (13mm) by the microscope objective's magnification (40x), then scaling in GIMP to make the bar an appropriate size for the crop. I checked Wikipedia, and it appears the track spacing for a CD-ROM is 1.6um, so I wasn't too far off.