T-Cell VII; Two days, and counting...
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I've finally got some days off, and on Monday, 3 Nov 2008, I'm going to launch this monster! With the end in sight, I've started final plumbing, anode work, and what is turning into an amazing amount of pneumatic tubing for agitation AND venting. I've got two sealed containers... both of them need to be vented, and both of them need to be agitated, or stirred, for proper function.
Thanks to TheSidewinder, I can now pretty much flood this blog with photos! Photos are always more interesting than text only. For those interested in publishing pictures to the web, the fastest, easiest, and cheapest (free!) photo editor I've ever tried is Googles Picasa, currently version 3. You'll have to Google to find it. I'm too lazy to execute a link. Anyway, the raw photos get dumped into Picasa, where they are cropped, tuned, and then FTP'ed to my server using WS_FTP LE, an excellent, lean, and fast FTP client.
Beware Chinese Optics! A few years back, I taught myself to engrave, in the style that grace firearms and knives. With my eyes aging a bit, and with modern engraving techniques demanding some really fine cuts, I researched, and purchased, an excellent Meiji stereo-zoom microscope, based upon strong recommendations. It was 3X the cost of a Chinese clone, but I was assured by experienced engravers that the Chinese simply haven't caught up with the rest of the world when it comes to optics.
The reason I'm on this tangent - with a large supply of MMO mesh material on hand, I needed to be able to track anode wear and erosion. I don't have a balance or scale capable of such a fine measurement, so really, all I can do is check the MMO surface for visual signs of pitting, flaking, erosion, and wear. There are inexpensive USB caneras that can be installed in place of one of the eyepieces on these microscopes, and I took a chance and bought one... Chinese-made.
I placed a small test anode (not yet used) underneath the scope, and checked it out using the native Japanese optics. Beautiful, bright, and clear. Then I installed the camera. Quite frankly, it sucked. It functioned, but no amount of fiddling would bring the image into focus. I took another chance by opening it. At the end of the camera is the CCD detector chip; at the front is a necessary 10X reducer lens. The CCD chip came free, and by machining a plastic adapter tube, I was able to mount only the CCD chip into the microscope eyepiece tube.
I now had 10X too much magnification, but at least I could get the subject into focus. I snapped a few pics of the MMO mesh. The translation to JPEG is poor, but at least I have a partial record of what the surface of this anode looks like under a microscope.
If there is erosion or wear of this MMO material, I am hopeful that I can detect it with a subsequent inspection under the scope.
I moved on to final plumbing chores. After yakking it up a bit on Science Madness with Tentacles, among others, I realized that my vision of a high-flow pump is probably not accurate... the circulation, in fact, is going to be pretty slow. And that is good! My greatest fear was having the electrolyte level in the EC rise too high, too fast, and either leak, or spill out. With a low flow, the electrolyte is going to trickle out the EC exit port near the top of the electrodes, and flow back down into the CC, via gravity.
I still wanted the path from EC to CC to be wide open, gravity assisted, and with at least a portion of it using clear tubing so I can see what the flow looks like. I created a hybrid assembly of CPVC tubing (common hardware store stuff), PVDF hose barb fittings, and Tygon tubing.
A threaded stub of CPVC pipe is installed, along with 1/2 of a CPVC union, at the EC exit port. It is necessary to replace the buna-n gasket in the union with one made of Viton, and this was an easy job with scissors and an X-acto knife. The CPVC pipe takes a 90-degree bend straight down to a "T" fitting, which is terminated in a ball valve. The ball valve can be used to take samples, or to drain most of the system entirely. I am not certain what the ball valve ball is made off, and it might not last, but being separate from the rest of the system, and cheap, it'd be no great loss.
The stem of the T is threaded 3/8" FPT for a kynar hose barb. This accepts a short length of Tygon tube, which in turn is routed to a 3/8" port on the lid of the CC. This particular port has an internal section of CPVC pipe, so the hot exhaust from the EC will be dumped deep in the CC. Being hot, it will attempt to rise, and I'll gain a bit of stirring and mixing this way.
On to the anode... this anode was cut from my fresh MMO mesh stock, and measures 3" X 6" in legth. The hanger (shank) measures 1" wide by 0.041" thick, of CP titanium. The spot welding went very well. I turned up yet another CPVC "carrier" and bored it out 1" for this shank. It was time to try the Sculpey clay trick! Using a vise to grip the shank, and a custom-bored mold of aluminum, I began to pack the Sculpey clay around the anode shank. I took the liberty of building it up pretty thick on the side which will be inside the EC...
The Sculpey hardens at only 230 degrees f. so I took the liberty of using our kitchen oven for this, as this large anode + mold would not fit into my small box furnace.
After 45 minutes, I removed the vise, anode, and mold, and allowed it to cool. The top side of the molding was perfectly flat, as I wanted it to be. This is the side that will be on top of the EC, visible to the outside. The hardened Sculpey plug was easily released from the aluminum mold with just the slightest finger pressure. It looked good!
I cleaned it up just a little bit. Then, treating it like any other piece of PVC plastic, I solvent-welded it into the turned CPVC anode carrier.
One of the things that always bothered me about my design was the fact that the anode, the carrier, and possibly a third component, a spacer device to fill the void between carrier and anode strap, needed to remain separate, as I couldn't lower the wide anode through a small hole. The carriers have a rim on the, thus can only be inserted so far; the rim then catches on the lid, and movement halts. This is good for security, but makes assembly awkward.
The carriers can be inserted from the bottom (barely; the cathode spacing is tight), and the o-ring grips very firmly, but I am paranoid that the carrier would then fall downward, resulting in a gaping hole and possibly a short between electrodes. It only took three weeks for me to figure out that I could secure the strap on the top with the electrical connection... by creating a strong aluminum clamp, and then affixing that to the strap, I could kill two birds - the electrical connection is made, and the carrier is fixed in the vertical axis by the carrier rim on the underside, and the aluminum clamp on the topside.
This is what came from that:
The body is a healthy block of 7075 aluminum, and the clamp at the 8:00 area on the picture is a separate, smaller piece of aluminum. Two small cap screws keep the separate pieces together, but allow a good clamping action. The body has a 316SS stud on top for the cable from the power supply, and is also tapped on the clamp end 1/4 - 20, for a stainless bolt (not shown) that will bear on the clamp, and squeeze the strap firmly. Each strap will need a hole in the appropriate location, but that would be necessary anyhow for the style of electrical contact that I plan on using.
If the Sculpey plugs work (and that is a BIG "if"), I can have separate anodes already affixed to their carrier; the setup should be both firm and gas tight. If the Sculpey fails, I will be reduced to using a separate insert and perhaps some PTFE tape. OR... I could simply turn some CPVC round stock, slot it with a bandsaw, and glue the mass together.
I'm sitting here shaking my head... Once I figured out that I could insert the carriers from the bottom, and use the clamp to secure the assembly, I should have skipped the Sculpey and gone right to creating a CPVC insert. With gobs of primer and glue, it'll be very strong and also gas tight. I think I will go out to my shop and pull the anode + sculpey apart, and start over. This is a good example of why I blog like crazy. I literally get good ideas while I'm hammering away on the keyboard.
Last series of pictures.. when I made the lid for the CC, I drilled and tapped no less than 9 threaded ports. Right now, 6 are populated. They get used up quickly.
On the left side, from the rear:
The Tee shaped object is the vent for the entire system. One of the arms will exit outside the shop via PTFE tubing. The other will take tubing connected to the vent on the EC. This way, if for some reason electrolyte ends up in the EC vent, either due to overflow or sputtering, it will find its way back to the CC. The next port is capped, while the near left port is a hose barb that will accept the output from the EC.
In the middle is a grey PVC bulkhead fitting that will take aquarium pump air for stirring and agitation, with a 1/4" PTFE tube inside the CC.
To the right, from the rear to front, is a cap, a thermowell fitting, and an angled fitting for the top of the sight glass, as shown in the last blog. At least one of these capped ports will be used for HCl dosing, and the other will probably act as a sampling/topoff port.
Monday, this sucker will live. Big caveat, with NO pH control. I am waiting right now on a pH electrode and a dosing pump, both from eBay. pH controllers are dirt cheap, cheaper than meters, which is odd, since a controller has a meter in it and displays pH at all times. The controller, a whopping $10 + shipping.
Dosing pumps are another matter. They don't seem to go as cheaply as pH controllers, but it is possible to find clean, used units at 1/4 the price of a new pump. A pump can easily be replaced by a gravity-fed dosing vat, using a solenoid valve. Another option is a sealed acid vat that is pressurized by an aquarium air pump on demand, displacing HCl into the system. Whatver you go for, be sure it can handle concentrated HCl. Most chemical metering/dosing pumps can.
This is probably the longest blog to date. The next blog will report on the actual performance on day 1, starting with some used electrolyte from previous runs, and topped off with fresh, saturated KCl. Thanks for hanging with me. Stay safe.
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