Loading New Celani Wires
We loaded new Celani wires into each cell. We are in the process of testing the first four calibration steps (so we don't overload the wire) in Helium so we can confirm that it behaves similarly to the bare wire. Here are some pictures of the process of installing the wire.
No, Malachi is not pretending to be a mime. What you can barely see is one meter of 14 layer Celani wire.
Once we wrapped it onto cell 1.0, we trimmed off a small piece of excess.
From a 100 cm piece this is what we didn't need in the test cell.
Below is a shot of cell 1.1. Note that this cell is designed to have the glass assembly separate easily from the rest of the unit. In this picture, Malachi is scraping off the coating from the Celani with the edge of a knife blade in order to make good electrical contact with the end of it.
Cell 1.0 got a 14 layer wire
Cell 1.1 got a 2 layer wire - the same kind that ST Microelectronics showed success with.
Both wires ended up with close to 95 cm worth of wire, which means we have a small scrap to keep as a control and take microscope images of. On both cells, they wrapped beautifully, just as expected. It seemed to Malachi and I that the wires with fewer layers were less brittle and crispy feeling and wrapped on the support more like the bare Isotan. The 2 layer wire also has a resistance of around 16 ohms compared to the 14 layer wire at closer to 18 ohms. The first wire we used was 300 layers and just over 18 ohms. So, it appears the wire gets more brittle and higher resistance with the first several layers and changes less with more and more layers.
Stainless Cell and Calorimeters
We now have 3 things that can be considered improved calorimeters compared to the first cell design.
Stainless Cell with Insulation Jacket
We insulated a stainless steel cell on Monday. The insulated cell will be able to handle high temperatures and pressures, and will give a much better signal to noise ratio. The reason for this is that it will get much warmer with every watt of power in the cell. That means instead of 48 or 100 watts to get it up to a high temperature, it should need 10 to 20 watts. And if the Celani Wire produces a few watts of heat, the resulting temperature difference will be much larger and easier to measure. We will measure across the insulation at 3 locations with thermocouples. The result is this should be a pretty effective isoperibolic calorimeter.
This is what it looks like. Malachi carving the mineral wool insulation.
Now with plugs on both ends
We decided we needed an aluminum jacket to attach the thermocouples to so we could remove the cell to work on it. We wrapped the aluminum tube with 3 aluminum bands and inserted the last couple centimeters of the thermocouple tip between the band and the tube. That should make great thermal contact.
Here you can see the foil tape exterior and the aluminum tube interior.
The external thermocouples were installed by coiling the tip up and taping it down under more foil tape. They are located just outside the insulation form the internal sensors. The stainless wall of the test cell and the aluminum sleeve should help even out the temperatures extremely well and give a pretty even temperature distribution around the cell and along the length of the cell.
When we calibrate this, we will operate it inside the air flow calorimeter. This double checks the calorimetry and provides a wonderfully consistent ambient temperature and enough air flow to keep the surface of the insulation as close to a consistent temperature as possible. This picture shows Malachi sizing up the space available for plumbing and wiring.
Here is an illustration of how it turned out. Once we get to the right point, we will put this on the public data flow with these temperature sensors.
RTD-Heat Shunt Type Calorimeter
Last week a few ideas we had learned about calorimetry came together and we made a relatively quick and dirty test assembly to try out those ideas. The idea is to make an insulated box with an inside and outside aluminum shell, insulation in between, and a few aluminum "heat shunt" fins as the dominant path for heat to flow from the inside skin to the outside skin. The heat flow will be proportional to the temperature across the fin, so all we have to do is measure that temperature difference along each edge of each fin that will give us an indication of the heat flow. It's similar in principle to the way a Seebek type calorimeter works by averaging the temperature difference in many, many places where the heat flows.
The fins and shell are made according to this highly technical diagram below. There are 4 pieces. One is highlighted in blue to make it distinguishable.
Here they are in 0.020" inch (0.5mm) thick aluminum (0.5mm). We also made an inside box to make that skin even more thermally conductive and a better structure.
Then we attach custom, linear RTDs to each edge of the fin.
Assemble the box with 1 inch (2.5 cm) thick polyisocyanurate foil faced insulation in the cavities, and hook together the RTDs
At the top and bottom are aluminum caps that help conduct the heat to the walls. You can see the inside bottom cap here.
Our first calibration indicates it does generally work. It has a long time constant - almost 2 hours to fully settle. Ambient thermal noise has a pretty big effect. We are learning that controlling the thermal environment is a huge issue for every version of calorimetry have looked at.
Here are 3 improved calorimeters in one picture. Just need more hours in the day in order to be able to fully qualify each one and do more tests with wires. The exciting thing is that once we do get comfortable with them, it should allow us to test wires 90 to 95% faster than we can today.
If we see anything interesting in the vertical, dual cell tests this week, the path to better quantify it is getting clearer.