Tube furnace rework

The figures from the writeup, one per screen, in order.

4 visuals arrow keys or j and k move between them

Section along the axis of the current furnace, to scale: a 15.9 mm quartz tube 305 mm long through a 150 mm square steel box of ceramic fibre blanket, 108 turns of nichrome over the central 150 mm under cement, one thermocouple, both ends open to the room

Figure 1. The build as the model sees it, to scale. The dimensions marked “measure” are placeholders until a tape measure and a multimeter replace them.

2 / 4 in the writeup: 4. The model

Predicted axial temperature profile of the current furnace at 700 and 1000 °C setpoints: a single arch over the winding falling to room temperature at the open ends, with ±5 °C zones of 33 and 26 mm

Figure 2. The predicted profile at two setpoints. The grey band is the winding. At 1000 °C the winding ends sit 200 to 300 K below the centre, depending on where the open-bore radiation is taken to leave.

3 / 4 in the writeup: 5. Predictions for the first run

Video 1. The run the table describes, as the model sees it. Top, the profile along the tube with the pieces coloured by their oxide. Bottom, the centre temperature against the setpoint, the relay power, and the oxide at the centre and ±2 and ±4 cm. The pieces go in at the start of the hold; the 25 nm they show at once is the thin-oxide offset the Deal-Grove model applies, which is the part of the model the oxide runs will test first.

4 / 4 in the writeup: 7. What it feeds: choosing the next furnace

Steady axial temperature profiles at 1000 °C for uniform, graded and zoned heaters in the v2 geometry, at nominal and triple end losses. Only the zoned profile is flat across the boat.

Figure 3. The v2 geometry at 1000 °C with 2 slm of gas. Left, nominal end losses. Right, end losses tripled. Only independent zones stay within ±1 K across the boat.