Low -- LAMP -- High
	Low -- WEIGHT -- High
	Simulation:  ON OFF
	Adjust sliders to control lamp power and counter-weight. Only a narrow range of inputs will results in a stable, oscillating diver. Thermal time-scales shortened to speed up simulation. Air volume above oil equal to oil volume.

Diver directions:

      For a simple device, the physics behind the diver can be quite convoluted. Roughly speaking, the diver's density should be matched to the liquid- in other words, just below neutrally buoyant so a slight change in volume causes it to float or sink. The liquid has a density of .87 in the simulation- thus the mass/volume (including the counter-weight) should also be about 0.87 Or slightly greater, so it sinks until hit by the light.

     However, if the diver is in a viscous liquid (with a small terminal velocity), it will rise very slowly, until the bottom of the diver is partly in the hot light beam. The upper part of the diver cools, and quickly reaches an equilibrium where the heat input expands the diver volume until its density just matches the liquid. Where upon the diver stalls. At lower viscosities, the diver's momentum, like a flywheel, drives it past the shield, and stalling is avoided.

     Similarly, if heat transfer to the liquid is fast, then the part of the diver out of the beam will cool too quickly, and again stall. And, of course, more light will be needed to raise the temperature of the diver if heat transfer is rapid. In the real diver, heat transfer is controlled by the thickness and material of the diver's sealed plastic bladder.

     The diver column is sealed from outside air pressure. The diver is so sensitive (particularly if designed for solar illumination) that barometric air pressure changes could prevent its operation. More importantly, even though the liquid is chosen to be very transparent, it does rise above room temperature. Mostly because the Plexiglas tank walls absorb infrared light.

     Many factors will cause the diver to sink. The hot oil heats the air above the liquid, raising its pressure. The hot liquid now takes up more space in the container, so it squeezes on the air above the liquid, causing the pressure to increase in the column AND in the diver. The rising temperature also thermally expand the liquid, reducing its density. All three factors cause the diver to sink. Conversely, as the oil heats, the air in the diver expands, helping it float.

     A puzzlement.

     Column height also matters. As the diver sinks, air within the bladder is compressed. This compression must eventually be overcome by a pressure increase due to a temperature rise within the diver. But, the lamp is only so bright; the maximum temperature rise is limited (in the real diver, to about 50 degrees Celsius), so the depth is limited as well.

     See if you can uncover these and other effects within the simulator. The sliders can be adjusted as the simulator runs. There is a narrow operating range for the diver- sometimes it will work for a while, and then stops. In practice, I use an external pump to increase the air pressure above the liquid until the diver oscillates- then seal off the column. This allows me to adjust pressure if small amounts of air diffuse out of the plastic diver bladder.

     Here is a movie of an open-bell solar diver. Note the weight is a chain, for reasons explained in our VW barometer....

     Good Luck!