a simple device, the physics behind the diver can be quite convoluted.
Roughly speaking, the diver density should be matched to the liquid- in
other words, neutrally buoyant so a slight change in volume causes it
to float or sink. The liquid has a density of 1 in the simulation- thus
the mass/volume should also be about 1. Or slightly greater, so it sinks
until hit by the light.
if the diver is in a viscous liquid (with a small terminal velocity),
it will rise very slowly, until the top of the diver is just hidden by
the shield. This part of the diver cools, and quickly reaches an equilibrium
where the heat input is matched by the heat output, until the net diver
density matches the liquid. Where upon the diver stalls, partly obscured
by the shield. At lower viscosities, the diver kinetic motion drives it
past the shield, and stalling is avoided.
if heat transfer to the liquid is fast, then the part of the diver hidden
by the shield 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 wall.
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, the liquid does rise above
room temperature. The hotter liquid causes the air within the diver to
expand, and unless compensated, causes the diver to bob to the surface.
Fortunately, the rising temperature cause the liquid to expand, reducing
its density. So the diver tends to sink. And, since the liquid now takes
up more space in the container, it squeezes on the air above the liquid,
causing the pressure to increase in the column AND in the diver. Again
tending to increase diver density. (The simulation actually models a temperature
gradient from the light to the top of the column, but the basic idea is
height also matters. As the diver dives, the air within 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 30
degrees Celsius), so the depth is limited as well.
if you can uncover these and other effects within the simulator. The sliders
and text boxes can be changed as the simulator runs. The yellow oval is
the light source, and the short vertical line the shield. The rapidly
varying numbers next to the diver and at the top of the column is the
temperature (roughly in Kelvin) inside the diver, and in the air above
the liquid. There is a narrow operating range for the diver- sometimes
it will work for a while, and then stop. Good Luck!
Falstad was kind enough to convert my
iBasic program to Java for posting on the web.