A Closer Look at the Physics Involved in Lava Lamps

Remember those retro desk ornaments of the 1960’s, those lamps filled with colorful wax that began to move when the lamp was lit? I’m talking about lava lamps, or as I like to call them, “Rayleigh–Taylor instability machines”. They may not be popular among today’s youth, but I still own one and I thought it would be interesting to look beyond the dyed blobs of wax and observe the physics involved in lava lamps.

Physical Processes of Lava Lamps, in Theory

What I discovered was that this is an example of a model where it’s pretty clear what the participating physical processes are. This is a case of coupling fluid dynamics with heat transfer, where the material properties are temperature-dependent. The varying interface between two immiscible liquids (taking into consideration gravity and surface tension, of course) also needs to be computed.

No Two Lamps are Alike

So, we know what physics are involved in developing lava lamps. Yet, the paradox here is that even so, no two lava lamps will ever produce the exact same flow pattern, even if they are manufactured in the same way and are from the same batch. Just the smallest variations in the lamp, or where it’s sitting, and when it is turned on is enough to create a completely different flow pattern, size of bubbles, and so forth. In the same way, no two different computer processes will ever achieve the same solution for this application. Why? Here it’s because of the variations in the processes that lead to different solutions of this highly nonlinear model.

Multiphysics model of a lava lamp. Click on image to enlarge.

No two lava lamps are alike, whether they’re sitting on your desk or are produced as multiphysics simulations. And isn’t that what made these retro lamps so mesmerizing in the first place?