Lava Lamp: Wax-Liquid Density Crossover (2D)

Heat Source

Heater temperature 72 °C

Cap / coolant temperature 24 °C

Fluid Properties

Carrier-liquid viscosity 120 mPa·s

Carrier-liquid expansion β_liq 2.5 ×10⁻⁴/K

Live Readout

Elapsed time

0.0 s

Avg blob temp

0 °C

Crossover temp

— °C

Avg Δρ (wax−liquid)

0 kg/m³

Avg Reynolds no.

0.00

Coalesce / split

0 / 0

How it works

A real lava lamp does not rise from simple heating — it rises because wax and the surrounding carrier liquid expand at different rates with temperature. Both are calibrated to nearly the same density at room temperature, but wax's volumetric expansion coefficient (β_wax ≈ 9×10⁻⁴ K⁻¹, fixed here) is larger than the liquid's (β_liq, the slider above). Each material's density follows:

ρ(T) = ρ₀ · (1 − β·(T − T_ref))

Because β_wax > β_liq, heating shrinks wax's density faster than the liquid's — above a crossover temperature (shown live) wax becomes lighter than the liquid and floats; below it, wax is denser and sinks. Raise β_liq toward β_wax and the crossover temperature climbs — eventually the heater can no longer float any wax at all, exactly like a real lamp with the wrong fluid mix.

Each blob's internal temperature relaxes toward the local ambient (a linear gradient from the heater at the base to the cool cap at the top) via Newton's law of cooling. Its motion is driven by the net buoyant force F = V·g·(ρ_liquid − ρ_wax) opposed by real Stokes drag F_d = 6πμrv, whose ratio to inertia is reported live as the Reynolds number — it should stay well under 1, confirming the flow is in the slow, viscous (Stokes) regime a real lamp operates in. Blobs that touch coalesce (volume and heat-weighted temperature are conserved), and a blob that grows too large re-splits under its own instability, both counted on the right.

Wax blob (hot → floats) Wax blob (cool → sinks) Heater base