# Transient Natural Convection between Two Plates at Different Temperatures

Transient Natural Convection between Two Plates at Different Temperatures

This Demonstration analyzes the transient free convection of a viscous incompressible fluid between two vertical plates at different temperatures. The fluid is initially at rest and the temperature of the fluid and the plates is the same. Convection occurs due to the Soret effect caused by a step change in the temperature of the plates [1].

The velocity and temperature profiles were obtained by solving the governing equations using the Mathematica function NDSolve. You can vary the temperature of the plates, the time and the Prandtl number (the ratio of the fluid momentum diffusivity to thermal diffusivity) to observe the temperature and velocity profiles.

Both the velocity and temperature are positive near the plate with positive dimensionless temperature and negative near the plate with negative dimensionless temperature; steady state conditions are reached faster with lower Prandtl numbers. Air at room temperature has a Prandtl number of 0.71, and for water at 18°C it is around 7.56; thus the thermal diffusivity is more dominant for air than for water.