Introduction

The onset of convection driven by buoyancy during unsteady-state heat conduction can be simulated with FLUENT.   The critical time and the sizes of plumes at various stages of development can be observed accurately.  The influence of transient Biot number on the onset of convection can be easily studied using the various thermal boundary conditions.  The results of simulations have been found to agree well with equations and theory developed by Tan and Thorpe (1992 and 1996).  Further theoretical Nusselt numbers for heat transfer from a plane surface can be derived from  Biot numbers, they have been found to be in good agreement with empirical correlations published in the literature.

Below is the simulation of unsteady-state cooling of water with constant heat flux (CHF) boundary condition from the top surface of the water:

Length = 0.031 m
Height = 0.06 m
Heat flux = 60.1 W/m²
Critical time = 70 sec
 
 

The simulation of unsteady-state heating of water with constant heat flux (CHF) boundary condition from the bottom surface of the water:

 
Length = 0.032 m
Height = 0.032 m
Heat flux = 9600 W/m²
Critical time = 100 sec
 
 

 
Watch the birth and death of the thermal/magic mushroom !!
 
If you want to have a customised magic mushroom, please contact us.
 
This simulation and animation is done by MSc student Tan Kah Yaw

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