| 11| Horizontal Cavities

Heating from cavity from below (when τ = 0o) :-

For Horizontal cavities there is a critical Rayleigh’s Number (RaL,C) = 1708

 1.    If RaL < 1708 – The fluid layer is considered Thermally Stable and the Nusselt Number can be                        calculated   by:

2.    If 1708 < RaL < 5x104 – Thermal Instability occurs resulting in formation of regular convection cells as        seen below.

        In this instance, the fluid in the corners of each of the cells moves very little and with convection only         occurring significantly at the centre of each of the cells. This results in less effective heat transfer.   

3.    If 3x105 < RaL < 7x109 – Then the fluid flow inside the cavity is Buoyancy driven turbulent flow.            the Nusselt Number can be calculated using the following equation:

Heating from cavity from above (when τ = 180o) :-

There is little fluid motion and the and the fluid layer is unconditionally stable and hence: