Quiz - Natural Convection

If a hot body is immersed in air at lower temperature, the fluid in contact with the body would naturally convect _____  

Ignoring radiation, for a horizontal heated rectangular cavity with $H/L, w/L \gg 1$ at $Ra=100$ the heat transfer is due primarily to: 

Look at following correlation for estimating the Nusselt number for external natural convection over a sphere.  
$\overline{Nu}_D=2+\frac{0.589 Ra_D^{1/4}}{[1+(0.469/Pr)^{9/16}]^{4/9}}$

The constant term “2” accounts for the heat transferred by:  

For an array of vertical channels operating in isothermal conditions, if $S\lt S_{opt}$

For horizontal heated rectangular cavities if $Ra_{L,c} \lt Ra_L \lt 5\times10^4$ :

When analyzing two concentric cylinders, the effective conductivity term indicates:  

 For an inclined plate colder than the surrounding fluid (Select all that apply): 

On Earth, a cold long horizontal cylinder is surrounded by warmer air. Due to natural convection the air in contact with the cylinder forms a boundary layer that: 

If the ratio $Gr_L/Re^2_L \ll 1$:

The Boussinesq approximation assumes that the density variations can be approximated with: