explain variable in nusselt number

uni/mmme/2047_thermodynamics_and_fluid_dynamics/heat_transfer.md

@@ -72,11 +72,12 @@ Nusselt number is a dimensionless number:
 $$\text{Nu} = \frac{hL}{k_f}$$
 
 where $k_f$ is conductivity of the fluid, $L$ is the representative length (e.g. diameter, length,
-internal width, etc.).
+internal width, etc.), and $h$ is heat transfer coefficient.
 
 Since $h$ is unknown a lot of the time, sometimes Nusselt number must be found through approximating
 by other dimensionless numbers: Prandtl, Reynolds, and Grashof.
 
+
 Nusselt number for a laminar forced flow is around 3.66.
 For a turbulent forced flow it is estimated to be: