 
 # PROBLEM 2.9 # 
(A/V)r=0.636422, (A/V)c=0.400000
 Hence Rr is greater than Rc
 With minimum value of d Vr=2650 cm^3 .
 This valume is much more than the minimum Vr necessary. 
Let us now consider the top riser when the optimum cylindrical shape is obtained with h=d/2 
and again (A/V)r = 6/d. However, with a large top riser,
 the cube loses its top surface for the purpose of heat dissipation.
 d should be greater than or equal to 18 cm
 The riser volume with minimum diameter is 2290 cm^3 