Consider a 2-mm-diameter sphere immersed in a fluid at 300 K and1 atm.
(a) If the fluid around the sphere is quiescent and extensive,show that the conduction limit of heat transfer from the sphere canbe expressed as NuD,cond = 2. Hint: Begin with theexpression for the thermal resistance of a hollow sphere, lettingr2 →∞ and then expressing the result in terms of theNusselt number.
(b) Considering free convection, at what surface temperaturewill the Nusselt number be twice that for the conduction limit?Consider air and water as the fluids.
(c) Considering forced convection, at what velocity will theNusselt number be twice that for the conduction limit? Consider airand water as the fluids.
