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Match List - I and List - II :

List - IList - II
(a) Free convection(i) \(\frac{hD}{K}\)
(b) Nusselt number(ii) \(\frac{K}{h_{0}}\)
(c) Thermal diffusivity(iii) \(\frac{K}{\rho Cp}\)
(d) Critical radius of insulation in case of cylinder(iv) Grashof number

Choose the most appropriate answer from the options given below :

  • A.(a)-(iv), (b)-(ii), (c)-(iii), (d)-(i)
  • B.(a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)
  • C.(a)-(iv), (b)-(i), (c)-(iii), (d)-(ii)
  • D.(a)-(ii), (b)-(iii), (c)-(iv), (d)-(i)

Answer: C

The correct matching is (a)-(iv), (b)-(i), (c)-(iii), (d)-(ii).

  • Free (natural) convection is characterised by the Grashof number (a-iv).
  • Nusselt number is \(\frac{hD}{K}\), convective over conductive heat transfer (b-i).
  • Thermal diffusivity is \(\alpha = \frac{K}{\rho C_{p}}\) (c-iii).
  • The critical radius of insulation for a cylinder is \(r_{c} = \frac{K}{h_{0}}\), with K the conductivity of the insulation and \(h_{0}\) the outside film coefficient (d-ii).

Option A gives Nusselt and the critical radius each other's expressions; option B pairs free convection with the Nusselt formula. For a sphere the critical radius would be \(2K/h_{0}\), but the question specifies a cylinder.

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