GATE AG 2021 • Q19 MCQ • 1 Mark

Section 7: Dairy and Food Engineering

Heat and Mass Transfer

Subtopic: Steady state heat transfer in conduction, convection and radiation

Question Statement:

One-dimensional generalized heat conduction equation representing temperature distribution in a sphere, based on thermal conductivity k, specific heat capacity Cp, density ρ, and energy generation E, can be written as (1/rⁿ)·∂/∂r(rⁿ·k·∂T/∂r) + E = ρCp·∂T/∂t, where the value of n is

Options:

  • (A) 1
  • (B) 2
  • (C) 3
  • (D) 4

Official Answer Key:

B

Step-by-Step Solution & Explanation

The generalized 1-D conduction equation with geometry factor n takes n = 0 for a plane wall (Cartesian), n = 1 for a cylinder, and n = 2 for a sphere — the spherical Laplacian in r involves r² in exactly this position. Hence n = 2, matching (B).

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