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For flow of fluid over a heated plate, the following fluid properties are known: viscosity = 0.001 Pa.s; specific heat at constant pressure = 1 kJ/kg.K; thermal conductivity = 1 W/m.K. The hydrodynamic boundary layer thickness at a specified location on the plate is 1 mm. The thermal boundary layer thickness at the same location is

1. 0.001 mm
2. 0.01 mm
3. 1 mm
4. 1000 mm

Correct answer: 1 mm

Solution

The thermal boundary layer thickness is often comparable to the hydrodynamic boundary layer thickness in flow over a heated plate, especially when the fluid properties are similar. Given that both layers are influenced by the same flow conditions and the thermal properties are not drastically different, it is reasonable to conclude that the thermal boundary layer thickness is also 1 mm.

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