The thickness of the thermal boundary layer would be

Question

A fluid flowing over a flat plate has the following properties: dynamic viscocity = 25 ´ 10^–6 kg/ms, specific heat = 2.0 kJ/kgK, thermal conductivity 0.05W/mK. The hydrodynamic boundary layer thickness is measured to be 0.5 mm. The thickness of the thermal boundary layer would be                           

      (a) 0.1mm                                                           (b) 0.5mm

      (c) 1.0mm                                                           (d) none