The heat transfer per meter length of the duct, in watts, is

Question

Statement for Linked Answer Q01 & Q02

An un-insulated air conditioning duct of rectangular cross section 1 m ´ 0.5 m, carrying air at 20⁰C with a velocity of 10 m/s, is exposed to an ambient of 30⁰C. Neglect the effect of duct construction material. For air in the range of 20-30⁰C, data are as follows: thermal conductivity = 0.025 W/m. K; viscosity = 18 mPa.s; Prandtl number = 0.73; density = 1.2 kg/m³. The laminar flow Nusselt number is 3.4 for constant wall temperature conditions and, for turbulent flow, Nu = 0.023 Re^0.8 Pr^0.33.  

1. The Reynolds number for the flow is

      (a) 444                            (b) 890                         (c) 4.44 ´ 10⁵                   (d) 5.3 ´ 10⁵

 

    2. The heat transfer per meter length of the duct, in watts, is

(a) 3/8                                   (b) 5.3                          (c) 89                              (d) 769