An L = 1-m-long vertical copper tube of inner diameter D_i = 20 mm and wall thickness t = 2 mm contains liquid water at T_w  ≈ 0°C. On a winter day, air at V = 3 m/s, T_∞ =–20°C is in cross flow over the tube. 

(a) Determine the heat loss per unit mass from the water (W/kg) when the tube is full of water.
(b) Determine the heat loss from the water (W/kg) when the tube is half full.