In a falling film evaporator, the inside and outside diameters of the tube wall are 25 mm and 27 mm, respectively. The tube is made of SS304 (thermal conductivity=15 W m^-1 K^-1) and the inside convective film coefficient is 750 W m^-2 K^-1. Outside the tube wall, film coefficient of condensing steam is 7175 W m^-2 K^-1. Based on the inside area of the tube, the overall heat transfer coefficient is