A hot fluid (k_fluid = 0.72 W/m∙K) is flowing as a laminar fully-developed flow inside a pipe with an inner diameter of 35 mm and a wall thickness of 5 mm. The pipe is 10 m long and the outer surface is exposed to air at 10°C. The average temperature difference between the hot fluid and the pipe inner surface is ΔT_avg = 10°C, and the inner and outer surface temperatures are constant. Determine the outer surface temperature of the pipe. Evaluate the air properties at 50°C. Is this a good assumption?