If the total resistance between the steam and the air (including the pipe wall and scale on the steam side) in Problem 6.12 is 0.05 m2 K/W, calculate the temperature difference between the outer surface of the inner pipe and the air. Show the thermal circuit. From Problem 6.12: In a long annulus (25 cm ID, 38 cm OD), atmospheric air is heated by steam condensing at 149?C on the inner surface. The velocity of the air is 6 m/s and its bulk temperature is 38?C.GIVENAtmospheric flow through an annulus with steam condensing in inner tubeDiameters Inside(Di) = 25 cm = 0.25 mOutside (Do) = 38 cm = 0.38 mSteam temperature (Ts) = 149?CAir velocity (V) = 6 m/sTotal resistance between the steam and air (At Rtot) = 0.05 (m2 K)/WAir bulk temperature (Tb) = 38?CFrom Problem 6.12 heat transfer coefficient on the outer surface of the inner pipe ( hc ) = 25.4 W/(m2 K)ASSUMPTIONSSteady stateSteam temperature is constant and uniformHeat transfer to the outer surface is negligibleAir temperature given is the average air temperatureThermal resistance of inner tube wall and condensing steam is negligible (Inner tube wall surface temperature =Ts)

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Alr To = 38°C V-6 m/s Do- 38 cm D-25 cm Steam T.- 149°C