Project ForgeWater flows through a tube of 3 cm internal diameter and length 20 m. The outside surface is heated electrically with uniform heat flux circumferentially and axially. Mean inlet and exit water temperatures are 10°C and 70°C. Mass flow rate is 720 kg/h. Disregard tube-wall thermal resistance. Internal heat transfer coefficient is 1697 W/m².K. Specific heat Cp of water is 4.179 kJ/kg.K. The inner surface temperature at the exit section of the tube is __________ °C (round off to one decimal place).
Explanation
Mass flow = 720/3600 = 0.2 kg/s. Q = m·Cp·ΔT = 0.2×4179×60 = 50,148 W. Uniform heat flux q″ = Q/(πDL) = 50,148/(π×0.03×20) ≈ 26,603 W/m². Wall surface temp at exit = T_fluid,exit + q″/h = 70 + 26,603/1697 ≈ 70+15.68 ≈ 85.7°C.
Source: GATE ME 2020 Session 2 (ME-2) (2020)
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