Liquid ethanol is a flammable fluid that has a flashpoint at 16.6°C. At temperatures above the flashpoint, ethanol can release vapors that form explosive mixtures, which could ignite when source of ignition is present. In a chemical plant, liquid ethanol is being transported in a pipe (k = 15 W/m·K) with an inside diameter of 3 cm and a wall thickness of 3 mm. The pipe passes through areas where occasional presence of ignition source can occur, and the pipe’s outer surface is subjected to a heat flux of 1 kW/m2. The ethanol flowing in the pipe has an average temperature of 10°C with an average convection heat transfer coefficient of 50 W/m2·K. Your task as an engineer is to ensure that the ethanol is transported safely and prevent fire hazard. Determine the variation of temperature in the pipe wall and the temperatures of the inner and outer surfaces of the pipe. Are both surface temperatures safely below the flashpoint of liquid ethanol?

FIGURE P2–71

 

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4, =1 kW/m? Liquid ethanol h, T. 4, =1 kW/m? Liquid ethanol h, T.