Liquid Freon-12 enters a smooth pipe at 12C with a mass flow rate of 0.06 kg/s....

 

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Liquid Freon-12 enters a smooth pipe at 12°C with a mass flow rate of 0.06 kg/s. The pipe has a diameter of 15 mm and a total length of 4.0 m. The outside wall of the pipe is wrapped with a variable electrical heating element that produces a uniform heat flux of 10.0 kWim overis cntire length. Neglecting entrance effects, determine: a) the temperature of liquid Freon-12 at the outlet; (6 marks) b) the inner surface temperature of the pipe at the outlet. (9 marks) Due to a leakage in the pipe, the pipe is replaced by a new one with a diameter of 25 mm, and the mass flow rate of liquid Freon-12 is reduced to 0.008 kg/s. The heating flux is also adjusted correspondingly to maintain the same outlet temperature of liquid Freon-12 as before. What will be the inner surface temperature of the pipe at the outlet now? c) (10 marks) You may assume the following properties of liquid Freon-12 to be constants in the temperature range of interest: p= 1330 kg/m', H=2.63x10 kg/m.s, Cp 0.96 kJ/kg.K, Pr 3,5 k = 0.073 W/m.K Liquid Freon-12 enters a smooth pipe at 12°C with a mass flow rate of 0.06 kg/s. The pipe has a diameter of 15 mm and a total length of 4.0 m. The outside wall of the pipe is wrapped with a variable electrical heating element that produces a uniform heat flux of 10.0 kWim overis cntire length. Neglecting entrance effects, determine: a) the temperature of liquid Freon-12 at the outlet; (6 marks) b) the inner surface temperature of the pipe at the outlet. (9 marks) Due to a leakage in the pipe, the pipe is replaced by a new one with a diameter of 25 mm, and the mass flow rate of liquid Freon-12 is reduced to 0.008 kg/s. The heating flux is also adjusted correspondingly to maintain the same outlet temperature of liquid Freon-12 as before. What will be the inner surface temperature of the pipe at the outlet now? c) (10 marks) You may assume the following properties of liquid Freon-12 to be constants in the temperature range of interest: p= 1330 kg/m', H=2.63x10 kg/m.s, Cp 0.96 kJ/kg.K, Pr 3,5 k = 0.073 W/m.K

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