A solution of sodium hydroxide leaves a dissolver at 80°C and is to be cooled to 40°C, using cooling water. The maximum flow rate of the solution will be 8000 kg/h. The maximum inlet temperature of the cooling water will be 20°C, and the temperature rise is limited to 20°C.

Design a double-pipe exchanger for this duty, using standard carbon steel pipe and fittings. Use pipe of 50 mm inside diameter, 55 mm outside diameter for the inner pipe, and 75 mm inside diameter pipe for the outer. Make each section 5 m long. The physical properties of the caustic solution are 

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temperature, °C specific heat, kJkg-¹°C-1 density, kg/m³ thermal conductivity, Wm-¹°C-1 viscosity, mN m 2 s 40 3.84 992.2 0.63 1.40 80 3.85 971.8 0.67 0.43