A double-pipe heat exchanger is to be used to heat 6000 kg/h of 22 mol percent hydrochloric acid. The exchanger will be constructed from karbate (impervious carbon) and steel tubing. The acid will flow through the inner karbate tube, and saturated steam at 100°C will be used for heating. The tube dimensions will be karbate tube inside diameter 50 mm, outside diameter 60 mm; steel tube inside diameter 100 mm. The exchanger will be constructed in sections, with an effective length of 3 m each.

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How many sections will be needed to heat the acid from 15 to 65°C? Physical properties of 22% HCl at 40°C: specific heat 4.93 kJkg-¹°C-¹, thermal conductivity 0.39 Wm-¹°C-1, density 866 kg/m³. Viscosity: temperature 20 mNm ²s 30 0.68 0.55 Karbate thermal conductivity 480 Wm-¹°C-1. 40 50 0.44 0.36 60 0.33 70°C 0.30