Question

The properties of the fluid are: density 895 kg/m³, viscosity 0.76 mNm^-2s. A double-pipe heat exchanger is to be used to heat 6000 kg/h of 22 mol per cent 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 100ºC 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. How many sections will be needed to heat the acid from 15 to 65ºC?

Physical properties of 22 % HCl at 40ºC:
Specific heat 4.93 kJkg^-1°C^-1,
Thermal conductivity 0.39 Wm^-1ºC^-1,
Density 866 kg/m3
Karbate thermal conductivity 480 Wm^-1ºC^-1.

Temperature (°C)	20	30	40	50	60	70
Viscosity (mN m-2s)	0.68	0.55	0.44	0.36	0.33	0.30

Answer 1