4. Unused engine oil (properties given below) is being heated in a double-pipe heat exchanger. The oil enters a 2.2 cm ID copper tube (wall thickness = 1 mm) at 4010 kg/hr at 44C and is to be heated to 66C. The annular space between the inner and outer pipes contains steam condensing at 115C, which may be taken as effectively the inside tube wall temperature. Calculate the length of the pipe required for the exchanger. T, C P, kg/m C kJ/kg. C , ms Pr 0 20 40 60 80 100 120 140 160 899.12 888.23 876.05 864.04 852.02 1.796 1.880 1.964 2.047 2.131 k, v, m/s W/m 'C Engine oil (unused) 0.00428 0.147 0.00090 0.145 0.00024 0.144 0.839 10 0.140 0.375 0.138 0.203 0.137 0.124 0.135 0.080 0.133 0.056 0.132 0.911 x 10-47,100 0.872 10,400 0.834 2,870 0.800 1,050 0.769 0.738 276 0.710 175 0.686 116 0.663 84 490 840.01 828.96 816.94 805.89 2.219 2.307 2.395 2.483