In a counter flow double flow pipe heat exchanger water flows through a copper tube (19 mm outside diameter and 16 mm inside diameter), at a flow rate of 1.48 m/s. The oil flows through the annulus formed by inner copper tube and outer steel tube (30 mm outside diameter and 26 mm inside diameter). The steel tube is insulated from outside. The oil enters at 0.4 kg/s and is cooled from 65 to 50°C whereas water enters at 32°C. Neglecting the copper tube wall thermal resistance, calculate the length of the tube required. Data: Nu = 0.023 (Re) 0.8 (Pr)0.4 Fouling factor, water side = 0.0005 m2 K/W Fouling factor oil side = 0.0008 m2 KW Water and Oil Properties Property Oil Water 850 995 Density (kg/m3) Heat capacity (kJ/kg.K) 1.89 4.187 Thermal conductivity (W/mK)