In a concurrent-fl ow tubular heat exchanger, a liquid food,
fl owing in the inner pipe, is heated from 20 to 40°C. In the
outer pipe the heating medium (water) cools from 90 to
50°C. The overall heat-transfer coeffi cient based on the inside
diameter is 2000 W/(m 2 °C). The inside diameter is 5 cm and
length of the heat exchanger is 10 m. The average specifi c heat
of water is 4.181 kJ/(kg °C). Calculate the mass fl ow rate of
water in the outer pipe.