In an concurrent-flow tubular heat exchanger, a liquid food, flowing in the inner pipe, is heated from 20 to 40 degree C. In the outer pipe the heating medium (water) cools from 90 to 50 degree C. The overall heat-transfer coefficient based on the inside diameter is 2000 W/(m2 oC). The inside diameter is 5 cm and length of the heat exchanger is 10 m. The average specific heat of water is 4.181 kJ/(kg oC). Calculate the mass flow rate of water in the outer pipe.