In a dairy operation, milk at a flow rate of 250 L /h and a cow-body temperature of 38.6°C must be chilled to a safe-to-store temperature of 13°C or less. Ground water at 10°C is available at a flow rate of 0.72 m3/h. The density and specific heat of milk are 1030 kg/m3 and 3860 J/kg · K, respectively.
(a) Determine the UA product of a counterflow heat exchanger required for the chilling process. Determine the length of the exchanger if the inner pipe has a 50-mm diameter and the overall heat trans- fer coefficient is U 1000 W/m2 · K.
(b) Determine the outlet temperature of the water.
(c) Using the value of UA found in part (a), determine the milk outlet temperature if the water flow rate is doubled. What is the outlet temperature if the flow rate is halved?