In a dairy operation, milk at a flow rate of 250 liter/hour and a cow-body temperature of 38.6°C must be chilled to a safeto-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 outlet temperature of the water.
(b) Determine the UA product of a counter flow 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 transfer coefficient is U = 1000 W/m2 . K.
(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?