Water at the rate of 60 kg/hour is heated from 35oC to 70oC by an oil with specific heat of 1.9kJ/kgK. The fluids are used in a counterflow double-pipe (or pipe-and-shell) heat exchanger (with oil flowing inside inner pipe and water in the surrounding annulus). The oil enters the exchanger at 110oC and leaves at 80oC. The ID of the inside pipe (made of copper) is 1.5cm and the OD is 1.75 cm. ID of the annulus is 3cm. As necessary, use properties for unused engine oil.
(a) Calculate the overall (UA) per unit length of the heat exchanger for heat transfer between oil and water.
(b) Calculate the length of the heat exchanger.
(c) Calculate the heat exchanger effectiveness.
(d) If a parallel flow configuration were used instead of the given counter flow configuration for the same inlet temperatures and flow rates for water and oil and for the same heat exchanger geometry, comment how will exit temperatures for oil and water change: increase, decrease or remain the same.
(e) If the length of the heat exchanger is doubled with the counter flow configuration, the same inlet temperatures and flow rates for water and oil, the same heat exchanger geometries and the same overall heat transfer coefficient, comment how will exit temperatures for oil and water change: increase, decrease or remain the same.