Hot oil is to be cooled in a double-tube counter-flow heat exchanger. The copper inner tubes have a diameter of 23 mm and negligible thickness. The inner diameter of the outer tube (the shell) is 47 mm. Water flows through the tube at a rate of 0.037 kg/s, and the oil through the shell at a rate of 0.019 kg/s. The oil and water enter at temperatures of 103 and 26 C, respectively. How long must the tube be made if the outlet temperature of the oil is to be 65C? (Use Log mean temperature difference). Assumptions: 1- Negligible heat loss to the surroundings. 2. Negligible kinetic and potential energy changes. 3. Constant properties. 4. Negligible tube wall thermal resistance and fouling factors. 5. Fully developed conditions for the water and oil 6. Evaluate water properties at T = 45 C (c,ave) 7. If Re-3000, assume the flow is laminar. If Re-3000, assume the flow is turbulent. Answer: