A shell-and-tube condenser is designed to condense a process stream at 120°C using water at 60 kg/s at the inlet temperature of 30°C. The water flows through the tubes. The copper tubes (thermal...

A shell-and-tube condenser is designed to condense a process stream at 120°C using water at 60 kg/s at the inlet temperature of 30°C. The water flows through the tubes. The copper tubes (thermal conductivity 401 W/m . K) have an OD and ID of 19 and 16 mm, respectively, and the tube length per pass is 2.5 m. There are a total of 800 tubes in the exchanger, with four tube passes on the tube side. Check through your calculations that the measured water outlet temperature under clean conditions is 89°C. Also determine the water velocity through the clean tubes. After six months of service, the exchanger was retested for fouling effects, and for the same water flow rate and inlet temperatures, the water outlet temperature was measured as 85°C. Compute the tube-side fouling resistance (factor) during the second test if the exchanger was clean originally, there was no fouling on the steamside, and the tube heat transfer surface area was the same under clean and fouled conditions. Explain what additional information you would need to compute the water velocity in the fouled tubes. Assume the condensing heat transfer coefficient to be 4000 W/m2 . K. Assume the following properties for water:
ρ
= 1000 kg/m3, Cp = 4180 J/kg. K, k = 0.59 W/m . K, and µ = 0.001 Pa. s. Hint: Use the DittusBoelter correlation for the tube-side heat transfer coefficient.