5.1.2 Heat transfer
The heat is transferred to the cooling water across the condenser tubes (Fig 4.14).
In any heating or cooling process, the resistance to heat transfer determines the relative temperature of the heated and cooled fluids.
The total resistance of the tube to heat transfer is determined by the sum of:
Logarithmic mean temperature difference (LMTD)
Consider Fig 4.15 which represents a condenser. The cooling water enters the condenser tubes at temperature tw1K, and its temperature is raised to tW2К at the outlet.
Wet steam enters the condenser and condenses completely at a constant temperature tsK, as it passes over the condenser tubes. These processes are represented in Fig 4.16.
Consider an element of tube length dl where the cooling water is at tw and the condensing fluid is at ts. The temperature difference is (ts - tw) = θ, and a small amount of heat, dΦ, is transferred across the element. From Newton's Law of cooling,