Application of entropy generation in selecting the diameter of condenser tubes

Abstract

By the use of data obtained from a simulator containing a thermal-flow model, the effect of a change in the inner diameter of a tube on entropy generation in a condenser of a power unit was examined. The analysis considered three inner diameters of the condenser tube (24, 26, and28 mm), variable cooling water temperature at the condenser inlet (within an annual range of changes), and a variable cooling water mass flow rate. The model took into account the entropy generation due to heat transfer and flow resistance from cooling water. It was observed that using a smaller tube diameter improves conditions for transferring the heat flow, increases the heat transfer coefficient from steam and water, and thereby increases the overall heat transfer coefficient. The increase in the velocity of water flowing through the tubes results in improving the heat transfer conditions, but its negative consequence is greater resistance to flow. Following the analysis, for nominal and less than nominal load, lower entropy generation was observed for diameters of 24 and26 mmthan for the current diameter of28 mm. The use of the same number of tubes of smaller diameter means that the heat transfer surface area, and thus the cost of building an exchanger, will be smaller.