Role of constraint volume and heat flux on the design of evaporator tubes of steam generator by entropy generation minimization

• A design method for evaporator tubes in steam generators using entropy generation minimization (EGM). • A new entropy generation model considering two-phase flow within the evaporator tubes. • The total entropy generation of the evaporator circuit while considering constraints like coolant volume, steam generation rate, and furnace heat flux. • Increasing evaporator diameter leads to a lower furnace height but requires a larger cross-sectional area. • The optimal evaporator diameter for minimum entropy generation depends on the available furnace heat flux. Higher heat flux allows for larger diameter tubes. • Selecting the constraint volume for the evaporator design should consider the available furnace heat flux to achieve the most efficient design for a desired steam generation rate. This paper proposes a design methodology for evaporator tubes of a steam generator by applying the entropy generation minimization (EGM) approach. A two-phase flow-based entropy generation model for steam generator evaporator tubes is developed, with coolant volume as a constraint. For a target steam generation rate, the total entropy generation of the evaporator circuit is minimized using system volume and furnace heat flux as two constraints. It is observed that for a fixed steam generation rate, with increasing evaporator diameter, the furnace height decreases while the cross-sectional area increases. The analysis reveals that for a steam generation rate of 100 kg/s and a fixed circuit volume of 47 m 3 , increasing the heat flux from 36 to 50 kW/m 2 shifts the EGM point from an evaporator diameter of 62 mm to 84 mm, respectively. On the other hand, the minimum point shifts to a diameter of 43 mm when the heat flux is decreased to 25 kW/m 2 . The present study concludes that the selection of the constraint volume for designing the evaporator downcomer circuit for a target steam generation rate should be done based on the available furnace heat flux to choose the most efficient design.