Entropy generation distribution characteristics of a supercritical boiler superheater during transient processes

摘要

A 1D dynamic modeling approach for surface heaters is developed and validated by comparing the calculation results with data from the available literature. Subsequently, the modeling approach is used for a superheater case study. The entropy generation of the superheater is calculated after undergoing step increasing the cold or hot inlet flow rate/temperature by 20%. The entropy generation for the hot side, the metal inside, the cold side, the entire heat transfer unit in different positions and the integral heater (ΔS_(TH)) are presented and analyzed. Results show that increasing the cold/hot fluid flow rate enhances the heat transfer quantity (Q_T) and ΔS_(TH) increase accordingly. With the increase in cold fluid inlet temperature, Q_T and ΔS_(TH) decrease. For hot inlet temperature increasing, Q_T and ΔS_(TH) increase. Additional entropy generation (ΔΔS_(TH)) occurs due to the deviation between the real-time and the steady-state thermal status. The shares of ΔΔS_(TH) are 0.7% and 6.7% during the transient process for the step increase in cold fluid inlet temperature and flow rate, respectively. ΔΔS_(TH) accounts for 1.5% and 3.0% at the beginning of the step increase in the hot fluid inlet temperature and flow rate, respectively.