Constructal design for supercharged boiler evaporator

Abstract

On the basis of constructal theory, constructal optimization of a supercharged boiler evaporator is implemented by taking a complex function composed of heat transfer rate (HTR) and flow pressure drop (FPD) as optimization objective. With the constraint of fixed heat transfer area, the optimal construct of the boiler evaporator with minimum complex function is obtained. The results show that when the outer diameter (OD) of the heat transfer tube (HTT) increases, the complex function decreases first and increases next, and there is an optimal OD of the HTT leading to the minimum complex function. Compared with the initial design point, the HTR, flue gas FPD and complex function after constructal optimization are decreased by 9.27%, 74.10% and 10.9%, respectively. Therefore, the complex function is a compromise of the heat transfer and flow resistance performances of the boiler evaporator. The minimum complex function decreases following the increases of heat preservation coefficient (HPC) and fuel consumption rate, and the decrease of excess air coefficient. Besides, increasing the HPC appropriately is propitious to improve the overall performance of the boiler evaporator. The excess air amount should be controlled when the fuel is completely burned. When the tube number in single row and the number of tube rows are chosen as the design variables, similar optimal results can be obtained. The results gained in this paper can offer some theoretical directions for the optimal designs of various boiler evaporators.