Constructal complex-objective optimization for tree-shaped hot water networks over a rectangular area using global optimization method

A tree-shaped hot water network over a rectangular area is investigated in this paper. Based on constructal theory, the total duct wetted surface and duct volume of the network are fixed. To optimize the thermal and flow performances of the networks simultaneously, a complex-objective function, defined as the ratio of dimensionless overall pressure drop to dimensionless farthest user temperature, is chosen as the optimization objective. The complex-objective function is minimized by optimizing the outer and inner insulation radiuses of the insulation radiuses, which is named as the global optimization method in this paper to distinguish the stepwise optimization method used in the previous model. The results show that the optimal constructs of the networks obtained by the minimum dimensionless complex-objective function are different from those obtained by the maximum farthest user temperature. For the volume constraint with the second construction sequence, when the dimensionless insulation volume V˜2=0.3, the dimensionless farthest user temperature and the dimensionless overall pressure drop based on the minimum complex-objective function are increased by 32.33% and 16.99%, respectively. Therefore, the complex-objective function shows a good compromise between user temperature and pressure drop, and becomes an excellent candidate objective for the performance optimization of the network compared with the single objective of the pressure drop or user temperature.