No abstract

Application requirements for avionics are often very strict. For example, the heat sinks of avionics need very good temperature uniformity, but the flow rate of coolant is very restricted. In addition, the use of micro-channels is not recommended due to the potential clogging issue. Considering these design requirements, we will discuss a multiple-objective optimal design method to obtain a good stacked mini-channel structure for avionics applications. In our thermal design, the design variables are the mini-channel geometry parameters. Temperature uniformity, entropy generation, max temperature of heat sink and pump work are chosen as the objective functions. A Multi Objective Genetic Algorithm (MOGA) and Fluent solver are used together to minimize multiple objective functions subject to constraints, and locate the Pareto front. By analyzing the multiple objective optimal results, we can draw the conclusion that the objective functions of T max and s g have same effect on the optimization, and the multiple optimal results are a set and not a single value. If mostly focusing on the temperature uniformity, we can recommend some optimal structures to design a stacked mini-channel heat sink.

Supercritical once-through utility boilers are increasingly common in flexible operations in China. In this study, the tube temperature changes at a vertical water-cooled wall are analyzed during a fluctuating flexible operation. There are considerable differences in the temperatures of the parallel tubes at the minimum load, and the resulting thermal stress distributions at a front water-cooled wall are established using structural calculation software ANSYS 17.1, USA. A wide thermal stress distribution occurs among the parallel tubes, and the local cyclic stress amplitudes under flexible operation are higher than those under cold, warm, hot, or load-following operations. Because of the water wall expansion structure at the furnace, the higher tube temperature areas suffer from compressive stress, while the lower tube temperature areas suffer from tensile stress. During flexible operation, combustion uniformity and a two-phase flow distribution can improve the safety of vertical water-cooled wall operation. The minimum load of the utility boiler should be set as a limitation, and the tube temperature is an important parameter affecting the thermal and cyclic stresses.

Solar‐aided coal‐fired power generation (SAPG) has been attracting more and more attentions in recent years. However, the multi‐objective optimization of SAPG system considering off‐design work conditions has not been fully studied. In this paper, a general system integration optimization method (GIOM) has been developed for integration schemes optimization, and Nondominated Sorting Genetic Algorithm‐II (NSGA‐II) algorithm is used for multi‐objective optimization of SAPG system. As a case study, a SAPG system that refers to a real 600 MWe supercritical coal‐fired power plant is optimized based on a typical day. By simultaneous optimization of both initial investment (P) and solar net electric generation (Esolar), the solar subsystem design schemes are optimized as Pareto optimal set. At last, to maximum Esolar/P, the final design scheme is selected from the Pareto optimal set, whose Esolar and P are 237.6 MWh and 113.5 M$, respectively. The results show that, the final design scheme is a heliostat field with instantaneous optical efficiency of 63.24% at the design point, the receiver power rating is 133 MWt, the tower height is 136.6 m, and distances of successive rows of the three zones are 13.6, 17.7, and 24.5 m, respectively. A larger or smaller size of solar subsystem is considered to be uneconomical.

Flow instability in parallel pipes is closely related with the application of direct steam generation (DSG) for parabolic trough solar power technology. Maldistribution of the flow rate may occur in heated parallel pipes with common inlet and outlet manifolds. The theoretical analysis on four parallel pipes that undergoes a process of heating and evaporation during different heating loads is carried out to indicate all the possible steady-state solutions. Stable solutions and unstable solutions are differentiated through linear stability analysis. It is shown that the more number of heated pipes, the more stable steady state solutions of the splitting ratios, and the greater range of uneven flow rate distribution. Transient analysis is applied to simulate the response of the system to finite disturbances and the performance due to variations in operating conditions by Simulink of Matlab. The results confirm the correctness of the linear stability analysis, and a hysteresis phenomenon is observed when a solution is turning to another solution, even for unstable ones. In addition, A method is proposed to improve flow distribution uniformity in parallel pipes by installing a resistant orifice at the inlet of each pipe where is not heated.