Simulation And Performance Analysis Of Metal-fueled Dual Closed-cycle Thermoelectric Hybrid Power System

The construction of UUV power system with high energy density and efficient energy conversion is the key research direction of navies of various countries.A closed Brayton cycle coupled with solid oxide fuel cell is an ideal solution for UUV power system with its high efficiency and high output power,which can meet the requirements of low quality and long service life of the system in underwater missions.In this paper,a metal-fueled dual closed-cycle thermoelectric hybrid power system with an aluminium-water reactor as the heat and hydrogen source,and a He-Xe mixed workload closed-cycle Brayton cycle and SOFC cycle as the power output is investigated.Firstly,the thermodynamic model of metal fuel double-closed cycle thermoelectric hybrid system,the aluminum-water reaction model,the physical property parameter model of He-Xe mixed working medium,the detailed one-dimensional SOFC model and the detailed mathematical model of the closed Brayton cycle are established.Based on this model,the comprehensive evaluation index of the thermoelectric hybrid system is established.Under the design condition,the output power of the hybrid system is 462.7k W,and the thermal efficiency is 36.88%.Within the range of parameter operation,sensitivity analysis of six important parameters,such as SOFC fuel utilization rate,isentropic efficiency of turbomachinery,heat exchanger efficiency,aluminum reaction rate,compressor pressure ratio and turbine inlet temperature,was carried out to study the variation law of hybrid system power,thermal efficiency,exergic efficiency and heat exchanger thermal conductivity.Secondly,the regression equations for the output power,the breakdown efficiency and the heat conductance of the heat exchanger of the hybrid system are obtained by using the response surface method to address the problem of mutual constraints and conflicts between multiple system performance indicators.The NSGA-II algorithm is used to carry out a multi-objective optimisation analysis of the metal-fuelled dual closed-cycle thermoelectric hybrid system with the optimisation objectives of maximising the cycle radiation efficiency,maximising the output power and minimising the heat exchanger thermal conductance,and to obtain the Pareto optimal solution set under the constraints.By using the TOPSIS decision algorithm,the optimal solution of the system after multi-objective optimisation is determined and the optimal operating conditions of the system under the constraints are obtained as a pressuriser pressure ratio of1.87,an aluminium reaction rate of 1.2 mol/s,a heat exchanger efficiency of 0.84 and a turbine inlet temperature of 1045 K.Under this operating condition,the output power of the hybrid system is 422.1 k W,the thermal efficiency is 44.6%,the thermal efficiency is 63.4%,and the thermal conductivity of the heat exchanger is 11 k W/K.Finally,the dynamic simulation model of metal fuel double-closed cycle thermoelectric hybrid system is established,and the operation characteristics and dynamic response process of the hybrid system under different operating conditions are analyzed,including variable flow rate,variable aluminum reaction rate and variable speed conditions.The research results show that under variable flow conditions,the flow increases,the turbine inlet temperature decreases,and the power and efficiency of the hybrid system decrease.When the reaction rate changes,the power and efficiency of the mixing system increase as the rate increases.Under variable speed,the speed increases,the power of closed Brayton cycle and hybrid system decreases,and the efficiency decreases first and then increases.