Performance Analyzes Of Integrated Alkaline Fuel Cell-thermoelectric Hybrid System

With the rapid development of global economy,the resource problems and environmental pollution caused by the existing energy structure are increasingly serious.It’s important to accelerate the transformation and upgrading of global energy structure.At the same time,developing renewable energy is also an important topic in today’s world.Fuel cell can directly convert chemical energy into electrical energy without producing other pollution.It has advantages of high efficiency and cleanness.The thermoelectric refrigerator can effectively utilize the waste heat generated by the fuel cell to convert the thermal energy into electrical energy,and it has the characteristics of simple structure,small volume,quick start,and flexible control.In this paper,a hybrid system mainly consisting of an alkaline fuel cell(AFC),a thermoelectric generator,and a thermoelectric cooler is established.The waste heat is transferred from the AFC to the TEG for additional electrical power generation via the Seebeck,and the generated electricity is subsequently delivered to power the TEC.The thermodynamic and electrochemical irreversible losses in each component are fully considered.The operating current density that permits the thermoelectric devices to effectively work is determined.The general performance characteristics of the hybrid system are revealed.The effects of some main operating and design parameters on the performance of the proposed are discussed through parametric analyses.The research contents of this paper are shown as follows:In the first chapter,the background of this paper is described.The development history of fuel cell is introduced.Then the development,advantages and types of alkaline fuel cells are listed.In addition,three important thermoelectric effects in semiconductor are introduced,and the research and application of thermoelectric refrigeration are described.In the second chapter,a mathematical model of the AFC is established.Under the premise of irreversible loss of the fuel cell itself,the expressions of output power,efficiency and entropy yield of fuel cell are derived.The numerical simulation and performance analysis of the AFC are carried out so as to obtain the optimization interval of the AFC.Finally,the effects of operating temperature,operating pressure and mass fraction of KOH solution on the performance of the AFC are analyzed.In the third chapter,a hybrid system mainly composed of an alkaline fuel cell,a thermoelectric generator,a thermoelectric cooler and a group of plate-fin heat exchanger is put forward.Based on thermodynamic and electrochemical theories,numerical expressions for the equivalent power output,energy efficiency,entropy generation rate and exergy efficiency of the hybrid system are respectively derived and the effective working range of current density in hybrid system is determined.The optimal ranges of current density,power density,energy efficiency and exergy efficiency are obtained through the relationship of the current density,power density,energy efficiency and exergy efficiency in the hybrid system.The influences of operating temperature,operating pressure,thermal conductance of the thermoelectric element and the number of thermoelectric elements on the performance of the hybrid system are discussed.At last,the comparison between the hybrid system and the fuel cell shows the superiority of the performance of the hybrid system,and it is found that the performance of the hybrid system can be further improved by adding the plate-fin heat exchanger.In the fourth chapter,under the model of AFC-TEG-TEC hybrid system established in the third chapter,a new configuration of combined an alkaline fuel cell and thermoelectric device,two-stage thermoelectric refrigerator driven by two-stage thermoelectric generator,is proposed.And the influence of plate-fin heat exchanger is considered in detail.Based on thermodynamic and electrochemical theories,the analytical formulas for the equivalent power output and efficiency of the hybrid system are derived.At same time,the entropy generation number of the plate-fin heat exchanger is also be derived.The entropy generation number of the plate-fin heat exchanger is chosen as the optimization objectives,the effects of operating temperature,figure of merit of thermoelectric materials,the temperature of environment,heat capacity rate of cooling fluid and operating electric current in terms of the performance of the hybrid system are evaluated.In the end,by analyzing the performance of hybrid system and plate-fin heat exchanger,the optimized operating ranges of hybrid system and plate-fin heat exchanger are obtained respectively.In the fifth chapter,the research contents of this paper are summarized.Some innovation points are listed.By comparing the hybrid system with the actual situation,some suggestions are put forward and the future research is prospected.