Improvement And Application Of Thermodynamic Analysis Model Of Radiative Heat Transfer Process Based On Entropy And Exergy Balance Equation

With the growing energy problems,the second-law of thermodynamics analysis for evaluating and optimizing system efficiency has become an increasing trend in recent years.Thermal radiation is one of the three forms of heat transfer process.Different with other heat transfer methods,thermal radiation has global and long-range characteristics,which makes the second-law of thermodynamics analysis for radiation processe more complicated.The present theoretical framework for radiation thermodynamics only gives the calculation of radiative entropy generation rate as well as the radiative exergy loss.However,the assessment of the thermodynamic efficiency of the radiation system cannot be made by these parameters.Therefore,this dissertation further improves the present thermodynamic analysis method of radiative heat transfer process based on the balance principle of entropy and exergy,proposes thermodynamic analysis model of radiative heat transfer process and apply the model to direct absorption solar collector and combustion processes.The main work contains the following four aspects:A derivation method of radiative entropy generation rate is proposed based on the entropy balance principle within the radiative heat transfer system.The radiative entropy generation rate in a one-dimensional non-grey parallel plate system,as well as that in a three-dimensional high-temperature combustion chamber are calculated.The entropy generation rates due to the irreversibility of the radiative heat transfer process in the two systems due to different media are investigated,and the results showed that solid particles have an important influence on the radiative entropy generation rate,and the entropy generation rate caused by the particles radiation in the three-dimensional furnace reaches more than 80% of the total entropy generation rate.Based on the radiative entropy generation rate and radiative entropy balance equations obtained from the first part of the dissertation,a exergy analysis model of radiative heat transfer process is proposed and the calculation method of exergy stored rate,exergy output rate and exergy efficiency are obtained.Meanwhile,the influence of the boundary conditions of the system and the distribution of the internal heat source on the thermodynamic efficiency of the heat transfer process is analyzed for the unsteady radiationconduction coupled heat transfer process.The results show that reducing the heat loss of the medium near the system boundary and enhancing the heat production of the medium inside the system can effectively improve the efficiency of the chamber in the system.The proposed thermodynamics model of radiative heat transfer process is further applied to develop the exergy analysis model of heat conduction-radiation heat transfer system with collimated irradiation.The effects of parameters of optical thickness,scattering rate and radiation-conduction coefficient on the thermodynamic efficiency of the system are analyzed numerically.Meanwhile,based on the above studies,numerical evaluation and experimental analysis of direct absorption solar collectors are carried out.In the numerical calculations,the effects of parameters such as particle diameter on the thermodynamic efficiency of the collector are analyzed.In the experimental analysis,the results of the proposed thermodynamic model for the evaluation of the thermodynamic efficiency of solar radiation collectors under different operating conditions and its feasibility are verified.The proposed thermodynamic model of the radiative heat transfer process is coupled with a conventional thermodynamic model of combustion process.The calculation methods of the exergy balance equation and the exergy efficiency are proposed under the considering of the radiative heat transfer process in flames.The thermodynamic analysis of ethylene diffusion flame under oxy-fuel atmosphere is carried out,and the effects of soot volume fraction and flame temperature are investigated.The results show that when the flame temperature is high,the exergy loss rate shows a tendency that increase gradually with the decrease of soot volume fraction and the increase of stoichiometric mixing fraction.