Molecular Simulation Of Adsorption And Energy Storage Of Metal-Organic Frameworks Nanofluids

Metal-organic frameworks（MOFs）,which is the new porous material,have larger specific surface area and porosity comparing with zeolite and carbon nanotubes etc...The implementation of organic media in low-grade energy recovery systems can lead to distinct advantages such like simple facilities and great off-design operation ability as compared to traditional heat-transfer media.Using the interaction of fluid/solid interface in nano porous materials to enrich low-grade energy can improve the efficiency of energy utilization and has a broad application prospect in energy storage.The The Metal-Organic Heat Carrier Nanofluids（MOHCs）,made by adding MOFs nanoparticles into the organic media,can enhance the absorbed heat of working fluids.However,the detailed characteristics of adsorption energy storage for MOHCs,and the effect of working conditions are not clear and need study furtherly.In this thesis,the characteristics and mechanisms of the adsorption and energy storage for MOHCs were investigated using the molecular simulation.Firstly,the molecular simulation and experimental study were carried out on the energy storage characteristics of two kinds of MOFs materials,UIO-66 and UIO-67,as well as two kinds of nanofluids,H₂O/UIO-66 and methanol/UIO-67.（1）The thermodynamic properties of UIO-66 and UIO-67 obtained by molecular dynamics simulation and experimental shown the similar trends.Consistently,molecular dynamics simulation can be used as an effective method to study the energy storage density of Metal-organic frameworks,（2）Both the results of molecular simulation and experiments suggested that the energy storage efficiency can be improved by adding UIO-66 and UIO-67 to hydrogen peroxide and methanol respectively.Secondly,the adsorption energy storage characteristics of four MOFs（MOF-5,MOF-74,UIO-66 and UIO-67）with six typical organic working media（HFC-170,HFC-161,HFC-152a,HFC-143a,HFC-134a and HFC-125a）were studied by molecular simulation method based on the analysis of simulation and experiments.The results showed that:（1）The adsorption capacity and heat of six organic working media in four MOFs demonstrated the similar trends.The adsorption capacity and adsorption heat increased with the pressure improvement at constant temperature,and the smaller the pressure,the adsorption capacity and adsorption heat change fastly with temperature.the adsorption capacity and adsorption heat remain constant with the increase of pressure after the saturated adsorption pressure.,The adsorption capacity and adsorption heat are inversely proportional to the temperature with constant pressure.（2）The adsorption capacity and adsorption were proportional to the specific surface area and porosity of MOFs for the same working media.The adsorption capacity and adsorption heat increased obviously when the number of fluorine atoms increased for the same MOFs.However,the adsorption capacity decreased as the adsorption heat decreased firstly,then increased and then decreased with the increase of the number of fluorine atoms.（3）The desorption heat was proportional to the specific surface area and porosity of MOFs for the same working media.For HC-170,the desorption heat remained unchanged in UIO-66 and MOF-74,and increased firstly and then remained unchanged in MOF-5 and UIO-67 with the increased fluorine atoms.For the HFC-161 HFC-152a,HFC-143a,HFC-134a and HFC-125a with fluorine atoms,the desorption heat fluctuates near constant value with the increase of pressure when the temperature difference is constant.The desorption heat decreases in MOF-5 and UIO-67,and decreases firstly and then keep the constant value in MOF-74,and remains unchanged for UIO-66 with the number of fluorine atoms increased.Finally,（1）The energy storage density of MOF-5,MOF-74,UIO-66 and UIO-67are proportional to temperature,and the?C_p increased with the density of MOFs.（2）The energy storage density of MOHCs increased with certain pressure and temperature ranges compared with pure organic working media.The changes of energy storage density are proportional to the porosity and specific surface area of MOFs.The energy storage density increased mainly in the low-pressure region for HC-170,and the lower right triangle regions for HFC-161,HFC-152a,HFC-143a,HFC-134a and HFC-125a,as the area of increasing energy storage density is proportional to the number of fluorine atoms in organic working media.