Molecular Simulations On Adsorption And Energy Storage Of Metal Organic Nanofluids Containing MOF-5 And MOF-74

With the continuous development of human society,the energy crisis and environmental problems have became the serious issues.Alleviating energy shortage and maintaining sustainable development is a constantly hot topic for discussing.Harvesting low-grade energy in nature and industry is one of the effective means to alleviate energy-related problems.However,due to the low temperature of the low-grade energy source,its efficiency is low.Using the fluid molecules'interaction of heat energy and surface energy during the adsorption and separation process in the nanoporous materials'solid surface can improve the heat absorption of circulating working medium and the utilization efficiency of energy.This technology has a great application prospect in low-grade energy recovery such as in Organic Rankine cycle and transcritical CO₂ cycle.In this paper,molecular dynamics simulation??MD?and Grand Canonical Monte Carlo?GCMC??methods are used to study the adsorption and energy storage of environment-friendly cyclic working medium in metal-organic framework?MOF?materials.The energy storage properties of three refrigerants,R1234yf,R1234ze?Z?and CO2,with MOF-5 as well as the energy storage properties of four refrigerants,R1234yf,R1234ze?Z?,R134a and R32,with M-MOF-74?M=Zn,Ni,Mg,Co?nanoparticles are simulated respectively.The main research contents and conclusions are as follows:Firstly,the adsorption and energy storage properties of R1234yf,R1234ze?Z?and CO2 in MOF-5 are discussed by using MD and GCMC methods.The results show that the adsorption quantity of CO2 in the MOF-5 is consistent with the experimental data.And the error of adsorption heat calculated by GCMC and the Clausius-clapeyron equation is less than 10%.The internal energy of MOF-5 obtained by MD simulation is also consistent with the data in the literature.The above three conclusions verify the correctness of the calculation method.And at the same temperature,the saturation adsorption capacity of R1234ze?Z?in MOF-5 is higher than that of R1234yf.Also,compared with R1234yf,R1234ze?Z?has a closer adsorption position and a larger adsorption heat in MOF-5.The interaction force of Zn atom in MOF-5 with R1234yf and R1234ze?Z?is higher than that of O atom in MOF-5.Adding MOF-5 nanoparticles to the working medium can improve the energy storage while the energy storage effect increases with the increase of the MOF-5 proportion.Under the same conditions,the energy storage effect of R1234yf/MOF-5 nanofluid is better than that of R1234ze?Z?/MOF-5 nanofluid.When the temperature difference between cold and heat source is 60K,the energy storage characteristic curves of R1234yf/MOF-5 nanofluid and R1234ze?Z?/MOF-5 nanofluid have a mutation point.Secondly,since the MOF-74 structure owns the largest unsaturated metal bit,four different MOF-74 structures are obtained by changing the atomic species of the central metal.And the adsorption and energy storage characteristics of R1234yf,R1234ze?Z?,R134a and R32 in M-MOF-74?M=Zn,Ni,Mg,Co?are simulated respectively.The results showed that in the same kind of MOF-74 material,the adsorption capacity of R32is the highest,followed by R134a.When the same adsorbent is adsorbed in M-MOF-74,the adsorption amount in Mg-MOF-74 is the largest,while the adsorption heat in Co-MOF-74 is the largest.Among the four kinds of MOF-74,adding Mg-MOF-74nanoparticles in working medium has the best energy storage effect,while adding Ni-MOF-74 nanoparticles in working medium have the worst energy storage effect.