The Property Simulation Of Aqueous Solutions Of Lithium Bromide Using Molecular Dynamics

In industrial field, Absorption heat pump (AHP) has been more and more widely used because of its energy-saving features. The properties of AHP working pair is very important to its effects. Traditionally experiments have been used to develop new AHP working pair as well as to get its properties, which are blind to some extreme cases. At the same time the experimental data in extreme conditions is hard to be obtained by the experiment. In other word, laboratory methods have some limitations. With the development of computer technology, molecular simulation has gained widely application in science and technology, which has become as important as experiment. The molecular dynamics simulations (MD) of lithium bromide aqueous solutions were carried out to investigate numerically the microstructure and thermochemical properties. The intermolecular force were described by Simple Point Charge/Extended (SPC/E) model for water, Lybrand Ghosh McCammon (LGM) force field for bromine ion and Aqvist force for lithium ion. In addition to the radial distribution functions, enthalpy, heat capacity and diffusion coefficients were computed for lithium bromide aqueous solutions at various temperatures and concentrations.Firstly, Water at different temperatures was investigated by MD simulation. The simulated radial distribution functions are in good agreement with the neutron diffraction data. With the increasing of temperature, the order of fluid structure decreases. Diffusion coefficients increases with a rise of temperature, while the simulated values are slightly larger than experimental ones, just the same as enthalpy and heat capacity. In brief, SPC/E model is feasible for the simulation of many properties of water.Secondly, microstructure of lithium bromide aqueous solutions can be gotten by MD simulation. The order of the intermolecular force is as follows:Li+ & Br->Li+&H2O> Br-&H2O>H2O&H2O. The results show that there is strong static electric interaction between Li+ and Br-, which much reduces the hydrogen bonding interactions of original pure water. In certain conditions, a moving gas-liquid interface has been observed in the simulated box. Main molecular at the interface is water which always enters and leaves through the interface, at the same time, Br- is closer to interface than Li+. Under the effect of temperature and concentration, the trend of change in intermolecular force is the same as that in literatures. Diffusion coefficients of all molecules become larger and larger with the rising of temperature as well as the reducing of concentration. The ion hydration offers resistance to the diffusivity of molecules. Computed enthalpies and heat capacities are always larger than their experimental values, which suggest that the internal energy of lithium bromide aqueous solutions has been overestimated by its existing models.