Monte Carlo Simulation Of Aqueous Solution Of Lithium Bromide As Working Fluid Of Absorption Heat Pump

Absorption heat pump(AHP) is an important industrial device for energy recovery. The thermodynamic properties of working pairs have important influence to the thermodynamic efficiency of absorption heat pump. At present the most commonly used working pairs in AHP are Lithium Bromide and water. It is of significance to study thermodynamic data of aqueous solution of Lithium Bromide for the development, design and optimization of absorption cycle.With the rapid development of computer science and technology, simulating calculation has become the third main way of modern scientific research. Molecular simulation technology, which calculates the microstructures of chemical products or materials and predicts the macroscopic properties, has become the emerging research field.In this thesis, part of thermodynamic properties of lithium bromide and water were simulated by Monte Carlo method with Towhee packages using Linux system. The intermolecular forces were approximated by rigid simple point charge SPC/E model for water, Lybrand Ghosh McCammon (LGM) forcefield for bromine ion and Aqvist forcefield for lithium ion.The molecular simulation of LiBr/H2O was carried out by NPT-Gibbs Ensemble Monte Carlo(GEMC). The simulations were carried out respectively at 80℃,100℃and 120℃under different pressures, and the corresponding composition and density data were obtained when the liquid phase and vapor phase were in equilibrium. The simulation results are in accord with literature data, which demonstrate the reliability of the force field models.Microcosmic structure properties of liquid phase were analyzed. The variation of the radial distribution function and coordination number between ions and water were studied at 100℃under different concentrations and pressures. The variation of the total configurational energy, Lennard-Jone potential and electrostatic potential of the liquid phase were also analyzed under different pressure at 80℃,100℃,120℃.Finally, the constant pressure specific heat capacities of aqueous solution of Lithium Bromide with various concentrations at 80℃and 100℃were calculated with two approaches, respectively. One approach was that the heat capacity was divided into two parts, the heat capacity of ideal gas and residual heat capacity. The first part was calculated with quantum chemistry method and the last part with NPT ensemble MC method. The other approach was the heat capacity was directly calculated by configurational enthalpy which was also got by using NPT ensemble MC method. By comparing the two approaches with referenced data, it is founded that the first method is much better than the second, because the second method does not consider intramolecular potential and kinetic energy.