Experimental And Molecular Dynamics Study On Thermal Conductivities Of Ionic Liquid [EMIM][DMP] With Water (Methanol Or Ethanol) And Nanofluids

Absorption heat pumps(AHPs)and absorption refrigeration systems are energy-saving devices.The most common working fluids NH3/Water and Water/LiBr both have some disadvantages.Thus,many studies have been carried out to develop new working fluids.Room temperature ionic liquids(RTILs)have the advantages of low volatility and flammability,high chemical and thermal stability,a wide electrochemical potential window and liquid temperature range,and superior dissolution properties,which have been widely applied to various fields.Previous studies have indicated that the binary solutions containing 1-ethyl-3-methylimida-zolium dimethylphosphate [EMIM][DMP] have the capacity to be new working fluid of absorption heat pump.However,there are few studies on transport properties of the three binary systems [EMIM][DMP] + Water/Ethanol/Methanol in the literature,especially for the study of thermal conductivity.Thus,experimental measurements and reverse nonequilibrium molecular dynamics simulations are used to investigate the thermal conductivities of the three binary solutions.On one hand,we aim to provide the new thermalphysical data for the IUPAC ionic liquid database(IL Thermo),on the other hand,we aim to test the feasibility of the RNEMD method.Experimental section: The IL [EMIM][DMP] was synthesized and purified in the laboratory.The thermal conductivity was measured using a thermal conductivity analyzer from 298.15 K to 353.15 K.For the aqueous solutions of IL,the results show that the experimental thermal conductivity decreases with increasing temperature for x1=1.0 and x1=0.6,while the opposite for x1=0.2 and x1=0.4;the thermal conductivity decreases with increasing temperature for the IL solutions of ethanol or methanol.Moreover,it shows a decrease with increasing IL concentration for the IL solutions of water and methanol and a reverse trend for the IL solution of ethanol.The thermal conductivity o f nanofluids increases with increas ing mass fraction of carbon nanotubes,the maximum enhancement ratio is 1.2907.Simulation section: Reverse nonequilibrium molecular dynamics simulations are used to investigate the thermal conductivities of the three binary solutions [EMIM][DMP] + Water/Ethanol/Methanol systems over a range of temperatures and ionic liquid concentrations.First,the structure of [EMIM][DMP] was initially optimized by density functional theory and atomic charges were obtained by C HELPG method.The simulated values and the trend in thermal conductivity agree well with the experimental data,and the relative deviations are fair in most cases,which suggest that the RN EMD method is feasible for predicting thermal conductivities when data is scare.It is also suggested that the accuracy of thermal conductivity results is relevant to the polarity of the component.In addition,the heat transfer mechanism of carbon nanotubes in the base fluid was studied.It is indicated that the thermal conductivity around the interface is very small,and longitudinal heat transfer is the largest contributor to thermal conductivity,and the thermal conductivity in this direction can be used as the thermal conductivity of the composite.In a word,the study provides the new thermalphysical data for the IUPAC ionic liquid database(IL Thermo),which is also useful for the AHP in our lab,and also tests the feasibility of the RNEMD simulation.