Research On Transfer Properties Of Ionic Liquid-based Nanofliuds

Absorption heat pump is a kind of important energy-saving devices, which can efficiently recover industrial waste heat and low temperature exhaust heat so that the energy efficiency is greatly raised. However, the traditional working pairs "H2O-LiBr" and "NH3-H2O" both have disadvantages respectively, hindered the promotion and application of it. In recent years, numerous studies have shown that ionic liquids have capacity to be new heat pump absorbent because of their high thermal stability, low vapor pressure and liquid process width both at home and abroad. There are few studies on transport properties of the ionic liquid binary solution by analysised the cureent research on ionic liquids. As for the absorption heat pump working pairs, the transfer properties are essential.We propose to disperse the multi-walled carbon nanotubes (MWCNTs) into [EMIM][DEP] and its aqueous solutions and the resulting nanofluids (INF&SNF) as the absorption heat pump working pairs, considering the low thermal conductivity of the organic solvent. And investigate the properties of the nanofluids including thermal conductivity, density, and viscosity.Prepared the ionic liquid [EMIM] [DEP] in the laboratory. The ionic liquid was characterized by hydrogen nuclear magnetic resonance spectrometer and the water content was analyzed by Karl Fischer method. The purchased MWCNTs was acidified and then characterized by transmission electron microscopy (TEM) and infrared absorption spectra (IR). Nanofluids were prepared by using the two-step method.The experiment measured the thermal conductivity of [EMIM][DEP](1)+H2O(2) at 298.15K-353.15K using thermal conductivity meter. Then the effective thermal conductivity of INF and SNF was measured at 298.15K-353.15K, and the density and viscosity of INF and SNF were measured at 298.15K-323.15K. Experimental results showed that, the thermal conductivity of nanofluids was increased in different degrees (1.3% to 9.7%) compared to its base liquid. Also there was varying degrees’increase of density and viscosity compared to their base liquid. At room temperature, the density of nanofluids increased about 1% compared to the base liquids and the viscosity of INF is 350 times that of water,2～4 times that of SNF with 1.0% mass fraction of MWCNTs. The viscosity of INF and SNF decreased rapidly with increasing temperature, and approximately equal to that of their base liquids at high temperature. Therefore, the addition of MWCNTs will not hinder the normal flowing of the working pairs in the absorber. The measured thermal conductivity, viscosity and density were correlated by using the literature models and the parameters’values were determined. The calculated results agreed well with the experimental values.The optimized stable configuration of ionic liquid was determined by using density functional theory (DFT) of GAUSSIAN 09 software. The thermal conductivities of [EMIM][DEP] at different temperature and [EMIM][DEP]+SWCNT were obtained from the Green-Kubo formulation. The results showed that simulative values were in good agreement with the experimental values, and that the force field and the method can be used to infer the effective thermal conductivity of nanofluids.In conclusion, this study provides the absorption heat pump with important basic data and provides the accurate force field and method for predicting the thermal conductivity of nanofluids based on [EMIM][DEP].