THERMOPHYSICAL PROPERTIES OF H_2O + (LiBr + LiNO_3 + LiI + LiCl) MIXTURE FOR ABSORPTION REFRIGERATION

摘要

Corrosion and crystallization are well known drawbacks of the water + lithium bromide mixture, a conventional working fluid for absorption refrigeration systems. To reduce these problems, an alternative fluid could be the aqueous solution of the quaternary salt system LiBr + LiI + LiCl + LiNO_3, being that the other lithium salts improve the properties of the LiBr + H_2O. Some thermophysical properties for this quaternary salt system are reported in literature, but they are not enough for an adequate simulation of the thermodynamic cycle. In this work, several thermophysical properties have been measured and calculated to complete the property database needed for an adequate simulation of the thermodynamic cycle: vapor pressure, enthalpy, viscosity and thermal conductivity. The vapor pressure of the quaternary salt mixture has been measured by the static method from 273.15 K to 393.15 K and 0.4 to 0.7 in total salt mass fraction. From these data, the vapor-liquid equilibrium and solution enthalpy have been calculated. Dynamic viscosity has been measured from 283.15 K to 393.15 K and from 0.45 to 0.70 in salt mass fraction, using the falling-ball method. Thermal conductivity has been measured using the transient hot-wire method, from 298.15 K to 328.15 K, in a salt mass fraction range from 0.45 to 0.65. Analytical correlations for each property, with temperature and composition, have been proposed, and pressure-temperature-composition and enthalpy-temperature-composition diagrams have been built. The experimental results have been compared with values reported in literature.