THERMOCHEMICAL STORAGE IN AN AMMONIA CHEMICAL HEAT PUMP USING CHLORIDE SALT IMPREGNATED INTO CARBON FABRICS AS BINDING AND THERMAL CONDUCTING MATERIALS

摘要

A chemical heat pump (thermochemical transformer) based on a reversible solid-gas reaction will be attractive if the process can store high energy density and if heating or cooling power is high enough. For that, the reactor must contain a maximum quantity of reactive mixture and the kinetics of the gas sorption (or desorption) reaction must be sufficiently fast. Mass and thermal transfer must be high, which implies good open porosity (or permeability) and high thermal conductivity of the solid reagent. In the case of ammonia-metallic chloride salt reaction, the uses of a salt-binder mixture (carbon, exfoliated graphite, graphite intercalation compounds and intercalated or impregnated carbon fibres) enhanced energy and power performances of the system. Another solution was found in our laboratory in order to more easily fill up the reactor of the heat pump: the use of impregnated carbon fabrics. Several carbon textiles from different kinds of fibre precursors (rayon, polyacrylonitrile) and treatments (high treatment temperature, surface activation …) were tested. Their gas permeability and thermal conductivity were determined. After impregnation with a metal chloride as nickel, manganese or magnesium chlorides, the materials were tested in a laboratory heat pump with ammonia gas as working fluid. Ammonia sorption kinetics, reaction advancement, cycle reversibility and other thermo-physical properties were measured. The method based on the modelling of the reactor was also used to determine the thermal conductivity of the impregnated textiles.