Study on the adsorption kinetics of metal chloride-ammonia working fluid pair under non-equilibrium conditions
Metal chloride/ammonia is a common working pair for chemical adsorption refrigeration and heat storage.Its existing kinetic model has the disadvantage of being complex or kinetic parameters change irregularly,and it cannot accurately and independently describe the adsorption process of multiple reaction stages.Taking MnCl2/NH3 and CaCl2/NH3 as representative working pairs,the sorption and desorption performances of composite sorbent of chloride and expanded natural graphite treated with sulfuric acid with mass ratio of 4∶1 were tested and investigated at the reaction pressures of 0.29,0.42 and 0.61 MPa.The experimental results showed that the reaction rate decreased with the deepening of the reaction.Thus,a novel sorption kinetic model based on sorption capacities concerning pressure potential(μ),reaction rate constant(k),and reaction hysteresis constant(n)was built by coupling the Sigmond function and the analogy model.The robustness test results evidenced that the fitting curves of the non-equilibrium kinetic model worked satisfactorily on rebuilding the experimental data points for different chlorides,reaction stages(Ca2-4-2 and Ca4-8-4),and reaction directions(sorption and desorption)with the goodness of fit(R2)higher than 0.97.Moreover,the model parameters changed regularly with the various working conditions.At the same reaction pressure,k is negatively correlated with sorption temperature,but positively correlated with desorption temperature,and|n|is negatively correlated with desorption temperature.
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