非平衡条件下金属氯化物-氨工质对的吸附动力学研究

Study on the adsorption kinetics of metal chloride-ammonia working fluid pair under non-equilibrium conditions

金属氯化物-氨是化学吸附式制冷和储热的常用工质对,其现有的动力学模型存在复杂或动力学参数变化无规律的问题,也不能准确地独立描述多反应阶段的吸附过程。以MnCl_(2)/NH3和CaCl_(2)/NH_(3)为代表工作对,针对0.29、0.42和0.61 MPa的反应压力,进行吸附/解吸性能测试,在类比模型基础上耦合Sigmond函数,建立考虑压力势(μ)、反应速率常数(k)和反应滞后常数(n)的吸附量型动力学模型。鲁棒性测试结果表明:针对不同氯化物、不同反应阶段(Ca_(2-4-2)和Ca_(4-8-4))和不同反应方向(吸附和解吸)所建立的非平衡动力学模型的拟合曲线与实验数据点吻合度较高,拟合优度R2均高于0.97;模型参数随工况呈规律变化,同一反应压力下k与吸附温度负相关,与解吸温度正相关,|n|与解吸温度负相关。

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 MnCl_(2)/NH3 and CaCl_(2)/NH_(3) 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(Ca_(2-4-2) and Ca_(4-8-4)),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.