Combined heat and mass transfer and adsorption dynamics in a honeycomb adsorbent
Abstract
Understanding of heat and mass transfer dynamics in the presence of physical adsorption/desorption as a weak surface chemical interaction represents one of the fundamental problems with wide applications in modern technology. A brief review of the pertinent literature dealing with heat and mass transfer in the thermal non-equilibrium adsorption systems is provided in order to assess the present understanding of the problem. The honeycomb structure widely used in the energy conversion technologies is used as a model system under investigation. A series of theoretical models having different levels of complexity is developed in order to obtain fundamental understanding of the process dynamics and nonlinear interactions between heat/mass transfer and adsorption/desorption. This includes the transient one- and two-dimensional models for heat and mass transfer, and the empirical Freundlich and simplified local density (SLD) statistical mechanics models for adsorption equilibrium. The transient, one-dimensional theoretical model for combined heat and mass transfer and adsorption/desorption dynamics is developed in order to predict the system dynamics and performance in general. The phenomenological models for transport coefficients are described in detail. The dynamics of the honeycomb adsorption column is studied using a transient one-dimensional heat/mass transfer model in conjunction with the semiempirical Freundlich adsorption isotherm. Parametric calculations of honeycomh adsorption dynamics are performed and discussed. The simplified statistical mechanics (SLD) model based on the "local density" approximation is employed as the theoretically sound approach for engineering calculations of adsorption equilibrium. Experiments are performed in order to support development of the model. The external (non-pore) and internal (micropore) specific surface area, total pore volume, and the mean micropore diameter are evaluated for two adsorbent materials using the nitrogen adsorption experiments. The SLD model parameters are estimated using available experimental data. The dynamics of the honeycomb adsorption column is then studied using a transient one-dimensional heat/mass transfer model in conjunction with the SLD models for adsorption. The results of numerical calculations are critically compared with available experimental data. A transient, two-dimensional theoretical model for combined heat and mass transfer and adsorption/desorption dynamics is developed in order to account for the local nonlinear interactions between heat and mass transfer and adsorption/desorption as the surface phenomena. A scale analysis is performed in order to obtain the order-of-magnitude estimates for characteristic time constants of the dynamic behavior of the system. Appropriate surface boundary conditions for heat and mass transfer in the presence of adsorption/desorption are formulated. Model predictions are compared with available experimental data for adsorption of water vapor in a honeycomb column. The findings demonstrate that it is critically important to account for a non-zero net mass flux due to adsorption/desorption at the adsorbent wall in order to obtain good agreement between the numerical simulations of the system dynamics and the measurements.
Degree
Ph.D.
Advisors
Viskanta, Purdue University.
Subject Area
Mechanical engineering|Chemical engineering
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