Mathematical modeling of gas–liquid membrane contactors using random distribution of fibers

This work presents a mathematical model for gas absorption in microporous hollow fiber membrane contactors by using a random distribution of fibers. The chemical absorption of carbon dioxide into aqueous amine solutions and sulfur dioxide into water were simulated by this model. The nonlinear mathematical expressions of the component material balance for the liquid, membrane, and gas were solved simultaneously by using a numerical method. The results from the model were compared with four sets of different experimental data in the literature. In addition, the contactors were modeled based on the assumption of regular arrangement of fibers in the shell side by using Happel's free surface as well as plug flow models. The plug flow model was employed to compare the various available equations in the literature for the shell side mass transfer coefficient. The results indicate that the channeling of gas in the shell side decreases the efficiency of contactor significantly. It was found that the random distribution of fibers is a suitable method to simulate the commercial modules. The results also indicate that, the regular Happel's free surface model and the plug flow model are more suitable for handmade modules. The influence of shell side channeling on the contactor performance were investigated in different fiber packing densities, and in various gas and liquid flow rates.     

Thermodynamic analysis of a thermal storage unit under the influence of nano-particles added to the phase change material and/or the working fluid

The thermal storage unit consists of two concentric cylinders where the working fluid flows through the internal cylinder and the annulus is filled with a phase change material. The system carries out a cyclic operation; each cycle consists of two processes. In the charging process the hot working fluid enters the internal cylinder and transfers heat to the phase change material. In the discharging process the cold working fluid enters the internal cylinder and absorbs heat from the phase change material. The differential equations governing the heat transfer between the two media are solved numerically. The numerical results are compared with the experimental results available in the literature. The performance of an energy storage unit is directly related to the thermal conductivity of nano-particles. The energy consumption of a residential unit whose energy is supplied by a thermal storage system can be reduced by 43?% when using nano-particles.