چكيده به لاتين
The heterogeneous chemical reaction in the packed bed is used in the separation process, decomposition process and fuel cells. Experimental study of the heterogeneous reaction in the packed bed is a costly and difficult task; also, these studies cannot show the changes occurring inside the packed bed and only show the overall performance of the system. Using numerical simulation is an inexpensive and fast way to observe the changes occurring inside the packed bed. In this thesis, the heterogeneous decomposition reaction in the packed bed is simulated as a one-step process. This type of heterogeneous reaction modeling extends the range of simulation conditions and accurately models the chemical reaction. ANSYS Fluent version 18.1 is used to perform this simulation. This simulation shows the changes occurring in the packed bed very accurately. Studying these changes is important for identifying and optimizing bed performance conditions.
Bed length and porosity coefficient are important parameters in determining overall system performance. Because increasing bed length, or decreasing its porosity coefficient, results in increased bed pressure drop, also decreasing bed length, or increasing its porosity coefficient, may result in the chemical reaction being incomplete. Pressure rise time is another important parameter. This parameter represents the time required to increase the chamber pressure from the initial value to the constant value and depends on many factors. These factors include, inlet fluid mass, inlet fluid concentration, substrate properties and chemical reaction rate. The rate of chemical reaction depends on the constituents used in the packed bed; Therefore, it is important to carry out experiments to obtain a decomposition rate. Also the distribution form of pellets in the packed bed is an important issue. Because it is effective in optimizing the packed bed and determining its porosity.
To determine the rate of decomposition reaction, a test stand was constructed and the parameters of the Arrhenius equation were obtained. Then another experiment was performed to determine the packed bed characteristics. This experiment determines the porosity coefficient and the distribution form of pellets in the packed bed. The results of this experiment show that the arrangement of pellets with a diameter of 1.9 mm in a packed bed with a diameter of 10 mm and a length of 30 mm is in the form of cubic and Hexagonal. In the simulation, the decomposition reaction is completed within 5 mm of the injector; this is one-sixth the length of the packed bed. Also, a code based on gas dynamics equations is written to calculate the chamber steady pressure and the pressure rise time. The results of this code are used to validate the simulation results.
Keywords: Heterogeneous reaction, Packed bed, Multiphase flow, Multicomponent flow
