RESUMO
Despite the common use of nonspherical catalyst pellets in chemical engineering applications, the packing structures of such pellets have not been as systematically studied and characterized as spherical packings. We propose a packing algorithm based on rigid body dynamics to simulate packing of nonspherical and possibly nonconvex pellets. The algorithm exerts a hard-body approach to model collision phenomena. The novelty is that the transition between moving and resting particles is controlled by a cutoff on the relative contact velocities, instead of artificially damping linear and angular velocities to stabilize the algorithm. The algorithm is used to synthesize packings of spheres, cylinders, and Raschig rings with tube-to-pellet diameter ratios 3-9.16. The packings are validated in terms of bulk porosity and radial void fraction distribution, finding satisfactory agreement with literature data. Denser packing structures are generated with high restitution coefficients and low friction coefficients. The confining tube walls play an important role, with highly fluctuating bulk porosities in narrow tubes.
RESUMO
The complexity and challenges in noncontact temperature measurements inside microwave-heated catalytic reactors are presented in this paper. A custom-designed microwave cavity has been used to focus the microwave field on the catalyst and enable monitoring of the temperature field in 2D. A methodology to study the temperature distribution in the catalytic bed by using a thermal camera in combination with a thermocouple for a heterogeneous catalytic reaction (methane dry reforming) under microwave heating has been demonstrated. The effects of various variables that affect the accuracy of temperature recordings are discussed in detail. The necessity of having at least one contact sensor, such as a thermocouple, or some other microwave transparent sensor, is recommended to keep track of the temperature changes occurring in the catalytic bed during the reaction under microwave heating.