DEM--CFD modeling and simulations of hydrodynamic characteristics and flow resistance coefficient in fixed-bed reactors

The ability to predict void fraction, pressure drop, and flow resistance coefficient in fixed-bed reactors is significant to their optimal design. In this study, the discrete element method (DEM) is combined with computational fluid dynamics (CFD) to simulate the hydrodynamic characteristics of fixed-beds. A realistic random packing structure for fixed-beds with spherical particles was generated via the DEM method and then meshed using Ansys ICEM software for the CFD simulation. A grid independency study was performed to select appropriate grid model parameters. A large set of numerical experiments was conducted to investigate the hydrodynamic characteristics with respect to different inlet velocities and particle sizes, and the simulated pressure drop data were used to calculate the flow resistance coefficient. The output flow resistance coefficients agreed well with those calculated by the classical models in laminar and turbulent flow regimes, thereby indicating the accuracy and advantage of the proposed DEM–CFD approach.

Front-end Solar Temperature And Humidity Control System

Solid dehumidification is one of the important components of the dehumidification air-conditioning system. As an important method of solid dehumidification, the dehumidification performance and regeneration performance of fixed-bed dehumidification have an important impact on the operation and energy saving of the dehumidification air-conditioning system. In view of the high air temperature and high humidity in South China, our design organically combines dehumidification fixed beds, semiconductor refrigeration devices, foam ceramic insulation panels and double-glazed windows. We have designed a photovoltaic-driven modular solar temperature regulating and dehumidifying purification wall suitable for building dehumidification. The dehumidification window can use daytime solar radiation to regenerate the dehumidification fixed bed after absorbing moisture, reducing the energy consumption of regeneration. At the same time, the design can also use semiconductor refrigeration devices to adjust the temperature and humidity of the window inlet air to improve the window's dehumidification and regeneration performance. We tested and studied the dehumidification and regeneration performance of the device under different working conditions through experimental tests, which provided a basis for the engineering application and theoretical analysis of the device.

SUPPORTING THE WATER RESERVOIR RESTORATION PROCESSES BY USING SELECTED TYPE OF BIOLOGICAL BEDS

Aim of the study: The work aims to assess the possibility of the application of selected types of biological beds to support the revitalization processes of strongly degraded water reservoirs. Material and methods: The authors reviewed the literature on biological methods used in the treatment processes of various types of wastewater. Certain types of beds have been selected that show tolerance to temperature changes and significant changes in organic pollutant loads. The self-purification potential of water and the role of natural methods in the revitalization of water reservoirs were characterized. The characteristics of biological methods based on MBBR moving and fixed beds are presented. Results and conclusions: The possibility of application of selected types of MBBR moving and fixed beds in supporting the treatment of highly contaminated surface waters were assessed. Biotechnological methods based on liquid and solid biopreparations normally used in water revitalization were discussed. It has been shown that when biotechnological methods are not able to operate efficiently, it is very beneficial to start additional biological processes to improve the efficiency of the revitalization process.