Feridun Hamdullahpur

Exergy analysis of fluidized bed drying of moist particles

Abstract Energy and exergy analyses are conducted of the fluidized bed drying of moist materials for optimizing the operating conditions and the quality of the products. In this regard, energy and exergy models are developed to evaluate energy and exergy efficiencies, and are then verified with experimental data (for the product, wheat) taken from the literature. The effects of inlet air temperature, fluidization velocity, and initial moisture content on both energy and exergy efficiencies are studied. Furthermore, the hydrodynamic aspects, e.g., the bed hold up, are also studied. The results show that exergy efficiencies are less than energy efficiencies due to irreversibilities which are not taken into consideration in energy analysis, and that both energy and exergy efficiencies decrease with increasing drying time.

Thermodynamic modeling of fluidized bed drying of moist particles

A thermodynamic analysis of the fluidized bed drying process of large particles is performed to optimize the input and output conditions. Energy and exergy models were used for the study. The effects of the hydrodynamic and thermodynamic conditions such as the inlet air temperature, the fluidization velocity and the initial moisture content on the energy efficiency and the exergy efficiency were analyzed. The analysis was carried out using two different materials, wheat and corn. It was observed that the thermodynamic efficiency of the fluidized bed dryer was the lowest at the end of the drying process in conjunction with the moisture removal rate. The inlet air temperature has a strong effect on thermodynamic efficiency for wheat, but for corn, where the diffusion coefficient depends on the temperature and the moisture content of particles, an increase in the drying air temperature did not result in an increase of the efficiency. Furthermore, the energy and exergy efficiencies showed higher values for particles with high initial moisture content while the effect of gas velocity varied depending on the particles. A good agreement was achieved between the model predictions and the available experimental results.

CFD SIMULATION OF THE GAS-SOLID FLOW IN THE RISER OF A CIRCULATING FLUIDIZED BED WITH SECONDARY AIR INJECTION

ABSTRACT A comprehensive investigation was carried out to study hydrodynamics aspects of secondary air injection in circulating fluidized beds. This article presents modeling and results of computational fluid dynamics simulations of gas-solid flow in the riser section of a laboratory-scale (ID = 0.23 m, height = 7.6 m) circulating fluidized bed with a radial secondary air injector. The gas-solid flow model is based on the two-fluid (Eulerian-Eulerian) approach, where both gas and solids phases are treated as interpenetrating continua. A granular kinetic theory model is used to describe the solids phase stresses. The simulation results are compared with measured pressure drop and axial particle velocity profiles; reasonable agreement is obtained. Qualitatively, excellent agreement is obtained in predicting the increase in solids volume fraction below secondary air ports, the accumulation of solids around the center of the riser due to momentum of secondary air jets, and the absence of the solids down-flow near the wall above the secondary air injection ports, which are the prominent features of secondary air injection observed in the experiments.

Exergy Analysis and Performance Evaluation of CNG to LNG Converting Process

A process for converting Compressed Natural Gas (CNG) to Liquefied Natural Gas (LNG) is modelled thermodynamically and effects of design and operating parameters on exergy destruction and performa ...

Transient Modeling of Direct Internal Reforming Planar Solid Oxide Fuel Cells

In this paper, a 2-D cross section of a single cell of a direct internal reforming planar SOFC is taken and a heat transfer model is developed. For this purpose, the cell is divided into five control volumes: anode interconnect, fuel channel, positive/electrolyte/negative (PEN) structure, air channel and cathode interconnect. Mass and energy balances are solved in these control volumes (2-D in solid structures, 1-D in gas channels). Ohmic, activation and concentration polarizations, convection effects in rectangular ducts and surface-to-surface radiation effects are also taken into account. For the numerical solution, fully implicit finite difference scheme is chosen. The input parameters of the model are inlet temperature and gas composition of air and fuel channel, pressure of the cell, cell voltage, mass flow rate at the fuel channel inlet, excess air coefficient and cell geometry. The model also gives temperature and current density distributions within the cell as output.Copyright

Reducing Greenhouse Gas Emissions from a Landfill Site Using Various Thermal Systems

Global warming, which is a specific case of global climate change, refers to the increase in the average temperature of the atmosphere and oceans in recent decades, and the projected continuation of this increase. The drivers of climate change are seen as: changes in the atmospheric concentrations of GHGs and aerosols, land cover, and solar radiation (IPCC, 2007). According to the Intergovernmental Panel on Climate Change (IPCC, 2007), most of the increase in global average temperatures since the mid-20th century is linked to the observed increase in the anthropogenic GHG concentrations.

Thermodynamic Modeling of an Integrated DIR-SOFC/Biomass Gasification System

In this paper, a direct internal reforming SOFC (DIRSOFC) integrated with a downdraft biomass gasifier is modeled thermodynamically. As a case study, wood is selected as the biomass material and performance of the system at different operating temperature levels are studied. Change of the operating cell voltage, air utilization ratio, power output of the SOFC and electrical efficiency of the system with current density are investigated. Results show that operating the system at low temperature level yields higher electrical efficiency and air utilization ratio.Copyright

Effect of Particulate Diffusion on the Free Turbulent Flow Based on Two-Fluid

This paper is concerned with the two-dimensional gas-solid turbulent plane-mixing layer. The solid phase is considered a continuum and a two-fluid model, which is coupled by source terms due to particle drag and diffusion. Finite volume scheme has been employed for the governing equations. The simulation results show that the ratio of particle diffusion coefficient and kinematics viscosity of the carrier gas, have significant influence on the prediction of particles trend. In addition, it is observed that the loading ratio has no significant effect on the gas-solid flow prediction. The results are compared with the existed experimental data’s of others. This kind of modeling will ease the time consuming, stochastic approach of the Eulearian-Lagrangian methods but needs further investigation on the particle diffusivity term.Copyright