Fundamentals of Natural Gas and Species Flow from Hydrates Dissociation
The primary goal of Professor Ahmadi's project is to provide a fundamental understanding of flow conditions of hydrate dissociation products in consolidated and unconsolidated sediment. He and his group are developing semi-analytical computational models to be used as tools for safety related issues. These include predicting the rate of natural gas pressure buildup during drilling in a hydrate reservoir, the nature of gas and water flows in the reservoir after hydrate dissociation, and the potential for sea floor instability. Availability of such an understanding, detailed experimental data and a computational tool, are crucial to the future development of technology for economical and safe natural gas production from hydrates in the 21st Century.
Professor Ahmadi and his group are developing a model (based on mechanical contact theory) for the chemical-mechanical polishing process. The goal of their research is to provide a fundamental understanding of the parameters that control the effectiveness of CMP for surface planarization. Their current work focuses on the abrasive particle, wafer, and pad contact and the abrasive and adhesive wear mechanisms in the chemical-mechanical polishing process. They are developing a model for interactions of pad asperities with abrasive particles and the wafer. Their analysis includes the influence of abrasive particle adhesion to the surface of the wafer. Also they are looking at the CMP process using hard and soft pads and dilute and concentrated slurries. In addition Professor Ahmadi and his students are also studying the effect of abrasive particle shapes, slurry pH, and colloidal forces on the removal rate.
Their model predictions are described in detail and compared with the available semi-empirical correlations in the paper " A Model for Mechanical Wear and Abrasive Particle Adhesion During the Chemical-Mechanical Polishing Process," by G. Ahmadi and X. Xia, Journal of the Electrochemical Society , 148 (3) G99-G109 (2001).
Atmospheric particle transport, dispersion and deposition, near a building model, are being studied by Professor Ahmadi and his group.. The stress transport model of FLUENT code is used for simulating the mean air flow. The instantaneous turbulence fluctuating velocity is simulated by a Gaussian filtered white noise model. A computational model is used for Lagrangian simulation of atmospheric particle transport, dispersion and deposition near the building. The model accounts for the drag and lift forces acting on the particle, as well as the effect of Brownian force, in addition to the gravitational sedimentation effects. For particles in the size range of 0.01 to 40 um, the corresponding deposition rates on various surfaces of the building model are evaluated and compared with experimental results.
Professor Ahmadi, in collaboration with Dr. Han and Dr. Greenspan of Dura Pharmaceuticals, is studying powder dispersion in inhalation drug delivery systems. Earlier, Professor Ahmadi and his students developed a computational model for providing a fundamental understanding of particle transport and deposition in the human lung. This model, which has applications to inhalation drug delivery, is used to evaluate the deposition rate of different size aerosols ( in the range of 0.01 to 20 microns) in various airways of the upper respiratory tract. Research results show that small particles ( less than a micron) deposit rather uniformly in the trachea, carina, and the main bronchus; while, the larger particles deposit very non-uniformly with a large number depositing on the carina. This work has significant implications in designing pharmaceutical inhalers for targeted dose delivery and for maximizing the therapeutic effect of drug transmission to the lung.
Dr. Ahmadi is also analyzing the dispersion and breakup of powder under the action of a strong shear field. The results provide insight into the design of drug delivery systems.
It is known that ash particles are not uniformly distributed in boilers, and segregation occurs based on particle size and composition (density). Typically, heavy (iron-rich) ash falls to the bottom of the boiler, while the light ash remains suspended and is transported by the hot gas. Depending on particle size and density (composition), some ash particles penetrate the boundary layer and deposit on the boiler walls, while others are swept away by the gas flow and leave through the exhaust. As a result, the rate of deposition and the composition of deposited ash may vary from region-to-region within the boiler. The main objective of Professor Ahmadi's project is to provide a fundamental understanding of transport and deposition of coal-ash in boilers. The general goal is to develop a procedure for using the available computational tools to optimally design the industrial boilers of the future.
CAMP Professor Vladimir Privman, Director of the Center for Quantum Device Technology, and his group are exploring implications of quantum physics for future nanotechnology and information processing. Modeling work related to this research is provided.
Quantum Mechanical Evolution to Perform Computations