Feng Z.-G.,UTSA |
Michaelides E.E.,TCU |
Mao S.,Los Alamos National Laboratory
Fluid Dynamics Research | Year: 2012
We investigate the hydrodynamic drag force on a viscous sphere in a fluid of different viscosities at small but finite Reynolds numbers when interfacial slip is present at the surface of the sphere. The sphere is small enough for it to retain its spherical shape, as is the case with most small droplets. By using a singular perturbation method, the exterior flow field of the droplet is decomposed into an inner region, where the viscous effects dominate, and an outer region, where the inertia is important. The interior flow of the viscous sphere is also solved analytically. By applying appropriate boundary conditions to the surface of the viscous sphere and matching the conditions between the inner and outer flow fields, stream functions up to the order of Re 2 log Re for both the exterior and the interior flow are obtained. Thus, an analytical expression for the drag force coefficient of the viscous droplet is derived. This general expression yields, as special cases, several other expressions that are applicable to spheres that translate rectilinearly under more restrictive conditions. One of the practical conclusions from this study is that the presence of interfacial slip can significantly reduce the drag force on a droplet. © 2012 The Japan Society of Fluid Mechanics and IOP Publishing Ltd.
Feng Z.-G.,University of Texas at San Antonio |
Musong S.G.,University of Texas at San Antonio |
American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FEDSM | Year: 2014
A novel numerical technique that utilizes a three-dimensional Immersed Boundary Method (IBM) to solve the thermal interactions between spherical particles in a fluid is developed. At first, the natural convection of an isolated isothermal sphere immersed in a viscous fluid is analyzed and a new correlation for the heat transfer rate from a single sphere is obtained for 0.5≤ Pr ≤200 and 0 ≤ Gr ≤500. Secondly, the free convection heat transfer rate of a pair of spheres (bi-sphere) and spherical clusters immersed in air (Pr=0.72) were investigated using this numerical technique. The interactions depend on the separation distance between the spheres. It was observed that an increase in the separation of two spheres in tandem or side-by-side within a certain range may enhance the average heat transfer rate, when the interparticle distance is more than five radii. The average heat transfer rate of a cluster of touching, identical spheres with the same Grashof number was found to decrease as the number of spheres increased in the cluster. Copyright © 2014 by ASME.
Fanchi J.R.,TCU |
Proceedings - SPE Annual Technical Conference and Exhibition | Year: 2011
Gas shales are an increasingly important source of natural gas found around the world. They can extend under population centers and require urban operations. The public perception of gas shale development operations can have an impact on the regulatory environment. The purpose of this paper is to report on the public perception of issues associated with urban operations in the Barnett Shale development area. Copyright 2011, Society of Petroleum Engineers.
International Journal of Heat and Mass Transfer | Year: 2015
Thermophoresis is the realization of the averaged Brownian motion of particles in a fluid, which is subject to a steady temperature gradient. At sufficiently long times, the stronger molecular impulses in the hotter fluid region drive particles towards the colder region, where the molecular impulses are weaker. The effect of the molecular impulses on the particles is described by a stochastic Brownian force. When this force is applied to an ensemble of particles the thermophoretic velocity is the average velocity of the ensemble. In this study the motion of an ensemble of 4000 spherical nanoparticles with the material properties of CNT, aluminum, aluminum oxide, copper and gold was simulated in four base liquids-water, ethyl glycol, engine oil and R134a. The ensemble-averaged results generate the thermophoretic velocity of these particles in the base liquids. It was observed that the computational results agree very well with the few experimental data available for liquids. The computational method is general and may be applied to all heterogeneous systems of nanoparticles in liquids. The numerical results yield very useful information on the process of thermophoresis in liquids as well as values of the thermophoretic coefficients in nanofluids. © 2014 Elsevier Ltd.
Edrisi B.H.,University of Texas at San Antonio |
Energy | Year: 2013
Geothermal energy is an excellent form of renewable energy, which is continuously available for the production of electric power. At present, a very high percentage of geothermal power is generated by power systems that directly use the geofluid from a geothermal reservoir to produce electricity, such as dry steam and flashing power systems. These power plants operate at higher temperatures, typically greater than 160 °C. It appears that most of these high temperature geothermal reservoirs have already been developed and this leaves only the lower temperature resources available for the expansion and for the next generation of geothermal power plants. This paper examines the operation of a new system, the binary-flashing power plant, which may be used to harness more efficiently the available energy of geothermal resources at the lower range of resource temperatures. The paper compares the operation of the binary-flashing systems with the typical binary systems using the following substances as working fluids: normal butane, isobutane, hexane, pentane, refrigerant-114, and ammonia. It is observed that when both systems are optimized, the binary-flashing units would produce 25% more work than the typical binary units and that hexane and pentane appear to be better working fluids for these units. © 2012 Elsevier Ltd.