Improving the Efficiency of Wind Power System by Using Natural Convection Flows

In this paper a numerical study of natural convection in a two dimensional convergent channel, with or without rectangular block, is carried out. The block is placed at the channel outlet and its thermal conductivity is set equal to that of air. One of channel planes is heated at constant temperature TH. The other one is maintained cold at TC TH. The governing equations are solved using a finite volume method and the SIMLEC algorithm for the velocity-pressure coupling is used. Special emphasis is given to detail the effect of the block size and Rayleigh number on the dynamics of velocity, heat transfer and the debit generated by natural convection. Results are given for the following control parameters, 104 ≤ Ra ≤ 106, Pr=0.71. The inlet and outlet opening diameters are, respectively, C1=c1/h= 0.2 and C2=c2/h=0.1. Three values of the block height are considered: B=b/h=0.1, 0.14 and 0.2. These results show that the heat transfer and the mass flow rate variations with Ra are similar to those occurring in the case of the vertical isothermal parallel planes. The effect of the block height on the flow structure and heat transfer is negligible

Numerical Study of Convective Heat Transfer in a Horizontal Channel

This study is devoted to the investigation of natural convection in a two dimensional horizontal channel with rectangular heated blocks at the bottom. The aspect ratio of the channel is A = L'/H' = 5. The blocks are heated with a constant temperature while the upper plane of the channel is cold. The governing equations are solved using a finite volumes method and the SIMPLEC algorithm is used for the treatment of the pressure-velocity coupling. Special emphasis is given to detail the effect of the Rayleigh number and blocks height on the heat transfer and the mass flow rate generated by natural convection. Results are given for the following values of control parameters: Rayleigh number (5×103 ≤ Ra ≤ 7×105), Prandtl number Pr=0.71, opening width (C = l'/H' = 0.15), blocks gap (D = d'/H' = 0.5) and blocks height (B = h'/H = 1/2, 1/4 and 1/8)

Determination of Physical Properties of Porous Materials by a Lattice Boltzmann Approach

In this work, flows in porous media are simulated by using a Lattice Boltzmann Method (LBM). A model D2Q9 with a single collision operator is proposed. This method is applied on 2D digital images obtained by a Scanning Electron Microscope technique (SEM), and followed by a special treatment in order to obtain an image of synthesis that is finally read by the numerical code. The first results tested on two-dimensional configurations show the reliability of this strategy in simulating with a good accuracy phenomena of heat and mass transport. The numerical study is extended to the prediction of physical parameters that characterize a porous material (in particular, permeability that can be hardly estimated experimentally)

Thermal Modulation Effects on Thermosolutal Convection in a Vertical Bridgman Cavity

The effects of oscillatory heating on thermosolutal convection in a cavity heated from below are investigated and discussed. The transient Navier-Stokes equations coupled with heat and mass balances are solved numerically by using a control-volume technique. It is assumed that the interface moves with constant growth velocity. The results show the presence of multiple solutions in response to simultaneous vertical temperature and species concentration gradients applied to the system. In particular, two critical frequencies are identified, one corresponding to low values of the buoyancy ratio N (N~1), accompanied with a decrease of flow intensity reaching a minimal value, the other occurring at higher value of N (N~50), accompanied with flow intensity increase reaching a maximal value

DEPARTMENT OF DEFENSE JOINT AIRCREW SURVIVAL FLIGHT VEST

The purpose of this research is to analyze the feasibility of a joint aircrew survival flight vest program to satisfy the performance requirements across the military Services. The Department of Defense (DOD) has multiple type, model, and series aircraft in its inventory to meet the capabilities validated by the Joint Requirements Oversight Council. Each aircraft comes with a variety of Aviation Life Support Systems such as the aircrew survival flight vest. There are a variety of aircrew survival flight vests across the DOD performing similar functions, such as ballistic protection, signaling and communications, and providing flotation in a maritime environment. In recent years, Defense Acquisitions programs have been becoming more joint by increasing commonality to cut costs by reducing redundant programs among the different services. Currently, the various aircrew flight vests that are being used remain under the control of several program executive offices. This research examined the feasibility of a joint aircrew survival flight vest by using a combination of the case study method and the cost-effectiveness analysis. We conclude that a joint aircrew survival flight vest with a modular design would be the most effective option. The services will have the flexibility to tailor the joint vest with modules to meet performance specifications.Outstanding ThesisMajor, United States Marine CorpsCaptain, United States Marine CorpsEnsign, United States NavyApproved for public release. Distribution is unlimited

Numerical Study of Thermosolutal Convection in Enclosures Used for Directional Solidification (Bridgman Cavity)

The present work is devoted to the numerical investigation of the interaction between thermal and solutal convection in enclosures used for modeling directional solidification. The full transient Navier--Stokes, energy and species conservation equations are solved numerically by using finite volumes technique

Exceptional Hyperthyroidism and a Role for both Major Histocompatibility Class I and Class II Genes in a Murine Model of Graves' Disease

Autoimmune hyperthyroidism, Graves' disease, can be induced by immunizing susceptible strains of mice with adenovirus encoding the human thyrotropin receptor (TSHR) or its A-subunit. Studies in two small families of recombinant inbred strains showed that susceptibility to developing TSHR antibodies (measured by TSH binding inhibition, TBI) was linked to the MHC region whereas genes on different chromosomes contributed to hyperthyroidism. We have now investigated TSHR antibody production and hyperthyroidism induced by TSHR A-subunit adenovirus immunization of a larger family of strains (26 of the AXB and BXA strains). Analysis of the combined AXB and BXA families provided unexpected insight into several aspects of Graves' disease. First, extreme thyroid hyperplasia and hyperthyroidism in one remarkable strain, BXA13, reflected an inability to generate non-functional TSHR antibodies measured by ELISA. Although neutral TSHR antibodies have been detected in Graves' sera, pathogenic, functional TSHR antibodies in Graves' patients are undetectable by ELISA. Therefore, this strain immunized with A-subunit-adenovirus that generates only functional TSHR antibodies may provide an improved model for studies of induced Graves' disease. Second, our combined analysis of linkage data from this and previous work strengthens the evidence that gene variants in the immunoglobulin heavy chain V region contribute to generating thyroid stimulating antibodies. Third, a broad region that encompasses the MHC region on mouse chomosome 17 is linked to the development of TSHR antibodies (measured by TBI). Most importantly, unlike other strains, TBI linkage in the AXB and BXA families to MHC class I and class II genes provides an explanation for the unresolved class I/class II difference in humans

Modeling of Ti-W Solidification Microstructures Under Additive Manufacturing Conditions

Additive manufacturing (AM) processes have many benefits for the fabrication of alloy parts, including the potential for greater microstructural control and targeted properties than traditional metallurgy processes. To accelerate utilization of this process to produce such parts, an effective computational modeling approach to identify the relationships between material and process parameters, microstructure, and part properties is essential. Development of such a model requires accounting for the many factors in play during this process, including laser absorption, material addition and melting, fluid flow, various modes of heat transport, and solidification. In this paper, we start with a more modest goal, to create a multiscale model for a specific AM process, Laser Engineered Net Shaping (LENS™), which couples a continuum-level description of a simplified beam melting problem (coupling heat absorption, heat transport, and fluid flow) with a Lattice Boltzmann-cellular automata (LB-CA) microscale model of combined fluid flow, solute transport, and solidification. We apply this model to a binary Ti-5.5 wt pct W alloy and compare calculated quantities, such as dendrite arm spacing, with experimental results reported in a companion paper