Abstract: It has been remarked that “invention is the mother of necessity” – not the other way around. Technology breakthroughs of themselves, can and do create world markets. In a very short period of history, the gas turbine, youngest of major energy conversion devices, has changed and created global markets in aviation, in marine propulsion and in generation of electric power. In this talk we will discuss how in less than 80 years the gas turbine has come to dominate aircraft propulsion and now, global electrical power generation. In 1939, the first gas turbines had a thermal efficiency of about 18%. Over the years, many thousands of engineers and researchers in academia, government and industry have worked to raise turbine inlet temperatures, increase pressure ratios, enhance combustion, perfect new materials and improve designs, so that modern gas turbines now achieve 40-45% in simple cycle operation. In combined cycle operation, the gas turbine has become the thermal efficiency superstar of the electric power plant world, bringing about combined cycle thermal efficiencies exceeding 60%. Today, gas turbine technology and testing improvements continue apace, and some of these will be discussed. Fuel usage is being drastically reduced in newer land-based gas turbines through the first practical use of recuperators and intercoolers. Small gas turbines are now being used to produce electricity from greenhouse gases at municipal waste water treatment plants. A commercial closed cycle helium gas turbine has been proposed to generate electricity, using a pebble bed modular nuclear reactor as a heat source. The engine in production for the F-135 Joint Strike Fighter is pushing the limits of jet engine technology and will lead to future improvements in gas turbine technology.
Biographical Sketch: Lee Langston received a BSME (1959) from the University of Connecticut, and an MS (1960) and a Ph.D. (1964) from Stanford University. He was with Pratt and Whitney Aircraft as a research engineer working on fuel cells, heat pipes and jet engines from 1964 to 1977. During these years, he also participated in mountain climbing activities in various parts of the world. He joined the mechanical engineering faculty at the University of Connecticut in 1977, rising to the rank of Professor in 1983. At UConn, he has taught graduate and undergraduate courses in heat transfer and fluid mechanics, with research activities involving the measurement, understanding and prediction of secondary flows in gas turbines. He served as Interim Dean of the School of Engineering in 1997-98 and became Professor Emeritus in 2003. He is a Life Fellow of the American Society of Mechanical Engineering Engineers (ASME), has served as Editor, ASME Journal of Engineering for Gas Turbines and Power (2001-2006) and was a member of the Board of Directors of the ASME International Gas Turbine Institute (IGTI). In 2015, he was the recipient of IGTI’s R. Tom Sawyer Award, for outstanding contributions in the field of gas turbines. For the past seventeen years Professor Langston has written a column and a variety of articles on gas turbine technology for IGTI and ASME’s Mechanical Engineering Magazine.
Abstract: Blood clots are required to stem bleeding and are subject to a variety of stresses, but they can also block blood vessels and cause heart attacks and strokes. We measured the compressive response of human platelet-poor plasma (PPP) clots, platelet-rich plasma (PRP) clots and whole blood clots and correlated these measurements with confocal and scanning electron microscopy to track changes in clot structure. Stress-strain curves revealed four characteristic regions, for compression-decompression: 1) linear elastic region; 2) upper plateau or softening region; 3) non-linear elastic region or re-stretching of the network; 4) lower plateau in which dissociation of some newly made connections occurs. Our experiments revealed that compression proceeds by the passage of a phase boundary through the clot separating rarefied and densified phases. This observation motivates a model of fibrin mechanics based on the continuum theory of phase transitions, which accounts for the pre-stress caused by platelets, the adhesion of fibrin fibers in the densified phase, the compression of red blood cells (RBCs), and the pumping of liquids through the clot during compression/decompression. Our experiments and theory provide insights into the mechanical behavior of blood clots that could have implications clinically and in the design of fibrin-based biomaterials. As a second topic we will consider thermal fluctuations of lipid bilayer membranes. Typically, membrane fluctuations are analyzed by decomposing into normal modes or by molecular simulations. We propose a new approach to calculate the partition function of a membrane. We view the membrane as a fluctuating elastic plate and discretize it into triangular elements. We express its energy as a function of nodal displacements, and then compute the partition function and covariance matrix using Gaussian integrals. We recover well-known results for the dependence of the projected area of the membrane on the applied tension and recent simulation results on the dependence of membrane free energy on geometry, spontaneous curvature and tension. As new applications, we compute elastic and entropic interactions of inclusions in membranes.
Abstract: Multiphase flows are ubiquitous in a wide range of natural processes and engineering applications. Although efforts to compute multiphase flows started as early as the beginning of the computational fluid dynamics (CFD), the progress was rather slow mainly due to the existence of interfaces that continuously evolve in time and often undergo large deformations leading to topological changes such as breakup and coalescence. In the case of confinement, the fluid-fluid interface strongly interacts with the complex channel wall and usually involve small features such as thin liquid films that are difficult to resolve computationally. Multi-physics effects such as soluble surfactant, phase change, chemical reactions, moving contact line and viscoelasticity make the problem even more complicated and challenging for computational simulations. In this talk, I will discuss our work towards addressing these challenges. I will first describe a front-tracking method developed for particle-resolved simulations of multiphase flows, where all relevant continuum length and time scales are fully resolved in all phases. Special emphasis will be placed on treatment of soluble surfactants, viscoelasticity and phase change (droplet evaporation and burning). Sample results will be presented for various multiphase flows encountered or inspired by bio/microfluidic applications. The microfluidic applications generally involve highly laminar low Reynolds number flows but the numerical method is not restricted to low Reynolds numbers and can be directly applied to turbulent multiphase flows at moderate and even high Reynolds numbers depending on available computational resources. Sample results will also be presented about effects of soluble surfactant on weakly turbulent bubbly flows at moderate Reynolds numbers. The talk will conclude with future directions and applications of presented method to large multi-scale and multi-physics problems of practical interest.
Christopher White, Associate Professor of Mechanical Engineering
Yongming Liu, Assistant Professor