Publications

Public perspectives of monkeypox in Twitter: A social media analysis using machine learning

No abstract is provided for this article.

Combined Heat and Mass Transfer by Natural Convection in a Vertical Enclosure

The phenomenon of natural convection caused by combined temperature and concentration buoyancy effects is studied analytically and numerically in a rectangular slot with uniform heat and mass fluxes along the vertical sides. The analytical part is devoted to the boundary layer regime where the heat and mass transfer rates are ruled by convection. An Oseen-linearized solution is reported for tall spaces filled with mixtures characterized by Le = 1 and arbitrary buoyancy ratios. The effect of varying the Lewis number is documented by a similarity solution valid for Le >1 in heat-transfer-driven flows, and for Le <1 in mass-transfer-driven flows. The analytical results are validated by numerical experiments conducted in the range 1≤H/L≤4, 3.5×105≤Ra≤7×106, −11≤n≤9, 1≤Le≤40, and Pr=0.7, 7. “Massline” patterns are used to visualize the convective mass transfer path and the flow reversal observed when the buoyancy ratio n passes through the value −1.

MIT—EEI Superconducting Synchronous Machine

In December 1968 the Edison Electric Institute authorized support of a research project on superconductors in large synchronous machines.* The purposes of the program are to demonstrate the practicality of utilizing superconductors for the field windings in large...

Natural convection in a vertical cylindrical well filled with porous medium

No abstract is provided for this article.

Cell and extracellular matrix growth theory and its implications for tumorigenesis

Cells associated with an abnormal (cancerous) growth exchange flows, morph freely and grow hand-in-glove with their immediate environment, the extracellular matrix (ECM). The cell structure experiences two mass flows in counterflow. Flowing into the structure are nutrients and flowing out is refuse from the metabolically active biomass within. The physical effect of the evolution of the cell and extracellular structure is more flow and mixing in that space, that is, more mixing than in the absence of a biological growth in that space. The objective of the present theory is to predict the increase in the size of the cell cluster as a function of its structure, and also to predict the critical cluster sizes that mark the transitions from one distinct cluster configuration to the next. This amounts to predicting the timing and the main features of the transitions from single cell to clusters with two, four, eight and more cells, including larger clusters with cells organized on its outer surface. The predicted evolution of the size and configuration of the cell cluster is validated successfully by comparison with measurements from several independent studies of cancerous and non-cancerous growth patterns.

Evolution of Airplanes, and What Price Speed?

No abstract is provided for this article.

Flow instabilities in gas-cooled cryogenic current leads

Gas-cooled cryogenic electric current leads which are operating at high ratios of current to mass flow are commonly used to supply electric current to superconducting magnets. Loss of coolant flow under such operating conditions will result in destruction of the lead and possible damage to the magnet itself. A flow instability, which results in loss of coolant flow, can occur in current leads due to the dependence of the kinematic viscosity of the coolant on the local temperature. This paper discusses the physical basis of the instability and presents an analysis which is used to describe the operation of current leads used in the EPRI-MIT 2000 kVA superconducting alternator. Details of the lead design and test results are included.

Thermal design and optimization

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Concurrent Reading and Writing with Mobile Agents

This paper presents a method using which a set of reading and writing agents concurrently read and update the global state of the network. In addition to the consistency of the snapshot and the reset states, our protocol preserves the atomicity of the reads and...

Integrative thermodynamic optimization of the environmental control system of an aircraft

In this paper we propose to optimize the geometric configuration of a component by maximizing the global thermodynamic performance of the much larger system that contains the component. This “integrative” approach departs from current thermodynamic optimization practice in which the configuration of a component (e.g., heat exchanger) is optimized by itself, in isolation. In the present example the larger system is an aircraft and the component is its environmental control system (ECS). We show that the configuration of the ECS impacts the performance (exergy destruction, fuel consumption) of the aircraft in two ways, not one: through its own irreversibility, and its weight-related contribution to the power required to sustain the flight. By minimizing the thermodynamic losses at the aircraft level, we deduce all the geometric details of the cross-flow heat exchanger that dominates the weight and structure of the ECS. The optimized geometry is robust with respect to changes in some of the operating parameters that have to be specified. The integrative method illustrated in this paper is generally applicable to the optimization of architecture in other systems where all the functions are driven by the exergy of the fuel installed onboard.

CONSTRUCTAL DESIGN AND THERMODYNAMIC OPTIMIZATION

This is a review of the main features of current activity in engineering thermodynamics research. It starts with the fundamentals of why processes and devices are inefficient: irreversibility, entropy generation (as distinct from the property entropy), exergy destruction, and the Gouy - Stodola theorem. The main trend today is the use of these principles to optimize global performance and configuration. The emphasis is on design, that is, the generation of the configuration of the energy system. This is accomplished by balancing (distributing, spreading) the irreversibilities of the energy system. This trend is fueled not only by the need for innovation (design without bias), but also by the availability of increasingly more powerful computational tools. The examples illustrated in this paper are counterflow heat exchangers, tree-shaped flow structures, flight, and sizes of organs for complex flow systems. At the fundamental level, the generation of the optimal configuration for maximal thermodynamic performance is an opportunity for engineers to shed light on the basics of self-optimization in nature. This latest trend at the engineering-science interface is constructal theory and design.

Assessing pneumonia identification from time-ordered narrative reports.

In this paper, we present a natural language processing system that can be used in hospital surveillance applications with the purpose of identifying patients with pneumonia. For this purpose, we built a sequence of supervised classifiers, where the dataset corresponding to each classifier consists of a restricted set of time-ordered narrative reports. In this way the pneumonia surveillance application will be able to invoke the most suitable classifier for each patient based on the period of time that has elapsed since the patient was admitted into the hospital. Our system achieves significantly better results when compared with a baseline previously proposed for pneumonia identification.

Constructal Conjugate Heat Transfer in Three-Dimensional Cooling Channels

This paper reports on three-dimensional geometric optimization of heat sinks and cooling channels where the objective is to maximize the global thermal conductance (minimize the thermal resistance), subject to two global constraints: fixed total volume and fixed channel volume. Heat transferred from the base is enhanced by two mechanisms, forced convection in the channel and conduction in the heat sinks. Numerical results showing the effects of dimensionless pressure drop, ratio of solid/fluid thermal conductivity on the optimized structure are reported. A test case shows a reduction of about 8% in thermal resistance when this method was applied to a known micro-channel heat sink model.

Theory of Rolling Contact Heat Transfer

This paper addresses the fundamentals of the phenomenon of steady heat transfer by rolling contact between two bodies at different temperatures. The contact region is modeled according to the classical Hertz theory, by which the bodies undergo elastic deformation and the contact area has the shape of an ellipse. In the first part of the study it is shown that when the two bodies make contact continuously over the elliptical area, the overall heat transfer rate is proportional to the square root of the Peclet number based on the ellipse semiaxis parallel to the tangential (rolling) velocity. In the same case the heat transfer rate increases as the square root of the normal force (F) between the two bodies. The second part of the study treats the case when the rolling contact is made through a large number of asperities (contact sites) distributed over the elliptical contact area. The heat transfer rate is again proportional to the square root of the Peclet number. When the asperities are distributed randomly, the heat transfer rate increases as F5/6. In the case of regularly distributed asperities that undergo elastic deformation, the heat transfer rate is proportional to F13/18. The high Peclet number domain covered by this study is discussed in the closing section of the paper.

Entropy generation through heat and fluid flow

Constructal multi-scale structure for maximal heat transfer density in natural convection

In this paper we investigate a new design concept for generating multi-scale structures in natural convection with the objective of maximizing the heat transfer density, or the heat transfer rate per unit of volume. The flow volume is filled with vertical equidistant heated blades of decreasing lengths. The spacings between the blades are optimized for maximal heat transfer density. Smaller blades are installed in the center plane between two adjacent longer blades, in the entrance region where the boundary layers are thin and the fluid is unheated. Based on the same principle, new generations of even smaller blades are added stepwise to the multi-scale structure. Constructal theory is applied to each new generation of blades, and this method leads to the optimal spacings between blades and the optimal lengths scales. As the number of length scales increase, the flow rate and the volume-averaged heat transfer density increase. It is also shown that there is a smallest (cutoff) length scale below which the boundary layers are no longer distinct, and where the sequence of generating optimal length scales ends. The maximized heat transfer density increases as the optimized complexity of the flow structure increases.

Fluid flow and heat transfer in vascularized cooling plates

In this study, the hydrodynamic and thermal characteristics of new vascular designs for the volumetric bathing of the smart structures were investigated numerically by addressing three-dimensional continuity, momentum, and energy conservation as a conjugate heat flow phenomenon. The numerical work covered the Reynolds number range of 50–2000, cooling channels volume fraction of 0.02, pressure drop range of 20–2×105 Pa, and six flow configurations: first, second, and third constructal structures with optimized hydraulic diameters and non-optimized hydraulic diameter for each system size 10×10, 20×20, and 50×50, respectively. The numerical results show that the optimized structure of cooling plates could enhance heat transfer significantly and decrease pumping power dramatically compared with the traditional channels. The difference in thermal resistance performance between optimized and non-optimized structures was found to increase and manifests itself clearly as the system size increased. The channel configurations of the first and second constructs are competitive in non-optimized configurations, whereas the best architecture was the third construct across all working conditions in non-optimized configurations.

Optimisation of film condensation with periodic wall cleaning

This is a theoretical and experimental study of the time-optimisation of condensation on a vertical wall when the film is removed periodically by a mechanical device. The objective is to fine-tune the periodic process so that the production of condensate and the heat transfer rate are maximal. The first part of the paper develops the scales of the periodic condensation process, and predicts the existence of an optimal condensation time interval. The analysis also predicts that the augmentation of condensation increases as the mechanical cleaning time decreases. These design optimisation opportunities are confirmed in the second part of the paper, which reports measurements of steam condensation on a vertical surface scraped periodically.