Heat transfer enhancement by oscillatory perturbation of a stable separated flow

Numerical and experimental results for laminar flow and forced convection in a grooved channel indicate that significant heat transfer enhancement is possible by appropriately-tuned modulation of a steady, separated flow. The frequency r response of the enhancement is strongly peaked around the frequency of the least stable (decaying) mode of the unmodulated flow, suggesting that a simple resonance phenomenon is responsible for the transport augmentation.     

Natural circulation of electrically conducting liquids in fusion reactor blankets

A simple model has been developed for heat transfer in fusion reactor blankets with liquid breeding regions, allowing for natural circulation and the presence of strong magnetic fields. The results have been compared with the limited information available.For typical fusion blanket dimensions and temperature differences, natural circulation can be the dominant heat transfer mechanism in the molten salt flibe even over 10 Tesla magnetic field strength; it will increase heat transfer appreciably in the liquid lithium-lead mixture Li₁₇Pb₈₃ for magnetic field strengths less than about 10 Tesla; and can be neglected in liquid lithium if the magnetic field is over 1 Tesla.     

A performance comparison of lithium,helium, and flibe cooled tube/header fusion blankets

The objective of this study is to provide a comparison of thermal-hydraulic and structural performance of lithium, helium, and flibe cooled fusion blankets based on a tube/header geometry in a liquid lithium breeder. Type 316 stainless steel and TZM are considered as representative near-term and long-term, high temperature blanket structural materials, respectively, to show the potentials of each coolant. The flibe-TZM system has the best characteristics, while lithium-316SS, helium-316SS, and helium-TZM are comparable but definitely more limited in operating conditions. These results suggest that molten salt-refractory metal systems deserve more attention.Nomenclature a radial direction half-width of region cooled by single tube (m) - A A=_st/_cD - A _w first wall area (m²) - b azimuthal half-width of region cooled by single tube (m) - B magnetic field strength (T) - C _p specific heat of coolant (J/kg-°C) - C ₁ pumping power ratio - D _h ,D _t header and cooling tube diameter (m) - E _F energy deposited in the blanket region per fusion neutron, determined from neutronic calculations; 15.2 MeV used in this study - F _c allowance factor in pressure loss calculations for lithium system - h heat transfer coefficient (W/m²-°C) - Ha Hartmann number,Ha=BD _c /gm - J the ratio of percent change of first wall loading to percent change of a design parameter - K _c ,K _Li,K _s thermal conductivity of coolant, lithium, and structure (W/m-°C) - L major on-axis circumference of reactor (m) - M blanket energy multiplication factor,M=E _F /14.1 - n number of coolant tubes per header - N number of blanket modules (or headers) azimuthally - N _t total number of coolant tubes - Nu Nusselt number,Nu = hD_t/K_c - P coolant pressure (Pa) - P header and total pressure loss (Pa) - P _r Prandtl number - q _w first wall neutron energy loading (W/m²) - q average volumetric heat generation rate in the blanket (W/m³) - q(r) volumetric heat generation rate in blanket (W/m³) - r radial distance from first wall (m) - r _e radial position of the tube close to the hottest spot in the lithium pool - R gas constant - R _w first wall radius (m) - S defined by Eq. (25) - t _t ,t _h coolant tube and header tube thickness (m) - ¯T average coolant temperature (°C) - T _in inlet temperature (°C) - T _Li,max maximum lithium pool temperature (°C) - T _w,max maximum tube temperature (°C) - T _c coolant temperature rise across blanket (°C) - T _F film temperature rise (°C) - T _m temperature rise between coolant tube and maximum in pool (°C) - T _w wall temperature rise (°C) - U _h coolant velocity at header inlet for lithium system (m/s) - U _t coolant velocity in coolant tubes (m/s) - U _h ,max maximum inlet velocity for the lithium system, given by Eq. (13) - W _s surface heat flux in coolant tube (W/m²) - V _m voltage drop across the tube in flibe system (V) - V _t total blanket volume (m³) - X axial length of coolant tubes (m) - X _e entry and exit tube length in flibe system (m) - Z radial thickness of blanket (m) - _c , _s fraction of blanket volume occupied by coolant and structural material (exclusive of header region) - ratio of the minimum value ofq(r) to q, 0.4 - coolant viscosity (kg/m-s) - fiction coefficient - coolant density (kg/m³) - _t tube density (m^–3) - _c , _s electrical conductivity of coolant and structure (1/-m) - _h hoop stress (Pa) - _y structural material design yield stress limit (Pa)     

Integrated solar collector storage system based on a salt-hydrate phase-change material

A new integrated collector storage (ICS) concept for low-temperature solar heating of water is described. The solar energy is stored in a salt-hydrate phase-change material (PCM) held in the collector and is discharged to cold water flowing through a surface heat exchanger located in a layer of stationary heat transfer liquid (SHTL), floating over an immiscible layer of PCM. A theoretical model for the charging process of the proposed integrated collector is presented. The model assumes one-dimensional transient heat conduction in the PCM and SHTL layers and neglects the effect of convection heat transfer in these regions. The model was solved numerically by an enthalpy-based finite differences method and validated against experimental data. The results of parametric studies on the effect of the transition temperature and of the thickness layer of the salt-hydrate PCM on the thermal performance of the charging process are also presented.     

Detecting moving shadows: algorithms and evaluation

Moving shadows need careful consideration in the development of robust dynamic scene analysis systems. Moving shadow detection is critical for accurate object detection in video streams since shadow points are often misclassified as object points, causing errors in segmentation and tracking. Many algorithms have been proposed in the literature that deal with shadows. However, a comparative evaluation of the existing approaches is still lacking. In this paper, we present a comprehensive survey of moving shadow detection approaches. We organize contributions reported in the literature in four classes two of them are statistical and two are deterministic. We also present a comparative empirical evaluation of representative algorithms selected from these four classes. Novel quantitative (detection and discrimination rate) and qualitative metrics (scene and object independence, flexibility to shadow situations, and robustness to noise) are proposed to evaluate these classes of algorithms on a benchmark suite of indoor and outdoor video sequences. These video sequences and associated "ground-truth" data are made available at http://cvrr.ucsd.edu/aton/shadow to allow for others in the community to experiment with new algorithms and metrics.     

MODELING AUGMENTED OXYGEN TRANSFER IN FLOWING BLOOD

Previous models of the oxygen-hemoglobin saturation curve are discussed for oxygen transfer in laminar blood flow. A second-order approximation is introduced and evaluated for modeling the saturation curve. Prior experimental results have shown that at high shear rates the effective diffusion coefficient of oxygen is a strong function of the slope of the hemoglobin saturation curve. The impact of this shear-induced augmentation on transfer at large oxygen driving pressures is discussed. An augmentation model is presented to evaluate this effect using multiple diffusion coefficient solutions for a tubular geometry. The results compare well with previous experimental measurements.     

Socially‐Relevant Design: The TOYtech Project at Smith College

As issues of professional and ethical responsibility are receiving greater emphasis in engineering programs, the view of engineering as a profession in service to humanity is becoming more widespread. One approach to fostering this perspective among engineering students is the inclusion of socially relevant design projects throughout the curriculum. In this paper we present an example of one such project used in the introduction to engineering course at Smith College (the largest women's college in the U.S.) in which students are challenged to design toys that introduce children to the principles that underlie technology (TOYtech, or Teaching Our Youth Technology). Based on student surveys, we found that the majority of the course learning objectives were achieved through the implementation of the project, with students emphasizing that the project taught them about the importance of working well in teams and of considering the societal impact of engineering practice. In addition, we present our findings regarding the psychological type distribution of our inaugural class of first‐year engineering students and compare these to national values for female engineering students as a whole. These preliminary Myers‐Briggs Type Indicator (MBTI) data suggest that our students are particularly responsive to the ethic of social responsibility in engineering, and that they are strong communicators in addition to possessing a well‐organized, practical approach to problem solving.     

Variance-Based Energy Loss Computation in Low Voltage Distribution Networks

This paper describes a method for calculating energy losses in any system element assuming that the transmitted energy across it is known. The method identifies two components of losses: load variance and load mean. The load variance component can be neglected for large loads, but it is significant for small loads, which are dominant in low voltage networks. Needed parameters for loss calculation are determined by two load duration curves (LDCs) per load type. The formulae for loss calculation in transformers and distribution lines of various phase systems are given, including the formulae for energy losses and average current in the neutral conductor. A new algorithm for voltage calculation at network nodes is proposed and shown to provide high accuracy of calculated losses. The method enables loss calculation for compounded (nonhomogeneous) loads and gives the exact relationship between traditional loss factor and the load factor     

An intelligent tutoring module controlled by BDI agents for an e-learning platform

INES (INtelligent Educational System) is an operative prototype of an e-learning platform. This platform includes several tools and technologies, such as: (i) semantic management of users and contents; (ii) conversational agents to communicate with students in natural language; (iii) BDI-based (Believes, Desires, Intentions) agents, which shape the tutoring module of the system; (iv) an inference engine; and (v) ontologies, to semantically model the users, their activities, and the learning contents. The main contribution of this paper is the intelligent tutoring module of the system. Briefly, the tasks of this module are to recognize each student (checking his/her system credentials) and to obtain information about his/her learning progress. So, it can be able to suggest to each student specific tasks to achieve his/her particular learning objectives, based on several parameters related to the existing learning paths and the student’s profile.