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Ephraim M Sparrow

Bio: Ephraim M Sparrow is an academic researcher from University of Minnesota. The author has contributed to research in topics: Heat transfer & Heat transfer coefficient. The author has an hindex of 77, co-authored 552 publications receiving 27226 citations. Previous affiliations of Ephraim M Sparrow include National Science Foundation & University of Illinois at Chicago.


Papers
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Journal ArticleDOI
TL;DR: In this article, the combined-mode natural convection/radiation heat transfer characteristics of highly populated arrays of rod-like cylindrical fin arrays were evaluated and it was found that fin fin arrays are highly enhancing in terms of heat transfer.
Abstract: Experiments were performed to determine the combined-mode natural convection/radiation heat transfer characteristics of highly populated arrays of rodlike cylindrical fins (i.e., pin fins). The fins were oriented with their axes horizontal and were attached to a vertical heated baseplate. The investigated parameters included the number of fins in the array, the fin length and diameter, the baseplate-to-ambient temperature difference, and the presence or absence of adjacent shrouding surfaces. Finning was found to be highly enhancing (up to a sixfold increase in heat transfer), and even the longest fins were highly efficient. When the number of fins was increased for fixed values of the other parameters, the heat transfer increased at first, attained a maximum, and then decreased. Arrays having different diameter fins yielded about the same performance when the surface area of the fin-baseplate assembly was held fixed. Shrouding surfaces positioned close to the array decreased the rate of heat transfer. Calculations showed that the contribution of radiation was substantial and was greatest for more populous arrays, for longer fins, and at small temperature differences.

81 citations

Journal ArticleDOI
TL;DR: In this paper, an analysis of laminar flow and heat transfer in channels whose walls are interrupted periodically along the streamwise direction was made, and the basic heat transfer and pressure drop results were employed to investigate whether an interrupted-wall channel experiences an augmented heat transfer rate compared with that for a parallel plate channel.
Abstract: An analysis has been made of laminar flow and heat transfer in channels whose walls are interrupted periodically along the streamwise direction. Such channels are frequently employed in high-performance compact heat exchangers. Numerical solutions of the mass, momentum, and energy conservation equations yielded local heat transfer and pressure drop results. These results were obtained for a range of Reynolds numbers and for several values of a dimensionless geometrical parameter characterizing the streamwise length L of the individual plate segments which make up the interrupted walls. The Prandtl number was fixed at 0.7 for all the calculations. The basic heat transfer and pressure drop results were employed to investigate whether an interrupted-wall channel experiences an augmented heat transfer rate compared with that for a parallel plate channel. For conditions of equal heat transfer surface area and equal pumping power, appreciably higher heat transfer rates prevailed in the interrupted-wall channel for a wide range of operating conditions. The augmentation was especially marked for relatively short channels and high Reynolds numbers. The results also demonstrated the existence of a new type of fully developed regime, one that is periodic. At sufficiently large downstream distances, the velocity and temperature profiles repeat their values at successive axial stations separated by a distance 2L and, in addition, the average heat transfer coefficient for a plate segment takes on a constant value.

80 citations

Journal ArticleDOI
TL;DR: A boundary-layer analysis of laminar film condensation on a vertical plate has been carried out to study the effects of superheated vapor and non-condensable gases as discussed by the authors.
Abstract: A boundary-layer analysis of laminar film condensation on a vertical plate has been carried out to study the effects of superheated vapor and noncondensable gases. For a pure, superheated vapor the effects of superheating on the surface heat transfer are accounted for by a simple modification of previously available results for saturated vapors. For a given temperature difference between the plate surface and the liquid-vapor interface, superheating increases the heat transfer to the surface, but only to a modest extent for most practical situations. Although free convection was not included in the analysis, its role has been estimated to be small. For noncondensable gases the analysis shows that the presence of a few per cent of noncondensable in the bulk of the vapor causes a great reduction in the surface heat transfer. The fact that the predicted reduction is substantially larger than that found experimentally indicates that free convection, which is not included in the analysis, plays an important role when noncondensables are present.

80 citations

Journal ArticleDOI
TL;DR: In this paper, a phase-change medium in a vertical tube was used to study the effect of fluid motions in the liquid melt induced by volume change and natural convection, with the former being significant only at early times.
Abstract: Experiments on the melting of a phase-change medium in a vertical tube yielded quantitative results both for the heat transfer and the timewise evolution of the melting front. The upper surface of the phase-change medium was bounded by an insulated air space, which accommodated the volume changes which accompany the melting process. Numerical solutions based on a pure conduction model were also performed for comparison purposes. It was found that the rate of melting and the heat transfer are significantly affected by fluid motions in the liquid melt induced by the volume change and by natural convection, with the former being significant only at early times. For melting initiated with the solid at the phase-change temperatures, the experimentally determined values of the energy transfer associated with the melting process were about 50 percent higher than those predicted by the conduction model. Furthermore, the measured values of the energy stored in the liquid metal were about twice the conduction prediction. A compact dimensionless correlation of the experimental results was achieved using the Fourier, Stefan, and Grashof numbers. Initial subcooling of the solid substantially decreased the rate of melting, with corresponding decreases in the energy transfers for melting and sensible heat storage.

79 citations


Cited by
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Journal ArticleDOI
TL;DR: A comprehensive review of spatiotemporal pattern formation in systems driven away from equilibrium is presented in this article, with emphasis on comparisons between theory and quantitative experiments, and a classification of patterns in terms of the characteristic wave vector q 0 and frequency ω 0 of the instability.
Abstract: A comprehensive review of spatiotemporal pattern formation in systems driven away from equilibrium is presented, with emphasis on comparisons between theory and quantitative experiments. Examples include patterns in hydrodynamic systems such as thermal convection in pure fluids and binary mixtures, Taylor-Couette flow, parametric-wave instabilities, as well as patterns in solidification fronts, nonlinear optics, oscillatory chemical reactions and excitable biological media. The theoretical starting point is usually a set of deterministic equations of motion, typically in the form of nonlinear partial differential equations. These are sometimes supplemented by stochastic terms representing thermal or instrumental noise, but for macroscopic systems and carefully designed experiments the stochastic forces are often negligible. An aim of theory is to describe solutions of the deterministic equations that are likely to be reached starting from typical initial conditions and to persist at long times. A unified description is developed, based on the linear instabilities of a homogeneous state, which leads naturally to a classification of patterns in terms of the characteristic wave vector q0 and frequency ω0 of the instability. Type Is systems (ω0=0, q0≠0) are stationary in time and periodic in space; type IIIo systems (ω0≠0, q0=0) are periodic in time and uniform in space; and type Io systems (ω0≠0, q0≠0) are periodic in both space and time. Near a continuous (or supercritical) instability, the dynamics may be accurately described via "amplitude equations," whose form is universal for each type of instability. The specifics of each system enter only through the nonuniversal coefficients. Far from the instability threshold a different universal description known as the "phase equation" may be derived, but it is restricted to slow distortions of an ideal pattern. For many systems appropriate starting equations are either not known or too complicated to analyze conveniently. It is thus useful to introduce phenomenological order-parameter models, which lead to the correct amplitude equations near threshold, and which may be solved analytically or numerically in the nonlinear regime away from the instability. The above theoretical methods are useful in analyzing "real pattern effects" such as the influence of external boundaries, or the formation and dynamics of defects in ideal structures. An important element in nonequilibrium systems is the appearance of deterministic chaos. A greal deal is known about systems with a small number of degrees of freedom displaying "temporal chaos," where the structure of the phase space can be analyzed in detail. For spatially extended systems with many degrees of freedom, on the other hand, one is dealing with spatiotemporal chaos and appropriate methods of analysis need to be developed. In addition to the general features of nonequilibrium pattern formation discussed above, detailed reviews of theoretical and experimental work on many specific systems are presented. These include Rayleigh-Benard convection in a pure fluid, convection in binary-fluid mixtures, electrohydrodynamic convection in nematic liquid crystals, Taylor-Couette flow between rotating cylinders, parametric surface waves, patterns in certain open flow systems, oscillatory chemical reactions, static and dynamic patterns in biological media, crystallization fronts, and patterns in nonlinear optics. A concluding section summarizes what has and has not been accomplished, and attempts to assess the prospects for the future.

6,145 citations

Journal ArticleDOI
TL;DR: The use of a latent heat storage system using phase change materials (PCMs) is an effective way of storing thermal energy and has the advantages of high energy storage density and the isothermal nature of the storage process.
Abstract: The use of a latent heat storage system using phase change materials (PCMs) is an effective way of storing thermal energy and has the advantages of high-energy storage density and the isothermal nature of the storage process. PCMs have been widely used in latent heat thermal-storage systems for heat pumps, solar engineering, and spacecraft thermal control applications. The uses of PCMs for heating and cooling applications for buildings have been investigated within the past decade. There are large numbers of PCMs that melt and solidify at a wide range of temperatures, making them attractive in a number of applications. This paper also summarizes the investigation and analysis of the available thermal energy storage systems incorporating PCMs for use in different applications.

4,482 citations

BookDOI
01 Jan 1996
TL;DR: The client would like to get a larger, approximately 3 cm in diameter, well fixed tissue sample, together with a detailed report of the clinical presentation, gross, and microscopic lesions, along with the submission of samples prepared in a similar manner by the client for processing.
Abstract: We wrote it to be read by, and taught to, senior undergraduates and starting graduate students, rather than studied in a research laboratory. We wrote it using the same style and sentence construction that we have used in countless classroom lectures, rather than how we have written our countless (and much-less read) formal scientificpapers. In this respect particularly, wehave been deliberate in notreferencing the sources of every experimental fact or theoretical concept (although we do include some hints and clues in the chapters). However, at the end of each chapter we have included groups of references that should lead you to the best sources in the literature and help you go into more depth as you become more confident about what you are looking for. We are great believers in the value of history as the basis for under- standing the present and so the history of the techniques and key historical references are threaded throughout the book. Just because a reference is dated in the previous century (or even the antepenultimate century) doesn’t mean it isn’t useful! Likewise, with the numerous figures drawn from across the fields of materials science and engineering and nanotechnology, we do not reference the source in each caption. But at the very end of the book each of our many generous colleagues whose work we have used is clearly acknowledged.

4,412 citations

Book
30 Sep 2010
TL;DR: Computer Vision: Algorithms and Applications explores the variety of techniques commonly used to analyze and interpret images and takes a scientific approach to basic vision problems, formulating physical models of the imaging process before inverting them to produce descriptions of a scene.
Abstract: Humans perceive the three-dimensional structure of the world with apparent ease. However, despite all of the recent advances in computer vision research, the dream of having a computer interpret an image at the same level as a two-year old remains elusive. Why is computer vision such a challenging problem and what is the current state of the art? Computer Vision: Algorithms and Applications explores the variety of techniques commonly used to analyze and interpret images. It also describes challenging real-world applications where vision is being successfully used, both for specialized applications such as medical imaging, and for fun, consumer-level tasks such as image editing and stitching, which students can apply to their own personal photos and videos. More than just a source of recipes, this exceptionally authoritative and comprehensive textbook/reference also takes a scientific approach to basic vision problems, formulating physical models of the imaging process before inverting them to produce descriptions of a scene. These problems are also analyzed using statistical models and solved using rigorous engineering techniques Topics and features: structured to support active curricula and project-oriented courses, with tips in the Introduction for using the book in a variety of customized courses; presents exercises at the end of each chapter with a heavy emphasis on testing algorithms and containing numerous suggestions for small mid-term projects; provides additional material and more detailed mathematical topics in the Appendices, which cover linear algebra, numerical techniques, and Bayesian estimation theory; suggests additional reading at the end of each chapter, including the latest research in each sub-field, in addition to a full Bibliography at the end of the book; supplies supplementary course material for students at the associated website, http://szeliski.org/Book/. Suitable for an upper-level undergraduate or graduate-level course in computer science or engineering, this textbook focuses on basic techniques that work under real-world conditions and encourages students to push their creative boundaries. Its design and exposition also make it eminently suitable as a unique reference to the fundamental techniques and current research literature in computer vision.

4,146 citations

Journal ArticleDOI
TL;DR: In this paper, a review of the history of thermal energy storage with solid-liquid phase change has been carried out and three aspects have been the focus of this review: materials, heat transfer and applications.

4,019 citations