901 publications from this institution
This paper considers the fundamental problem of how to shape rectangular high-conductivity inserts (fins) that are mounted on the rim of and protrude into a disc-shaped body that generates heat. The objective is to minimize the global thermal resistance by optimizing geometrically the distribution of a fixed amount of high-conductivity material through the material of lower conductivity. In addition to the fin geometry, three other design parameters are considered: the ratio between the high conductivity and low conductivity k ̃ , the relative amount of high conductivity material φ, and the number of sectors of the disc-shaped body, N. It is shown analytically and numerically that the thermal resistance can be minimized with respect to the fin aspect ratio, λ. The optimized geometry and performance are reported graphically as functions of k ̃ , φ and N. Good agreement is found between the analytical solution and the numerical results.
Superconducting magnets are energized through helium vapour-cooled cryogenic current leads operating at high ratios of current to mass flow. The high current operation where lead temperature, runaway, and eventual burn-up are likely to occur is investigated. A simple criterion for estimating the burn-up operation conditions (current, mass flow) for a given lead geometry (cross-sectional area, length, heat exchanger area) is presented. This article stresses the role played by the available heat exchanger area in avoiding burnup at high ratios of current to mass flow.
No abstract is provided for this article.
This paper addresses the fundamental heat transfer augmentation question of how to arrange a stack of parallel plates (e.g. fins of heat sink, printed circuit boards) in a free stream such that the thermal resistance between the stack and the stream is minimum. It is shown that the best way of positioning the plates relative to one another is by spacing them equidistantly. When the overall dimensions of the stack are specified, there is an optimal number of plates for minimum thermal resistance. The optimal number and minimum resistance are anticipated theoretically and correlated into compact formulas that agree with numerical and experimental results in the ReL range 102-104. Finally, it is shown that a stack with more plates than the optimal number can be modeled more expediently as a porous block immersed in a free stream.
Realistic models of energy systems demand the treatment of installations and their flowing surroundings together, more so when the installations are large and their spheres of impact greater. The interface between energy systems and the environment is formed by...
This paper addresses the fundamental problem of optimizing the geometry of an electromagnet by maximizing at the same time its magnetic performance and thermal performance. The solenoid has a cylindrical shape and a uniform current density. Cooling discs made of high thermal conductivity material are inserted in the coil to collect the heat generated by Joule heating. The collected heat is evacuated to the ambient. For a given magnetic performance and volume, the maximum temperature inside the electromagnet is minimized by selecting the shape of the coil (length and outer radius), the number of cooling discs, and the amount of high thermal conductivity material. The two objectives pursued in this geometric optimization (magnetic and thermal) show that the constructal design method can be extended to the generation of architecture for multi-objective systems.
Most of the studies of convection in porous media published before 1970 were motivated by geophysical applications, and many published since have geophysical ramifications; see, for example, the reviews bys Cheng (1978, 1985b). On the other hand, geothermal reservoir...
No abstract is provided for this article.
Biologists have treated the view that fundamental differences exist between running, flying and swimming as evident, because the forms of locomotion and the animals are so different: limbs and wings vs body undulations, neutrally buoyant vs weighted bodies, etc. Here we show that all forms of locomotion can be described by a single physics theory. The theory is an invocation of the principle that flow systems evolve in such a way that they destroy minimum useful energy (exergy, food). This optimization approach delivers in surprisingly direct fashion the observed relations between speed and body mass (M(b)) raised to 1/6, and between frequency (stride, flapping) and M(b)(-1/6), and shows why these relations hold for running, flying and swimming. Animal locomotion is an optimized two-step intermittency: an optimal balance is achieved between the vertical loss of useful energy (lifting the body weight, which later drops), and the horizontal loss caused by friction against the surrounding medium. The theory predicts additional features of animal design: the Strouhal number constant, which holds for running as well as flying and swimming, the proportionality between force output and mass in animal motors, and the fact that undulating swimming and flapping flight occur only if the body Reynolds number exceeds approximately 30. This theory, and the general body of work known as constructal theory, together now show that animal movement (running, flying, swimming) and fluid eddy movement (turbulent structure) are both forms of optimized intermittent movement.
This note summarizes the results of a numerical study designed to question (i.e., refute or validate) Chao et al.'s1 and Bertin and Ozoe's2 conclusion that the critical Rayleigh number increases substantially as the Prandtl number becomes very small. The numerical method is based on the finite-difference control volume formulation and the complete equations for two-dimensional (2-D) time-dependent flow. The present results show that the lowest attainable Rayleigh number for numerically simulated convection increases as Pr decreases below 0.1. These results also extend the Prandtl number domain of the observations down to Pr=10−4 and indicate that the natural shape of a single roll in this Pr range is approximately square. The discrepancy between these observations and the constant Rac=1,707.8 of the linear stability analysis is attributed to the extrapolation method on which the numerical convection-onset Ra data1,2 were based. It is shown that the numerical results agree with the linear stability constant Rac=1,707.8 and Schlüter et al.'s9 small amplitude perturbation analysis.
Ephraim Maurice SparrowOn Thursday Aug. 1, 2019, we were deeply saddened to hear that Professor Ephraim M. Sparrow passed away at the age of 91 years. Professor Ephraim M. Sparrow was born on May 27, 1928, and through his extensive professional career he became one of the best-known and respected researchers in the field of heat transfer. He received his B.Sc. and M.S. in 1948 and 1949, respectively, from the Massachusetts Institute of Technology (MIT). Then, he moved to Harvard University to receive his M.A. and Ph.D. in 1950 and 1952, respectively. His Ph.D. thesis is titled “Free Convection With Variable Properties and Variable Wall Temperature” under the supervision of Professor Howard Wilson Emmons.After finishing his Ph.D. in 1952, Professor Ephraim M. Sparrow joined Raytheon, where he worked on different heat transfer problems such as radar, electronics cooling, and the first microwave oven. Later, he joined the National Advisory Committee for Aeronautics (NACA) (now National Aeronautics and Space Administration (NASA)), Lewis Flight Propulsion Laboratory, Cleveland, OH where he worked on fluid mechanics and heat transfer. He had many publications from his work in NASA such as two papers [1,2] in the first issue of ASME Journal of Heat Transfer (JHT), which was published in February 1959 with 15 papers, two papers [3,4] in the second issue of JHT (May 1959), one paper [5] in the third issue of JHT (August 1959), and two papers [6,7] in the fourth issue of JHT (November 1959).In 1959, he started his career at the Thermodynamics and Heat Transfer Laboratory (THTL), Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN. THTL was established by Professor Ernst R. G. Eckert in 1950. Within the period 1968–1980, Professor Ephraim M. Sparrow served as the fluid mechanics chairman program. Within the period 1986–1988, Professor Ephraim M. Sparrow worked at the National Science Foundation (NSF), first as Program Manager of Heat Transfer and posteriorly as the CBET division director in the engineering directorate. At NSF, he stressed the need to focus on practical problems and important fundamental issues. At the time of his death, he was both the longest serving faculty member and the oldest in the Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN.During his academic life, Professor Sparrow supervised more than 250 Master's degree students and more than 100 doctoral degree students. Many of his previous Ph.D. graduate students became professors at well-known universities across the globe. Professor Sparrow has published many papers, reports, and books on fluid mechanics, and heat transfer such as Refs. [8] and [9]. His paper in ASME Journal of Heat Transfer (JHT), which was published in May 1977 about “Fully Developed Flow and Heat Transfer in Ducts Having Streamwise-Periodic Variations of Cross-Sectional Area” [10] was his most cited paper. He pioneered research in many important areas of heat transfer and his extensive contributions provided tremendous incentive to researchers and engineers around the world.In May 1988, Eph's 60th Birthday was celebrated with an article published in the International Journal of Heat and Mass Transfer [11]. Following his 60th birthday in 1988 until his death in 2019, Eph did not show any evidence of slowing down and was, in his typical manner, very active in pursuing his research interests. Professor Ephraim M. Sparrow was very active until the last year of his life. For example, he had these publications in 2019 [12–18].During his academic career, following Professor W. H. Giedt in 1972, Professor Ephraim M. Sparrow served as the Editor of the ASME Journal of Heat Transfer until 1980 when this position was succeeded by Professor K. T. Yang.In 1979, he cofounded with Professor W. J. Minkowycz the journal titled Numerical Heat Transfer in order to serve as a forum for the dissemination of ideas and research in the field of numerical heat transfer and computational fluid dynamics (CFD). He was the guest editor on many occasions. For example, he was the guest editor of a Biomedical-Related Special Issue in the International Journal of Heat and Mass Transfer with Professor John P. Abraham, University of St. Thomas, in November 2008 [19]. He was co-author with Professors J. P. Abraham, and R. D. Lovik in a paper about “Unsteady, three-dimensional fluid mechanic analysis of blood flow in plaque-narrowed and plaque-freed arteries” in the Biomedical-Related Special Issue [20]. Also, volume 50, Advances in Heat Transfer was edited by Ephraim M. Sparrow, John P. Abraham, and John M. Gorman.1 This volume had six chapters. Professor Ephraim M. Sparrow was the co-author of the first chapter about “Enhancement of Jet Impingement Heat Transfer by Means of Jet Axis Switching” [21].Furthermore, the contributions of Professor Ephraim M. Sparrow have spanned many areas and have been recognized by numerous honors and awards. They include: Max Jakob Memorial Award in 1976, Member of the National Academy of Engineering in 1986, Monie A. Ferst Award in 1993, Fellow of the American Society of Mechanical Engineers (ASME), and the ASME Ralph Coates Roe Medal.In July 2020, there will be a Memorial Track of Professor Ephraim Sparrow for celebrating his life and research contributions. This special symposium will be organized by the Heat Transfer Division (HTD) in his memory. Contributions for this symposium are solicited from all pertinent technical topic areas involving personal recollections from the three programs: ICNMM 2020, SHTC 2020, and FEDSM 2020 at Rosen Shingle Creek, Orlando, FL, July 12–15, 2020.2It is hard to find proper words to express our feelings at this sad moment, but without any doubt the professional community will remember Professor Ephraim M. Sparrow as an excellent and prolific scientist, teacher, mentor and above all a pleasant and honest person, and a highly respectful colleague with an outstanding character and ethics. We will all miss him dearly.
This paper outlines the fundamentals of the methods of exergy analysis and entropy generation minimization (or thermodynamic optimization—the minimization of exergy destruction). The paper begins with a review of the concept of irreversibility, entropy generation, or exergy destruction. Examples illustrate the accounting for exergy flows and accumulation in closed systems, open systems, heat transfer processes, and power and refrigeration plants. The proportionality between exergy destruction and entropy generation sends the designer in search of improved thermodynamic performance subject to finite-size constraints and specified environmental conditions. Examples are drawn from energy storage systems for sensible heat and latent heat, solar energy, and the generation of maximum power in a power plant model with finite heat transfer surface inventory. It is shown that the physical structure (geometric configuration, topology) of the system springs out of the process of global thermodynamic optimization subject to global constraints. This principle generates structure not only in engineering but also in physics and biology (constructal theory). Copyright © 2002 John Wiley & Sons, Ltd.
This paper is a review of current work on the optimal distribution of discrete heat sources cooled by laminar natural convection. The global objective is to maximize the global conductance between the wall and the fluid, or to minimize the hot-spot temperatures when the total heat generation rate and global system dimensions are specified. Three scenarios are investigated: (i) a large number of small heat sources mounted on a vertical wall facing a fluid, (i) a small number of finite-size heat sources mounted on the side wall in a two-dimensional enclosure, and (iii) a heated area on the wall of a vertical diverging or converging channel with chimney flow. For (i) and (ii), it is shown that the optimal distribution is not uniform (the sources are not equidistant), and that as the Rayleigh number increases the heat sources placed near the tip of a boundary layer should have zero spacings. In configuration (iii), the geometry is free to change in three directions: by varying the space between the walls, the distribution of heating along the walls, and the angle between the two walls. Numerical simulations cover the Rayleigh number range 105 ≤ RaH ≤ 107, where H is the channel height. Nonuniform wall heating is modeled as an isothermal patch of varying height, which is placed near the entrance of the channel, or near the exit. It is shown that for maximal heat transfer rate density it is better to place the heated sections at the channel entrance. The optimal angle between the two walls is approximately zero when RaH is large. The optimized spacing is of the same order of magnitude as the optimal spacing reported earlier for parallel isothermal walls. The robustness of flow architectures with optimized distribution of heat sources is discussed.
This paper brings to the attention of the AES community our experience with developing and trying out a new course that focuses on the generation of system configuration (geometry, architecture, and drawing) during the optimization of performance. The configuration is free to morph. Real systems are destined to remain imperfect because of finiteness constraints. They are plagued by resistances to the flow of fluid, heat, and electricity. Resistances are always finite because of constraints. The balancing and distributing of resistances (irreversibility) through the available volume is the mechanism that generates the architecture. Our approach to this key topic is evolutionary, and from simple to complex. In the 2004 format, the course covers several main topics: the relationship between optimization and the generation of configuration, multi-scale hierarchical structures for fluid flow and heat flow, and tree-shaped networks for collection and distribution. The paper relies on classroom-level examples to illustrate these topics. The paper also discusses the teaching method, and the applicability of this course concept to other domains (cost minimization, urban design, etc.).
No abstract is provided for this article.
The design of thermally efficient supports for cryogenic vessels is approached with renewed interest in view of today’s large-scale applications of superconductivity [1]. In large superconducting systems such as electric machines and magnetic energy storage...
This paper shows that it is possible to distribute a finite amount of insulation in an optimal way that minimizes the overall heat transfer rate from a nonisothermal wall to the ambient. The optimal insulation thickness for a plane wall varies as the square root of the local wall-ambient temperature difference. Corresponding variational-calculus results are developed for cylindrical walls covered with insulation. The heat loss reduction associated with using the optimal thickness is greater when the wall is plane, as opposed to cylindrical, and when the wall temperature variation in the x direction has a greater second derivative, d2 T/dx 2. It is shown finally that the best insulation for a single-phase stream suspended in an environment of different temperature is the insulation with uniform thickness.
