Publications

This paper reviews some of the most basic flows that effect the dispersal of heat and mass in environmental configurations. Two important classes of environmental flows are discussed: free turbulent flows (shear layers, jets, plumes and wakes) and free flows in porous media (plumes, wakes behind concentrated sources of heat and mass, plumes, penetrative convection). These flows are ‘free’ from the effect of confining boundaries. The emphasis is on fundamental mechanisms and the methods (use the simplest first) that have been developed for the prediction and description of environmental flows. Copyright © 2003 John Wiley & Sons, Ltd.

No abstract is provided for this article.

The vascularization of smart materials with the property of localized self-cooling is investigated here on the basis of a simple configuration. A solid body (slab) is subjected to intense heat flux from one side; temperatures are controlled by pumping a coolant from the other side. The coolant flows through parallel channels that traverse the slab. The objective is to find the channel configuration that maintains the least nonuniform temperature distribution in the solid (i.e., the coolest hot spots). The optimal spacing between channels and the minimum hot-spot excess temperature are deduced analytically for two configurations, equidistant parallel-plates channels, and arrays of equidistant parallel cylindrical channels. These analytical results are confirmed based on numerical simulations of the conjugate heat transfer in channels and surrounding solid material. The results for the optimal geometry and performance are robust: they are essentially the same for parallel-plates and cylindrical channels.

This paper reports a fundamental study of the fluid dynamics inside a triangular (attic-shaped) enclosure with cold upper wall and warm horizontal bottom wall. The study was undertaken in three distinct parts. In the first part, the flow and temperature fields in the cavity are determined theoretically on the basis of an asymptotic analysis valid for shallow spaces (H/L → 0, where H and L are the attic height and length). It is shown that in the H/L → 0 limit the circulation consists of a single elongated cell driven by the cold upper wall. The net heat transfer in this limit is dominated by pure conduction. In the second part of the study, the transient behaviour of the attic fluid is examined, based on a scaling analysis. The transient phenomenon begins with the sudden cooling of the upper sloped wall. It is shown that both walls develop thermal and viscous layers whose thicknesses increase towards steady-state values. The criterion for the existence of distinct thermal layers in the steady state is (H/L)½RaH¼ > 1, where RaH is the Rayleigh number based on attic height. The corresponding criterion for distinct viscous wall jets is (H/L)½RaH¼Pr−½ > 1, where Pr is the Prandtl number. The third phase of this study focused on a complete sequence of transient numerical simulations covering the ranges H/L = 0.2, 0.4, 1; RaH/Pr = 10, 103, 105; Pr = 0.72, 6. The numerical experiments verify the flow features described theoretically in the first two parts of the study. The effect of thermal convection on the net heat transfer between the bottom and top walls is illustrated numerically. Finally, the transient numerical experiments show that in the present parametric domain the single-cell circulation pattern is stable with respect to the Bénard instability expected in fluid layers heated from below.

Vascular structures are contemplated for cooling the skins and leading surfaces of future high speed aircraft. This paper evaluates the proposal to cool with a flow architecture shaped as trees (dendritic) a parallelepipedic body that is heated uniformly. The coolant enters the body through one face and exits through the opposite face. The vasculature connects the two faces, and consists of trees that alternate with upside down trees. The fields for fluid flow and heat transfer are determined numerically in three dimensions. The effect of local pressure losses at bends, junctions and entrances is documented. Designs with tree-shaped architectures having up to four levels of bifurcation are evaluated for fluid flow and heat transfer performance, and are compared with the performance of a design with a single sheet of fluid sweeping the upper surface of the body. The fluid flow conductance of the tree designs increases when the number of bifurcation levels increases. The thermal performance of tree designs can be improved by endowing the tree design with more freedom such that the bifurcations generate asymmetric daughter channels. The tree designs outperform the fluid sheet design dramatically: the global thermal resistance of the tree designs is roughly one tenth of the global thermal resistance of the fluid sheet design.

This paper explores alternatives to the usual thermodynamic optimization formulation, where the thermodynamic performance of a system is improved subject to physical size constraints (e.g., entropy generation minimization). The alternative is to minimize the physical size subject to specified thermodynamic performance. It is shown that the alternate optimization leads to the same physical design—the same configuration—as the usual optimization. This is demonstrated by means of three examples: power plant model with two heat exchangers, power plant model driven by a hot stream of single-phase fluid, and refrigerator model with irreversibility due to imperfect insulation. Copyright © 1999 John Wiley & Sons, Ltd.

: The techniques for heat transfer augmentation play an important role in the development of efficient and inexpensive equipment for heat exchange processes. In the present study, the effectiveness of a given augmentation technique was determined based on the amount of irreversibility (waste of useful energy) introduced by the technique into the heat exchanger where it is to be used. This report summarizes the main results obtained during the past two years under research contract N00014-79-C-0006 at the University of Colorado. The report is organized into three distinct parts. The first part contains a fundamental investigation of the entropy generation mechanism in elementary heat transfer configurations. The second part describes in quantitative terms the irreversibility minimization potential of some of the most common augmentation techniques, namely, swirl-flow devices and roughened surfaces. The final part considers the entropy generation penalty associated with the use of extended surfaces (fins) in convective heat transfer. This part shows how the fin geometry may be selected so that the fin performs its prescribed heat transfer duty with minimum generation of entropy. (Author)

Energy and water are commonly described as “problems,” like not having enough money in the bank. In this chapter we show that energy and water are not “commodities,” rather they are flows that sustain human life. They are not two flows but one...

Professor Franz Mayinger is one of the well-known names in the field of thermodynamics, heat transfer, and multiphase flow and well-respected among his colleagues in the thermodynamics, heat transfer, and multiphase flow community all over the world. He was born on Sept. 2, 1931, in Augsburg, Germany. He received his Dipl.-Ing. and Dr.-Ing. in 1955 and 1961, respectively, from Lehrstuhl für Thermodynamik (the chair for Thermodynamics), Mechanical Engineering Department at the Technische Universität München (the Munich Technical University), München, Germany.During 1956–1961, Professor Franz Mayinger started his professional life as a research assistant at the “Lehrstuhl” (chair) and Institute of Thermodynamics at the Technische Universität München (the Munich Technical University), München, Germany. After completing his Dr.-Ing. in 1961, Professor Franz Mayinger joined MAN Nürnberg as a Chief Engineer and the Research Department Head for Nuclear and Process Engineering from 1962 to 1969. He started his academic life in the Institut für Verfahrenstechnik der Universität Hannover (Institute of Chemical Engineering, University of Hannover), Hannover, Germany, as full professor and director in 1969. During 1973/1974 and 1979/1980, Professor Franz Mayinger served as Dean of the Mechanical Engineering Department at the Universität Hannover (University of Hannover), Hannover, Germany. He then became a director for the prestigious Chair of the Thermodynamics A at the Technische Universität München (the Munich Technical University), München, Germany, in 1981. Professor Franz Mayinger was a deserving successor to this chair that had been held before by Carl von Linde (June 11, 1842–Nov. 16, 1934), Moritz Schröter (Feb. 25, 1851–Mar. 12, 1925), Ernst Kraft Wilhelm Nusselt (Nov. 25, 1882–Sept. 1, 1957), Ernst Schmidt (Feb. 11, 1892–Jan. 22, 1975), and Ulrich Grigull (Mar. 12, 1912–Oct. 20, 2003). Professor Franz Mayinger initiated the first research in the multiphase flow field. He continued the heat convection examination and encouraged combustion research. In addition, he implemented using of new optical measurement techniques like laser-induced fluorescence and holographic interferometry in the institute. Furthermore, he was involved in the Seventh International Heat Transfer Conference (IHTC-7), at the Technische Universität München (the Munich Technical University), München, Germany, Sept. 6–10, 1982. IHTC-7 was organized under the authority of the Assembly for International Heat Transfer Conferences by DECHEMA Deutsche Gesellschaft für chemisches Apparatewesen e.V., Frankfurt/Main, Germany, in cooperation with the International Scientific Committee, the Deutsche Gesellschaft für Chemie-und Verfahrenstechnik (DGCV), and the German Scientific and Executive Committees. Also, he was elected as the Dean of the Mechanical Engineering Department at the Technische Universität München (the Munich Technical University), München, Germany, during 1986/1987. Finally, he became an Emeritus Professor of this chair in 1999. During 1995–1998, he was the founding Dean of the Faculty for Applied Natural Sciences at the Bayreuth University, Bayreuth, Germany. From 1998 to 2009, he had been the Chairman of the Board of this university. He served as the member of Reactor Safety Commission at the Federal Department of Environment (1971–1992) and the Chairman of this Commissions in 1983/1984 and in 1990, Chairman of the Commission of Accidents and Failures in Chemical Plants at the Federal Department of Environment (1992–1996), member of the Advisory Board of Science and Technology of the Government of Bavaria (1993–1999), and member of the Senate of the German Research Society (1977–1983). From 1991 to 1997, he was a member of the Advisory Board for Science of the Federal Government of Germany. Within the period of 1998–2002, he was the Scientific Chairman of the Bavarian Elite Academy. He has been frequently invited as a lecturer and speaker by different institutions in the Europe, U.S., China, Japan, and other countries.Professor Franz Mayinger has published over 350 scientific papers as well as several books, on thermodynamics, heat and mass transfer, multiphase flow, power engineering, optical measurement techniques, and reactor safety, such as Refs. [1–9]. He was a former editor of Wärme- und Stoffübertragung (Heat and Mass Transfer) Journal.Professor Franz Mayinger is the recipient of several international awards like Max Jakob Award of the American Society of Mechanical Engineers (ASME) and American Institute of Chemical Engineering (AIChE) in 1991. He received an Honorary Doctorate from the University of Hannover in 1994 and the University of Bayreuth in 2006, Medallion “Bene Meritus” of the Bavarian Minister for Science and Art in 1995, Bavarian Supreme Medal of Merits in 1995, Bavarian Medal for Environmental Research in 1996, Bavarian Medal for Environmental Research in 1998, and Ernest Solvay Award in 2000, Bayerischer Maximiliansorden für Wissenschaft und Kunst (Bavarian Maximilian Order for Science and Art), the highest award of Bavaria for scientific work in 2001, and Emeritus of Excellence of Technische Universität München (the Munich Technical University) in 2005.Professor Franz Mayinger has served in several scientific societies as the member of the Bavarian Academy of Sciences, German Academy of Technical Sciences, German Supreme Scientific Board, and the Bavarian Leadership Academy president.On the occasion of his 85th birthday, on behalf of his students, colleagues, and friends all over the world, we wish him a very happy birthday and a continuous active life in good health and happiness with his wife Frau Franziska Mayinger, children Thomas, Brigitte, and Wolfgang as well as grandchildren!

Heat transfer is a mature science, and so is thermodynamics. They are almost 200 years old having developed largely independently until the 1980s. Maturity comes from the usefulness and success of the thermal sciences. This review uses the thermodynamics of heat transfer to focus on aspects that are usually not discussed in physics: performance, purpose, function, objective and direction of evolutionary design. The article illustrates the unity of the thermal sciences discipline (heat transfer +thermodynamics + constructal law), and uses the opportunity to correct a few recent interpretations of the thermodynamics of heat transfer regarding dissipative engines and energy storage.

This paper examines the interaction by natural convection between a fluid-saturated porous medium and a fluid reservoir separated by a vertical impermeable partition. The two fluid systems are maintained at different temperatures. The analysis is simplified by assuming Pr > > 1 in the fluid reservoir. It is shown analytically that the flow and temperature fields in the boundary layer regime consist of two fluid layers in counterflow. The interface temperature is shown to increase monotonically with altitude. The important dimensionless group which governs the fluid mechanics is B = (kRaK1/2) / (k′Ra1/4), where k, k′, RaK and Ra are, respectively, the porous medium conductivity, reservoir fluid conductivity, Darcy-modified Rayleigh number based on partition height, and the reservoir Rayleigh number based on partition height. The effect of parameter, B, on the flow, temperature, and heat transfer is documented in the range 0 < B < ∞.

No abstract is provided for this article.

No abstract is provided for this article.

This paper reports the optimal geometry of an array of fins that minimizes the thermal resistance between the substrate and the flow forced through the fins. The flow regime is laminar. Two fin types are considered: round pin fins, and staggered parallel-plate fins. The optimization of each array proceeds in two steps: The optimal fin thickness is selected in the first step, and the optimal thickness of the fluid channel is selected in the second. The pin-fin array is modeled as a Darcy-flow porous medium. The flow past each plate fin is in the boundary layer regime. The optimal design of each array is described in terms of dimensionless groups. It is shown that the minimum thermal resistance of plate-fin arrays is approximately half of the minimum thermal resistance of heat sinks with continuous fins and fully developed laminar flow in the channels.

This note focuses on Kladias and Prasad's claim that the critical Rayleigh number for the onset of Bénard convection in an infinite horizontal porous layer increases as the Prandtl number decreases, and argues that the critical Rayleigh number (Rac) depends only on the Darcy number (Da), as linear stability analysis indicates. The two-dimensional steady-convection problem is then solved numerically to document the convection heat transfer effect of the Rayleigh number, Darcy number, Prandtl number, and porosity. The note concludes with an empirical correlation for the overall Nusselt number, which shows the effect of Prandtl number at above-critical Rayleigh numbers. The correlation is consistent with the corresponding correlation known for Bénard convection in a pure fluid.

This paper outlines the place occupied by the constructal law in thermodynamics, and provides a vision of the future development of energy engineering as a transdisciplinary science of systems of systems. Natural and man-made flow systems do not exist in isolation. The optimal balance between engineered flow systems and their surroundings is achieved through the optimal distributing of thermodynamic imperfections. The paper traces the development of constructal theory from a principle of maximisation of flow access in morphing configurations to engineering discoveries, such as optimal internal spacings, tree-shaped flow networks, machine flight, and multi-scale flow structures for maximal heat transfer density. The introduction of constructal theory and design in thermodynamics education is also discussed.

This paper shows that in a space filled with assemblies of cylinders cooled by natural convection the heat transfer density can be increased progressively by the use of cylinders of several sizes, and the optimal placement of each cylinder in the assembly. Smaller cylinders are placed closer to the entrance to the assembly, in the wedge-shaped flow regions occupied by fluid that has not yet been used for heat transfer. The paper reports the optimized flow architectures and performance for structures with one and two cylinder sizes, which correspond to structures with one and two degrees of freedom. The heat transfer rate density increases as the optimized structure becomes more complex. The optimized cylinder diameters are relatively robust, i.e., insensitive to changes in complexity and flow regime (Rayleigh number). The optimized spacings decrease monotonically as the Rayleigh number increases. The structure performance can be improved by endowing the cylinder assemblies with more degrees of freedom.