Dusan P. Sekulic

Extended Surface Heat Transfer

Preface. Convection with Simplified Constraints. Convection with Real Constraints. Convective Optimizations. Convection Coefficients. Linear Transformations. Elements of Linear Transformations. Algorithms for Finned Array Assembly. Advanced Array Methods and Array Optimization. Finned Passages. Compact Heat Exchangers. Longitudinal Fin Double-Pipe Exchangers. Transverse High-Fin Exchangers. Fins with Radiation. Optimum Design of Radiating and Convecting-Radiating Fins. Multidimensional Heat Transfer in Fins and Fin Assemblies. Transient Heat Transfer in Extended Surfaces. Periodic Heat Flow in Fins. Boiling From Finned Surfaces. Condensation on Finned Surfaces. Augmentation and Additional Studies. Appendix A: Gamma and Bessel Functions. Appendix B: Matrices and Determinants. References. Author Index. Subject Index.

Thermodynamics and the destruction of resources

This book is a unique, multidisciplinary effort to apply rigorous thermodynamics fundamentals to problems of sustainability, energy, and resource uses. Applying thermodynamic thinking to problems of sustainable behavior is a significant advantage in bringing order to ill-defined questions with a great variety of proposed solutions, some of which are more destructive than the original problem. The chapters are pitched at a level accessible to advanced undergraduate and graduate students in courses on sustainability, sustainable engineering, industrial ecology, sustainable manufacturing, and green engineering. The timeliness of the topic and the urgent need for solutions make this book attractive to general readers as well as specialist researchers. Top international figures from many disciplines, including engineers, ecologists, economists, physicists, chemists, policy experts, and industrial ecologists, make up the impressive list of contributors.

Numerical and experimental studies of self-sustained oscillatory flows in communicating channels

Abstract A combined numerical and experimental investigation of flow fields and thermal phenomena in communicating channels is performed to gain insight into the operation of compact heat exchange surfaces with interrupted plates. The geometric parameters are selected to excite and sustain the normally damped Tollmien-Schlichting modes. As a result, traveling waves are observed at relatively low Reynolds numbers, inducing self-sustained oscillatory flows that significantly enhance mixing. The critical Reynolds number at which oscillations are first observed in the periodic, fully developed flow region is determined. The numerical results are obtained by direct numerical simulation of the time-dependent energy and Navier-Stokes equations using a spectral element-Fourier method. The oscillatory heat transfer phenomenon is visualized experimentally using real-time, holographic interferometry. For periodic, fully developed flow conditions, the temperature fields are recorded utilizing high-speed cinematography. The experimental visualizations of the thermal waves verify the numerical predictions of the thermal-fluid structure and evolution of communicating-channels flows.

The second law quality of energy transformation in a heat exchanger

This paper presents the entropy generation (irreversibility) concept as a convenient method for estimating the quality of the heat exchange process in heat exchanger analysis. The entropy generation caused by finite temperature differences, scaled by the maximum possible entropy generation that can exist in an open system with two fluids, is used as the quantitative measure of the quality of energy transformation (the heat exchange process). This measure is applied to a two-fluid heat exchanger of arbitrary flow arrangement. The influence of different parameters (inlet temperature ratio, fluid flow heat capacity rate ratio, flow arrangements) and the heat exchanger thermal size (number of heat transfer units) on the quality of energy transformation for different types of heat exchangers is discussed. In this analysis it is assumed that the contribution of fluid friction to entropy generation is negligible.

Solid state Si diffusion and joint formation involving aluminum brazing sheet

Abstract The paper provides information about the use of in situ determined diffusion coefficients of silicon for modeling of a brazed joint formation, i.e. formation of the equilibrium surface of a molten Al+ x Si alloy at the onset of solidification in the joint. Diffusion coefficients of Si were determined (within both the joint and/or residue zone) to analyze its migration across the clad–core interface of an Al brazing sheet, including both the period prior to reaching brazing temperature range, and the peak brazing temperature range. Subsequently, diffusion coefficients were used to predict the joint formation during brazing. Migration of silicon is not uniform along the clad–core interface during brazing and depends, in addition to material characteristics and process parameters, on the vicinity of the joint zone. It is argued that, due to these alterations, the joint formation modeling must be performed by using in situ determined diffusion coefficients. The diffusion coefficients determined directly from electron probe microanalysis (EPMA) scans at different locations along the cladding sheet and within the joint zone differ between each other and when compared to the literature data. This variation influences the outcome of the residue formation modeling; hence the joint formation modeling may be affected. The relation between these phenomena is briefly discussed and quantitative data regarding diffusion coefficients, and in particular an approach to utilization of these data in modeling of joint formation, are provided.

Minimum exergy requirements for the manufacturing of carbon nanotubes

The purpose of this paper is to address both the high values, and the large variation in reported values for the energy requirements for the production of carbon nanotubes. The paper includes an estimate of the standard chemical exergy for single walled carbon nanotubes, as well as a historical look at how the minimum physical flow exergy improved as the HiPco process developed.

A thermodynamic framework for analyzing and improving manufacturing processes

In this paper, we present the formulation of a framework for the quantitative thermodynamic analysis of manufacturing processes and systems. Since manufacturing typically involves the input of high-quality material/energy and/or dissipation of low-quality energy/waste to manipulate a material, an approach that combines both the first and the second laws of thermodynamics is appropriate. This formulation helps emphasize that the improvement of manufacturing processes and systems is more a question of both utilizing the quantity and conserving the quality of energy than merely conserving energy. We conclude with two examples of its application, the first a comparison of metal casting technologies and the second a contrast between high-throughput CNC machining and a slower process rate grinding operation.

Capillary rise of liquids over a microstructured solid surface.

The location of the triple line as a function of time has been recorded for a series of organic liquids, with various surface tension to viscosity ratios, wicking upward a rough Cu(6)Sn(5)/Cu intermetallic (IMC) substrate. The complex topographical features of such an IMC rough surface are characterized by surface porosity and surface roughness. A theoretical model for wicking upward a rough surface has been established by treating the rough IMC surface as a two-dimensional porous medium featuring a network of open microtriangular grooves. The model is verified against experimental data. The study confirms that the kinetics of capillary rise of organic liquids in a nonreactive flow regime over a porous surface having arbitrary but uniformly distributed topographical features involves (i) surface topography metrics (i.e., permeability, tortuosity/porosity, and geometry of the microchannel cross section); (ii) wicking features (i.e., contact angle and filling factor); and (iii) physical properties of liquids (i.e., surface tension and viscosity). An excellent agreement between theoretical predictions and experimentally obtained data proves, for a selected filling factor η, validity of the analytically established model. Scaled data sets show that, for a given rough surface topography, (i) wicking kinetics of considered liquids depend on properties of liquids, that is, surface tension to viscosity ratios and contact angles; (ii) the filling factor for all tested liquids is an invariant, offering good prediction within the range of ~0.9-1.0. The distance of the wicking front versus square root of time relationship was well established throughout the whole considered wicking evolution time.

A fallacious argument in the finite time thermodynamics concept of endoreversibility

Finite time thermodynamics is a well established field of applied thermodynamics. The key assumption of this approach is the validity of the concept of endoreversibility. In this article, a hypothesis is formulated, and subsequently formally proved, that this concept rests on a fallacious argument. The concept of endoreversibility is inherently inconsistent with the postulated set of assumptions because the internal reversibility of a thermal system appears to be contradictory to an existence of external finite area heat exchangers that communicate with the endoreversible internal part across the finite temperature gaps. The irreversibilities contributed by the system components are inherently interconnected. As a consequence, the maximum power efficiency between the given temperature levels TL and TH>TL, as predicted by finite time thermodynamics assuming that the heat input into the system is free to vary, i.e., 1−(TL/TH)1/2, is incorrect. In addition, the magnitude of this figure of merit may be even s...

Capillary Driven Molten Metal Flow over Topographically Complex Substrates

A theoretical model of a capillary driven flow of liquid metal through topography features of rough surfaces has been verified by a study of molten solder (Sn-Pb) spreading over Cu(6)Sn(5)/Cu(3)Sn/Cu intermetallic (IMC) substrates. Flow through microgrooves over a rough IMC substrate is considered as spreading through an isotropic porous medium featuring a network of open microgrooves having predefined free-flow area cross sections. The relative margin of deviation between theoretically predicted and empirically determined locus of points of triple line locations is within the range of 5-15%. This margin supports the validity of the developed, analytically formulated square root power law model for a whole spreading domain in terms of (i) geometry of topographical features of the rough surface (i.e., effective intrinsic permeability, porosity/tortuosity, and microchannel cross section geometry), (ii) wetting/spreading features (equilibrium contact angle and filling factor), and (iii) molten metal/substrate properties (viscosity and surface tension). Experimental data involving triple line kinetics represent the data set of locations of the triple line versus time obtained by in situ monitoring of the spreading of molten metal systems over IMC substrates by using the controlled atmosphere hot stage microscopy.