Abstract: Publication date: Available online 17 October 2019Source: Advances in Heat TransferAuthor(s): Marc T. Dunham, Terry J. Hendricks, Kenneth E. GoodsonAbstractIn this chapter we review the fundamental principles of thermoelectric phenomena, devices, and optimization techniques, with a focus on the multi-scale design of thermoelectric energy generators (TEGs). TEG technology represents a fascinating case study of the interplay between thermal and electrical transport, with pronounced multi-scale impacts from nanoscale phonon and electron transport to the design of efficient heat exchangers in the optimization of a complete system. We explore several of these areas in detail, with particular attention given to the effects of temperature-dependent thermoelectric material properties on the optimal ratio of hot-to-cold side heat exchanger thermal resistances and the relation to the second law of thermodynamics in the macroscale system design. These conclusions are then connected to theory behind the design of thermoelectric materials through nanoengineering. Finally, we explore cost considerations related to TEG system heat exchanger design, offering a new perspective in the approach to the technoeconomic optimization of TEG power systems.

Abstract: Publication date: Available online 11 October 2019Source: Advances in Heat TransferAuthor(s): Brent W. Webb, Vladimir P. Solovjov, Frédéric AndréAbstractThis review documents the history and theoretical development of the Spectral Line Weighted-sum-of-gray-gases (SLW) model. The SLW model is a so-called global engineering model for prediction of radiation transfer in gaseous media. The model bases the gas radiative properties on local thermodynamic properties (temperature, species concentration, etc.), and has been developed for use with any arbitrary solver of the Radiative Transfer Equation (RTE). This review first presents the fundamental groundwork for the SLW model, followed by the detailed theoretical development of the model with associated publication references. The model was first formulated for isothermal, homogeneous single-component gases. As part of this formulation a new gas property distribution function, the Absorption Line Blackbody Distribution Function (ALBDF) was proposed, and the ALBDF has been generated from detailed spectroscopic databases for H2O, CO2, and CO over a range of gas temperature, mole fraction (where appropriate), and total pressure. The SLW model was then extended to treat non-isothermal, non-homogeneous gases, mixtures of gas species, and model application in scenarios featuring non-gray particulates and/or boundaries. In all of its development the SLW model has been rigorously tested against benchmark line-by-line spectral integration solutions of the RTE using the same spectroscopic database as used in the generation of the ALBDF. Work continues on the refinement of the SLW model, enhancing its accuracy in prediction of radiative transfer. Finally, this review will summarize work-to-date utilizing the SLW model in coupled heat transfer scenarios—comprehensive combustion simulations, combined natural convection and radiation, etc.

Abstract: Publication date: Available online 4 October 2019Source: Advances in Heat TransferAuthor(s): Ravi Radhakrishnan, Samaneh Farokhirad, David M. Eckmann, Portonovo S. AyyaswamyAbstractNanoparticles submerged in confined flow fields occur in several technological applications involving heat and mass transfer in nanoscale systems. Describing the transport with nanoparticles in confined flows poses additional challenges due to the coupling between the thermal effects and fluid forces. Here, we focus on the relevant literature related to Brownian motion, hydrodynamic interactions and transport associated with nanoparticles in confined flows. We review the literature on the several techniques that are based on the principles of non-equilibrium statistical mechanics and computational fluid dynamics in order to simultaneously preserve the fluctuation-dissipation relationship and the prevailing hydrodynamic correlations. Through a review of select examples, we discuss the treatments of the temporal dynamics from the colloidal scales to the molecular scales pertaining to nanoscale fluid dynamics and heat transfer. As evident from this review, there, indeed has been little progress made in regard to the accurate modeling of heat transport in nanofluids flowing in confined geometries such as tubes. Therefore the associated mechanisms with such processes remain unexplained. This review has revealed that the information available in open literature on the transport properties of nanofluids is often contradictory and confusing. It has been very difficult to draw definitive conclusions. The quality of work reported on this topic is non-uniform. A significant portion of this review pertains to the treatment of the fluid dynamic aspects of the nanoparticle transport problem. By simultaneously treating the energy transport in ways discussed in this review as related to momentum transport, the ultimate goal of understanding nanoscale heat transport in confined flows may be achieved.

Abstract: Publication date: Available online 26 September 2019Source: Advances in Heat TransferAuthor(s): Josua P. Meyer, Marilize EvertsAbstractThe laminar and turbulent flow regimes have been extensively investigated from as early as 1883, and research has been devoted to the transitional flow regime since the 1990s. However, there are several gaps in the mixed convection literature, especially when the flow is still developing. The purpose of this chapter is to combine fragmented previous work of the authors to create a new coherent body of work with new perspectives. Specifically, focusing on the heat transfer and pressure drop characteristics of developing and fully developed flow in smooth horizontal tubes for forced and mixed convection conditions. The flow regimes that were covered were laminar (forced and mixed convection), transitional (forced and mixed convection), quasi-turbulent and turbulent.

Abstract: Publication date: Available online 11 September 2019Source: Advances in Heat TransferAuthor(s): L.E. Olsen, J.P. Abraham, L. Cheng, J.M. Gorman, E.M. SparrowAbstractThe canonical problem of flow over a square cylinder has been studied extensively in the scientific literature. Nevertheless, there are some critical issues which are not fully understood. Here, an extensive review of the literature is presented and brought together in a single repository. Next, remaining questions are identified such as: Which CFD models are most able to calculate fluid drag and heat transfer between the fluid and the cylinder' What are the mesh requirements for hydrodynamic and thermal analysis' How important is the blockage effect for cylinders that are placed in confined spaces (such as wind tunnels)' Do upstream effects significantly alter the results (such as upstream flow development, velocity profile, and turbulence intensity)' What aspect ratio is sufficient for a three-dimensional prism to approximate a two-dimensional square cylinder' Finally, how do three-dimensional flow patterns differ from those in two-dimensions' This manuscript attempts to answer these questions and provide practical recommendations to academic and industrial scientists. One key result from this work is the development of new correlating equations for both the drag coefficient and the Nusselt number for a wide range of Reynolds numbers and thermal conditions. The results presented here agree very well with accepted correlations from the literature, however these new correlations cover a much wider range of Reynolds numbers than previously published correlating equations.

Abstract: Publication date: Available online 24 June 2019Source: Advances in Heat TransferAuthor(s): Afshin J. GhajarAbstractThis chapter provides an overview of transitional flow in tubes, with particular emphasis on the entrance geometry and the development region. The discussion also deals with flows that may exhibit buoyant motion (secondary flow) and property variations. Practical and easy to use correlations for friction factor and heat transfer coefficient in the transition region as well as the laminar and turbulent regions are recommended. The application of some of the recommended correlations is illustrated with practical solved problems.