A comprehensive review and comparison on heatline concept and field synergy principle
TL;DR: A comprehensive review and comparison on heatline concept and field synergy principle have been made based on more than two hundreds of related publications as mentioned in this paper, where the role and function of heat line concept is to visualize the heat transfer path while that of field synergy theory is to reveal the fundamental mechanism of heat transfer enhancement and to guide the development of enhanced structures.
Abstract: A comprehensive review and comparison on heatline concept and field synergy principle have been made based on more than two hundreds of related publications. The major conclusions are as follows. Both heatline concept and field synergy principle are important contributions to the developments of single-phase convective heat transfer theories. The role and function of heat line concept is to visualize the heat transfer path while that of field synergy principle is to reveal the fundamental mechanism of heat transfer enhancement and to guide the development of enhanced structures. None of them can be used to deduce the other, nor none of them can be derived from the other. Hence, there is no problem of mutual remake between them at all. If heatlines are constructed by solving a Poisson equation additional computational work should be done; However, either the synergy number or the synergy angle both can be obtained by using numerical results without additional computational work. Further research needs for both heatline concept and field synergy principle are also provided.
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TL;DR: In this article, the authors investigated the optimization applications in thermal transfer such as heat exchangers, fuel cell, porous medium, solar energy receiver vortex generators and diesel particulate filter, which can improve the heat transfer performance significantly.
Abstract: How to improve the efficiency of heat transport, conversion and management has been the research focus of thermal energy application and related disciplines. Since the Field Synergy Principle theory was put forward, it has been further studied and developed in a wider scope which is an effective research method for enhancing convective heat transfer and other heat transfer processes. This paper investigated the optimization applications in thermal transfer such as heat exchangers, fuel cell, porous medium, solar energy receiver vortex generators and diesel particulate filter, which can improve the heat transfer performance significantly. The field synergy direct application can improve the heat transfer capacity of the finned heat exchanger remarkably with a 7% increase of heat transfer capability and about 14.4% less aluminum for the fin. The heat transfers efficient of the wave fin with elliptic improved 30% with the larger averaged intersection angle compared to wavy fin after field synergy optimized. Better use effects have emphasized the utilization of the synergy approaches to enhance the heat transfer combined with other theories, the total time rates of entropy generation are 7.3 × 10−2 W·K−1 and that is 8.2 × 10−2 W·K−1 after field synergy and minimum entropy generation principle majorization with the same viscous dissipation of 2.4 × 10−8 W. The research results explore extensions of the field synergy theory highly desirable attributes to more diverse and broader applications, which provide a way of thinking and research method for the further thermal energy conversion and management development as far as possible.
75 citations
TL;DR: In this paper, the effect of channel geometry on overall performance was studied to understand the fluid flow and heat transfer characteristics of micro-channel heat sinks having groove sidewalls, and the results indicated that the overall performance can be greatly improved by arranging grooves on channel sidewalls.
Abstract: Microchannels are effective heat sinks for integrated electronic circuits. However, it remains unclear what form of channels will be most effective in improving the overall performance of microchannel heat sinks. The effect of channel geometry on overall performance was studied to understand the fluid flow and heat transfer characteristics of microchannel heat sinks having groove sidewalls. Five types of silicon-based microchannel heat sinks were designed, and the periodic grooves arranged on channel sidewalls were rectangular, triangular, trapezoidal, water-droplet, and semicircular in shape. A three-dimensional computational fluid dynamics model was developed, validated, and used to optimize the geometric structure. Comparisons were made between different groove shapes in order to determine the optimum structure. The results indicated that the overall performance can be greatly improved by arranging grooves on channel sidewalls. The significant improvement of overall performance can be achieved with all the groove shapes except rectangles. When the Reynolds number falls within the range from 194 to 610, triangles are the optimum groove structure in terms of the level of the maximum heat transfer performance improvement, but with a significant increase in pressure drop. Water-droplet shaped grooves offer many advantages and improvements that make them the preferred choice for the development of microchannel heat sinks. They offer significant advantages as an effective heat transfer enhancement structure at higher Reynolds numbers, and allow for the lowest pressure drop at lower Reynolds numbers due to the vortexes formed inside the grooves.
50 citations
TL;DR: In this paper, a three-dimensional computational model is developed based on conservation equations of mass, momentum, and energy, and validated against the established empirical correlations to predict heat transfer and pressure drop for practical applications.
Abstract: Tape insert has been commonly adopted as heat transfer enhancement method in a thermal system. Most studies dealing with tape insert have been focused on straight tube. Helical coil tube, on the other hand, has been proven to have higher heat transfer than straight tube. It is of interest to combine both enhancement methods and obtain the optimum heat transfer enhancement. The main objective of this study is, therefore, to numerically investigate flow behaviour and the corresponding heat transfer in helical tube with twisted tape insert subjected to constant wall temperature. A three-dimensional computational model is developed based on conservation equations of mass, momentum, and energy, and is validated against the established empirical correlations. Good agreement is achieved between the numerical prediction and the empirical correlation calculation within the considered range of Reynolds ( R e = 100 − 2000 ) and Dean Numbers ( D e = 25 − 1200 ). The effects of twist ratio, inlet Reynolds number and wall temperature are evaluated and discussed in the light of numerical result. It is found that adding twisted tape insert in helical heat exchanger can enhance heat transfer performance by up to four times as compared to conventional straight tube heat exchanger, at a cost of higher frictional pressure drop. Lower twisting ratio gives rise to a higher heat transfer enhancement as it promotes higher secondary flow. At low Pr (air), heat transfer enhancement ratio increases as Re is increased; however, at high Pr (water), heat transfer enhancement ratio is higher at Re 500–1000. Finally, Nu and f correlations are developed to predict heat transfer and pressure drop for practical applications.
48 citations
TL;DR: In this paper, the authors summarized constructal design progress performed by the authors for eight types of heat sinks with ten performance indexes being taken as the optimization objectives, respectively, by combining the methods of theoretical analysis and numerical calculation.
Abstract: This review paper summarizes constructal design progress performed by the authors for eight types of heat sinks with ten performance indexes being taken as the optimization objectives, respectively, by combining the methods of theoretical analysis and numerical calculation. The eight types of heat sinks are uniform height rectangular fin heat sink, non-uniform height rectangular fin heat sink, inline cylindrical pin-fin heat sink (ICPHS), plate single-row pin fin heat sink (PSRPHS), plate inline pin fin heat sink (PIPHS), plate staggered pin fin heat sink (PSPHS), single-layered microchannel heat sink (SLMCHS) with rectangular cross sections and double-layered microchannel heat sink (DLMCHS) with rectangular cross sections, respectively. And the ten performance indexes are heat transfer rate maximization, maximum thermal resistance minimization, minimization of equivalent thermal resistance which is defined based on the entransy dissipation rate (equivalent thermal resistance for short), field synergy number maximization, entropy generation rate minimization, operation cost minimization, thermo-economic function value minimization, pressure drop minimization, enhanced heat transfer factor maximization and efficiency evaluation criterion number maximization, respectively. The optimal constructs of the eight types of heat sinks with different constraints and based on the different optimization objectives are compared with each other. The results indicated that the optimal constructs mostly are different based on different optimization objectives under the same boundary condition. The optimization objective should be suitable chosen based on the focus when the constructal design for one heat sink is performed. The results obtained herein have some important theoretical significances and application values, and can provide scientific bases and theoretical guidelines for the thermal design of real heat sinks and their applications.
45 citations
TL;DR: In this paper, the phase change behavior of a two-dimensional rectangular thermal storage tank, containing PCM with graphite foam insert, fully or partially filling the tank, was studied, and the results showed that with a fixed mass of foam, it is preferred to increase the foam porosity to fully fill the tank as opposed to a design with a lower porosity foam that only partly fills the tank.
Abstract: The aim of this paper is to shorten the melting/solidification time of a high-temperature phase change material (PCM) using graphite foam inserts. Specifically, the phase change behaviour of a two-dimensional rectangular thermal storage tank, containing PCM with graphite foam insert, fully or partially filling the tank, was studied. The composite enclosure was designed assuming it was heated or cooled from the left side wall for charging or discharging, respectively, while the other three walls were perfectly insulated. First, the effect of foam porosity (0.8, 0.85, 0.9, and 0.95), under fully-filled scenarios, was numerically investigated. Then the phase change behaviour of four partially-filled scenarios, with averaged 0.9 porosity, was carried out. The 0.9 porosity foam case showed an excellent cycle performance. With this case, it only takes 68.2 and 65.1 min for entire melting and solidification, respectively. For a tank with no insert, it will take 164/856 min, respectively, to entirely melt/solidify the same mass of PCM as that of the 0.9-porosity-case. As expected, lower porosity values lead to higher heat transfer through conduction. However, our results show that with a fixed mass of foam, it is preferred to increase the foam porosity to fully fill the tank as opposed to a design with a lower porosity foam that only partly fills the tank. Finally, given the high graphite to PCM thermal conductivity ratio, the heat transfer through the foam is mainly due to conduction. Based on this assumption, a theoretical model is presented in parallel to numerical results. Our analysis for a foam-saturated PCM storage tank shows that the dimensionless time taken for completely melting the PCM, expressed as Fourier number, scales with Fo ρ PCM , s ρ PCM , l k eff k PCM , l e Ste .
34 citations
References
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Book•
01 Jan 1980
TL;DR: In this article, the authors focus on heat and mass transfer, fluid flow, chemical reaction, and other related processes that occur in engineering equipment, the natural environment, and living organisms.
Abstract: This book focuses on heat and mass transfer, fluid flow, chemical reaction, and other related processes that occur in engineering equipment, the natural environment, and living organisms. Using simple algebra and elementary calculus, the author develops numerical methods for predicting these processes mainly based on physical considerations. Through this approach, readers will develop a deeper understanding of the underlying physical aspects of heat transfer and fluid flow as well as improve their ability to analyze and interpret computed results.
21,858 citations
TL;DR: In this paper, an analog between convection and conduction with heat sources is made to have a further understanding of the mechanism of convective heat transfer, and three ways to raise the strength of heat sources/convection terms, and consequently to enhance the heat transfer are presented.
Abstract: An analog between convection and conduction with heat sources is made to have a further understanding of the mechanism of convective heat transfer. There are three ways to raise the strength of heat sources/convection terms, and consequently to enhance the heat transfer: (a) increasing Reynolds and/or Prandtl number, (b) increasing the fullness of dimensionless velocity and/or temperature profiles, (c) increasing the included angle between the dimensionless velocity and temperature gradient vectors. Some approaches of heat transfer enhancement are suggested based on such a novel concept of heat transfer enhancement.
654 citations
TL;DR: In this paper, the concept of field synergy (coordination) principle is briefly introduced and then its numerical verification is presented, with focusing being paid on the application for developing new type of enhanced techniques.
Abstract: In this paper the concept of field synergy (coordination) principle is briefly introduced first, and then its numerical verification is presented. A dimensionless number, field synergy number Fc, is defined as an indication of the synergy degree between velocity and temperature field for the entire flow and heat transfer domain. It is found that for the ideal case, this number should equal one, and for most of the engineering heat transfer cases, its value is far from being equal to one, showing a large room for the heat transfer enhancement study. Then the applications of the principle are discussed, with focusing being paid on the application for developing new type of enhanced techniques. Three examples are provided to demonstrate the importance and feasibility of the field synergy principle.
406 citations
TL;DR: Proposition d'une nouvelle methode de visualisation du transfert de chaleur dans un ecoulement de fluide. Application a la convection naturelle dans une enceinte carree chauffee lateralement
Abstract: Proposition d'une nouvelle methode de visualisation du transfert de chaleur dans un ecoulement de fluide. Application a la convection naturelle dans une enceinte carree chauffee lateralement
387 citations
TL;DR: In this paper, the concept of enhancing parabolic convective heat transfer by reducing the intersection angle between velocity and temperature gradient is reviewed and extended to elliptic fluid flow and heat transfer situation.
Abstract: The concept of enhancing parabolic convective heat transfer by reducing the intersection angle between velocity and temperature gradient is reviewed and extended to elliptic fluid flow and heat transfer situation. Five examples of elliptic flow are provided to show the validity of the new concept (field synergy principle). Two further examples are supplemented to demonstrate the importance of the concept in the design of the enhanced surfaces.
310 citations