Showing papers on "Constructal law published in 2020"

Finite element analysis of hybrid nanofluid flow and heat transfer in a split lid-driven square cavity with Y-shaped obstacle

Abstract: The constructal design-based model is reported to analyze the thermal control and heat augmentation inside a split lid-driven square cavity. A Y-shaped obstacle is placed within the cavity, which is filled with Al2O3–Cu–water hybrid nanofluids. The concept of the split-lid-driven cavity is utilized for the first time. The governing flow mathematical structure is obtained in terms of a system of partial differential equations and converted to a non-dimensional form through dimensionless variables. The numerical experiments are performed by employing a Galerkin finite element scheme for different values of involved physical parameters. The effects of pertinent parameters on the streamlines, isotherms, dimensionless temperature, and Nusselt numbers are investigated for different values of the Richardson number. Due to the simultaneous motion of the split-lids, the streamlines and isotherms show symmetrical distribution. The local Nusselt number increases with the moving split-lids and attains the maximum value when both lids meet. The average Nusselt number decreases with an increase in the Richardson number. It is important to note that the Y-shaped obstacle enhances the heat transfer rate in the cavity.

Constructal design progress for eight types of heat sinks

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.

Performance Optimization of a Condenser in Ocean Thermal Energy Conversion (OTEC) System Based on Constructal Theory and a Multi-Objective Genetic Algorithm.

Abstract: Constructal optimization of a plate condenser with fixed heat transfer rate and effective volume in ocean thermal energy conversion (OTEC) system is performed based on constructal theory. Optimizations of entropy generation rate ( S ˙ g ) in heat transfer process and total pumping power ( P sum ) due to friction loss are two conflicting objectives for a plate condenser. With the conventional optimization method, the plate condenser is designed by taking a composite function (CF) considering both S ˙ g and P sum as optimization objectives, and employing effective length, width, and effective number of heat transfer plates as design variables. Effects of structural parameters of the plate condenser and weighting coefficient of CF on design results are investigated. With a multi-objective genetic algorithm, the plate condenser is designed by simultaneously optimizing S ˙ g and P sum , and the Pareto optimal set is obtained. The results demonstrate that CFs after primary and twice-constructal optimizations are respectively reduced by 7.8% and 9.9% compared with the initial CF, and the effective volume of the plate condenser has a positive impact on the twice minimum CF. Furthermore, the Pareto optimal set can provide better selections for performance optimizations of plate condensers.

Constructal design of a non-uniform heat generating disc based on entropy generation minimization

Abstract: Non-uniform heat generating phenomenon is ubiquitous in real electronic devices. Based on this point, this paper researches the entropy generation rate (EGR) performance of a non-uniform heat generating (NUHG) disc. In this NUHG model, constructal design of the radial-pattern disc is performed with the conditions of constant- and variable-cross-sectional highly conductive routes (HCRs), respectively. The overall generation of heat over the entire disc area stays invariable, while the geometry of the disc is free to morph. The influence of heat generation non-uniformity on the optimized geometry of the disc is studied. The results manifest that increasing the thermal conductivity ratio and area ratio of HCRs both can reduce the EGR. Increasing the number of elements involved in the disc will compel the optimal HCRs to stretch towards the centre. In the areas with more heat generation and severer heat conduction requirement, more high conductivity material should be arranged to converge more heat flow and reduce the EGR aroused during the heat transfer process. The dimensionless EGR slumps by 11.5% on account of the employment of variable-cross-sectional HCR stratagem. Henceforth, the variable-cross-sectional HCR structure can reduce the EGR and improve its thermal performance. Additionally, the results obtained by minimizing EGR are compared with those obtained by minimizing maximum temperature difference. The primary novelty of this paper is introducing entropy generation minimization theory into the constructal design of radial-pattern disc with both non-uniform heat generation and constant- and variable-cross-sectional HCRs, which can provide benefits to the designs of practical electronic devices and the improvement of heat transfer performance.

Thermal management of electric vehicle battery cells with homogeneous coolant and temperature distribution

Abstract: Electric vehicles play an integral role in eliminating pollution related to transportation, especially if the electricity is generated via renewable sources However, storing electricity onboard requires many battery cells If the temperature of the cells is not strictly regulated, their capacity decreases in time, and they may burn or explode due to thermal runaway Battery thermal management systems emerged for safe operations by keeping the battery cell temperatures under limit values However, the current solutions do not yield uniform temperature distribution for all the cells in a pack Here, we document that constant temperature distribution can be achieved with uniform coolant distribution to the channels located between batteries The design process of the developed battery pack begins with a design used in current packs Later, how the shape of the distributor channel affects flow uniformity is documented Then, the design complexity was increased to satisfy the flow uniformity condition, which is essential for temperature uniformity The design was altered based on a constructal design methodology with an iterative exhaustive search approach The uncovered constructal design yields a uniform coolant distribution with a maximum of 081% flow rate deviation along channels The developed design is palpable and easy to manufacture relative to the tapered manifold designs The results also document that the peak temperature difference between the cells decreases from a maximum of 12 K to 04 K Furthermore, homogenous distribution of air is one of the limiting factors of the development of metal–air batteries This paper also documents how air can be distributed uniformly to metal–air battery cells in a battery pack

Human evolution is biological & technological evolution.

Abstract: We are the human & machine species. The homo is just the inner part. The evolution of the human & machine species is oriented in time from the naked man to the man with progressively more powerful add-ons (artifacts, contrivances, devices, machines, science). In evolution, the flow system morphs with freedom in the discernible direction identified as the constructal law. In all evolutionary designs, what works is kept.

Computational Modeling and Constructal Design Theory Applied to the Geometric Optimization of Thin Steel Plates with Stiffeners Subjected to Uniform Transverse Load

Abstract: Stiffened thin steel plates are structures widely employed in aeronautical, civil, naval, and offshore engineering. Considering a practical application where a transverse uniform load acts on a simply supported stiffened steel plate, an approach associating computational modeling, Constructal Design method, and Exhaustive Search technique was employed aiming to minimize the central deflections of these plates. To do so, a non-stiffened plate was adopted as reference from which all studied stiffened plate’s geometries were originated by the transformation of a certain amount of steel of its thickness into longitudinal and transverse stiffeners. Different values for the stiffeners volume fraction (φ) were analyzed, representing the ratio between the volume of the stiffeners’ material and the total volume of the reference plate. Besides, the number of longitudinal (Nls) and transverse (Nts) stiffeners and the aspect ratio of stiffeners shape (hs/ts, being hs and ts, respectively, the height and thickness of stiffeners) were considered as degrees of freedom. The optimized plates were determined for all studied φ values and showed a deflection reduction of over 90% in comparison with the reference plate. Lastly, the influence of the φ parameter regarding the optimized plates was evaluated defining a configuration with the best structural performance among all analyzed cases.

How the thermal environment shapes the structure of termite mounds.

Abstract: A computational model has been developed to predict the role of environment in the forms and functions of termite mounds. The proposed model considers the most relevant forces involved in the heat ...

Constructal Design of an Arrow-Shaped High Thermal Conductivity Channel in a Square Heat Generation Body.

Abstract: A heat conduction model with an arrow-shaped high thermal conductivity channel (ASHTCC) in a square heat generation body (SHGB) is established in this paper. By taking the minimum maximum temperature difference (MMTD) as the optimization goal, constructal designs of the ASHTCC are conducted based on single, two, and three degrees of freedom optimizations under the condition of fixed ASHTCC material. The outcomes illustrate that the heat conduction performance (HCP) of the SHGB is better when the structure of the ASHTCC tends to be flat. Increasing the thermal conductivity ratio and area fraction of the ASHTCC material can improve the HCP of the SHGB. In the discussed numerical examples, the MMTD obtained by three degrees of freedom optimization are reduced by 8.42% and 4.40%, respectively, compared with those obtained by single and two degrees of freedom optimizations. Therefore, three degrees of freedom optimization can further improve the HCP of the SHGB. Compared the HCPs of the SHGBs with ASHTCC and the T-shaped one, the MMTD of the former is reduced by 13.0%. Thus, the structure of the ASHTCC is proven to be superior to that of the T-shaped one. The optimization results gained in this paper have reference values for the optimal structure designs for the heat dissipations of various electronic devices.

A mathematical analysis for constructal design of tree flow networks under unsteady flow

Abstract: Tree flow networks play an important role in both natural and man-made systems In an effort to develop a deeper understanding of the optimal design of these networks, we have developed a simple an

Numerical Analysis of the Influence of Empty Channels Design on Performance of Resin Flow in a Porous Plate

Abstract: This numerical study aims to investigate the influence of I and T-shaped empty channels’ geometry on the filling time of resin in a rectangular porous enclosed mold, mimicking the main operating principle of a liquid resin infusion (LRI) process. Geometrical optimization was conducted with the constructal design (CD) and exhaustive search (ES) methods. The problem was subjected to two constraints (areas of porous mold and empty channels). In addition, the I and T-shaped channels were subjected to one and three degrees of freedom (DOF), respectively. Conservation equations of mass and momentum for modeling of resin/air mixture flow were numerically solved with the finite volume method (FVM). Interaction between the phases was considered with the volume of fluid method (VOF), and the effect of porous medium resistance in the resin flow was calculated with Darcy’s law. For the studied conditions, the best T-shaped configuration resulted in a filling time nearly three times lower than that for optimal I-shaped geometry, showing that the complexity of the channels benefited the performance. Moreover, the best T-shaped configurations were achieved for long single and bifurcated branches, except for configurations with skinny channels, which saw the generation of permanent voids.

Thermoelectric and solar heat pump use toward self sufficient buildings: The case of a container house

Abstract: This paper studies an innovative heat pump that couples both solar and thermoelectric contributions and evaluates its implementation in an energy-efficient container house for civil inhabitation. The strong point of the proposed design is that it can be personalized according to the specific needs of the building. The building and the air conditioning system has been evaluated according to the first and second law of thermodynamics. In particular, different options have been considered by a holistic method that aims to produce arbitrary system configurations such as Industry 4.0 Digital Twin and constructal law based design. The building system has been studied by considering the climatic data in the location of Bologna (Italy). The solar contribution has been analysed monthly. The solar gains by transparent elements have been estimated. The resulting configuration produces the design of an innovative building. It benefits from three qualifying elements. Sandwich walls include high-efficiency Vacuum Insulated Panels (VIP) for minimizing heat dispersions. The evaluation of seasonal shading has allowed optimizing smart windows. An innovative cogeneration heat pump couples solar energy and heating–cooling by mean of thermoelectric effect with heat recovery from photovoltaic systems. The acclimatization is realized by Peltier cells and heat recovery (during winter) from photovoltaic modules. A complete analysis and dimensioning of the building and heat pump is provided, demonstrating the advantages of the proposed system.

Rotary regenerator: Constructal thermoeconomic optimization

Abstract: In this research, rotary regenerator (RR) is optimized using constructal theory. For this aim, a heat exchanger with two branches is considered. RR effectiveness and total annual cost (TAC) are deliberated as objective functions and 9 design variables are selected. The multi-objective optimization algorithm is used to obtain the optimal values of objective functions and design variables. The optimum results in the case of constructal are contrasted with optimum results in the conventional RR. The optimum results showed better thermoeconomic results in the case of constructal than conventional RR for the effectiveness higher than 0.6572. As an example, effectiveness improved by 6.98% in the case of constructal in comparison to conventional RR for the constant value of TAC=1821$/year. In addition, the optimum results showed 4.55% improvement in the maximum effectiveness in constructal compared with conventional RR. Finally, distribution of design parameters along with some important parameters such as heat transfer surface area and pressure drop for both studied cases are illustrated, compared and discussed.