Modelling the Behaviour of Thermal Energy Harvesting Devices With Phase-change Materials

The paper presents a general theoretical model of the behaviour of thermal energy harvesting devices (TEHDs), in which phase-change materials (PCMs) are used for energy storage. The main aim of the model is to establish a set of conditions, under which these devices operate in an optimal way, that is, achieve the highest thermal buffering capacity and rapidly exchange heat with the adjacent phase. An expression for the characteristic harvesting time is derived under the optimal performance assumption from the constructal theory viewpoint. A dimensionless criterion, which characterises the performance of PCMs is introduced. Further, a non-field solution of the energy equation governing the heat transfer process within TEHDs with PCMs has been obtained. An expression for the effective thermal effusivity is then derived. Finally, a concise procedure for the best choice of PCMs in TEHDs under a given set of the boundary conditions and geometrical constraints has been formulated.

Effects of constructal theory on thermal management of a power electronic system

Thermal management of power electronics (PE) systems is a long-lasting challenge in their industrial applications. It is important to provide a uniform temperature distribution on the surface of the insulated gate bipolar transistors and diodes. The thermal management of a PE module is the main objective of the present study. The flow characteristics and the effects of the constructal theory on the heat transfer performance of the cooling system have been numerically investigated. The governing equations have been discretized using the finite volume method, and validation has been done to make sure the results are reliable. The effects of different channels configurations on decreasing the chips’ temperature and uniform temperature distribution on the chips’ surface have been studied. The flow characteristics and heat transfer performance at different mass flow rates for different channel configurations have been studied by presenting the results of the average chips’ temperature, Nusselt (Nu) number, pressure loss, and standard temperature deviation. Moreover, different temperature distribution contours have been presented to show the performance of different configurations. The results revealed that by changing the channels’ configuration from the conventional straight channel to leaf-inspired channels (case B and C), the cooling performance is improved.

Constructal Equivalent Thermal Resistance Minimization for Tau-Shaped Fin

With the aid of constructal theory and entransy theory, a Tau-shaped fin (TAUSF) is investigated in this paper, and the widths of the bend end and elemental fins are assumed to be different. The construct of the TAUSF is optimized by the minimum equivalent thermal resistance (ETR) obtained by entransy dissipation rate. The constraints of total enveloping volume and fin material volume are considered. The results show that in the specified range of width ratio, the twice minimum ETR of the TAUSF can be yielded by an optimal width ratio and an optimal length ratio. In addition, comparing the optimal performance of the TAUSF with the counterpart of a T-shaped fin, the former sacrifices a small amount of heat transfer performance and its stiffness increases due to its structure with the bend end. The optimal structure of the TAUSF yielded from ETR minimization is conspicuously different with the counterpart yielded from maximum thermal resistance minimization. Comparing the thermal performances of the two optimal constructs, the ETR of the former optimal construct is declined by 10.58%, whereas the maximum thermal resistance is augmented by 5.22%. The former optimal construct can lead to the uniformity of temperature gradient and the reduction in thermal stress, and can guide the engineering designs of practical fins.

The history of economics and the Constructal Theory

The signs of a new crisis appear. Some countries are moving towards real assets (gold, oil); the real estate market froze, as did the credit market; sales are on a global decline. The world has become accustomed to economic cycles and crises. At the theoretical level, efforts are aimed at finding practical methods of prevention and especially of combating the negative effects on economic cycles. The market of theories regarding the internal causes and mechanisms of economic cycles has stabilized. The theoretical barricades were formed and strengthened and now the projectiles are thrown from one side to another. Demand theories and supply theories give partial explanations, but with claims of total theories. Is it possible to see something new at the theoretical level about the causes and mechanisms of economic cycles? We think so. We believe that the Constructal Theory of Professor Adrian Bejan has an explanatory power over the present theories about the causes of the economic cycles. The perspective offered by this theory is new and offers explanations for aspects that are difficult to understand in other theories. Through this article we want a rewriting of economic history, from the perspective and through the lens of this theory. We believe that we offer a broader and deeper explanation of the causes of economic cycles using a theoretical tool borrowed from other sciences, but with great explanatory powers in the social sciences. We will rewrite the economic history by discussing: S-evolution of economic stages; overlapping economic flow systems; systems evolving from one another; increased resource consumption and increased resource efficiency. The results of this study indicate that abusive interventions in the economic system create problems. The economic system, which is essentially a flow system, like any other system, must be allowed to evolve freely.

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

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.