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Microchannels are important devices to improve the heat exchange in several engineering applications as heat, ventilation and air conditioning, microelectronic cooling, power generation systems and others. The present work performs a numerical study of a microchannel with two trapezoidal blocks subjected to laminar flows, aiming to analyze the influence of the boiling process on the geometric configuration of the microchannel. Constructal Design and Exhaustive Search are used for the geometrical evaluation of the blocks. The Mixture multi-phase model and the Lee phase change model were both employed for the numerical simulation of the boiling process. In this study, the influence of the height and higher width of the first block (H11/L11) over the heat transfer rate and pressure drop for different magnitudes of the ratio between the lower width and higher width (L12/L11) was investigated. It is considered water in monophase cases and water/vapor mixture for multiphase flow. Two different Reynolds numbers (ReH = 0.1 and 10.0) were investigated. Results indicated that, for the present thermal conditions, the consideration of boiling flows were not significant for prediction of optimal configurations. Results also showed that in the cases where the boiling process was enabled, the multi-objective performance was higher than in the cases without boiling, especially for ReH = 0.1.

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Recent studies underline that simple and non-invasive retrofit solutions can recover natural ventilation potential in existing buildings under temperate climate. Nonetheless, the efficiency of these solutions in dense urban contexts under hot and humid climate remains unclear. This paper aims to evaluate the thermal comfort gains caused by natural ventilation when retrofitting an office building in downtown Rio de Janeiro. Computational Fluid Dynamics (CFD) and thermal simulations are carried out on Ansys CFX and Design builder to assess indoor air flow before and after retrofit. The diagnosis of the current scenario indicates that the surrounding buildings block a significant part of the wind flow, and occupants experience only a few hours of thermal comfort during the year, especially on lower floors. To increase indoor air flow, the fixed upper windows were transformed into pivot windows and kept open permanently. This measure increases the annual hours of thermal comfort by 0.5-35%, depending on the floor and the adaptive comfort model. These findings suggest that natural ventilation itself may not be sufficient to ensure occupants' comfort throughout the year under the investigated context.

Significant advancements in developing earth-air heat exchanger models have been detected in the past several decades. It is worth mentioning that this type of device takes advantage of the Earth's constant temperature to cool or heat spaces in buildings so that the identification of its most appropriate geometric configurations to reduce energy consumption is still an actual challenge. In this context, the present paper is focused on the geometric evaluation of several earth-air heat exchangers arrangements according to the Constructal Design method. The performance indicators are the minimization of its soil volume occupation, the minimization of its airflow pressure drop, and the maximization of its thermal potential. Therefore, from a straight duct named Reference Installation, 26 complex geometries have been outlined here using the numerical-analytical investigation. Many ideas emerged from this study: the use of serpentine with low spacing between ducts reduced nearly 39% of the soil volume occupied by the device compared to Reference Installation, showing its applicability in urban regions. In addition, configurations with few curves benefited the decrease of air pressure drop, allowing a performance 30% superior to the most complex shapes. Instead, complex designs can be recommended for thermal potential increase, although the influence of the different configurations over this indicator was not substantial since the maximum improvement achieved between the best and worst shapes proved to be around 6%. Finally, when the three performance indicators are concomitantly considered, several complex geometries reached an overall performance superior to the Reference Installation.

This article unveils the geometric characteristics of boats with sails of many sizes, covering the range 102–105 kg. Data from one hundred boat models are collected and tabulated. The data show distinct trends of convergent evolution across the entire range of sizes, namely: (i) the proportionality between beam and draft, (ii) the proportionality between overall boat length and beam, and (iii) the proportionality between mast height and overall boat length. The review shows that the geometric aspect ratios (i)–(iii) are predictable from the physics of evolution toward architectures that offer greater flow access through the medium.

Here we show theoretically that the design of a thermochemical energy storage system for fast response and high thermal power can be predicted in accord with the constructal law of design. In this fundamental configuration, the walls of the elemental cylinder are impregnated with salt, while humid air is blown through the tube. Cases with constant salt volume or constant fluid volume or both are considered. It is shown that the best design in each case meets the equipartition of imperfections principle. The predictions are confirmed by full numerical experiments, allowing to consider various shape ratios and study their impact on the overall performance.

Body-freedom flutter characteristics of flying wing aircraft vary with engine placement. Here, we show why a certain design parameter (engine placement) influences the aeroelastic flight envelope o...

International audience; Here we document the performance of a radiant cooling panel made of flow channels sandwiched between a suspended metal plate and an insulation layer. The flow passages represent the crucial element of the panel. In the present work, the heat transfer and flow characteristics of the panel are investigated. A numerical study is conducted to explore the role played by the flow architectures on the overall performance of the panel in steady state, subjected to radiation and convection heat fluxes from the bottom. A comparison between serpentine and canopy-to-canopy (dendritic) flow channels is presented. In all the cases, the following geometrical constrains apply: fixed plate area and flow volume. From one configuration to the other, the flow is given more freedom to morph in accord with the Constructal approach. We demonstrated that the dendritic architecture allows a significant improvement in the cooling panel performance, with more cooling capacity and less pumping power. In addition, we showed that the morphing of the panel itself toward more compactness is also a way to increase the ratio of cooling capacity/pumping power.

International audience; Ventilated slabs are used to provide indoor comfort by taking advantage of thermal inertia. The underlying difficulty is that the computational cost is high, which is hardly compatible with an exhaustive study of dynamic behavior at room scale. This paper presents a methodology for obtaining a lumped model based on the identification of the transfer functions for constant airflow rate systems. The transfer functions were combined into a state space model, which is able to obtain the main heat fluxes with good accuracy at a much lower computational cost. The study moved to room scale in order to further understand how a ventilated slab influences the heat balance. Increasing the number of ducts promoted better indoor temperature stability but the impact was slight. The mass flow rate, on the other hand, appeared to be crucial. This result underlines the need to tailor a control law specifically to the ventilated slab.

Here we document the behavior at wall scale of a hemp-based hygroscopic material under various temperature and moisture dynamic conditions. The wall was made of precast hemp concrete (HC) blocks with air cavities. It was tested within a bi-climatic chamber and monitored thanks to hygrothermal sensors in the wall and in the chambers. The results from an in-house heat and moisture transfer model were compared to the experimental data, using the actual thermal and hygric characteristics of the hemp-based material determined in a previous study. The experiments allowed to demonstrate how the heat and moisture transport phenomena within the wall are coupled, particularly how a temperature difference can be a sufficient driving force for the release of moisture. The work points out the impact of moisture adsorption on heat release and on the temperature changes within the wall. Finally the numerical model served also to the modelling of an equivalent wall made of concrete to help highlighting the moisture dumping capability of the bio-based material, together with its thermal insulation capacity.

The liver is not only the largest organ in the body but also the one playing one of the most important role in the human metabolism as it is in charge of transforming toxic substances in the body. Understanding the way its blood vasculature works is key. In this work we show that the challenge of predicting the hepatic multi-scale vascular network can be met thanks to the constructal law of design evolution. The work unveils the structure of the liver blood flow architecture as a combination of superimposed tree-shaped networks and porous system. We demonstrate that the dendritic nature of the hepatic artery, portal vein and hepatic vein can be predicted, together with their geometrical features (diameter ratio, duct length ratio) as the entire blood flow architectures follow the principle of equipartition of imperfections. At the smallest scale, the shape of the liver elemental systems—the lobules—is discovered, while their permeability is also predicted. The theory is compared with good agreement to anatomical data from the literature.

International audience; The use of radiant systems for cooling purposes in buildings is attracting considerable attention, particularly for Suspended Radiant Ceiling Panels (SRCPs). However, the arrangement of the panels on the ceiling and the influence on radiative heat transfer is rarely discussed in the literature. The objective of this paper is to provide a numerical study of the radiative heat transfer at room scale when the size and the number of SRCPs varies. It has been observed that the use of a single large panel would result in a low average temperature, which is desirable, but also in poor uniformity of the temperature field. Here, a genetic algorithm is proposed and tuned to determine the positions of multiple SRCPs that would improve uniformity. It is shown that much better uniformity can be obtained, with only a moderate increase in the average temperature, for 10 panels or more. The differences between the use of a single large panel and multiple panels is noteworthy when SRCPs cover from 10 to 70% of the ceiling area.

Alternate temperature systems are widely used in environmental tests in which the refrigeration device consumes the most energy. In this paper, we present a thermodynamic analysis of modified designs of an alternate temperature system. The modified designs are based on three methods: cold storage, independent air ducts and multi-source cooling. The cold storage method converts part-load operation to full-load operation and the cold storage-based designs decrease the work (or energy) consumption and the equivalent size of the refrigeration device simultaneously. The cold storage and the multi-source cooling improve the performance significantly, while the independent air ducts only have weak effect on the performance. When the refrigerant and the single-phase coolant (coming from the cold storage unit) cool the circulated air together, optimal area allocation between the evaporator and the coolant heat exchanger exists. We also explain the factors that affect the degree of improvement in product designs.

Capillary flows are an attractive feature for passive water harvesting as they require no external driving force to pull the fluid out within the capillary network. Here we analyze the architecture of capillary flow networks in a steady state, and the impact of the network morphology on the maximum mass flow rate that can be extracted for a fixed network volume and fixed network footprint. We develop a search algorithm to test the possible locations of all the junction and bifurcation nodes and the changes in diameter ratios with the objective of obtaining the maximum mass flow rate from the network. We define the capillary strength as a local indicator to determine the geometrical parameters of each channel that allow the overall mass flow rate to be sustained. It is shown that the diameter ratio of connected tubes for maximum mass flow rate depends on the distance from the network outlet, and therefore does not follow the Hess–Murray law. The superiority of dendritic architectures in the roots and canopy branches of capillary trees is demonstrated.

With the growing interest on electric vehicles comes the question of the thermal management of their battery pack. In this work, we propose a thermally efficient solution consisting in inserting between the cells a liquid cooling system based on constructal canopy-to-canopy architectures. In such systems, the cooling fluid is driven from a trunk channel to perpendicular branches that make the tree canopy. An opposite tree collects the liquid in such a way that the two trees match canopy-to-canopy. The configuration of the cooling solution is predicted following the constructal methodology, leading to the choice of the hydraulic diameter ratios. We show that such configurations allow extracting most of the non-uniformly generated heat by the battery cell during the discharging phase, while using a small mass flow rate.

WOS:000414107200047; International audience; In the context of energy transition, new construction materials are being developed, with the concern of being more eco-friendly all along their life cycle. This includes bio-based materials like hemp concrete. Based on experimental data, this paper documents a model predicting heat and moisture transfer through hemp concrete. Scale analysis allows to go further into the description by identifying the dominant driving forces both for moisture and heat transfer, for different classes of relative humidity. The case study deals with a material submitted to a variation in temperature and relative humidity on its surface. A significant change is noticed around a relative humidity psi=95%. Below this threshold the temperature gradient is the main driving force for moisture transfer. The dominant mechanism becomes the capillary pressure gradient when psi \textgreater 95%. In the latter relative humidity range, phase change enthalpy becomes in the same order of magnitude as conduction heat transfer. (C) 2017 Elsevier B.V. All rights reserved.

The main thrust of this study is to bring insight into the influence of the flow channels layouts on the global performance of suspended radiant cooling panels. The flow passages, set on the upper side of a metal plate, represent the crucial part of the panel. Water is conveyed to the panel via these channels to extract the heat flux absorbed by the underneath plate. Therefore, the distribution of the flow over the surface of panel is the key toward efficient panels design. Applying a Constructal approach, the objective of the present work, is to explore the thermal and hydraulic performances of radiant panels equipped with different flow architectures. Including the standard serpentine configuration, branching flow designs are investigated. The flow architectures are categorized into two groups according to the location of the inlet and outlet of the working fluid and further sub-categorized based on the flow arrangements. The influence of the Reynolds number is reported. It is concluded that the proposed Constructal flow structures have the potential of improving the overall efficiency of radiant panels in terms of temperature distribution, cooling capacity, and pumping power demand.

International audience; Earth to Air Heat Exchanger (EAHE) is a well-known technique used to preheat or precool outdoor air before blowing it into a building. However, its geometry is often very simple as it consists in one or multiple straight pipes, while more complex arrangement can be found for heat exchangers. In this paper, we explore the advantage of designing an EAHE as a network by using the Constructal Law point of view. A methodology is first proposed to design a single pipe EAHE when the need is defined in terms of cooling power, overall efficiency and enthalpy difference between the inlet air and the ground. Next, the single pipe EAHE is used as a reference for designing a tree-shaped network under the constraint of identical fluid volume and cooling power. The geometrical features are allowed to change for the different branches of the network. The network coefficient of performance is found to increase significantly with the bifurcation level, illustrating the superior performances of the network. This approach was found to be robust as the improvements were not depending on the cooling demand or the environmental conditions. However, further work is needed to move from this analytical result to practical considerations.

This work documents the study of two concepts of open reactors for thermochemical energy storage. While classical thermal storage uses sensible or latent heat to store thermal energy, thermochemical energy storage uses an endothermic / exothermic chemical reaction. The process studied is based on the hydration and dehydration of a reactive salt by a flow of moist air in order to release and store heat respectively. The first concept studied is a storage module composed by the pattern “one salt bed surrounded by an inlet and an outlet channel, placed in parallel”. The second concept is a storage module made of by tubes impregnated with the reactive salt on their intern face. In this configuration, the tubes and the impregnated salt layer length scales are in the order of micrometer. Both concepts are presented using the Constructal law of design. In the first concept, air flows through the salt bed, corresponding to a forced convection through porous media problem, whereas in the second concept the air flow licks the impregnated salt and the chemical reaction occurs within the salt thanks to diffusion only. The analytical part is based on the Constructal law approach. From the main trends in terms of pressures distribution the geometrical features are deduced to obtain the design of compact and thermally efficient systems. Next, the discovered trends are backed up with numerical experiments. The geometrical dimensions are morphed with the purpose to move towards better performances. A ratio β between the heat produced by the chemical reaction within the entire module and the overall pumping power necessary to blow the fluid is determined to compare the configurations of each concepts. In accord with Constructal design, the number of salt beds in the first concept is morphed to reach equipartition of imperfections. The results show that with this evolution, the ratio β increases. In the second concept, the salt volume must be allocated in such a way that the time for water vapor diffusion through the salt matches the time for hydration / dehydration.

International audience; The hygroscopic, insulating and agronomic properties of hemp concrete make it a promising building material for addressing the sustainable building challenge. Part I of this series of two papers described a characterization of the thermal properties of a prefabricated hemp concrete block, confronting the impact of different methods of measurement. Part II focuses on the hygric properties, which describe moisture transfer and storage. The sorption isotherm was measured at 23 °C and 45 °C, considering distinct experimental procedures (saturation salt solution (SSS) methods with single relative humidity step or stepwise equilibrium, and Dynamic Vapour Sorption (DVS)). Differences were observed in the results and hypotheses are formulated considering the distinct drying procedures between SSS and DVS methods or the specific water vapour sorption process on cellulose-based materials. With the measurements at two temperatures, the isosteric heat of sorption is evaluated which allows an evaluation of the sorption at any temperature. The water vapour permeability was measured with dry and wet cups. Different parameters were tested: thickness (5 and 8 cm), air velocity (0.5 and 2 m s−1) and calculation method (standard calculations, consideration of the water vapour interface resistances). Each parameter, with the chosen values, had an impact of around 10% on the final water vapour permeability calculated. The capillary absorption coefficient was evaluated through capillary uptake measurements, leading to an estimation of the liquid transfer coefficient, albeit 12 times lower than the one evaluated thanks to the dry and wet water vapour permeabilities. All these observations underline the significant impact of experimental parameters and methods on the determination of hemp concrete hygric properties and support the necessity to develop more specific measurement methods for such permeable and hygroscopic bio-based building materials.

Hemp concrete is seen as a possible solution for addressing the energy, health and comfort issues of sustainable buildings, thanks to its hygrothermal properties and environmental qualities. This paper aims to determine the physical and thermal properties of an industrial prefabricated hemp concrete block based on hemp shiv and a lime-metakaolin binder. When available, distinct measurement methods were applied and confronted on this precast material in order to evaluate the impact of the experimental procedure on the results. Concerning air permeability, the present study shows that a measurement method initially intended for regular concrete can be adapted to the specific behaviour of highly permeable material such as hemp concrete. The thermal conductivity was measured with a guarded hot plate and a hot wire. Hot wire measurements on different moist states of the material allowed the self-consistent scheme to be applied for the evaluation of the thermal conductivity as a function of the humidity. Two direct measurement methods, differential scanning calorimetry (DSC) on the components and use of a Calvet calorimeter on the hemp concrete, and one indirect method, through effusivity measurement, were adopted for evaluating the specific heat capacity of the material. The original method proposed using DSC was shown to be as accurate as direct calorimetric measurement. The direct measurement methods gave similar results while the indirect one led to a much lower value. A comprehensive analysis of the measurement values available in the literature on hemp concretes confirmed this trend. This first paper highlights the significant influence of the testing method on the determination of the thermal properties of a precast hemp concrete, especially on the heat capacity measurement. This result emphasizes the need for a large inter-laboratory experimental campaign, applied to bio-aggregate based concrete, in order to form the basis of recommendations for adequate physical and thermal characterization methods for these bio-based building materials. A second part of this study will investigate the hydric properties of the same material.

International audience; This paper documents an analytical and numerical study of thermochemical energy storage in an open reactor. The analysis of the pressure losses and temperature distributions allows to predict what the geometrical features of the reactor should be. A numerical model simulating the thermochemical process is then presented and validated. In accord with the Constructal design methodology, the module configuration is morphed following the trends obtained in the analytical part, to head for better overall performances. The results show that the ratio between the heat produced by the chemical reaction within the entire module and the overall pumping power necessary to blow the fluid through the module increases as the imperfections reach equipartition. In terms of module configuration, this means (i) an increase in the number of salt layers and (ii) aspect ratios moving the module volume towards more compactness.

Phase change materials (PCM) may be used as a thermal energy barrier for applications requiring insulation. This project explores the behavior of pure PCM within a two-dimensional rectangular cavity as a thermal barrier using a new thermal barrier efficiency metric. The dimensionless parameters are determined that dictate the efficiency for one-dimensional transport with cyclical heat flux loading on one side and a convective boundary condition on the opposite side. Two limiting conditions for the PCM behavior (No Phase Change and Full Phase Change) are studied analytically, and numerical models show that the predicted thermal barrier efficiency exceeds these limits, suggesting that the limiting conditions provide useful conservative estimates of PCM performance in designing PCM thermal barriers. Results show that both the No Phase Change limit and Full Phase Change efficiencies decrease with increasing Fourier and decreasing Biot numbers. An expression is derived for the CFD-predicted thermal barrier efficiency as a function of No Phase Change and Full Phase Change efficiencies and the Fourier number when Bi = 0.2.

WOS:000384779300059; International audience; This paper illustrates the morphing of flow architecture toward greater performance in a counterflow heat exchanger. The architecture consists of two plenums with a core of counterflow channels between them. Each stream enters one plenum and then flows in a channel that travels the core and crosses the second plenum. The volume of the heat exchanger is fixed while the volume fraction occupied by each plenum is variable. Performance is driven by two objectives, simultaneously: low flow resistance and low thermal resistance. The analytical and numerical results show that the overall flow resistance is the lowest when the core is absent, and each plenum occupies half of the available volume and is oriented in counterflow with the other plenum. In this configuration, the thermal resistance also reaches its lowest value. These conclusions hold for fully developed laminar flow and turbulent flow through the core. The curve for effectiveness vs number of heat transfer units (N-tu) is steeper (when N-tu \textless 1) than the classical curves for counterflow and crossflow. (C) 2016 Elsevier Ltd. All rights reserved.

Summary Salt-gradient solar ponds (SGSPs) are water bodies that capture and accumulate large amounts of solar energy. The design of an SGSP field has never been analyzed in terms of studying the optimal number of solar ponds that must be built to maximize the useful energy that can be collected in the field, or the most convenient way to connect the ponds. In this paper, we use constructal design to find the optimal configuration of an SGSP field. A steady-state thermal model was constructed to estimate the energy collected by each SGSP, and then a complementary model was developed to determine the final temperature of a defined mass flow rate of a fluid that will be heated by heat exchangers connected to the solar ponds. By applying constructal design, four configurations for the SGSP field, with different surface area distribution, were evaluated: series, parallel, mixed series-parallel and tree-shaped configurations. For the study site of this investigation, it was found that the optimal SGSP field consists of 30 solar ponds of increasing surface area connected in series. This SGSP field increases the final temperature of the fluid to be heated in 22.9%, compared to that obtained in a single SGSP. The results of this study show that is possible to use constructal theory to further optimize the heat transfer of an SGSP field. Experimental results of these configurations would be useful in future works to validate the methodology proposed in this study. Copyright © 2016 John Wiley & Sons, Ltd.

WOS:000375425800025; International audience

Here we document how the design of the elemental component of a designed reactor for thermochemical energy storage can be improved for better energy performance and less pumping power. The pore channels are made of cylinders with walls are covered by salt reacting with the water vapor molecules of the blown humid air. The design of such open systems is changed to dendritic configurations while keeping the salt and fluid volumes constant. Morphing the configuration from I-shaped to Y-shaped architectures allows to increase the heat exchanges. Additional improvements are obtained when the geometric features of the dendritic configurations are chosen to follow constructal design.

The present work is guided by the Constructal theory to identify the best shapes for the cavity inserted in a cylindrical solid body with a constant heat generation rate. From the assertion that a system must evolve to persist in time, an evolution of the elemental (I-shaped) cavity to a tree-shaped cavity with two branches added to a single branch is proposed. With these modifications, two restrictions (area occupied by the trunk and area occupied by the branches of the cavity) and seven degrees of freedom are used to represent the geometry. The study focused on investigating the effect of the degrees of freedom associated with the cavity branches and the number of cavities. Results show that the optimization of each new degree reduces the maximum excess of temperature. However, the results obtained with a more complex cavity were similar to those obtained by the elemental cavity in reducing the maximum excess temperature. In practical terms, the results are similar. Despite the similarity between the present results and those achieved with a most simple shape. The increase of performance with the increase of degrees of freedom studied here indicates that for complete optimization, the performance of complex shapes can surpass that of the simplest cavity.

This paper documents the results of a study on the relationship of the pore structure and the transport properties of potassium- and sodium-based geopolymers. The pore structure was investigated by water porosity, mercury intrusion porosimetry and thermoporometry. The geopolymers transport properties were determined using a set of experiments, including natural diffusion of tritiated water and two electrical methods (direct current and Electrochemical Impedance Spectrometry). The geopolymers microstructure corresponds to materials with a pore structure made of poor access dimensions around 7 nm (potassium-based geopolymers), and 20 nm (sodium-based geopolymers) connected to larger pores not detected by MIP but revealed by thermoporometry. As a result, the transport properties appear to be higher than expected.

This work documents the modeling of ionic transfer through porous materials under an external electrical field. A pore model network that accounts for the electrical double layer impact was developed and scaled up at the porous material level. The model is adapted to two different materials, both belonging to the class of mesoporous materials: a monomodal porous glass, and a cement paste with mineral additions. The comparison between numerical results and experiments on migration and tritium natural diffusion questions the concept of formation factor applied to such mesoporous materials.

International audience; Abstract—The outdoor thermal comfort is influenced by the perception and satisfaction of the pedestrians, especially in hot and arid climates. Accordingly, the researchers look for the appropriate methods to reduce the Urban Heat Island and thus to enhance the outdoor thermal comfort level of pedestrians. However, there is limited research conducted on the outdoor thermal comfort in hot and arid climate. This work is an investigation study conducted in an urban area (Haifa Street) in Baghdad city, characterized by an arid climate with very high temperatures in summer season reaching 50℃. This study focuses on investigating possible mitigation strategies to ensure how we could improve the thermal comfort at pedestrian level for an urban area with intricate Western design (high–rise buildings, a large spacing between the buildings, asymmetrical canyon geometry, and lack of vegetation). We created four different scenarios to assess the role of vegetation elements such as trees, grass, and different shading patterns. The evaluation was performed in the hottest day in summer. For each scenario, the mean radiant temperature, specific humidity, air temperature, and wind speed distributions have been analyzed using ENVI-met software. Thermal comfort is assessed using the PET thermal index (Physiological Equivalent Temperature) and Predicted Mean Vote (PMV). The results reveal that the PET index can be reduced to 10.4 ℃, the temperature can be decreased of about 2.4℃ and PMV to 3. The study shows how the urban factors such as the aspect ratio, vegetation cover, shadings, and geometry of the canyon are crucial elements that urban planners and municipalities have to take into account, especially for new urban developments.

WOS:000419407500030; International audience; The work documents the design of Earth-Air Heat Exchangers based not only on sensible heat transfer, but also on latent heat exchanges. We compare the impact of the climate of Brazil and south of France on the relevance of such systems. The duct length is determined in order to obtain maximum underground heat exchanges. A time dependent model combined to actual weather data is developed to show when an underground heat exchanger becomes a good option in a tropical climate. The three-dimensional version of the model accounts for heat transfer in the soil and for heat and moisture transfer along the underground pipe. The comparison with a 1D model allows to propose a straightforward approach to assess the cooling/heating potential of different climatic regions. (C) 2017 Elsevier Ltd. All rights reserved.

WOS:000415391800002; International audience; Here we show the performance of a cooling system consisting of one stream that morphs while embedded in a square plate heated uniformly. Several configurations are considered in order to establish the evolutionary direction in which the thermal performance of the cooling system is improving. First, serpentine shapes are considered. The total length of serpentine length is fixed, and the number of meanders is varied. The stream inlet and outlet are free to migrate on the perimeter of the heated plate. The results show that the serpentine with four elbows maintains lower peak temperatures when the inlet and the outlet of the duct are positioned in the middle of the side of the plate. We report the configuration in which the thermal conductance is maximum. Second, we analyzed the effect of various loop cooling configurations such as square, circular and clover leaf. Each loop is centered on the center of the plate, and its length is free to vary. The minimum peak temperature is achieved when the length of the circular loop is L-C = 2.5 L, and when the length of the square loop is L-C = 2.8 L. The clover leaf designs show even better performance. (C) 2017 Elsevier Ltd. All rights reserved.