The performance of PEM fuel cells strongly depends on the operating temperature, being negatively impacted when the equipment works outside of a prescribed temperature range. In this work, a novel liquid-based cooling approach is proposed to keep the average temperature of the heated plate within a temperature range with minimum energy consumption. The strategy consists in switching the coolant pumping on when the average temperature of the cold plate reaches the upper limit of the temperature range, and turning it off once the average temperature coincides with the lower limit. Four canopy-to-canopy and five single-channel configurations are experimentally and numerically tested for three different values of the pumping power. The maximum deviation of the cycle time (plate heating followed by cooling) between the experimental measurements and the numerical simulations is 8 % for all configurations, confirming the validity of the numerical approach. Among the tested designs, canopy-to-canopy configurations with four or more branches exhibit the shortest cycle time under all studied conditions, in both experiments and simulations. The cycle time was found to describe a linear relation with the ratio between conduction in the cold plate and convection in the channel, i.e., distance to the channel and coolant mass flow rate. An additional single-channel configuration was designed and built specifically to test the validity of the linear correlations derived, estimating the cycle time with theoretical, numerical and experimental calculations for the coolant mass flow rate. The deviation between these predictions and the experimentally measured cycle time is below 5 % for all cases.

Data centers require thermal solutions allowing to dissipate always higher heat loads with minimal pumping power. This work presents a methodology to design vascularized hierarchical flow networks for two-phase evaporative cooling, searching for minimum friction losses in flow distribution and collection networks. Two network configurations are considered: a ladder configuration, in which inlet and outlet channels are located on the same side, and a canopy-to-canopy configuration, with inlet and outlet on opposite sides of the network. The theoretical framework developed allows to determine optimal diameter ratios along hierarchical branches under constant refrigerant volume. The results demonstrate that a hierarchical diameter distribution reduces significantly the total pressure losses compared to single-diameter networks. In addition, we show that the reduction in friction losses depends strongly on the vapor quality, with the maximum improvement obtained between 0.50 and 0.60. Finally, the canopy-to-canopy network achieves the lowest overall friction losses and exhibits less sensitivity to the thermodynamic quality, making it the most efficient architecture for two-phase evaporative cooling applications.

Compressed Air Energy Storage (CAES) is a promising solution for large-scale energy storage; yet heat generated during the air compression phase (and heat needs during expansion) prevent CAES to be largely adopted. This study explores the potential of integrating Phase Change Material (PCM) inserts within a liquid piston compression chamber to overcome these thermal inefficiencies. The objective is to mitigate the temperature rise and therefore improve thermal management. Two novel configurations-horizontal dendritic PCM nets and forest of vertical PCM trees-are designed to favor the absorption of the heat generated during compression. A validated numerical model with piston walls at constant temperature is used to simulate the process, accounting for air compression, PCM thermal response, and heat exchange mechanisms. Results show that both PCM configurations significantly reduce the average air temperature rise by up to 20 K compared to a baseline case without PCM, with the forest of vertical PCM trees structure offering better temperature uniformity and enhanced latent heat absorption. The PCM-based inserts can facilitate quasi-isothermal compression, thereby improving CAES efficiency without requiring active cooling methods.

In this research, a numerical investigation is conducted using COMSOL Multiphysics to examine both melting and solidification of the PCM lauric acid, placed in a vertical rectangular enclosure. The system is subjected to bottom heating and cooling, with or without metallic fins. The study focuses on evaluating the effect of the presence of metallic inclusion on the speed of the phase transition front and the consequent duration of the melting and solidification processes. The presented findings are the average liquid fraction over time, location of the phase change front, and temperature distribution within the cavity. The obtained outcomes highlight how different heat transfer processes, conductive and convective, are involved at various time instants during the PCM charging and discharging phases, as well as the heat transfer improvement yielded by the presence of metallic fins, which reduces the time needed for melting (solidification) by about 75% (86%). In addition, solid drops falling is observed when the horizontal melt layers spreading from the fin tops come in contact.

In this chapter, we review our work on battery cells. We start by developing a methodological approach to assess the thermal and electrical behavior of a battery cell as a function of the environmental conditions. The methodology is illustrated by results obtained during an experimental campaign conducted within our group. Next, we present the constructal law of evolutionary design and show how it can be applied to the thermal management of battery cells. We then continue by describing the strategy related to constructal design and finally provide some numerical results highlighting the added value of the method.

Greenery strategies and shaded pedestrian passages have become requirements for designing smart cities in developed countries. One of the most difficult challenges for designers is designing cities in hot and arid climates while maintaining a proper level of outdoor thermal comfort. The designers focus on creating a comfortable climate for people throughout the afternoon under the hot sun, particularly in countries where summer temperatures rise excessively for more than seven months per year, as in Iraq. This study compares two Baghdad cities: Haifa Street, which was built in 1984 on a Western design pattern, and the second city, which the researchers designed according to the requirements of construction in an arid climate, such as street and building orientation, aspect ratio, sky view factor, the influence of courtyards, and the role of albedo. The second city is planned to cover the same total area as the first. The results of the two cities were compared and analyzed using ENVI-met software. To conduct a comparison between the two cities on a typical summer day, two indices, PMV and Tmrt, were used. The results showed that the proposed new city design reduced Tmrt and PMV, contributing to improved thermal comfort. The proposed design reduced the Tmrt value in the model by 10.5°C in proportions of 90% of the total urban area. Furthermore, the suggested design offers superior thermal values on a typical summer day than Haifa Street.

The use of renewables in the energy mix as a contribution against global warming requires efficient solutions to mitigate the intermittency of renewable energy sources.In building applications, this includes to be able to store thermal energy, and to use it through effective systems.In this talk we will cover the case of thermochemical storage as an example of thermal energy storage, and will show how the storage reactors can be designed to increase the heat exchanges while maintaining their compactness.Next, we will show that the same methodology can be applied to systems for indoor thermal comfort, and will take the example of radiant systems for cooling and maintaining indoor thermal comfort.The work will highlight the superiority of designs based on tree-shaped configurations for improving the heat transfer while decreasing the friction losses of the heat transfer fluid.In both examples, the theoretical framework relies on the search for maximum flow access by evolving the shape and morphology of the flow networks

Here we document the design method of an air-based thermally activated building system (TABS) suited for the retrofitting of tertiary buildings, for cooling purposes mainly. The first phase of this work provides a general design and checks its consistency with the specifications of tertiary buildings by means of basic energy balances. Second, a numerical model of both the TABS and the room is developed under a finite element method multi-physics environment to better estimate the transient heat transfer for the proposed retrofitting solution. This results in the specifications for building at 1:1 scale prototype whose construction is documented.

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. (C) 2018 Elsevier Ltd. All rights reserved.

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.

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 subcategorized 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.

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.