The transition to sustainable or green(er) cities requires the development and implementation of many innovative technologies. It is vital to ensure that these technologies are themselves as sustainable and green as possible. In this context, smart materials offer excellent prospects for application. They are capable of performing a number of tasks (e.g., repair, opening/closing, temperature measurement, storage and release of thermal energy) without embedded electronics or power supplies. In this short review paper, we present some of the most promising smart material-based technologies for sustainable or green(er) cities. We will briefly present the state-of-the-art in smart concrete for the structural health monitoring and self-healing of civil engineering structures, phase-change materials (PCM) for passive air-conditioning, shape-memory materials (SMA) for various green applications, and meta-surfaces for green acoustics. To better illustrate the potential of some of the solutions discussed in the paper, we present, where appropriate, our most recent experimental results (e.g., embedded SAW sensors for the Structural Health Monitoring of concrete structures). The main aim of this paper is to promote green solutions based on smart materials to engineers and scientists involved in R&D projects for green(er) cities.
Most batteries generate a significant amount of heat during charge or discharge, which has to be dissipated by adequate cooling, as the temperature of the battery is a crucial parameter for the battery performance. An ideal battery thermal management system (BTMS) should be able to maintain a uniform temperature among all battery cells within the entire battery pack. A passive BTMS can compensate for the temperature deviations and maintain temperature uniformity in the battery pack without the use of active cooling components. The aim of this work is to investigate thermal management by a phase change material (PCM) for their feasibility and effectiveness for electric vehicle (EV) battery modules. In this type of latent heat storage, a PCM is melted by internally generated heat, which is released again during solidification on cooling. This novel form of a thermal management system could achieve the advantages of a compact, lightweight and energyefficient system. Therefore, this work focuses on the implementation of such materials in a battery pack. After comprehensive market research, suitable PCMs that meet the requirements were identified and we studied experimentally these PCMs in a dedicated setup. Detailed solidification and melting processes were examined and new measured PCM data is reported. During the experiments, specially developed test setups were used to check datasheets and to clarify open questions. A system of single battery cells was designed to provide the PCM with the best possible geometric spaces within the battery module. In order to certifying the thermal behaviour of battery systems with passive PCM cooling, Computational Fluid Dynamic (CFD) models of batteries and surrounding thermal mass have been developed and could confirm the previous assumptions and calculations.
To estimate state-of-charge (SOC) and state-ofhealth (SOH) of a lithium ion battery as exact as possible, the terminal voltage, the terminal current and the cell temperature have to be measured. The easiest model of a battery is an ohmiccapacitive (R-C) series-parallel circuit. Two measurement methods are shown how to get ready to estimate SOC and SOH in a simple but precise manner. The first measurement is a defined capacity package being discharged a battery until the battery is empty. The packages give data points in the correlation curve for open-circuit-voltage (OCV) and SOC. This is base for SOC estimation. To take degradation into account hundred full cycles are examined on the test cells with 15 parameter variations on the above mentioned three parameters voltage, current and temperature.
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