Showing papers on "Thermal energy published in 2021"

Hybrid energy harvesting technology: From materials, structural design, system integration to applications

Abstract: The last decade has witnessed significant advances in energy harvesting technology for the realization of self-charging electronics and self-powered wireless sensor nodes (WSNs). To conquer the energy-insufficiency issue of a single energy harvester, hybrid energy harvesting systems have been proposed in recent years. Hybrid harvesting includes not only scavenging energy from multiple sources, but also converting energy into electricity by multiple types of transduction mechanisms. A reasonable hybridization of multiple energy conversion mechanisms not only improves the space utilization efficiency but can also boost the power output significantly. Given the continuously growing trend of hybrid energy harvesting technology, herein we present a comprehensive review of recent progress and representative works, especially focusing on vibrational and thermal energy harvesters which play the dominant role in hybrid energy harvesting. The working principles and typical configurations for piezoelectric, electromagnetic, triboelectric, thermoelectric and pyroelectric transduction effects are briefly introduced. On this basis, a variety of hybrid energy harvesting systems, including mechanisms, configurations, output performance and advantages, are elaborated. Comparisons and perspectives on the effectiveness of hybrid vibrational and thermal harvesters are provided. A variety of potential application prospects of the hybrid systems are discussed, including infrastructure health monitoring, industry condition monitoring, smart transportation, human healthcare monitoring, marine monitoring systems, and aerospace engineering, towards the future Internet-of-Things (IoT) era.

Phase change material-integrated latent heat storage systems for sustainable energy solutions

Abstract: Thermal energy plays an indispensable role in the sustainable development of modern societies. Being a key component in various domestic and industrial processes as well as in power generation systems, the storage of thermal energy ensures system reliability, power dispatchability, and economic profitability. Among the numerous methods of thermal energy storage (TES), latent heat TES technology based on phase change materials has gained renewed attention in recent years owing to its high thermal storage capacity, operational simplicity, and transformative industrial potential. Here, we review the broad and critical role of latent heat TES in recent, state-of-the-art sustainable energy developments. The energy storage systems are categorized into the following categories: solar-thermal storage; electro-thermal storage; waste heat storage; and thermal regulation. The fundamental technology underpinning these systems and materials as well as system design towards efficient latent heat utilization are briefly described. Finally, the exciting research opportunities available to further improve the overall energy efficiency of integrated TES systems are discussed.

Review of heat transfer enhancement techniques for single phase flows

Abstract: The thermal energy exchange between a flowing fluid and its confining channel is a ubiquitous process in modern society. To enhance the fluid-to-wall or wall-to-fluid heat transfer, several techniques have been developed to maximize the contact area between the fluid and the inner wall and/or disrupt the flow to enhance circulation or induce turbulence. Deployment of channels having features capable of enhancing heat transfer enables the reduction of heat exchanger size while maintaining performance. Reduction in equipment size is critical due to the ability to minimize the required volume of costly working fluids and to mitigate potential safety concerns associated with total system fluid volume. Here, a comprehensive review of single-phase heat transfer enhancement techniques is presented. The article provides a thorough comparison by analyzing the heat transfer rate, pressure drop, and other operational aspects. Single-phase heat transfer enhancement methods are divided into active and passive techniques. Active methods such as electrohydrodynamic (EHD), magnetohydrodynamics (MHD), or mechanical motion require external power to create enhancement. Passive methods such as dimples, fins, or tape inserts do not require external input and rely only on surface modification. Although active methods are more expensive and difficult to implement compared to passive techniques, it enables active control of heat transfer augmentation. This review develops and summarizes key learning data for design optimization enabled by additive manufacturing and machine learning algorithms, helping to inform these next-generation heat exchanger design methodologies for a plethora of modern applications such as electrification of vehicles, computing, and classical industries.

Short-Term Self-Scheduling of Virtual Energy Hub Plant Within Thermal Energy Market

Abstract: Multicarrier energy systems create new challenges as well as opportunities in future energy systems. One of these challenges is the interaction among multiple energy systems and energy hubs in different energy markets. By the advent of the local thermal energy market in many countries, energy hubs’ scheduling becomes more prominent. In this article, a new approach to energy hubs’ scheduling is offered, called virtual energy hub (VEH). The proposed concept of the energy hub, which is named as the VEH in this article, is referred to as an architecture based on the energy hub concept beside the proposed self-scheduling approach. The VEH is operated based on the different energy carriers and facilities as well as maximizes its revenue by participating in the various local energy markets. The proposed VEH optimizes its revenue from participating in the electrical and thermal energy markets and by examining both local markets. Participation of a player in the energy markets by using the integrated point of view can be reached to a higher benefit and optimal operation of the facilities in comparison with independent energy systems. In a competitive energy market, a VEH optimizes its self-scheduling problem in order to maximize its benefit considering uncertainties related to renewable resources. To handle the problem under uncertainty, a nonprobabilistic information gap method is implemented in this study. The proposed model enables the VEH to pursue two different strategies concerning uncertainties, namely risk-averse strategy and risk-seeker strategy. For effective participation of the renewable-based VEH plant in the local energy market, a compressed air energy storage unit is used as a solution for the volatility of the wind power generation. Finally, the proposed model is applied to a test case, and the numerical results validate the proposed approach.

Advances in thermal energy storage systems: methods and applications

Abstract: Hot water tanks are today the most commonly used thermal energy storages. The design of the hot water tank is strongly influencing the heat loss of the tank and the thermal stratification inside the tank. Recommendations on good design of hot water tanks are given. Water pit heat storages used in district heating systems are introduced. These heat storages have recently been introduced in large Danish solar heating plants. Measurements of yearly heat storage efficiencies of the water pit heat storages are given. Future trends on hot water stores are given.

Transactive Energy Supported Economic Operation for Multi-Energy Complementary Microgrids

Abstract: Multi-energy complementary microgrids (MECMs) provide an important means to accommodate renewable energy sources due to their abundant adjustable resources and flexible operation modes. However, limited capacity and controllability are the main obstacles that prevent MECMs from participating in the market. In this study, we develop a transactive energy (TE) mechanism-supported energy sharing strategy to coordinate interconnected MECMs in a regional integrated energy system (RIES), where the uncertainty of renewable energy and loads is taken into account via stochastic programming. An RIES operator is introduced to trade with the utility grid as an intermediate player between the electricity market and MECMs. For the TE mechanism, we employ alternating direction method of multipliers (ADMM) algorithm to achieve distributed optimization of energy sharing, which is based on the average of the shared energy residual over all MECMs. A clear economic interpretation exists in the method, wherein shared electrical and thermal energy prices can be obtained. Case studies demonstrate the effectiveness of the multi-energy sharing scheme considering integrated demand response (IDR). Moreover, the distributed algorithm can be implemented and converge easily while respecting MECMs’ individual benefits and private information.

A review on liquid air energy storage: History, state of the art and recent developments

Abstract: Liquid air energy storage (LAES) represents one of the main alternatives to large-scale electrical energy storage solutions from medium to long-term period such as compressed air and pumped hydro energy storage. Indeed, characterized by one of the highest volumetric energy density (≈200 kWh/m3), LAES can overcome the geographical constraints from which the actual mature large-scale electrical energy storage technologies suffer from. LAES is based on the concept that air can be liquefied, stored, and used at a later time to produce electricity. Although the liquefaction of air has been studied for over a century, the first concept of using cryogenics as energy storage was proposed for the first time in 1977 and rediscovered only in recent times. Indeed, the need for alternative energy vectors in the energy system attracted many researchers to discover the potential of the use of cryogenic media. This has brought the realization of a first LAES pilot plant and a growing number of studies regarding LAES systems. The main drawback of this technology is the low round-trip efficiency that can be estimated around 50–60% for large-scale systems. However, due to its thermo-mechanical nature, LAES is a versatile energy storage concept that can be easily integrated with other thermal energy systems or energy sources in a wide range of applications. Most of the literature published is based on thermodynamic and economic analysis focusing on different LAES configurations. This paper provides a collection of the papers published on LAES and it classifies the various studies conducted in different categories. Future perspectives show that hybrid LAES solutions with efficient design of the waste energy recovery sections are the most promising configuration to enhance the techno-economic performance of the stand-alone system.

Emerging Pyroelectric Nanogenerators to Convert Thermal Energy into Electrical Energy.

Abstract: Pyroelectric energy harvesting systems have recently received substantial attention for their potential applications as power generators. In particular, the pyroelectric effect, which converts thermal energy into electrical energy, has been utilized as an infrared (IR) sensor, but upcoming sensor technology that requires a miniscule amount of power is able to utilize pyroelectric nanogenerators (PyNGs) as a power source. Herein, an overview of the progress in the development of PyNGs for an energy harvesting system that uses environmental or artificial energies such as the sun, body heat, and heaters, is provided. It begins with a brief introduction of the pyroelectric effect, and various polymer and ceramic materials based PyNGs are reviewed in detail. Various approaches for developing polymer-based PyNGs and various ceramic materials-based PyNGs are summarized in particular. Finally, challenges and perspectives regarding the PyNGs are described.

Melting heat transportation in radiative flow of nanomaterials with irreversibility analysis

Abstract: Melting phenomenon of PCMs (phase change materials) is mostly complemented with resilient variation in density of thermal heat. Thermal energy created from numerous sources can be stored in form of latent heat combination throughout melting process of a phase change materials. Thermal energy can be unconfined during the solidification processes. MPCS (microencapsulated phase change slurry) has noteworthy advantages particularly in high energy density and narrow temperature range for various heat energy application. Melting heat transportation has attracted the consideration of scientists and engineers due to its tremendous applications of technological, solidification, casting and industrial processes. A variety of phase change materials with low cost are commercially accessible and do significant work in different circumstances of temperature. Main motivation here is to investigate irreversibility in MHD convection flow of viscous liquid with melting effect over a stretched surface. Slip condition and Lorentz force behaviors are accounted. Energy expression is developed through dissipation, heat radiation and Joule heating. Irreversibility exploration is modeled through second law of thermodynamics. Brownian diffusion and thermophoresis are taken. First order chemical reaction is deliberated. Nonlinear expressions are reduced to ordinary one employing transformation. The obtained systems are solved for the convergent solutions through ND-solve method. Variation of velocity field, entropy rate, temperature, Bejan number and concentration distribution are scrutinized. Velocity filed rises versus higher melting variable. Larger melting parameter decreases the temperature distribution. Concentration and temperature have similar effects against thermophoresis variable. Bejan number and entropy rate have opposite outcome via melting parameter. Higher radiation parameter reduces the entropy rate. For higher radiation both entropy rate and Bejan number have same effect. Main observations are concluded.

Heat transfer enhancement in fin-and-tube heat exchangers – A review on different mechanisms

Abstract: Fin-and-tube heat exchangers are the mostly used heat exchangers for thermal energy conversion with wide range of applications such as air conditioning, refrigeration, automotive industry, electronic devices, and the like. Demand of more efficient cooling by more compact heat exchangers leads to tremendous researches on this subject. In this paper, a detailed review of experimental and numerical researches upon different mechanisms of heat transfer enhancement in fin-and-tube heat exchangers are performed and the relevant influences and operating conditions are thoroughly reviewed. Effects of different geometrical parameters on heat transfer and pressure drop in each mechanism are also discussed in details. Furthermore, comparisons between different mechanisms of heat transfer improvement and some novel compound designs of fin-and-tube heat exchangers are discussed. In addition, some special researches on surface treatment, particle deposition, thermal contact, and fabrication material in fin-and-tube heat exchangers are described. Finally, some developed correlations for calculation of heat transfer and pressure drop characteristics of fin-and-tube heat exchangers with their ranges of validation are classified and compared.

The design of phase change materials with carbon aerogel composites for multi-responsive thermal energy capture and storage

Abstract: Phase change materials (PCMs) have been widely used as thermal energy storage systems; however, traditional PCMs can only be triggered by temperature for thermal energy storage, which greatly limits their versatility in the application of capturing thermal energy. Herein, we propose a multi-responsive thermal energy capture and storage system involving Fe-doped carbon aerogel as a supporting matrix and eicosane as a PCM. With the ability to respond to light, electricity, and magnetism as well as temperature simultaneously, the designed PCM system demonstrates excellent performance for converting solar, electric and magnetic energy into thermal energy stored as latent heat in the materials. Furthermore, our multi-responsive PCM demonstrates a mild transition onset temperature of 35 °C, relatively large thermal energy storage density of 212 J g−1, shape stability without liquid phase leakage in transition, and excellent phase transition stability even after 1000 heating–cooling cycles. Our reported PCM may shed light on the development of complementary multi-energy utilization.

Thermophysical properties of graphene-based nanofluids

Abstract: Heat transfer operations are very common in the process industry to transfer a huge amount of thermal energy, i.e., heat, from one fluid to another for different purposes. Many fluids are used as heat transfer fluid (HTF), in which water is the most common HTF due to its high specific heat, availability, and affordability. However, conventional HTFs, including water, have a lower thermal conductivity, which is the most critical thermophysical property, hence decreased heat transfer efficiency. The addition of solid particles of highly thermally conductive material, specifically at nano-size, i.e., nanoparticles NPs, result in nanofluid NF, which has evolved over the last two decades as efficient HTF and have been investigated in a wide range of applications. Among NPs, graphene (Gr) based materials have shown very high potential as NF due to the very high thermal conductivity up to 5,000 W/m.K, hence higher thermal conductivity NF. This work aims to thoroughly discuss the thermophysical properties of Gr-based NFs, including thermal conductivity, heat capacity, density, and viscosity. The discussion focus on the thermophysical properties as it is the ultimate determinator of the heat transfer characteristics of the HTF, such as the convective and the overall heat transfer coefficient as well as the heat transfer capacity of the NF. The discussion expands to the relative enhancement in such thermophysical properties reaching up to a 40% increase in thermal conductivity, as the most critical thermophysical property. The discussion shows that Gr-based NF has a much higher thermal conductivity relative to widely studied metal oxide NF and at much lower content, and lower density and viscosity increase, which is critical for determining the pumping power requirements. Critical challenges facing the application of Gr-based NFs such as cost, stability, increased density and viscosity, and environmental impacts are thoroughly discussed with mitigation recommendations given.

MXene based advanced materials for thermal energy storage: A recent review

Abstract: Energy storage is a critical issue and it becomes increasingly vital due to rapidly diminishing of fossil fuels and as renewable energy resources are currently intermittent. The thermal energy storage is the dawn of thermal management field. The lack of low conversion ability of energy storage materials limits its effectiveness. However, highly performance MXene catches special attention in recent decade due to exceptional mechanical, thermal and other properties. In literature, most of the work is related to specific methods for preparation of MXene. So, this review summarizes all major techniques for preparation MXene that discussed in literature and different important properties as well as various applications of MXene are also covered in this study. These 2D materials exhibit superior and comprehensive thermal as well as optical properties. Thermal energy based on phase change material/MXene composites can alleviate the crisis of energy and fulfil the energy demands. The various applications of MXene in the field of thermal energy are also covered in the current review that were not discussed as one study in literature. These applications include solar energy storage, hybrid photovoltaic thermal system, electronic applications, desalination and other areas of thermal management field. The results suggest that these 2D materials have extraordinary properties along massive impact on thermal energy storage and conversion compared to conventional materials. These results encourage and attract young researchers and scholars to get some direction and advancement in thermal management field in their future work.

Near-Field Thermophotovoltaic Conversion with High Electrical Power Density and Cell Efficiency above 14.

Abstract: A huge amount of thermal energy is available close to material surfaces in radiative and nonradiative states, which can be useful for matter characterization or energy harvesting. Even though a full class of novel nano-engineered devices has been predicted over the last two decades for exploiting near-field thermal photons, efficient near-field thermophotovoltaic conversion could not be achieved experimentally until now. Here, we realize a proof of principle by approaching a micron-sized indium antimonide photovoltaic cell at nanometer distances from a hot (~800 K)

Carbon aerogel based composite phase change material derived from kapok fiber: Exceptional microwave absorbility and efficient solar/magnetic to thermal energy storage performance

Abstract: Herein, we report a facile yet efficient strategy for fabricating a carbonized kapok fiber aerogel (CKF) based composite PCM, by incorporating magnetic guest of Fe3O4 nanoparticles and encapsulating thermal energy guest of lauric acid (LA). The obtained LA/CKF@Fe3O4 composite PCMs (CPM) shows an ultrahigh latent heat of 97.5% that of LA. Besides, the integration of Fe3O4 contributes to the CPM with excellent microwave absorption performance by achieving an optimal balance between the impedance matching and the high loss characteristics. The minimum reflection loss for CPM-30 is −17.3 dB at 8.4 GHz within thickness of 5.5 mm, far exceeding the practical demand of −10 dB. Furthermore, the CPM can also realize efficient solar/magnetic to thermal conversion. To the best of our knowledge, this is the first example of carbon aerogel based composite PCM prepared by facile yet renewable method that also exhibits ultrahigh thermal energy capacity, enhanced thermal conductivity, superior microwave absorption property and efficient solar/magnetic to thermal conversion performance. This study paves a way for designing of high-performance composite PCMs with numerous energy storage forms and functions by extending the reported system to other natural microtubules and functional guests.