Showing papers on "Thermal energy published in 2016"

A single-atom heat engine

Abstract: Heat engines convert thermal energy into mechanical work and generally involve a large number of particles. We report the experimental realization of a single-atom heat engine. An ion is confined in a linear Paul trap with tapered geometry and driven thermally by coupling it alternately to hot and cold reservoirs. The output power of the engine is used to drive a harmonic oscillation. From direct measurements of the ion dynamics, we were able to determine the thermodynamic cycles for various temperature differences of the reservoirs. We then used these cycles to evaluate the power P and efficiency η of the engine, obtaining values up to P = 3.4 × 10(-22)joules per second and η = 0.28%, consistent with analytical estimations. Our results demonstrate that thermal machines can be reduced to the limit of single atoms.

High-efficiency electrochemical thermal energy harvester using carbon nanotube aerogel sheet electrodes

Abstract: Conversion of low-grade waste heat into electricity is an important energy harvesting strategy. However, abundant heat from these low-grade thermal streams cannot be harvested readily because of the absence of efficient, inexpensive devices that can convert the waste heat into electricity. Here we fabricate carbon nanotube aerogel-based thermo-electrochemical cells, which are potentially low-cost and relatively high-efficiency materials for this application. When normalized to the cell cross-sectional area, a maximum power output of 6.6 W m−2 is obtained for a 51 °C inter-electrode temperature difference, with a Carnot-relative efficiency of 3.95%. The importance of electrode purity, engineered porosity and catalytic surfaces in enhancing the thermocell performance is demonstrated. Conversion of low-grade waste heat into electricity is an important energy harvesting strategy. Here, the authors fabricate carbon nanotube aerogel-based thermo-electrochemical cells, which are potentially low-cost and relatively high-efficiency materials for this application.

A review of solar parabolic trough collector

Abstract: Solar energy is one among the freely available clean forms of renewable energy. Many technologies have been developed in India for extracting energy from assorted renewable energies, but the maximum extraction of thermal energy from solar energy is the most promising challenge. This paper focuses on the performance and efficiency of solar parabolic trough collector. It also reviews the pertinent applications of solar energy such as air heating system, desalination, refrigeration, industrial heating purposes and power plants. This paper will be useful for researchers concentrating on solar energy using parabolic trough collector.

An ice-templated assembly strategy to construct graphene oxide/boron nitride hybrid porous scaffolds in phase change materials with enhanced thermal conductivity and shape stability for light–thermal–electric energy conversion

Abstract: Latent heat energy storage and release media of organic phase change materials (PCMs) are promising to utilize thermal energy coming from solar radiation for effective thermal management. However, the inherently low thermal conductivity and poor photoabsorption of organic PCMs lead to slow thermal charging/discharging rates, hindering the direct thermal energy conversion and storage. Here, we demonstrate that multifunctional PCMs with high thermal conductivity, improved shape-stability and efficient light–thermal–electric energy conversion can be fabricated by introducing polyethylene glycol (PEG) into graphene oxide (GO)/boron nitride (BN) hybrid porous scaffolds (HPSs) constructed via an ice-templated assembly strategy. Owing to the self-assembly of thermally conductive fillers during ice-growth, the obtained PCMs exhibit a high thermal conductivity (as high as 1.84 W m−1 K−1 at 19.2 wt% of BN), which is much higher than that of the composites fabricated by the solution blending method. Furthermore, the obtained composite PCMs with high energy storage density and excellent thermal stability can also be utilized to realize efficient light-to-thermal and light-to-electric energy conversion and storage, providing promising application potential in advanced energy-related devices and systems for solar energy utilization and storage.

Solar-thermal conversion and thermal energy storage of graphene foam-based composites

Abstract: Among various utilizations of solar energy, solar-thermal conversion has recently gained renewed research interest due to its extremely high energy efficiency. However, one limiting factor common to all solar-based energy conversion technologies is the intermittent nature of solar irradiation, which makes them unable to stand-alone to satisfy the continuous energy need. Herein, we report a three-dimensional (3D) graphene foam and phase change material (PCM) composite for the seamlessly combined solar-thermal conversion and thermal storage for sustained energy release. The composite is obtained by infiltrating the 3D graphene foam with a commonly used PCM, paraffin wax. The high macroporosity and low density of the graphene foam allow for high weight fraction of the PCM to be incorporated, which enhances the heat storage capacity of the composite. The interconnected graphene sheets in the composite provide (1) the solar-thermal conversion capability, (2) high thermal conductivity and (3) form stability of the composite. Under light irradiation, the composite effectively collects and converts the light energy into thermal energy, and the converted thermal energy is stored in the PCM and released in an elongated period of time for sustained utilization. This study provides a promising route for sustainable utilization of solar energy.

Thermally Chargeable Solid-State Supercapacitor

Abstract: Ubiquitous low-grade thermal energy, which is typically wasted without use, can be extremely valuable for continuously powering electronic devices such as sensors and wearable electronics. A popular choice for waste heat recovery has been thermoelectric energy conversion, but small output voltage without energy-storing capability necessitates additional components such as a voltage booster and a capacitor. Here, a novel method of simultaneously generating a large voltage from a temperature gradient and storing electrical energy without losing the benefit of solid-state no-moving part devices like conventional thermoelectrics is reported. Thermally driven ion diffusion is used to greatly increase the output voltage (8 mV K−1) with polystyrene sulfonic acid (PSSH) film. Polyaniline-coated electrodes containing graphene and carbon nanotube sandwich the PSSH film where thermally induced voltage-enabled electrochemical reactions, resulting in a charging behavior without an external power supply. With a small temperature difference (5 K) possibly created over wearable energy harvesting devices, the thermally chargeable supercapacitor produce 38 mV with a large areal capacitance (1200 F m−2). It is anticipated that the attempt with thermally driven ion diffusion behaviors initiates a new research direction in thermal energy harvesting.

How AGN Jets Heat the Intracluster Medium -- Insights from Hydrodynamic Simulations

Abstract: Feedback from active galactic nuclei (AGN) is believed to prevent catastrophic cooling in galaxy clusters. However, how the feedback energy is transformed into heat, and how the AGN jets heat the intracluster medium (ICM) isotropically, still remain elusive. In this work, we gain insights into the relative importance of different heating mechanisms using three-dimensional hydrodynamic simulations including cold gas accretion and momentum-driven jet feedback, which are the most successful models to date in terms reproducing the properties of cool cores. We find that there is net heating within two `jet cones' (within ~30 degrees from the axis of jet precession) where the ICM gains entropy by shock heating and mixing with the hot thermal gas within bubbles. Outside the jet cones, the ambient gas is heated by weak shocks, but not enough to overcome radiative cooling, therefore forming a `reduced' cooling flow. Consequently, the cluster core is in a process of `gentle circulation' over billions of years. Within the jet cones, there is significant adiabatic cooling as the gas is uplifted by buoyantly rising bubbles; outside the cones, energy is supplied by inflow of already-heated gas from the jet cones as well as adiabatic compression as the gas moves toward the center. In other words, the fluid dynamics self-adjusts such that it compensates and transports the heat provided by the AGN, and hence no fine-tuning of the heating profile of any process is necessary. Throughout the cluster evolution, turbulent energy is only at the percent level compared to gas thermal energy, and thus turbulent heating is not the main source of heating in our simulation.

Efficient Solar-Thermal Energy Harvest Driven by Interfacial Plasmonic Heating-Assisted Evaporation

Abstract: The plasmonic heating effect of noble nanoparticles has recently received tremendous attention for various important applications. Herein, we report the utilization of interfacial plasmonic heating-assisted evaporation for efficient and facile solar-thermal energy harvest. An airlaid paper-supported gold nanoparticle thin film was placed at the thermal energy conversion region within a sealed chamber to convert solar energy into thermal energy. The generated thermal energy instantly vaporizes the water underneath into hot vapors that quickly diffuse to the thermal energy release region of the chamber to condense into liquids and release the collected thermal energy. The condensed water automatically flows back to the thermal energy conversion region under the capillary force from the hydrophilic copper mesh. Such an approach simultaneously realizes efficient solar-to-thermal energy conversion and rapid transportation of converted thermal energy to target application terminals. Compared to conventional ext...

An overview on current application of nanofluids in solar thermal collector and its challenges

Abstract: The increase in energy demands and depletion of fossil fuel for power generation are the major concern nowadays. Utilization of renewable energy sources can be regarded as one of the options to tackle these issues. Renewable energy such as solar powered energy can be harnessed by using solar thermal collector. An efficient solar thermal collector must be coupled with fluids which possess superior thermal and optical properties. New generation of heat transfer fluid such as nanofluid is proven to have good prospect to be utilized in the solar collector. Thus, this article reviews the current researches on application of nanofluids in solar collector and probable challenges that might need to be faced in the development of an efficient solar thermal collector with nanofluid.

A review on thermal conductivity enhancement of paraffinwax as latent heat energy storage material

Abstract: Increasing energy demand calls for the implementation of proper thermal energy storage which is one of the most important components of solar energy conversion systems. Phase change material based latent heat energy storage systems have emerged as a promising option to effectively store thermal energy. Generally, paraffin wax is used as the most common phase change material for low to medium temperature storage applications because it has a large latent heat and low cost besides being stable, nontoxic and non-corrosive. The performance of paraffin wax based latent heat energy storage systems (LHESS) is limited by its poor thermal conductivity. In this paper, the previous experimental and theoretical research studies on LHESS using paraffin wax as phase change material with different performance enhancement techniques are reviewed. Further, research works related to dispersing different kind of nanoparticles in paraffin wax for the enhancement of its thermal conductivity are comprehensively reviewed with respect to synthesis, characterization and thermophysical properties of the nanoenhanced phase change material.

Review on Thermionic Energy Converters

Abstract: Thermionic energy converter (TEC) is a heat engine that generates electricity directly using heat as its source of energy and electron as its working fluid. Despite having a huge potential as an efficient direct energy conversion device, the progress in vacuum-based thermionic energy converter development has always been hindered by the space charge problem and the unavailability of materials with low work function. It is only recently that researchers have started to look back into this technology as recent advances in manufacturing technology techniques have made it possible to solve these problems, making TECs a viable option in replacing current energy production systems. The focus of this paper is to review the challenges of producing efficient and practical TECs, along with recent findings and developments in mitigating these challenges. Furthermore, this paper looked into potential applications of TECs, based on recent works and technologies, and found that, with certain improvements, it can be applied in many sectors.