Results 1 - 10 of 20861
Results 1 - 10 of 20861. Search took: 0.031 seconds
|Sort by: date | relevance|
[en] Highlights: • Mode 4 has the highest exergy efficiency. • Mode 2 has the largest exergy density. • Second heat exchanger has the largest exergy destruction. - Abstract: Advanced adiabatic compressed air energy storage system plays an important role in smoothing out the fluctuated power from renewable energy. Under different operation modes of charge-discharge process, thermodynamic behavior of system will vary. In order to optimize system performance, four operation modes of charge-discharge process are proposed in this paper. The performance difference of four modes is compared with each other based on energy analysis and exergy analysis. The results show that exergy efficiency of mode 4 is the highest, 55.71%, and exergy density of mode 2 is the largest, 8.09 × 106 J m−3, when design parameters of system are identical. The second heat exchanger has the most improvement potential in elevating system performance. In addition, a parametric analysis and multi-objective optimization are also carried out to assess the effects of several key parameters on system performance.
[en] India has committed to Paris Agreement to generate 30 per cent of its total electricity from renewable Sources by 2030. Roof top solar system will help it to some extent. It is also expected that the distribute; generation (roof top solar PV) at the consumer end will compensate to the acute power shortage in several states. (author)
[en] Grid connected solar system is an emerging technology to harvest solar incident radiation for production of electricity which can be fed to the grid directly. As part of the energy conservation activities as well as considering the importance the Government of India has given to harness Solar Energy, IGCAR has initiated projects in this line. To start with, a pilot plant of 30 kWp grid connected solar plant is installed and commissioned on 14th August 2015. On an average, this system, produces 120 to 150 units of electricity per day. On days with good solar insolation the production clocked 175 units. This is the largest solar system installed at Kalpakkam so far. All the operations are automatic and no manual intervention is envisaged for normal operation. It is not provided with any battery backup as the electricity generated is transferred to the gird on real time basis and no storage is necessary. This arrangement will ensure better efficiency at a lesser capital and maintenance cost
[en] In simulation of fluid injection in fractured geothermal reservoirs, the characteristics of the physical processes are severely affected by the local occurence of connected fractures. To resolve these structurally dominated processes, there is a need to develop discretization strategies that also limit computational effort. In this paper, we present an upscaling methodology for geothermal heat transport with fractures represented explicitly in the computational grid. The heat transport is modeled by an advection-conduction equation for the temperature, and solved on a highly irregular coarse grid that preserves the fracture heterogeneity. The upscaling is based on different strategies for the advective term and the conductive term. The coarse scale advective term is constructed from sums of fine scale fluxes, whereas the coarse scale conductive term is constructed based on numerically computed basis functions. The method naturally incorporates the coupling between solution variables in the matrix and in the fractures, respectively, via the discretization. In this way, explicit transfer terms that couple fracture and matrix solution variables are avoided. Numerical results show that the upscaling methodology performs well, in particular for large upscaling ratios, and that it is applicable also to highly complex fracture networks.
[en] We present the results of a detailed study of the first accurate 3D ground state interaction potential energy surface (PES) of the Ne–Li2 system by quantum calculations using the coupled-cluster singles and doubles excitation approach with perturbative treatment of triple excitations [CCSD(T)]. The calculations were carried out for the frozen molecular equilibrium geometries and for an extensive range of the remaining two Jacobi coordinates, R and θ, for which a total of about 1976 points is generated for the surface. Mixed basis sets, aug-cc-pVTZ for the Ne atom and cc-pCVTZ for the Li atom, with an additional (3s3p2d2f1g) set of midbond functions are used. The ab initio points on the PES are fitted to a 96-parameter algebraic form with an average absolute error of 0.00000255% and a maximum error less than 0.00888%. The experimental results are compared with our ab initio potential surface calculations. Our PES gives more accurate results along with the experimental data.
[en] Highlights: • The study focussed on the techno-economic assessment of thermal energy storage systems. • Data-intensive bottom-up models for each storage systems were developed. • Costs for sensible, thermo-chemical, and latent heat storage systems were developed. • The electricity cost from using these thermal energy storage systems is $0.02–$1.19/kWh. - Abstract: In this paper, a data-intensive cost model was developed for sensible heat, latent heat and thermochemical storage systems. In order to evaluate the economic feasibility of storage systems, five scenarios were developed depending on the method of storage. The five scenarios considered were indirect sensible heat, direct sensible heat using two tanks, direct sensible heat using one tank, latent heat and thermochemical storage. A Monte Carlo simulation was performed for all the scenarios to examine the uncertainty in the levelized cost of electricity when parameters such as solar multiple, plant capacity, storage duration, capacity factor, and discount rate are changed. The levelized cost of electricity ranges for individual scenarios are; 0.08–0.59 $/kWh for indirect sensible heat, 0.03–0.22 $/kWh for direct sensible heat using two tank, 0.02–0.16 $/kWh for direct sensible heat using one tank, 0.06–0.43 $/kWh for latent heat, and 0.22–1.19 $/kWh for thermochemical storage. The results indicate that when uncertainty is taken into account, the investment cost for thermochemical storage is clearly higher than other scenarios. This study will provide key information for industry and policy makers in decision making and in determining the economic viability of thermal energy storage systems.
[en] Highlights: • Heat transfer for PCHE in TEG was investigated in detail by 3D CFD analysis. • Experimental data for a 200-W TEG implemented with PCHEs are newly presented. • Power density of the TEG was sufficiently high at low temperature. • Reduction of TEG flow rate requirements from use of PCHEs is estimated. - Abstract: Printed circuit heat exchangers (PCHEs) are employed to improve the compactness of a thermoelectric generator (TEG). PCHEs allows miniaturization of the heat exchanger without excessive additional cost, and permit high temperature and pressure (up to 1100 K and 600 bar) of working fluid, which enable high thermoelectric conversion efficiency. To investigate the pressure loss and thermal resistance of a PCHE in detail, three-dimensional computational fluid dynamic (CFD) analysis is conducted. Experimental results of the proposed TEG with PCHEs are newly presented. The TEG provides power density of 233.1 kW/m3 at inlet temperatures of 448.15 K (hot side) and 293.15 K (cold side), which is the highest value in literature for a low-temperature TEG (<505.15 K hot side). Based on the models of friction and heat transfer in a PCHE validated by the experiment, it is noted that the flow rate required for the heat exchangers in a TEG producing a given amount of electrical power can be reduced by adaption of PCHEs. Such novel results on the TEG with PCHEs might be helpful for more compact design and expands the applicability of TEGs for waste heat recovery.
[en] Recent advances in science and technology of materials fabrication, engineering of work functions, and micrometer gap machining between emitter and collector are making thermionic conversion/converter (TEC) of solar energy an emerging technology. As the converter is the lightest of all devices with highest direct power conversion density (per unit area of the converting surface), it has, potential for substituting photovoltaic technology to a large extent and for deployment in space as a power source. This article summarizes the current efforts/technologies in the field, and discusses their inherent merits and demerits towards realizing the goal of achieving high conversion efficiency and simulation of performance evaluation of a solar TEC. We also discuss the use of both metals and nanomaterials, critical roles of work functions of both emitter and collector, collector temperature, absorptivity and emissivity of the surfaces, radiation losses, and use of both metals and nanomaterials in the efficiency of conversion of solar energy. We further deal with the role of correcting thermionic emission current density equation in the simulation of solar TEC performance. We discuss briefly the possible methods of space-charge control in future in a solar TEC. (author)
[en] Highlights: • Steam generation is due to boiling/vaporization in localized solar absorption area. • Hypothesized nanobubble is unlikely to occur under normal solar concentrations. • A photothermal efficiency of 80.3% was achieved for 12.75 ppm GNP dispersion. • A specific absorption rate of ~50 kW/g was achieved for 1.02 ppm GNP dispersion. Steam production is essential for a wide range of applications, and currently there is still strong debate if steam could be generated on top of heated nanoparticles in a solar receiver. We performed steam generation experiments for different concentrations of gold nanoparticles dispersions in a cylindrical receiver under focused natural sunlight of 220 Suns. Combined with mathematical modelling, it is found that the initial stage of steam generation is mainly caused by localized boiling and vaporization in the superheated region due to highly non-uniform temperature and radiation energy distribution, albeit the bulk fluid is still subcooled. Such a phenomenon can be well explained by the classical heat transfer theory, and the hypothesized ‘nanobubble’, i.e., steam produced around the heated nanoparticles, is unlikely to occur under normal solar concentrations. For future solar receiver design, attention should be paid to focus and trap more solar energy at the superheated region while minimizing the temperature rise of the bulk fluid.
[en] Highlights: • Physics of black material for light-to-heat conversion. • The absorbers using various black materials are identified. • The state-of-the-art design of the photothermal sheets. • The devices with their steam releasing property are highlighted. Solar energy-to-heat conversion for steam generation is an essential metrology for power generation, water purification and desalination. Harvesting light energy and converting it to heat as terminal energy by black photothermal sheets is a novel strategy to attain this goal. This technology rely on use of black nanomaterials as light absorber to increase the absorption and conversion efficiency of solar energy. Fundamental understanding of their structure-property has to be fully exploited for further developing efficient solar-to-heat systems. This report summarizes physical understanding and experimental advances in development of black photothermal sheets for solar water evaporation. We examine the popular photothermal systems with remarkable vapor generation performance to identify the state-of-the-art of the device design. Three groups of the photothermal sheet are discussed in terms of different light-harvesting materials, such as carbon-based sheets, plasmonic sheets as well as semiconducting sheets. The physical difference of these novel devices with their steam releasing property are also highlighted.