Journal of Solar Energy Engineering, Transactions of the ASME
1528-8986
0199-6231
Mỹ
Cơ quản chủ quản: ASME , The American Society of Mechanical Engineers(ASME)
Lĩnh vực:
Renewable Energy, Sustainability and the EnvironmentEnergy Engineering and Power Technology
Các bài báo tiêu biểu
Predicted Efficiency of a Low-Temperature Nanofluid-Based Direct Absorption Solar Collector Due to its renewable and nonpolluting nature, solar energy is often used in applications such as electricity generation, thermal heating, and chemical processing. The most cost-effective solar heaters are of the “flat-plate” type, but these suffer from relatively low efficiency and outlet temperatures. The present study theoretically investigates the feasibility of using a nonconcentrating direct absorption solar collector (DAC) and compares its performance with that of a typical flat-plate collector. Here a nanofluid—a mixture of water and aluminum nanoparticles—is used as the absorbing medium. A two-dimensional heat transfer analysis was developed in which direct sunlight was incident on a thin flowing film of nanofluid. The effects of absorption and scattering within the nanofluid were accounted for. In order to evaluate the temperature profile and intensity distribution within the nanofluid, the energy balance equation and heat transport equation were solved numerically. It was observed that the presence of nanoparticles increases the absorption of incident radiation by more than nine times over that of pure water. According to the results obtained from this study, under similar operating conditions, the efficiency of a DAC using nanofluid as the working fluid is found to be up to 10% higher (on an absolute basis) than that of a flat-plate collector. Generally a DAC using nanofluids as the working fluid performs better than a flat-plate collector, however, much better designed flat-plate collectors might be able to match or outperform a nanofluids based DAC under certain conditions.
Tập 131 Số 4 - 2009
Thermodynamic Study of Advanced Supercritical Carbon Dioxide Power Cycles for Concentrating Solar Power Systems Supercritical CO2 (s-CO2) operated in a closed-loop Brayton cycle offers the potential of higher cycle efficiency versus superheated or supercritical steam cycles at temperatures relevant for concentrating solar power (CSP) applications. Brayton-cycle systems using s-CO2 have a smaller weight and volume, lower thermal mass, and less complex power blocks versus Rankine cycles due to the higher density of the fluid and simpler cycle design. The simpler machinery and compact size of the s-CO2 process may also reduce the installation, maintenance, and operation cost of the system. In this work we explore s-CO2 Brayton cycle configurations that have attributes that are desirable from the perspective of a CSP application, such as the ability to accommodate dry cooling and achieve greater than 50% efficiency, as specified for the U.S. Department of Energy SunShot goal. Recompression cycles combined with intercooling and/or turbine reheat appear able to hit this efficiency target, even when combined with dry cooling. In addition, the intercooled cycles expand the temperature differential across the primary heat exchanger, which is favorable for CSP systems featuring sensible-heat thermal energy storage.
Tập 135 Số 4 - 2013
Radiative Heat Transfer Analysis in Plasmonic Nanofluids for Direct Solar Thermal Absorption The present study reports a novel concept of a direct solar thermal collector that harnesses the localized surface plasmon of metallic nanoparticles suspended in water. At the plasmon resonance frequency, the absorption and scattering from the nanoparticle can be greatly enhanced via the coupling of the incident radiation with the collective motion of electrons in metal. However, the surface plasmon induces strong absorption with a sharp peak due to its resonant nature, which is not desirable for broad-band solar absorption. In order to achieve the broad-band absorption, we propose a direct solar thermal collector that has four types of gold-nanoshell particles blended in the aquatic solution. Numerical simulations based on the Monte Carlo algorithm and finite element analysis have shown that the use of blended plasmonic nanofluids can significantly enhance the solar collector efficiency with an extremely low particle concentration (e.g., approximately 70% for a 0.05% particle volume fraction). The low particle concentration ensures that nanoparticles do not significantly alter the flow characteristics of nanofluids inside the solar collector. The results obtained from this study will facilitate the development of highly efficient solar thermal collectors using plasmonic nanofluids.
Tập 134 Số 2 - 2012
On the Performance of the Savonius Wind Turbine An extensive wind tunnel test program is described which assesses the relative influence of system parameters on the Savonius rotor performance. The parametric study leads to an optimum configuration with an increase in efficiency by around 100 percent compared to the reported efficiency of ≈12–15 percent. Of particular interest is the blockage correction procedure which is vital for application of the wind tunnel results to a prototype design, and facilitates comparison of data obtained by other investigators. Next, using the concept of a central vortex, substantiated by a flow visualization study, a semiempirical approach to predict the rotor performance using measured stationary blade pressure data is developed. The simple approach promises to be quite effective in predicting the rotor performance, even in the presence of blockage, and should prove useful at least in the preliminary design stages.
Tập 111 Số 1 - Trang 71-81 - 1989
Optimization of a Closed-Cycle OTEC System Optimization of an Ocean Thermal Energy Conversion (OTEC) system is carried out by the Powell Method (the method of steepest descent). The parameters in the objective function consist of the velocities of cold sea water and warm sea water passing through the heat exchangers, the phase change temperature, and turbine configuration (specific speed, specific diameter, ratio of blade to diameter). Numerical results are shown for a 100-MW OTEC plant with plate-type heat exchangers using ammonia as working fluid, and are compared with calculation results for the case when the turbine efficiency is fixed.
Tập 112 Số 4 - Trang 247-256 - 1990
Moment-Based Load and Response Models With Wind Engineering Applications A general method is shown here to model wind loads and responses for reliability applications. This method characterizes the short-term loads and responses by a few summary statistics: specifically, by a limited number of statistical moments. A suite of moment-based models are derived and applied here, illustrating how this statistical moment information can best be utilized. Two examples are shown: the fatigue analysis of a wind turbine component, and the vibration response of a fixed structure to nonlinear wind drag loads. [S0199-6231(00)00702-4]
Tập 122 Số 3 - Trang 122-128 - 2000
Fluidized Bed Technology for Concentrating Solar Power With Thermal Energy Storage A generalized modeling method is introduced and used to evaluate thermal energy storage (TES) performance. The method describes TES performance metrics in terms of three efficiencies: first-law efficiency, second-law efficiency, and storage effectiveness. By capturing all efficiencies in a systematic way, various TES technologies can be compared on an equal footing before more detailed simulations of the components and concentrating solar power (CSP) system are performed. The generalized performance metrics are applied to the particle-TES concept in a novel CSP thermal system design. The CSP thermal system has an integrated particle receiver and fluidized-bed heat exchanger, which uses gas/solid two-phase flow as the heat-transfer fluid, and solid particles as the heat carrier and storage medium. The TES method can potentially achieve high temperatures (>800 °C) and high thermal efficiency economically.
Tập 136 Số 3 - 2014
Improvement of the Performance of Solar Energy or Waste Heat Utilization Systems by Using Phase-Change Slurry as an Enhanced Heat-Transfer Storage Fluid This paper is concerned with the benefits of using phase-change slurries as enhanced heat-transfer/storage working fluids in solar energy and waste heat utilization systems. Literature is cited to show that a slurry containing a phase-change material as the dispersed phase promises to have much higher heat-transfer coefficients than conventional single-phase working fluids. Because of the latent heat, the phase-change slurry also requires lower pumping rates and smaller storage tanks than single-phase fluids for the same energy content. These benefits are documented by comparisons of temperature drops, pumping rates, pumping powers, and the sizes of storage tanks for a generic energy collection system operating with and without a slurry.
Tập 107 Số 3 - Trang 229-236 - 1985
Convective Heat Transfer Coefficients in a Building-Integrated Photovoltaic/Thermal System This paper presents an experimental study for the development of convective heat transfer correlations for an open loop air-based building-integrated photovoltaic/thermal (BIPV/T) system. The BIPV/T system absorbs solar energy on the top surface, which includes the photovoltaic panels and generates electricity while also heating air drawn by a variable speed fan through a channel formed by the top roof surface with the photovoltaic modules and an insulated attic layer. The BIPV/T system channel has a length/hydraulic diameter ratio of 38, which is representative of a BIPV/T roof system for 30–45 deg tilt angles. Because of the heating asymmetry in the BIPV/T channel, two average Nusselt number correlations are reported as a function of Reynolds number: one for the top heated surface and the other for the bottom surface. For the top heated surface, the Nusselt number is in the range of 6–48 for Reynolds numbers ranging from 250 to 7500. For the bottom insulated surface, the Nusselt number is in the range of 22–68 for Reynolds numbers ranging from 800 to 7060. This paper presents correlations for the average Nusselt number as a function of Reynolds number; this correlation is considered adequate for the design of BIPV/T systems where forced convection dominates. Local Nusselt number distributions are also presented for laminar and turbulent flow conditions.
Tập 133 Số 2 - 2011
A Fundamental Equation for Exergy Balance on Solar Collectors This paper presents the exergy balance equation on a solar collector which acts as the fundamental and principal expression for the solar thermal design. The equation fully explains the exergy loss processes and can be used to derive the approximate optimum operating condition for solar collectors. Furthermore, using the equation, it can be shown that two different collectors, an evacuated tubular collector and a flat-plate collector, have both nearly equal capabilities in exergy gain despite large differences in technological efforts and expenses to produce them. In addition, ways for improvement for a solar collector are also discussed here briefly.
Tập 110 Số 2 - Trang 102-106 - 1988