Search

High-fidelity numerical simulations are used to thoroughly analyze the evolution of the wake behind a megawatt-scale offshore wind turbine. The wake features are classified in terms of wake dynamics composition and the associated turbulence characteristics originating from the inner and outer sections of the blades. Understanding the wake is essential for developing compact layouts for future wind farms. We employed a transient Sliding Mesh Interface (SMI) technique to analyze the fully dynamic wake evolution of the offshore NREL 5MW full turbine. Our high-fidelity results have been validated against previously published results in the literature. We thoroughly investigated the dominant structures of the wake using Proper Orthogonal Decomposition (POD) techniques, which we applied to transient simulations of fully developed flows after five wind turbine revolutions over the snapshot data. Our findings show that the inner section of the blades, which is composed of airfoils with larger cross-sections, is responsible for the dominant components of the wake, while the contribution of the wake from the outer section of the blade is significantly lower. Therefore, designing more aerodynamic sections for the blade’s inner section can help reduce the dominant wake components and thus decrease the inter-turbine distance in future wind farms.

This work pertains to the transient modeling and comparative study of active solar thermal space and water heating systems using liquid and air-type solar thermal collectors as the main energy source. The study utilizes TRNSYS to simulate the two systems in the context of Taxila's weather data (located at 33.74°N, 72.83°E), with the goal of meeting peak space and domestic water heating demands of 20 kW and 200 lit/day, respectively. The liquid water-based system (S-1) is primarily composed of a liquid solar collector, thermal storage, an auxiliary heater, connections to the hot water supply, and the space heating load through a water–air heat exchanger. In contrast, the air-based system (S-2), employs a pebble bed storage to store heat extracted from the solar thermal air collector. The heated air is subsequently used directly for space heating and passed through an air–water heat exchanger for water heating. Dynamic simulations of both systems span the entire winter season, and various performance metrics, including solar fraction, primary energy savings, and solar collector thermal efficiency, are computed. The results revealed that at the same collector area, the liquid water-based system (S-1) shows a higher solar fraction than the air-based systems (S-2) while the primary energy savings of the S-1 resulted in lower values than S-2 at smaller collector areas (< ∼30 m2) but surpasses the S-2 with increasing collector size. The optimal collector tilt for both systems is determined to be 50°, while specific storage volumes corresponding to maximum primary energy savings are estimated to be 100 and 40 L/m2 for S-1 and S-2, respectively. [ABSTRACT FROM AUTHOR]

In this work, analytical modeling and theoretical analysis of a recently developed unique design of a solar cooker cum dryer (SCCD) have been conducted to predict its thermal characteristics under a given set of input parameters. The energy balance equations of the main components of the cooking compartment are iteratively solved to determine the unknown temperatures of the SCCD unit when it operates as a pure cooker and when the same acts as an air heater for the food drying compartment. The influence of design parameters such as air velocity, glazing thickness, spacing between glazing, back reflector, and surface coatings of the absorber plate has been studied and quantified. The analytical model has been tested by simulating and validating the modeling results with the experimental data for different days of the year Moreover, further experiments are conducted on the SCCD in drying mode to quantify its thermal performance in natural versus forced convection of the airflow through the SCCD and to demonstrate its effectiveness in comparison to open sun food drying. The obtained results show that the SCCD unit attain cooking and drying temperatures in the suitable range of 80–135℃ and 50–70℃, respectively. The experimental results of the SCCD unit as a food dryer revealed that the Page model with higher adequacy is found to be the best fit for all three modes of food drying in the SCCD unit. It is found that in comparison to drying of tomatoes in the open sun which took ⁓13 hrs, forced convection of airflow in the SCCD unit resulted in the least time of ⁓7.5 hrs to achieve the desired level of moisture content. The energy and exergy efficiency of the SCCD in cooking mode was estimated to be in the range 2.1–15.5% and 1.1–5.6%, while it was 7.5–16.5% and 26.6–50.7% in drying mode, respectively. [ABSTRACT FROM AUTHOR]

Batch-type solar collector is a tilt-able water-heating solar-thermal system comprising an isosceles-trapezoidal enclosure housing a circular-cylinder absorber at the bottom wall, insulated side-walls, and flat-top glazing. Free convection of air inside such trapezoidal enclosure is studied numerically by varying the tilt angle of the whole enclosure from 0°-70°. The influence of tilt on the flow field has been demonstrated by plotting the streamlines and isotherms. The present study successfully identifies the importance of enclosure-tilt in quantifying heat-loss between absorber and glazing by developing a computational correlation between Nusselt and Rayleigh as a function of tilt. The correlation trend is non-monotonic over the range of angular Rayleigh numbers numerically experimented with having a peak around angular Rayleigh number 3·105 corresponding to the tilt-angle 30°. The irregular-shaped cavity implies that the heat transfer correlations already existing for regular-shaped cavities may not be used otherwise they will draw implausible conclusions and this argument identifies the novelty of the present study. [ABSTRACT FROM AUTHOR]

Solar cookers and dryers are normally used as separate units due to different operating temperature requirements for cooking and drying of food products. A unique design of a compounded solar cooker and dryer unit is presented in this paper and its performance is evaluated on the basis of outdoor experimentation. Two separate compartments serving as cooker and dryer units are joined together by providing small air flow passages in such a manner that the lower high-temperature cooker portion also acts as an air heater for the upper low-temperature dryer unit and the movement of air is by buoyancy-driven natural convection flow across the entire unit. Experiments are performed to assess the performance of the developed combined unit in terms of various performance factors such as figures of merits (F1, F2 ), energy efficiency, heat utilization factor (HUF), coefficient of performance (COP), and dryer efficiency. A promising feature of the proposed unit is the attainment of two different temperature ranges in the cooker (80 °C – 135 °C) and the dryer compartment (35 °C – 65 °C) under the same ambient conditions. The figure of merits of the cooking unit are determined to be 0.11 (F1 ) and 0.303 (F2 ). The heat utilization factor, coefficient of performance, and drying efficiency of the dryer unit are evaluated to be 34 %, 66 %, and 14 %, respectively. [ABSTRACT FROM AUTHOR]

This paper introduces a novel design of a double glazed box type solar cooker having an L-shaped absorber plate with one internal (bottom) and two external plane reflectors. A series of experiments were performed to access the cooker's thermal performance at the location of Taxila (33.74°N, 72.80°E) in Pakistan during the year 2017. The cooker's performance is evaluated in terms of maximum absorber plate temperature and other thermal performance indicators like first and second figures of merits (F1 and F2), parameter index, energy efficiency, and utilizable efficiency. The experimentally obtained values of all the performance indicators are found to be in the recommended ranges specified in the literature. An increment of about 30% in the absorber plate temperature is estimated for the case of the proposed L-shaped absorber plate along with an internal (bottom) reflector as compared to the case of no internal reflector and a conventional horizontal absorber plate. The first figure of merit of the proposed cooker is estimated to be 0.12, thus classifying it in grade A category. Furthermore, the solar cooker is manufactured at a nominal cost of ∼130 USD, making it a competitive product in the market. [ABSTRACT FROM AUTHOR]

Energy consumption of heating and/or cooling auxiliary devices in solar sorption cooling systems is one of the major factors of reduction in primary energy savings. This work simulates and analyzes the dynamic operation of a solar thermal double effect absorption cooling system for three strategies of employing hot and/or cold auxiliary devices and the influence of instituting the entire solar collector field in series versus parallel arrangement. An auxiliary heater is installed in the hot storage to absorption chiller loop in configuration-1 (C-1) to maintain the desired generator temperature. An auxiliary cooler is employed in configuration-2 (C-2) to furnish the cooling load in conjunction with an absorption chiller energized only by the evacuated tube solar collector (ETC). In configuration-3 (C-3) both auxiliary heater in the storage to chiller loop and auxiliary cooler in the chiller to load loop are modeled for three percentage contributions of the required cooling load by the double effect absorption and water-cooled vapor compression chiller i.e., 50-50 (C-3a), 70–30 (C-3b), and 30–70 (C-3c), respectively. Simulation results demonstrated that at lower collector areas C-2 resulted in considerably higher primary energy savings (∼58%) and solar fraction (∼14.4%) in comparison to C-1 and C-3. The serial connection of the entire solar field resulted in better primary energy savings in C-2 while for C-1 and C-3 parallel arrangement gave rise to higher primary energy savings than the serial arrangement. • Analysis of solar cooling system with different options of auxiliary heater/cooler. • Configuration with only auxiliary cooler resulted in the highest energy savings. • Serial connection of solar field resulted in better primary energy savings in C-2. • Parallel arrangement of solar field showed higher energy savings for C-1 and C-3. [ABSTRACT FROM AUTHOR]

The reliance on Computational Fluid Dynamics (CFD) simulations has drastically increased over time to evaluate the aerodynamic performance of small-scale wind turbines. With the rapid variability in customer demand, industrial requirements, economic constraints, and time limitations associated with the design and development of small-scale wind turbines, the trade-off between computational resources and the simulation's numerical accuracy may vary significantly. In the context of wind turbine design and analysis, high fidelity simulation under full geometric and numerical complexity is more accurate but pose significant demands from a computational standpoint. There is a need to understand and quantify performance deterioration of high fidelity simulations under reduced geometric or numerical approximation on a single small scale turbine model. In the present work, the flow past a small-scale Horizontal Axis Wind Turbine (HAWT) was simulated under various geometric and numerical configurations. The geometric complexity was varied based on stationary and rotating turbine conditions. In the stationary case, simple 2D airfoil, 2.5D blade, 3D blade sections are evaluated, while rotational effects are introduced for the configuration 3D blade, rotor only, and the full-scale wind turbine with and without the inclusion of a nacelle and tower. In terms of numerical complexity, the Single Reference Frame (SRF), Multiple Reference Frames (MRF), and the Sliding Meshing Interface (SMI) is analyzed over Tip Speed Ratios (TSR) of 3, 6, 10. The quantification of aerodynamic coefficients of the blade ( C l , C d ) and turbine ( C p , C t ) was conducted along with the discussion on wake patterns in comparison with experimental data. [ABSTRACT FROM AUTHOR]