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CFD Analysis on the Thermal Hydraulic Performance of an SAH Duct with Multi V-Shape Roughened Ribs
Anil Kumar, Man-Hoe Kim
November 28, 2018 (v1)
Keywords: heat transfer enhancement, SAH, solar energy, thermal hydraulic performance
This study presents the heat transfer and fluid flow characteristics in a rib-roughened SAH (solar air heater) channel. The artificial roughness of the rectangular channel was in the form of a thin circular wire in discrete multi V-pattern rib geometries. The effect of this geometry on heat transfer, fluid flow, and performance augmentation was investigated using the CFD (computational fluid dynamics). The roughness parameters were a relative discrete distance of 0.69, a relative rib height of 0.043, a relative rib pitch of 10, a relative rib width of 6.0, and a flow-attack-angle of 60°. The discrete width ratios and Reynolds numbers ranged from 0.5 to 2.0 and from 2000 to 20,000, respectively. The CFD results using the renormalization k-epsilon model were in good agreement with the empirical relationship. This model was used to investigate the heat transfer and fluid flow characteristics in the multi V-pattern rib roughened SAH channel. The thermo-hydraulic performance was found to be... [more]
A Design Alternative to Improve the Interconnection Capability of New Distributed-Generation Installations into Existing Griddle
José Agüero-Rubio, Javier López-Martínez, José Ignacio Rojas-Sola, Ángel Jesús Callejón-Ferre
November 28, 2018 (v1)
Keywords: distributed generation, distribution grids, grid-connected, installation efficiency, low voltage feeders, sustainable cities
Most distributed-generation facilities are performed on pre-built distribution grids. The design conditions of these existing grids may limit the ability of new users to get a connection due to technical and/or cost constraints. This work proposes a simple solution, adjusted to the relevant regulations and embodied in a radial distribution grid of Spanish low voltage, to improve the interconnection of distributed generation, usually grid connected photovoltaic systems. The proposed solution, based on increasing the section of the neutral line, achieves a capacity of increasing the length of the supply grid by more than 20%.
Fundamental Active Current Adaptive Linear Neural Networks for Photovoltaic Shunt Active Power Filters
Muhammad Ammirrul Atiqi Mohd Zainuri, Mohd Amran Mohd Radzi, Azura Che Soh, Norman Mariun, Nasrudin Abd Rahim, Shahrooz Hajighorbani
November 28, 2018 (v1)
Keywords: artificial neural network (ANN), current harmonic, digital signal processor (DSP), photovoltaic (PV), shunt active power filter (SAPF), Simulink/MATLAB, total harmonic distortion (THD)
This paper presents improvement of a harmonics extraction algorithm, known as the fundamental active current (FAC) adaptive linear element (ADALINE) neural network with the integration of photovoltaic (PV) to shunt active power filters (SAPFs) as active current source. Active PV injection in SAPFs should reduce dependency on grid supply current to supply the system. In addition, with a better and faster harmonics extraction algorithm, the SAPF should perform well, especially under dynamic PV and load conditions. The role of the actual injection current from SAPF after connecting PVs will be evaluated, and the better effect of using FAC ADALINE will be confirmed. The proposed SAPF was simulated and evaluated in MATLAB/Simulink first. Then, an experimental laboratory prototype was also developed to be tested with a PV simulator (CHROMA 62100H-600S), and the algorithm was implemented using a TMS320F28335 Digital Signal Processor (DSP). From simulation and experimental results, significant... [more]
Life Cycle Assessment of a HYSOL Concentrated Solar Power Plant: Analyzing the Effect of Geographic Location
Blanca Corona, Diego Ruiz, Guillermo San Miguel
November 28, 2018 (v1)
Subject: Energy Policy
Keywords: biomethane, Chile, environment, Kingdom of Saudi Arabia, Life Cycle Assessment (LCA), Mexico, Natural Gas, solar energy, South Africa, Spain
Concentrating Solar Power (CSP) technology is developing in order to achieve higher energy efficiency, reduced economic costs, and improved firmness and dispatchability in the generation of power on demand. To this purpose, a research project titled HYSOL has developed a new power plant, consisting of a combined cycle configuration with a 100 MWe steam turbine and an 80 MWe gas-fed turbine with biomethane. Technological developments must be supported by the identification, quantification, and evaluation of the environmental impacts produced. The aim of this paper is to evaluate the environmental performance of a CSP plant based on HYSOL technology using a Life Cycle Assessment (LCA) methodology while considering different locations. The scenarios investigated include different geographic locations (Spain, Chile, Kingdom of Saudi Arabia, Mexico, and South Africa), an alternative modelling procedure for biomethane, and the use of natural gas as an alternative fuel. Results indicate that... [more]
Numerical Modeling of Variable Fluid Injection-Rate Modes on Fracturing Network Evolution in Naturally Fractured Formations
Yu Wang, Xiao Li, Bo Zhang
November 28, 2018 (v1)
Keywords: hydraulic fracturing, hydraulic fracturing effectiveness, numerical simulation, variable injection-rate technology
In this study, variable injection-rate technology was numerically investigated in a pre-existing discrete fracture network (DFN) formation, the Tarim Basin in China. A flow-stress-damage (FSD) coupling model has been used in an initial attempt towards how reservoir response to variable injection-rates at different hydraulic fracturing stages. The established numerical model simultaneously considered the macroscopic and microscopic heterogeneity characteristics. Eight numerical cases were studied. Four cases were used to study the variable injection-rate technology, and the other four cases were applied for a constant injection-rate in order to compare with the variable injection-rate technology. The simulation results show that the variable injection-rate technology is a potentially good method to a form complex fracturing networks. The hydraulic fracturing effectiveness when increasing the injection-rate at each stage is the best, also, the total injected fluid is at a minimum. At the... [more]
A New Predictive Model Based on the ABC Optimized Multivariate Adaptive Regression Splines Approach for Predicting the Remaining Useful Life in Aircraft Engines
Paulino José García Nieto, Esperanza García-Gonzalo, Antonio Bernardo Sánchez, Marta Menéndez Fernández
November 28, 2018 (v1)
Keywords: aircraft engine, artificial bee colony (ABC), multivariate adaptive regression splines (MARS), prognostics, reliability, remaining useful life (RUL)
Remaining useful life (RUL) estimation is considered as one of the most central points in the prognostics and health management (PHM). The present paper describes a nonlinear hybrid ABC⁻MARS-based model for the prediction of the remaining useful life of aircraft engines. Indeed, it is well-known that an accurate RUL estimation allows failure prevention in a more controllable way so that the effective maintenance can be carried out in appropriate time to correct impending faults. The proposed hybrid model combines multivariate adaptive regression splines (MARS), which have been successfully adopted for regression problems, with the artificial bee colony (ABC) technique. This optimization technique involves parameter setting in the MARS training procedure, which significantly influences the regression accuracy. However, its use in reliability applications has not yet been widely explored. Bearing this in mind, remaining useful life values have been predicted here by using the hybrid ABC⁻... [more]
Simultaneous Optimization of Topology and Component Sizes for Double Planetary Gear Hybrid Powertrains
Weichao Zhuang, Xiaowu Zhang, Huei Peng, Liangmo Wang
November 28, 2018 (v1)
Subject: Optimization
Keywords: energy management, hybrid electric vehicles (HEVs), optimal design methodology, topology optimization
Hybrid powertrain technologies are successful in the passenger car market and have been actively developed in recent years. Optimal topology selection, component sizing, and controls are required for competitive hybrid vehicles, as multiple goals must be considered simultaneously: fuel efficiency, emissions, performance, and cost. Most of the previous studies explored these three design dimensions separately. In this paper, two novel frameworks combining these three design dimensions together are presented and compared. One approach is nested optimization which searches through the whole design space exhaustively. The second approach is called enhanced iterative optimization, which executes the topology optimization and component sizing alternately. A case study shows that the later method can converge to the global optimal design generated from the nested optimization, and is much more computationally efficient. In addition, we also address a known issue of optimal designs: their sens... [more]
Development of a Novel Bidirectional DC/DC Converter Topology with High Voltage Conversion Ratio for Electric Vehicles and DC-Microgrids
Ching-Ming Lai
November 28, 2018 (v1)
Keywords: bidirectional dc/dc converter (BDC), dc-microgrid, electric vehicle (EV), high voltage conversion ratio
The main objective of this paper was to study a bidirectional direct current to direct current converter (BDC) topology with a high voltage conversion ratio for electric vehicle (EV) batteries connected to a dc-microgrid system. In this study, an unregulated level converter (ULC) cascaded with a two-phase interleaved buck-boost charge-pump converter (IBCPC) is introduced to achieve a high conversion ratio with a simpler control circuit. In discharge state, the topology acts as a two-stage voltage-doubler boost converter to achieve high step-up conversion ratio (48 V to 385 V). In charge state, the converter acts as two cascaded voltage-divider buck converters to achieve high voltage step-down conversion ratio (385 V to 48 V). The features, operation principles, steady-state analysis, simulation and experimental results are made to verify the performance of the studied novel BDC. Finally, a 500 W rating prototype system is constructed for verifying the validity of the operation principl... [more]
Analytical Model for Voltage-Dependent Photo and Dark Currents in Bulk Heterojunction Organic Solar Cells
Mesbahus Saleheen, Salman M. Arnab, M. Z. Kabir
November 28, 2018 (v1)
Keywords: analytical model, charge collection, current-voltage characteristics, dark current, organic solar cells, trapping/recombination
A physics-based explicit mathematical model for the external voltage-dependent forward dark current in bulk heterojunction (BHJ) organic solar cells is developed by considering Shockley-Read-Hall (SRH) recombination and solving the continuity equations for both electrons and holes. An analytical model for the external voltage-dependent photocurrent in BHJ organic solar cells is also proposed by incorporating exponential photon absorption, dissociation efficiency of bound electron-hole pairs (EHPs), carrier trapping, and carrier drift and diffusion in the photon absorption layer. Modified Braun’s model is used to compute the electric field-dependent dissociation efficiency of the bound EHPs. The overall net current is calculated considering the actual solar spectrum. The mathematical models are verified by comparing the model calculations with various published experimental results. We analyze the effects of the contact properties, blend compositions, charge carrier transport properties... [more]
Performance Comparison on Repowering of a Steam Power Plant with Gas Turbines and Solid Oxide Fuel Cells
Masoud Rokni
November 28, 2018 (v1)
Keywords: CO2 emission, combined cycles (CC), hybrid cycles, repowering, solid oxide fuel cell (SOFC)
Repowering is a process for transforming an old power plant for greater capacity and/or higher efficiency. As a consequence, the repowered plant is characterized by higher power output and less specific CO₂ emissions. Usually, repowering is performed by adding one or more gas turbines into an existing steam cycle which was built decades ago. Thus, traditional repowering results in combined cycles (CC). High temperature fuel cells (such as solid oxide fuel cell (SOFC)) could also be used as a topping cycle, achieving even higher global plant efficiency and even lower specific CO₂ emissions. Decreasing the operating temperature in a SOFC allows the use of less complex materials and construction methods, consequently reducing plant and the electricity costs. A lower working temperature makes it also suitable for topping an existing steam cycle, instead of gas turbines. This is also the target of this study, repowering of an existing power plant with SOFC as well as gas turbines. Different... [more]
Torque Ripple Reduction of a Novel Modular Arc-Linear Flux-Switching Permanent-Magnet Motor with Rotor Step Skewing
Xiangdong Liu, Zhongxin Gu, Jing Zhao
November 28, 2018 (v1)
Keywords: cogging torque, finite element method (FEM), harmonics, modular arc-linear flux-switching permanent-magnet motor (MAL-FSPM), period ratio of cogging torque to back electromotive force (EMF), rotor step skewing, torque ripple
A novel modular arc-linear flux-switching permanent-magnet motor (MAL-FSPM) used for scanning system instead of reduction gearboxes and kinematic mechanisms is proposed and researched in this paper by the finite element method (FEM). The MAL-FSPM combines characteristics of flux-switching permanent-magnet motor and linear motor and can realize the direct driving and limited angular movement. Structure and operation principle of the MAL-FSPM are analyzed. Cogging torque model of the MAL-FSPM is established. The characteristics of cogging torque and torque ripple are investigated for: (1) distance (dend) between left end of rotor and left end of stator is more than two rotor tooth pitch (τp); and (2) dend is less than two rotor tooth pitch. Cogging torque is an important component of torque ripple and the period ratio of the cogging torque to the back electromotive force (EMF) equals one for the MAL-FSPM before optimization. In order to reduce the torque ripple as much as possible and af... [more]
Economic Impacts of Increased U.S. Exports of Natural Gas: An Energy System Perspective
Kemal Sarıca, Wallace E. Tyner
November 28, 2018 (v1)
Subject: Energy Policy
Keywords: MARket ALlocation (MARKAL)-Macro, U.S. natural gas export policy
With the recent shale gas boom, the U.S. is expected to have very large natural gas resources. In this respect, the key question is would it be better to rely completely on free market resource allocations which would lead to large exports of natural gas or to limit natural gas exports so that more could be used in the U.S.. After accounting for the cost of liquefying the natural gas and shipping it to foreign markets, the current price difference leaves room for considerable profit to producers from exports. In addition, there is a large domestic demand for natural gas from various sectors such as electricity generation, industrial applications, and the transportation sector etc. A hybrid modeling approach has been carried out using our version of the well-known MARket ALlocation (MARKAL)-Macro model to keep bottom-up model richness with macro effects to incorporate price and gross domestic product (GDP) feedbacks. One of the conclusion of this study is that permitting higher natural... [more]
Electrical Market Management Considering Power System Constraints in Smart Distribution Grids
Poria Hasanpor Divshali, Bong Jun Choi
November 28, 2018 (v1)
Keywords: demand side management (DSM), electrical vehicle (EV), micro-grid (MG), power market, power stability, smart grid (SG), source side management (SSM)
Rising demand, climate change, growing fuel costs, outdated power system infrastructures, and new power generation technologies have made renewable distribution generators very attractive in recent years. Because of the increasing penetration level of renewable energy sources in addition to the growth of new electrical demand sectors, such as electrical vehicles, the power system may face serious problems and challenges in the near future. A revolutionary new power grid system, called smart grid, has been developed as a solution to these problems. The smart grid, equipped with modern communication and computation infrastructures, can coordinate different parts of the power system to enhance energy efficiency, reliability, and quality, while decreasing the energy cost. Since conventional distribution networks lack smart infrastructures, much research has been recently done in the distribution part of the smart grid, called smart distribution grid (SDG). This paper surveys contemporary l... [more]
The Applicability of Traditional Protection Methods to Lines Emanating from VSC-HVDC Interconnectors and a Novel Protection Principle
Shimin Xue, Jingyue Yang, Yanxia Chen, Cunping Wang, Zhe Shi, Miao Cui, Botong Li
November 28, 2018 (v1)
Keywords: distance protection, fault resistance, fault ride through (FRT), pilot protection, VSC-HVDC interconnector
Voltage source converter (VSC)-based high voltage direct current (VSC-HVDC) interconnectors can realize accurate and fast control of power transmission among AC networks, and provide emergency power support for AC networks. VSC-HVDC interconnectors bring exclusive fault characteristics to AC networks, thus influencing the performance of traditional protections. Since fault characteristics are related to the control schemes of interconnectors, a fault ride-through (FRT) strategy which is applicable to the interconnector operating characteristic of working in four quadrants and capable of eliminating negative-sequence currents under unbalanced fault conditions is proposed first. Then, the additional terms of measured impedances of distance relays caused by fault resistances are derived using a symmetrical component method. Theoretical analysis shows the output currents of interconnectors are controllable after faults, which may cause malfunctions in distance protections installed on line... [more]
Prospects of Biodiesel Production from Macadamia Oil as an Alternative Fuel for Diesel Engines
Md Mofijur Rahman, Mohammad Rasul, Nur Md Sayeed Hassan, Justin Hyde
November 28, 2018 (v1)
Subject: Other
Keywords: alternative fuel, blending, emission, macadamia oil, properties
This paper investigated the prospects of biodiesel production from macadamia oil as an alternative fuel for diesel engine. The biodiesel was produced using conventional transesterification process using the base catalyst (KOH). A multi-cylinder diesel engine was used to evaluate the performance and emission of 5% (B5) and 20% (B20) macadamia biodiesel fuel at different engine speeds and full load condition. It was found that the characteristics of biodiesel are within the limit of specified standards American Society for Testing and Materials (ASTM D6751) and comparable to diesel fuel. This study also found that the blending of macadamia biodiesel⁻diesel fuel significantly improves the fuel properties including viscosity, density (D), heating value and oxidation stability (OS). Engine performance results indicated that macadamia biodiesel fuel sample reduces brake power (BP) and increases brake-specific fuel consumption (BSFC) while emission results indicated that it reduces the averag... [more]
Application of a Diffuser Structure to Vertical-Axis Wind Turbines
Koichi Watanabe, Shuhei Takahashi, Yuji Ohya
November 28, 2018 (v1)
Subject: Other
Keywords: vertical-axis wind turbine, wind acceleration device, wind lens, wind tunnel experiment
The effects of using a wind acceleration device (wind lens) with vertical-axis wind turbines in wind tunnel experiments were examined. A wind lens consists of a diffuser and flanges, and this study investigated the optimum parameters of their configuration with regard to the power augmentation of the turbines. The wind lens with a flat-panel-type diffuser demonstrated power augmentation by a factor of 2.0 compared with an open wind turbine. An increase from 5° to 20° in the semi-open angle of the diffuser made it possible to generate a 30% high power output over a wide range of tip speed ratios. On that basis, an optimum semi-open angle was determined. For the flat-panel-type diffuser, a recommended diffuser length is the half of the throat width, and its semi-open angle is 20°.The inlet enhanced power augmentation over a wide range of tip speed ratios. The optimum location for the wind lens in the streamwise direction was aligned with the center of the vertical-axis wind turbines. The... [more]
Statistical Analysis of Wave Climate Data Using Mixed Distributions and Extreme Wave Prediction
Wei Li, Jan Isberg, Rafael Waters, Jens Engström, Olle Svensson, Mats Leijon
November 28, 2018 (v1)
Keywords: extreme wave, mixed-distribution model, ocean wave modelling, wave climate, wave energy converter
The investigation of various aspects of the wave climate at a wave energy test site is essential for the development of reliable and efficient wave energy conversion technology. This paper presents studies of the wave climate based on nine years of wave observations from the 2005⁻2013 period measured with a wave measurement buoy at the Lysekil wave energy test site located off the west coast of Sweden. A detailed analysis of the wave statistics is investigated to reveal the characteristics of the wave climate at this specific test site. The long-term extreme waves are estimated from applying the Peak over Threshold (POT) method on the measured wave data. The significant wave height and the maximum wave height at the test site for different return periods are also compared. In this study, a new approach using a mixed-distribution model is proposed to describe the long-term behavior of the significant wave height and it shows an impressive goodness of fit to wave data from the test site.... [more]
Exploring the Spatial Heterogeneity of Individual Preferences for Ambient Heating Systems
Cristiano Franceschinis, Riccardo Scarpa, Mara Thiene, John Rose, Michele Moretto, Raffaele Cavalli
November 28, 2018 (v1)
Keywords: ambient heating systems choices, mixed logit model, spatial variables, willingness to pay
The estimation and policy use of spatially explicit discrete choice models has yet to receive serious attention from practitioners. In this study we aim to analyze how geographical variables influence individuals’ sensitivity to key features of heating systems, namely investment cost and CO₂ emissions. This is of particular policy interest as heating systems are strongly connected to two major current environmental issues: emissions of pollutants and increased use of renewable resources. We estimate a mixed logit model (MXL) to spatially characterize preference heterogeneity in the mountainous North East of Italy. Our results show that geographical variables are significant sources of variation of individual’s sensitivity to the investigated attributes of the system. We generate maps to show how the willingness to pay to avoid CO₂ emissions varies across the region and to validate our estimates ex-post. We discuss why this could be a promising approach to inform applied policy decision... [more]
Energy Optimization and Management of Demand Response Interactions in a Smart Campus
Antimo Barbato, Cristiana Bolchini, Angela Geronazzo, Elisa Quintarelli, Andrei Palamarciuc, Alessandro Pitì, Cristina Rottondi, Giacomo Verticale
November 28, 2018 (v1)
Keywords: energy management system, renewable energy sources (RESes), smart city, smart grid
The proposed framework enables innovative power management in smart campuses, integrating local renewable energy sources, battery banks and controllable loads and supporting Demand Response interactions with the electricity grid operators. The paper describes each system component: the Energy Management System responsible for power usage scheduling, the telecommunication infrastructure in charge of data exchanging and the integrated data repository devoted to information storage. We also discuss the relevant use cases and validate the framework in a few deployed demonstrators.
A Computational Analysis of Functionally Graded Anode in Solid Oxide Fuel Cell by Involving the Correlations of Microstructural Parameters
Chao Wang
November 28, 2018 (v1)
Subject: Materials
Keywords: conventional non-graded electrodes, functionally graded electrodes (FGEs), microstructural parameters correlations, numerical simulation, solid oxide fuel cells (SOFCs)
Functionally-graded electrodes (FGEs) have shown great potential in improving solid oxide fuel cells’ (SOFCs) performance. In order to produce predictions of real FGE operations, a comprehensive numerical model that takes into account all the microstructure parameters, together with two sub model correlations, i.e., porosity-tortuosity, and porosity-particle size ratio, is utilized, aiming to provide a novel approach to demonstrate the advantages of FGEs for SOFCs. Porosity grading and particle size grading are explored by using this implemented model as a baseline. Multiple types of grading cases are tested in order to study the FGEs at a micro-scale level. Comparison between the FGEs and conventional non-graded electrodes (uniform random composites) is conducted to investigate the potential of FGEs for SOFCs. This study essentially focuses on presenting a new perspective to examine the real-world FGEs performance by involving the correlations of physically connected micro-structural... [more]
Low-Temperature, Chemically Grown Titanium Oxide Thin Films with a High Hole Tunneling Rate for Si Solar Cells
Yu-Tsu Lee, Fang-Ru Lin, Ting-Chun Lin, Chien-Hsun Chen, Zingway Pei
November 28, 2018 (v1)
Subject: Materials
Keywords: band alignment, chemically grown, heterojunction, hole tunneling, titanium oxide
In this paper, we propose a chemically grown titanium oxide (TiO₂) on Si to form a heterojunction for photovoltaic devices. The chemically grown TiO₂ does not block hole transport. Ultraviolet photoemission spectroscopy was used to study the band alignment. A substantial band offset at the TiO₂/Si interface was observed. X-ray photoemission spectroscopy (XPS) revealed that the chemically grown TiO₂ is oxygen-deficient and contains numerous gap states. A multiple-trap-assisted tunneling (TAT) model was used to explain the high hole injection rate. According to this model, the tunneling rate can be 10⁵ orders of magnitude higher for holes passing through TiO₂ than for flow through SiO₂. With 24-nm-thick TiO₂, a Si solar cell achieves a 33.2 mA/cm² photocurrent on a planar substrate, with a 9.4% power conversion efficiency. Plan-view scanning electron microscopy images indicate that a moth-eye-like structure formed during TiO₂ deposition. This structure enables light harvesting for a high... [more]
Dynamic Energy Management of Hybrid Energy Storage Systems with a Hierarchical Structure
Chang Ye, Shihong Miao, Qi Lei, Yaowang Li
November 28, 2018 (v1)
Keywords: energy management, hierarchical storage structure, hybrid system
In power system control unicontrol with single storage units or centralized control with multiple storage units to meet different level targets is challenging. Considering the charge and discharge characteristics of storage devices, this paper proposes a hierarchical configuration structure of a battery and supercapacitor mixed storage scenario, and develops a convenient control method for accessing various DC loads and can central manage mass batteries in one place. Aiming at the optimal management of large scale battery storage, the paper proposes a three-layer battery hierarchical control structure and the control objects and control circuits are discussed. Simulation studies are used to verify the control effect of the hierarchical storage system and the results show that the strategy can effectively decrease photovoltaic output fluctuation.
Numerical Study of Solidification in a Plate Heat Exchange Device with a Zigzag Configuration Containing Multiple Phase-Change-Materials
Peilun Wang, Dacheng Li, Yun Huang, Xingang Zheng, Yi Wang, Zhijian Peng, Yulong Ding
November 28, 2018 (v1)
Keywords: heat exchange, multiple phase-change-materials (m-PCMs), numerical modelling, Process Intensification, solidification, zigzag configuration
Latent heat thermal energy storage (TES) plays an important role in the advocation of TES in contrast to sensible energy storage because of the large storage energy densities per unit mass/volume possible at a nearly constant thermal energy. In the current study, a heat exchange device with a zigzag configuration containing multiple phase-change-materials (m-PCMs) was considered, and an experimental system was built to validate the model for a single PCM. A two-dimensional numerical model was developed using the ANSYS Fluent 14.0 software program. The energy fractions method was put forward to calculate the average Ste number and the influence of Re and Ste numbers on the discharge process were studied. The influence of phase change temperature among m-PCMs on the solidification process has also been studied. A new boundary condition was defined to determine the combined effect of the Re and Ste numbers on the discharging process. The modelling results show that for a given input power... [more]
Experimental Study of Natural Convection Cooling of Vertical Cylinders with Inclined Plate Fins
Jong Bum Lee, Hyun Jung Kim, Dong-Kwon Kim
November 28, 2018 (v1)
Subject: Other
Keywords: inclined plate fin, natural convection, nusselt number
In this paper, natural convection from vertical cylinders with inclined plate fins is investigated experimentally for use in cooling electronic equipment. Extensive experimental investigations are performed for various inclination angles, fin numbers, and base temperatures. From the experimental data, a correlation for estimating the Nusselt number is proposed. The correlation is applicable when the Rayleigh number, inclination angle, and fin number are in the ranges 100,000⁻600,000, 30°⁻90°, and 9⁻36, respectively. Using the correlation, a contour map depicting the thermal resistance as a function of the fin number and fin thickness is presented. Finally, the optimal thermal resistances of cylinders with inclined plate fins and conventional radial plate fins are compared. It is found that that the optimal thermal resistance of the cylinder with inclined fins is 30% lower than that of the cylinder with radial plate fins.
Combined Turbine and Cycle Optimization for Organic Rankine Cycle Power Systems—Part B: Application on a Case Study
Angelo La Seta, Andrea Meroni, Jesper Graa Andreasen, Leonardo Pierobon, Giacomo Persico, Fredrik Haglind
November 28, 2018 (v1)
Keywords: axial turbine, cycle optimization, mean line model, organic Rankine cycle (ORC), Surrogate Model, turbine design, turbine performance
Organic Rankine cycle (ORC) power systems have recently emerged as promising solutions for waste heat recovery in low- and medium-size power plants. Their performance and economic feasibility strongly depend on the expander. The design process and efficiency estimation are particularly challenging due to the peculiar physical properties of the working fluid and the gas-dynamic phenomena occurring in the machine. Unlike steam Rankine and Brayton engines, organic Rankine cycle expanders combine small enthalpy drops with large expansion ratios. These features yield turbine designs with few highly-loaded stages in supersonic flow regimes. Part A of this two-part paper has presented the implementation and validation of the simulation tool TURAX, which provides the optimal preliminary design of single-stage axial-flow turbines. The authors have also presented a sensitivity analysis on the decision variables affecting the turbine design. Part B of this two-part paper presents the first applic... [more]
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