Design charts for impulse turbine wave energy extraction using experimental data

This study presents newly developed charts to aid in early design of impulse turbine for wave energy extraction. These charts, based on the available experimental data, represent a simple approach to the performance evaluation of the turbine. The novel approach is applied in a case study that considers the optimum diameter design selection of next-generation impulse turbine power take-off. This allowed the selection of the correct impulse turbine sizing for a required rated power. The result is consistent for such an application, where the optimum rotor diameter would be 1.6 m for a maximum rated power of 400 kW.     

Design optimization and site matching of direct-drive permanent magnet wind power generator systems

This paper investigates the possible site matching of the direct-drive wind turbine concepts based on the electromagnetic design optimization of permanent magnet (PM) generator systems. Firstly, the analytical models of a three-phase radial-flux PM generator with a back-to-back power converter are presented. The optimum design models of direct-drive PM wind generation system are developed with an improved genetic algorithm, and a 500-kW direct-drive PM generator for the minimal generator active material cost is compared to demonstrate the effectiveness of the design optimization. Forty-five PM generator systems, the combinations of five rated rotor speeds in the range of 10–30 rpm and nine power ratings from 100 kW to 10 MW, are optimally designed, respectively. The optimum results are compared graphically in terms of the generator design indexes. Next, according to the design principle of the maximum wind energy capture, the rotor diameter and the rated wind speed of a direct-drive wind turbine with the optimum PM generator are determined. The annual energy output (AEO) is also presented using the Weibull density function. Finally, the maximum AEO per cost (AEOPC) of the optimized wind generator systems is evaluated at eight potential sites with annual mean wind speeds in the range of 3–10 m/s, respectively. These results have shown the suitable designs for the optimum site matching of the investigated PM generator systems.     

Transonic turbine blade loading calculations using different turbulence models – effects of reflecting and non-reflecting boundary conditions

The objective of this study is to simulate the transonic gas turbine blade-to-blade compressible fluid flow. We are interested mainly in the determination of the pressure distribution around the blade. The particular blade architecture makes these simulations more complex due to the variety of phenomena induced by this flow.Our study is based on the experiment performed by Giel and colleagues. Tests were conducted in a linear cascade at the NASA Glenn Research Center. The test article was a turbine rotor with design flow turning of 136° and an axial chord of 12.7 cm.Simulations were performed on an irregular quadratic structured grid with the FLUENT software package which solves the Navier–Stokes equations by using finite volume methods. Two-dimensional stationary numerical simulations were made under turbulent conditions allowing us to compare the characteristic flow effects of Reflecting Boundary Conditions (RBC) and Non-Reflecting Boundary Conditions (NRBC) newly implemented in FLUENT 6.0. Many simulations were made to compare different turbulence models: a one equation model (Spalart–Allmaras), several two-equation models (k–ε, RNG k–ε, Realizable k–ε, SST k–ω), and a Reynolds-stress model (RSM). Also examined were the effects of the inlet turbulence intensities (0.25% and 7%), the exit Mach numbers (1.0 and 1.3) and the inlet Reynolds numbers (0.5 × 10⁶ and 1 × 10⁶). The results obtained show a good correlation with the experiment.     

Design and cost analysis of low head simple reaction hydro turbine for remote area power supply

This paper is aimed at exploring the performance characteristics of a simple reaction hydro turbine for power generation. Using principles of conservation of mass, momentum and energy, the governing equations have been identified for an ideal case of no frictional losses. The paper also describes the conception of a cross-pipe rotor for remote area electricity production. Using the ideal governing equations an optimized geometry of the rotor was selected for the working head of 5 m. Theoretical analysis of the self-governing characteristics has been presented. Experiments were carried out for 2, 3, 4 and 5 m head and evaluated against theoretical results. Split pipe turbine model is presented with detail layout, while different methods of experimentation are explored for different output requirements with varied heads. Various losses in the system are discussed, quantified and included in the graphical format. It is also demonstrated that the experimental power outputs do not have the same tendencies as theoretical predictions and decreases due to jet interference beyond a certain rotational speed as it passes the maximum power point.     

Air-side thermal hydraulic performance of offset strip fin aluminum heat exchangers

Experimental studies on the air-side heat transfer and pressure drop characteristics for 16 types offset strip fins and flat tube heat exchangers were performed. Parameters including fin space s, fin height h, fin thickness t, fin length l and flow length d, a series of tests were conducted in region of air-side Reynolds number 500–7500, at a constant tube-side water flow rate of 2.5 m³/h. The air-side thermal performance data were analyzed using the effectiveness-NTU method. The heat transfer coefficients and pressure drop data with different fin space s, fin height h, and fin length l were reported in terms of frontal air velocity. The general correlations for Colburn j-factor and Fanning fraction f-factor were derived by regression analysis and F significance test. The correlations for j and f factors can predict 95% and 90% of the experimental data within  ± 10%. And the average deviations of predictive data for the j and f factors are 0.2% and 1.2%, mean deviations are 4.2% and 5.3%.     

Mist film cooling simulation at gas turbine operating conditions

Air film cooling has been successfully used to cool gas turbine hot sections for the last half century. A promising technology is proposed to enhance air film cooling with water mist injection. Numerical simulations have shown that injecting a small amount of water droplets into the cooling air improves film-cooling performance significantly. However, previous studies were conducted at conditions of low Reynolds number, temperature, and pressure to allow comparisons with experimental data. As a continuous effort to develop a realistic mist film cooling scheme, this paper focuses on simulating mist film cooling under typical gas turbine operating conditions of high temperature and pressure. The mainstream flow is at 15 atm with a temperature of 1561 K. Both 2D and 3D cases are considered with different hole geometries on a flat surface, including a 2D slot, a simple round hole, a compound-angle hole, and fan-shaped holes. The results show that 10–20% mist (based on the coolant mass flow rate) achieves 5–10% cooling enhancement and provides an additional 30–68 K adiabatic wall temperature reduction. Uniform droplets of 5–20 μm are used. The droplet trajectories indicate the droplets tend to move away from the wall, which results in a lower cooling enhancement than under low pressure and temperature conditions. The commercial software Fluent is adopted in this study, and the standard k–ε model with enhanced wall treatment is adopted as the turbulence model.     

Decomposition reaction of LiPF6-based electrolytes for lithium ion cells

The decomposition of LiPF₆ electrolytes with water was studied by measuring the water content after storage. The solvents used were ethylene carbonate (EC) + diethyl carbonate (DEC), EC + dimethyl carbonate (DMC), propylene carbonate (PC) + DEC, and PC + DMC mixed by the volume ratio 1 to 1, respectively. The experimental results were in good agreement with −d[H₂O]/dt = k[H₂O]²[LiPF₆]. We obtained rate constants (k) from this empirical equation, with k increasing in the order of EC + DMC < EC + DEC < PC + DMC < PC + DEC. This order is in inverse proportion to the order of the dielectric constants of these solvents. Nonionized LiPF₆ dissociates to PF₅ and LiF in organic solvents, and PF₅ reacts with water. A solvent with a high dielectric constant increases the ionization of LiPF₆, thereby suppressing the reaction with water.     

Hydrodynamics and heat transfer in swirl flow under conditions of one-side heating. Part 1: Pressure drop and single-phase heat transfer

The paper gives the basic results of experimental investigation of hydrodynamics and heat transfer in heat-absorbing devices of the ITER thermonuclear reactor, which are subjected to one-side heating. The entire array of experimental data is obtained in the following range of parameters of water flow: pressure p = 0.7–2.0 MPa, mass flux G = 340–25,000 kg/(m² s), inlet water temperature T_in = 15–60 °C. The experiments are performed with turbulent swirl flows of water for twisted tapes with the flow swirl coefficient k = 0.90, 0.66, 0.49, 0.39, 0.25, 0.19, and 0, as well for test sections without a tape. Given in the first part of the paper are the data on pressure drop and single-phase convective heat transfer. Appropriate calculation formulas are derived, which reliably generalize the experimental data.     

Optimised mixing and flow resistance during shear flow over a rib roughened boundary

A series of numerical investigations has been performed to study the effect of lower boundary roughness on turbulent flow in a two-dimensional channel. The roughness spacing to height ratio, w/k, has been investigated over the range 0.12 to 402 by varying the horizontal rib spacing. The square roughness elements each have a cross-sectional area of (0.05 H)², where H is the full channel height. The Reynolds number, Re_τ is fixed based on the value of the imposed pressure gradient, dp/dx, and is in the range 6.3 × 10³ − 4.5 × 10⁴. A Reynolds Averaged Navier–Stokes (RANS) based turbulence modelling approach is adopted using a commercial CFD code, ANSYS-CFX 14.0. Measurements of eddy viscosity and friction factor have been made over this range to establish the optimum spacings to produce maximum turbulence enhancement, mixing and resistance to flow. These occur when w/k is approximately 7. It is found that this value is only weakly dependent on Reynolds number, and the decay rate of turbulence enhancement as a function of w/k ratio beyond this optimum spacing is slow. The implications for heat transfer design optimisation and particle transport are considered.     

Heat transfer in rotating scale-roughened trapezoidal duct at high rotation numbers

An experimental study of heat transfer in a radially rotating trapezoidal duct with two bevel walls roughened by deepened scales is performed with cooling applications to gas turbine rotor blades. Laboratory scale heat transfer data along the centerlines of two scale-roughened walls is generated within the parametric ranges of 7500 ? Re ? 15,000, 0 ? Ro ? 1.8 and 0.13 ? Δρ/ρ ? 0.42. No previous study has examined the heat transfer in a rotating scale-roughened channel and the present Ro range extends considerably from other researches to date. A selection of experimental data illustrates the individual and interactive impacts of Re, Ro and buoyancy number (Bu) on local heat transfer through which the manners of isolated and synergetic influences of Coriolis force and rotating buoyancy on heat transfer are examined. Local Nusselt number ratios between rotating and static channels on the stable (leading) and unstable (trailing) scale-roughened surfaces with Ro varying from 0.1 to 1.8 fall in the ranges of 0.8–2 and 1.1–2.5, respectively. Rotating buoyancy effects are weakened as Ro increases that impair local heat transfer for the present test configurations. Empirical heat transfer correlations for developed flow regions on two scale-roughened surfaces are derived that permit the evaluation of interactive and individual effects of Re, Ro and Bu on local heat transfer.     

Simulation and experiment of thermal energy management with phase change material for ageing LiFePO4 power battery

Thermal energy management performance of ageing commercial rectangular LiFePO₄ power batteries using phase change material (PCM) and thermal behavior related to thermal conductivity between the PCM and the cell are discussed in this paper. The heat sources are simplified according to the experimental results of the cells discharged at 35 A (≈5 C). 3-D modules of a single cell and battery pack are formulated, respectively. The results show that the thermal resistance in the cell leads to an inevitable temperature difference. It is necessary to improve the thermal conductivity and to lower the melting point of the PCM for heat transfer enhancement. The PCM with a melting point lower than 45 °C will be more effective for heat dissipation, with a desired maximum temperature below 50 °C. The temperature difference in the whole unit before PCM melting will be decreased significantly. In addition, a proper k_PCM:k_c is necessary for a well designed battery thermal energy management system.     

Performance evaluation method of solar-assisted heat pump water heater

The present study derives a simple linear correlation for the performance evaluation of different solar-assisted heat pump water heater (ISAHP). The correlation was derived from the principle of energy conservation with some simplifications. The correlation is then verified using the long-term outdoor field test data of four different ISAHP. The problems of seasonal repeatability and method of data scattering were examined. From that, a standard performance test method is proposed. The test method suggests that only the measurement of instantaneous solar incident radiation on horizontal surface, ambient temperature, hot water temperature in the storage tank, total mass of water in the storage tank and total power input to the ISAHP are required. It is suggested to select the value of COP at T_f − T_a,ave = 15 °C as the characteristic COP for performance comparison of ISAHP. It is found from the test results that the same performance correlation holds for ISAHP operating with single or dual energy source.     

Suitability of three different two-equation turbulence models in predicting film cooling performance over a rotating blade

The suitability of three different two-equation turbulence models in predicting film cooling effectiveness on a rotating blade was investigated and they are the commonly used standard k-ε model, the k-ω model and the shear stress transport k-ω model. To fulfill this target, both numerical simulation and the experimental investigation were carried out for a rotating blade having a flat test surface with a 4 mm diameter straight circular cooling hole in 30° inclined injection. The blade rotated at five different speeds of 0, 300, 500, 800 and 1000 rpm. The momentum ratio was set to be 0.285 and the Reynolds (Re_D) number based on the mainstream velocity and hydraulic diameter of the mainstream channel is 1.45 × 10⁵. The averaged density ratio was chosen to be 1.026 with air as both the coolant and the mainstream. Comparison between the numerical work and the experimental results indicated that (1) the rotating speed is the most critical parameter influencing the film cooling effectiveness distributions and the pressure surface could be remarkably different from the suction surface, (2) as for the algebraic averaged film cooling effectiveness, numerical predictions of the three turbulence models all overshoot compared with the experimental results, (3) among the three turbulence models, the standard k-ε model gave the poorest prediction.     

Exergy and reliability analysis of wind turbine systems: A case study

The present study undertakes an exergy and reliability analysis of wind turbine systems and applies to a local one in Turkey: the exergy performance and reliability of the small wind turbine generator have been evaluated in a demonstration (1.5 kW) in Solar Energy Institute of Ege University (latitude 38.24 N, longitude 27.50 E), Izmir, Turkey. In order to extract the maximum possible power, it is important that the blades of small wind turbines start rotating at the lowest possible wind speed. The starting performance of a three-bladed, 3 m diameter horizontal axis wind turbine was measured in field tests. The average technical availability, real availability, capacity factor and exergy efficiency value have been analyzed from September 2002 to November 2003 and they are found to be 94.20%, 51.67%, 11.58%, and 0–48.72%, respectively. The reliability analysis has also been done for the small wind turbine generator. The failure rate is high to an extent of 2.28×10⁻⁴ h⁻¹ and the factor of reliability is found to be 0.37 at 4380 h. If failure rate can be decreased, not only this system but also other wind turbine systems of real availability, capacity factor and exergy efficiency will be improved.     

Heat transfer study in a discoidal system: The influence of rotation and space between disks

This article presents an experimental study of the local heat transfer on the rotor surface in a discoidal rotor–stator system air-gap in which an air jet comes through the stator and impinges the rotor. To determine the surface temperatures, measurements were taken on the rotor, using an experimental technique based on infrared thermography. A thermal balance was used to identify the local convective heat transfer coefficient. The influence of the dimensionless spacing interval G between the disks and of the rotational Reynolds number Re was measured and compared with the data available in bibliography. Local convective heat transfer coefficients were obtained for an axial Reynolds number Re_j = 41.6 × 10³, a rotational Reynolds number Re between 0.2 × 10⁵ and 5.16 × 10⁵, and a dimensionless spacing interval G ranging from 0.01 to 0.16.     

An experimental and numerical study of forced convection in a microchannel with negligible axial heat conduction

Experiments are conducted for laminar forced convection of water in a microchannel under partially-heated and fully-heated conditions on one wall with negligible axial heat conduction. The microchannel had a trapezoidal cross-sectional shape, with a hydraulic diameter of 155 μm and a heating length of 30 mm. Three-dimensional numerical simulations, based on the Navier–Stokes equations and energy equation, are obtained for forced convection of water in this microchannel under the same experimental conditions. It is found that the numerical predictions of wall temperatures and local Nusselt numbers are in good agreement with experimental data. This confirms that classical Navier–Stokes and energy equations are valid for the modeling of convection in a microchannel having a hydraulic diameter as small as 155 μm. For a microchannel with the same cross-sectional shape with one-wall heated and a heating length of 100 mm, numerical results show that the thermal entrance length is given by z = 0.15RePrD_h, with the fully-developed Nusselt number approaching a constant value of 4.00.     

Mass transfer coefficients associated with the mixing of a confined gas volume by the random motion of loose spheres

This investigation quantifies the change in mass transfer within a confined gas volume subjected to mixing by loose spheres. A cylindrical vessel containing between 1 and 50 Teflon spheres in a tracer gas is vigorously shaken. Extractive sampling provides time histories of tracer gas concentrations extracted from the vessel. Fitting the results from a simple 1-D mass transfer model to the experimental data yields an effective mass transfer coefficient k′ for each experimental condition. Compared to diffusive mass transfer where k′ = D_ab = 7.58 × 10⁻⁶ m²/s, k′ exhibits a cubic dependency on the number of spheres with a maximum at 17 spheres where k′ = 3.5 × 10⁻³ m²/s.     

Wind energy as a potential generation source at Ras Benas,Egypt

Analysis of the wind characteristics in Ras Benas city located on the east coast of Red Sea in Egypt using measured data (wind, pressure and temperature) and Weibull function were made.Statistical analysis model to evaluate the wind energy potential was introduced. According to the power calculations done for the site, the annual mean wind density is 315 kW/m² at a height of 70 m above ground level. This station has a huge wind energy potential for electricity generation, especially during spring and summer seasons, comparing with some European countries.In addition, the monthly wind turbine efficiency parameter (η_monthly) has been calculated by using a commercial wind turbine 1 MW with 70 m hub height to help designers and users in evaluating the potentialities and choosing the suitable wind turbine for the considered site. The use of wind turbine with capacity greater than 1000 kW at this station was recommended.Ras Benas station was selected to install 30 MW-wind farm consists of 20 commercial wind turbines (Nordex S 77) with hub heights and Rotor diameter were 100 and 77 m, respectively. This site has annual wind speed more than 9.8 m/s at 100 m height and enough area to locate these turbines.The estimated energy production using WASP Program of these wind farm was 130 GWh/year. Furthermore, the production costs was found 1.3€ cent/kWh, which is a competition price at the wind energy world market.     

Effect of nanoparticles size on thermal performance of nanofluid in a trapezoidal microchannel-heat-sink

This paper deals with spherical nanoparticles size effects on thermal performance and pressure drop of a nanofluid in a trapezoidal microchannel-heat-sink (MCHS). Eulerian–Eulerian two-phase numerical approach is utilized for forced convection laminar, incompressible and steady three dimensional flow of copper-oxide nanoparticles with water as base fluid at 100 to 200 nm diameter and 1% to 4% volume concentration range. Continuity, momentum, energy and volume conservation equations are solved at whole of the computational domain via finite volume method. Obtained results signify that pressure drop increases 15% at Re = 500 and 1% volume concentration while nanoparticles diameter increases from 100 to 200 nm. By increasing volume concentration, nanoparticles size effect becomes more prominent and it is observed that increment rate of pressure drop is intensified for above 150 nm particles diameter. Unlike the pressure drop, heat transfer decreases with an increase in nanoparticles diameter. Also, it is observed that with an increase in nanoparticles diameter, average Nusselt number of base fluid decreases more than that of the nanoparticles and this signifies that base fluid has more efficacy on thermal performance of copper-oxide nanofluid.     

Development research on composite adsorbents applied in adsorption heat pump

A novel adsorbent design technique base on the concept of Kelvin equation was proposed to develop hydrophilic adsorbent applicable to water vapor adsorption heat pump (AHP) for high performance. In the process, the composite adsorbent was prepared after silica gel was synthesized in the pores of activated carbons by impregnating activated carbons in sodium silicate solution. Two kinds of activated carbons were tested to produce composite adsorbent and to investigate the performance by measuring the adsorption isotherms of water vapor and pore structure characteristics. All adsorption isotherms of the silica impregnated activated carbons prepared shifted to a lower region of water vapor pressure compared to those of the raw activated carbons. The volume-based amount of adsorption in the AHP operation range (φ = 0.1–0.4) for the adsorbents prepared at sodium silicate solution concentration of 10 wt.% and impregnating time of 48 h are 5.88 and 2.62 times that of the raw activated carbons (AC1 and AC2), respectively. Based on the Kelvin equation, it is clarified that the contact angle and the volume of pore radius greater than 1.2 nm decrease with the increase of sodium silicate solution concentration for the novel composite adsorbents, which contributes the isothermals shift to lower relative pressure range.