Aero—Acoustics of Modern Transonic Fans—Fan Noise Reduction from Its Sources

The noise of aerodynamics nature from modern transonic fan is examined from its sources with the perspective of noise reduction through aero-acoustics design using advanced Computational Fluid Dynamics (CFD) tools. In particular the problems associated with the forward propagating noise in the front is addressed. It is identified that the shock wave spillage from the leading edge near the fan tip is the main source of the tone noise. Two different approaches have been studied to reduce the forward arc tone noise and two state-of-art transonic fans are designed using the strategies developed. The following rig tests show that while the fans exhibit other noise problems, the primary goals of noise reduction have been achieved through both fans and the novel noise reduction concept vindicated.     

Photographic Study of Obstacle—Induced Disturbations of Transonic Turbine Cascade Flow

INTRoDUCTIONTheturbineandtalalcompressorcascadeflowsarestronglyeduellcedbyb0ththeupstreamanddown-8treamunsteadybotmdaryconditions.Theunsteadi-ness0fthesllowsisduetotherelativemotionofthestatorandrotorblades.Thispr0blemhasbeeninVeSigatednumericallyandexperimelltallyforovertenyears.ThemajorityofthepapersconsideredtheeffectofuPstreamb0undaryconditions.Sharmaetal.(1992)estAnatedthatthewakesandtheshockwavesatthetrailinedgesofthestatorcascadecausethelossesofther0torcascadefiownearlytwiceaslarg…     

Challenges of Tomorrowm——Fire Hazards of Systems Using Renewable Sources of Energy

Dramatic climate change, caused by over consumption of coal, oil and other traditional energy sources, as well as exhaustion of their reserves, imposed technological need to look for their substitution with new, renewable energy sources. The exploitation of these new forms of energy, solar, wind, earth and bio-fuels, initiated the development and application of new technologies, so far unused in practice. Rapid development and wide application of installations for use of renewable energy in many households and companies opened a whole new risk and danger in the fire protection field. With the purpose of introducing this problem to engineers in the area of fire protection, health and safety at work, this paper systematically presents various types of facilities for exploitation of renewable energy sources as well as potential dangers, risks and issues related to their safe operation.     

Noise Characteristics of Centrifugal Blower with Low Solidity Cascade Diffuser （Noise Reduction by means of Small Groove Located at LSD Blade Leading Tip）

This paper deals with the effect of the blade tip-groove of the low solidity cascade diffuser (LSD) on the blower characteristic and the noise generated by the LSD. The small grooves were set up at the root and/or tip near the leading edge of the LSD blade. In order to clarify the mechanism of noise increase due to LSD and also to reduce the noise, the relationships between the noise increase based on the LSD, the LSD performance and the secondary flow formed additionally by the tip-groove were investigated experimentally as well as numerically, especially analyzing flow behaviors in the LSD in view points of flow separation on the suction surface of the LSD blade and the secondary flow on the side walls. By reducing the stagnation region smaller near the root and/or tip of the LSD blade leading edge, the secondary flow behavior changes remarkably around the LSD blade, as a result, the noise level and the blower characteristics vary. It can be concluded that, by means of a small tip-groove located only at the shroud side near the LSD blade leading edge, the noise generated by the LSD can be reduced without deteriorations of the LSD performance and the blower characteristics as well.     

Flow Field and Performance of Cross Flow Fans——Experimental and Theoretical Investigations

Due to the construction and the operating principle the prediction of performance of Cross Flow Fans (CFF) is difficult and the knowledge about the internal flow regime is limited. To investigate the impact of geometrical parameters on the performance of CFF, experimental investigations, using Particle Imaging Velocimetry (PIV), and CFD calculations were carried out. Some results of PIV measurements and CFD calculations are presented, which give an impression of the internal flow and confirm the numerical calculations.     

Effects of Diffuser Vane Geometry on Interaction Noise Generated from a Centrifugal Compressor

The characteristics of interaction tone noise radiated from a centrifugal compressor with a vaned diffuser are discussed by experiments, including visualization techniques using the oil-film method. Research attention is paid to the leading edge geometries of the diffuser vanes that are deeply related to the generation mechanism of the interaction tone noise. The compressor-radiated noise can be reduced by several decibels by setting some clearances in both the hub and shroud surfaces of the diffuser wall along with some decline in the pressure-rise coefficient. Since the decline turned out to be caused by the flow impingement and also by the secondary flow within the diffuser passages, several new types of diffuser vane geometries which do not detract from both the performance and noise level are developed and utilized for the experiments. The presented diffuser vane geometries will offer a few basic guidelines for the diffuser vane design.     

Passive Control of Transonic Flow Fields with Shock Wave Using Non—equilibrium Condensation and Porous wall

When non-equilibrium condensation occurs in a supersonic flow field, the flow is affected by the latent heat released. In the present study, in order to control the transonic flow field with shock wave, a condensing flow was produced by an expansion of moist air on a circular bump model and shock waves were occurred in the supersonic parts of the fields. Furthermore, the additional passive technique of shock / boundary layer interaction using the porous wall with a cavity underneath was adopted in this flow field. The effects of these methods on the shock wave characteristics were investigated numerically and experimentally. The result obtained showed that the total pressure loss in the flow fields might be effectively reduced by the suitable combination between non-equilibrium condensation and the position of porous wall.     

Assessment of Signals from a Tissue Phantom Subjected to Radiation Sources of Temporal Spans of the Order of a Nano-, Pico-, and Femto-Second—A Numerical Study

This article reports and analyzes signals originating from a human tissue phantom subjected to a short-pulse laser that can have a temporal span of the order of a nano-, pico-, or a femto-second. Temporal spans having both step and Gaussian distributions are considered. To assess the case of an actual tissue phantom which is an inhomogeneous medium, results have been analyzed by also considering tissue phantom to be a homogeneous medium having the same optical thickness as that of the total optical thickness of the inhomogeneous (real) tissue. Signals for a laser having a temporal span of the order of a nano-second have been found to be more distinct and last longer. With inhomogeneous tissue, for both step and Gaussian temporal profiles, temporal spans of the signals have been found to be more. The analysis has been done using the finite volume method.     

The value of domestic building energy efficiency — evidence from Ireland

Following the transposition of the EU Energy Performance of Buildings Directive into Irish law, all properties offered for sale or to let in Ireland are obliged to have an energy efficiency rating. This paper analyses the effect of energy efficiency ratings on the sale and rental prices of properties in the Republic of Ireland. Using the Heckman selection technique we model the decision to advertise the energy efficiency rating of a property and the effect of energy efficiency ratings on property values. Our results show that energy efficiency has a positive effect on both the sales and rental prices of properties, and that the effect is significantly stronger in the sales segment of the property market. We also analyse the effect of energy efficiency across different market conditions and we find that the effect of the energy rating is generally stronger where market conditions are worse.     

Technical aspects of production and analysis of biodiesel from used cooking oil—A review

The increasing awareness of the depletion of fossil fuel resources and the environmental benefits of biodiesel fuel has made it more attractive in recent times. The cost of biodiesel, however, is the major hurdle to its commercialization in comparison to petroleum-based diesel fuel. The high cost is primarily due to the raw material, mostly neat vegetable oil. Used cooking oil is one of the economical sources for biodiesel production. However, the products formed during frying, can affect the transesterification reaction and the biodiesel properties. This paper attempts to review various technological methods of biodiesel production from used cooking oil. The analytical methods for high quality biodiesel fuel from used cooking oil like GC, TLC, HPLC, GPC and TGA have also been summarized in this paper. In addition, the specifications provided by different countries are presented. The fuel properties of biodiesel fuel from used cooking oil were also reviewed and compared with those of conventional diesel fuel.     

Harmonising bioenergy resource potentials—Methodological lessons from review of state of the art bioenergy potential assessments

Published estimates of the potential of bioenergy vary widely, mainly due to the heterogeneity of methodologies, assumptions and datasets employed. These discrepancies are confusing for policy and it is thus important to have scientific clarity on the basis of the assessment outcomes. Such clear insights can enable harmonisation of the different assessments. This review explores current state of the art approaches and methodologies used in bioenergy assessments, and identifies key elements that are critical determinants of bioenergy potentials. We apply the lessons learnt from the review exercise to compare and harmonise a selected set of country based bioenergy potential studies, and provide recommendations for conducting more comprehensive assessments. Depending on scenario assumptions, the harmonised technical biomass potential estimates up to 2030 in the selected countries range from 5.2 to 27.3 EJ in China, 1.1 to 18.8 EJ in India, 2.0 to 10.9 EJ in Indonesia, 1.6 to 7.0 EJ in Mozambique and 9.3 to 23.5 EJ in the US. From the review, we observed that generally, current studies do not cover all the basic (sustainability) elements expected in an ideal bioenergy assessment and there are marked differences in the level of parametric detail and methodological transparency between studies. Land availability and suitability lack spatial detail and especially degraded and marginal lands are poorly evaluated. Competition for water resources is hardly taken into account and biomass yields are based mostly on crude ecological zoning criteria. A few studies take into account improvements in management of agricultural and forestry production systems, but the underlying assumptions are hardly discussed. Competition for biomass resources among the various applications is crudely analysed in most studies and key assumptions such as demographic dynamics, biodiversity protection criteria, etc. are not explicitly discussed. To facilitate more comprehensive bioenergy assessments, we recommend an integrated analytical framework that includes all the key factors, employs high resolution geo-referenced datasets and accounts for potential feedback effects.     

Life cycle assessment of energy generation from biogas—Attributional vs. consequential approach

Many studies that apply life cycle assessment methodology avoid a strict differentiation between attributional (aLCA) and consequential (cLCA) life cycle assessment. The main distinction that can be made is that an aLCA approach describes a state of average production systems of an economic system while in contrast the consequential approach describes changes (induced by political decisions) in production systems within the economic system. The task of this study was to analyze a biogas system from an environmental point of view and thereby to work out the methodological differences of aLCA and cLCA approaches. The Life cycle inventory quantity primary energy demand (PED) as well as the impact categories global warming potential (GWP), eutrophication (EP), acidification (AP) and photochemical ozone creation potential (POCP) were analyzed. The aLCA approach was split into three scenarios, a physical, an economic and a core product focused one (with focus on the main product) to show the impact of by-product handling. The cLCA approach was split into a local scenario using on-site data and a general scenario using higher aggregated data to show the effects of substitution caused by the introduction of a new technology. The results of the two approaches were compared with the environmental impact of the current average and marginal German electricity mix. Global warming potential per functional unit varied between 3.8 g and 12.5 g of CO2 equivalent in the biogas scenarios. Compared to the average and marginal German electricity mix savings in PED, GWP and partly in AP and POCP can be achieved. However, high variations in the proportion to the reference electricity system, the total quantity results as well as the contribution of single processes to the total result were found. This makes it indispensable to distinguish accurately between the aLCA and the cLCA approach.     

Study of the Thermal Behavior of Multi Tube Tank in Heat Recovery from Chimney—Analysis and Optimization

This work discusses the utilization of multi tube tank heat exchanger for waste heat recovery. The thermal behavior of the system is studied in order to understand the contribution of the different heat transfer modes governing the system. As application, heating water in residential application from chimney heat recovery is considered. A prototype illustrating the suggested system is implemented and tested. Different waste heat scenarios by varying the quantity of burned firewood (heat input) are experimented. The temperature at different parts of the system and the gas flow rates of the exhaust pipes are measured. Measurements showed that the temperature of 95 L tank of water can be increased by 68°C within one hour. Obtained results show that the convection and radiation exchanges at the bottom surface of the tank have a considerable impact on the total heat transfer rate of the water (as high as 70%). Moreover, the proposed system allows saving 9.8 L of gasoline, 10.6 L of diesel or 15 kg of wood for 12 hours of chimney operation.     

The economics of visual disamenity reductions of offshore wind farms—Review and suggestions from an emerging field

The offshore wind power generation market is currently experiencing large growth rates on a global scale and investments exceeding several billion euro are being made. From a welfare economic point of view there is a non-trivial economic trade-off between offshore wind generation costs and the visual impacts from offshore wind farms. Offshore wind farms close to the shore generate cheaper electricity, but also cause higher levels of visual impacts compared to locations at larger distances. In the present paper we carry out a review of the stated preference studies that have elicited the demand for visual disamenity reduction from offshore wind farms. The review has three objectives: (a) to present the results of the different surveys; (b) to explore the more technical parts of the different surveys; and (c) to present the frontiers in the assessment of the demand for visual disamenity reductions associated with offshore wind farm locations. The paper is based on the results from five different studies. The review indicates that locations of offshore wind farms which are close to the shore generate significant welfare losses and that these can be reduced by locating the wind farms at more distant locations. The results also show that the welfare economic costs vary in terms of a range of socio demographic characteristics, experience with wind turbines and recreational activities. Finally, the review suggests that the welfare impacts related to the spatial distribution of the wind farms, intergenerational effects and experience with wind turbines are potential areas that would be beneficial to explore in future studies.     

The Potential Function for Double Square—Well Model and Its Application to Calculation of the Second Virial Coefficient

In the present paper, the mechanism of molecular aggregation and the character of potential function for square-well model have been investigated with the principle of molecular thermodynamics, leading to the potential function for double square-well (DSW) model. In addition, the equation of second virial coefficient for DSW model is derived from the statistical mechanics method. The above equation obtained has been verified by tests and the test results are excellent. It is concluded that this equation can well represent the behaviour of fluid molecules.     

Biofuels from microalgae—A review of technologies for production,processing, and extractions of biofuels and co-products

Sustainability is a key principle in natural resource management, and it involves operational efficiency, minimisation of environmental impact and socio-economic considerations; all of which are interdependent. It has become increasingly obvious that continued reliance on fossil fuel energy resources is unsustainable, owing to both depleting world reserves and the green house gas emissions associated with their use. Therefore, there are vigorous research initiatives aimed at developing alternative renewable and potentially carbon neutral solid, liquid and gaseous biofuels as alternative energy resources. However, alternate energy resources akin to first generation biofuels derived from terrestrial crops such as sugarcane, sugar beet, maize and rapeseed place an enormous strain on world food markets, contribute to water shortages and precipitate the destruction of the world's forests. Second generation biofuels derived from lignocellulosic agriculture and forest residues and from non-food crop feedstocks address some of the above problems; however there is concern over competing land use or required land use changes. Therefore, based on current knowledge and technology projections, third generation biofuels specifically derived from microalgae are considered to be a technically viable alternative energy resource that is devoid of the major drawbacks associated with first and second generation biofuels. Microalgae are photosynthetic microorganisms with simple growing requirements (light, sugars, CO₂, N, P, and K) that can produce lipids, proteins and carbohydrates in large amounts over short periods of time. These products can be processed into both biofuels and valuable co-products.This study reviewed the technologies underpinning microalgae-to-biofuels systems, focusing on the biomass production, harvesting, conversion technologies, and the extraction of useful co-products. It also reviewed the synergistic coupling of microalgae propagation with carbon sequestration and wastewater treatment potential for mitigation of environmental impacts associated with energy conversion and utilisation. It was found that, whereas there are outstanding issues related to photosynthetic efficiencies and biomass output, microalgae-derived biofuels could progressively substitute a significant proportion of the fossil fuels required to meet the growing energy demand.     

Selected Papers from the Eleventh Brazilian Congress of Thermal Sciences and Engineering—ENCIT 2006

The Brazilian Congress of Thermal Sciences and Engineering—ENCIT is organized under the auspices of the Brazilian Society of Mechanical Sciences and Engineering—ABCM. It has been held every other year since 1986, and its last editions had more than 400 presentations of peer-reviewed papers. The ENCIT series of congresses has successfully served as the major forum for the interaction of professionals from academia, industry, and government within the heat transfer, thermodynamics, and fluid mechanics communities in Brazil.     

Lignites from the Plains region of Alberta,Canada—Part 2: Elemental geochemistry

Mineralogy and elemental concentration of two coal seams in Alberta, Canada, were determined using X-ray diffractometry and X-ray fluorescence (XRF). Minerals consist mainly of quartz and calcium minerals, the latter as calcite and vaterite, and oxalate (whewellite). Clay minerals are present as kaolinite, reflecting peat deposition in an acidic environment. Most elements in the coal show depletion compared to Clarke values. Some elements are associated with mineral matter (e.g., Ti, Ba, Si, Al, K, Mg, and Y) and increase with ash. Na, Mn, Sr, and Cu are associated with macerals. High phosphorous and strontium in one interval may be related to the high concentration of whewellite.