Influences of a Kind of Groove-blade on the Flow Field in a Compressor Cascade

This paper presents an experimental investigation of effects of a kind of streamwise-grooved blades on the flowfield in a compressor cascade.The flow field downstream the cascade and the boundary layer on the suctionsurface were measured using a mini 5-hole pressure probe at different incidence angles.The flow field in thegroove cascade was compared with that in the smooth cascade.The measurement results indicate that:(1)thegroove surface can restrain the development of the boundary layer on the suction surface;(2)the grooves canrestrain the radial migration of the low-energy fluids in the boundary layer on the suction surface;(3)the grooveblades can reduce total pressure loss and flow blockage in the cascade at the incidence angles of 0°,5°and 8°;(4)the maximum benefit of 8.6% loss reduction was obtained at the incidence angle of 5° while negative benefit of-3.0% loss reduction occurred at the incidence angle of-5°.     

Optimal sizing of a solar–biogas-based cooking system for a cluster of villages

Energy supplies particularly in remote and far-flung rural areas are in pathetic situation. Leave aside other needs, most of the rural communities still use wood as a source of energy for cooking. Burning of wood is not only an inefficient method, but also hazardousness for the person working on the stove. People have been working for cleaner and efficient means of cooking for decades. Solar cooker- and biogas-based cook stoves are two of the successfully implemented technologies in this area. Although solar cooker requires no maintenance, the initial investment is quite high for a cluster of villages. In addition to this, the intermittency involved in solar energy makes this an unreliable source.

In this paper, a cluster of villages of Narendra Nagar block of Tehri Garhwal district of Uttarakhand, India, has been studied in terms of their thermal requirements. The potential of solar energy and biomass energy has been estimated. An integrated solar–biogas system has been proposed to satisfy this cooking demand. To obtain the optimal sizes of solar cooker and biogas generator, MATLAB codes have been developed. It was found that this system is more economical and much reliable than the other two cases.     

Simulation of a Turbulent Impinging Jet into a Layer of Porous Material Using a Two–Energy Equation Model

This article presents numerical results for a turbulent jet impinging against a flat plane covered with a layer of permeable and thermally conducting material. Distinct energy equations are considered for the solid porous material attached to the wall and for the fluid that impinges on it. Parameters such as Reynolds number, porosity, permeability, thickness, and thermal conductivity of the porous layer are varied in order to analyze their effects on the local distribution of Nu. The macroscopic equations for mass, momentum, and energy are obtained based on volume-average concept. The numerical technique employed for discretizing the governing equations was the control volume method with a boundary-fitted nonorthogonal coordinate system. The SIMPLE algorithm was used to handle the pressure-velocity coupling. Results indicate that inclusion of a porous layer eliminates the peak in Nu at the stagnation region. For highly porous and highly permeable material, simulations indicate that the integral heat flux from the wall is enhanced when a thermally conducting porous material is attached to the surface.     

Thermal Emission of a Disc Body of Semitransparent Material

INTRODUCTIONThethermalemissionofseveraJshapesofsemi-transparelltbodieshasbeeninvestigatedinthepastdecades.Forexample,Mcmahonderivedananalyt-icalexPressionforthehemisphericalendssivityofasemitransparentparallelslabl1];Gardonpresentedamethodforevaluatingtheemissivityofaglassslabl21;byimprovingtheGardon'smethod,Isardcalculatedtheendssivitiesofglassspheres,cylindersandtubes,andobtainedanapproximateexpressionwithtwoex-ponentialtermsl3];TuInerandLove,byusingtheMollterCarlomethod,simulatedthe…     

Numerical Simulation of the Flow over a Model of the Cavities on a Butterfly Wing

ＮｕｍｅｒｉｃａｌＳｉｍｕｌａｔｉｏｎｏｆｔｈｅＦｌｏｗｏｖｅｒａＭｏｄｅｌｏｆｔｈｅＣａｖｉｔｉｅｓｏｎａＢｕｔｔｅｒｆｌｙＷｉｎｇＲｏｄｒｉｇｕｅＳａｖｏｉｅ；ＹｖｅｓＧａｇｎｏｎ（ＵｎｉｖｅｒｓｉｔｙｄｅＭｏｎｃｔｏｎ，Ｃａｍｐｕｓｄ＇Ｅｄｍｕ...     

Optimization Study of a Coanda Ejector

The Coanda effect has long been employed in the aerospace applications to improve the performances of variousdevices.This effect is the ability of a flow to follow a curved contour without separation and has well been util-ized in ejectors where a high speed jet of fluid emerges from a nozzle in the ejector body, follows a curved sur-face and drags the secondary flow into the ejector.In Coanda ejectors,the secondary flow is dragged in the ejec-tor due to the primary flow momentum. The transfer of momentum from the primary flow to the secondary flowtakes place through turbulent mixing and viscous effects.The secondary flow is then dragged by turbulent shearforce of the ejector while being mixed with the primary flow by the persistence of a large turbulent intensitythroughout the ejector.The performance of a Coanda ejector is studied mainly based on how well it drags thesecondary flow and the amount of mixing between the two flows at the ejector exit.The aim of the present studyis to investigate the influence of various geometric parameters and pressure ratios on the Coanda ejector per-formance.The effect of various factors,such as,the pressure ratio, primary nozzle and ejector configurations onthe system performance has been evaluated based on a performance parameter defined elsewhere.The perform-ance of the Coanda ejector strongly depends on the primary nozzle configuration and the pressure ratio.The mix-ing layer growth plays a major role in optimizing the performance of the Coanda ejector as it decides the ratio ofsecondary mass flow rate to primary mass flow rate and the mixing length.     

Alternative Use of a Compressed Component of a Digestate from Agricultural BGSs （Biogas Stations）

The paper presents the results of a two-year research of properties and the way of use of briquettes and pellets made of separated and partially dehydrated digestate from agricultural BGSs （biogas stations）. Digestate is a by-product of BGS. There are approximately 170 agricultural BGSs operating in the Czech Republic. Unprocessed digestate with the dry mass content around 6% is usually applied to soil as a lighter mineral fertilizer. If digestate is separated and the separated solid component of the digestate is further dehydrated to 14 % moisture, it can be processed by pressing to the form of very solid pellets and briquettes, also with various additives. It was also ascertained that mechanical strength and shape of briquettes does not change due to long-term storage. In this form, the compressed digestate can be used in various ways. One of the ways is its energetic use by direct burning. That is why we have observed its calorific value and combustion heat. Another alternative use of compressed digestate from BGS is its application in targeted treatment of in particular mechanical properties of soil and its water regime. The briquettes and pellets have great water sorption properties--the briquette retains water and as a consequence grows up to four times in size. This specific property was analysed and it was ascertained that the speed of water sorption depends on the composition of the compressed mixture （i.e., the type of material and the size of its particles）, but also on the total weight of the produced briquettes （i.e., their size）. Similar dependency was ascertained for other briquette materials that were analysed.     

Distribution of air–water annular flow in a header of a parallel flow heat exchanger

The air and water flow distribution are experimentally studied for a heat exchanger composed of round headers and 10 flat tubes. The effects of tube protrusion depth as well as header mass flux, and quality are investigated, and the results are compared with previous 30 channel data. The flow at the header inlet is annular. For the downward flow configuration, water flow distribution is significantly affected by tube protrusion depth. For flush-mounted geometry, significant portion of water flows through frontal part of the header. As the protrusion depth increases, more water is forced to rear part of the header. The effect of header mass flux or quality is qualitatively the same as that of the protrusion depth. For the upward flow configuration, however, significant portion of water flows through rear part of the header. The effect of protrusion depth is the same as that of the downward flow. However, the effect of header mass flux or quality is opposite to the downward flow case. Compared with the previous 30 channel configuration, the present 10 channel configuration yields better flow distribution. Possible explanation is provided from flow visualization results.     

Computational and Experimental Study of Pinch on the Performance of a Vaneless Diffuser in a Centrifugal Compressor

This study focuses on the vaneless diffuser of a centrifugal compressor.The examined stage consists of an un-shrouded impeller,a parallel wall vaneless diffuser and a volute.The walls of the diffuser were movable allowingdifferent pinch configurations to be investigated.The baseline geometry had no pinch i.e.the height of the dif-fuser was equal to the height of the impeller flow channel plus the axial running clearance.The work consists ofboth numerical and experimental parts.Quasi-steady, turbulent,fully 3D numerical simulations were conducted.The inlet cone,rotor and diffuser were modelled.Six different configurations were studied.The height of thepinch was altered and the pinch made to different walls was tested.Two of the numerically studied cases werealso experimentally investigated.The overall performance of the compressor,the circumferential static and totalpressure and the spanwise total pressure distribution before and after the diffuser were measured.The numericaland experimental studies showed that the pinch improved the efficiency of the compressor.     

Reconstruction of a heat exchanger network under industrial constraints — the case of a crude distillation unit

Heat exchanger network retrofit using a pinch based approach is presented. In this approach, the criterion of minimum sensitivity of heat exchanger to fouling effects is accounted for. The present paper introduces this criterion without explaining its details that are described in the literature. A summary is given of HEN reconstruction in a crude distillation unit processing 4.2 million ton crude oil per year. While the total heat quantity of hot streams is 110 MW, the heat recovery in the existing HEN is 60 MW. Using Pinch Analysis, the target value of heat recovery at ΔT_min=10 K was determined at 91 MW. Measurements were carried out on the existing HEN with the aim to determine the influence of fouling effects on the heat transfer in the exchangers. Taking local constraints including fouling into account, HEN reconstruction was proposed. The heat savings in the reconstructed HEN was estimated at 75 MW.     

Computational Analysis of a Variable Ejector Flow

The present study addresses a variable ejector which can improve the ejector efficiency and control the re-circulation ratio under a fixed operating pressure ratio. The variable ejector is a facility to obtain specific recirculation ratio under a given operating pressure ratio by varying the ejector throat area ratio. The numerical simulations are carried out to provide an understanding of the flow characteristics inside the variable ejector. The sonic and supersonic nozzles are adopted as primary driving nozzles in the ejector system, and a movable cone cylinder, inserted into a conventional ejector-diffuser system, is used to change the ejector throat area ratio. The numerical simulations are based on a fully implicit finite volume scheme of the compressible, Reynolds-Averaged Navier-Stokes equations. The results show that the variable ejector can control the recirculation ratio at a fixed operating pressure ratio.     

Numerical Simulation of a Negative Impulsive Wave

ＮｕｍｅｒｉｃａｌＳｉｍｕｌａｔｉｏｎｏｆａＮｅｇａｔｉｖｅＩｍｐｕｌｓｉｖｅＷａｖｅＴｏｓｈｉａｋｉＳＥＴＯＧＵＣＨＩ；ＭａｎａｂｕＴＡＫＡＯ（ＤｅｐａｒｔｍｅｎｔｏｆＭｅｃｈａｎｉｃａｌＥｎｇｍｅｅｒｉｎｇ，ＳａｇａＵｎｉｖｅｒｓｉｔｙ，Ｈｏｎｊ...     

Flow of Viscous Oil in the Volute of a Centrifugal Pump

IntroductionIn a centrifugal pumP, the imPeller and the volutetogether decide its perfOrmance[']. Thus the volute is animportant element for a centrifugal pumP and theinvestigation into the flow in a volutC has drawn moreattenhons continuously. Bowerman and Acosta (l957)explored the flow in a volute and tWo-dimensionalcentrifugal impeller by using a Fltot probe[']. The resultshave shown that fOr efficien operation, the volute mustbe matched to the imPeller at the design flow rate. Atdesig…     

Eco Insulation Materials： Reduction of Cooling Loads of a House Made of Breeze Block or Laterite in a Dry Tropical Climate

In this paper, we study the influence ofeco materials for roof insulation and fiber-reinforced mortar coatings on cooling loads of a home in dry tropical climate. The walls of the house are made of cinderblock or laterite and the insulating material of a roof panel is made with lime （24%）, cement （6%）, water （50%） of vegetable fibers hibiscus sabdariffa （16%）, tree widespread in Burkina Faso and sugar cane bagasse （4%）. This panel roof insulation and the fiber-reinforced mortar were characterized at the Laboratory of Physics and Chemistry of the environment by the hot plate method. The building is modeled in TRNSYS using climate data from the city of Ouagadougou. The results obtained show that in the warmer months of the year, that is to say in March and April, the relative differences between heat gains the configurations ＂breeze block-coating mortar and roof not insulated＂ and ＂laterite- fiber-reinforced mortar coating and insulated roof＇ vary between 15.6% and 16.8%. The configuration ＂laterite-fiber-reinforced mortar coating and insulated roof allows a reduction of annual heat gains of 15.5% compared to the configuration ＂breeze block-coating mortar and roof not insulated＂.     

Accounting for external costs in a study of a Swedish district-heating system – An assessment of environmental policies

Sweden has historically had strict emission control by implementation of economic policy instruments with the aim of internalising the external costs of air pollution. This study aims to evaluate how well current Swedish policy instruments reflect the environmental costs associated with heat generation in several district-heating (DH) plants in the DH system of Göteborg. Furthermore, it aims to simulate and evaluate the operation of the DH system based on its social cost-effectiveness which takes into account the DH system’s private and external costs (non-internalised environmental costs). The study shows that the economic policy instruments do not fully internalise all external costs whereas for certain technologies, the costs in terms of taxes, emission permits, environmental fees, etc. are higher than the environmental costs caused by the pollutants, given the environmental cost estimates used in the study. The simulation results show that the deviating internalisation of external costs affects the economic ranking of the different plants within the studied DH system. The estimated loss in social-cost effectiveness of the operation of the DH system of Göteborg is noticable but relatively small if compared to the variable heat generation costs for most of the studied DH plants.     

Effects of a Kind of Non-smooth Blade on the Performance of an Axial Fan

This paper presents an experimental investigation of effects of a kind of streamwise-grooved blade on theperformance of an axial-flow fan.The flow field at 25% chord downstream from the trailing edge at hub wasmeasured using a 5-hole pressure probe at different mass-flow conditions.The fan performance of the grooveblades was compared with that of the smooth blades.The measurement results indicate that:(1)the non-smoothblades increase mass flow of the fan at the same throttle conditions except a near stall condition;(2)thenon-smooth blades reduce the relative total pressure loss in the rotor passage and increase the fan's total pressurerise at the test mass-flow conditions except the near stall condition;(3)Negative benefits are obtained at a nearstall condition when the smooth blades are replaced by the non-smooth ones.The fan mass flow decreases 0.9%while the total-pressure rise decreases 2.4% at the near stall condition.     

Structure and properties of lithium trivanadate—a potential electroactive material for a positive electrode of secondary storage

Quantum-chemistry calculations were carried out to predict not only the structure, but also the energetic and electrical parameters of lithium trivanadates of the formulae Li_1+xV₃O₈ (where x=1, 2 and 3). Altogether 21 entities were considered: four with the formula LiV₃O₈, 14 with the formula Li₂V₃O₈ two with the formula Li₃V₃O₈ and one with the formula Li₄V₃O₈. A lithium–vanadium bronze with the formula Li_1.3V₃O₈ was synthesised and investigated in order to compare experimental and predicted characteristics. The presence of Li_1+xV₃O₈ units in the synthesised material was confirmed by infrared (IR) measurements. The predicted value of the open circuit voltage (OCV) change for the insertion of one lithium atom equal to 0.559 V compares well with the experimental value of 0.52 V for the insertion of the first lithium atom into the synthesised bronze. These results form the basis for predicting the properties and modelling or technologically interesting electroactive materials.     

Comparison of a Reaction Front Model and a Finite Difference Model for the Simulation of Solid Absorption Process

ＣｏｍｐａｒｉｓｏｎｏｆａＲｅａｃｔｉｏｎＦｒｏｎｔＭｏｄｅｌａｎｄａＦｉｎｉｔｅＤｉｆｆｅｒｅｎｃｅＭｏｄｅｌｆｏｒｔｈｅＳｉｍｕｌａｔｉｏｎｏｆＳｏｌｉｄＡｂｓｏｒｐｔｉｏｎＰｒｏｃｅｓｓ￥ＺｉｋａｎｇＷｕ；ＡｒｎｅＪａｋｏｂｓｅｎ；Ｘｉｕｇａｎ...     

Study of a Novel Rotary Cyclone Gas-Solid Separator

Based on the analytical study of the characteristics of fine particle motion in swirling flow, a new design idea on flow organization and construction aimed at increasing the positive radial flow in the separation chamber of the rotary cyclone separator (PRV type) was proposed. Experimental verification including the test of variation of separation efficiency and pressure loss with the first and secondary flow ratio show that this new type separator has higher and more stable separation efficiency in broad flow ratio range while the pressure loss is far below the conventional rotary cyclone separator and even comparable with that of simple cyclone separator