scispace - formally typeset
Search or ask a question

Showing papers in "Jsme International Journal Series B-fluids and Thermal Engineering in 1998"


Journal ArticleDOI
TL;DR: In this article, a simple but reliable correlation for a drag coefficient, CD, of single bubbles under a wide range of fluid properties, bubble diameter and acceleration of gravity were developed based on a balance of forces acting on a bubble in a stagnant liquid and available empirical correlations of terminal rising velocities of single bubble.
Abstract: Simple but reliable correlations for a drag coefficient, CD, of single bubbles under a wide range of fluid properties, bubble diameter and acceleration of gravity were developed based on a balance of forces acting on a bubble in a stagnant liquid and available empirical correlations of terminal rising velocities of single bubbles. The proposed CD consists of three equations, each of which corresponds to pure, slightly contaminated and contaminated systems. The effect of a frictional pressure gradient due to a liquid flow is also taken into account by introducing a concept of an effective body acceleration. Terminal rising velocities of single bubbles were calculated using the proposed CD, and compared with measured data under the condition of 10-2

517 citations


Journal ArticleDOI
TL;DR: In this article, a conical hot film anemometer is used to measure the slip velocity of a real fluid at the wall of a square duct with a highly water repellent wall, and the velocity profile with the slip is measured.
Abstract: A real fluid does not slip at the surface of a solid boundary. Most experimental results of a Newtonian fluid satisfy with this condition. If a real fluid can slip freely over the surface of a solid boundary, how can we deduce the slip velocity. The purpose of this study is to experimentally clarify fluid slip velocity of Newtonian fluids at the duct wall. Velocity profiles of tap water and 20 wt% glycerin solution flowing in a square duct with a highly water repellent wall were measured by means of a conical hot film anemometer. Consequently, the velocity profile with the slip is measured, and the laminar drag reduction phenomena and the friction factor formula for a square duct with fluid slip at the wall have been obtained

80 citations


Journal ArticleDOI
TL;DR: In this paper, a higher-order finite difference method (FDM) has been developed for the body-fitted coordinate system and the consistency and the conservatior property of FDMs are discussed for the collocated grid.
Abstract: To apply the direct numerical simulation (DNS) and the large-eddy simulation (LES) of turbulence to flow fields of complicated geometry, a higher-order finite difference method (FDM) has been developed for the body-fitted coordinate system The consistency and the conservat ior property of FDMs are discussed for the collocated grid As numerical examples, DNS results of decaying isotropic turbulence and DNS/LES results for plane channel flow are shown and the influence of variable arrangement is examined The results by the consistent 'interpolation' method for gradient form on the collocated grid agree well with those by other proper FDMs and the spectral method

66 citations


Journal ArticleDOI
TL;DR: In this paper, the local skin friction coefficient and re-examination of the Reynolds-number effect on the mean flow quantities were made in a zero-pressure gradient, smooth wall, turbulent boundary layer.
Abstract: Measurement of the local skin friction coefficient and re-examination of the Reynolds-number-effect on the mean flow quantities were made in a zero-pressure gradient, smooth wall, turbulent boundary layer. In order to do this fairly, the two-dimensionality of the flow field was carefully adjusted. And, the wall shear stress rw was determined by direct measurement using a floating element device. The Reynolds number based on the momentum thickness R θ =U 1 θ/ν ranges from 840 to 6 220. The present experimental results of c f propose a new empirical formula which well represents the present experimental data and confirms that the Karman constant x= 0.41, which implies a slope of the logarithmic linear layer, is independent of R θ down to R θ =860, whereas the additive constant varies with R θ . The magnitude of the wake parameter takes an asymptotic value of 0.62 if the Reynolds number is sufficiently high. The effect of R θ on all the turbulent intensities is evident even within the viscous sublayer. The constant stress layer does exist in the Reynolds shear stress profiles despite that the constant value varies with R θ

52 citations


Journal ArticleDOI
TL;DR: The large-eddy simulation technique is more suitable for these flows, and recent work in the area of largeeddy simulations of bluff body flows is summarised, with emphasis on work by the author's research group and on experiences gained from two LES workshops.
Abstract: The flow past bluff bodies, which occurs in many engineering situations, is very complex, involving often unsteady behaviour and dominant large-scale structures, and it is therefore not very amenable to simulation by statistical turbulence models. The large-eddy simulation technique is more suitable for these flows, and recent work in the area of large-eddy simulations of bluff body flows is summarised, with emphasis on work by the author's research group as well as on experiences gained from two LES workshops. Results are presented and compared for the vortex-shedding flow past square and circular cylinders and for the flow around a surface-mounted cube. The performance, the cost and the potential of the LES method for simulating bluff body flows, also vis-a-vis statistical turbulence models, is assessed.

44 citations


Journal ArticleDOI
TL;DR: The recent work on large eddy simulation (LES) of turbulent flows at the Center for Turbulence Research is reviewed in this paper, including progress on issues surrounding the governing equations and filtering, subgrid scale and wall layer modeling, and spatial discretization.
Abstract: The recent work on large eddy simulation (LES) of turbulent flows at the Center for Turbulence Research is reviewed. This includes progress on issues surrounding the governing equations and filtering, subgrid scale and wall layer modeling, and spatial discretization. Recent results from LES of separated flows, and two promising applications of LES to flows encountered in combustors are presented

40 citations


Journal ArticleDOI
TL;DR: In this article, a model which takes the preferential diffusion effect into consideration, is proposed to predict the premixed turbulent burning velocity, using the local burning velocity as a reference instead of the original laminar burning velocity.
Abstract: In our previous work, we found that the preferential diffusion in a turbulent flame played an important role in its turbulent combustion characteristics, and estimated the local burning velocity in premixed turbulent combustion experimentally, taking account of the preferential diffusion effect. In this study, a model, which takes the preferential diffusion effect into consideration, is proposed to predict the premixed turbulent burning velocity, using the local burning velocity as a reference instead of the original laminar burning velocity. The model can be explained as follows. The turbulence affects the turbulent burning velocity by increasing the flame surface area and stretching the flame. Consequently, the turbulent burning velocity and quenching limit are determined by the balance of both effects. The predicted velocities are compared with the measured turbulent burning velocities where the fuel, equivalence ratio and the laminar burning velocity were varied extensively. As a result, quantitative accuracy of this simple model is confirmed.

39 citations


Journal ArticleDOI
TL;DR: In this paper, the aerodynamic effectiveness of winglets on the performance of a horizontal axis wind turbine was evaluated using a vortex lattice method with a free wake model, which can be applied to arbitrary blade shapes and the model needs no parameter based on empirical data about the wake geometry.
Abstract: The objective of this paper is to show numerically the aerodynamic effectiveness of winglets on the performance of a horizontal axis wind turbine (HAWT). The winglets used in this study are an inclined extension of the rotor blade. For the numerical analysis, a vortex lattice method with a free wake model was used, as the method can be applied to arbitrary blade shapes and the model needs no parameter based on empirical data about the wake geometry. Calculations were performed on the flow field of the rotor wake and the rotor performance, and results were compared between rotors with and without winglets. To examine the effects on the strength of blades, the flatwise bending moment was also calculated. A small installation angle of winglets causes a large increase in the power coefficient but a small increase in the flatwise bending moment compared with the blades with radially extended winglets.

39 citations


Journal ArticleDOI
TL;DR: In this article, the performance and aerodynamics of a Wells turbine using a three-dimensional flow solver for the Reynolds-averaged Navier-Stokes equations are investigated.
Abstract: The Wells turbine is one element in a chain of devices by which the oceans' wave power resource can be tapped This paper reports a study of the performance and aerodynamics of a Wells turbine using a three-dimensional, flow solver for the Reynolds-averaged Navier-Stokes equations Calculations have been performed for a monoplane device comprised of NACA 0015 blades under the conditions: Reynolds number 8×10 5 , tip Mach number 04, hub-to-tip ratio 06 and tip clearance 2% To study the effect of solidity calculations were performed for different numbers of blades It is shown that the predicted effect of solidity on the turbine pressure drop, torque and efficiency agrees qualitatively and quantitatively with experimental data The discrepancies can be partly explained by geometric differences between the experimental and numerical turbines It is also shown that increasing turbine solidity increases the resistance to stall by strengthening the blade-to-blade interactions in the hub region

31 citations


Journal ArticleDOI
TL;DR: In this article, the authors measured rotating stall signal patterns in a vaneless diffuser in a centrifugal compressor with a radial bladed impeller and identified abrupt rotating stall at several different impeller rotational speeds.
Abstract: We present the measured rotating stall signal patterns in a vaneless diffuser in a centrifugal compressor with a radial bladed impeller. Unsteady flow and rotating stall in the vaneless diffuser were investigated by measuring unsteady velocity fluctuations at several different diffuser radius ratios and axial distances using a hot wire anemometer. The flow characteristics in terms of the radial and tangential velocity components and the flow angle distribution in the vaneless diffuser during rotating stall were investigated using phase-locked averaging techniques. The results clearly identified abrupt rotating stall at several different impeller rotational speeds. According to the experimental results, two different mechanisms exist for the development of the reverse flow zone in a vaneless diffuser. One is dominated by the extension of the reentering flow from the diffuser exit, and the other is dominated by the growth of the local flow separation zone on the hub and shroud side. The fluctuation in the flow direction increases as the diffuser radius ratio increases and is dominated by the strength of the reverse flow

29 citations


Journal ArticleDOI
TL;DR: In this article, pressure drop and heat transfer for flow-boiling of water in small-diameter tubes under atmospheric pressure were discussed, and the results of experiments were compared with those of several existing correlations and models.
Abstract: Pressure drop and heat transfer for flow-boiling of water in small-diameter tubes under atmospheric pressure were discussed. The results of experiments were compared with those of several existing correlations and models. The experiments were carried out using atmospheric-pressure water in tubes with inner diameter D ranging from 2.0 to 6.0 mm, heated length L from 4.0 to 680.0 mm, inlet water subcooling ΔT in from 70 to 90 K, and mass velocity G from 100 to 10 170 kg/(m 2 s). The highest heat flux q attained was 33 MW/m 2 . Interesting phenomena were observed in small-diameter tubes with a very short heated length. The most suitable correlations for predicting the pressure drop and heat transfer in small-diameter tubes were also discussed.

Journal ArticleDOI
TL;DR: In this article, an electrohydraulic servovalve that uses fresh water as a pressure medium (water hydraulic servvalve) is developed. But the servovalves cannot be operated with such a hostile fluid.
Abstract: An electrohydraulic servovalve that uses fresh water as a pressure medium (water hydraulic servovalve) is developed. conventional electrohydraulic servovalve cannot be operated with such a hostile fluid. In this paper, we explain the structure and functions of components, and the relationship between them, as well as the developmental procedure of the water hydraulic servovalve. The basic idea for the servovalve is to support the spool of the valve with hydrostatic bearings and to lead the water from the bearings to the flapper-nozzle system. The hydrostatic bearings constitute a laminar restriction that takes the place of the turbulent restriction in the conventional flapper-nozzle system. We also explain the design procedure of the hydrostatic bearing in the valve and the relationship between electromagnetic elements and fluidic elements. The water hydraulic servovalves fabricated show good characteristics of smooth motion, endurance and controllability, as well as good dynamic characteristics.

Journal ArticleDOI
TL;DR: In this article, the role of vortex dislocations is discussed and it is shown how encouraging their formation can reduce drag, in addition to describing the improved insight that can be provided by computational fluid dynamics, the likely impact of new, nonintrusive measurement techniques is also assessed.
Abstract: The understanding of bluff body flows and their prediction are important in many areas of industrial development. The complex nature of these flows provides a challenge to both experimental and computational fluid dynamicists. Some of the more recent advances are reviewed, including the understanding of the near wake region and the instabilities that develop there. The role of vortex dislocations is discussed and it is shown how encouraging their formation can reduce drag. In addition to describing the improved insight that can be provided by computational fluid dynamics, the likely impact of new, non-intrusive measurement techniques is also assessed.

Journal ArticleDOI
TL;DR: In this article, the effect of 3D shape tabs on the mixing rate of a co-flowing stream was studied using a laser Doppler velocimetry (LDV) technique.
Abstract: The velocity field associated with it nozzle flow emanating into a co-flowing stream was measured using a Laser Doppler Velocimetry (LDV) technique. The present work concentrates on the effect of small tabs introduced at the nozzle exit plane on mixing of the jet. The effect of tab geometry on mixing rate has been studied. The principal objective of the present measurements was to study the effect of introducing a 3-D shape to the tab geometry, rather than plain 2--D tabs of small thickness. Three different 3-D shape tabs were studied. The mixing improvement for all 3-D shape tabs was found to be substantially reduced compared to the plain 2-D tab results for the same projected area. Therefore, attempts to reduce the drag and performance loss penalty of the tabs were accompanied by significant reductions in tab mixing effectiveness

Journal ArticleDOI
TL;DR: In this article, an upward plane jet impinging on the free surface of a shallow rectangular tank oscillates without any external periodic force, and the imbalance generates propagating waves, and a surface level gap appears there.
Abstract: An upward plane jet impinging on the free surface of a shallow rectangular tank oscillates without any external periodic force. The movement of the impinging point leaves additional fluid mass on the surface behind the point, which does not balance the momentum supplied by the jet. The imbalance generates propagating waves, and a surface level gap appears there. The level gap is flattened not by the waves but by the vertical motion of water columns. The imbalance causes lateral displacement of jet, which in turn causes the imbalance, forming a positive feedback loop. The above model explains well why the frequency corresponds to that of water column oscillation in a partitioned tank with the same water depth, and the oscillation region has a wide range above a certain velocity limit determined by the water depth.

Journal Article
TL;DR: In this article, the adaptive forced rejection approach for a single periodic output disturbance with an unknown period and its application to unbalance vibration suppression in rotor-magnetic bearing systems is discussed.
Abstract: This study is concerned with the adaptive forced rejection approach for a single periodic output disturbance with an unknown period and its application to unbalance vibration suppression in rotor-magnetic bearing systems.A discrete recursive technique is applied to estimate the unknown disturbance period and then to internally and adaptively generate a pseudofeedforward reference signal such as that this disturbance is eliminated.Simulations are carried out.The results indicate that both the estimation algorithm of an unknown period and reference signal adaptive generation algorithm are stable.Finally, the approach is applied to a problem of unbalance vibration suppression in rotor-magnetic bearing systems.Approximately 20 dB and 7 dB reductions in unbalance vibrations were experimentally obtained in the horizontal and vertical directions of the front and rear sides of the rotor, respectively.The experimental results show that the proposed algorithm is effective for achieving unbalance vibration suppression.

Journal ArticleDOI
TL;DR: In this article, a high-speed video camera with an image intensifier was used to measure flame spread in a suspended fuel droplet array in a high pressure ambience, where seven droplets of the same size were arranged at equal horizontal spacing.
Abstract: Flame spread phenomena in a suspended fuel droplet array were experimentally investigated for n-hexadecane in a high-pressure ambience. Seven droplets of the same size were arranged at equal horizontal spacings. Flame spread rates were measured based on OH emission histories detected by a high-speed video camera with an image intensifier for droplet diameters of 0.50, 0.75, and 1.0 mm at ambient pressures from 0.1 to 2.0 MPa. Results show that, as droplet spacing becomes smaller, flame spread rate increases and attains a maximum value at a specific spacing. A further decrease in droplet spacing causes the spread rate to decrease due to the large latent heat of vaporization. Experiments were also conducted in a microgravity field to determine if these characteristics of flame spread are affected by natural convection.

Journal ArticleDOI
TL;DR: In this paper, the effect of initial CO 2 concentration on NO destruction and regeneration was investigated as part of their ongoing research on NO emission from CO 2 recycled coal combustion, which could realize easy CO 2 recovery and drastic N() reduction simultaneously.
Abstract: The effect of initial CO 2 concentration on NO destruction and regeneration was investigated as part of our ongoing research on NO emission from CO 2 recycled coal combustion, which could realize easy CO 2 recovery and drastic N() reduction simultaneously. Experiments were carried out in a flat flame burner for CH 4 /O 2 /Ar/NO/CO 2 flame at various excess oxygen ratios (from 0.6 to 1.2) and CO 2 concentrations (from 0% to 48%). It was found that CO 2 has a pronounced negative effect on the destruction of NO under fuel-rich condition. In contrast, under fuel- lean condition, the effect of CO 2 becomes smaller even at high CO 2 concentrations. Kinetic modeling showed that a large part of NO is regenerated through the reaction N+CO 2 = NO+CO at high CO 2 concentrations. The effect of CO 2 is not so significant under fuel-lean condition because this reaction is no longer competitive with other NO formation reactions in this case.

Journal ArticleDOI
TL;DR: Using a highly water-repellent coating wall, a new type of drag reduction for a rotating disk in Newtonian fluid have been clarified experimentally as mentioned in this paper, where the authors measured the moment of rotating disks with highly water repellent-wall and with smooth aluminum wall and found that the maximum drag reduction ratio was about 45% in aqueous solution of glycerin at concentration of 40 wt%, and that viscous properties had a slight effect upon the drag reduction.
Abstract: Using a highly water-repellent coating wall, new type of drag reduction for a rotating disk in Newtonian fluid have been clarified experimentally. Measurements were carried out to measure the moment of rotating disks with highly water-repellent-wall and with smooth aluminum wall. The clearance between the disk and the housing wall was varied at 5, 10, and 20 mm thick. Tested fluids were tap water and aqueous solution of glycerin at concentration of 30 wt% ahd 40 wt%. The experimental data of the moment of the rotating disk with highly water-repellent wall in housing decreased comparing with the data of smooth plane disk. It was shown that the maximum drag reduction ratio was about 45% in aqueous solution of glycerin at concentration of 40 wt%, and that the viscous properties had a slight effect upon the drag reduction.

Journal ArticleDOI
TL;DR: In this article, the authors focus on sterically hindered amines and a new absorber packing for CO 2 recovery from fossil fuel power plant flue gas, and the results of optimum steam system analysis are indicated.
Abstract: As a countermeasure for global warming, the development of CO 2 recovery technology from fossil fuel power plant flue gas has continued. MEA processes are widely used for CO 2 recovery from combustion flue gas in beverage use, etc. However, if we consider power plant scale CO 2 recovery, the biggest theme is the reduction of energy needed to recover CO 2 , Our presentation focuses in sterically hindered amines and a new absorber packing. Also, the result of optimum steam system analysis are indicated. CO 2 disposal method is needed with the combination of CO 2 recovery, therefore CO 2 subterranean disposal method is also discussed as the practical way.

Journal ArticleDOI
TL;DR: In this paper, the suction performance, cavitation development, and internal flow fields of the impeller of a flat-helical inducer with two blades were analyzed. But they did not consider the effect of alternate blade cavitation, in which cavity development evolves on one blade while it weakens on the other.
Abstract: Analysis of the suction performance, cavitation development, and internal flow fields of the impeller of a flat-helical inducer with two blades were performed. As the suction pressure is reduced, the balanced cavity development on both blades is destroyed. Alternate blade cavitation, in which cavity development evolves on one blade while it weakens on the other, can occur. When it does, the theoretical and actual pump heads can decrease quickly. Investigations were conducted to determine how this phenomenon develops.

Journal ArticleDOI
TL;DR: In this paper, the stability and dynamic characteristics of an axisymmetrically oscillating magnetic liquid column subjected to a uniform magnetic field in the presence of gravity were analyzed using potential theory based on a magnetic field perturbation method.
Abstract: This paper presents the stability and dynamic characteristics of an axisymmetrically oscillating magnetic liquid column subjected to a uniform magnetic field in the presence of gravity. Initially, the axisymmetric mode response of a magnetic liquid column is analyzed using potential theory based on a magnetic field perturbation method. Then, an experiment is described in which a liquid column is formed between Helmholtz coils and vibrated vertically to produce axisymmetric oscillations by an electodynamic exciter. The surface frequency response of the column is measured optically using a high-speed video camera, a strobovision-snalyzer and a stroboscope. The results show that the magnetic field exerts a stabilizing effect on the column and the resonance frequency increases for increased liquid column aspect ratio(diameter / height). Both the experimental interfacial response and resonance frequency show good agreement with the theoretical prediction.

Journal ArticleDOI
TL;DR: In this paper, a two-dimensional bubble plume which is confined by two parallel plates is analyzed and the parametric dependency, such as influence of the bubble size distribution and void fraction, on the whole two-phase behavior is clarified and experimental validation is conducted.
Abstract: Detailed flow structure of bubbly flows observed in a bubble plume is investigated numerically using the Euler-Lagrange model where the bubbly flow is treated as a continuum and each bubble is tracked in the flow. The governing equations are formulated with emphasis on the translational motion of the bubble in non-uniform unsteady liquid flow. Improvement of the present numerical method is confirmed by comparison with the Eulerian method, and the numerical results are validated by the comparison with the two kinds of experimental results, i.e., global flow pattern visualized by direct-lighting method, and local bubble motion measured by particle imaging velocimetry. In this paper, two-dimensional bubble plume which is confined by two parallel plates is analyzed and the parametric dependency, such as influence of the bubble size distribution and void fraction, on the whole two-phase behavior is clarified and experimental validation is conducted.

Journal ArticleDOI
TL;DR: In this paper, the forces acting on and flow patterns around a rigid bluff body submerged in an oscillatory flow were studied and compared with those from other studies using a U-tube water tank to verify the experimental setup.
Abstract: The forces acting on and the flow patterns around a rigid bluff body submerged in an oscillatory flow were studied. The force coefficients on a circular cylinder were measured and compared with those from other studies using a U-tube water tank to verify the experimental setup. Then, measurements of both in-line and transverse forces of a square cylinder at an angle of attack of 0° were made in a relatively wide range of Keulegan Carpente (KC) numbers from 1 to 90. For both circular and square cylinders, the force signals were analyzed spectrally to obtain major frequencies. Flow visualization was also employed to confirm the relationship between flow patterns and force coefficients. It is evident that several classes of flow patterns appear within the measured KC range, and that variations of the in-line and transverse forces are related closely to vortex motions.

Journal ArticleDOI
TL;DR: In this paper, the system of oxygen/recycled flue gas combustion for the removal of carbon dioxide from pulverized-coal fired power plants, the combustion characteristics of pulverised coal, and the trial designing of a 1, 000 MWe coal-powered power plant were studied.
Abstract: The system of oxygen/recycled flue gas combustion for the removal of carbon dioxide from pulverized-coal fired power plants, the combustion characteristics of pulverized coal, and the trial designing of a 1 000 MWe pulverized-coal power plant were studied. The flame propagation speed of pulverized-coal cloud was measured in a microgravity combustion chamber at O 2 /CO 2 , O 2 /N 2 and O 2 /Ar atmosphere. NO x and SO 2 emissions from the system were investigated in the industrial scale combustion test facilities. Based on these results and the previous works, the trial designing of a 1 000 MWe pulverized--coal fired power plant applying this combustion system was also studied. As for the heat absorption performance of the boiler furnace, a 3 dimensional numerical analysis was applied to a large utility boiler furnace. It was compared with another promising system CO 2 -recovery, pulverized-coal power plant combined with amine absorption process.

Journal ArticleDOI
TL;DR: In this paper, a high temperature air combustion with high flame stability, flame volume enlargement, greenish flame color, and low NO x emissions was shown to improve thermal field uniformity.
Abstract: Combustion using combustion air with the condition of 1 010°C and 3.0% oxygen content diluted air, has shown unique characteristics A high flame stability, flame volume enlargement, greenish flame color and low NO x emissions were the characteristics of the combustion named here as high temperature air combustion. Flame with an enlarged volume having low flame luminosity was one of the important findings which implies a heat release rate in unit space of the flame decreased. The flame temperature profile thus became more homogeneous than ordinary flames. This potential that the high temperature air combustion may improve thermal field uniformity can cause a revolution of combustion technology on the high performance industrial furnace design.

Journal ArticleDOI
TL;DR: In this article, the characteristics of NOx emission in high-temperature air combustion technology were investigated numerically, and two kinds of methods were used: detailed chemistry and transport properties were used for a laminar diffusion flame, and a simplified reaction scheme was used for calculating a turbulent flame in a furnace.
Abstract: The characteristics of NOx emission in the high-temperature air combustion technology were investigated numerically. Two kinds of methods were used. Detailed chemistry and transport properties were used for a two-dimensional laminar diffusion flame, and a simplified reaction scheme was used for calculating a turbulent flame in a furnace. Results show that the thermal mechanism dominates NOx emission in high-temperature air combustion. If only the preheated air temperature is increased, NOx emission will rise significantly. However, the combination of air preheating and flue gas recirculation not only improves the combustion efficiency, but also suppresses NOx emission in the combustion process.

Journal ArticleDOI
TL;DR: In this paper, the authors measured exhaust emissions from a commercial DI diesel engine with a wide range of fuel properties such as cetane number, aromatic content and type, and distillation temperature, and found that total aromatic content was the controlling factor for NO x emission and PM emission mainly depended on polycyclic aromatic content in the fuel.
Abstract: Exhaust emissions (HC, CO, NO x , PM, and PAH (polycyclic aromatic hydrocarbons in PM)) from a commercial DI diesel engine were measured for petroleum-derived fuels with a wide range of fuel properties. Fuel properties such as cetane number, aromatic content and type, and distillation temperature were adjusted to be independent from each other. The test results showed that total aromatic content was the controlling factor for NO x emission, and PM emission mainly depended on polycyclic aromatic content in the fuel. The increases in PM emission with increase in aromatics was mainly caused by the increase in SOF emission. Both of NO x and PM emissions were seldom affected by cetane number and 90% distillation temperature. Therefore, chemical characteristics of fuel are the controlling factor for NO x and PM emission, not the physical properties. The amount of sulfate in PM proportionally increased with increase in sulfur content of fuel. PAH emission was evaluated by analyzing SOF using a high performance liquid chromatography with a chemiluminesence detector. Also, the PAH highly depended on aromatic content, and the emission characteristics caused by aromatics was quite similar to PM emission.

Journal ArticleDOI
TL;DR: In this paper, the authors verified the dynamic equation of state derived from a thermodynamic model representing simultaneous heat and mass transfer from the liquid supply front to the solid-liquid interface in a liquid saturated porous medium.
Abstract: An experimental study has verified the dynamic equation of state derived from a thermodynamic model representing simultaneous heat and mass transfer from the liquid supply front to the solid-liquid interface in a liquid saturated porous medium. Measurement of pore liquid pressure at the solid-liquid interface fixed on the top surface of an Ohya-tuff specimen (the porous medium) enabled us to experimentally verify the relationship between temperature, pore liquid pressure and solid pressure at the interface, and liquid supply pressure. This experimental method was established by re-verifying the so-called Clausius-Clapeyron equation (GCCE), the static equation for a porous medium without liquid flow. This study also clarified the relationship between the dynamic equation of state and the GCCE on the pore liquid pressure-liquid supply pressure plane.

Journal ArticleDOI
TL;DR: In this article, a detailed experimental investigation of turbulent heat transfer in radially rotating circular smooth-walled and square rib-roughened ducts with focuses on the variable rotational effects along the leading and trailing surfaces of these two test ducts due to differences in the shape of the cross section and the surface conditions of duct walls.
Abstract: In this paper we describe a detailed experimental investigation of turbulent heat transfer in radially rotating circular smooth-walled and square rib-roughened ducts with focuses on the variable rotational effects along the leading and trailing surfaces of these two test ducts due to differences in the shape of the cross section and the surface conditions of duct walls. The experimental data reconfirmed the presence of strong notation-induced secondary flows for both the test sections with an attendant relative increase in local heat transfer on the trailing surface. On the leading surfaces of both test sections, heat transfer was significantly less than that of the pure forced convection level. In qualitative terms, even with the agitated flow field caused by ribs inside the square ribbed duct, considerable rotational effects within the ribbed duct occurred in a similar manner to that found inside the circular smooth-walled duct. However, with equivalent rotating conditions, the heat transfer impediment on the leading surface was more severe for the ribbed duct than for the smooth-walled duct and the heat transfer enhancement on the trailing surface of the ribbed duct was significantly alleviated. A low degree of peripheral heat transfer variation was found in the ribbed test duct. Since the difference between smooth-walled or rib-roughened ducts is considerable, the selection of either circular smooth-walled or square ribroughened coolant dhannel for gas turbine rotor blades must be performed after considering the variable rotational effects in order to achieve the optimum design of an internal cooling system.