Showing papers in "Transactions of The Korean Society of Mechanical Engineers B in 1997"
TL;DR: In this paper, the authors calculated the pressure transients and aerodynamic drag for two-trains running in a tunnel for a wide range of train speed, and compared with the results of previous tunnel tests and calculations for one train.
Abstract: As a high-speed train enters a tunnel, a compression wave is generated ahead of it due to the piston action of train. The compression waves propagate along the tunnel and reflect backward at the exit of tunnel. A complex wave phenomenon appears in the tunnel, because of the successive reflections of the pressure waves at the exit and entrance of tunnel. The pressure waves can give rise to large pressure transients which impose the fluctuating loads on the running train. It is highly needed that the pressure transients should be predicted to design the train body and to improve the comfort for the passengers in the train. In the present study, the pressure transients and aerodynamic drag for two-trains running in a tunnel were calculated numerically for a wide range of train speed, and compared with the results of the previous tunnel tests and calculations for one train. The present calculation results agreed with ones of the tunnel tests, and the mechanism of pressure transients was made clear.
6Â citations
TL;DR: In this paper, the performance and heat transfer characteristics of an air conditioning system filled with hydro- carbon refrigerants are experimentally investigated, and the cooling capacity and the coefficient of performance are obtained as test results.
Abstract: Performance and heat transfer characteristics of an air conditioning system filled with hydro- carbon refrigerants are experimentally investigated. Single component hydrocarbon refrigerants (propane, isobutane, butane and propylene) and binary mixtures of propane/isobutane and propane/butane are considered as working fluids in the air conditioning system. Performances of each refrigerant are obtained at several compressor speeds and temperature levels of secondary heat transfer fluids. The cooling capacity and the coefficient of performance are obtained as test results. Heat transfer data of selected refrigerants are achieved from overall conductance measurement. Average heat transfer coefficients at different mass fluxes are shown and they are also displayed for different heat capacities of the system. Experimental results show that some hydrocarbon refrigerants have better characteristics than R22.
5Â citations
TL;DR: In this paper, an experimental study has been performed on the effect of baffle parameters on shell-side heat transfer in a conventional shell-and-tube heat exchanger, and it was shown that the new correlation improves the accuracy of the Bell-Delaware method considerably.
Abstract: An experimental study has been performed on the effect of baffle parameters on shell -side heat transfer in a conventional shell-and-tube heat exchanger. The baffle spacing distance and the number of baffle were varied to investigate the behavior of unequal baffle spacing correction factor which is appeared in the Bell Delaware method for prediction of the shell-side heat transfer coefficient. It was obvious that heat duties obtained from the experiment significantly deviated from those calculated by the conventional Bell-Delaware method. A new correlation of the unequal baffle spacing correction factor was developed. It was shown that the new correlation improves the accuracy of the Bell-Delaware method considerably. This result may induce the use of the Bell-Delaware method in developing a computer software for design of shell-and-tube heat exchangers.
5Â citations
TL;DR: In this article, heat transfer and flow measurements from a convex curved surface to a circular impinging jet have been made, and the results show that the stagnation point Nusselt number increases with increasing value of d/D. The formation of secondary maxima is attributed to an increase in the turbulence level resulting from the transition from a laminar to a turbulent boundary layer.
Abstract: The heat transfer and flow measurements from a convex curved surface to a circular impinging jet have been made. The flow at the nozzle exit has a fully developed velocity profile. The jet Reynolds number (Re) ranges from 11,000 to 50,000, the dimensionless nozzle-to-surface distance (L/d) from 2 to 10, and the dimensionless surface curvature (d/D) from 0.034 to 0.089. The results show that the stagnation point Nusselt number (N ) increases with increasing value of d/D. The maximum Nusselt number at the stagnation point occurs at L/d .ident. 6 to 8 for all Re's and d/D's tested. For larger L/d, N dependency on Re is stronger due to an increase of turbulence in the approaching jet as a result of the more active exchange of momentum with a surrounding air. The local Nusselt number decreases monotonically from its maximum value at the stagnation point. However, for L/d=2 and Re=23,000, and for L/d.leq.4 and Re=50,000, the stream wise Nusselt number distributions exhibit secondary maxima at r/d .ident. 2.2. The formation of the secondary maxima is attributed to an increase in the turbulence level resulting from the transition from a laminar to a turbulent boundary layer.ndary layer.
4Â citations
TL;DR: A nonlinear low-Reynolds-number k-epsilon model of Park and Sung was extended to predict the flows over a step with inclined wall, where a boundary layer flow without separation and a separated and reattaching flow coexist.
Abstract: A nonlinear low-Reynolds-number k-.epsilon. model of Park and Sung was extended to predict the flows over a step with inclined wall, where a boundary layer flow without separation and a separated and reattaching flow coexist. For a better prediction of the flows, a slight modification was made on the function of the wall damping( ) and the model constant ( ) in the .epsilon.-equation. The model performance was validated by comparing the model predictions with the experiment. It was shown that the flows over a step with inclined wall are simulated successfully with the present model.ent model.
4Â citations
TL;DR: In this paper, the authors measured condensation heat transfer coefficients (HTCs) of three refrigerants (CFC-11, HCFC-123 and HCFC141b) on plain and low fin tubes and also to find out the optimum fin density of the low fin tube.
Abstract: In this study, condensation heat transfer coefficients(HTCs) of CFC-11, HCFC-123 and HCFC-141b are measured, which are used/or considered as working fluids in centrifugal chillers. The main objectives of this study are to measure and compare the HTCs of various refrigerants on plain and low fin tubes and also to find out the optimum fin density of the low fin tubes. To accomplish these goals, HTCs of three refrigerants are measured for the plain tube as well as 4 types of low fin tubes. All measurements are carried out at the vapor temperature of 39.deg. C with the wall temperature difference of 3 .deg. C ~ 8.deg. C. For all the refrigerants tested, a low fin tube of 28 fins per inch yielded the best performance among all the tubes tested. For the plain tube, the HTCs of CFC-11 and HCFC-141b were very similar and those of HCFC-123 were 10% lower than those of CFC-11.Thus, it can be concluded that HCFC-123 and HCFC-141b are acceptable as alternative refrigerants for CFC-11 from the view point of condensation heat transfer.
4Â citations
TL;DR: In this paper, a numerical technique for simulating incompressible viscous flow with free surface is presented, which can be applied to irregular mesh system, and can be easily extended to three dimensional geometries.
Abstract: A numerical technique for simulating incompressible viscous flow with free surface is presented. The flow field is obtained by penalty finite element formulation. In this work, a modified volume of fluid (VOF) method which is compatible with 4-node element is proposed to track the moving free surface. This scheme can be applied to irregular mesh system, and can be easily extended to three dimensional geometries. Numerical analyses were done for two benchmark examples, namely the broken dam problem and the solitary wave propagation problem. The numerical results were in close agreement with the existing data. Illustrative examples were studied to show the effectiveness of the proposed numerical scheme.
3Â citations
TL;DR: In this article, the effects of concave hemispherical surface curvature on the local heat transfer from a turbulent round impinging jet were experimentally investigated, and the liquid crystal transient method was used for these measurements.
Abstract: The effects of concave hemispherical surface curvature on the local heat transfer from a turbulent round impinging jet were experimentally investigated. The liquid crystal transient method was used for these measurements. This method, which is a variation on the transient method, suddenly exposes a preheated wall to an impinging jet while video recording the response of liquid crystals for the measurement of the surface temperature. The Reynolds number ranges from Re=11,000 to 50,000, the nozzle-to- surface distance from L/d=2 to 10, and the surface curvature from D/d=6 to 12.The present results are also compared to those for the flat plate case. In the experiment, the local Nusselt numbers tend to increase in all regions with an increasing surface curvature. The maximum Nusselt number for all Reynolds numbers occurred at L/d .ident. 6 and a second maximum in the Nusselt number occurred at R/d .ident. 2 for both Re=23,000 and Re=50,000 in the case of L/d=2 and for Re=50,000 only in the case of L/d=4. Meanwhile, as the surface curvature increases, the value of the secondary maximum Nusselt number decreases. All the other cases exhibit monotonically decreasing values of the Nusselt number along the curved surface. The stagnation point Nusselt numbers are well correlated with Re, L/d, and D/d.
3Â citations
TL;DR: In this article, a rotating axial-flow fan is analyzed with Reynolds averaged Navier-Stokes equations and standard k-epsilon turbulence model, and the flowfield is not significantly affected by the thickness of the blade.
Abstract: Computational and experimental investigations on the three-dimensional flowfield through an automotive cooling fan are carried out in this work. Steady, incompressible, three-dimensional, turbulent flow through a rotating axial-flow fan is analyzed with Reynolds averaged Navier-Stokes equations and standard k-.epsilon. turbulence model. The governing equations are discretized with finite-volume approximations in non-orthogonal curvilinear coordinates. Computational static pressures on the casing wall agree well with the experimental data which are measured in this work. And, they are sensitive to the change of tip clearance. The flowfield is not significantly affected by the thickness of the blade. The k-.omega. model gives the static pressure rise on the casing wall which is similar to that with the k-.epsilon. model.
3Â citations
TL;DR: In this article, the combustion characteristics of methane gas and hydrogen supplemented methane gas in a constant volume combustion chamber were investigated and the main results obtained from the study can be summarized as follows.
Abstract: In the present study, investigations were carried out to obtain data on combustion characteristics of methane gas and hydrogen supplemented methane gas in a constant volume combustion chamber. The main results obtained from the study can be summarized as follows. The maximum combustion pressure increases as the initial pressure and hydrogen supplement rate increase, the total burning time is shorten by lowering the initial pressure and by increasing the hydrogen supplement rate. The maximum flame temperature and NO concentration increase by the initial pressure and hydrogen supplement rate increase. The flame propagation processes in near stoichiometric mixture are propagated with a spherical shape, but in excess rich or lean mixtures are propagated with a elliptical shape. And, they are changed an unstable elliptical shape flame with very regular cells by increasing the hydrogen supplement rate.
3Â citations
TL;DR: In this article, the authors investigated the condensing heat transfer characteristics of hydrocarbon refrigerants and found that pure and mixed hydrocarbon mixtures have higher heat transfer degradation due to composition variation during condensation.
Abstract: Condensing heat transfer characteristics of hydrocarbon refrigerants are experimentally investigated. Single component hydrocarbon refrigerants (propane, isobutane, butane and propylene) and binary mixtures of propane/isobutane and propane/butane are considered as test fluids. Local condensing heat transfer coefficients of selected refrigerants are obtained from overall conductance measurement. Average heat transfer coefficients at different mass fluxes and heat transfer rates are shown and compared with those of R22. Pure hydrocarbon refrigerants have higher values of heat transfer coefficient than R22. It is also found that there is a heat transfer degradation for hydrocarbon mixtures due to composition variation during condensation. Measured condensing heat transfer coefficients are compared with predicted values by available correlations. An empirical correlation for pure and mixed hydrocarbon is developed, and it shows good agreement with experimental data. (author). 24 refs., 10 figs., 2 tabs.
TL;DR: In this paper, the authors studied the temperature distribution and heat transfer characteristics of TEFC induction motor with thermal network program for more efficient design and better cooling performance of it, and compared the simulation results with those of real motor test and the two results showed a good agreement.
Abstract: We studied the temperature distribution and heat transfer characteristics of TEFC induction motor with thermal network program for more efficient design and better cooling performance of it. We knew the characteristics and the windage loss of outer cooling fan from fan test experiments. Frame axial and peripheral heat transfer coefficients and endwinding heat transfer coefficient were measured by various model experiments and then, compared with other experimental results. Frame was the main heat transfer surface, load-side and fan-side surface were not thermally symmetric from the heat flux distribution analysis. Steady and unsteady temperature distributions were measured by real motor experiments. From the results, we knew that rotor surface temperature was higher than coil temperature and the hottest spot in the coil was loadside endwinding outside surface. We compared the simulation results with those of real motor test and the two results showed a good agreement.
TL;DR: In this paper, the early flame development was observed using a fiber optic spark plug, which enabled measurement of the flame front arrival times on a cycle-to-cycle basis on a cyclic basis.
Abstract: The diagnostic used to observe the early flame development was a fiber optic spark plug, which enabled measurement of the flame front arrival times on a cycle-to-cycle basis. The data obtained with this fiber optic spark plug were analyzed to obtain two parameters to describe the behavior of the flame kernel : an expansion speed and a convection velocity. In addition, synchronized cylinder pressure data were taken to compare with the fiber optic spark plug data on a cyclic basis. Heat release analysis was performed on the cylinder pressure data to obtain the mass burning profile of the charge for each cycle. There was a significant correlation observed in the initial flame duration and the kernel expansion speed with dwell angle.
TL;DR: In this article, a numerical study on the chaotic stirring of the screw extruder model was performed, and two nonlinear dynamical tools that are Poincare sections and Lyapunov exponents were used in analysing the stirring effect.
Abstract: Numerical study on the chaotic stirring of the screw extruder model proposed has been performed. The velocity field was used in obtaining the trajectories of passive particles for studying the stirring effect of the screw extruder. Two nonlinear dynamical tools, that are Poincare sections and Lyapunov exponents, were used in analysing the stirring effect. The Poincare sections and the Lyapunov exponents show that the stirring effect is most satisfactory, when n(the number of flights in a section) is 1, for the case a (aspect ratio ; flight height divided by the spacing between flights) being O.1. It is also required to set n=3, or 5 at a= 0.2, 0.3 for a uniform stirring.
TL;DR: In this article, the authors investigated the effect of a vertical bleed duct on the compression wave propagating into a model tunnel, and the results showed that the VFD reduces the maximum pressure gradient of compression wave front by about 30 percent, compared with the straight tunnel without the bleed duct.
Abstract: When a high-speed railway train enters a tunnel, a compression wave is generated ahead of the train and propagates along the tunnel, compressing and accelerating the rest air in front of the wave. At the exit of the tunnel, an impulsive wave is emitted outward toward the surrounding, which causes a positive impulsive noise like a kind of sonic boom produced by a supersonic aircraft. With the advent of high-speed train, such an impulsive noise can be large enough to cause the noise problem, unless some attempts are made to alleviate its pressure levels. For the purpose of the impulsive noise reduction, the present study investigated the effect of a vertical bleed duct on the compression wave propagating into a model tunnel. Numerical results were obtained using a Piecewise Linear Method and testified by experiment of shock tube with an open end. The results showed that the vertical bleed duct reduces the maximum pressure gradient of compression wave front by about 30 percent, compared with the straight tunnel without the bleed duct. As the width of the vertical bleed duct becomes larger, reduction of the impulsive noise is expected to be greater. However the impulsive noise is independent of the height of the vertical bleed duct.
TL;DR: In this article, the influence of oxygen/coal ration and pressure on the maximum production of CO and H in Chinese Datong coal has been evaluated, and it was found that the optimal gasification condition from low pressure runs was oxygen /coal ratio of approximately 0.9 where CO was produced about 40% and H, about 20%.
Abstract: Entrained coal gasification tests with Datong coal were performed to assess the influence of oxygen/coal ration and pressure. When gasification condition in oxygen/coal ratio has changed from 0.5 to 1.0, optimal gasification condition from low pressure runs was oxygen/coal ratio of approximately 0.9 where CO was produced about 40% and H, about 20%. Under the pressure condition of 12-14 atmospheres, optimal oxygen/coal ratio value was in the region of 0.6 where CO was produced about 55% and H2about 25%. From these results, it was found that the oxygen/ coal ratio for the maximum production of CO and H, was decreasing with the increase in gasifier pressure and also, with increasing oxygen content, carbon conversion was increased. For the Chinese Datong coal, cold gas efficiency was in the range of 40-80%.
TL;DR: In this article, the effect of steam injection on the power and efficiency of a simple cycle gas turbine cogeneration system was investigated with an off-design operation of the gas turbine and the compressor performance map.
Abstract: This paper describes a methodology and results for the analysis of a small steam injected gas turbine cogeneration system. A performance analysis program for the gas turbine engine is utilized with modifications required for the model of steam injection and the heat recovery steam generator (HRSG). The object of simulation is a simple cycle gas turbine engine under development which adopts a centrifugal compressor. The analysis is based on the off-design operation of the gas turbine and the compressor performance map is utilized. Analyses are carried out with the injection ratio as the main parameter. The effect of steam injection on the power and efficiency of gas turbine and cogeneration capacity is investigated. Also presented is the variation in the main operating parameters inside the HRSG. Remarkable reduction in NOx generation by steam injection is confirmed. In addition, it is observed that for the 100% power operation the temperature of the cooled first nozzle blade decreases by 100.deg. C at full steam injection, which seems to have a favorable effect on the engine life time.
TL;DR: In this paper, an axisymmetric laminar jet diffusion flame has been numerically modelled to account for the detailed chemical kinetics and the variable transport properties, and the preferential diffusion effects on the diffusion flame in the high-pressure environment are also discussed in detail.
Abstract: An axisymmetric laminar jet diffusion flame has been numerically modelled. The present study employs the refined physical submodels to account for the detailed chemical kinetics and the variable transport properties. It is found that preferential diffusion resulting from variable transport properties significantly influences the hydrogen diffusion flame structure in terms of the spatial distribution for temperature, species concentration, thermal and mass diffusivity, Lewis number, and NO concentration. The preferential diffusion effects on the diffusion flame in the high-pressure environment are also discussed in detail.
TL;DR: In this paper, the authors measured the pressure of a five-hole probe for a full range of yaw and pitch angles and complete pressure coefficient maps were obtained based on these maps.
Abstract: Pressures of a five-hole probe were measured for a full range of yaw and pitch angles and complete pressure coefficient maps were obtained. Based on these maps, various features of five-hole probe pressures were revealed and new five-hole probe calibration coefficients were devised. The new calibration coefficients show non-diverging characteristics for any flow direction and one-to-one correspondence for a wide range of flow angles. These calibration coefficients expand the valid flow angle range of five-hole probe calibration by .+-.10 degrees and complement a critical defect of five-hole probe zone-division calibration method which has not been known yet. Moreover new non-diverging calibration coefficients have advantages in nulling methods, too.
TL;DR: In this paper, the authors focused on the temperature rise of TEFC induction motor with respect to various thermal parameters and found that frame heat transfer had the most important effect on coil temperature rise But those of air gap and rotor fan had no effect.
Abstract: At design stage of new motor or when taking remedial action of old motor, a lot of information can be obtained from thermal parameters analysis This study focused on the temperature rise of TEFC induction motor with respect to various thermal parameters Frame heat transfer had the most important effect on coil temperature rise But those of air gap and rotor fan had no effect This fact shows fan action is more important than fin action in the case of rotor fan Coil temperature can be more decreased by cooling near the heat sources than any other parts from the results of thermal conductivity and loss tests Variation of cooling air flow rate and motor volume effects on coil temperature were also tested These tests suggest that improvement of cooling fan performance is important in reducing the coil temperature rise Thermal equivalent program was verified by comparison of some experimental results
TL;DR: In this article, an experiment was performed to local heat transfer coefficient and Nusselt number in the circular duct of 180.deg. bend for Re=6*10, 8*10 and 1*10 at swirling flow and non-swirling flow conditions.
Abstract: An experiment was performed to local heat transfer coefficient and Nusselt number in the circular duct of 180.deg. bend for Re=6*10, 8*10 and 1*10 at swirling flow and non-swirling flow conditions. The test tube with circular section was made by stainless which has curvature ratio 9.4. The wall of test tube was heated directly by electrical power to 3.51 kw and swirling motion of air was produced by a tangential inlet to the pipe axis at the 180 degree. Measurements of local wall temperatures and bulk mean temperature of air are made at four circumferential positions in the 16 stations. The wall temperatures show particularly reduced distribution curve at bend for non-swirling flow but this effect does not appear for swirling flow. Nusselt number distributions for swirling flow which was calculated from the measured wall and bulk temperatures were higher than that of non-swirling flow. Average Nusselt number of swirling flow increased about 90 ~ 100% than that of non-swirling flow whole through the test tube. The Nu/N values at the station of 90.deg. for non-swirling flow and swirling flow are respectively about 2.5 and 4.8 at Re=6*10. Also that is good agreement with Said's result for non-swirling flow. flow.
TL;DR: In this article, a numerical simulation has been carried out for three-dimensional turbulent flows around an Ahmed body, where the Reynolds-averaged Navier-Stokes equation is solved with the SIMPLE method in general curvilinear coordinates system.
Abstract: A numerical simulation has been carried out for three-dimensional turbulent flows around an Ahmed body. The Reynolds-averaged Navier-Stokes equation is solved with the SIMPLE method in general curvilinear coordinates system. Several k-.epsilon. turbulence models with two convective difference schemes are evaluated for the performance such as drag coefficient, velocity and pressure fields. The drag coefficient, the velocity and pressure fields are found to be changed considerably with the adopted k-.epsilon. turbulence models as well as the finite difference schemes. The results of simulation prove that the RNG k-.epsilon. model with the QUICK scheme predicts fairly well the tendency of velocity and pressure fields and gives more reliable drag coefficient. It is also demonstrated that the large difference between simulations and experiment in the drag coefficient is due to relatively high predicted values of pressure drag from vertical rear end base.
TL;DR: In this article, the applicability of the RNG k-epsilon model to the analysis of the complex flows is studied The governing equations based on a non-orthogonal coordinate formulation with Cartesian velocity components are used and discretized by the finite volume method with non-staggered variable arrangements.
Abstract: In this study, the applicability of the RNG k-epsilon model to the analysis of the complex flows is studied The governing equations based on a non-orthogonal coordinate formulation with Cartesian velocity components are used and discretized by the finite volume method with non-staggered variable arrangements The predicted results using the RNG k-epsilon model of three complex flows, ie, the flow over a backward-facing step and a blunt flat plate, the flow around a 2D model car are compared to these from the standard k-epsilon model and experimental data That of the unsteady axisymmetric turbulent flow within a cylinder of reciprocating model engine including port/valve assembly and the spray characteristics within a chamber of direct injection model engine are compared to these from the standard k-epsilon model and experimental data The results of reattachment length, separated eddy size, average surface pressure distribution using the RNG k-epsilon model show more reasonable trends comparing with the experimental data than those using the modified k-epsilon model Although the predicted rms velocity using the modified k-epsilon model is lower considerably than the experimental data in incylinder flow with poppet valve, predicted axial and radial velocity distributions at the valve exit and in-cylinder region show good agreements with the experimental data The spray tip penetration predicted using the RNG k-epsilon model is more close to the experimental data than that using the modified k-epsilon model The application of the RNG k-epsilon model seems to have some potential for the simulations of the unsteady turbulent flow within a port/valve-cylinder assembly and the spray characteristics over the modified k-epsilon model
TL;DR: In this article, the authors analyzed the thermodynamic behavior of a composite system composed of two simple thermal subsystems with constant heat capacities, and the changes of the states and the potential work of the composite system are shown as the interaction between the subsystems in the composite systems.
Abstract: Thermodynamic behavior of a composite system which is composed of two simple thermal subsystems with constant heat capacities is analyzed, and several thermodynamic phenomena are investigated. The changes of the states and the potential work of the composite system are shown as the interaction between the subsystems in the composite system. The potential work is defined as the possible maximum available work from the composite system, and it is a thermodynamic property of the composite system. The decrease of the potential work is the same as the available work output from the composite system in reversible processes. The dissipation of available work is directly connected to the generation of entropy. The concepts of exergy and internal energy can be explained as a special case of the potential work.
TL;DR: The present study has tested most of loss models previously published in the open literature and found an optimum set of empirical loss models for a reliable performance prediction of centrifugal compressors and recommends a modified parasitic loss model.
Abstract: The present study has tested most of loss models previously published in the open literature and found an optimum set of empirical loss models for a reliable performance prediction of centrifugal compressors. In order to improve the prediction of efficiency curves, this paper recommends a modified parasitic loss model. Predicted performance curves by the proposed optimum set agree fairly well with experimental data for a variety of centrifugal compressors. The prediction method developed through this study can serve as a tool for preliminary design and assist the understanding of the operational characteristics of general purpose centrifugal compressors.
TL;DR: In this paper, a series of experiments were carried out to study the effect of the rotational direction of the belt skimmer on the rate of oil recovery using Bunker C oil.
Abstract: Oil spill over the sea and the river become a serious problem in these days. Two different approaches are used to clean up the spilled oil by means of chemical dispersion and mechanical devices. If it is possible, removing spilled oil using mechanical devices are highly desirable in order not to worry about the secondary contamination from chemical treatment. One of the major unsolved problems using mechanical devices has been the recovery of highly viscous oil spill. So, the systematic experimental data for treating very viscous oil are still wanting. In the present study a series of experiments were carried out to study the effect of the rotational direction of the belt skimmer on the rate of oil recovery using Bunker C oil. Three different situations, namely, upward, downward and up-and-downward pickup rate have been investigated for variable belt speed. The results showed that the rate of oil recovery for downward pickup was much higher than that for upward pickup. The major mechanism to recover the oil using a belt skimmer has been confirmed that oil sticks to the belt surface while moving to the water rather than moving upward. For the removal of spilled oil the optimal belt speed under the present experimental conditions was found to be about 200 ~ 270 mm/s just before the starvation started. The present experimental results would provide the basis for understanding the performance characteristics and physics of various types of skimmers.
TL;DR: In this article, the effects of intake port eccentricity and a partition between the two intake ports on the incylinder swirl characteristics in a 4-valve diesel engine having the 2 intake ports, one is a helical intake port and the other is a tangential intake port, were investigated by using the impulse swirl meter(ISM) in a steady flow test rig.
Abstract: The effects of intake port eccentricity and a partition between the two intake ports on the incylinder swirl characteristics in a 4 valve diesel engine having the two intake ports, one is a helical intake port and the other is a tangential intake port, were investigated by using the impulse swirl meter(ISM) in a steady flow test rig. Mean flow coefficient ( , swirl ratio ( ) and the mass flowrate through the two intake ports with and without intake port partition were measured. The results showed that the characteristics of in-cylinder swirl ratio formed by a 4-valve cylinder head were largely affected by valve eccentricity ratio ( ) and the existence of an intake port partition between the two intake ports. Mean flow coefficient ( ) increases and swirl ratio ( ) decreases in case of being the partition between the two intake ports. And also the mass flowrate through the tangential intake port is 19.0% and 7.7% more than that of the helical intake port in case of the two intake ports with and without partition respectively.ively.
TL;DR: In this paper, an approximate analytical solution for the initial transient process of close contact melting occurring between a phase change material kept at its melting temperature and an isothermally heated flat surface is derived.
Abstract: An approximate analytical solution for the initial transient process of close-contact melting occurring between a phase change material kept at its melting temperature and an isothermally heated flat surface is derived. The model is so developed that it can cover both rectangular and circular cross-sectional solid blocks. Normalization of simplified model equations in reference to the steady solution enables the solution to be expressed in a generalized form depending on the liquid-to-solid density ratio only. A selected result shows an excellent agreement with the previously reported numerical data, which justifies the present approach. The solution appears to be capable of describing all the fundamental characteristics of the transient process. In particular, dependence of the solid descending velocity oft the density ratio at the early stage of melting is successfully resolved. The effects of other parameters except the density ratio on the transient behaviors are efficiently represented via the steady solution implied in the normalized result. A simple approximate method for estimating the effect of convection on heat transfer across the liquid film is also proposed.
TL;DR: In this article, a packet of waves consisting of a Tollmien-Schlichting wave and a pair of Squire waves evolves in a flat-plate laminar boundary layer using a large eddy simulation with a dynamic subgrid-scale model.
Abstract: Flow characteristics are numerically investigated when a packet of waves consisting of a Tollmien-Schlichting wave and a pair of Squire waves evolves in a flat-plate laminar boundary layer using a large eddy simulation with a dynamic subgrid-scale model Characteristics of early stage transitional boundary layer flow such as the LAMBDA vortex, variation of the skin friction and backscatter are predicted Smagorinsky constants and the eddy viscosity obtained from the dynamic subgrid-scale model significantly change as the flow evolves Far Field noise radiated from the transitional boundary layer shows the dipole and quadrupole characteristics owing to the wall shear stress and the Reynolds stresses, respectively
TL;DR: In this article, a simultaneous measurement of wall skin friction and near-wall streamwise velocity fluctuations is performed using hot film and hot wire anemometers to investigate the relation between them.
Abstract: A simultaneous measurement of the wall skin friction and near-wall streamwise velocity fluctuations is performed using hot film and hot wire anemometers to investigate the relation between them. Near-wall turbulence statistics measured with a hot-wire probe are in good agreement with previous results. Turbulence properties of the wall skin friction fluctuations measured with a hot film also show fairly good agreements with those measured by others except that rms level is lower in the present study. Long-time averaged space- time correlations show that the wall skin friction is highly correlated with a turbulence structure which is tilted from the wall in the streamwise direction. Tilting angles are obtained from the phase shifts between the wall skin-friction and streamwise velocity fluctuations. The convection velocity of the near-wall streamwise velocity obtained from the space-time correlation is in good agreement with that from the direct numerical simulation database.