Showing papers in "Transactions of the Japan Society of Mechanical Engineers. B in 1988"
TL;DR: Based on geometrical relationships of the involute teeth of a scroll expander, equations of volume, pressure and output torque were derived in this article, and practical losses which occur in the scroll exander were analyzed theoretically.
Abstract: In recent years, scroll machinery has been put into practice as compressors, taking advantage of their high efficiency and low vibration. Based on geometrical relationships of involute teeth of a scroll expander, equations of volume, pressure and output torque are derived. Moreover, practical losses which occur in the scroll expander are analyzed theoretically. The interference of teeth at the end of the suction process decreases pressures in expansion chambers, which lessens the torque and the suction flow rate of the expander. The interference of teeth at the beginning the discharge process prevents a sudden drop of the pressure in the discharge chamber and recovers the under-expansion loss. Leakages through axial clearances increase the flow rate of the expander and decreases torque greatly. An experimental scroll expander showed reasonable performance and recorded its maximum efficiency of 75%.
26 citations
TL;DR: In this article, the inlet velocity range (based on the minimum flow area) was varied from 2.1 to 20 m/s, while the condensation temperature difference range varied from 3 to 30 K.
Abstract: Film condensation of downward flowing R-113 vapor at near atmospheric pressure on in-line and staggered bundles of smooth tubes was experimentally investigated. The inlet vapor velocity range (based on the minimum flow area) was varied from 2.1 to 20 m/s, while the condensation temperature difference range was varied from 3 to 30 K. Based on the momentum and heat transfer analogy for the condensing film flow, empirical equations for the heat transfer coefficient were derived for both the in-line and staggered tube bundles. These equations compared well with most of the available experimental data for both refrigerants and steam.
24 citations
TL;DR: In this paper, the authors investigated the heat-mass transfer and pressure drop performances during dehumidification of moist air flowing between plate fin and tube heat exchangers which are mainly used in air conditioners.
Abstract: The heat-mass transfer and pressure drop performances during the dehumidification of moist air flowing between plate fin and tube heat exchangers which are mainly used in air conditioners were investigated experimentally. The experimental results revealed the following. The heat transfer performance with condensation was equal to that without condensation, in consideration of dehumidified water on the surface of a heat exchager. The analogy between heat and mass transfer under dehumidification was not completely substantiated. The mass transfer coefficient is smaller than that of theoretical analogy.
23 citations
TL;DR: In this article, an experimental study for the dynamic behavior of a liquid in a cylindrical container subject to horizontal oscillation is presented, where the nonlinear effects on dynamic characteristics of the liquid surface response are investigated.
Abstract: An experimental study is presented for the dynamic behavior of a liquid in a cylindrical container subject to horizontal oscillation. The nonlinear effects on dynamic characteristics of the liquid-surface response are investigated. At low excitation accelerations, the liquid surface responds in a concentric standing wave. For excitation accelerations above a critical value, a surface instability leads to azimuthal standing waves at half the excitation frequency. The time-dependent amplitudes of the standing waves have been measured using an optoelectronic device equipped with a laser diode as a light source. The frequency spectrum of the local surface deformation also has been computed using fast-Fourier-transform methods. It was found that a subharmonic bifurcation occurred at the critical excitation acceleration. At higher excitation accelerations, the free surface responses became chaotic. In order to visualize the attractor, phase portraits were constructed by embedding the trajectories in a two-dimensional phase space.
19 citations
TL;DR: In this paper, the critical inlet flow angle for rotating stall is derived based on the Senoo method for low frequency shaft vibration in high pressure compressors with vaneless diffusers.
Abstract: The rotating stall of centrifugal compressors which often causes low frequency shaft vibration in high pressure compressors is experimentally examined. Pressure fluctuations of low specific speed centrifugal compressors with a vaneless diffuser are measured by pressure transducers. Rotating stall is caused by a vaneless diffuser. The critical inlet flow angle for rotating stall depends not only on diffuser width ratio b/r2 but also contraction ratio b/b2. An empirical prediction formula of critical flow angle for stall based on the Senoo method is derived.
18 citations
TL;DR: In this paper, the forced convective boiling of non-azeotropic refrigerant mixtures of R22 and R114 inside a horizontal tube with internal spiral grooves is presented.
Abstract: Experimental results of forced convective boiling of nonazeotropic refrigerant mixtures of R22 and R114 inside a horizontal tube with internal spiral grooves are presented. Pure refrigerants R22 and R114 and three kinds of their mixtures containing about 25, 50 and 75 mol% R114 are tested in the ranges of mass velocity of 77 to 347 kg/(m2s) and of pressure of 0.6 to 7 bar. The axial distributions of refrigerant temperature and heat transfer coefficient for mixed refrigerants depend on the concentration, while those for pure refrigerants of R22 and R114 show similar behavior. An empirical correlation concerning the heat transfer coefficient of pure and mixed refrigerants is proposed as a function of the boiling number, Lockhart-Martinelli parameter and liquid heat transfer coefficient for a smooth tube.
13 citations
TL;DR: In this paper, a planar heat pipe was employed to determine the effective thermal conductivity of screen wicks saturated with a liquid, and its value was calculated from the heat transfer coefficient in the condenser of the heat pipe positioned horizontally.
Abstract: An experimental study was performed on the effective thermal conductivity of screen wicks saturated with a liquid. A planar heat pipe was employed to determine the effective thermal conductivity, and its value was calculated from the heat transfer coefficient in the condenser of the heat pipe positioned horizontally. A comparison of the existing correlations with the present experimental data indicated that the effective thermal conductivity of screen wicks could be predicted by Maxwell's equation derived for the case where wick materials (or screens) were dispersed in working liquids. It was also found that, in predicting the effective thermal conductivity by Maxwell's equation, the thickness and porosity of multilayer screen wicks had to be estimated accurately by taking account of the intermeshing between screen layers.
13 citations
TL;DR: In this article, the heat transport characteristics of a thermosyphon were experimentally investigated using R 113, methanol and water as the working fluid, and non-dimensional expressions were derived for relating the heat transfer at the cooling and heating sections.
Abstract: The heat transport characteristics of a thermosyphon are experimentally investigated using R 113, methanol and water as the working fluid. The condensation heat transfer at the cooling section shows a trend similar to the Nusslelt's prediction for its temperature difference, while the measured values are considerably lower when the upward vapor velocity is high, as in the case of water. Based on the characteristics in heat transfer at the cooling and heating sections, non-dimensional expressions are derived for relating the heat transfer at the cooling and heating sections, non-dimensional expressions are derived for relating the heat transport rate of thermosyphons to the temperature difference between the heating and cooling sections.
12 citations
TL;DR: In this article, the behavior of unvaporized spray and its fuel concentration distribution after impinging on a plane wall of the combustion chamber were investigated by the image analysis of shadow photographs of fuel spray.
Abstract: In order to clarify a mixing process of injected fuel and air at a combustion chamber of a diesel engine, the behavior of unvaporized spray and its fuel concentration distribution after impinging on a plane wall of the combustion chamber were investigated by the image analysis of shadow photographs of fuel spray. Experimental studies were conducted with variation of the patterns of injection pressure, ambient gas densities and diameters of injection nozzles under the conditions which fuel was injected perpendicularly to an acrylic plate wetted by fuel. The mixing between fuel and ambient gas was promoted by the spray impingement, and the shorter the distance between the injection nozzle and the wall was placed, the bigger the mixing was effected. More quantities of ambient gas entrained into spray was observed by the spray impingement on a wall than one of free spray, especially with bigger diameter of nozzles. The empirical relations for the spray development after impingement on the plane wall were obtained and compared with experimental results. (12 figs, 1 tab, 9 refs)
11 citations
TL;DR: In this paper, a vertical plate with a horizontal partition plate has been investigated experimentally and the results show that the three dimensional flow appears behind the plate when the height of the partition plate, H, exceeds a certain value.
Abstract: Natural convective heat transfer from a vertical plate with a horizontal partition plate has been investigated experimentally. The expemiments were carried out with water, for modified Rayleigh numbers ranging from 6.0×107 to 1011, and for various heights of partition plates in the range of 0-70 mm. The flow and temperature fields are visualized. The results show that the three dimensional flow appears behind the plate when the height of the partition plate, H, exceeds a certain value. The transition to turbulence is found to occur at higher values of H. The local heat transfer coefficients are measured to examine the effect of the partition plate. It is revealed that the heat transfer rates decrease in the upstream region of the partition plate when compared with those for the no partition plate. On the other hand, the heat transfer rates behind the partition plate increase significantly at high values of H.
11 citations
TL;DR: In this paper, an experimental investigation was carried out with initiation and propagation of shock waves in the exhaust pipe in an internal combustion engine, and it was shown that the nonlinear effect should be taken into account at the design stage of engine muffler.
Abstract: In connection with the reduction of the exhaust noise of an internal combustion engine an experimental investigation was carried out with initiation and propagation of shock waves in the exhaust pipe in an internal combustion engine. The pressure measurements along the exhaust pipe clearly show that shock waves exsit in the exhaust pipe when the engine is running at high speed. In order to obtain a direct evidence of the existene of shock waves in the exhaust pipe, a flow visualization Study was conducted by using holographic interferometry, and shock waves were found. This indicat that, the non-linear effect should be taken into account at the design stage of engine muffler.
TL;DR: In this article, it was shown that the velocity profile changes smoothly from laminar to turbulent in the upstream but becomes peculiar in the downstream due to the development of the transition region.
Abstract: In the preceding report, it was made clear that there exists two types of flow transition from laminar to turbulent in an accelerated flow depending on the degree of acceleration. In order to determine the mechanism of these types of transition the present measurements were performed and the change of the velocity profile at each time step was compared at two different stations. The results show that in the case of relatively large acceleration (r0/ustT>10-3), flow transition takes place simultaneously over the whole area in a pipe due to the flow instability. On the contrary, in the case of relatively small acceleration ((r0/ustT<10-3), flow transition takes place near the pipe inlet and forms a discontinuous surface (transition surface) propagating to the downstream with a velocity larger than the mean flow velocity. In this case the velocity profile changes smoothly from laminar to turbulent in the upstream but becomes peculiar in the downstream due to the development of the transition region.
TL;DR: In this paper, velocity profiles of the laminar flow in the developing region of an axially rotating pipe are analyzed numerically and compared with the experimental results when an uniform axial flow is introduced into it.
Abstract: In this paper, velocity profiles of the laminar flow in the developing region of an axially rotating pipe are analyzed numerically and are compared with the experimental results when an uniform axial flow is introduced into it. It is found that the axial velocity in the rotating pipe exceeds the value of the Poiseuille flow at the center, and a backward flow appears near the wall as the swirl ratio becomes large. The greater the swirl ratio N becomes, the more remarkable it tends to become ; but at about N = 3 experiments show that the rotation of the pipe causes the flow to become unstable and the development of the flow is delayed.
TL;DR: In this paper, an improved k-emodel based on the consideration of two length scales, one very near the wall and the other in the fully turbulent region, is proposed.
Abstract: After re-examining apparent problems of previous k-eturbulence models, the present authors propose an improved k-emodel based on the consideration of two length scales, one very near the wall and the other in the fully turbulent region. Main features of the present model are as follows: (1) it does not require any additional terms in the transport equations in order to improve numerical predictions in the wall region and / or to facilitate numerical computation, (2) it gives the physically correct limiting behavior of turbulence quantities such as k, e, - uv^^- and fμas the wall is approached, (3) the function fμ, usually called a damping factor, is presently called a conversion factor of length scales because of its physical meaning, (4) the present model allows for a direct comparison between the predicted and measuredein the wall region.
TL;DR: In this article, a picture processing technique is applied to study the flame motion in a direct-injection diesel engine, and two-dimensional cross-correlation coefficients of flame luminosity between two successive frames are obtained.
Abstract: A picture processing technique is applied to study the flame motion in a direct-injection diesel engine. From the high-speed photographs, two-dimensional cross-correlation coefficients of flame luminosity between two successive frames are obtained. The location and value of the maximum coefficients give us the mean and fluctuating velocities of the flame, respectively. The results show that the fluctuating velocity obtained in a wide region is almost independent of measuring position and size in the middle and later stages of combustion, indicating that the turbulent flow field is almost uniform and isotropic over the space. Furthermore, the effects of the swirl and chamber geometry on the flame behavior are discussed in detail.
TL;DR: In this article, an experimental study was conducted to examine the heat transfer enhancement in forced convective channel flow by means of the ionic wind induced between the plate wall and negative wire electrodes, which were put at the center line of the channel.
Abstract: An experimental study was conducted to examine the heat transfer enhancement in forced convective channel flow by means of the ionic wind induced between the plate wall and plural negative wire electrodes, which were put at the center line of the channel. A theoretical analysis was also performed on electric, flow, and temperature field taking account of the interactions among these fields. Firstly, the combined flow field where the cellular secondary motion occured owing to the field's interaction was characterized in conjunction with the bulk flow velocity and the electric field strength. Secondly, the enhancement of convective heat transfer rate was recognized, especially under low Reynolds number, and its mechanism was clarified. On the basis of these results, the heat transfer performance was shown in connection with the amount of electric power and pumping power.
TL;DR: In this paper, the authors measured a 3D wall-jet along a convex wall and showed that the wall static pressure along the centerline decreases considerably, and a significant increase of the vertical jet width compared with that of the spanwise one is observed.
Abstract: A circular turbulent wall-jet along a convex wall was measured in comparison with that along a flat plate, and the flow characteristics of the three-dimensional wall-jet under a streamwise curvature effect was examined. By hot-wire anemometry, all velocity components were measured so that the components of turbulent intensity, the Reynolds stresses, and the mean streamwise vorticity were fiqured out. The main conclusions are as follows : 1) there are two pairs of secondary flows in the circular wall-jet along a flat plate, 2) an additional pair of secondary flows appears in the case of the flow along a convex wall 3) as an effect of curvature, the wall static pressure along the centerline decreases considerably, and 4) a significant increase of the vertical jet width compared with that of the spanwise one is observed.
TL;DR: In this article, a distribution of instantaneous heat transfer coefficients around the flow reattachment region behind a two-dimensional backward-facing step was accumlated as time-continuous data, in order to clarify the heat transfer mechanism at that region.
Abstract: A distribution of instantaneous heat transfer coefficients around the flow reattachment region behind a two-dimensional backward-facing step was accumlated as time-continuous data, in order to clarify the heat transfer mechanism at that region. For this purpose, ten heat flux meters based on a constant temperature method were arrayed on the bottom surface of the step. The ensemble-averaged heat transfer coefficients were calculated on the condition that the maximum instantaneous heat transfer coefficient appeared at a specified heat flux meter. The position, where the peak in the ensemble-averaged distributions shows the maximum, located a about a one step height upstream of the time-averaged reattachment point. In general, the position of the maximum instantaneous heat transfer coefficient moves downward and appears discontinuously near the time-averaged reattachment point.
TL;DR: In this paper, the effects of the velocity gradients on hot wire anemometry with an X hot wire probe were theoretically analyzed and a new method of measuring which eliminates those errors was proposed based on the results of the analysis.
Abstract: The effects of the velocity gradients on hot wire anemometry with an X hot wire probe were theoretically analyzed. Analysis showed a strong possibility that the values obtained from the traditional way of measurements with an X hot wire probe involve serious experimental errors caused by the velocity gradients. A new method of measuring which eliminates those errors was proposed based on the results of the analysis. The new method includes the use of two X hot wire probes, one of which is the reflected image of the other, and the taking of arithmetic means of the values obtained from those probes. The validity of the analysis was confirmed by measuring a turbulent flow in a square duct with rough walls on two opposite sides. The results of measurements showed that the new method is very effective for the measurement of quantities, such as the secondary flow velocities and the turbulent shear stresses, quantities which are very sensitive to the effects of velocity gradients.
TL;DR: In this paper, an application of the Weis-Fogh mechanism to pumps was studied and a pilot pump was built and the characteristics were investigated experimentally, and it was shown that this mechanism works well for pumps.
Abstract: An application of the Weis-Fogh mechanism to pumps was studied. A pilot pump was built and the characteristics were investigated experimentally, and it was shown that this mechanism works well for pumps. From the point of of view of the specific speed, the characteristics of this pump are similar to those of diagonal flow pumps. The maximum efficiency was about 24%. A flow visualization about the wing was performed and clusters of vortices were found to be produced periodically in the wake. Some possibilities for raising the efficiency were discussed.
TL;DR: In this article, boundary layer fences were installed at the back of the cascade in parallel with the side walls to trap the passage and trailing vortices, which effectively reduced secondary flow and loss.
Abstract: This paper studies the effects of blade boundary fences on secondary flow and losses in a turbine cascade. Boundary layer fences were installed at the back of the cascade in parallel with the side walls. A wind tunnel test was conducted on the basis of different distances (Zf) between the fences and the endwalls. The fences effectively reduced secondary flow and loss. The total loss (the sum of net loss and secondary kinetic energy), net loss (average mass loss occurring between the upstream and downstream sides of the cascade), and secondary loss are minimized when Zf equals the inlet boundary layer thickness (d). The three losses decreased by 21, 12, and 32% respectively in comparison to the case of ordinary cascades. The passage vortex, trailing vortex, trailing secondary flow region thickness, and secondary kinetic energy were minimized when Zf = 2/3d. These values decreased by 30, 60, 40, and 50% respectively in comparison to the case of ordinary cascades. In the Zf range from 2/3d to 4/3d, fences shut up and trap the passage and trailing vortices. (14 figs, 2 tabs, 19 refs)
TL;DR: In this article, an air-turbine with self-pitch-controlled blades for wave power utility, experimental investigations have been performed by model testing of turbine rotors with fixed staggered blades under steady operating conditions.
Abstract: In order to develop an air-turbine with self-pitch-controlled blades for wave power utility, experimental investigations have been performed by model testing of turbine rotors with fixed staggered blades under steady operating conditions. Twelve kinds of rotors have been manufactured and tested to investigate the effect of setting angle, thickness/chord ratio, aspect ratio and solidity on the turbine performance. The results have shown that the self-pitch-controlled turbine is superior to the wells turbine both in starting and running characteristics. A suitable choice of the design factors has been suggested.
TL;DR: In this article, an analysis of the one-dimensional two-phase flow of magnetic fluid in a diverging duct is developed for a low-quality case, taking into account the slip and pulsation of gas bubbles.
Abstract: An analysis of the one-dimensional two-phase flow of magnetic fluid in a diverging duct is developed for a low-quality case, taking into account the slip and pulsation of gas bubbles. It is shown that the injection of gas bubbles in the throat effectively increases the pressure rise in the diverging duct under a nonuniform magnetic field. Furthermore, the analytical results are confirmed by an experimental study in which the effect of magnetic field on the total pressure loss in the test loop is measured.
TL;DR: In this article, the authors derived a fundamental differential equation describing the constriction resistance phenomenon caused by the inhomogeneity of the surface heat flux, which can be determined by a Biot number defined with the interfacial heat transfer coefficient, the departing drop radius and with the surface thermal conductivity, in addition to a few characteristic parameters.
Abstract: The effect of the thermal conductivity of the condenser material on the dropwise condensation heat-transfer has been studied analytically. By taking account of the contribution of the droplet resistance in the individual dropsize class to the thermal resistance in the transient dropwise condensation, the authors derive a fundamental differential equation describing the constriction resistance phenomenon caused by the inhomogeneity of the surface heat flux. It is found from the nondimensionalized form of the fundamental equation that the constriction resistance can be determined by a Biot number defined with the interfacial heat-transfer coefficient, the departing drop radius and with the surface thermal conductivity, in addition to a few characteristic parameters. By applying the so-called equilibrium region of small drops as the drop-size distribution, this equation is solved numerically so that the effects of these parameters on the heat-transfer coefficient are presented.
TL;DR: In this article, a single spray was impinged on a flat wall at a normal angle, and the growth of the spray was photographed, not only with transmitted light but also with scattered light through a narrow slit.
Abstract: In the experiments presented here, diesel fuel oil was injected into a high pressure chamber in which compressed air or CO2 gas at room temperature was charged. A single spray was impinged on a flat wall at a normal angle. The growth of the spray was photographed, not only with transmitted light but also with scattered light through a narrow slit. The temporal and spatial distribution of the droplets density in the impinging spray applying the concentric circle model was calculated using data collected by the laser light extinction method. From these results, detailed information concerning the droplets density in the impinging diesel spray was obtained. The effects of ambient density, distance from the wall to the nozzle, and injection pressure on the impinging spray were revealed. Finally, experimental equations for the radius and the height of the impinging spray were obtained.
TL;DR: In this paper, a general method of solution using the boundary element method (BEM) is developed for multi-dimensional inverse problems of heat conduction, and a concrete formulation is presented for the one-dimensional problem in which the surface temperature and the surface heat flux are sought from the temperature measured at two interior points.
Abstract: A general method of solution using the boundary element method (BEM) is developed for multi dimensional inverse problems of heat conduction. A concrete formulation is presented for the one-dimensional problem in which the surface temperature and the surface heat flux are sought from the temperature measured at two interior points. By solving the Beck's problem, the stability of the calculation is studied, and the result is compared with that of the method based on the Duhamel theorem. A simple two-dimensional problem is also dealt with in an attempt to show the applicability of the present method.
TL;DR: In this article, complete condensation of nonazeotropic binary mixtures of R11-R113 refrigerants is experimentally studied, and the axial distribution of the local heat transfer coefficients is derived to correlate condensation heat transfer performance.
Abstract: Complete condensation of nonazeotropic binary mixtures of R11-R113 refrigerants is experimentally studied. The test apparatus consists of two concentric horizontal tubes, with the vapor mixture flowing in the inner tube and the cooling water in the annular space in the countercurrent direction. The composition and the mass flow rate of the binary-component mixture are systematically varied. Through the measurement of the local temperature of the wall, the cooling water and the vapor along the tube axis, the axial distribution of the local heat transfer coefficients are obtained. An empirical equation is derived to correlate condensation heat transfer performance.
TL;DR: In this paper, a theory on combustion similarity in diesel engines is presented, which is based on the correspondence of fundamental equations of change, i.e. continuity, motion, and energy equations, and correspondence of initial and boundary conditions for the different size engines.
Abstract: The paper presents a theory on combustion similarity in diesel engines, and contributes to the realization of scale model-experiments. The theory is based on the correspondence of fundamental equations of change, i.e. continuity, motion, and energy equations, and the correspondence of initial and boundary conditions for the different size engines. As a result of the investigation, it was found that there exists a possibility of combustion similarity for different size diesel engines. The similarity conditions were identified on engine configuration, injection system, fuel properties, swirl ratio, engine revolution, droplet size of the fuel spray, temperature of the cylinder wall and ignition lag.
TL;DR: In this article, the turbulent heat transfer of combined forced and natural convection along a vertical flat plate was investigated experimentally both on the aiding and the opposing flows of air, and it was found that the non-dimensional parameter Z (=Gr*x/NuxRex)2.7Pr 0.6) can predict the behavior of heat transfer both for air and water.
Abstract: The turbulent heat transfer of combined forced and natural convection along a vertical flat plate is investigated experimentally both on the aiding and the opposing flows of air. Local heat transfer coefficients are measured in the vertical direction. The results show that the local Nusselt numbers for the aiding flow become smaller than those for the forced and the natural convection, while the Nusselt numbers for the opposing flow are increased significantly. These results are compared with the previous results for water. It was found that the non-dimensional parameter Z (=Gr*x/NuxRex)2.7Pr0.6) can predict the behavior of heat transfer both for air and water. Furthermore, the natural, the forced, and their combined convection regions can be classified in terms of the above parameter.