Pumping system characteristics are surveyed theoretically and explored in tests under the condition of 60 kPa suction head to improve cavitation performance in a pumping system with two jet pumps and one turbo pump. One of the two jet pumps is connected to a suction pipe upstream from the turbo pump and the other one is to a delivery loop downstream. Also analytical and experimental studies are carried out on the relationship between pumping system efficiency and individual pump efficiency, using a pumping system with a jet pump connected to the suction pipe upstrean from a centrifugal pump.

View full abstract

A slipstream emanating from a triple point in the Mach reflection of a shock wave, which is assumed to be a discontinuous surface in the three-shock theory, from a high-speed mixing layer. In the present paper, the slipstream in the Mach reflection has been investigated in detail and visualized by means of the shadowgraph method. Numerical simulations have been performed using the discrete vortex method. Also, the transition from laminar to turbulent mixing layer have been studied experimentally and numerically.

View full abstract

This paper presents time histories of unsteady forces acting on a flat plate which made a cycle of pitching motion, in a uniform main flow, about its mid-chord position. Measurements were made possible by the use of a novel balance which could simultaneously detect all of drag, lift and moment as functions of time during the pitching motion. The angle of attack of the plate was increased from zero to an angleα_r at a constant angular velocity, and then immediately decreased fromα_r to zero at the same angular velocity. The time histories of the drag and lift showed a maximum value at a particular phase of the pitching motion. The maximum drag and lift increased with increasing non-dimensional angular valocity k which is the circumferential velocity of the edges of the plate divided by the main-flow velocity. In particular, the maximum drag forα_r=90°and k=0.49 was approximately three times larger than the drag of a stationary normal plate.

View full abstract

After re-examining apparent problems of previous k-εturbulence models, the present authors propose an improved k-εmodel 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, ε, - uv^^^- and f_μas the wall is approached, (3) the function f_μ, 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 measuredεin the wall region.

View full abstract

The flow field downstream of a sudden, circular channel expansion was classified into three regions: the jet and recirculation region, the reattachment region, and the redeveloping region. The limits between them were determined by the tuft method. An empirical formula for the reattachment length was proposed. The axial distributions of the root mean square value of pressure and heat transfer fluctuations on the wall of the larger pipe exhibited peak values. The peak positions agreed well with one another and they were located around the limit between the jet and recirculation region and the reattachment region. Also, the axial distribution of the turbulence intensity measured near the wall had a peak. Its position was in fairly good agreement with the positions of the above mentioned two peaks.

View full abstract

The turbulence production of turbulent flows with different inlet conditions through two types of conical diffusers is calculated with the measured velocity profile and turbulence shear stress distribution at each section in the conical diffuser. The static pressure calculated with the turbulence production is compared with the measured pressure at the same section. The pressure drop caused by turbulence production nearly coincides with the measured one at any section.

View full abstract

In the 1st. report, a theoretical and experimental analysis of flow patterns occuring around a single flat plate set on the lower wall of the flow passage, as the simplest type of turbulence promoter, was described. This 2nd report describes an experimental analysis in the case of a single flat plate set on the upper wall of the flow passage. The experimental results show that the relationships among the Reynolds number, the blockage ratio C and the coefficient of lossξ, are almost the same in both cases, but that the coefficient of mean pressure fluctuationζ, is larger when the flat plate is set on the lower than when set on the upper wall. The distributions of the peaks of the coefficients of the pressure fluctuation were also determined. These experimental results are very useful not only for the design of turbulence promoters but also for the design of heat conducters.

View full abstract

The flow field in a wall attachment amplifier was visualized and analyzed numerically, and the flow pattern was made clear in the former studies (1) (2) (3). Also, the field-diving method using the k-εturbulent flow model was developed, and its effectiveness has been confirmed by the experiment of flow visualization and velocity measurement. In this study, the variations of the input and output static characteristics of a wall attachment device were made clear by numerical analysis and experiments changing the splitter distance, supply and control flow rate. In this case, a FLIP-FLOP-type logical device was used as the wall attachment device. The numerical method used was the flow-field diving method using the k-εturbulent model, as in the former reports. The input and output static characteristics were determined from the velocity and pressure distributions obtained by using this numerical analysis method. The experiments were performed by changing the Reynolds number, control flow rate and splitter distance. The results were compared with analytical values with which they were in good agreement. From these results, the effects that the variation of splitter distance, control flow rate and supply flow rate exerted on the characteristics of the device were made clear, and the effectiveness of the flow-field dividing method for the calculation of the characteristics was confirmed.

View full abstract

An experimental investigation was conducted to determine the mechanism and conditions of governing the boundary-layer transition phenomena which were induced by a circular cylinder placed at some distance apart from a plate. The cylinder of 1.0 mm in diameter was placed 0.25 m downstream from the leading edge of the plate, and gap to diameter ratios were selected to be 0.3, 0.5 and 0.6. These ratios were chosen because they were found to have different characteristics on the boundary-layer transition in the former experiments. Mean velocity distribution, intensity of turbulence and distribution spectra in the wake flow were measured for each gap condition under the unit Reynolds number of U₀/ν=3.5×10⁵ (m<-1>). The results obtained are as follows. In the case of the gap ratio of 0.6, boundary-layer transition occurs by the direct interference between the wake of the cylinder and the laminar boundary-layer of the plate. On the contrary, the transition at the ratio of 0.5 is observed to be shed from the cylinder. In the case of the ratio of 0.3, no vortices were observed and the mechanism of transition was similar to that of a tripping wire which has no gap with the plate.

View full abstract

A simple model is proposed to analyze the pulsatile flow of Bingham plastic fluids. The present model contains the effect that the value of the turbulent viscosity coefficient depends on the acceleration of the flow, and the turbulent viscosity coefficient is given by the acceleration parameter. It is found that the experimental results (1st report) can be explained by this effect quite well. Lastly, the characteristics of the pulsatile flow of Bingham plastic fluids accompanied with the relaminarization are discussed by this model. In addition, it is suggest that the relaminarization of Bingham plastic fluids occurs easily compared with the Newtonian fluids.

View full abstract

The meniscus instability for Newtonian fluids of glycerine, silicone oil and castor oil was previously studied by the authors. In the present paper, a water solution of polyacrylamide (separan) is used as a sample liquid. The viscosity of the fluid depends on the strain rate of flow; this dependency is a power function of the strain rate and the power index can be easily changed by the concentration of separan. A linear instability analysis on the meniscus of the fluid, when two plates confining the fluid are separated, is carried out using a constitutive equation of a power-law fluid. As a result of the analysis, a modified capillary number for non-Newtonian fluid which also includes the one for Newtonian fluid is defined, and the relation between the wavelength of the disturbance on the meniscus and the modified capillary number is derived. The experimental results for the wavelength of disturbance and the energy required to separate two plates are investigated with respect to the modified capillary number. It is found that both results obey an exponential relation.

View full abstract

A simulation program for rarefied gas flow with the pressure conditions given at the upstream and downstream boundaries has been developed. With the pressure conditions given at the upstream and downstream boundaries, flow velocities at these boundaries are revised in every time-step with the number of molecules going in and out. Then, a steady solution with the continuous flow properties at the upstream and downstream boundaries is obtained by averaging the flow poperties after the appropriate time. The algorithm of molecular movements and collisions is based on the Direct Simulation Monte Carlo Method by Bird. Results of the calculation by this program are compared with and verified by the Dong's empirical results for 2-D Poiseuille flow.

View full abstract

The motion of a small particle is studied in a viscous flow through a narrow and sinusoidally wavy channel. Assuming that the ratio of the amplitude to the period, the aspect ratio, is small in the walls of the channel, an approximate solution of the equations of motion on the fluid and the particle is found maintainig the precision of the third order of the ratio. It is found that there is only one kind of trajectory along which it is possible for a small particle to pass through the wavy channel. The condition under which a particle passes through the channel is found as a relation of the aspect ratio, the Stokes number, the Reynolds number and the amplitude of the wavy channel. This condition is shown concretly in the aspect ratio-amplitude space by choosing the Stokes number and the Reynolds number as the parameter.

View full abstract

Analytic solutions for viscous shear flows past a circular cylinder are studied with the Oseen approximation. The governing equation for the velocity field is composed of the equations for the Oseen approximation. The governing equation for the velocity field is composed of the equations for the Oseen velocities and the linear perturbation ones, (u^ε', v<ε'>), containing the shear parameter`ε'. The latter velocities are evolved from the successive approximation based on the Oseen solution of vorticity. The formal solutions for u of these velocity fields can be written by superimposing the nonsymmetric solutions of the Oseen ones on the above velocities u^ε'. On the basis of these solutions, the expansion formulas of the stream function, Ψ, and the vorticity, ζ, are respectively obtained up to the fourth powers of the Reynolds number, Re. Flow patterns withε=0.1, 0.16 and 0.5 are shown at Re=0.1. Furthermore, the expansion formulas of lift, moment and pressure distribution are obtained. In the range of Re from 0.01 to 1/0, the value of lift, moment and pressure distribution are obtained. In the range of Re from 0.01 to 1.0, the value of lift gives rise to minus values and these decrease in proportion toε. These results are qualitatively in agreement with ones of numerical solutions whenεis under 0.5.

View full abstract

A discrete-vortex method is employed to simulate a two-dimensional reattaching jet issuing from the metering orifice of spool valves. The process of reattaching jet formation is investigated in detail. The behavior of the vortex shedding near the orifice outlet is discussed by comparing the simulated results with the potential jet solution obtained by von Mises and the flow visualization results. A prediction of the vortex pattern of the reattaching jet and the pressure distribution is undertaken. The simulated results of the pressure distribution on the wall are found to agree with the experimental results. In the present simulation, the potential solution in the absence of a discrete vortex is obtained numerically by solving Laplace equations and a numerical grid is used to simulate the jet by a discrete-vortex method.

View full abstract

An investigation of erosion-corrosion was carried out using an impingement jet apparatus and vibratory water bath. Obtained results were as follows: (1). The mass loss of the damaged material increased with the jet velocity in the range of V=0-0.5m/s, and got the largest at the velocity V=0.5m/s. Then the loss at V=1.5-6.0m/s became as small as that at V=0m/s. The mall loss was proportional to the area of damaged surface. (2) Pitting occurred in the surface of the target material number impingement jet flow. The diameter of a produced pit decreased with increasing the jet velocity, but the depth of the pit was independent on the velocity, (3) The oxidation number of the iron oxide of the corrosion products in the flow was relatively low. (4) The mass loss in pressure vibrating field is larger than that in a static field, and the damage pattern is unumiform compared with that in the static field.

View full abstract

In this paper, we present a numerical simulator of unsteady flow velocity profile in the entrance region of a circular pipe by means of finite difference method (FDM). The simulator is useful in verifying the accuracy of velocity profiles estimated by the model-based technique proposed by us, since an approximated fluid line model of the entrance region in the pipe is used for the technique. The accuracy of the simulator itself is verified by comparing velocity profiles obtained by the simulator with (1) an analytical solution for fully developed flow and (2) experimental results for the entrance flow. The experimental results were obtained by using a beam scanning laser Doppler velocimeter (BS-LDV) which was developed in our laboratory and which can measure the velocity profile on a line by scanning the laser beam in a very short period of time.

View full abstract

When a viscoelastic fluid flows out from a horizontally placed rectangular duct, many cracks and upheavals are formed on the upper surface of the jet. This anomalous phenomenon is reported for the first time by authors. We investigate the appearance critical point of this anomalous phenomenon is reported for the first time by authors. We investigate the appearance critical point of this anomalous phenomenon under various conditions. Fourteen ducts having various heights, widths and lengths are used in this study. They have a knife edge and semi-cylinder shaped duct exits. We also use four kinds of fluids having different flow properties. Moreover, we find an empirical formula for the appearance critical point of the anomalous phenomenon making use of the dimensional analysis method.

View full abstract

The flow characteristics of a three-dimensiomal air jet issuing from nozzle 20-60 mm in diameter, which is parallel to a horizontal wall with the vertical distance, have been experimentally investigated. The contours of the jet boundary at a section perpendicular to the axis are approximately expressed by two different circular arcs, and in order to express the variation of the contour along the axis, an empirical expression for the locus of the points of the axial maximum velocities and expressions for two typical radial radii from the points are determined, respectively. The distributions of decay of the maximum velocity profiles along the radial radii and the distribution of shearing stress at the wall are clarified. The bend of the main streamline which is a feature of the present jet, the locus of the maximum velocities, is clarified.

View full abstract

An experiment was performed for two-phase flow of air-water mixtures through a multiple channel consisting of three subchannels. Each subchannel was interconnected to the other two by a gap clearance, and the respective cross-sectional area of each subchannel was different, with equal area ratio of 1.5. The purpose was to provide such data on the flow distributions so as to be applicable for the improvement of subchannel analysis. Data on the fully developed flow distributions of both phases are presented and compared with those obtained from other multiple channels. A practical method to calculate the flow distributions in a multiple channels. A practical method to calculate the flow distributions in a multiple channel is proposed also in this paper.

View full abstract

Experimental and analytical investigation are conducted on flow instability in a horizontally installed liquid nitrogen shell and tube-type heat exchanger. The experiments are carried out by making use of water steam as a secondary fluid, and it is observed that flow instability occures in the range of large inlet flow rate. An anemometer using a hot film as a sensor is used to measure inlet velocity perturbation of liquid nitrogen. Mode analysis of the inlet velocity perturbation reveals that there exists a fundamental mode and its higher harmonics up to the third. As the period of the fundamental mode is nearly equal to the transit time for a fluid particle to travel through the heated tube, which is obtained by a static analysis, it is suggested that flow instability is of the density wave type. Moreover, static instability that is accompanied with a fall of the pressure drop is also observed in the vicinity of the stability boundary. The analysis of the static heat transfer and pressure-drop characteristics can simulate the experimental data.

View full abstract

The GSMAC-FEM (Generalized Simplified Marker and Cell FEM) which is an extension of the SMAC-FDM is a stable and fast scheme for the incompressible viscous flow. The rotation form of the Navier-Stokes equation in which velocity and Bernoulli function are interpolated as a linear function and a constant function. This interpolation is simple and convenient in making the mesh system. On the contrary, the approximation which is mentioned above makes it difficult to analyze inlet-exit flow including the Neumann's boundary conditions. The present paper shows a modified GSMAC method which is available for high Reynolds flows with Neumann's boundary conditions (especially the pressure boundary).The modified scheme consists of an algorithm which satisfies the continuity equation much more than the previous GSMAC method.

View full abstract

A new iterative method has been developed for calculating steady flows in a square cavity. The steady stream function vorticity equations are discretized with the central finite difference approximation and the resulting system of equations are solved by using the group-explicit-iterative (GEI) method. The calculations are carried out for the case with Reynolds number as high as 10000 on 257×257 grid points. The computed results are in excellent agreement with those by other methods.

View full abstract

A numerical method for analyzing steady two-dimensional incompressible viscous flow is proposed. In this method, the unsteady Navier-Stokes equations are solved using a time-splitting method and a convective-difference scheme, and an elliptic equation for pressure by Gaussian elimination. The distinctive feature of the method is to make use of the convective-difference scheme, in which the substantial derivative term is integrated along a path line and the convective-difference scheme, in which the substantial derivative term is integrated along a path line and the values at the upstream end are interpolated based on a polynomial or an exponential or an exponential function. The method has second-order accuracy, and the continuity condition is satisfied completely. Entrance flows of a parallel walled duct and square cavity flows were solved to verify the effectiveness of the method. The method can be applied to the relatively high Reynolds number flows.

View full abstract

The paper describes an analysis of viscous pumps with shrouded pockets using incompressible fluids. It was found that there is a linear relation between the flow rate and the discharge pressure. The optimum pump geometry for the maximum flow rate is presented. Frictional torque is examined for the optimized pump geometry. Finally, the characteristics of the pumps proposed in this paper are compared with those of spiral groove viscous pumps which are frequently used.

View full 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.

View full abstract

The long span gates vibrating in the streamwise direction push and draw the water in the reservoir, thus the gate is accompanied by an added mass of water. Moreover, the waves propagating in the upstream direction are formed on the free reservoir surface, thus resulting in a fluid damping effect on the vibrating gates. The added mass and fluid damping coefficient was derived theoretically in a dimensionless form in a previous study. To verify the theoretical results of the added mass and fluid damping coefficient, the experimental results of a model test are presented in this study. A planar vertical gate undergoes free damped vibrations in air and still water, respectively. The added mass and fluid damping coefficient are calculated from the measured frequencies and damping ratios of the damped vibrations. Consequently, it is shown that there is good agreement between the theoretical and experimental results.

View full abstract

Experiments have been performed systematically to investigate the performance and flow characteristics for a wide range of mixed-flow-type conical walled annular diffusers. The configuration of this type of diffusers consists of a circular inlet cross-sectional portion and conically diverging inner and outer walls having the same cone angle or different angles. All diffusers were tested in low-speed air flow with the inlet flow condition that the velocity profile is uniform in the core region except for a thin boundary layer on the wall. Systematic data on pressure recovery coefficients are presented comprehensively on the performance chart together with optimum geometry lines of diffusers both at constant diffuser length and at constant diverging area ratio. The performance chart and locations of the optima obtained for this type of diffuser are more similar to those reported previously for simple conical diffusers without inner walls than those for conical walled annular diffusers that consist of annular inlet and annular diverging portions.

View full abstract

The dynamic properties of a ship's propulsion mechanism consisting of two-series wings in a square channel are experimentally investigated. The time history of the trust and the drag acting on the wings moving in a circulation water tank are measured. In order to clarify the effect of the interaction of the two wings, They are equipped to move in a short distance. The opening angle and the moving speed are the same for the two wings, and the phase of the motion of the two is taken two cases, the same and reversed. For each case, the propulsive efficiency is calculated, and the difference of the properties between the two wings is discussed.

View full abstract

The flow in the narrow gap between the rotor and side plate of a rotary vane compressor with nonaxisymmetric boundary conditions is studied. The pressure, velocity and temperature distributions in a flow field are calculated by the Finite Element Method. For the steady-state solution of temperature distribution, Matsuda's Implicit Time Marching Method is employed. The results of this investigation indicate the possibility of simplified development and design of this type compressor.

View full abstract

Steady characteristics of an aerofoil in a two-dimensional subsonic shear flow are analyzed by the singularity method. First, on the assumption of small disturbances, fundamental solutions which represent a vortex and source are introduced from an equation for perturbed pressures. The solutions have two kinds of singularity: one is the same singularity as in a uniform flow and the other is logarithmic. Then, the thin aerofoil theory is applied to an aerofoil with a thickness. A source distribution is determined by only a thickness of aerofoil. However, a vortex distribution is determined by solving the integral equation, which includes the interferential term between the thickness and the vorticity of a shear flow. In a shear layer and a jet flow, lift forces acting on a flat plate and a Joukowsky symmetrical aerofoil are calculated. A flat plate in a faster part of the shear flow has less lift than that in a uniform flow. Lift on a Joukowsky aerofoil is strongly influenced by the vorticity of the shear flow.

View full abstract

A specially constructed pneumatic actuator has been manufactured on a trial basis. This actuator is meritorious in that it does not have a rod such as an air cylinder and has a considerably long stroke. The principle of this actuator is similar in construction to air motors, and the driving object mounted on a vane moves along a grooved bench. The groove base is n the shape of a rack with wide pressure angles. The air pressure is supplied to the space which is composed of the vane and rack, and then the driving object is moved by vane-applied air pressure. The air leakage passing through the narrow slits of the actuator must be avoided to obtain good moving performance. This report has investigated both theoretically and experimentally the processing accuracy of the device to obtain excellent performance considering the air leakage from the narrow slits.

View full abstract

A two-dimensional liquid meniscus being attached to an inclined plate was chosen to investigate the physical mechanism of wetting observed macroscopically. In order to consider the macroscopic wetting behavior from a thermodynamic viewpoint, the Helmholtz free energy of the system was obtained theoretically. The system shows thermodynamic stability corresponding to a minimum of the free energy when the meniscus is attached to the solid surface at the contact angle. This result agrees with the popular view. In the case of a meniscus formed under a horizontal plate, however, there is no minimum of free energy, and the system is stable when the meniscus is attached to the solid surface at an angle between the advancing and receding contact angles.

View full abstract

The distributions of local void fraction and heat-transfer coefficient of an air-water two-phase flow in helical coils were measured, and the effects of coil diameter and set angle on the heat-transfer characteristics were investigated. When the coil axis is horizontally placed, it is found that, at a high gas-phase velocity which forms the annular flow, there are still fairly large differences in the void fraction and the local heat-transfer coefficient between the upper and lower positions on the coil. It is shown that the average heat-transfer coefficients can be divided into three regions by Martinelli's parameter, 1/X_tt, for coils of any diameter. Among these regions, the effects of the set angle are significant at the second and third region. Finally, correlations between the average heat-transfer coefficient and 1/X_tt are proposed.

View full abstract

An experimental and analytical study was performed to investigate decaying natural convection after sudden stop of heat generation in a fluid. Experiments were carried out with a dilute electrolyte which could be heated by passing an alternating current through it. The temperature profiles and the heat transfer coefficients were determined with an interferometer. The goverrning differential equations were solved numerically to simulate the velocity and temperature distributions. From these results, the transient aspects for the decaying natural convection of heat generating fluid were clarified in detail

View full abstract

A detailed hot-wire measurement has been made to establish universal knowledge for a turbulent natural convection boundary layer. The measurement of wall shear stress determined from mean velocity profiles on firm theoretical grounds yields an important result concerning the concept of the viscous sublayer for natural convection. The streamwise development of the turbulent boundary layer is systematically investigated for mean velocity, mean temperature, and both velocity and temperature fluctuations. The reliability of Reynolds stress and turbulent heat flux measurements is verified by the perfect agreement with the theoretical values calculated from mean momentum and thermal energy equations with measurements of mean velocity and temperature. Turbulent quantities obtained indicate quantitatively that the natural convection boundary layer has unique turbulent structures which are rarely seen in other turbulent boundary layers.

View full abstract

An experimental study has been made of the saturated boiling heat transfer for water and R 113 in a narrow vertical rectangular channel (20 mm wide and 200 mm long) at atmospheric pressure, in which the vertical heated surface (10 mm long, 20 mm wide) is located on one side at a position 150 mm from the entrance and bubbles are forcibly passed through it for a designated period of 0.033 to 1.0 sec. The clearance of the channel can be changed from s=2 mm to s=7 mm, and thus the size of the bubble can be controlled independently of the clearance to be equal to 30, 20, and 10 mm in length. The experiment shows that the length of the passing bubble significantly enhances the heat transfer and the clearance has a weak effect on its enhancement when a bubble of the same length passes through it.

View full abstract

Time-dependent three-dimensional N-S and energy equations are solved numerically for the laminar flow and heat transfer in a curved tube with straight inlet and outlet sections. The results clearly explain the effects of curvature in the upstream of the straight section and the existence reverse flow in the main flow direction of the curved section. The heated section adopted only in the curved tube does not show much effect on the upstream straight section. In the reverse flow field which appeared in the curvature, profound heat flow was found to wards the upstream. To explain the reverse flow effects, the dissipation term in the main flow direction becomes important and can be treated numerically.

View full abstract

The heat-transfer mechanism of the evaporator of a thermosyphon-type heat pipe is considered in this paper. The rate and the coefficient of heat transfer of 9 test pieces were measured. The amount of the working fluid and the surface structures were different for all the test pieces. The occurrence of nucleate boiling in both the liquid film and the pool side was confirmed. As a result of the nucleate boiling in the liquid film, and because the heat transfer performance is dependent on the nucleate boiling heat transfer, the capability of the thermosyphon-type heat pipe has improved; however, the existence of the dry-out had a negative effect on the performance of the system.

View full abstract

The boiling heat transfer and the break-out of the liquid film occurring on the surface of the evaporator of a thermosyphon-type heat pipe are considered in this paper. The inside of the evaporator of the thermosyphon was simulated in order to observe the phenomenon; the liquid film occurring on the surface was heated, initiating. Nucleate boiling in the liquid film. As a result, the break-out of the liquid film took place; however, in order for the stabilization of the nucleate boiling to settle down, different surface structures were used. It was seen that for grooved and meshed surfaces, the liquid film was preserved and at the same time an increase in the evaporation and in the boiling heat transfer was noticed; however, the dry-out also increased.

View full abstract

A new method of the construction of the colloidal dam in the aquifer utilizing the chamical reaction of Fe ion was investigated experimentaly, with the following results. (1) The clogging of the Fe (OH)₃ in the one-dimensional experiments decreased the permeability, when the water, enriched with Fe ion, flowed for a long time. But the clogging is crushed and swept out when the inverse pressure gradient of more than 1.0×10⁴ [Pa/m] was added. (2) The apparent thermal diffusivity decreased together with the permeability of the aquifer in the experiments with the two-dimensional model. It shows that the regional flow of the ground water gets out of the way from the colloidal domain constructed in the aquifer. (3) The field experiments showed that Fe ion was stored in the aquifer, decreasing the apparent thermal diffusivity by the yearly cycles. After the infection and recovery teatment the colloidal dam grows in the shape of a doughnut in the region where the pressure-gradient is less than 1.0×10⁴ [Pa/m] in the aquifer.

View full abstract

A numerical heat transfer analysis in the combustion chamber of a pebble bed regenerative heat exchanger has been carried out for the heating period. A radiative zone method coupled with chemical an two-dimensional fluid dynamic calculations is employed in the analysis, and the results well explain the measured data. The analysis also shows that higher temperature can be obtained at the top of the pebble bed by optimizing the geometries of the combustion chamber and the burner.

View full abstract

This study was undertaken as part of an effort for effective treatment of wastes and utilization of their energy. It is an application of the spectacular advantages of porous media to energy conversion and transport, which has already been successfully applied to the combustion augmentation of extremely low calorific gases and solid poor combustibles with high water contents. This paper describes the performance of an experimental combustor with a porous-medium energy converter applied to the combustion augmentaion of a poorly combustible liquid. Mixtures of water and methanol were used as the test fuels. Results show that the self-sustained combustion of fuels having up to 76.5% water content has been realized in the experiments: the theoretical combustion temperature of which was 684°C. The energy balance of the combustor has also been clarified using a one-dimensional analnsis of radiation heat transfer.

View full abstract

Fundamental studies of electrodes and electrolyte tiles were carried out for molten carbonate fuel cell (MCFC). The cathode performance was improved by adding silver to it. Small and uniform pores of matrix were formed by crushing secondary particles of r-LiA10_z. The calculated results of the temperature distribution of MCFC were in reasonable agreement with the experimental results. The power output 12.4 kW was obtained by a 30-cell stack with 3600 cm² electrodes at a current density of 150 mA/cm².

View full abstract

The compound configuration of a flat plate and a parabolic trough solar collector was considered on the basis of exergy (available work). The economical analysis was executed taking the heat collection temperature and the collector cost as parameteters. Two systems were treated in connection with the way in which the constant heat collection temperature was determined. One is the system in which it is determined by a factor other than the collector performance, such as the load demand. The other is the system in which it is determined by the collector performance, and is optimized by maximizing the yearly exergy output. As a result, the compound configuration produces only a slight increase in output. From an economical point of view, however, the former system can decrease the exergy cost by a maximum of over 50%, in which case the heat collection temperature is at the upper limit of the flat plate collector. On the other hand, the latter system can decrease the exergy cost by a maximum of about 10%. Therefore, it is concluded that the flexibillity in setting the heat collection temperature significantly decreases the effect of the compound configuration.

View full abstract

For the thermal energy storage utilizing an aquifer, the selection of a suitable site is the most important process. The investigation to determine the proper process for site selection has been continued, based on previous field experiments and analyses. The results are as follows. (1) A process for the selection of a site suitable for aquifer thermal energy storage has been proposed. (2) A new method for determining the most suitable site in terms of values of the apparent thermal diffusivity of the aquifer has been proposed. This model is based on the analytical results of temperature recovery in the well after stepwise injection of warm water in the aquifer. (3) The experimental results obtained showed good agreement with those of the proposed method.

View full abstract

Pressure drop experiments under no-heat-transfer conditions were performed on Offset Strip Fin surfaces having 36 different geometries. Data were taken on scaled-up test cores of approximately five times that of the actual heat exchangers. These cores consist of three groups having different strip lengths. Each of these groups further are divided into four smaller groups of different fin thicknesses, and each of these small groups have three different fin spacings. The empirical correlation obtained by these experiments show that the friction factors of the Offset Strip Fin surfaces are a function of the number of strips and the ratio of the fin thickness to the fin spacng. The result is directly applicable to the selection of optimum fin geometries.

View full abstract

The present study proposes to use fluidized bed heat exchangers to improve thermal performances of high temperature heat exchangers for Stirling engines. Seven pot-type heat exchangers consisting of U-tubes with 6 mm outer diameter were inserted in a hot fluidized bed to measure heat transfer coefficients at the outer tube surfaces in the bed temperature range up to 400°C. Three different sizes of alumina particles were used as the bed material. The effects of particle size, tube number, fin size, superficial velocity, bed temperature, etc., were investigated. Also, the uniformity in temperature in the fluidized bed was found to be food enough to be used for heat exchangers of Stirling engines.

View full abstract

This paper investigates methanol combustion behavior with different metals in the combustion chamber wall, and determines means to improve ignitability. The results indicate that among the metals tested iron is the most effective in improving methanol ignition. In IDI engines, ignition is affected more by the metal in the chamber wall than in DI engines, as in the case of combustion systems where more unburnt methanol tends to remain longer. The in-chamber concentration of formaldehyde, an intermediate product of methanol combustion, appears to be an important determinant for methanol ignition. To achieve smooth ignition without misfiring, a specific formaldehyde concentration is necessary immediately prior to methanol injection in the combustion chamber.

View full abstract

The increase of the cetane number of diesel fuel and the compression ratio are effective methods of improving the cold startability and exhaust emissions during warming up. In this study, the correlation between the cetane number and compression ratios on the cold startability and the exhaust emissions were investigated at various soak temperatures. It was found that the increase of one compression ratio was equal to the decrease of 9 cetane number and to the lewering of soak temperature of 4°C when the staring time was the same level, and the effect of cetane number on the starting time indicated almost constant rates at various soak temperatures.

View full abstract