Showing papers in "Jsme International Journal Series B-fluids and Thermal Engineering in 1997"
TL;DR: In this article, heat transfer coefficients in nucleate pool boiling of five binary mixtures were measured under atmospheric pressure on an upward-facing heated surface for a wide range of heat flux from about 15 percent of the critical heat flux to close to it.
Abstract: Heat transfer coefficients in nucleate pool boiling of five binary mixtures were measured under atmospheric pressure on an upward-facing heated surface for a wide range of heat flux from about 15 percent of the critical heat flux to close to it. Mixtures were : methanol / water, ethanol / water, methanol / ethanol, tehanol / n-butanol, and methanol / benzene. As has been observed in many previous experiments, heat transfer coefficients of mixtures were reduced in comparison with interpolated values between their constituent components. This reduction was a function of the mixture composition and became more pronounced with an increase in heat flux. To provide a simpler and more reliable prediction of heat transfer coefficients of mixtures, Thome correlation was modified so as to include the effect of heat flux in a dimensionless form. A newly developed correlation in this way was verified to predict heat transfer coefficients for the present five mixtures well within ±20 percent accuracy lines.
52 citations
TL;DR: In this paper, a numerical method is developed to simulate unsteady axisymmetric flow with a free surface, based on a finite-volume solution of the equations on an orthogonal curvilinear coordinate system.
Abstract: A numerical method is developed to simulate unsteady axisymmetric flow with a free surface. The method is based on a finite-volume solution of the equations on an orthogonal curvilinear coordinate system. A new iteration technique is used for the boundary condition of the free surface in order to stabilize the solution. The numerical method is applied to the simulation of unsteady motion of a single deformed bubble rising through a quiescent liquid. The numerical results show good quantitative agreement with those of experiments and calculations reported previously by other researchers. In the present study, the transient phenomena of an initially spherical bubble as it reaches the steady state are investigated. It is known experimentally that the rising bubble begins to show an unsteady three-dimensional(spiral or zigzag)motion beyond certain critical Reynolds and Weber numbers. Our numerical results suggest that the growth of axisymmetric shape oscillation causes three-dimensional motions of a rising bubble.
50 citations
TL;DR: In this paper, a wavelet cross-correlation analysis is used to express the statistical crosscorrelation of two arbitrary signals in terms of scale and time delay, and its main properties are presented.
Abstract: A new cross-correlation method, which is called wavelet cross-correlation analysis and is used to express the statistical cross-correlation of two arbitrary signals in terms of scale and time delay, is proposed and its main properties are presented. By analyzing two test signals, it is shown that wavelet cross-correlation does not have the limitations of classical cross-correlation. As a practical application to fluid mechanics, wavelet cross-correlation is employed to determine the cross-correlation relationships between the x-components of the fluctuation velocities at two points on opposite sides of the centerline amd along the centerline of a plane turbulent jet in terms of period and time delay. In the distributions of the wavelet cross-correlation coefficients, similar structures with various scales are observed instantaneously, and the period of eddy and apparent flapping motions can be determined easily in terms of period and time delay. It is found that the apparent flapping behavior appears first in region with an intermediate period. It is also revealed that a similar structure with a high period consists of similar structures with a low period, i.e., a large eddy contains small eddies.
49 citations
TL;DR: A new type of sheath flow chamber with low pressure loss was developed using micro-machining, formed by laminating three 100-μm-thick, photoetched, metal plates, andpressure loss was reduced to one-tenth of that which occurs with conventional glass flow chambers.
Abstract: A new type of sheath flow chamber with low pressure loss was developed using micro-machining. The chamber was formed by laminating three 100-μm-thick, photoetched, metal plates. The device uses sheath-flow geometry : particles in suspension, which enter the chamber via an axial specimen nozzle, are enveloped by a buffering sheath flow and transported to a square capillary tube with cross-section of 300 μm×300μm. Finite element viscous-flow analysis is used to examine the flow behavior in the quasi-two-dimensional passage configuration which produces the fluid-dynamic focusing flow. Experimental measurement showed a smooth constricted sheath flow, and pressure loss was reduced to one-tenth of that which occurs with conventional glass flow chambers.
41 citations
TL;DR: In this article, a theoretical analysis of mixed lubrication has been carried out for a piston ring package of an automotive reciprocating engine as a method to elucidate better specifications of rings for reducing friction loss, where starved inlet boundary conditions have been employed for oil film on each ring based upom experimental results obtained through scanning laser-induced-fluorescence oil film thickness measurement.
Abstract: Theoretical analysis of mixed lubrication has been carried out for a piston ring package of an automotive reciprocating engine as a method to elucidate better specifications of rings for reducing friction loss. The starved inlet boundary conditions have been employed for oil film on each ring based upom experimental results obtained through scanning laser-induced-fluorescence oil film thickness measurement. With consideration of oil starvation, the predicted oil film thickness at compression rings was in better agreement with that measured than the former prediction under fully flooded inlet conditions. Film thickness at the 1st compression ring under full load firing conditions was predicted to be smaller than that during motoring, which also agreed with the experimental results, due to the different inlet conditions assumed for the oil film at the 2nd compression and upper rail of the oil ring under different operating conditions. The predicted oil film thickness was much smaller than that measured at both rails of the oil ring, which seems to have been caused mainly by limitations of the spatial analysis of the LIF measurement. Effects of the change of the oil ring surface profile due to tilting during sliding, of vescosity variation and of cylinder bore distortion were not negligible, but were not considered in the analysis.
28 citations
TL;DR: In this article, a neural network was applied for the color-to-temperature transformation of the thermosensitive liquid crystal film to measure the local heat transfer coefficient on the endwall.
Abstract: Experiments were conducted to measure the local heat transfer on an endwall with pin fin array. Heat transfer behavior was examined for the cases of a single pin, a single row, in-line and staggered arrays having six streamwise rows. Thermosensitive liquid crystal film was used to measure the local heat transfer coefficient on the endwall. Neural network was applied for the color-to-temperature transformation of the thermosensitive liquid crystal. Local heat transfer on the endwall having a single row of pin fin was affected by flow acceleration between the pin fins rather than the horseshoe vortex around the pin fin. Therefore, the average Nusselt number exhibited a good correlation to the Reynolds number Renax, which was based on the average velocity of the minimum flow area, regardless of the pin fin spacing. For in-line and staggered arrays, the average Nusselt numbers correlated with the Reynolds number Remaxdecreased with the reduction of the pin fin spacing.
27 citations
TL;DR: In this article, the authors describe an experimental study on the simultaneous reduction of NO x and soot in diesel engines achieved using a new mixture preparation method, to produce a lean uniform mixture, a new type of injection equipment was used with various injection timings.
Abstract: We describe an experimental study on the simultaneous reduction of NO x and soot in diesel engines achieved using a new mixture preparation method. To produce a lean uniform mixture, a new type of injection equipment was used with various injection timings. Between the late and very early injection timings, there was an injection timing range at which the amount of NO x produced was extremely low and soot was not emitted. NO x production was suppressed to a level one hundredth that of conventional DI diesel engines. However, with increasing load, NO x production increased sharply and strong diesel knocking occurred. This indicated that NO x production was strongly influenced by the process of mixture formation.
25 citations
TL;DR: In this paper, the potentialities of a Dul'nev cubic unit cell model for predicting the thermal and radiative properties of open-cellular porous materials were examined, and the feasibility of using the unit-cell model to predict the heat transfer characteristics of a conducting-radiating, open-cells porous ZrO2 layer was indicated.
Abstract: To establish a model for predicting the thermal and radiative properties of open-cellular porous materials, the potentialities of a Dul'nev cubic unit cell model are examined. First, the accuracy of Dul'nev's formula for the conductive effective thermal conductivity is quantitatively evaluated and then, on the basis of Dul'nev's model, analytical expressions for the radiative properties, such as the extinction coefficient, albedo and asymmetry factor of a phase function, are derived, and their validities are confirmed. Finally, the feasibility of using Dul'nev's unit cell model to predict the heat transfer characteristics of a conducting-radiating, open-cellular porous ZrO2 layer is indicated.
24 citations
TL;DR: In this article, the fluid elastic vibration problems of two cylinders and a cylinder row are simulated using the CFD technique and the characteristic phenomena of vortex shedding, coupled with two-cylinder motion and fluid elastic instability of cylinder row, are successfully simulated.
Abstract: Fluid elastic vibration of tube bundles is one of the most important factors that must be considered in the design of heat exchangers. Since this phenomenon is caused by the interaction between flow and structure, and is hence very complex and sensitive in nature, the design criteria established through many experiments, based on envelopes of the scattered data, have been the only reliable tools for the designers. The authors have developed an accurate CFD technique to solve this moving boundary problem. The fluid elastic vibration problems of two cylinders and a cylinder row are simulated using the CFD technique. The characteristic phenomena of vortex shedding, coupled with two-cylinder motion and fluid elastic instability of a cylinder row are successfully simulated.
23 citations
TL;DR: In this article, the authors simulated the flow field of a supersonic flow chemical oxygen-iodine laser by solving three-dimensional Navier-Stokes equations and the effects of the mixing/ reacting zone structure on the resulting gain region are studied.
Abstract: The flow field of a supersonic flow chemical oxygen-iodine laser is simulated by solving three-dimensional Navier-Stokes equations and the effects of the mixing/ reacting zone structure on the resulting gain region are studied. It is assumed that the flow is laminar and the water vapor condensation due to the supersonic cooling is ignored. A chemical kinetic model encompassing 21 chemical reactions and 10 chemical species is used to determine the chemical composition of the gas mixture. The present results demonstrate that a pair of contrarotating vortices generated behind the I 2 jet greatly enhances the mixing and the simultaneous chemical reaction to produce the excited iodine atom with the singlet oxygen. In the present calculation, the small signal gain coefficient is overestimated to some extent as compared with the experimental one. It is thought that the overestimation is caused by the imperfect chemical kinetic model as well as by ignoring the water vapor condensation and the boundary layers on the upper and lower wall in the present calculation.
23 citations
TL;DR: In this paper, a numerical approach to the analysis of the mechanism of wavy interface generation in explosive welding is presented, which is based on a two-dimensional finite difference scheme for elastic-plastic materials.
Abstract: Wavy interface generation is an interesting characteristic of explosive welding. There have been many theoretical and experimental discussions of the mechanism of wavy interface generation, but there is no consensus of opinion as yet. We report on a numerical approach to the analysis of the mechanism of wavy interface generation in explosive welding. The wavy interface generation process is calculated using a two-dimensional finite difference scheme for elastic-plastic materials. In this simulation the equations for a symmetric collision between copper plates are solved. The concept behind this study is that the wavy interface and vortex street are caused by the velocity distribution of shear flow and periodic disturbance at the interface. The calculation results show the deformation process of the wavy interface and we obtain qualitative agreements between numerical and experimental results.
TL;DR: In this article, the lattice BGK method is applied to the simulation of a two-dimensional laminar flow over a backward-facing step, and its incompressible version, as well as the new algorithm for boundary conditions, are described.
Abstract: The lattice BGK method is applied to the simulation of a two-dimensional laminar flow over a backward-facing step. The method and its incompressible version, as well as the new algorithm for boundary conditions, are described. Quantitative comparisons with experimental and other numerical studies are made for three cases.
TL;DR: In this article, an on-line methodology to solve the inverse heat conduction problems of a hollow cylinder is presented, where a new input estimation technique based on the concept of Kalman filtering is developed for estimating unknowns in real time, such as the what of the heat source or the heat flux on the boundary of the hollow cylinder.
Abstract: An on-line methodology to solve the inverse heat conduction problems of a hollow cylinder is presented. A new input estimation technique based on the concept of Kalman filtering is developed for estimating unknowns in real time, such as the what of the heat source or the heat flux on the boundary of the hollow cylinder. A recursive relation between the observed value of the residual sequence with unknown heat flux and the theoretical residual sequence of the Kalman filter that assumes known heat flux is formulated. A real time least squares algorithm is derived that uses the residual innovation sequence to compute the magnitude of heat flux. This recursive approach facilitates practical implementation and its capabilities are demonstrated in several typical cases with discontinuous and time-varying heat flux inputs.
TL;DR: In this article, the Nusselt number of regenerator wire meshes of a Stirling engine in oscillatory flow is estimated by using a cylindrical probe having two thermocouples attached on opposite sides of the cylinder facing the direction of oscillator flow.
Abstract: This paper describes in detail experimental results on flow resistance and heat transfer of regenerator wire meshes of a Stirling engine in oscillatory flow. The results show that for Re>300, the friction factor of wire mesh became lower than that in previous studies. It has been clarified that the friction factor in a decelerating period becomes higher than that in an accelerating period under the condition that both Valensi number and maximum Reynolds number exceed certain values. A new experimental method for estimating Nusselt number of wire mesh in oscillatory flow is proposed. This method employs a cylindrical probe having two thermocouples attached on opposite sides of the cylinder facing the direction of oscillatory flow. It has been clarified that Nusselt number of wire mesh becomes a function of Reynolds number and open area ratio. Also, experiments on spring mesh were carried out.
Journal Article•
TL;DR: In this paper, the attenuation and distortion of the compression wave were measured in three Shinkansen tunnels and the results were compared with the numerical values calculated using a second-order TVD scheme.
Abstract: When a high-speed railway train enters a tunnel, a compression wave is generated ahead of the train and propagates along the tunnel. The attenuation and distortion of the compression wave were measured in three Shinkansen tunnels and the results were compared with the numerical values calculated using a second-order TVD scheme. The strength of a compression wave is exponentically attenuated with distance as it propagates along the tunnel in both slab and ballast track tunnels, and the attenuation in the ballast track tunnel is considerably larger than that in the slab track tunnel. In the slab track tunnel, the compression wave is steepened as it propagates, while it spreads in the ballast track tunnel. The criterion for judgment whether the compression wave is steepend or spreads is expressed by the value of acoustic Reynolds number of about 10∼15.
TL;DR: In this article, the effect of cycle-to-cycle spray variations on emissions under no load conditions and lower engine speeds was investigated and the results showed that when these variations are suppressed, it results in reduced hydrocarbon emission and less white smoke.
Abstract: To study cycle-to-cycle variations in diesel spray direction, images of the spray shape, needle valve motion and sac inner flow of multi-hole-type nozzles were recorded using a high-speed drum camera and two CCD cameras. It was observed that needle valve offset and one-sided sac inner flow during fuel injection induced fluctuation in spray direction and deformation of spray shape.Experiments on the effect of cycle-to-cycle spray variations on emissions under no load conditions and lower engine speeds revealed that when these variations are suppressed, it results in reduced hydrocarbon emission and less white smoke.
TL;DR: In this paper, a fluorescence image diagnostic method was developed to observe the distribution and behavior of oil film on a piston surface in detail using a light source with appropriate spectrum characteristics for measurement of the thickness of thin oil films.
Abstract: A fluorescence image diagnostic method in which a filtered Xe-flash lamp and a video camera are used has been developed to observe the distribution and behavior of oil film on a piston surface in detail. A light source with appropriate spectrum characteristics for measurement of the thickness of thin oil films was employed after theoretical consideration of the absorption spectrum of the fluorescent dye and the oil with the fluorescent dye. A simple correction for measurement results obtained for a curved surface and calibration were carried out. The use of this system ensures that the distribution and behavior of oil film on the piston skirt and piston rings can be quantitatively measured, and the system is shown to have practical applications.
TL;DR: In this paper, a study of vortex structure and fluid mixing in pulsatile flow through grroved channels by numerical simulation and experimental flow visualizations is presented, and the agreement between simulations and experiments in terms of unsteady vortex motion is satisfactory.
Abstract: A study of vortex structure and fluid mixing in pulsatile flow through grroved channels by numerical simulation and experimental flow visualizations is presented. The simulations correspond to experiments for pulsatile flows with / without flow reversal in two grooved channels with different cavity lengths, with Reynolds and Womersley numbers in the ranges of 46.8
TL;DR: In this article, an oblique wave can be generated in a flat-plate boundary layer with a roughness element attached to the plate inclined and an acoustic forcing, which is known to induce three-dimensionalization modes that are observed in the later stages of boundary-layer transition.
Abstract: An attempt to control the three-dimensionalization process of T-S waves by utilizing the receptivity of a three-dimensional roughness element on a flat-plate boundary layer to outer acoustic disturbances is carried out by wind-tunnel experiments. The term "receptivity"(1)describes the process through which external distur-bances are transformed into instability waves in a boundary layer. It is known that several types of oblique waves can be found in the three-dimensionalization process in the later stages of the boundary-layer transition. In the present experiment, we artificially introduce oblique waves in the boundary layer in order to control the boundary-layer transition. It is shown that an oblique wave can be generated in a flat-plate boundary layer with a roughness element attached to the plate inclined and an acoustic forcing. An attempt to induce three-dimensionalization modes that are observed in the later stages of boundary-layer transition is also carried out. However, the natural three-dimensional mode flow structures could not be generated by our method.
TL;DR: In this article, the authors investigated the regeneration of quasi-streamwise vortices using a data base obtained by high-resolution LES (Large Eddy Simulation) for channel flow.
Abstract: Regeneration of quasi-streamwise vortices is investigated using a data base obtained by high-resolution LES(Large Eddy Simulation)for channel flow. It has been revealed that quasi-streamwise vortices are regenerated both at the upstream of the upstream end of a parent vortex and at the downstream end of a parent vortex. In both cases, the new vortex has a vorticity of opposite sign to that of the parent vortex and comprises a chain line of vortices in the flow direction with the parent vortex, which is one of the basic organized structures in the near-wall region. It has also been revealed that the main contribution to the generation of new vortices at their infant stage is the tilting of wall-normal vortices, and that to their sustenance at grown-up stage is stretching effect.
TL;DR: In this paper, the authors investigated the effect of the stretching effect on the production of quasi-streamwise vortices in a two-dimensional channel, where one wall is stationary and the other is in sinusoidal oscillation normal to the mean flow.
Abstract: It is intended to investigate the mechanism of drag reduction of a turbulent flow in a channel by wall oscillation normal to main flow, in this report. DNS is carried out in which one wall of a two-dimensional channel is stationary but the other is in sinusoidal oscillation normal to the mean flow. The most effective oscillation period is adopted and about 35% reduction in drag is confirmed. For this case, generation terms of quasi-streamwise vorticity are examined from various points of view. It is shown that quasi-streamwise vortices which play a key role in sustaining wall turbulence are most strongly affected in the buffer layer. Vorticity production rate fluctuates with the phase of wall oscillation and is enhanced at some definite favorable phase but suppressed as a whole, in one period of oscillation. The stretching effect as well as tilting effect is important. However, the latter affects mainly weak chaotic vortices and hence the role of the former which modulates coherent quasi-streamwise vortices is more substantial. The suppression of vorticity generation by stretching is due to the decrease of inclination angle of a vortex to a wall. It is demonstrated that the fall of production rate of quasi-streamwise vorticity due to stretching effect is substantial for the phenomenon. The periodical fluctuation of the attitude angle, i.e., the inclination angle to the wall and the slant angle of a vortex to mean flow, aggravates the production. This mechanism is a straightforward extension of the one commonly found in the usual near wall turbulence.
TL;DR: In this paper, a prechamber model was installed in a constant volume test rig (CVR) for the investigation of pre-chamber mixing processes and the dominant influence on the mixing process was investigated and the analysis of mixture homogeneity at ignition timing.
Abstract: Quartz prechamber models have been installed in a constant volume test rig (CVR) for the investigation of prechamber mixing processes. Planar laser induced fluorescence of acetone has been used for a 2-dimensional visualization of flow structure and quantitative analysis of mixture formation. The prechamber was initially filled with acetone seeded in nitrogen. A jet of lean mixture in an actual lean-burn gas engine was simulated using a flow of pure nitrogen from the CVR. Two different shapes of prechambers were investigated and the dominant influence on the mixing process is presented. Special emphasis was laid on the analysis of mixture homogeneity at ignition timing. The investigations provided an insight into the flow structures inside prechambers. The dominant influence of prechamber shape, especially around its mouth, on flow structures as well as on mixture homogeneity at ignition timing was proved.
TL;DR: In this paper, a linear analysis model for a free piston Vuilleumier heat pump (FPVM) was constructed to derive closed form solutions for the operating frequency, phase angle and displacer strokes during self-excited operation and forced oscillation.
Abstract: A linear analysis model for a free piston Vuilleumier heat pump (FPVM) was constructed to derive closed form solutions for the operating frequency, phase angle and displacer strokes during self-excited operation and forced oscillation. Using the linear analysis, conditions for self-excited operation and the effects of connecting the hot and the cold displacers by a spring on the dynamic motion of the displacers and the FPVM performance were investigated. Energy flow in the FPVM was also obtained. A simple 2nd order isothermal simulation combined with the linear analysis was developed which enabled calculation of the FPVM performance characteristics. It was found that the simulation results were qualitatively in good agreement with the experimental results during self-excited operation. Simulation was used to calculate the dependence of the dynamic motion of the displacers and the FPVM performance on the spring constants, displacer masses and damping coefficients.
TL;DR: In this article, the characteristics of low-speed streaks in the turbulent channel flow of a drag-reducing surfactant solution are studied by employing the hydrogen-bubble flow visualization method.
Abstract: The characteristics of low-speed streaks in the turbulent channel flow of a drag-reducing surfactant solution are studied by employing the hydrogen-bubble flow visualization method. The mean velocity profiles and the distributions of streamwise turbulence intensity are also obtained. It is shown that, at a large drag reduction rate DR, the profile of the streamwise turbulence intensity has a plateau region around its peak. In the drag-reducing flow, the mean spanwise streak spacing reaches minimum at some distance from the wall. In the drag-reducing flow of high-density(1000 ppm)surfactant solution, the low-speed streaks appear intermittently at the Reynolds number smaller than those for the 'hump' of the f-Re curve(f:friction factor). The mean spanwise streak spacing very near the wall increases as DR becomes large. It is speculated that the nondimensional wall-normal distance y+ of the center of streamwise vortices is larger for the flow of large DR compared with that for the Newtonian fluid flow.
TL;DR: In this paper, a wavelet auto-correlation analysis was used to analyze the fluctuating velocities at various positions in a plane turbulent jet, and it was found that the peaks of WR(α, τ) in the high period region correspond to the large peaks of R(τ), and the peaks in the low period region are equivalent to the small peaks of r(τ).
Abstract: To investigate the eddy structure of turbulent shear flow in both physical-space and Fourier-space, a new combination of conventional techniques of signal processing, called wavelet auto-correlation analysis, has been developed based on wavelet transform. The wavelet auto-correlation analysis provides the unique capability for describing the auto-correlation characteristics of arbitrary signals in terms of period and time delay. The wavelet auto-correlation technique was used to analyze the fluctuating velocities at various positions in a plane turbulent jet. It was found that the peaks of WR(α, τ) in the high period region correspond to the large peaks of R(τ), and the peaks of WR(α, τ) in the low period region are equivalent to the small peaks of R(τ). The branching structures in WR(α, τ) reveal that a periodic large eddy motion contains the periodic small eddy motions. In the shear layer at x/d=10, the periodic eddy motions with α=15, 40, 75, 100 and 150 ms are clearly observed.
Journal Article•
TL;DR: In this article, the combined 3-point method was proposed to measure profiles that include high-frequency components whose spatial wavelengths are shorter than the probe distance, and cancel the influence of the z-directional error and the pitching error in the scanning motion.
Abstract: The combined 3-point method, which combines the generalized 3-point method with the sequential 3-point method, is described in the present paper. The combined 3-point method can not only measure profiles that include high-frequency components whose spatial wavelengths are shorter than the probe distance, but also cancel the influence of the z-directional error and the pitching error in the scanning motion. In the combined 3-point method, some data points from a profile evaluated by the generalized 3-point method are chosen as reference points of the standard area and are used to determine the relative heights among the data groups of the sequential 3-point method. An automatic selection method was used to select the standard area correctly and quickly. Theoretical analyses and computer simulations were performed to confirm the effectiveness of the combined 3-point method. Experimental profile measurements were also carried out using three capacitance-type displacement probes.
TL;DR: In this paper, the reaction zone structure of asupersonic flow chemical oxygen-iodine laser (COIL) is simulated solving the two-dimensional Navier-Stokes squations in order to clarify the reaction zones structure and the effects of water vapor condensation precisely.
Abstract: The reaction zone structure of asupersonic flow chemical oxygen-iodine laser(COIL)is simulated solving the two-dimensional Navier-Stokes squations in order to clarify the reaction zone structure and the effects of water vapor condensation precisely. A chemical kinetic model consisting of 10 chemical species and 21 chemical reactions is used to determine the chemical composition of the mixture. The liquid phase is modeled as a number of droplet classes. Each class contains only droplets of a certain range of sizes, which is approximated as one average size. The calculation shows that the I2 gas injected into the singlet oxygen through a two-dimensional slit mixes very slowly and the small signal gain coefficient is high only in a narrow layer where the mole fraction of I(2P1 / 2)reaches a high value. Nonequilibrium condensation takes place during supersonic expansion, generating water droplets whose size much smaller than the wave length of COIL. Condensation reduces the small signal gain coefficient, since the temperature rise caused by latent heat suppresses the generation of I(2P1 / 2).
TL;DR: In this paper, a mixed convection from a horizontal cylinder imbedded in saturated electrically conducting fluid is investigated using nonsimilarity boundary layer transformation, where variable wall temperature is assumed at the cylinder surface as the thermal boundary condition.
Abstract: Mixed convection from a horizontal cylinder imbedded in saturated electrically conducting fluid is investigated using nonsimilarity boundary layer transformation. Variable wall temperature is assumed at the cylinder surface as the thermal boundary condition. The problem is solved numerically using the finite difference technique and double-checked using a local nonsimilarity solution. The effects of the magnetic field on the velocity and temperature profiles, wall shear stress, and Nusselt number are presented. The non-Darican flow model is adopted. The effects of the inertial and boundary parameters on the solution in the presence of a magnetic field are also presented. The problem is solved covering the entire regime of mixed convection.
TL;DR: In this article, a two-phase model is introduced for consideration of heat propagation even into the particle phase, and the effectiveness of the model is confirmed using a laboratory test apparatus in two dimensions.
Abstract: Recently the impetus towards use of aquifer as thermal storage systems has increased. Since the surface of free aquifers fluctuates irregularly due to both inflow and outflow of groundwater, treatment is difficult compared with the case of confined aquifers. In the case of free aquifers, non-equilibrium heat transfer between fluid and particle phases exerts much influence. Even in confined aquifers, the unsteady heat transfer is marked under marble or gravel-component. The inherent properties of soils are dismissed and part of them are reflected poorly in apparent properties such as equivalent heat capacity of conductivity. Therefore, even superficial velocity has been wrongly estimated. In this paper, a two-phase model is introduced for consideration of heat propagation even into the particle phase. Then, the effectiveness of the model is confirmed using a laboratory test apparatus in two dimensions. Finally, significant deviations of temperature propagation by the particle sizes are simulated.