Takao Inamura

Spray Characteristics of Liquid Jet Traversing Subsonic Airstreams

The spray characteristics of a liquid jet traversing subsonic airstreams were experimentally investigated. The disintegration phenomena of liquid jets were observed by instantaneous photographs and high-speed video movies. The waves on the liquid jet surface are three dimensional and show very complicated behaviors. These waves are an important cause of the liquid jet disintegration. Droplet mass e uxes were measured using an isokinetic sampling probe. Empirical equations of their distributions that are expressed by the standard normal function were deduced. Droplet sizes and droplet velocities were measured by a phase Doppler particle analyzer. At low air velocity, the mean droplet diameter reaches its maximum in the peripheral mixing region. At high air velocity, however, the mean droplet diameter reaches its maximum in the core region. The droplet velocity peaks in the peripheral mixing region over the whole range of the air velocity.

Characteristics of Liquid Film and Spray Injected from Swirl Coaxial Injector

The liquid film flow on the inner wall of the center post of a swirl coaxial injector was analyzed theoretically. The development of the boundary layer in the liquid-film flow and the transition from laminar to turbulencewere studied. The film thickness at the post exit was measured using a contact needle probe, and the predicted film thickness was compared with the measurements. The film thickness varies in the azimuthal direction due to the geometry of the liquid inlet. The average film thickness at the post exit increases as the post length increases. The sheet cone angle and breakup length were measured using photography and a contact mesh probe, and their empirical equations were deduced by modifying those of a simplex swirl injector, taking into account the liquid momentum loss due to a long center post. These equations predict the sheet cone angle and breakup length well, except for small liquid flow rates. The mean droplet size and droplet velocity were measured by a phase Doppler particle analyzer. The measured spray characteristics exhibited characteristics similar to those of a conventional airblast atomizer.

Hydrodynamic evaluation of axillary artery perfusion for normal and diseased aorta

Axillary artery perfusion is an attractive alternative to reduce the frequency of atheroembolism in extensive atherosclerotic aorta and aortic aneurysms. This study was conducted to evaluate the flow dynamics of axillary artery perfusion. Transparent glass models of a normal aortic arch and an aortic arch aneurysm were used to evaluate hydrodynamic properties. Streamline analysis and distribution of the shear stress was evaluated using a particle image velocity method. In the normal aortic arch model, rapid flow of 80 cm/s from the right axillary artery ran out from the brachiocephalic artery and grazed the lesser curvature of the aortic arch. There was secondary reversed flow in the ascending aorta. Flow from left axillary perfusion went straight to the descending aorta. In the aortic arch aneurysm model, flow from both axillary arteries hit the lesser curvature of the aortic arch and went into the ascending aorta with vortical flow. Distribution of shear stress was high along the jet from the ostium of the brachiocephalic artery and left subclavian artery. Flow in the aortic arch and the ascending aorta was unexpectedly rapid. Special care must be taken when the patient has frail atheroma around arch vessels or the lesser curvature of the aortic arch during axillary artery perfusion.

Flow Velocity and Turbulence in the Transverse Aorta of a Proximally Directed Aortic Cannula: Hydrodynamic Study in a Transparent Model

BACKGROUND The objective of this study was to visualize and characterize the effect of cannula tip direction on flow within transverse aortic arch. METHODS A hydrodynamic analysis of the Dispersion arterial cannula (Edwards Lifescience LLC, Irvine, CA) was performed using particle image velocimetry in glass perfusion models of healthy and aneurysmal aortic arches. Flow velocity, streamline, distribution of magnitude of the strain rate tensor (function of shear stress), and degree of flow turbulence were comparatively analyzed for cannula tip directed toward the aortic arch (standard direction) and toward the aortic root (root direction). RESULTS Standard direction cannulation in the model of the healthy aorta showed the flow velocity in the transverse aortic arch was rapid, the streamlines were nonlinear, and the magnitude of the strain rate tensor was high along aortic curvatures. Conversely, directing the cannula tip toward the aortic root generated slower and less turbulent flow in the transverse aortic arch despite high velocity and turbulence and nonlinear streamlines in the ascending aorta. In the aneurysmal aortic arch model, the flow velocity was more rapid in the area where aortic arch vessels originated, and a reversely directed vortex was observed between the aneurysm and the origination of the arch vessels. In the root direction model, the flow velocity distribution was slower than that in the standard direction. CONCLUSIONS Directing the cannula tip of the Dispersion cannula toward the aortic root generated slower and less turbulent flow in the transverse arch of the glass models of both healthy and aneurysmal aortic arches.

Prediction of Mean Droplet Size of Sprays Issued from Wall Impingement Injector

The purpose of this study is to make a numerical model that predicts the spray characteristics of a wall impingement injector. The film flow on the wall was analyzed theoretically using the laminar boundary-layer model. The biquadratic velocity profile was employed for the laminar boundary layer. The thickness of the liquid film on the wall was measured by an automatic thickness measurement system, which was newly developed for the present study and is based on the contact needle method. From the measurements, the film thickness decreased first toward the periphery, and then increased along the line that was perpendicular to the liquid injection direction. The theoretical analysis of the film thickness on the wall agreed well with the measurements. The sizes of the droplets from the newly developed wall impingement injector were predicted by using the proposed theoretical analysis of a film flow and the existing liquid-film breakup model. From the measurements from the phase Doppler particle analyzer, the mean droplet size decreased once toward the spray periphery and then increased. This trend of the droplet size was coincident to that of the liquid-film thickness at the edge of the wall. The mean droplet size decreased as the liquid injection pressure increased. The predictions of the droplet size agreed well with the measurements.

Effect of Liquid Disintegration on Flow Instability in a Recessed Region of a Shear Coaxial Injector

A liquid jet disintegration phenomenon in the recessed region of a shear coaxial injector was examined to find the relation between the difference of the recess depth and flow instability which may induce combustion instability of liquid rocket engines. An injector with a rectangular cross section and a recess for a central post, which modeled the shear coaxial injector element employed in liquid rocket engines, was constructed. The injector was made of transparent acrylic glass to allow observation of the disintegration phenomenon in the recess. Cold-flow tests with water and nitrogen gas with ambient pressures of 0.2, 0.3 and 0.4 MPa were conducted. Results showed that a condition arose in which the flow in the recess was choked by two-phase flow. The choked flow was accompanied by vibration of the central post which caused a significant change of the disintegration pattern from moderate disintegration to violent disintegration. A similar transition from a fiber-type flow to a super-pulsating disintegration flow reported by Chigier and Reitz was also observed under non-choked conditions for a coaxial injector without a recessed region. The boundary of the transition was found to depend on certain values of ReL/(WeG) 0.5 for each recess depth, including the two-phase choked flow condition. This means that the transition from a fibertype flow to super-pulsating disintegration leads to the transition from a non-choked flow to a choked flow.

Hydrodynamics of Aortic Cannulae During Extracorporeal Circulation in a Mock Aortic Arch Aneurysm Model

This study was designed to analyze flow pattern, velocity, and strain on the aortic wall of a glass aortic arch aneurysm model during the extracorporeal circulation, and to elucidate the characteristics of flow pattern in three different aortic cannulae. Different patterns of large vortices and helical flow were made by each cannula. With the curved end-hole cannula, the high velocity flow (approximately 0.6-0.8 m/s) was blowing to the aneurismal wall without attenuating the strain rate tensor (approximately 0.2-0.25/s). With the dispersion cannula and the Soft-Flow cannula, cannular jet was attenuated in the ascending aorta creating a large vortex at a velocity less than 0.5 m/s, and the strain rate tensor on the aneurismal wall was small (less than 0.15/s). In conclusion, end-hole cannula should not be used in the operation of aortic arch aneurysm. Dispersion-type aortic cannulae were less invasive on the aortic arch aneurismal wall, but particular attention to alternative cannulation sites should be paid in cases with severe atherosclerosis on the ascending aortic wall.

Experimental fluid dynamics of transventricular apical aortic cannulation.

To clarify the flow pattern from a transventricular apical aortic cannula, hydrodynamic analysis of transventricular apical aortic cannulation (apical cannulation) was performed using particle-image velocimetry in a glass aortic model. Simulated apical cannulation using a 7-mm Sarns Soft-Flow cannula and the newly developed 7-mm apical aortic cannula was compared with standard aortic cannulation. The flow-velocity, streamline, and distribution of magnitude of the strain rate tensor (function of shear stress) were analyzed. Streamline analysis revealed a steady and organized flow profile in apical cannulation as compared with that in standard aortic cannulation. The magnitude of the strain rate tensor decreased within a few centimeters from the exit of the apical cannula.

Turbulence and Heat Transfer of a Hairpin Vortex Formed Behind a Cube in a Laminar Boundary Layer

We report numerical simulations of three-dimensional unsteady separated flow and heat transfer around a cube mounted in a laminar boundary layer. The separated shear layer rolls up and a hairpin vortex is generated periodically behind the cube. A horseshoe vortex is also formed ahead of the cube. Heat transfer around the cube is high due to the horseshoe vortex. Since the hairpin vortex interacts with horseshoe vortices downstream of the cube, the heat transfer increases around the center of the spanwise direction. The hairpin and horseshoe vortices generate local areas of high turbulence.

STUDY ON NEW ICE SLURRY GENERATOR USING NaCl AQUEOUS SOLUTION AT LOW CONCENTRATION

A cold thermal energy storage system has been developed for HVAC. There are many ice-based cooling systems operating around the world. Ice slurry, which is a mixture of fine ice crystals and liquid water, is utilized in ice storage systems owing to its good flowability and large latent heat of fusion. For slurry ice production techniques, there are presently a number of commercially available ice slurry generators (e.g., Supercooled slurry ice generator, Scraper type generator, and Vacuum type generator, etc.). In the present study, a new method was developed to generate ice slurry without the deposition of an ice layer on a cooled surface. The basic components of the experimental apparatus is a cooling brine circulating loop, a high pressure pump, a valve, an aqueous solution flow loop containing the test section, which is made of transparent acrylic, and the associated instrumentation. This new method is based on freezing-point depression of the aqueous solution, which is maintained under high-pressure conditions. To control the timing for solidification and to generate ice slurry, we investigated the relationships among the pressure and temperature of the aqueous solution. The freezing phenomenon of the aqueous solution in the test section was observed in detail. As a result, we developed a new ice slurry generator based on the new method that controls the pressure and temperature of the aqueous solution. Experimental results showed that the characteristics of the ice slurry generation were closely related to the pressure and initial stage temperature of the test fluid. Finally, the optimum operation condition of the ice slurry generator based on visualization experiment was discussed.