The swirling flow of a viscoelastic fluid in a cylindrical casing is investigated experimentally, using aqueous solutions of 0.05–1.0wt.% polyacrylamide as the working fluid. The velocity measurements are made using laser Doppler anemometer. The aspect ratios H∕R (H: axial length of cylindrical casing; R: radius of rotating disk) investigated are 2.0, 1.0, and 0.3. The Reynolds numbers Re0 based on the zero shear viscosity and the disk-tip velocity are between 0.36 and 50. The velocity measurements are mainly conducted for the circumferential velocity component. The experimental velocity data are compared to the velocity profiles obtained by numerical simulations using Giesekus model and power-law model. It is revealed that at any aspect ratios tested the dimensionless circumferential velocity component Vθ′ decreases with increasing Weissenberg number We. Both the Giesekus and power-law models could predict the retardation of circumferential velocity fairly well at small We. The extent of the inverse flow region, where the fluid rotates in the direction opposite to the rotating disk, is clarified in detail.

Automatic reed valves are widely used to control refrigerant gas flow in reciprocating compressors for automotive air conditioners. The oil film in the clearance between the reed and the valve seat causes a delay in opening of the valve. This opening delay of the discharge valve leads to over compression, which increases losses such as friction in sliding components and gas overheating. Therefore it is important to understand the behavior both of the oil film and the elastic reed deformation in order to reduce losses due to the delay. This study aims to develop an experimental setup that enables simultaneous visualization of the oil film rupture and measurement of the reed deformation, and to observe this behavior during the valve opening process. The gas-compression stroke is simulated by controlling compressed air with an electromagnetic valve. The oil film rupture is visually observed using a high speed camera through a special valve seat made of glass. The total deformation of the cantilever reed is identified by multipoint strain measurement with 12 strain gauges. The experiment finds that the opening process is divided into four stages. In the first stage, the reed remains stuck to the seat and deforms while the bore pressure increases. In the second stage, cavitation occurs in the oil film and the film starts to rupture. In the third stage, the oil film ruptures and the bore pressure starts to decrease. Finally, in the fourth stage, the reed is separated from the seat and the gas flows through the valve. Reducing the reed/seat contact area changes the reed deformation in the first stage, thereby increasing the reed/seat distance and realizing an earlier oil film rupture and a shorter delay.

The swirling flow of viscoelastic fluid in a cylindrical casing is investigated experimentally, using aqueous solutions of 0.05–1.0 wt% polyacrylamide as the working fluid. The velocity measurements are made using laser Doppler anemometer. The aspect ratios H/R (H: axial length of cylindrical casing, R: radius of rotating disc) investigated are 2.0, 1.0 and 0.3. The Reynolds numbers Re0 based on the zero shear viscosity and the disc tip velocity are between 0.36 and 50. The velocity measurements are mainly conducted for the circumferential velocity component. The experimental velocity data are compared with the velocity profiles obtained by numerical simulations using Giesekus model and power-law model. It is revealed that at any aspect ratios tested the dimensionless circumferential velocity component Vθ’ decreases with increasing Weissenberg number We. The Giesekus model could predict this retardation of circumferential velocity fairly well at small We, but the power-law model could not. The extent of the inverse flow region where the fluid rotates in the direction opposite to the rotating disc is clarified in detail.

On the opening delay of a discharge reed valve for compressors caused by the oil film in the clearance between the reed and the valve seat, effects of design conditions on the opening delay are analyzed through the experiment and the numerical simulation. Investigated are three kinds of conditions, the time rate of the bore pressure (compression speed), the oil viscosity, and the thickness of the reed. The experiment shows that the over-compression by the delay increases with increasing each of three condition values. The simulation reproduces qualitatively the effect of the bore pressure rate on the delay. The smaller bore pressure rate makes, under a certain bore pressure, the larger film thickness or the larger cavitation bubble diameter that results in the oil film rupture and the valve opening under the smaller bore pressure. The simulation also reproduces qualitatively the effect of the reed thickness. The larger reed thickness with the larger bending rigidity leads to the smaller reed deformation, the smaller oil film thickness, and the longer delay. On the oil film viscosity, the simulation fails in reproducing the change in the delay. The fail is due to the change in the oil film thickness of the simulation being smaller than that of the experiment. The experiment and simulation results indicate that, on all three conditions, the change in the increase of the oil film thickness leads to the change in the valve opening time and thereby the over-compression.

In a discharge reed valve for compressors, the oil stiction by the oil film between the reed and the valve seat is investigated experimentally, and a simulation model is developed. Through a model experiment, the initial oil film thickness is measured by an interferometry method, and the valve displacement and the bore pressure are measured from the stiction to the valve opening. The opening delay time together with the initial oil film thickness is measured while changing the contact area and the oil species. In the simulation model, the deformation of the reed and the pressure of the oil film as a result of cavitation are coupled. In order to take into account the tensile stress in the oil film, a cavitation model directly simulating the expansion of cavitation bubbles is developed (herein, dynamic cavitation model). In the experiment, a smaller contact area, a larger initial film thickness, and a smaller oil viscosity yield a shorter delay. In the simulation, the dynamic cavitation model is advantageous in representing the experimental delay time. In particular, with respect to the relationship between the initial film thickness and the delay time, the dynamic cavitation model with an initial bubble radius that depends on the oil film thickness yields results similar to the experimental results.