Laser Focus Displacement Meter Research Articles

An experimental investigation on characteristics of liquid film thickness of gas-liquid Taylor flow in square/rectangular microchannel applied in microreactor

Microchannel reactors employing Taylor flow is 1 – 3 orders of magnitude higher than traditional reactor in handling gas-liquid reaction processes, which has found important applications in oxidation, hydrogenation, chlorination, fluorination and absorption involved in chemical industry. Liquid film thickness of gas-liquid Taylor flow in circular microchannel has been widely investigated, whereas the variation and distribution of liquid film thickness in square/rectangular microchannel are lack of comprehension. In the present work, experiments were conducted to investigate the variation of liquid film thickness in square channels with hydraulic diameter Dh = 0.3, 0.5, 0.7, 1.0 mm, and rectangular channels with a depth of 0.5 mm and widths of 0.3, 0.5, 0.7, 1.0 mm under the condition of air-water and the addition of surfactant Tween-20. The liquid film thicknesses were measured using a laser focus displacement meter (LFDM), the bubble shapes and velocities were compared using high speed photography. The experimental results illustrate that the dimensionless bubble diameter in square/rectangular microchannels can be divided into initial stage, reduction stage and stable stage with the increasing of capillary number Ca. The initial, reduction and stable stage of the dimensionless bubble diameter are all influenced by the channel hydraulic diameter, aspect ratio, asymmetry effects and surface tension coefficient of working fluid. In square channels with Dh = 0.3, 0.5, 0.7, and 1.0 mm, the dimensionless bubble diameter enters the reduction stage at Ca = 0.019, 0.015, 0.011, and 0.009, respectively. Besides, an empirical formula of dimensionless bubble diameter was developed using the dimensionless groups Ca, Re, Bo, and Li/Dh to describe the characteristics of liquid film thickness in square/rectangular microchannel.

Measurements of the liquid film thickness for annular flow during flow condensation in a circular tube

Liquid film thicknesses of R245fa and zeotropic mixtures of R134a/R245fa were measured during flow condensation in circular micro-channel using a CCD camera and a Laser Focus Displacement Meter (LFDM). The fluctuation characteristics were studied along with the average liquid film thickness and the thermal resistance. The average liquid film thickness had no obvious association with the temperature glide. The liquid film fluctuation frequency was most strongly affected by the vapor-liquid interface shear force with the liquid film thickness determining the fluctuation range. Larger mass fluxes weakened the thinning effect of the mass flux. With increasing R134a mass fraction, the impact of mass flux was much obvious. With increasing R134a mass fraction, the liquid film thermal resistance increased. The laminar liquid film momentum equation was used to develop a simple method to predict the mean liquid film thickness.

Dynamics of evaporating thin liquid films in microchannel

Aiming at flow boiling in a micro circular tube with the inner diameter of 0.5 mm, experimental investigation on the flow and heat transfer characteristics of the thin liquid film has been carried out. Water was used as working fluid, and it was heated by a transparent ITO heater. The thickness of the thin liquid film was measured by a laser focus displacement meter, and the flow boiling visualization was performed simultaneously by using a high-speed camera. The result of synchronized flow visualization and flow boiling measurement showed that the temperature and pressure fluctuation was strictly consistent with the bubble cluster generation. The mechanism of flow boiling instability was analyzed. The void fraction based characteristics such as the bubble and liquid slug duration, and pair generation period were obtained from the dynamic distribution diagram of liquid film thickness. The experimental data of void fraction showed a good agreement with the homogeneous model. The temporary thin liquid film variation provides an opportunity to probing the physics of bubble dynamics and instability during flow boiling.

Measurement of liquid film thickness on moving plate during dip-coating process

Dip-coating can be used to obtain a relatively uniform film thickness on a substrate and is widely used in industry. The thickness of the liquid film is a very important parameter for the desired function. In this study, a laser focus displacement meter is used to measure the liquid film thickness. The thickness of liquid film coated on the withdrawing plate increases initially and then becomes constant as time passes. The liquid film of the constant film thickness zone is in good agreement with these two existing correlations. For the transition region where the liquid film thickness increases, a comparison of the profiles of dimensionless liquid film thickness shows that as the withdrawal speed increases, the profile of dimensionless liquid film thickness becomes more convex. However, at a capillary number higher than 0.1, the profiles are consistent within a certain range. It is confirmed that the profile of dimensionless liquid film thickness can be classified into a viscous dominant region and a surface tension dominant region, similar to the tendency of liquid film thickness in the constant film thickness region.

Liquid film thicknesses of oscillating slug flows in a capillary tube

Liquid film thickness is an important parameter for predicting boiling and condensation heat transfer coefficients in a microscale slug flow. In the present study, liquid film thickness of oscillating slug flow in a capillary tube is experimentally investigated under adiabatic condition. Laser focus displacement meter is used to measure the initial liquid film thickness. Circular tube with inner diameter of 1 mm is used for the test tube, and water and ethanol are used as working fluids. Measurement is carried out using a capillary tube with one open end and the other connected to a stepping motor. Driving frequency is ranged from 1 to 10 Hz at equivalent slug stroke of 31.7 mm and 51.2 mm. As the frequency and equivalent slug stroke are increased, the liquid film thickness deviates from that in the steady condition and becomes thinner or thicker under flow acceleration or deceleration, respectively. The empirical correlations for the initial liquid film thickness under acceleration and deceleration conditions proposed in the previous study (Youn et al., 2015, 2016) well predict the liquid film thicknesses of the oscillating flows within 15% accuracy.

Experimental Study of Water Film Dynamics Under Wind Shear and Gravity

Aircraft icing poses a serious threat to flight safety. Unfrozen impinging water on the surface of the aircraft will run back under the effect of high-speed airflow, altering liquid distribution and heat transfer characteristics. In this paper, a series of experiments are conducted over a wide range of wind speeds (), film Reynolds numbers (), and inclined angles (, , ) to investigate the dynamics of thin water film on an aluminum substrate. The superficial morphology of the water film is investigated by a high-speed camera, and the instantaneous film thicknesses are measured by a laser focus displacement meter based on a confocal chromatic technique. The interface shape is found to consist of an underlying thin film and multiple scaled fluctuations; therefore, the results are divided into two parts for analysis: the mean film thickness and the root-mean-square thickness. A relationship between the mean film thickness and the wind speed, the film Reynolds number, the inclined angle is proposed. After nondimensionalized processing based on the triangular relationship, the averaged film thickness data agree with the previous model of an error within 25%. New correlations to calculate the interfacial shear stress and superficial roughness are suggested within the experimental range.

The effect of bubble deceleration on the liquid film thickness in microtubes

Liquid film thickness is an important parameter for predicting boiling and condensation heat transfer coefficients in microtube slug flows. In the present study, the effect of bubble deceleration on the liquid film thickness is experimentally investigated under adiabatic condition. The laser focus displacement meter is used to measure the liquid film thickness. Circular tubes with three different inner diameters, D=0.7, 1.0 and 1.3mm, are used. Measurement is carried out using a microtube with one open end and the other connected to an actuator motor. Water, ethanol and FC-40 are used as working fluids. It is found that deceleration makes the liquid film thicker than that in the steady flow, and it deviates from the steady case as the deceleration rate is increased. Liquid film thickness remains nearly unchanged just after the onset of deceleration, and then gradually decreases and eventually converges to the steady thickness as the velocity is further decreased. Finally, an empirical correlation is proposed to predict initial liquid film thickness in decelerated flows.

Evaluation of erythrocyte flow at a bearing gap in a hydrodynamically levitated centrifugal blood pump.

We have developed a hydrodynamically levitated centrifugal blood pump for extracorporeal circulatory support. In the blood pump, a spiral groove bearing was adopted for a thrust bearing. In the spiral groove bearing, separation of erythrocytes and plasma by plasma skimming has been postulated to occur. However, it is not clarified that plasma skimming occurs in a spiral groove bearing. The purpose of this study is to verify whether plasma skimming occurs in the spiral groove bearing of a hydrodynamically levitated centrifugal blood pump. For evaluation of plasma skimming in the spiral groove bearing, an impeller levitation performance test using a laser focus displacement meter and a microscopic visualization test of erythrocyte flow using a high-speed microscope were conducted. Bovine blood diluted with autologous plasma to adjust hematocrit to 1.0% was used as a working fluid. Hematocrit on the ridge region in the spiral groove bearing was estimated using image analysis. As a result, hematocrits on the ridge region with gaps of 45 μm, 31 μm, and 25 μm were calculated as 1.0%, 0.6%, and 0.3%, respectively. Maximum skimming efficiency in this study was calculated as 70% with a gap of 25 μm. We confirmed that separation of erythrocyte and plasma occurred in the spiral groove bearing with decrease in bearing gap in a hydrodynamically levitated centrifugal blood pump.

The effect of initial flow velocity on the liquid film thickness in micro tube accelerated slug flow

Liquid film thickness is an important parameter for predicting boiling and condensation heat transfer in micro tubes. In the present study, the effect of initial flow velocity on the liquid film thickness in accelerated flows under adiabatic condition is experimentally investigated. The laser focus displacement meter is used to measure the initial liquid film thickness. Circular tube with inner diameter of 1mm was used for the test tube, and water, ethanol and FC-40 are used as working fluids. When the flow is accelerated from small initial velocities under small Bond number condition, initial liquid film thickness is identical to that of steady flow at small capillary numbers, and then deviates from the steady condition and eventually follows that of accelerated flow from zero initial velocity as capillary number is increased. When the flow is accelerated from large initial velocities, initial liquid film thickness deviates from the steady condition earlier and starts to follow that of accelerated flow from zero initial velocity as capillary number is increased. It is found that the initial flow velocity cannot be neglected in accelerated flows especially at large initial flow velocities and at large Bond numbers. Finally, an empirical correlation is proposed for the initial liquid film thickness of accelerated flows that accounts for the initial flow velocities.

D113 細管内加速流における初期速度の液膜厚さへの影響(一般講演(5))

The effect of initial flow velocities on the liquid film thickness in micro-channel accelerated slug flow under adiabatic condition is experimentally investigated. Laser focus displacement meter was used to measure the liquid film thickness. Distilled water was used as a working fluid. Circular tube with inner diameter of 1 mm and length of 500 mm was used. The effects of the initial steady flow velocities, acceleration, and axial distance were evaluated. As the initial flow velocity increases, the liquid film thickness slightly increases at the constant acceleration and axial distance. The experimentally obtained results were compared to the previous correlation in which initial flow velocity is not considered. For each Bo, the liquid film thickness at small axial distance is deviated from the correlation which becomes large with increasing initial flow velocity. At large Z, the correlation well predicts the liquid film thickness which means that the effect of initial flow velocity is negligible at large Z. Also the deviation becomes significant with increasing Bo. The effect of initial flow velocity should be considered in low Bo and Z.

506 動圧浮上遠心血液ポンプのスラスト軸受形状がインペラ浮上特性に与える影響(OS9 オーガナイズドセッション《ライフサポートによる光学技術》)

We have developed a hydrodynamically levitated centrifugal blood pump as a bridge to decision pump. However, since the bearing stiffness of the hydrodynamic bearing is small, the bearing gap tends to become narrow. The purpose of this study is to evaluate the improvement of the impeller levitation performance due to the effect of the thrust bearing geometry with spiral groove on impeller levitation performance in a hydrodynamically levitated centrifugal blood pump. We compared the geometric models that have different groove width. The numerical analysis was performed in order to calculate the bearing stiffness. The impeller levitation performance test was conducted using a mock circulation loop and a laser focus displacement meter. As a result, it was found that the sudden contraction model achieved an improvement of the impeller levitation performance in a hydrodynamically levitated centrifugal blood pump.

The effect of liquid film evaporation on flow boiling heat transfer in a micro tube

Flow boiling in micro channels is attracting large attention since it leads to large heat transfer area per unit volume. Generated vapor bubbles in micro channels are elongated due to the restriction of channel wall, and thus slug flow becomes one of the main flow regimes. In slug flow, sequential bubbles are confined by the liquid slugs, and thin liquid film is formed between tube wall and bubble. Liquid film evaporation is one of the main heat transfer mechanisms in micro channels and liquid film thickness is a very important parameter which determines heat transfer coefficient. In the present study, liquid film thickness is measured by laser focus displacement meter under flow boiling condition and compared with the correlation proposed for an adiabatic flow. The relationship between liquid film thickness and heat transfer coefficient is also investigated. Initial liquid film thickness under flow boiling condition can be predicted well by the correlation proposed under adiabatic condition. Under flow boiling condition, liquid film surface fluctuates due to high vapor velocity and shows periodic pattern against time. Frequency of periodic pattern increases with heat flux. At low quality, heat transfer coefficients calculated from measured liquid film thickness show good accordance with heat transfer coefficients obtained directly from wall temperature measurements.

DROPLET IMPACT ON SHEAR-DRIVEN LIQUID FILMS

This paper investigates the interaction between the impact of a liquid droplet and a moving liquid film in which a shearing airflow is present above the liquid film. Visualization of droplet trajectory, deformation, and impact outcome are provided. Droplet diameters used in this study range from 2.4 to 4.8 mm, water film thicknesses are between 0.2 and 1.7 mm, and the shearing air velocity within the rectangular duct is between 4.5 and 15 m/s. Two high-speed cameras are used to track the droplet and visualize the film surface. A laser focus displacement meter is used to obtain the instantaneous and average film height. By analyzing the acquired images, along with the film height, different regimes for both droplet deformations in shearing air and impact outcomes are observed. A regime map is produced relating the air, film, and droplet properties with the outcomes of the interaction between the droplet and the moving water film. The shearing air has an important effect on the interaction process before the impact by deforming the droplet and confining the film thickness; it also influences the impact process during and after the impact. Where the droplets retain their spherical shape before impact (low shearing air velocity), the transition between splash and deposition agree with published results obtained for droplet impact onto static films. The waviness of the film has no clear effect on the impact outcomes but does have an important effect on the way splash occurs with a big difference in the size of secondary droplets.

Measurement of liquid film thickness in a micro parallel channel with interferometer and laser focus displacement meter

In the present study, liquid film thicknesses in parallel channels with heights of H = 0.1, 0.3 and 0.5 mm are measured with two different optical methods, i.e., interferometer and laser focus displacement meter. Ethanol is used as a working fluid. Liquid film thicknesses obtained from two optical methods agree very well. At low capillary numbers, dimensionless liquid film thickness is in accordance with Taylor’s law. However, as capillary number increases, dimensionless liquid film thickness becomes larger than Taylor’s law for larger channel heights. It is attributed to the dominant inertial effect at high capillary numbers. Using channel height H for dimensionless liquid film thickness δ 0/ H and hydraulic diameter D h = 2 H as the characteristic length for Reynolds and Weber numbers, liquid film thickness in a parallel channel can be predicted well by the circular tube correlation previously proposed by the authors. This is because curvature differences between bubble nose and flat film region are identical in circular tubes and parallel channels.

The effect of bubble acceleration on the liquid film thickness in micro tubes

Liquid film thickness is an important parameter for predicting boiling heat transfer in micro tubes. In the previous study ( Han and Shikazono, 2009a), liquid film thickness under the steady condition was investigated and an empirical correlation for the initial liquid film thickness based on capillary number, Reynolds number and Weber number was proposed. However, under flow boiling conditions, bubble velocity is not constant but accelerated due to evaporation. It is necessary to consider this bubble acceleration effect on the liquid film thickness, since it affects viscous, surface tension and inertia forces in the momentum equation. In addition, viscous boundary layer develops, and it may also affect the liquid film thickness. In the present study, the effect of bubble acceleration is investigated. Laser focus displacement meter is used to measure the liquid film thickness. Ethanol, water and FC-40 are used as working fluids. Circular tubes with three different inner diameters, D = 0.5, 0.7 and 1.0 mm, are used. The increase of liquid film thickness with capillary number is restricted by the bubble acceleration. Finally, an empirical correlation is proposed for the liquid film thickness of accelerated flows in terms of capillary number and Bond number based on the bubble acceleration.

S0803-1-6 着霜過程における霜層の構造と成長特性に関する研究(高効率ヒートポンプの要素技術とその応用)

The phenomenon of frosting is quite important in evaluation of efficiency of heat pump. In this study, measurements were carried out on the thickness and density of frost layer in frosting process using Laser focus displacement meter. The results showed that the growth of frost layer is devided into three stages. In the first stage, growth rate is small and density of frost layer is high. In the second stage, growth rate becomes large and density becomes lower. Finally, growth rate becomes small again and density increases again.

B209 垂直上昇環状二相流における液滴飛散特性に及ぼす壁面濡れ性の影響(OS8 熱流動),動力エネルギーシステム部門20周年,次の20年への新展開)

To evaluate the effect of wall surface wettability on the characteristics of upward gas-liquid annular two-phase flow in a vertical pipe, an experimental study was performed using two test pipes: an acrylic pipe and a FEP pipe. Measured contact angles on the acrylic and FEP pipe surfaces were 60° and 80°, respectively. Basic flow characteristics such as liquid film thickness and liquid entrainment ratio were respectively measured by a laser focus displacement meter and a suction method. At relatively high gas flow rate and low liquid flow rate conditions, a reduction of the surface wettability by the FEP pipe enhanced the interfacial waves on liquid film, and caused an increase in the liquid entrainment ratio and a decrease in the liquid film thickness.

Measurement of the liquid film thickness in micro tube slug flow

Slug flow is one of the representative flow regimes of two-phase flow in micro tubes. It is well known that the thin liquid film formed between the tube wall and the vapor bubble plays an important role in micro tube heat transfer. In the present study, experiments are carried out to clarify the effects of parameters that affect the formation of the thin liquid film in micro tube two-phase flow. Laser focus displacement meter is used to measure the thickness of the thin liquid film. Air, ethanol, water and FC-40 are used as working fluids. Circular tubes with five different diameters, D = 0.3, 0.5, 0.7, 1.0 and 1.3 mm, are used. It is confirmed that the liquid film thickness is determined only by capillary number and the effect of inertia force is negligible at small capillary numbers. However, the effect of inertia force cannot be neglected as capillary number increases. At relatively high capillary numbers, liquid film thickness takes a minimum value against Reynolds number. The effects of bubble length, liquid slug length and gravity on the liquid film thickness are also investigated. Experimental correlation for the initial liquid film thickness based on capillary number, Reynolds number and Weber number is proposed.

OS0906 アルミニウム合金破壊挙動の衝撃速度依存性に関する研究(衝撃工学とその応用,オーガナイズドセッション)

Fracture toughness K_<IC> or J_<IC> is generally used as criterion for safety design. These criteria are defined under plane sirain condition. Shear lips on crack surface is caused in case of thin plates fracture. Therefore, fracture mechanism in thin plates is not clarified. And some of these fracture behavior depends on loading speed. In this study, three point bending fracture experiments are demonstrated to gain basic data for elastic plastic fracture in thin plates. The specimens are consists of aluminum alloy. Pure mode I and mixed mode fracture experiments are done under quasi-static loading and dynamic loading. Roughness on crack surfaces are evaluated using laser focus displacement meter. Fracture path, crack surface trend and surface roughness are depended on loading speed.

Measurement of Liquid Film Thickness by a Fringe Method

A technique was developed and tested to measure the local thickness of a droplet or a liquid film on a surface of an opaque or thick single transparent plate by an interference fringe pattern that was easily formed by reflecting laser lights. Monochromatic epi-illumination through an objective lens of a conventional microscope was provided by a 5 mW or 300 mW laser and a filter to remove the noise caused by laser speckle. The incremental height difference of the liquid layer between neighboring maxima or minima of fringes was evaluated from the wavelength of the laser light and the refractive index of the liquid. Estimation error of a local inclination angle was discussed using ray tracing under parallel illumination approximation. Droplet profiles evaluated from the interferogram that were obtained by the present fringe method agreed well with those by Laser Focus Displacement Meter. Measurement was made to ensure the usefulness of the present technique. It was made clear that the contact angle of a liquid droplet could be obtained precisely and swiftly, even in small size or small contact angle, and that instantaneous three-dimensional profile of a liquid film on a bubble moving in a microchannel could be measured. The fringe method had sufficient potential to obtain more detailed information about three-dimensional characteristics of liquid film in flows such as the generation, breakdown, and growth of waves and the liquid film on a bubble at the beginning of movement.