Film Flow Research Articles

Experimental Investigation of Runback Water Flow Behavior on Aero-Engine Rotating Spinners with Different Wettabilities

The accumulation of ice on the aero-engine inlet compromises engine safety. Traditional hot air anti-icing systems, which utilize bleed air, require substantial energy, decreasing engine performance and increasing emissions. Superhydrophobic materials have shown potential in reducing energy consumption when combined with these systems. Research indicates that superhydrophobic surfaces on stationary components significantly reduce anti-icing energy consumption by altering runback water flow behavior. However, for rotating aero-engine components, the effectiveness of superhydrophobic surfaces and the influence of surface wettability on runback water flow remain unclear due to centrifugal and Coriolis forces. This study investigates the runback water flow behavior on aero-engine rotating spinner surfaces with varying wettabilities in a straight-flow spray wind tunnel. The results demonstrated that centrifugal force reduces the amount of runback water on the rotating spinner compared to the stationary surface, forming rivulet flows deflected opposite to the direction of rotation. Furthermore, wettability significantly affects the flow characteristics of runback water on rotating surfaces. As the contact angle increases, the liquid water on the rotating spinner transitions from continuous film flow to rivulet and bead-like flows. Notably, the superhydrophobic surface prevents water adhesion, indicating its potential for anti-icing on rotating components. In addition, the interaction between rotational speed and surface wettability enhances the effects, with both increased rotational speed and larger contact angles contributing to higher liquid water flow velocities, promoting the rapid formation and detachment of rivulet and bead-like flows.

The Effect of the Initiator/Activator/Accelerator Ratio on the Degree of Conversion, Film Thickness, Flow, and Cytotoxicity of Dual-Cured Self-Adhesive Resin Cements.

Although self-adhesive resin cements are convenient and less technique-sensitive materials for dental clinicians, they exhibit a lower degree of conversion due to acidic components in their composition. Supplementation of the initiator, accelerator, and activator in self-adhesive resin cements has been suggested to compensate for the lower degree of conversion. This study aimed to evaluate the effects of different combinations of self-curing initiators, self-curing activators, and accelerators on the degree of conversion (DC) of self-adhesive resin cements. A dual-cured self-adhesive resin was prepared using six combinations of initiators, activators, and accelerators. The change in the DC over time was evaluated with and without light curing. The film thickness, flow properties, and cytotoxicity of each formulation were assessed. The results showed that all supplemental components had an effect on increasing the DC, but a greater increase in the DC was observed in the following order: activator, accelerator, and initiator. The cytotoxicity of the resin cements was related to the DC values, as resin cements with lower DC values exhibited higher cytotoxicity. The film thickness met the ISO standards for all groups. The results suggest that utilizing an activator is the most effective approach to enhance the DC in self-adhesive resin cement and that cytotoxicity tended to increase with lower DC values, whereas film thickness and flow properties demonstrated no correlation with DC values.

Experimental design of a film flow cleaning rig equipped with in-line process analytical technology (PAT) tool for real-time monitoring

The main purpose of this research was to develop an experimental film flow cleaning rig that can be combined with Process analytical technology (PAT) tools to reduce cleaning time and costs. Here, we show that the use of in-line UV–Vis was successful for real-time monitoring of the cleaning process of olanzapine as a challenging residue to clean. The cleaning process was found to be affected by the properties of the olanzapine soil, and the study showed the competing effects of mechanical lift-off and dissolution action with methanol as a solvent. However, The method is limited by the cleaning mechanisms, with the dissolution being the only mechanism that can be accurately quantified using an in-line UV–Vis PAT tool. This experimental approach can be used to optimize cleaning process conditions and solvent choices at the bench scale before deployment. The material of which the cleaning rig was printed limited the solvent that could be used for this study, and future modifications will include a more chemical-resistant material.

Simulation Analysis of Non-concentric Squeeze Film Damper

Squeeze film dampers are components that provide additional damping for rotating motors. In general, in order to achieve the best results of the squeeze film damper, it is necessary to appropriately increase the damping value, reduce the stiffness and set a reasonable eccentricity. In the process of designing the squeeze film damper, we can apply the rotor dynamics module of COMSOL software to model and simulate it, so as to achieve better simulation results and lay a foundation for the subsequent development and design of the product. In COMSOL software, in order to simplify the modeling of rotor components, we usually model squeeze film dampers based on the damping coefficient. The model calculates the damping coefficient for a short squeeze film damper and compares the results with the analytically calculated values. In addition, the damping coefficient depends on the position of the journal in the damper, i.e., the magnitude of the eccentricity. In this paper, by analyzing the dimensionless damping coefficient, bearing stiffness, journal displacement, and fluid load at different eccentricity, and plotting the fluid pressure distribution and the average oil film flow rate of the squeeze film damper, we can find the most suitable range of eccentricity and the damage-prone part of the damper, which can provide an important reference for the actual design of the squeeze film damper.

Gravity-driven thin film flow of a third-grade fluid on a movable inclined plane with slip boundary condition

The prime aim and essence of this study are to present a closed-form solution of the unidirectional velocity field for thin film flow generated by a third-grade liquid moving over a fixed or movable inclined plane in the presence of partial slip boundary condition. Consideration of partial slip makes this problem different from other published research works. Here lies the novelty of this study. The nondimensional, unidirectional velocity profiles rely on the material parameter of third-grade fluid, slip parameter and initial velocity of the movable plane. Study discloses that the fluid’s velocity decelerates with raising the material property of grade-3 fluid and it accelerates with the slip parameter and initial velocity of the inclined plane. The outcomes of this study are deliberated physically at length.

A numerical inquiry of the MHD radiative thin film nanofluid flow and heat transfer augmentation for Ni and Ta nanoparticles of different shapes dispersed in C 12 H 26–C 15 H 32 over an unsteady, curved stretching surface

Thin films are a versatile technology used in various industries, including light-emitting diodes, magnetic recording media, electronic device manufacturing, and optical coating. They are crucial for studying quantum phenomena, superlattices, and multiferroic materials. Their small size allows for better thermal transport studies due to the combination of thin film flow and nanoparticles. Therefore, this study aims to investigate thin film flow and heat transfer with the effects of thermal radiations, magnetic field, and velocity slip in association with tantalum ( Ta ) and nickel ( Ni ) nanoparticles that emerged in kerosene oil ( C 12 H 26 − C 15 H 32 ) toward a curved stretching surface. A review of the pertinent literature indicates that no research has previously been done on the present problem of an unsteady thin film flow across a curved stretching surface. The problem under consideration is modeled by choosing the curvilinear coordinate system. The controlling nonlinear system of partial differential equations is transformed into the system of ordinary differential equations by using an appropriate similarity transformation and then solved numerically using the BVP 4 C technique in MATLAB . The impact of significant physical parameters on velocity, temperature, skin friction, and Nusselt numbers are depicted through graphs and radar charts. The investigation highlights the significant influence of magnetohydrodynamics ( MHD ) , thermal radiation, volumetric fraction, and velocity slip on the enhancement of nanofluid temperature. It is also noted that cylindrical-shaped Ta nanoparticles exhibited the maximum velocity, while blade-shaped Ni nanoparticles showed the lowest. Moreover, the maximum and minimum temperatures were observed for blade-shaped Ni nanoparticles and cylindrical Ta nanoparticles, respectively. Additionally, the maximum and minimum values of skin friction are found for cylindrical Ni nanoparticles and blade-shaped Ta nanoparticles, respectively. Similarly, the maximum and minimum Nusselt numbers are recorded for cylindrical Ta nanoparticles and blade-shaped Ni nanoparticles, respectively.

Unsteady MHD‐radiative thin film flow with heat transfer over a stretching surface in porous media

AbstractThis study conducts a computational analysis to explore how magnetic fields, radiation, heat, and mass transfer collectively influence a horizontal stretching sheet within a porous medium. The research focuses on elucidating the dynamics of thin film flow through the formulation of time‐dependent equations and subsequent transformation of fluid flow equations into ordinary differential equations via similarity transformation. The numerical solution is attained employing the Runge–Kutta fourth‐order method coupled with a shooting technique. MATLAB software is utilized to generate graphs and numerical values, offering a detailed representation of engineering‐relevant physical quantities in tabular form. The investigation revealed notable trends associated with varying parameters. Increasing unsteadiness parameters lead to a reduction in velocity, temperature, and concentration fields, while the temperature distribution demonstrates a positive correlation with radiation parameters. Moreover, elevated Prandtl numbers and unsteadiness parameters correspond to augmented heat and mass flux, respectively. Of particular significance is the observed heightened heat transfer rate during the transition from a Prandtl number of 1 (representing air) to 2 (representing oil), alongside an increased mass transfer rate with the escalation in Schmidt number from 0.62 (representing hydrogen) to 0.78 (representing ammonia). A comparative analysis of the numerical findings with existing literature demonstrates excellent agreement, affirming the validity and relevance of the present study. These insights offer valuable implications for understanding and optimizing heat and mass transfer processes in porous media, with potential applications in various engineering and scientific domains.

Mode Transition Of A Flexible Film Motion In The Circular Cylinder Wake

The fluid-structure interaction between a flexible film and the wake of a circular cylinder is an abstract of a series of natural phenomena like flag flapping and fish swimming. Diverse patterns of both solid deformation and fluid dynamics arise in this coupling system as the nondimensional parameters are varied. In our recent experiments, we find that beyond the extensively studied periodic coupling process, irregular processes also emerge in this system under specific conditions. However, due to the complexity inherent in the irregular coupling processes, no in-depth investigation into this topic is available yet. In this work, we delve into the irregular aperiodic flutter of a flexible film behind a circular cylinder in the uniform flow as well as the related irregular evolution of flow structures. Two representative cases of film streamwise length (L/D) pertinent to the irregular process, specifically L/D=3 and L/D=4, have been investigated experimentally in the wind tunnel with time-resolved synchronized measurements of both film deformation and flow field. Continuous wavelet transform and virtual dye visualization are employed to extract the time-frequency characteristics of film motion and Lagrangian coherent structures in the flow fields during the film’s irregular flutter, respectively. It is determined that the irregular flutter is aperiodic in terms of the overall view, but it also encompasses transient quasi-periodic stages as its motion modes alter. Hence, we term this irregular flutter as the “hybrid flutter” state. In the quasi-periodic stages of the hybrid flutter, the large-scale vortex structures are periodically formed on the surfaces of the film and evolve in the wake as a Kármán vortex street. The periodic formation of large-scale vortices exerts periodic alternating force on the film, which, therefore, leads to the quasi-periodic flutter of the film with the second-order mode. By comparison, the aperiodic stage entails the significant extension of the separated shear layers in such a way that the whole film is enveloped by the shear layers; then, large-scale vortices are formed downstream of the film’s trailing edge. In this scenario, no periodic force is acted on the film; as a result, the film flutters aperiodically with the first-order mode.

Comparative Analysis Of Brightness-Based Laser-Induced Fluorescence (BBLIF) And Structured Planar Laser-Induced Fluorescence (S-PLIF) For Film Thickness Measurement In Two-Phase Flow

Improved understanding of the interactions between gas and liquid phases in gas sheared film flow is crucial for n improved capability to employ computational modelling in the future to optimize systems, thereby reducing environmental impact, increasing efficiency, and enhancing productivity. This abstract compares two techniques for measuring the thickness of the film in different regimes visible in a rectangular cross-section gas-sheared liquid film rig, namely previously published Brightness Based Laser Induced Fluorescence (BBLIF) data and Structured Planar Laser Induced Fluorescence (S-PLIF) from the current investigation. The study presents and compares examples at a specific liquid flow rate (8 litres per minute) for superficial gas velocities in the range 1 m/s to 10 m/s, noted as being in different flow regimes. The investigation reveals that the S-PLIF technique produces results that are within the uncertainty bands of the BBLIF data for most scenarios. However, in the transition regime, statistical variations emerge. The frequency content of the two film heights is analyzed using a Hilbert-Huang Technique. This shows clearer results for the S-PLIF than for BBLIF which is attributed to the erratic values that can occur in BBLIF when total internal reflection occurs. It is concluded that the S-PLIF technique demonstrates promise as a reliable method for determining film thickness which is highly advantageous as it can be applied to images obtained with seeded flow intended for PIV analysis. The S-PLIF film thickness data can be used for generating automated masks for PIV analysis concurrently conducted in both the gas and liquid phases. This advancement facilitates the enhanced capability to advance understanding of complex fluid dynamics and optimize system performance.

Effect of the dynamic contact angle on electromagnetically driven flows in free liquid films

We study the effect of a dynamic contact angle on an electromagnetically driven flow in a horizontal free electrolyte film stretched between two coaxial cylindrical electrodes and placed in a uniform magnetic field. The flow dynamics and film deformation are described using the reduced hydrodynamic model derived in the lubrication approximation in [A. Pototsky and S. A. Suslov, J. Fluid Mech., 984, A75 (2024)]. The linearized molecular kinetic model is used to relate the dynamic and static contact angles to the wetting-line friction coefficient. Steady azimuthal flow is found for arbitrary static contact angles. Linear stability of the base azimuthal flow with respect to azimuthally invariant perturbations is studied using the numerical continuation method. We find that the flow stability is highly sensitive to variations of the wetting-line friction coefficient and the static contact angle. The least stable azimuthal flow is found for the frictionless contact line corresponding to a free film that remains perpendicular to the surface of the electrodes. The azimuthal flows are found to experience a supercritical Hopf bifurcation upon which they transition to a stable oscillatory dynamic regime characterized by alternating squeezing and swelling of the film near the inner and outer electrodes.

Flow analysis of temperature-dependent variable viscosity Phan Thien Tanner fluid thin film over a horizontally moving heated plate

Comprehending the temperature-dependent variable viscosity Phan Thien Tanner fluid film flow over a horizontal heated plate with surface tension is essential to enhancing coating and lubrication process prediction models. This paper accords with the flow analysis of a temperature-dependent variable viscosity Phan Thien Tanner fluid film over a horizontal heated plate. The flow over a heated plate occurs as a result of the plate’s motion and the surface tension gradient. The Adomian decomposition method is utilized to solve a system of linear and nonlinear ordinary differential equations, resulting in series-form solutions. The series-form expressions for flow variables such as velocity, temperature, volume flow rate, and surface tension are derived. Moreover, the positions of stationary points are computed using MATHEMATICA. The analysis delineated that when the inverse capillary number, variable viscosity parameter, Deborah number, elongation parameter, and Brinkman number increase, the stationary points move closer to the heated plate. The temperature also rises with an increase in these parameters. The temperature rises with increasing viscous dissipation while it lowers with increasing thermal diffusion. When the Deborah number is high, the Phan Thien Tanner fluid behaves like a solid and the flow is only driven by the motion of the plate. A comparison between Newtonian and Phan Thien Tanner fluids is made for velocity, temperature, and stationary points as a special case.

Numerical investigation of electrically conducting thin film flow and heat transfer improvement for various shaped $$Sn-PG$$ and $$W-PG$$ nanofluids over an unsteady curved stretching surface

Numerical investigation of electrically conducting thin film flow and heat transfer improvement for various shaped $$Sn-PG$$ and $$W-PG$$ nanofluids over an unsteady curved stretching surface

Numerical simulation of the liquid film thickness distribution of horizontal tubes under cross-airflow

During the working process of the falling film evaporator, the airflow generated by evaporation process affects the falling film flow process. A three-dimensional model consisting of two horizontal tubes was conducted, which only considered the flow of one liquid column unit. The effect of cross-airflow on the liquid film thickness distribution of tube 1 and tube 2 in the jet mode was studied. The gas is air, the liquid is pure water, and the flow of gas and liquid begins simultaneously. The fluctuation and thickness distribution of the liquid film were analyzed. The research results indicate that liquid film fluctuation occur at the moment when the fluid falls from the first tube to the second tube, and continue to exist thereafter. When the airflow is applied, at l*=0.5, for the tube 1, the liquid film thickness from θ=45° to 90° areas is relatively flat; At l*=1, for the tube 2, the smallest liquid film thickness is located near θ=90° and 270°. The airflow has a certain inhibitory effect on the liquid film waviness on the windward side. The main reason why the liquid film thickness on the leeward side is greater than that on the windward side is due to the offset of the liquid column. The stability of the liquid column, which means that the liquid column does not offset, can ensure the stability of the falling film flow process.

Insights on phase speed and the critical Reynolds number of falling films.

We revisit the studies of gravity-driven viscous falling films with and without imposed shear stress to provide new perspectives on phase speed and the critical Reynolds number for surface instability. We use the traditional long-wave expansion technique implemented for investigating the linear stability analysis [C.S. Yih, Phys. Fluids 6, 321 (1963)0031-917110.1063/1.1706737]. The principal purpose is to create a unified relationship between the leading-order phase speed and the critical Reynolds number that will hold for falling films on impermeable substrates with or without shear stress acting at the liquid film surface. The analytical result demonstrates that the critical Reynolds number for the onset of surface instability is [5/(2c_{0})]cotθ, where c_{0} is the leading-order phase speed of the surface mode and θ is the angle of inclination with the horizontal. Clearly, the critical Reynolds number of the surface mode is explicitly dependent on the leading-order phase speed. Furthermore, we reveal that the basic parallel flow with or without imposed shear stress is linearly unstable to infinitesimal disturbances if the modified Reynolds number, Re_{M}=(Rec_{0}/cotθ)[ReistheReynoldsnumber,andθ≠π/2], is greater than its critical value of 5/2, which is independent of the shear stress applied at the film surface. In addition, it is demonstrated that Re_{M} controls the surface instability in the long-wave regime for both shear-imposed and non-shear-imposed film flows.

Liquid film flow rate from measurements of disturbance wave characteristics for applications in thin film flow

Liquid film flow rate from measurements of disturbance wave characteristics for applications in thin film flow

Analysis of oil film flow characteristics and lubrication performance of thrust bearing of 1000MW Hydraulic Turbine Unit

Abstract Hydro-generator unit is the core component of the hydropower station, and the stability of the shaft system directly determines the safety of the hydropower station. Thrust bearing is the only component to bear axial load, and working performance directly affects the stable operation and efficiency of the unit. In this study, a full 3D model of the shaft system of a 1000 MW hydro-generator unit is established, and the oil flow of thrust bearing oil film and oil in the oil tank considering the spray system and the overall model is analysed by means of the thermo-hydrodynamic method. The results show that the load increases with increasing inclination angle. Within certain limits, the pressure and temperature of the oil film increase with increasing inclination. And there are many vortices in the tank. Although the spray system reduces the oil churn, the lubricating oil flow between pads is chaotic. The loss is mainly caused by the chaotic flow between pads. Analyzing the effects of oil film thermal effects on bearing loads, lubricant flow, and bearing surface temperatures of tilting pads provides valuable insights for bearing design and maintenance guidance.

Film thickness characterization in dual-axis spin coating of a sphere

The versatility of spin coating technology makes it a preferred method for producing the thin film layers used to manufacture products from solar panels and smartphones to sunglasses and CDs. However, the process requires a flat, rigid substrate to produce uniform films, which limits its use to planar devices. A novel multi-axis manipulator has been developed to extend the application of spin coating, enabling controlled thin film deposition onto curved surfaces. Various rotational schemes were studied to link the flow of a liquid film over a curved surface to forces induced by complex rotational dynamics. When the angular velocity exceeds a threshold, centrifugal force dominates the flow, pushing the fluid away from the instantaneous axis of rotation. This produces axisymmetric coating profiles when using consistent single or dual-axis rotation. Areas of near uniformity present around the spin axis poles for single-axis rotation and around the substrate’s equator for dual-axis schemes. Sensitivities between the spherical substrate dynamics and the evolving fluid flow were investigated, exploring the parameters that promoted the production of uniform curved film layers for microfabrication processes. This enabled the evolution of the spin coating technique to effectively form curved polymer coatings with improved thickness control. The presented research outlines the capabilities of a multi-axis spin coating machine when used to coat spherical substrates. Therefore, enabling the use of fluid mechanics models to identify the optimal motion kinematics required to create uniform curved films.

Effect of hemispherical ash slag simulants on the thickness distribution and fluctuation characteristics of turbulent liquid film

To explore the influence of ash slag adhering to the scrubbing-cooling tube on the turbulent falling film flow, three hemispheres with different radii (R = 2 mm, 4 mm, and 6 mm) were used to simulate the slag. Ultrasonic Doppler Velocimetry was used to investigate the liquid film’s thickness distribution and fluctuation characteristics under Reynolds number of liquid film Ref ≈8.75 × 103 ––2.63 × 104. The liquid film thickness distribution at low Reynolds numbers exhibits an isosceles triangle when subjected to R = 4 mm and 6 mm hemispheres. At high Reynolds numbers, the average thickness of the liquid film is smaller downstream of the three simulants. The simulants can enhance the liquid film’s perturbations. A mathematical model has been established to predict the mean liquid film thickness on hemispherical simulants, and the relative difference is within 10 %. The probability density distribution curves of the instantaneous liquid film thickness on the simulant exhibit multimodality.

Impact of variable viscosity, thermal conductivity, and Soret–Dufour effects on MHD radiative heat transfer in thin reactive liquid films past an unsteady permeable expandable sheet

AbstractSignificance of magnetohydrodynamic effect on a viscous (temperature‐dependent) and chemically reactive thin fluid film flow past an unsteady permeable stretchable plate with Soret–Dufour effects, nonlinear thermal radiative, and suction under the action of a convective type of boundary condition is analyzed. The problem consists of nonlinear governing basic equations that are highly nonlinear due to the existence of nonlinear thermal radiative terms in the energy equation. Analytical solutions are challenging to achieve for such types of problems, so a numerical scheme adopts the numerical solution. Computed solutions indicate that decreasing the Dufour number (and simultaneously increasing the Soret number) enhances heat flux, whereas the reverse trend is estimated for the concentration gradient field. The influence of magnetization indicates a decrement in the thin liquid film velocity distribution, whereas an increment is observed in temperature and solutal gradient profiles. Further, an enhancement in thermoradiative values focuses on decreasing the heat flux profiles, whereas a decreasing trend is determined in the solutal gradient by incrementing the Schmidt number. The variations of the velocity field, temperature, and concentration gradients are shown for the unsteady parameter lying in the range [0.8, 1.4]. Similarly, the range of different parameters utilized are [0.0, 1.0], [0.0, 2.0], [0.8, 1.5], [0.5, 2.0], [0.0, 1.0], [0.2, 3.0], [1.0, 2.0], [0.0, 3.0], [0.4, 1.0], and [0.4, 1.0]. The novelty of the present study lies in its analysis of complex fluid dynamics phenomena and their implications for various industrial processes and engineering applications, including coating processes, heat exchangers, microfluidics, and biomedical engineering. The insights gained from the study can contribute to developing more efficient and innovative research in these areas. Further, we have compared the present results with those available in the literature under some special cases and found them to be in excellent agreement.

Falling film flow and heat transfer on a horizontal tube under the shearing of vertical vapor

Falling film evaporators are commonly employed in a wide range of industrial applications, with a particular emphasis on the management of vapor generated during operations. It is widely recognized that vapor streams have a significant influence on falling film flow and heat transfer. In this paper, we conducted numerical investigations of this issue in the presence of vertical vapor streams and validated the present numerical results against previous experimental data. The results indicate that the length of the liquid tongues and the interaction time between two liquid films are affected by both downward and upward vapor streams. The effect of vertical vapor on the film thickness is dependent on the vapor’s orientation and position on the tube. Typically, is decreased by 25 % at z* = 0 and vg = 4.0 ms−1 and is increased by 20 % at z* = 0 and vg = 4.0 ms−1. The downward vapor enhances heat transfer on the top half of the tube’s periphery while weakening it on the bottom half, while the upward vapor contributes to heat transfer enhancement mainly in the detachment zone. Overall, the vertical vapor stream causes substantial redistributions of the heat transfer coefficient, velocity vector, and liquid film thickness in three distinct zones. Downward and upward vapor streams predominantly impact the upper and lower parts of the tube, respectively. Within the current velocity range, it is evident that vertical vapor streams consistently lead to an average enhancement in heat transfer.