Liquid-film Transfer Research Articles

Interfacial Liquid Film Transfer Printing of Versatile Flexible Electronic Devices with High Yield Ratio

AbstractEmerging flexible electronic devices differ widely in terms of material, shape, scale, and structure. The conventional solid‐contact stamp transfer printing method easily causes cracks and interfacial delamination in large‐area, intricately‐patterned multilayered devices. Liquid film transfer printing (LTP) is presented as a strategy to obtain flexible devices with a high yield ratio regardless of the device material, scale, shape, and structure. In this technique, the liquid film is used to hydrolyze and break the chemical bonds between the film and silicon wafer substrate. Thus, there is less stress on the device during the transfer process. In addition, the buoyancy and surface tension of the liquid film help the flexible device to unroll itself on the liquid surface. In the experiments, flexible devices of different types and with extreme properties consistently achieved a transfer printing yield ratio of 98.57%. The sensitivity of temperature sensor change before and after LTP is less than 2%. The real‐time and visualized comparisons of the stress distribution and evolution during LTP and solid‐contact methods demonstrated that the LTP maximum strain is 70% smaller than the latter method. Thus, LTP has great potential for sophisticated and system‐level flexible device transfer printing and integration.

Influence of Surface Topography on Heat Transfer in Shear-Driven Liquid Films

Thin gas-driven liquid films find numerous industrial applications. They are used for fuel preparation in airblast atomizers of modern gas turbines. Strong shear forces at the gas-liquid interface destabilize the liquid-gas interface and lead to development of interfacial waves. In this study, the heat transfer in liquid films driven by turbulent gas flow is investigated experimentally over a wide range of parameters. A liquid film is formed on vertical heated unstructured and micro-structured tubes. The Reynolds number of the gas flow is varied between 104 and 105, and the Reynolds number of the liquid film flow is varied between 80 and 800. Wall heat fluxes up to 30 W/cm2 are applied. The heat transfer coefficient strongly depends on the gas and liquid Reynolds numbers. Using the micro-structured tube leads to a heat transfer enhancement of up to 80 %.

Improvement of oxygen transfer efficiency in aerated ponds using liquid-film-assisted approach

In aerated ponds, oxygen is generally supplied through either diffused or mechanical aeration means. Surface transfer and bubble transfer both contribute significantly to oxygen transfer in a diffused aeration system. In the present study, a liquid-film-forming apparatus (LFFA) is successfully developed on a laboratory scale to improve considerably the surface transfer via the unique liquid film transfer technique. The experimental results show that the volumetric mass transfer coefficient for LFFA alone is found to be as much as 5.3 times higher than that for water surface and that the total volumetric mass transfer coefficient for the liquid film aeration system increases by 37% in comparison with a conventional aeration system. Additionally, by tuning finely the structural parameters of the LFFA, it can also lead to high dissolved oxygen (DO) water with the DO percent saturation greater than 90%. More importantly, this result is accomplished by simply offering a single-pass aeration at a depth as shallow as 26 cm. As a result, the objective of economical energy consumption in aerated ponds can be realized by lowering the aeration depth without sacrificing the aeration efficiency. It is noteworthy that the data presented in this study are acquired either numerically or experimentally.

Enhancement of Oxygen Transfer Efficiency in Diffused Aeration Systems using Liquid-Film-Forming Apparatus

Surface transfer and bubble transfer both contribute significantly to oxygen transfer in a diffused aeration system. In the present study, liquid-film-forming apparatus is successfully developed on a laboratory scale to improve considerably the surface transfer via the unique liquid film transfer technique. The experimental results show that the volumetric mass transfer coefficient for liquid-film-forming apparatus alone is found to be as much as 5.3 times higher than that for water surface and that the total volumetric mass transfer coefficient for liquid film aeration system increases by 37 % in comparison with conventional aeration system. Additionally, by tuning finely the structural parameters of the liquid-film-forming apparatus, it can also lead to high dissolved oxygen water with the dissolved oxygen percent saturation greater than 90 %. More importantly, this result is accomplished by simply offering a single-pass aeration at the depth as shallow as 26 cm. As a result, the objective of economical energy consumption in diffused aeration systems can be realized by lowering the aeration depth without sacrificing the aeration efficiency.

A numerical model for the thermocapillary flow and heat transfer in a thin liquid film on a microstructured wall

PurposeThis paper aims to study thermocapillarity‐induced flow of thin liquid films covering heated horizontal walls with 2D topography.Design/methodology/approachA numerical model based on the 2D solution of heat and fluid flow within the liquid film, the gas above the film and the structured wall is developed. The full Navier‐Stokes equations are solved and coupled with the energy equation by a finite difference algorithm. The movable gas‐liquid interface is tracked by means of the volume‐of‐fluid method. The model is validated by comparison with theoretical and experimental data showing a good agreement.FindingsIt is demonstrated that convective motion within a film on a structured wall exists at any nonzero Marangoni number. The motion is caused by surface tension gradients induced by temperature differences at the gas‐liquid interface due to the spatial structure of the heated wall. These simulations predict that the maximal flow velocity is practically independent from the film thickness, and increases with increasing temperature difference between the wall and the surrounding gas. It is found that an abrupt change in wall temperature causes rupture of the liquid film. The thermocapillary convection notably enhances heat transfer in liquid films on heated structured walls.Research limitations/implicationsOur solutions are restricted to the case of periodic wall structure, and the flow is enforced to be periodic with a period equal to that of the wall.Practical implicationsThe reported results are useful for design of the heat transfer equipment.Originality/valueNew effects in thermocapillary convection are presented and studied using a developed numerical model.

Influence of t-butanol and of pH on hydrodynamic and mass transfer parameters in an ozonation process

Ozone treatment is a complex process including mass transfer from gas to liquid before oxidation itself. In addition, oxidation proceeds via two synergistic pathways, i.e. molecular ozone oxidation and radical by-products oxidation. In order to study the relative importance of both pathways at the laboratory scale, the use of t-butanol (radical scavenger) is convenient, as it will inhibit the radical pathway. Meanwhile, this will modify the surface tension of the solution, then the bubbles characteristics and, finally, the mass transfer parameters. This study investigated the influence of t-butanol and of pH on both hydrodynamics and transfer parameters in a semi batch ozone bubble column. Image analysis was used to monitor the bubble shape and the slip velocity. The Sauter diameter and gas hold-up were determined in order to calculate the specific interfacial area ( a). Besides, a procedure based on two mass balances for ozone allowed the simultaneous determination of the overall transfer coefficient ( k L a), the self-decomposition kinetic rate constant and the liquid/gas solubility ratio. It was established that the addition of t-butanol at a concentration of 10 −3 mol L −1 lead to smaller bubbles and increased the interfacial area by 30%. The overall transfer coefficient ( k L a) was also increased by 30%, while the liquid film transfer coefficient ( k L) remained almost constant (3.9 × 10 −4 m s −1). This result was not consistent with the values obtained from Higbie's relation, which indicates that the liquid film coefficient ( k L) should increase when t-butanol is added.

Modeling photocatalytic destruction of the organic contaminants in continuous stir flow reactor

Thin-film technique is becoming an industry standard for the preparation of TiO 2 -based photocatalyst for organic destruction. The catalyst provides several advantages over the conventional powder TiO 2 in the treatment of wastewater and groundwater. In this study, a continuous stir flow reactor model is developed capable of describing the photocatalytic process. The model incorporates the following fundamental mechanisms: adsorption, diffusion, liquid-film transfer, UV attenuation, and photocatalytic reaction. All of the simulation results indicate that there exists a highly nonlinear relation between each of these parameters and the destruction rate. Various incident light intensities also are incorporated to simulate the energy efficiency. The simulations illustrate that the photocatalytic model can be used to elucidate the effect of process variables. It is also possible to “custom-design” a catalyst for the treatment of a particular waste stream.

Flux of gases across the air–water interface studied by reversed-flow gas chromatography

In the present work the reversed-flow gas chromatographic technique was applied for the study of flux of gases across the air–water interface. The model system was vinyl chloride–water, which is of great significance in food and environmental chemistry. Using suitable mathematical analysis, equations were derived by means of which the following physicochemical quantities were calculated: diffusion coefficient of vinyl chloride (VC) into water, partition coefficient of VC between the water (at the interface and the bulk) and the carrier gas nitrogen, overall mass transfer coefficients of VC in the gas (nitrogen) and the liquid (water), gas and liquid film transfer coefficients of VC, gas and liquid phase resistances for the transfer of VC into the water, and finally the thickness of the stagnant film in the liquid phase, according to the two-film theory of Whitman. From the variation of the above parameters with temperature, as well as the volume and the free surface area of the water, useful conclusions concerning the mechanism for the transfer of VC into water were extracted. These are discussed in comparison with the same parameters calculated from empirical equations or determined experimentally by other techniques.

Vacuum degassing using microporous hollow fiber membranes

Abstract This study evaluated the performance of vacuum degassing using microporous hollow fiber membranes for the removal of dissolved gases from aqueous solutions. The experiments and analysis in this study were done in a batch reactor configuration. The membrane module was designed with individually sealed unconfined fibers, which fluidize in the flow providing excellent contact between the fibers and the water. The performance of the hollow fiber membrane module was monitored by measuring the change in dissolved oxygen (DO) with time in the reservoir. A preliminary model was developed to describe the degassing process. The overall oxygen mass transfer coefficient ( K ) in the system model was calculated assuming liquid film transfer control. The empirical correlation Sh =0.018 Re 0.83 Sc 0.33 (Ahmed and Semmens, 1992) was used to calculate K to predict the performance of the system. Initial assumptions that C *=0 (i.e. pure vacuum) showed a good agreement between observed and predicted values at low Reynolds numbers. However, increasing deviation of results with increasing Reynolds number was found. A validation of the empirical correlation used and an evaluation of the effect of C * was therefore further investigated. Mass transfer is controlled by the resistance in the liquid phase. Analysis of the total gas pressure differentials within the fibers showed C *>0. Partial pressures of the gases inside the fiber are dependent on the liquid phase boundary layer ( C *>0). Below Re ∼2500 mass transfer across the membrane appears to be the limiting step. Above Re ∼2500 the performance of the system appears to be limited by the flow of the gasses within the fiber lumen. Flux of water vapor into fibers cannot be neglected in determining the total gas pressure within the fiber lumen.

Heat and momentum transfer in liquid films with temperature-dependent viscosity

The distributions of film velocity, temperature, and thickness at the inlet of a film heat exchanger at large thermal Peclet numbers are shown to depend on a dimensionless parameter. Analytical solutions are obtained for small and large values of the parameter.

A kinetic model for photocatalytic degradation of organic contaminants in a thin-film TiO 2 catalyst

The thin-film technique is becoming a standard for the preparation of TiO 2-based photocatalysts for organic degradation. The catalyst alleviates the drawback of poor settleability associated with the powder TiO 2 traditionally used. In addition, the thin-film catalyst can be connected to an external power source to reduce the recombination of UV-activated electrons and holes, thereby increasing the quantum efficiency. The immobilization of TiO 2 on a solid carrier as a thin-film catalyst introduces several mechanisms not normally found in conventional TiO 2 slurry process. These mechanisms have been identified to include at least liquid–film transfer, adsorption, diffusion and photocatalytic reaction in a thin-film. A mathematical model was developed to incorporate these mechanisms for the photodegradation of organic molecules in a batch reactor. The model was verified using the data of 4-chlorophenol degradation obtained from the literature. The thin-film photocatalytic model was then used to investigate the effect of catalyst properties on the photodegradation of organics. The properties investigated included adsorption capacity, diffusion in the catalyst, UV attenuation and film thickness. The results of model simulation show that the effects of catalyst properties on the degradation of organics are highly nonlinear. There is an optimal film thickness that yields a maximum rate of photodegradation. The model not only provides insights into the effect of these underlying mechanisms but also can be used as a tool to assist the design of a thin-film photocatalyst.

Étude numérique de l'évaporation dans un courant d'air humide laminaire d'un film d'eau ruisselant sur une plaque inclinée

Numerical study of the evaporation in laminar humid air flow of a liquid film flowing over an inclined plate. By using an implicit centered finite differences method with a non-uniform grid, the authors study numerically the evaporation of a thin liquid film flowing over an inclined plate in a forced humid-air flow. They consider the existence of two-dimensional laminar boundary-layers with variable physical properties and show that the term of enthalpy diffusion is always negligible, whether the plate is adiabatic, isothermal or heated by a constant heat flux density. By using in the liquid film transfer equations which are one-dimensional, partially two-dimensional and two-dimensional, the authors additionally show the following features. If the plate is adiabatic, the liquid mass flow rate is without influence on the transfers and the gas–liquid interface behaves like an isotherm surface at rest. In this case, one may use a one-dimensional model in the film whatever liquid mass flow rate is. If the wall is isotherm or heated by a constant heat flux and when the liquid mass flow rate is less than 10 −3 kg·m −1·s −1, the one-dimensional model is sufficient; if it is included in the interval [10 −3 kg·m −1·s −1, 10 −2 kg·m −1·s −1[, the partially two-dimensional model is useful; if it is superior to 10 −2 kg·m −1·s −1, it is necessary to use the two-dimensional model. Generally, whatever the thermal conditions on the plate are, heat transfer is dominated by the liquid-vapor transition.

Balance Equations for Molecular Distillation

We have derived balanced equations for continuous molecular (short-path) distillation of a binary mixture in a falling film evaporator. The relation of heat and mass transfer in liquid films on both the evaporating and condensing surfaces were taken into account, as well as the mass transfer in the vapor phase in the distillation gap. Individual balance equations were coupled by boundary conditions into a closed set of partial differential equations. By introducing the streams, we have transformed partial differential equations into the simple form of ordinary differential equations. These were solved numerically or approximately for some selected problems in isothermal (e.g., for turbulent film on evaporation surface) and nonisothermal regimes and for the influence of reevaporation from the condenser. These developed mathematical formulations can be used to model various operational situations in a molecular evaporator or to evaluate the influence of some parameters on the molecular distillation process.

Evaporation heat transfer in liquid films flowing down horizontal smooth and longitudinally profiled tubes

The heat transfer mechanism of liquid film flowing down horizontal tubes has been studied by experimental determination of local and average heat transfer coefficients. The method of its enhancement has been developed based on the breakdown of the heat boundary layer by longitudinal fins and grooves. The calculated functions and recommendations on geometrical parameters of profiling, which allow enhancing the heat transfer from a surface to a liquid film by a factor of 1.4–1.9 and overall “vapor-liquid” heat transfer by a factor of 1.3–1.5, are given.

Determination of Reaeration Coefficients: Whole-Lake Approach

Onondaga Lake, N.Y., experiences a marked annual dissolved oxygen depletion over the entire water column at fall turnover. Depletion occurs as a result of the entrainment of reduced substances that have accumulated in the lake's hypolimnion over the summer. Recovery (return to near-saturated conditions) occurs over a period of 3–4 weeks. Observations of dissolved oxygen (DO) levels during the recovery period of two years are used to calculate the reaeration coefficient ( K a,20= 0.22 d −1 in 1989, and 0.13 d −1 in 1990) and the liquid film transfer coefficient for oxygen ( K L,20= 2.64 m⋅d −1 in 1989, and 1.50 m⋅d −1 in 1990). Local wind measurements are used to develop an empirical relationship between wind speed ( U10, m⋅s −1) and K L,20: K L,20=α⋅U10β, with α= 0.2; β= 1.0 for U10≤ 3.5 m⋅s −1 and α= 0.057; and β= 2.0 for U10> 3.5 m⋅s −1. Model output and field observations are compared with estimates generated using other published relationships.

Mathematical modeling of bio-physico chemical processes in activated carbon columns

Predictive mathematical models which describe the adsorption and biological phenomena in the plug-flow stationary solid phase column and completely mixed recycle fluidized bed were developed. The models incorporate liquid film transfer, biodegradation and diffusion in the biofilm, adsorption onto the adsorbent, as well as biofilm growth. The model equations are solved by a combination of orthogonal collocation and finite difference techniques. Computer simulations were conducted to compare the performance of the two models. Sensitivity tests were also performed to determine the effects of physical and biological parameters on model profiles.

Bioactive Adsorber Model for Industrial Wastewater Treatment

A predictive mathematical model that describes the adsorption and biodegradation phenomena in recycle fluidized‐bed (RFB) adsorbers was developed. The model incorporated liquid film transfer, biodegradation and diffusion in the biofilm, adsorption onto activated carbon, and biofilm growth. The model equations were solved by a combinatorial technique involving the methods of orthogonal collocation and finite differences. Computer simulations of the model were used for adsorber performance predictions from parameters obtained from adsorption equilibrium and kinetic studies, biokinetic experiments, and correlation techniques. Sensitivity tests were also performed to determine the effect of physical and biological parameters on model profiles. Recycle fluidized adsorber experiments were conducted to test the predictive capability of the model. Two ideally biodegradable compounds, glucose and sucrose, as well as two actual wastewaters, a dairy waste and a landfill leachate, were used to compare the predicted model profiles with experimental data for nonbioactive and bioactive RFB adsorbers. The performance predictions obtained from modeling were in satisfactory agreement with the experimental data.

Mass transfer in liquid films during absorption Part II. Solubilities and diffusivities of He, N 2 and C 3H 8 in aqueous ethylene glycol solutions at 25°C

New data are reported for the solubilities and diffusivities of helium, nitrogen and propane in highly viscous aqueous ethylene glycol solutions, the composition of which corresponds to the mole fraction of ethylene glycol x EG ≥ 0.93. Results of independent measurements are compared with the literature when possible and discussed.

Mass transfer in liquid films during absorption Part III. Dependence of the liquid-side mass transfer coefficient on the molecular diffusivity of gases at high values of the schmidt number

New experimental values of the liquid-side mass transfer coefficient k L were obtained for the absorption of helium, nitrogen and propane into a film of a highly viscous aqueous solution of ethylene glycol (kinematic viscosity v = 1.4 × 10 m 2 s −1), flowing down the vertical surface of an expanded metal sheet and down a smooth wetted wall. The purpose of the experiments performed in the range of Reynolds numbers 8 < Re < 70 and of Schmidt numbers 5800 < Sc < 75700 was to study the mass transfer mechanism at the gas-liquid interface by the experimental determination of the value of exponent m in the relationship between k L and the molecular diffusivity of a gas, k L ≈ D m . In the case of a smooth wetted wall the mean value of the exponent was close to 0.5 and the results were interpreted by the surface renewal model. In the case of an expanded metal sheet the mean value of the exponent was m = 0.64 and the film-penetration model was the most suitable for the interpretation of the experimental results.

Mass transfer in liquid films during absorption part I. Comparison of mass transfer models with experiments

Experimental values of the liquid-side mass transfer coefficient k L for absorption of gases of low solubility in a liquid film flowing down a smooth and a rough wetted wall and down an expanded metal sheet are compared with selected mass transfer models. It is shown that the set of published k L values available is insufficient to evaluate the most suitable model with which to describe the mass transfer mechanism. One of the distinguishing features of the various mass transfer models is the value of exponent m in the dependence of k L on molecular diffusivity, k L ∼ D m . The range of published experimental values is 0.5 < m < 0.7; nevertheless, these results are insufficient for this purpose as well. It is shown that experimental determination of exponent m in the range of high Schmidt numbers could give new information about the phenomena very near the gas—liquid interface which is of importance when discussing the mass transfer mechanism in a liquid film during absorption. In discussing different models in this work special attention is given to the recently published film-penetration model proposed to evaluate k L for absorption into a liquid film on an expanded metal sheet.