Average Film Thickness Research Articles

Research the influence of excipients on the technological properties of captopril fast dissolving films

Drug-loaded films are of great interest among fast-dissolving drug-delivery systems. The creation of fast-dissolving films for the treatment of cardiovascular diseases is important.The first inhibitor of angiotensin-converting enzyme to appear on the world market was captopril, which is used to treat hypertension, chronic heart failure and others. Captopril has an antihypertensive effect, which manifests itself within 5–15 minutes after sublingual administration.
 The aim of our study was to develop the technology of captopril fast dissolving films by solvent casting method and analyze the influence of groups of excipients on technological properties of the films.
 The influence of the character of polymers, plasticizers, disintegrants and sweeteners on the technological properties of experimental batches of captopril fast dissolving films was studied. Such technological indicators as uniformity of weight, thickness, swelling index,tensile strength, elongationand disintegration time were studied.
 The influence of excipients' composition on the technological indicators of captopril fast dissolving films has been researched. It was found out that the effect of the type of polymer had the decisive influence on all parameters of films.The selected plasticizer determined the elasticity (films' elongation), film thickness and weight variation. Optimal values of the average weight and thickness of captopril films are provided by the use of a polymer in the combination of HPMC with PEG 4000 or a combination of HPMC with PEG 6000, as a plasticizer – glycerin or PEG 400. The best results of films' swelling were obtained with the introduction of HPMC brands Metolose® 90 SH 100 000 or Metolose® 65 SH 50, Polyplasdone XL-10 crospovidone, propylene glycol and sorbitol. The disintegration time less than 3 min was observed in all investigated film compositions, except those containing PVA. The highest value of tensile strength for captopril films was obtained using HPMC brand Metolose® 65 SH 50 or Metolose®90 SH 100 000.
 Using the desirability function, the optimal excipients within the studied groups were selected.It has been established that the optimal values of the technological parameters of captopril films can be achieved using Hydroxypropyl MethylcelluloseVivapharm® E15, polyethylene glycol 400, sodium starch glycolate and sorbitol.

Experimental studies and numerical simulation of cold spray technique to investigate the effect of operating parameters on the thickness of Fe/TiO2 self-cleaning film

A self-cleaning solution based on sol-gel and hydrothermal processes was applied to prepare the self-cleaning Fe/TiO2 surfaces on a ceramic substrate using the cold spray method. Moreover, a numerical method was employed to investigate the effect of spraying operation conditions, including carrier gas pressure, the standoff distance, and traverse speed on the coated layer thickness. Seven samples were prepared under different spray operating conditions. The results indicated that as the pressure increases from 2 to 4 bar, the average film thickness increases from 1.7 to 5.5 μm. In addition, when traverse speed rises to 1.8 cm/s, the surface coating substantially becomes thinner to <2 μm. Besides, it was observed that the coating thickness has the maximum value at a certain standoff distance between the spray gun and the substrate surface. Finally, the results were compared with those of the numerical simulation, properly consistent with a maximum relative error of <5%. Besides, the photocatalytic decomposition rate of formic acid by the coated surface at the spray pressure of 4 bar, the traverse speed of 1.2 cm/s, and the standoff distance of 10 cm was >94%. Additionally, the antibacterial tests showed a high potent surface activity against S. aureus and E. coli. Bacteria. Consequently, the proposed optimum condition was proved to be appropriate for preparing self-cleaning coatings.

IR absorptance of thin carbon multi-walled nanotubes layers

The IR transmittance and reflectance spectra of thin films which consist of multi-walled carbon nanotubes (MWCNT) are measured in the range from 2 to 17 μm. The MWCNT films of various thicknesses not exceeding 1.2 μm were deposited on silicon substrates with Si3N4/Al2O3 dielectric layers. It is shown that the deposition of an Al2O3 layer with a thickness of 2 nm allows to significantly improve the homogeneity and continuity of the MWCNT films. A technique is proposed for measuring the average thickness of rough MWCNT films by means of atomic force microscopy after laser engraving. Suggested method of spectra processing allows to estimate the spectral dependence of the IR radiation absorptance in MWCNT films, which are diffusely scattering objects and have a large absorption coefficient.

Liquid film characteristics measurement based on NIR in gas–liquid vertical annular upward flow

Liquid film plays a crucial role in void fraction, friction pressure drops, momentum and heat transfer in the two-phase flow. The film thickness measurement experiments of annular flow at four pressure conditions have been conducted using near-infrared sensor. The signal is processed by variational mode decomposition, whose parameters are optimized using the sparrow search algorithm. The envelope spectrum and Pearson correlation coefficient judgment criteria were adopted for signal reconstruction, and the value of the liquid film thickness is obtained. The effect (such as flow rate, pressure, entrainment, etc) of the liquid film thickness are analyzed theoretically. The characterization parameters Weg″, Wel, Nμl and X mod have been extracted and optimized, and a new average liquid film thickness correlation is proposed. The laboratory results indicate that the mean absolute percentage error of the predictive correlation is 4.35% (current data) and 12.02% (literatures data) respectively.

Investigation of average asphalt film thickness of dense graded asphalt mixtures with compaction effects

The asphalt mixtures with inadequate durability may become too lean, resulting in low rutting and fatigue resistance. The asphalt film thickness (AFT) has been used as a crucial property for the durability of asphalt mixtures. However, the relationship between AFT and volumetric properties is ambiguous with the absence of compaction effects in the standard film thickness equation. This study aims to investigate the relationship between AFT and volumetric properties of dense-graded asphalt mixtures with consideration of the compaction degree. The compaction-property-dependent (CPD) AFT model considering compaction effects was proposed and compared with the standard AFT equation. Then, asphalt mixtures with 112 different gradations were used to calculate the AFT with and without compaction effects. The relationship between new AFT and volumetric parameters (Pb, VMA, VFA, Vc, Vfine and Vfiller) was investigated by linear correlation analysis. After that, two regression models and a back-propagation (BP) neural network were used to predict the new AFT with volumetric parameters. By comparing the prediction accuracy of these models, a reasonable model with higher prediction accuracy was selected. Results show that the new AFT is 2% to 30% less than the AFT in the standard model, and the surface area of air void boundary has a negative effect on the new AFT. The correlation analysis indicates that the new AFT of dense-graded asphalt mixtures has a rough correlation with changes in VMA, binder content and VFA. The prediction accuracy of the BP neural network has the highest R-squared. The relative importance and sensitivity analysis of the BP neural network verified a relatively good relationship between VMA and new AFT. These findings can give a considerable interest for the tendency of using the new AFT to supplement the current specified VMA criteria.

Effect of winding angles on flow and heat transfer characteristics in the shell side of spiral wound heat exchangers

A three-dimensional model is established to investigate the flow and heat transfer characteristics influenced by the winding angle in the shell side of a spiral wound heat exchanger. Numerical simulations are conducted with the winding angle varying from 0° to 20° and the Reynolds number varying from 430 to 1935. The flow states of different conditions are observed, and the film thickness is measured in the axial and circumferential directions. Moreover, the heat transfer characteristics of the liquid falling film flow are investigated at constant wall temperature. The results indicate that the winding angle has a distinct effect on the flow and heat transfer characteristics. Under the same Reynolds number, the local film thickness distribution varies with the winding angle, and the average film thickness in the axial direction decreases with the increase of winding angle. The local heat transfer coefficient distribution is consistent with that of film thickness, and the average heat transfer coefficient increases with the Reynolds number but decreases with the winding angle. Based on the results, a comprehensive heat transfer correlation involving winding angles is developed, the deviations of the data are within ± 3%.

Exploring stability of a nanoscale complex solid solution thin film by in situ heating transmission electron microscopy

Combining thin film deposition with in situ heating electron microscopy allows to understand the thermal stability of complex solid solution nanomaterials. From a CrMnFeCoNi alloy target a thin film with an average thickness of ~10 nm was directly sputtered onto a heating chip for in situ transmission electron microscopy. We investigate the growth process and the thermal stability of the alloy and compare our results with other investigations on bulk alloys or bulk-like films thicker than 100 nm. For the chosen sputtering condition and SiNx substrate, the sputter process leads to the Stranski–Krastanov growth type (i.e., islands forming on the top of a continuous layer). Directly after sputtering, we detect two different phases, namely CoNi-rich nanoscale islands and a continuous CrMnFe-rich layer. In situ annealing of the thin film up to 700°C leads to Ostwald ripening of the islands, which is enhanced in the areas irradiated by the electron beam during heating. Besides Ostwald ripening, the chemical composition of the continuous layer and the islands changed during the heating process. After annealing, the islands are still CoNi-rich, but lower amounts of Fe and Cr are observed and Mn was completely absent. The continuous layer also changed its composition. Co and Ni were removed, and the amount of Cr lowered. These results confirm that the synthesis of a CrMnFeCoNi thin film with an average thickness of ~10 nm can lead to a different morphology, chemical composition, and stability compared to thicker films (>100 nm).Impact statementExploring stability of a complex solid solution thin film by in situ heating transmission electron microscopy is a study of the thermal stability of sputtered complex solid solution thin films with thicknesses of ~10 nm. Complex solid solution materials have a promising electrocatalytic behavior due to the interplay of multi-element active sites. In order to understand their catalytic properties, it is important to identify the different structure-composition-activity correlations. Thus, our investigation helps to clarify and to understand the stability of nanoscale complex solid solution with an average film thickness of ~10 nm.Graphic abstractCombining sputter deposition with in situ heating transmission electron microscopy allows to understand the thermal stability of nanoscale complex solid solution thin films.

Prediction of the tribological characteristics of non‐Gaussian rough surfaces during sliding wear in mixed lubrication

AbstractIn mixed lubrication, material wear is inevitably caused due to solid contact. Simultaneously, the surface morphology after wear will affects the lubrication performance. To understand this coupling process, virtual surface reconstruction technology and mixed lubrication sliding wear model were applied to predict the evolution of wear characteristics and lubrication characteristics during wear in this study. The effects of the roughness root mean square (RMS), roughness direction and wavelength ratio on the contact area ratio, the contact load ratio, accumulated wear, film thickness and the friction coefficient were analysed. The results indicated that the contact area ratio and the contact load ratio and the friction coefficient decreased and average film thickness increased with the increase in the number of the wear cycles. In addition, a surface with low‐roughness RMS, longitudinal roughness texture and high‐wavelength ratio is suitable for improving lubrication performance and reducing wear.

Falling film co-current flow cyclone demister for separating high-boiling droplets: Gas-liquid flow pattern and performance

In many processes, the product gas stream contains liquid droplets that easily condense or solidify, which can deteriorate demister performance and even block equipment during gas–liquid separation. We proposed a falling film co-current flow cyclone demister (F2CFCD) to solve the above problems. The novel idea is that an additional stream of solvent fluid is added to the gas stream containing the droplets. After injecting the demister, the solvent fluid forms a film on the wall of F2CFCD. When the droplets are separated to the wall surface by centrifugal force, they are dissolved by the liquid film, thereby avoiding crust formation. In this work, the gas–liquid flow characteristics and the performance of F2CFCD are investigated numerically and experimentally. A hot-wire anemometer (HWA) is used to measure the gas velocity, and a conductivity method is used to measure the liquid film thickness. A coupled numerical model of the RSM-DPM and Eulerian wall film (EWF) model is applied to discuss the effect of the gas–liquid flow rate on the flow field in the demister. The liquid volume flow rates ranges from 0.5–10.5 m3/h, and the gas volume flow rates range from 640–894 m3/h. The gas flow pattern and the liquid film flow regimes are explored in the F2CFCD. A film thickness model is established to evaluate the average film thickness in the waterfall regime. Experimental observations illustrate that F2CFCD has a high separation efficiency for droplets under all conditions.

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.

Experimental study of hydrodynamic parameters regarding on geyser boiling phenomenon in glass thermosyphon using wire-mesh sensor

The thermosyphon is a type of heat exchanger that has been widely used in many applications. The use of thermosyphons has been intensified in recent years, mainly in the manufacture of solar collectors and various industrial activities. A thermosyphon is a vertical sealed tube filled with a working fluid, consisting of, from bottom to top, by an evaporator, an adiabatic section, and a condenser. The study of geyser-boiling phenomena, which occurs inside the thermosyphon is of extreme importance, therefore the experimental analysis of the parameters related to the two-phase flow (liquid-steam), such as void fraction, bubble frequency, bubble velocity, and bubble length are necessary, since these parameters have a significant influence on heat transfer. In this work, a pair of wire mesh sensors was used, a relative innovative technology to obtain experimental values of the reported quantities for measuring these parameters of slug flow in thermosyphons. An experimental set-up is assembled and the sensors are coupled to the thermosyphon enabling the development of the experimental procedure. Here is presented an experimental study of a glass thermosyphon instrumented with two wire-mesh sensors, in which the aforementioned slug flow hydrodynamic parameters inherent to the geyser type boiling process are measured. It was measured successfully, as a function of the heat load (110, 120, 130, 140, and 150 W), the void fraction (instantly and average), liquid film thickness, translation velocity of the elongated bubbles, lengths of the bubbles, and the liquid slug (displaced by the bubble rise up). It was observed that the higher the heat load, the lower is the bubble translation velocity. For all heat loads, based on the measured length of liquid slug (consequent displacement of liquid volume), caused by bubbles rise from evaporator to condenser, it could be affirmed to some extent that both boiling regime (pool and film) exist in the evaporator. The measured average void fraction (80%) and liquid film thickness (around 2.5 mm) during the elongated bubble passages were approximately constant and independent of the heat load.

Study of film thickness characteristics on the inclined plate

The gravity-driven flowing film has been widely used in the fields of heat removal. This work studied film thickness characteristics on the inclined plate with the laser-induced fluorescence technique. The periodic fluctuations of the film were observed, the statistical characteristics of the film thickness were obtained and the three-dimensional structure of the film wave was reconstructed. The experiment results showed that the maximum film thickness increases stepwise with increasing Reynolds number, while the average film thickness increases smoothly. An experimental correlation was proposed by considering the surface waves with variable amplitudes. This new correlation is also in accordance well with other experimental data. Meanwhile, a numerical study based on the diffuse-interface method was conducted. The error between the numerical and experimental results is approximately 10% at the angle of 30°. At angles of 30°, 45°, and 60°, the numerical results showed that the film thickness increased sharply as the distance increases but the rate of growth gradually slows down and remains almost constant when the distance increases continuously. The local velocity of the film is negatively related to the distance from the wall.

Experimental study of wavy-annular flow in a rectangular microchannel using LIF method

This article aims at studying gas-liquid flow in a rectangular microchannel with a high aspect ratio (200 × 2045 μm). Liquid and gas phases were 95% ethanol and nitrogen mixture. Experimental flow characteristics are obtained using high-speed visualization and laser-induced fluorescence (LIF) methods. Using the LIF method for wavy-annular flow, the average film thickness, liquid film distribution, and liquid film width were measured. The dependences of the liquid film width and the average film thickness on gas superficial velocity are presented in graphical form and analyzed. An increase in gas superficial velocity causes growth of the liquid film width and thickness of the liquid film, which indicates the process of liquid transfer from the menisci area to the liquid film. For different liquid velocities and the same gas superficial velocities, close values of averaged liquid film thickness were observed for flow with 2D waves and 3D waves on liquid film.

Fractal simulation of surface topography and prediction of its lubrication characteristics

A machined surface has observable fractal characteristics, with infinite local and overall self-similar consistency. Therefore, the fractal theory is considered to provide a better description of the morphological characteristics of rough surfaces, which accurately reflects the randomness and multi-scale characteristics of rough surfaces and it is not comparable with the surface characteristics obtained based on statistical parameters limited by sampling length and device resolution. In this study, the Weierstrass-Mandelbrot (W-M) function was applied to construct a fractal reconstruction surface, and the mixed elastohydrodynamic lubrication model was used to investigate the lubrication characteristics of real and reconstructed surfaces under the same fractal parameters. The effects of the fractal parameters on the fractal surface lubrication characteristics were further analyzed. The results demonstrate that the lateral roughness fractal surface provides greater resistance to the entrained flow of lubricant, which leads to a larger average film thickness, than the longitudinal roughness and isotropic fractal surface. With the increase in fractal dimension, the surface roughness peak density increases, which reduces the surface film thickness by 47%, and the friction coefficient increases by 46%. The lubrication parameter fluctuates slightly with the change in the number of overlapping ridges M of the fractal surface. Generally, M has little effect on the surface lubrication characteristics.

Circumferential incoherent distribution of film thickness for multi-dimensional two-phase annular flow

Annular flow in rod bundle geometry is characterized by multi-dimensional properties in terms of two distinct length scales, rendering no consensus yet on an available model for predicting the circumferential incoherent distribution of film thickness. Current paper presents a semi-empirical but original correlation based on pertinent underlying physics. Gas phase Reynolds number is used to illustrate the gas–liquid interfacial shear-off mechanism. Liquid source term is scaled by the combination of void fraction and liquid volumetric flux. Circumferential shear stress produced by secondary flow is employed to denote mass transport in subchannel. Four available datasets including 189 data points are collected to develop and validate the proposed correlation from both cross-sectional and subchannel local regions perspectives. The majority of data can be correlated with the maximum relative error of ± 20.0%. Based upon the heuristic correlation, the circumferential incoherent distribution of film thickness is analyzed. The average film thickness on center rod increases slightly as the liquid velocity increased, since most of liquid phase migrates to corner region leading to a dramatically increase in film thickness on rod nearby duct wall. Two dependent factors are mainly responsible for the rod peripheral distribution of liquid thickness, in which the hydrodynamic effect dominates over the secondary flow factor, but the secondary flow makes the peripheral distribution of film thickness more uniform. Among the hydrodynamic parameters, both void fraction and gas velocity contribute to the thinning of the liquid film, but the increasing of liquid thickness along with rod periphery is attributed to the variation of subchannel characteristic length.

Post-Annealing Effects on the Structure and Semiconductor Performance of Nanocrystalline ZnTe Thin Films Electrodeposited from an Aqueous Solution Containing Citric Acid

Using the potentiostatic electrodeposition technique, zinc telluride nanocrystalline thin films and an array of nanowires were synthesized in a citric acid bath. Electrodeposited zinc telluride thin films with stoichiometric compositions were obtained at a cathode potential of approximately −0.8 V versus Ag/AgCl, which was in a more noble region compared with the equilibrium potential of zinc. The average thickness of the zinc telluride thin films was approximately 3 μm, and the average growth rate was approximately 3 nm s−1. The as-deposited zinc telluride thin films had an amorphous phase with a black tint. By contrast, the zinc telluride thin films annealed at 683 K had a crystalline phase with a reddish-brown tint. The electrodeposited single-phase zinc telluride exhibited an optical absorption performance in a wavelength region that was shorter than 559 nm. At the annealing temperature of 683 K, the zinc telluride films exhibited an energy band gap of 2.3 eV, which was almost identical to that of single-crystal zinc telluride. The resistivity of the as-deposited amorphous-like zinc telluride thin films was approximately 2 × 105 Ω·m, whereas that of the samples annealed at 683 K was around 2 × 103 Ω·m, which was smaller than that of single-crystal zinc telluride. A three-dimensional nanostructure constructed with the zinc telluride nanowire array was also demonstrated using a template synthesis technique.

Effect of complex agent concentration on the structural and morphological properties of CuAlS2 thin films prepared by chemical bath deposition technique

CuAlS2 thin films have been prepared on glass substrates by chemical bath deposition (CBD) technique at a substrate temperature (Ts) 75C, pH value 10.5, and fixed deposition time 40 minutes. In this study effect of molar concentrations (0.03, 0.05, and 0.06 M) of complex agent Na2EDTA on structural, morphological, and topological properties of deposit thin films were studied by using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) with cross section, and atomic force microscopy (AFM), respectively. The result showed that all prepared films were amorphous structures. The cross section analysis showed a good adhesion between prepared films and glass substrates, average thickness of films was affected by concentration of complex agent, where was low at 0.03 and 0.06 M, while was high at 0.05 M. The prepared films showed homogenous and uniform spherical nanoparticles with average grain size (64 to 79 nm) increased with increasing complex agent concentration. AFM images showed that the prepared films at 0.05 and 0.06 M had the same structures as conical and spherical shapes with the homogenous distribution on the surface of the films compared with that at 0.03 M. Also, the surface roughness, and root mean square (rms) roughness were varied in the range (0.33 to 1.74 nm) and (0.44 to 2.34 nm), respectively, where the less roughness were found at 0.05 M complex agent. The prepared films at 0.05 M complex agent showed the best properties which can be useful for many applications in optoelectronics devices.

Application of the laser-induced fluorescence to study local characteristics of a gas-liquid flow in rectangular microchannel

The Laser-Induced Fluorescence (LIF) method was used to characterize liquid phase distribution in rectangular slit microchannel with cross-section 200×1205 μm for horizontal gas-liquid flow. Ethanol and nitrogen were used as working liquid and gas accordingly. The feature of this study is an application of hydraulic focusing cross-junction mixer for obtaining elongated bubble and transition flows in the microchannel with a high aspect ratio. Using LIF measurements for elongated bubble and transition flows the liquid film distributions were obtained for different distances from the bubble top and average liquid film thickness was compared with the prediction according to Taylor’s law.

Experimental and numerical study on the falling film flow characteristics outside circular tube applied in floating liquefied natural gas (FLNG) under offshore conditions

Spiral wound heat exchanger (SWHE) relying on falling film evaporation and boiling is often used for FLNG. The performance of SWHE can be impacted strongly by the motion of the FLNG caused by the wave and typhoon. The falling film characteristics of SWHE outside circular tube are studied experimentally and numerically by a visualization experimental device based on the high-speed camera and a numerical model based on the dynamic grid. The results show that the wave crest of the liquid film moves to the titled side under offshore conditions. The evolution process of falling film flow pattern outside circular tube with the tilt angle of 9° can be divided into four stages: droplet formation and migration, liquid column formation and migration, liquid column coalescence, liquid sheet formation. A correlation permitting the prediction of the falling film flow pattern outside circular tube and the other one permitting the prediction of the average film thickness of circular tube are developed respectively based on the experimental and numerical data.

Experimental evaluation on characteristics of a falling-film flow on the horizontal tube subject to ultrasonic field

The falling-film flow characteristics significantly influence the heat and mass transfer process in the horizontal tube absorber. This study experimentally investigates the effect of ultrasonic field on the flow mode transition and thickness distribution of the liquid film on the horizontal tube. The water-calcium chloride (CaCl2/water) was selected as the working fluid. The effects of the factors, such as the tube diameter, tube spacing, solution concentration, ultrasonic power, sound source distance and ultrasonic incidence angle, on the hydrodynamics of the liquid flow were analyzed. The results show that the mode transition Reynolds number increases with the increasing ultrasonic power, but reduces comparing to that without ultrasound. Moreover, in the column mode, the fluctuation range of the film thickness decreases with the increase of the ultrasound power; and the ultrasonic field help increase the average film thickness outside the tube and enhance the uniformity of liquid film.