Viscosity Decay Research Articles

Characterization of cell wall polysaccharides of purple pitaya (Hylocereus sp.) pericarp

While the fruit pulp of purple pitaya (Hylocereus sp.) is highly valued, its pericarp is unsuitable for consumption. Cell wall polysaccharides of fruit pericarp were analyzed to identify potential valorization of this by-product. The alcohol insoluble residue (AIR) was extracted yielding 6.16±0.09% on FW of AIR, which was subsequently fractionated into water-, oxalate-, acid- and alkali-soluble pectins, hemicellulose and cellulose. Water and oxalate-soluble pectin were the major pectin fractions. Anhydrouronic acid (AUA) contents of the AIR and of the fractions were measured using the m-hydroxydiphenyl (MHDP) assay, resulting in 24.1% of the AIR. AUA contents were higher in the water (WSP) and oxalate (OXP) soluble pectin fractions, reaching 46.62 and 56.16% of their total, respectively. Moreover, the degree of esterification (DE) of the AIR and its fractions was determined spectrophotometrically, where the highest DE values were found in the WSP and acid (HSP) soluble fractions. Fractions were analyzed for their neutral sugar composition by gas chromatography after derivatization. Pectin fractions were mainly composed of arabinose, galactose and rhamnose, while the hemicellulose fraction mainly consisted of glucose and xylose. The thickening properties of the AIR were evaluated after determining relative viscosities of AIR solutions and comparing the data with various mathematical models. With increasing shear rates a power law decay of shear viscosity was observed for AIR solutions indicating structure viscous shear-thinning behavior. Flow curves of 1% solutions of commercial thickeners showed high similarity to a 5% solution of pitaya AIR, thus indicating the requirement of further purification of the pitaya AIR.

Analysis of the factors affecting the inherent viscosity of oriented polylactides during hydrolytic degradation

This study focuses on analyzing the effects of several factors on the rate of decay of inherent viscosity (iv) during hydrolytic degradation. The analysis was made for oriented PLLA, 96L/4D PLA and 80L/20D,L PLA. The analyzed polymers were found to have identical rate of iv loss (P<0.05), given that the materials have otherwise similar initial material properties. The effect of the post-processing residual monomer was dose dependent, i.e. the higher the monomer content the faster the degradation (P<0.05). Samples with a smaller diameter (1.1mm) were found to have a faster rate of iv loss than the samples with a larger diameter (4mm) (P<0.05). A multiple linear regression analysis was used to create a five-component linear model to predict changes in the materials' inherent viscosity. This model yielded accurate predictions during the initial stages of the hydrolytic degradation process where the iv loss was virtually linear.

Steady and unsteady non-Newtonian inelastic flows in a planar T-junction

Steady and unsteady laminar flows in a planar 2D T-junction, having a dividing or bifurcating flow arrangement (one main channel with a side branch at 90°), are studied numerically for non-Newtonian inelastic fluids whose rheological characteristics are similar to those of blood. These computational fluid dynamics simulations explore a wide range of variation of inertia (through the Reynolds number, Re), flow rate ratio (proportion of extracted to inlet flow rates, β) and shear thinning (the power-law index of the model, n), and investigate their influence on the sizes and intensities of the recirculating eddies formed near the bifurcation, and on the resulting distribution of the shear stress fields. Such flow characteristics are relevant to hemodynamics, being related to the genesis and development of vascular diseases, like the formation of atherosclerotic plaques and thrombi near arterial bifurcations.To represent the decay of viscosity with shear rate we apply the Carreau-Yasuda equation, one of the most utilized Generalized Newtonian Fluid model in blood simulations. In many comparisons of the present parametric study it was require that the level of inertia was kept approximately the same when n was varied. This implied a consistent definition of Re with the viscosity calculated at a representative shear rate.

Mechanical degradation of elastomers in the presence of silica and inhibitors using a new design of mechano reactor

A newly designed mechanochemical reactor has been home built and used to investigate mechanical degradation of SBR rubber and SBR/SiO2 blends under N2 and O2 atmosphere and in the presence of aromatic amines (DTPD) and tetramethyl piperidine (HALS) radical inhibitors. Continuous on line determination of torque, temperature and O2 uptake have been made together with solution viscosity and mechano-radical yields at definite time intervals. The fraction of mechanical energy resulting in chemical effects is determined to be less than 0.01%. Chain scission and crosslinking are found to be major mechanochemical reactions with crosslinking acquiring importance with increasing the processing time. According to the results of COGEF type DFT UB3LYP 6-311++G (d,p) relaxed scan computations, the favoured chain scissions sites are predicted to be the ones leading to allylic (prominent) and benzylic radicals. The kinetics of mechano-radicals formation is coherent with torque and viscosity decay kinetics being expressed by the equation [R•](mol/kg)=−0.0775×10–2t2+0.6755×10–2t.The mechano-radical yield is greater than expected from the chain scission yield; furthermore, oxygen and radical inhibitors have minor effects on torque and viscosity decay kinetics in the first part of the process where chain scissions are dominant, whilst they do inhibit crosslinking. It is inferred from these results that a significant part of permanent chain scissions takes place via caged-radical disproportionation and that only scavengeable mechano-radicals escaping cage reactions are responsible for the initiation of crosslinking.From free radical chemistry analysis supported by DFT calculations it is inferred that H abstraction and 1-3 double bond addition by chain scission allyl radicals can be major paths for crosslinking initiation, the addition mechanism acquiring importance with increasing reaction time. The oxygen uptake is approximately linear with process time and consequently does not fit the formation and decay kinetics of scavengeable mechano-radicals; it is suggested that the contribution by other mechanisms involving mechanical excitation coupled with thermal activation may be important. The addition of SiO2 filler causes an increase of total absorbed mechanical energy and a decrease of the equilibrium molecular weight limit (enhanced chain scissions). In contrast, the scavengeable mechano-radicals yield is found to be less than 50% of that determined in the absence of SiO2. These observations are related to the mechanical degradation of bound rubber in conditions of enhanced cage effect and build up of frictional energy by silica-rubber Van der Waals interaction.

Effect of Alcohol in Starch‐Thickened Fillings on the Storage Stability of Dark Chocolate Pralines

AbstractCommercial praline shells made from dark chocolate were filled with a mixture of invert sugar syrup, wine distillate and sucrose, which was adjusted to a viscosity of approximately 4 Pa·s by addition of pregelatinized starch. The pralines which also contained malt extract were subjected to storage at 20 and 24 °C. The liquefaction rate induced by enzymes of the malt extract depended on ethanol (0–15% w/w) and moisture content (approximately 30%) of the filling, and on storage temperature. The decay of apparent viscosity immediately after adding malt extract was delayed when ethanol was present in the filling, implying that viscosity stability after mixing and during subsequent processing is improved. Softening of the praline shells and fat bloom formation also depended on the ethanol concentration of the filling. A cross‐comparison with praline shells which were filled with pure invert sugar syrup implies that the enzymes of the malt extract do not exhibit a negative influence on praline shell firmness. Electron micrographs give evidence that ethanol in contact with chocolate causes structural damage which results in a partial solubilization of praline shells.

Tailoring alcoholic fillings for praline production with one-shot depositors

One-shot depositing is a state-of-the-art technique for the production of filled chocolate products, including pralines. One important pre-requisite for using this technique is that shell chocolate mass and filling need to have similar viscosity and density to allow sufficient processing. Aim of the study was to tailor the formulation of alcoholic fillings to ensure that (a) the fillings can be processed with one-shot depositors (high viscosity, approximately 5 Pa s) and (b) the fillings meet typical requirements for consumption (low viscosity, approximately 0.2 Pa s) by using modified starch as a thickener and starch-degrading enzymes for controlled starch hydrolysis. The results show that the first goal can be achieved by adjusting thickener concentration to the ethanol content of the filling and the alcoholic substrate (pure ethanol or wine distillate, 60%(v/v)). The controlled use of amylase-containing malt extract allows adjusting viscosity decay during processing and subsequent storage of the one-shot pralines.

Rheological Study of O/W Concentrated Model Emulsions for Heavy Crude Oil Transportation

The oil-in-water emulsion is increasing in popularity as a cost-reducing method for “heavy” crude oil transportation. In order to analyze the effect of oil-in-water ratio and emulsifier amount on the viscosity of the final emulsion, concentrated model-emulsion of oil-in-water were rheologically characterized. Two emulsification methods were investigated: batch and “in-flow” in a lab scale plant. Comparison revealed the effect of the emulsifier amount both on the viscosity decay during time and on the final emulsion viscosity. Qualitative microscopy results revealed a rather wide drop size distribution for systems exhibiting a lower viscosity value.

A MODEL FOR VISCOSITY REDUCTION IN POLYSACCHARIDES SUBJECTED TO HIGH‐PRESSURE HOMOGENIZATION

ABSTRACT Three polysaccharides (alginate, K‐carrageenan, xanthan) dispersed in water and exhibiting Newtonian or pseudoplastic (Power Law) flow properties were subjected to high‐pressure homogenization (0 to 300 MPa) and one to five homogenization cycles. An exponential decay in viscosity was observed in the three processed polysaccharides due to both homogenization pressure and number of homogenization cycles. A 75–85% viscosity reduction and a viscosity plateau was reached after the polysaccharide dispersions were subjected to a sufficient homogenization pressure and/or number of homogenization cycles. A modified exponential decay model was proposed to describe a sudden reduction in viscosity and the observed constant minimum viscosity values after sufficient homogenization. The model was adjusted by minimizing the sum of squared differences between observed and modeled viscosity values. The model exhibited good correlation coefficient with experimental observations for the three polysaccharides tested (r &gt; 0.98) and error analysis showed negligible fixed errors (bias) and normally distributed random differences between experimental and modeled viscosity values.PRACTICAL APPLICATIONSPolysaccharides are extensively used to modify textural properties of fluid and semi‐solid foods. For a given polysaccharide, texture will be greatly affected by molecular weight. This manuscript shows the effect of high pressure homogenization on viscosity reduction for the polysaccharides alginate, K‐carrageenan and xanthan gum. High‐pressure homogenization offers the potential to be used for the manufacture of polysaccharides with targeted viscosity properties.

A viscometric study of the biodegradation of photographic gelatin by fungi isolated from cinematographic films

Abstract The biodegradation of photographic gelatin grade (Bloom 225) material was studied by viscometry in aqueous solution (at 37 °C, 6.67% w/w) using filamentous fungi isolated and identified from cinematographic film stored in different Spanish archives. From viscosity data, different variables such as molecular weight and chain scission were calculated. To ensure initial spore suspension concentration was standardized for all the biodegradation experiments, a correlation between transmittance at 530 nm of fungal spore suspensions and the corresponding cytometric determination of populations was established for all the fungal strains studied in this work. The bioassay experiments were carried out at 25 and 4 °C using an initial concentration of fungi of 4.5×105 conidia/mL except in the case of the genus Alternaria, where the concentration was 10 times lower. The fungal strains were three species of Aspergillus, i.e., A .ustus, A. nidulans var. nidulans, A. versicolor, seven Penicillium chrysogenum strains, and Cladosporium cladosporioides, Alternaria alternata, Mucor racemosus, Phoma glomerata, and Trichoderma longibrachiatum. All were gelatinase positive. Through the viscosity decay profiles with bioassay-time and the corresponding calculated chain scission, the relative quantitative gelatinase efficiency of these fungi has been evaluated.

Structural breakdown and build-up in bentonite dispersions

An experimental study on the rheology of bentonite aqueous dispersions is presented. The viscoelastic response of the system as a function of the pH has been studied. Solid-like behaviour has been observed in all cases. Stress sweeps in dynamic tests have shown that the extent of the linear viscoelastic region and the consistence of the systems are pH dependent. The viscosity of the dispersions depends on the steady shear rate and the time of shearing. It is shown that the dispersions show thixotropic viscosity, i.e., shear thinning with a long relaxation time as a unique function of shear. An experimental approach for viscosity decay at constant shear rate for step-up experiments and viscosity increase at constant shear rate for step-down experiments is tested. The rate parameters for the decay and increase of the viscosity are found to be a power-law function of the shear rate.

Biodegradation of type-B gelatine by bacteria isolated from cinematographic films. A viscometric study

The biodegradation of photographic grade gelatine (Bloom 225) material has been studied by viscometry in aqueous solution (at 37°, 6.67%w/w) using bacteria isolated and identified from cinematographic film stored in different Spanish archives. From viscosity data, different variables such us molecular weight and chain scission were calculated using literature equations and the results were checked using two bloom gelatine grades of 75 and 225 g. In all the bioassay experiments the initial concentration of bacteria (25 × 10 6 cell/ml) remained constant and different temperatures (37, 30, 20 and 4 °C) were employed. From the 13 studied bacteria only six were gelatinase active. They were members of the genuses Bacillus ( B. amyloliquefaciens, B. subtilis, B. megaterium, B. pichinotyi, B. pumilus) and Staphylococcus ( S. hominis). Through the viscosity decay profiles with bioassay-time and the corresponding calculated chain scission, the relative quantitative gelatinase efficiency of these bacteria has been evaluated. The influence of the temperature on the biodegradation has also been determined and, at 4 °C only four species of Bacillus were active in the biodegradation of gelatine in the time scale of 3 months. A synergistic effect in the biodegradation of gelatine was observed with the natural mixture of Bacillus amyloliquefaciens and subtilis present in the cinematographic polymer sample.

Repetitive rebrightening of EG Cancri: Evidence for viscosity decay in the quiescent disk?

A WZ Sge-type dwarf nova, EG Cancri, exhibited six consecutive mini-outbursts with a mean interval of about seven days after the end of the main outburst in 1996/1997. Most unusual was that the star abruptly entered into a deep faint minimum after such frantic activities. We propose that this peculiar phenomenon may be understood in terms of viscosity decay in the cold disk. In this picture, the viscosity is produced by MHD turbulence due to the magneto-rotational instability (\Balbus-Hawley instability) and dies down exponentially with time when the disk becomes cold because the magnetic elds decay due to nite conductivity in the cold disk (Gammie & Menou 1998). But the viscosity is refreshed to a high value every time when a mini-outburst occurs (i.e., the disk becomes hot again). It is argued that a sudden cessation of repetitive mini-outbursts may be brought about by a very small reduction in viscosity or a small increase in its decay rate, which may in turn be produced most likely by stochastic fluctuations of magnetic elds. Numerical simulations based on a simple model reproduce the observed light curve of EG Cancri very well. We discuss possible causes why the reflares after the main outburst occur mostly in the WZ Sge-type stars.

Interaction effects on the time dependence of the magnetization in recording particles

The influence of the magnetostatic interactions on the time dependence of the magnetization of assemblies of particles, which are used in magnetic recording, with various packing fraction is analyzed. The time effects are studied with measurements of magnetization decay and deduction of magnetic viscosity S, fluctuation field Hf, and activation volume Vac. The magnetostatic interactions among the particles are evaluated with measurement of the ΔM deviations from the Wohlfarth equation and calculation of the “Δ plot area,” which expresses the overall effect of the interactions. The experimental results show a general weakening of time effects with the increase of packing and interactions. The magnetization decay, S and Hf decrease, and Vac increases, when p or Δ plot area increase. The strengthening of the interactions supports the thermal stability of the particle magnetization. The result is discussed in relation to the evolution of the magnetization reversal induced by the presence of interactions, which make the occurrence of a coherent switching mode more probable.

The growth of Rayleigh-Taylor-type instabilities in the lithosphere for various rheological and density structures

Cold, dense mantle lithosphere overlying hotter, lighter, asthenosphere creates a potential instability that should be enhanced if mantle lithosphere is mechanically thickened. For timescales shorter than those during which significant heat diffuses, this instability can be treated as a Rayleigh-Taylor instability, whose basic condition consists merely of a heavy layer overlying a lighter one in a gravitational field. We have calculated growth rates of small-amplitude perturbations as a function of wavelength for several structures and boundary conditions of geological interest. In the absence of thermal diffusion, the wavelengths at which instabilities grow most rapidly are likely to be about eight times the characteristic depth scale for exponential viscosity decay, which, for typical lithosphere, yields wavelengths between 40 and 90 km. Thermal diffusion, however, smoothes out temperature-induced density perturbations and thus slows the growth of short-wavelength instabilities. As a result, wavelengths for realistic lithospheric structures are expected to increase to 100 to 200 km, with maximum values up to 300 km. As this is of the order of lithospheric thickness, a Rayleigh-Taylor instability should produce only small anomalies in topography and gravity at the Earth's surface above the downwelling. For plausible ranges of lithospheric parameters, perturbations exhibit exponential growth, with growth rates as large as 10−14 s−1. Such rapid growth rates correspond to e-folding times of three million years, for asthenospheric viscosities of about 1019 Pa s. Viscosities greater than about 1021 Pa s allow thermal diffusion to slow growth rates to the point of stopping Rayleigh-Taylor growth completely. To simulate mechanical thickening of the lithosphere, we also include in our calculations non-zero horizontal strain rates, which can cause folding and boudinage instabilities. Folding instabilities will grow faster than those due solely to gravity when compression rates exceed about 10−15 to 10−16 s−1, corresponding to shortening of 100 per cent in 30 to 300 million years. For strain rates of this magnitude, unstable growth occurs at wavelengths about 4 to 6 times the thickness of the lithosphere, as several others have previously shown. These wavelengths are significantly longer than those produced by the layered density structure alone.

Nonlinear rheology of a concentrated spherical silica suspension:

Time-dependent nonlinear flow behavior was investigated for a model hard-sphere suspension, a 50 wt% suspension of spherical silica particles (radius = 40 nm; effective volume fraction = 0.53) in a 2.27/1 (wt/wt) ethylene glycol/glycerol mixture. The suspension had two stress components, the Brownian stress σ B and the hydrodynamic stress σ H After start-up of flow at various shear rates $$\dot \gamma $$ , the viscosity growth function η+ (t, $$\dot \gamma $$ ) was measured with time t until it reached the steady state. The viscosity decay function η− (t, $$\dot \gamma $$ ) was measured after cessation of flow from the steady as well as transient states. At low $$\dot \gamma $$ where the steady state viscosity η ( $$\dot \gamma $$ ) exhibited the shear-thinning, the η− (t, $$\dot \gamma $$ ) and η+ (t, $$\dot \gamma $$ ) data were quantitatively described with a BKZ constitutive equation utilizing data for nonlinear relaxation moduli G (t, γ). This result enabled us to attribute the thinning behavior to the decrease of the Brownian contribution η B = σ B / $$\dot \gamma $$ (considered in the BKZ equation through damping of G (t, γ)). On the other hand, at high $$\dot \gamma $$ where η ( $$\dot \gamma $$ ) exhibited the thickening, the BKZ prediction largely deviated from the η+ (t, $$\dot \gamma $$ ) and η+ (t, $$\dot \gamma $$ ) data, the latter obtained after cessation of steady flow. This result suggested that the thickening was due to an enhancement of the hydrodynamic contribution η H = σ H / $$\dot \gamma $$ (not considered in the BKZ equation). However, when the flow was stopped at the transient state and only a small strain (<0.2) was applied, η H was hardly enhanced and the η− (t, $$\dot \gamma $$ ) data agreed with the BKZ prediction. Correspondingly, the onset of thickening of η+ (t, $$\dot \gamma $$ ) was characterized with a $$\dot \gamma $$ -insensitive strain (≌ 0.2). On the basis of these results, the enhancement of η H (thickening mechanism) was related to dynamic clustering of the particles that took place only when the strain applied through the fast flow was larger than a characteristic strain necessary for close approach/collision of the particles.

Magnetization stability and interactions in particulate recording media

The basic magnetic properties of fine particles used in magnetic recording media are studied. The examined materials are α-Fe metal, iron oxide (pure and Co-doped), chromium dioxide (pure and Ir- or Fe/Sb-doped) and barium ferrite (pure and Co/Ti-doped) particles. The magnetostatic interactions among the particles are analysed with the evaluation of the remanence curves. In metal particles the different roles of positive and negative interactions are investigated and the results are interpolated to the condition of ‘zero’ interactions. In the other particles the ionic additions weaken the interaction strength. The time-dependent magnetic behaviour is evaluated with measurements of magnetization decay and subsequent deduction of magnetic viscosity, fluctuation field and activation volume. The time effects are found to be related both to the interparticle interactions which reduce the magnetic viscosity and to the presence of substituting ions which lower the thermal stability of the magnetization. These results are discussed in correlation with the evolution of the magnetization switching mode of the particles induced by the interactions and by the ionic additions in the crystal structure.

Linear viscoelasticity of concentrated hard-sphere dispersions

The viscoelastic behaviour of model near hard-sphere continuous potential r-36 dispersions have been determined using Brownian dynamics simulations in a hydrodynamics-free approximation. Two methods were used to obtain the real and imaginary components of the complex shear viscosity, eta ' and eta ", respectively: first, calculating a time correlation function under no-shear conditions using a Green-Kubo formula; secondly applying finite-strain amplitude oscillatory shear cycles in the linear response limit to the contents of the BD cell. We find that the normalized stress autocorrelation function can be approximated very well by a two-parameter stretched exponential over the complete volume fraction range. The state dependence of the derived spectrum of relaxation times is determined. As for experimental systems the complex viscosity scales with a 'longest' relaxation time, in dimensionless form, D0 tau 1/a2, where a is the radius of the particle and D0 is the self-diffusion coefficient in the zero-density limit. Also in the intermediate-frequency regime 40<a2 omega /D0<400 we find that both the real and imaginary parts of the complex shear viscosity decay as approximately omega -1/2 in agreement with experiment and theory. The Newtonian viscosities obtained using eta '( omega to 0) agree well with the predictions of the Krieger-Dougherty equations. The product of the Newtonian viscosity and the long-time self-diffusion coefficient increases linearly with volume fraction for most of the fluid range.

Self-diffusion and viscoelasticity of dense hard-sphere colloids

Brownian dynamics (BD) simulation is used to calculate the viscoelasticity of model near-hard-sphere colloidal liquids using a continuous potential r–n interaction between the model colloidal particles. The exponent n was varied between 6 and 72. The real and reciprocal components of the complex shear viscosity, η′ and η″, were computed via time-correlation functions under no-shear conditions using a Green–Kubo formula. Also, oscillatory shear non-equilibrium BD was employed at finite strain amplitude in the linear-response regime. We find that the normalised stress autocorrelation function can be approximated very well by a two-parameter stretched exponential over the complete volume-fraction range. The parameters used to specify the stretched exponential and also the viscosities and long-time self-diffusion coefficients are quite sensitive to the value of n at a chosen volume fraction. The Newtonian viscosity decreases and the long-time self-diffusion coefficient increases with the softness of the interaction, in agreement with experiment. The value n= 36 gives best agreement with the experimental data, and therefore appears to be a good ‘effective’ interaction which we suggest includes the time-averaged effects of the many-body hydrodynamics to some extent.The state dependence of the derived spectrum of relaxation times is determined. As for experimental systems, the complex, viscosity scales with the dimensionless (‘longest’) relaxation time, Doτ1/a2, where a is the radius of the particle and Do is the self-diffusion coefficient in the zero-density limit. Also in the intermediate frequency regime 20 < a2ω/Do < 200 we find that both the real and imaginary parts of the complex shear viscosity decay as ca. ω–1/2 in agreement with experiment.

Rheological behaviour of gelled, waxy North Sea crude oils

The design of subsea pipelines carrying waxy crude oil, especially in Northern and arctic areas, is largely controlled by start-up pressure drop requirements. The correct measurement of rheological parameters associated with start-up and line-clearing of gelled crude oil pipelines, is thus important for proper design of pumping capacity and pipeline dimensions. In Part 1, the yielding behaviour of some waxy North Sea crude oils was studied by means of different controlled stress experiments, using a controlled stress rheometer (CSR) with cone-and-plate geometry and a model pipeline. Strong dependence of yield stress on cooling rate and stress loading rate was observed. Reasonably good estimates of yield stress, as compared to model pipeline results, were obtained with the CSR. CSR measurements are thus considered to be a valuable supplement to model pipeline experiments, particularly for comparative purposes, such as flow improver screening. In Part 2, the time-dependent rheological properties of two waxy oils were studied under controlled stress and controlled shear rate conditions, mainly in the cone-and-plate geometry. Two different approaches for modelling of viscosity decay at constant shear stress, based on a first-order rate equation and the Bingham rheological equation of state respectively, reproduced experiments reasonably well. Equilibrium properties obtained in different instruments (controlled stress/ controlled shear) and geometries (cone-and-plate and concentric cylinder) agreed within about 15% for shear rates between 14 and 700 s −1. At constant temperature, the broken-down apparent viscosity recovered moderately at rest, whereas the breakdown of static yield stress was essentially irreversible. Slight temperature cycling (±1° C) induced rebuilding of a weak structure, but did not restore the original gel strength completely.

Heat transfer with condensation at a steam-water interface in a horizontal channel.

Condensation of steam on a subcooled water layer was studied in a cocurrent horizontal channel at atmospheric pressure through experimental and numerical analysis. The liquid and vapor Reynolds numbers, based on hydraulic diameters, were varied experimentally from 6900 to 21900 and from 7700 to 19700, respectively. The experimental results showed promotion of heat transfer by the existence of interfacial waves. The numerical analysis predicted a heat transfer coefficient lower than the experimental results. This discrepancy can be explained by the fact that the numerical results showed decay of turbulent viscosity near the interface because of severe restriction of turbulent values.