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Paper and fiber board are dried by threading a continuous wet web around each of a series of 50 to 70 dryer drums. The cylinders are internally heated by condensing steam. Part of a conventional multicylinder dryer section is shown. The dryer felt is a highly porous material whose main purpose is to hold the paper sheet in close contact with the dryer shell to increase the heat transfer between the paper and dryer shell to increase the heat transfer between the paper and dryer and to help prevent shrinkage and deformation of the paper sheet. The sheet moisture content entering the drying section is 150 to 200% (dry basis) and the final moisture content varies from 2 to 9%. Many attempts have been made to analyze the paper drying process both theoretically and experimentally. Most theoretical models contain critical assumptions that considerably simplify the heat and mass transport phenomena within the sheet during drying. Kirk and Iida provide a review of existing paper drying simulation models. Most of the existing models assume variables such as temperature, moisture content, or thermal conductivity remain uniform through the sheet thickness, and that water fluxes are negligible. Furthermore, a majority of the modelsmore » have been developed for corporate use and the details of the models have remained proprietary. A better understanding of the transport phenomena in the paper sheet is needed to model the heat and mass flow through the paper accurately. A flexible model for the entire drying system could aid in the design and maintenance of dryer systems, overall system efficiency, and improved product quality.« less

The rate of through drying paper in the constant rate drying period was measured for 210 combinations of temperature and throughflow rate of air, basis weight, and initial moisture content of paper. The volumetric heat and mass transfer was represented by use of a characteristic dimension, determined simultaneously from a new momentum transport treatment for drying air flow through a moist sheet.

Deformation mechanisms in steady-state creep are adopted to interpret the rate-determining mechanism in the hot-pressing of the MgO-excess, near-stoichiometric, and Al 2 O 3 -excess compositions of magnesium aluminate (MgAl 2 O 4 ) spinel. Effective stress has been modified to account for stress multiplication arising from the sintering of porous powder compacts. Stress exponents of n =1.5 to n =3–4.3, and activation enthalpies of Δ H ≈495 kJ/mol for a high-stress regime and 473 kJ/mol for a low-stress regime suggest that the rate-controlling mechanism transits from a climb-controlled dislocation mechanism in the beginning to diffusion controlled by oxygen diffusion in the later stage. The transition stress decreases with the content of Al 2 O 3 . Calculated creep rates and grain-size exponent of p ≈2 further suggest that the Nabarro–Herring creep dominates the densification in low-stress regimes. Sigmoidal hot-pressing curves observed in Al 2 O 3 -excess compositions are characterized by the zero-densification-rate period, which represents the incubation time required for the recovery of hardened microstructure. Similar to the stress-dip test, the zero-densification-rate period is originated from the decreasing effective stress during hot-pressing. The internal stress accumulated upon hot-pressing exceeds the decreasing effective stress and results in the incubation time.

The authors have investigated inactivation kinetics of mixed microbial populations, which consist of component subpopulations following first-order inactivation kinetics. Populations which had undergone previous partial heat treatment were also included in the study. As the survivor ratio is the Laplace transform of the rate constant distribution, an analysis of survival functions following nth-order inactivation kinetics (n > 1) resulted in a gamma distribution of the first-order rate constants. The expected value of the gamma distribution is proportional to the resulting nth-order rate constant and inversely proportional to the nth-order time constant. According to the theory, the nth-order time constant and survivor ratio are independent of the initial microbial concentration. The temperature effect has been treated with the restriction that a monotonously increasing functional relationship exists between first-order rate constants at two different temperatures. This monotonous function relates first-order rate constants of the same subpopulation. The Laplace transformation method is applicable to create analytical functions for fitting them to measured semilogarithmic survivor curves, if these curves are of the concave type.

The determination of corrosion parameters from the experimental dependence of the non-linear polarization resistance of corroding electrodes on the amplitude of sinusoidal modulation of the electrode potential has been proposed in the literature, by using a theoretical expression which takes the influence of electrolyte resistance into consideration. It is shown that this expression is only valid for low amplitudes of the perturbation signal, neglecting the influence of the ohmic drop. Moreover, if the electrolyte resistance is non-negligible and no IR compensation is carried out experimentally, this theoretical expression is incorrect, leading to erroneous values for the corrosion parameters. An alternative method is proposed, based on numerical calculation of the non-linear polarization resistance.

Behavior of a falling paper in a two-dimensional fluid is investigated by introducing a simple phenomenological model including the lift and friction terms. Five falling patterns are discovered with the increase of friction coefficients: periodic rotation, chaotic rotation, chaotic fluttering, periodic fluttering, and simple perpendicular fall. Irregular motions of the fall are explained in terms of low-dimensional chaos.

The behavior of superheated steam and air as drying fluids during the constant rate period of drying paper under impinging jets was compared in the jet temperature range 20 ≤ Tj 465°C for jet Reynolds numbers of l000 ≤ Rej ≤ 12000. At equal mass flux, steam drying is faster than air drying above the inversion temperature of 175°C. Also, the specific blower power for steam drying is much lower than for air drying at temperatures in the range of industrial importance. Superheated steam impingement drying can therefore lead to important capital investment and energy cost reductions, relative to air drying. Le comportement de la vapeur surchauffee et de I'air utilises comme fluides de sechage dans la periode de sechage par jets de papier a vitesse constante a ete compare dans la gamme. de temperatures des jets de 20 ≤ T, ≤ 465°C pour des nombres de Reynolds de jets de 1000 ≤ Re, ≤ 12000. A flux massique egal, le sechage a la vapeur est plus rapide que le sechage a I'air au-dessus de la temperature d'inversion de 175°C. En outre, la puissance des ventilateurs pour le sechage a la vapeur est bien inferieure a celle necessaire pour le sechage a I'air dans les gammes de temperatures interessant l'industrie. Le sechage par des jets de vapeur surchauffee peut donc conduire a un investissement en capital moindre et a des reductions des couts d'energie importants, comparativement au sechage a l'air.

Cure reactions in paper–phenolic composite systems were studied by differential scanning calorimetry. A phenomenological approach was used to characterize the cure kinetics. Various kinetic models including homogeneous reaction, diffusion-controlled reactions, surface reaction and phase boundary movement, and nucleation and growth-type kinetic models have been tested. Kinetic analyses using integral and derivative procedures on dynamic and isothermal data indicate that the cure reaction data can be described well with the homogeneous first-order reaction model or the Jander three-dimensional diffusion model. The activation energies are found to be in the range 20–40 kj/mol. © 1994 John Wiley & Sons, Inc.

Pyrolysis and steam gasification of paper have been conducted experimentally using a fixed bed reactor. Five temperatures (600 to 1000°C in steps of 100°C) were considered in both the pyrolysis and gasification process with the aim to obtain a comprehensive data. The obtained results were used to determine kinetic parameters using the nonlinear least-squares minimization method. A simplified pyrolysis and gasification model is suggested. Kinetic parameters where obtained using Aspen Plus software. The obtained kinetic parameters and the suggested mechanism were tested against the experimental data. The focus of this study is to develop a simplified mechanism capable of predicting the performance of a continuous flow reactor. The simulation of pyrolysis and gasification has been carried out using Aspen plus Software code. The non-random two liquid (NRTL) thermodynamic model was utilized to calculate the activity coefficients in the liquid phase while the Hayden– O’Conell equation of state was used to model the vapor phase. The estimation of energy consumption was calculated based on the energy required by endothermic reactions of pyrolysis and gasification.

La penetration de solutions de CMC et de sauces de couchage dans des feuilles de papier a ete etudiee experimentalement et modelisee par l'equation de Lucas-Washburn (Lepoutre, 1978) modifiee de facon a tenir compte de l'angle de contact dynamique et de la rheologie des sauces. On a egalement effectue une simulation numerique de la penetration du fluide basee sur la resolution par elements finis des equations de Navier-Stokes. Les predictions numeriques et les predictions de l'equation de Lucas-Washburn ont ete comparees avec les donnees experimentales montrant les limites des modeles.

It has been claimed [S. Westerberg, C. Wang and G.A. Somorjai, Surf. Sci. 582 (2005) 137] that the CO coverage on Pt(1 1 1) is proportional to the intensity of the band of linear CO observed by sum frequency generation vibrational spectroscopy, this assertion being based on an assumed agreement between a literature value of the adsorption heat of CO on Pt(1 1 1) and that calculated by applying the Langmuir model to the adsorption isotherms obtained by assuming the proportionality mentioned above. We show here, in the first place, that Langmuir’s equation was wrongly applied by Westerberg et al., the value of the adsorption heat obtained with a correct application of Langmuir’s model to the assumed adsorption isotherms being 73.5 kJ mol−1 instead of that of 113 kJ mol−1. In the second place, and far more importantly, we emphasize that Langmuir’s model, based on a constancy of the adsorption heat, cannot be applied to the adsorption of CO on Pt, a system for which the adsorption heat decreases markedly with increasing coverage. Therefore, the above value of 73.5 kJ mol−1 for the adsorption heat of CO on Pt(1 1 1), although obtained through a correct application of Langmuir’s equation, is invalid. Finally, application of the thermodynamic, and therefore model-independent, Clausius–Clapeyron equation to the adsorption isotherms given by Westerberg et al. yields adsorption heats that increase markedly with increasing coverage, which conclusively proves that the assumed adsorption isotherms are essentially wrong, and therefore that the claimed proportionality between the CO coverage on Pt(1 1 1) and the intensity of the sum-frequency-generation band of linear CO does not obtain.

Abstract In this paper the Gradient Theory of inhomogeneous fluids interface will be discussed and applied to compute the interfacial tension of hydrocarbon mixtures. The two inputs of the Gradient Theory model are the Helmholtz free energy densities of homogeneous bulk phases and the influence parameters of inhomogeneous interface. The bulk phase properties are calculated by the Peng-Robinson Equation of State. The pure component influence parameters are obtained from a correlation based on pure component experimental surface tension data, and the mixture influence parameters are determined from the geometric mixing rule. Experimental interfacial tension data for binary hydrocarbon mixtures and real petroleum fluids from two gas condensate reservoirs are collected and used to evaluate the Gradient Theory and Parachor Method. It is found that the accuracy of the Gradient Theory is superior to the Parachor Method which is traditionally used in the oil industry for interfacial tension predictions. 1 Introduction It is well known that the interfacial tension is regarded as one of important thermophysical parameters in many industrial processes. For example, in gas liquid separation process, there are strong dependencies between liquid interfacial tensions and gas-liquid separation performance, because both droplet size distribution and re-entrainment are sensitive to interfacial tension in the scrubber. In addition surface tension also plays important role in oil recovery process, extraction process, refinery process, etc. In spite of the importance of interfacial tension in petroleum industry, there is still a considerable lack of reliable experimental data in the open literature, especially near the critical conditions. Therefore, the theoretical and semi empirical prediction of interfacial tensions are of particular significance. There are several approaches which have been proposed for the estimation of interfacial tensions. These approaches can be divided into two categories: empirical correlations and statistical thermodynamics-based method which takes into account the density gradient between the bulk phase interfaces. The simple estimation method includes the Parachor Method [1-2], the Corresponding State Correlation [3] and the Perturbation Theory [4], which are not satisfactory for estimating interfacial tension of mixtures that exhibit strong hydrogen bonding. The statistical thermodynamics based methods include the Density Function Theory [5-6] and the Gradient Theory [7-8]. The Gradient Theory is of particular importance for practical computations of surface and interfacial tensions. It was originated by Rayleigh and Van der Waals [7] and rediscovered by Cahn and Hilliard in 1958 [8]. In this work the Gradient Theory of inhomogeneous fluid interface will be applied to obtain the interfacial tension of the hydrocarbon mixtures. The short descriptions of the Gradient Theory can be found in section 2. The Peng-Robinson Equation of State will be recalled in the section 3 and is utilized to compute some thermodynamic properties of the vapor/liquid phases and the interface. Finally the predicted interfacial tensions will be compared to experimental tensions. The superiority of the Gradient Theory is that it simultaneously can simulate mixture compound density profiles over the interfaces which are hardly accessible in experimental observation and measurement. The density profiles are very useful for theoretical studies and characterization of the interfacial behaviors of the hydrocarbon mixtures.

The phasing out of fully halogenated halocarbons becomes effective at the end of 1995 by international agreement. Under the same ozone depletion issue, the companion fluids HCFCs are suffering a similar fate, as they are considered controlled substances with a virtual phase-out by 2020, and more drastic reductions may be proposed in the near future. Some international action might also be agreed upon on refrigerants with regard to the threatened environmental emergency of anthropogenic global warming. Therefore, in choosing replacement fluids primary concern must be given to minimising the total warming impact, which, for most applications, calls for improved energy efficiency. During recent years, industry has scrutinised and proposed a number of new synthesised products as immediate drop-in or long-term replacements for fluids harmful to the environment. Together with some single-component new generation refrigerants, quite a few two-component, three-component or even four-component mixtures, both with zeotropic and azeotropic behaviour, are being considered. The main issues associated with the use of the new generation refrigerants are discussed, such as behaviour with oil; flammability; efficient use of temperature glides, fractionation and heat-transfer degradation with zeotropic mixtures. The full environmentally friendly option of resorting to natural fluids is also considered by examining some recent innovative applications as refrigerants of some hydrocarbons, ammonia, carbon dioxide, water and air.

Experimental investigations have shown that the enhancement in heat transfer coefficients for air flow in a channel roughened with angled ribs is on the average higher than that roughened with 90 deg ribs of the same geometry. Secondary flows generated by the angled ribs are believed to be responsible for these higher heat transfer coefficients. These secondary flows also create a spanwise variation in heat transfer coefficient on the roughened wall with high levels of heat transfer coefficient at one end of the rib and low levels at the other end. In an effort basically to double the area of high heat transfer coefficients, the angled rib is broken at the center to form a V-shaped rib, and tests are conducted to investigate the resulting heat transfer coefficients and friction factors. Three different square rib geometries, corresponding to blockage ratios of 0.083, 0.125, and 0.167, with a fixed pitch-to-height ratio of 10, mounted on two opposite walls of a square channel in a staggered configuration, are tested in a stationary channel for 5000 < Re < 30,000. Heat transfer coefficients, friction factors, and thermal performances are compared with those of 90 deg, 45 deg, and discrete angled ribs. The V-shaped ribs are tested for both pointing upstream and downstream of the main flow. Test results show that: (a) 90 deg ribs represent the lowest thermal performance, based on the same pumping power, and is essentially the same for the 2:1 change in blockage ratio, (b) low-blockage-ratio (e/Dh = 0.083) V-shaped ribs pointing downstream produced the highest heat transfer enhancement and friction factors. Among all other geometries with blockage ratios of 0.125 and 0.167, 45 deg ribs showed the highest heat transfer enhancements with friction factors less than those of V-shaped ribs, (c) thermal performance of 45 deg ribs and the lowest blockage discrete ribs are among the highest of the geometries tested in this investigation, and (d) discrete angled ribs, although inferior to 45 deg and V-shaped ribs, produce much higher heat transfer coefficients and lower friction factors compared to 90 deg ribs.

An experimental apparatus, with the features of fast heating rate and continuous record of reaction parameters, was developed to study kinetics of fast pyrolysis. The temperature effects, at a range of 400°C to 900°C, on pyrolysis rate, products profile, gas quality and quantity, and so on, were studied and the results are listed and analyzed. The effect of secondary reaction of gas phase at 700°C was tested and the regression result is expressed in an experimental formula. Based on the experimental results, the three-stage-reaction mechanism module is suggested. The kinetic expression to calculate gas formation rate is concluded as: dαdt=Aexp(-ERT)(1-α)n . The kinetic parameters of A, E, and n at different temperatures are given in the paper.

We comment here on the title paper and find that it is a series of misconceptions and misrepresentations of previous reports by Fleischmann, Pons and co-workers. It is shown that the conclusions reached by the authors lead to gross errors in the prediction of the observed responses of the electrochemical calorimeters described in the original work and that the correct methods of analyses are indeed those we originally described as well as those which have been outlined in subsequent publications. We find that the authors have not validated their own methods and have not provided sufficient information to allow assessment of their work.

We have studied the dynamics of two-phase flow in highly compressible porous media. As an application, we consider a (1 + 1)-dimensional 'transverse' flow model of water removal in a paper machine press section. Within the model, the system of water, air and the fibrous solid network is perceived as a homogeneous mixture of three interacting fluids under an external, time-dependent load. The flow of the three components is governed by the continuity equations and the generalized Darcy's laws. The rate of strain of the solid matrix is determined using a phenomenological stress-strain relationship which can include hysteresis and permanent deformation. The effective stress also includes the drag applied to the solid matrix by flowing water and air. The interactions (drag forces) between the three components are determined from either experimental effective permeabilities or interaction terms derived from a simple 'annular plug' capillary flow model.

An apparatus was constructed for determination of the thermal contact conductance for a paper handsheet/metal interface and for measurement of the effective thermal conductivity of handsheet samples. Bone-dry Bleached Southern Mixed Kraft handsheets with a water retention value of 1.832 were used to study the effect of pressure on thermal contact conductance and to measure the effective thermal conductivity of samples at various sheet density levels. A regression model describing the interface thermal contact conductance as a function of pressure and basis weight was derived. The contact conductance increases with increasing pressure or with decreasing basis weight. At a pressure of 2.3 kPa, the value of the interface contact conductance for the bone-dry samples considered ranges from approximately 97 W/m{sup 2}K for a sheet of 348.7 g/m{sup 2} basis weight to 200 W/m{sup 2}K for a sheet of 68.0 g/m{sup 2} basis weight. For pressures near 300 kPa, these values increase to 146 and 452 W/m{sup 2}K, respectively. The effective thermal conductivity of the handsheet samples was derived from measured values of overall joint conductance and interface contact conductance. The results indicate that the thermal conductivity of the bone-dry samples increases with increasing sheet density, ranging from 0.14 W/mK tomore » 0.70 W/mK for sheet densities of 90 kg/m{sup 3} to 500 kg/m{sup 3}, respectively, for the samples considered.« less

This communication concerns some doubtful results included in a recent comment by N. Freidoonimehr and A.B. Rahimi, Journal of Molecular Liquids 216 (2016) 99–102.

The effect of length scale in free-stream turbulence is considered for heat transfer in laminar boundary layers. A model is proposed that accounts for an “effective” intensity of turbulence based on a dominant frequency for a laminar boundary layer. Assuming a standard turbulence spectral distribution, a new turbulence parameter that accounts for both turbulence level and length scale is obtained and used to correlate heat transfer data for laminar stagnation flows. The result indicates that the heat transfer for these flows is linearly dependent on the “effective” free-stream turbulence intensity.

The present study compares measured and computed heat transfer coefficients for high-speed boundary layer nozzle flows under engine Reynolds number conditions (U∞=230 ÷ 880 m/s, Re* = 0.37 ÷ 1.07 × 106). Experimental data have been obtained by heat transfer measurements in a two-dimensional, nonsymmetric, convergent–divergent nozzle. The nozzle wall is convectively cooled using water passages. The coolant heat transfer data and nozzle surface temperatures are used as boundary conditions for a three-dimensional finite-element code, which is employed to calculate the temperature distribution inside the nozzle wall. Heat transfer coefficients along the hot gas nozzle wall are derived from the temperature gradients normal to the surface. The results are compared with numerical heat transfer predictions using the low-Reynolds-number k–ε turbulence model by Lam and Bremhorst. Influence of compressibility in the transport equations for the turbulence properties is taken into account by using the local averaged density. The results confirm that this simplification leads to good results for transonic and low supersonic flows.

Designs of heat exchangers for heat recovery from humid air are described. A mathematical model for heat transfer with simultaneous mass transfer is constructed, based on heat and mass balances. Methods for solution are shown for two cases: 1. The water on the exhaust side of the heating surface is only condensate, whose heat content may be neglected. Also, the case of only partially condensing heat transfer surface is discussed. 2. The heating surface is flushed with abundant water. - Each case is illuminated with a calculation example.

Le sechage du papier par des jets de vapeur surchauffee connait une periode de vitesse constante suivie d'une periode de ralentissement dans une large gamme de conditions operatoires. La vitesse constante de sechage, etudiee ici dans la gamme de temperatures des jets de 150≤T j , ≤465°C et pour des nombres de Reynolds de jets de 1000≤Re j , ≤12000, est predite avec un ecart de ±12% par l'expression de transfert de chaleur utilisant la correlation de Martin (1977) pour le coefficient de transfert de chaleur corrige pour le transfert de matiere par le facteur d'approximation de l'ecoulement de Couette, et un rapport des proprietes pour tenir compte de la difference de temperature importante entre le jet et le papier

Budrugeac and Segal (Int. J. Chem. Kinet.33, 564, 2001) have generally criticized the integral isoconversional methods for producing a systematic error in the activation energy, whose value varies with the extent of conversion. We stress that this error is practically eliminated in the advanced integral isoconversional methods when using integration over small time segments (Vyazovkin, S. J. Comput Chem.22, 178, 2001) © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 418–420, 2002

This article reviews Advances in Thermodynamics of the van der Waals Fluid. by David C. Johnston 118 pp. , 2014. Price: $50 (paper). ISBN 978-1-627-05531-4.

The review presents the results of experimental investigations of nucleation in superheated light and heavy water in the range of nucleation rates from 104 to 1029 s−1m−3. A study is performed of the kinetics of crystallization of droplets of superheated water and amorphous water layers. Measurements have been made of the density, sound velocity, dielectric constant of light and heavy water in the vicinity of the phase equilibrium line with deep entry into the region of metastable (superheated) states. The local and integral characteristics of streams of boiling-up water flowing out into the atmosphere through a short channel have been investigated. One can see the determining role of a vapor phase in such a process at a temperature above 0.9T c , where T c is the temper-temperature at the critical point.

The data of the paper I.A. dos Santos on LiF–LuF 3 system are in good agreement with the, earlier published date of P.P. Fedorov e. a., for exception of the LuF 3 polymorph transition, temperature.

The literature reviewed indicates that oxygen concentration, diluents, and pressure in combustion-test environments can influence the ignition and flame-spread rates of nonmetals. Increased oxygen concentrations result ineasier ignition and higher flame-spread rates. The flame-spread rate is generally a non-linear function of oxygen concentration, indicating that different processes are controlling combustion at different oxygen concentrations. The effect of oxygen concentration is higher at the minimum conditions required for ignition and at near-extinction conditions. Diluents affect the ignition and flame-spread mites in oxygen/diluent mixtures due to their effects on the thermal conductivity, specific heat, and diffusivity of the mixtures. Helium, which has a higher thermal conductivity than nitrogen, was shown to be a better inhibitor of ignition processes. Nitrogen/oxygen environments, which have higher heat capacity and lower diffusivity than helium/oxygen mixtures, generally result in lower flame-spread rates. The data also indicates that ircreased test pressures generally result in easier ignition and higher flame-spread rates. However, hither pressures can affect ignition and flame-spread in opposing ways by affecting the gas-phase kinetics of the combustion process. The effects of test pressure are more pronounced at minimum conditions for ignition or at near-extinction conditions.

In, we present counter-arguments to the statements done on Kokalj’s comment to our previous paper. Particularly, we present the reasons why our results differ from his. The difference emerges on the treatment of magnetization. While Kokalj allows for self consistent adjustment of magnetization, we constrained value in our calculation to be close to that of the bulk. We argue in what follows the reasons for doing this and why we believe this is the most suitable approach to the problem considered.