Heat Of Wetting Research Articles

Simulation of Liquid Diffusion-Controlled Drying of Shrinking Thin Slabs Subjected to Multiple Heat Sources

Although a detailed mathematical model incorporating all physical mechanisms of moisture and heat transfer in the material would yield valuable design information, it is not feasible to do this on a routine basis for the design of dryers. A simple liquid diffusion model was developed in the present study to quantitatively assess the influence of various operating parameters of engineering interest in drying of heat-sensitive materials. Heat of wetting, temperature, and moisture dependent effective diffusivity and thermal conductivity, changes in product density and drying-induced ideal shrinkage of the product are considered in this model. The effects of combining convection with conduction, radiation, and volumetric heating using a microwave field are simulated in view of the increasing interest in multimode heat input drying processes. Numerical results are reported on drying of potato slices to demonstrate how the moisture and temperature profiles as well as drying performance are affected by multi-mode heat input. Effects of key parameters e.g., drying air velocity, temperature, relative humidity, and product thickness are computed and discussed.

The Hydrophobicity Study of Silica and Glass Surfaces Modified with Polyalkylhydrosiloxanes

A procedure based on the analysis of the shape of a sessile drop was used to measure the contact angles of water in air, θa = 93°–97°, for quartz and glass plates modified with polyalkylhydrosiloxanes. The specific heat of wetting, q = 36 mJ/m2, and the surface pressure of adsorbed water film, π = 48 mJ/m2, were determined from adsorption-calorimetric experiment on macroporous disperse silica modified with polymethylhydrosiloxane GKZh-94M. The contact angle in saturated water vapors, θv = 84°, was calculated from these values. It was shown that the liquid-phase modification of silica and glass with polyalkylhydrosiloxanes leads to distinct hydrophobization of the studied surfaces.

An elasto-plastic model for non-isothermal analysis of flow and deformation in unsaturated porous media: formulation

A rigorous and unified treatment of the theory of non-isothermal flow and deformation in unsaturated porous media is presented. The governing equations based on the equations of equilibrium, the effective stress concept, Darcy's law, Fourier's law and the conservation equations of mass and energy are derived using a systematic macroscopic approach. The thermo-hydro-mechanical coupling processes taken into account include: thermal expansion, thermal convection by moving fluid, fluid flux due to temperature gradient (Soret effect), phase exchange (vaporisation, condensation), heat exchange between the phases, heat of wetting, and heat due to phase compression. Both elastic and elasto-plastic constitutive equations are developed. All model coefficients are identified in terms of measurable parameters. The governing equations derived are general in nature, embodying all previously presented formulations in the field. For example, when the heat of wetting, and that heat due to phase compression are neglected, and it is assumed that the vapour is at the saturated liquid pressure, with all phases in thermal equilibrium, and that the forced convection is negligible, the theory of heat and mass transfer presented by Thomas and his coworkers is obtained. Also when the pore air volume reduces to zero and the thermal equilibrium is assumed, the thermo-elastic model for fluid saturated media presented by McTigue [J. Geophys. Res. 91 (B9) (1986) 9533] is recovered.

Heat-pump/energy-store using silica gel and water as a working pair

The possibilty of using silica gel and water as a reversible pair, in a thermochemical heat-pump/energy-store has been studied theoretically and experimentally during both heating and cooling modes. With silica gel absorbing water by 25±2% of the dry silica gel's weight, the heat of adsorption and the heat of wetting of 2712.43±30 kJ/kg SiO 2 and 94.43± 15 kJ/kg SiO 2 have been achieved respectively. The concentration rate for the two reaction pair was investigated and a general relationship that governed the adsorption rate with time has been deduced.

Determining the Contact Angle of a Nonwetting Liquid in Pores by Liquid Intrusion Calorimetry

A microcalorimetric method is proposed to determine the contact angle of a nonwetting liquid within a mesoporous solid. It is based on the simultaneous measurement of the heat and work of wetting, as the pressure is raised. The method simply requires a previous determination of the surface area to be wetted. It allows one to carry out liquid intrusion porosimetry without any a priori assumption on the contact angle. This method is, in principle, applicable to mercury porosimetry. Its feasibility is shown here for water in porous hydrophobic silicas.

Effect of Fiber Structure on Heat of Wetting of Cotton and Regenerated Cellulosic Fibers

A new calorimeter is constructed to precisely measure the heat of wetting of cotton, regular viscose rayon, high wet strength viscose rayon, and Tencel®. Our purpose is to investigate the relationship between the heat of wetting and structural characteristics of fibers such as crystal and fiber structure, degree of crystallinity, and water absorbency properties (water regain, moisture regain, and bound water content of fibers). Despite its relatively high water regain, cotton has the lowest heat of wetting among the fibers studied so far. The heat of wetting of cellulosic fibers depends slightly on fiber and crystal structure but decreases proportionally with the increasing degree of crystallinity of the fibers. The heat of wetting is closely related to the amount of bound water estimated by differential scanning calorimetry. These results are discussed from the viewpoint of designing high performance cellulose materials.

湿潤発熱機能性繊維の開発 （第１報） 毛繊維の湿潤熱の熱分析

This studies are to clarify the mechanism of heat of wetting on wool fibers in relation to thier molecular structure and finaly to develope new functional fibers generating heat of wetting by means of molecular designing.At first thermal analysis on wool fibers with an improved differential calorimeter was conducted and then the exothermic value of heat of wetting on various fibers was measured. In the obtained results it was confirmed that the exothermic phenomenon of adsorbed moisture on wool fibers are correlated with three hydrophilic functional groups, especially amino group which existed in protein of wool fiber.

湿潤発熱機能性繊維の開発 第３報 湿潤発熱機能性アクリル繊維の開発

湿潤発熱機能性繊維の開発 第３報 湿潤発熱機能性アクリル繊維の開発

Coupled Heat-Moisture-Air Transfer in Deformable Unsaturated Media

A mathematical model is developed to simulate coupled heat, moisture, and air transfer in deformable unsaturated porous media. A constitutive model that includes thermo-hydro-mechanical coupling effects for a non-isothermal unsaturated medium and fully coupled heat and moisture transfer is used to establish the coupled nonlinear governing equations. These equations are expressed explicitly using displacements, capillary pressure, air pressure, and temperature (and evaporation rate) as basic variables. This allows the incorporation of porous medium deformation, moisture retention hysteresis, and soil inhomogeneities into the theory. The heat of wetting, heat sink due to thermal expansion of the medium, phase change between liquid water and vapor water, and compressibility of liquid water are also included in the model. A mixed-type finite element formulation of the nonlinear governing equations is presented. The focus of this paper is primarily on the establishment of a consistent set of governing equations. Nonlinear dependencies of \Isome\N material properties have not been treated due to the lack of experimental data. Numerical solutions for heating, infiltration, and loading of a soil column portray the principal features of the coupled fields and confirm the general validity of the present model.

ポリパラフェニンテレフタルアミドの結晶化度，微結晶サイズが水分収着特性に及ぼす影響

Moisture sorption properties and their relation both to noncrystallinity and to crystallite size were investigated for as-polymerized poly (p-phenylene terephthalamide) (PPTA) paricles. Degree of crystallinity in the PPTA particles after heat-treatment estimated from a wide-angle X-ray diffraction measurements was at most 64%, which was lower than that in regular Kevlar. Crystallite size for the PPTA particles was also smaller than that for regular Kevlar. However, crystal lattice struture was almost the same between the particle specimens and Kevlar fibers. The plot of moisture regain vs. heat of wetting showed linear relation, indicating nearly the same magnitude of interaction of water to the amide groups both for the PPTA particles and for Kevlar fibers.The ralation between the heat of wetting (or moisture regain) and degree of noncrystallinity linearly changed among the four kinds of fibers. However, the heat of wetting (or moisture regain) for the PPTA particles showed higher values than estimated from the linear relation in the plot obtained for the fibers. This suggested the difference in the three dimensional noncrystalline stucture between PPTA particles and fibers. Higher amount of free amide groups and easier accessibility of water to the amide groups due to the random orientation of the molecular chains enabled the higher moisture sorption in the as-polymerized PPTA particles.

97/03701 Influence of wetting heat in water to coals slurry-ability

Wetting Heat of varied-rank coals in water was measured by using SETARAM C80D Calorimeter. The data were correlated to the coals` slurryability which is characterized by the solid load at the viscosity of 1000 mPa.s and 25{degrees}C. The results showed that the heat of wetting by water decreases as coal rank increases in the range of brawn coal to bituminous coal with Carbon content of 89-90%(daf), and then, increase a little for the anthracite. This trend fitted well to the relationship of slurryability to coal rank. The heat of wetting was also correlated to the inherent moisture content and the oxygen content of coal, which are commonly considered as slurryability indication parameters. Hence, the wetting heat is another measure of coal`s slurryability.

Selective liquid sorption and wetting of pillared montmorillonites

AbstractPillared montmorillonite was used as an adsorbent for binary mixtures of hydrocarbons and alcohols (benzene/n-heptane; ethanol/cyclohexane; ethanol/toluene; propanol/ toluene). The adsorbent was prepared from the Na-form of a bentonite from Milos by reaction with polyhydroxoaluminium solutions. The adsorption behaviour of the pillared montmorillonite was characterized by the adsorption excess isotherms and the heats of immersion. Sorption capacities and wetting properties differed significantly from those of the Na-montmorillonite. Benzene was adsorbed preferentially from mixtures with n-heptane. Ethanol and propanol were also preferentially adsorbed from mixtures with cyclohexane and toluene but the curves showed azeotropic points at molar fractions of alcohols of 0.7-0.9. The calorimetric data revealed the partially hydrophobic character of the pillared montmorillonite. The heat of wetting of benzene or toluene on the pillared samples was distinctly higher than that of ethanol whereas ethanol gave the highest wetting enthalpies on Na-montmorillonite.

Moisture Sorption and Diffusion in Polyacrylonitrile Fiber: Interaction between Nitrile Groups and Sorbed Water.

Moisture sorption properties of polyacrylonitrile (PAN) fiber has been investigated. Sorption isotherm at 25°C and heat of wetting for PAN fiber were compared with those for acrylic fibers with known chemical compositions. The moisture regain at 65% r. h. was 1.37% (w/w) and heat of wetting for the dried PAN fiber was 0.6 cal/g, which were comparable values to those for the acrylic fibers. Diffusion of moisture into PAN fiber was observed using a gravimetric method at 25°C. The sorption/desorption curve below 70% r. h. was nearly identical, which indicated that interaction between water molecules and nitrile group in polymer chain was not significant. The results obtained in this study suggest that the averaged interaction between water and nitrile group is very weak. On the other hand, the exothermic property for heat of wetting and IR spectrum pattern for OH stretching indicated the possibility of the strong interaction between the sorbed water molecules and a very few nitrile groups.

Thermodynamics of Moisture Sorption by the Giant-Timber Bamboo

The thermodynamic interaction of water with giant-timber bamboo (Phyllostachys bambusoides Sieh. & Zucc.) was investigated. Thermodynamic properties were evaluated based on isosteric calculations from sorption isotherms at 20, 30, 40 and 50°C. The results show that. compared to wood, giant-timber bamboo exhibits less hygroscopicity and greater hysteresis. The differential heat of sorption. Q was found to be an exponential function of fractional moisture content, m, and decreased somewhat with increasing temperature. The relation Q s = (Q s ) o exp(-B 1 m) was considered to he reasonably adequate, but a better fit was provided by the equation Q s = A 2 + B 2 m + C 2 exp(-D 2 m) so that it was used in the calculation of the heat of wetting, W, and the integral heat of sorption, (W o - W). The differential heat of sorption at ovendry condition fell within the range observed for wood and other lignocellulosic material, The free energy, G., and the entropy, S., of sorbed water were in close agreement with those observed for wood, reconfirming the theory that definite enthalpy, free energy, and entropy changes accompany the sorption of water by lignocellulosic materials.

Heat of wetting (hydration) of xanthan as determined by calorimetry

Heat of wetting (hydration) of xanthan as determined by calorimetry

The Behavior at the Shrinkage Limit of Clay Undergoing Drying

Abstract In this paper, possible links between the shrinkage limit and distinct changes in other properties of a clay soil undergoing drying are discussed. These properties include the volumetric air content of the soil, the heat of wetting, the tensile strength, the total suction, and the thermal resistivity of the soil. The distinct changes are of interest in themselves, and possible explanations for them are briefly discussed. For soil under extremely dry conditions, more importance should perhaps be attached to using the shrinkage limit as an index to changes in soil behavior, and this topic warrants further research.

Investigation of the porous structure of activated carbons prepared by pyrolysis of agricultural by-products in a stream of water vapor

The processes of formation of the porous structure and the changes taking place on the surface of carbon adsorbents during their preparation by water-vapor pyrolysis from various agricultural by-products are investigated. Some of the sorption parameters of the adsorbents, such as specific surface area, assessed by argon thermal desorption, heat of wetting by hexane, and thermal effects of argon adsorption at 25°C are determined. The experimental data prove that the adsorbent without proper properties depends on the nature of the raw material, the final temperature of the process, and the duration of treatment at the final temperature. A similarity is found between the dynamics of pore-formation and development of new surfaces of the activated carbons prepared from coconuts and nuts, as well as those from almonds and apricots.

Interaction of metal particles for magnetic recording with media formulation components

The interaction of commercially available, iron-based magnetic particles with certain particulate media formulation components has been investigated using the technique of flow microcalorimetry. The heat of wetting of these particles by solvents has been found to be a function of the solvent dipole moment and particle coercivity and surface area. Di(2-ethyl hexyl) phosphoric acid, a model dispersant, appears to interact chemically with a particle of high coercivity. Solvent basicity influences the heat and extent of interaction of the dispersant.<lz> <lz> <lz> <lz> <lz> <lz> <lz>

Surface properties of suspended solids in stratified estuaries (Krka River estuary and Rhône River delta)

Three surface parameters—specific surface area (SSA), heat of wetting (Hw), and cation exchange capacity (CEC)—of estuarine suspended solids were studied in relation to the organic matter (dissolved or particulate). Natural suspended solids were studied in two stratified river mouths—the Krka River estuary and the Rhône River delta. The same studies were performed with model solids, well defined by chemical composition and preparation (controlled pore glass, silanized controlled pore glass and calcite) after exposure to natural water samples from the Krka River estuary. On the basis of the studied parameters, the existence of two types of organic compounds that mediate the surface properties of particulates was indicated: (1) hydrophilic, with high density of functional groups, reactive and degradable, and coinciding with ‘river type organic matter’, and (2) hydrophobic, less reactive and thus more persistent, and coinciding prevalently with ‘marine type organic matter’. Generally, it was found that high Hw values (100–300 μJ cm −2) reflect the influence of surface functional groups that originate primarily from the reactive organics (adsorbed or particulate). An extreme value of Hw (523 μJ cm −2) was found at a location of high biological productivity and high anthropogenic influence.

Dielectric investigation of the effect of ethylamine on viscose rayon

AbstractThe effect of treating viscose rayon by aqueous ethylamine of 73.5% w/w for different treatment times on two dielectric relaxation processes (γ and β) observed initially in viscose was studied. Thus, measurements of dielectric constants, ϵ′, and dielectric loss, ϵ″, at frequencies of 0.1–10000 kc/s over a temperature range of 298–333 K, were carried out on four treated samples for 0.5, 1, 2, and 4 h of immersion in ethylamine. Some physical properties were also determined a priori, namely, dissolution and ash content percentages, as well as accessibility toward water and iodine molecules by measurements of heat of wetting and iodine absorption, respectively. In comparison with viscose rayon, the following results were obtained: (i) The γ‐relaxation process was gradually removed by the action of ethylamine, and completely disappeared in samples treated for 2 and 4 h. For this process, the loss, magnitude of polarization, shape parameter, and relaxation frequency decreased with the increase of the time of treatment. (ii) The β‐relaxation process appeared in all samples investigated over the entire working temperature range. The loss maximum and magnitude parameter decreased with lengthening the time of treatment, whereas the shape parameter and the relaxation frequency increased, all tending toward limiting values over practically the same immersion period of 2–4 h. The results obtained from dielectric measurements, as well as those from other physical measurements, suggested that the viscose fiber obtained after treatment of 0.5 h in ethylamine had acquired some compact structure in the residual low fractions, in which the γ‐process was supposed to originate, and that further lengthening of the period of immersion resulted, however, in the development of a less‐closely packed structure in the amorphous regions of the fiber, where the β‐process originated. Based on the above, it was finally concluded that the treatment of viscose rayon with ethylamine of the above concentration resulted in several fractions, which vary in the degree of lateral order of arrangement of the chain molecules; i.e., in the relative arrangement of the polar groups in adjacent chains which govern the interchain forces and in turn the dielectric absorption. At the same time, the explanation of the results obtained in this work supports a previous interpretation suggested for the γ‐ and β‐relaxation processes in viscose.