Liquid Wicking Research Articles

Unsteady-state Liquid Transport in Engineered Nonwoven Fabrics having Patterned Structure

The initial stage of liquid absorption in unsaturated nonwoven fabrics (e.g. dry wipes, absorbent materials and hygiene products) is an unsteady-state fluid flow. For the purpose of the engineering design of these nonwoven products, there is a need to predict the unsteady-state fluid flow in both homogeneous anisotropic nonwoven structures and heterogeneous patterned nonwoven fabrics having a dual-scale porosity structure. In this paper, the unsteady-state liquid wicking in homogeneous anisotropic nonwoven fabric structure has been modeled, and the relationship between unsteady-state liquid absorption in patterned nonwoven fabrics and its structural parameters has been established based on the fabric structural parameters.

Comment on “The effect of evaporation on the wicking of liquids into a metallic weave” by N. Fries, K. Odic, M. Conrath and M. Dreyer

A recent paper reported capillary rise and evaporation experiments in metallic wicks, as well as a mathematical model. The authors found a consistent discrepancy between the model predictions and data: The model over-predicted the capillary height rise by about 20%. The model used assumes that the porous medium is either fully wet or dry, an assumption that is particularly unsuited to evaporation from the wick surface. An alternative variable-saturation model is proposed that provides a possible explanation for the 20% discrepancy reported by the authors.

Capillary pressure and liquid wicking in three-dimensional nonwoven materials

The capillary pressure and liquid wicking in fibrous nonwoven materials depend on the structural arrangement of fibers in three dimensions, which is influenced by the method and conditions used to manufacture the material. By adapting the hydraulic radius mechanism and drag force theory, a model is established for predicting the directional capillary pressure in three-dimensional nonwoven materials. As a case study, equations to predict the velocity of liquid wicking in a one-dimensional wicking strip test for nonwovens having a three-dimensional fiber orientation distribution are given based on the newly established capillary pressure model. These models and equations are based on measurable structural parameters including the fiber orientation distribution, fiber diameter, and fabric porosity.

Pore network modelling using image processing techniques

PurposeThe knowledge of structural parameters of nonwovens media is poorly understood. The pores size distribution (PSD) function is one of those parameters. The difficulty is not only the understanding of the distribution of pores but also the identification of pores geometry distribution (PGD) and their behaviour concerning the dynamic fluid transportation. The purpose of this paper is to present an efficient and reliable method based on image analysis which on one hand, performs the estimation of the PSD function and takes into account the geometric aspect of pores, and on the other hand, analyses liquid wicking in very thin filter media.Design/methodology/approachThe proposed methods, in this paper, are applied on thin filter media made of polyester. The samples have not sudden any treatment. The authors set up an optical test bed in order to observe the dynamic properties of the samples. Dynamic raw data about the liquid wicking are extracted directly from video sequences using the appropriate test bed. The structural parameters are extracted from the non‐wetted samples.FindingsObtained results allow a better understanding of the liquid wicking in very thin filter media. In addition to the PSD function, the PGD function adds informations about the shape of pores. The dynamic data of the liquid wicking explains that pores have different behaviour when liquid reached them. It can be deduced from this study that the fluid transport in the pore network is defined by three main parameters: geometric parameter (size, shape), capillary action and pores connection in the network.Research limitations/implicationsThe led back‐lighting system is not sufficient to observe precisely the liquid wicking. An additional front‐lighting will be added in further studies.Originality/valueThe extraction of dynamic properties from video sequences, by performing image analysis is an original method to characterise the porosity in thin media filter.

The effect of evaporation on the wicking of liquids into a metallic weave

Wicking of liquids into porous media is of great importance to many applications. One example are propellant management devices (PMD) used in spacecraft tanks. PMDs are designed to ensure gas free delivery of propellant during all acceleration conditions of the flight. This might be achieved by a metallic weave which is wetted by the propellant and thus prevents gas from entering below a critical bubble point pressure. In the case of cryogenic or volatile liquids the weave may dry out and refilling of the structure becomes an important issue. In this study we analyze the wicking of different liquids into a dry Dutch twilled weave (DTW 200 × 1400 ) by combining experimental and analytical approaches. Experiments were performed under isothermal and terrestrial conditions to investigate the role of evaporation for the capillary rise. The standard wicking model from Lucas and Washburn is enhanced to account for evaporation and gravity effects, too. By comparing the experimental results with the enhanced wicking model we find good qualitative agreement. It is also noted that evaporation may have a major impact on the wicking process.

Evaporation heat transfer characteristics of a grooved heat pipe with micro-trapezoidal grooves

A detailed mathematical model predicting the effect of contact angle on the meniscus radius, thin film profile and heat flux distribution occurring in the micro-trapezoidal grooves of a heat pipe has been presented. The model can be used to determine the maximum evaporating heat transfer rate in the evaporator including the effects of disjoining pressure and surface tension. The equation of meniscus radii calculation in the evaporator at given heat load based on the liquid wicks configuration has been put forward. The numerical results show that while the capillary limitation governs the maximum heat transport capability in a grooved heat pipe, the thin film evaporation determines the effective thermal conductivity in a grooved heat pipe. The ratio of the heat transfer through the thin film region to the total heat transfer through the wall to the vapor phase decreases when the contact angle increases. The superheat effects on the heat flux distribution in the thin film region also have been conducted and the results show that the disjoining pressure plays an important role in this region. The current investigation will result in a better understanding of thin film evaporation and its effect on the effective thermal conductivity in a grooved heat pipe.

Wicking process of penetrants and inkjet inks on printing media

In this study, the dynamics of liquid capillary wicking (known as absorption, penetration, or imbibition) is discussed for a penetrant of an inkjet ink and commercial magenta inks. Different concentrations of penetrants on various printing media were tested, as well as magenta inks from HP and Canon. Penetrants are very efficient to wick inks on printing media and to reach maximum wicking area fast. The wicking areas of the penetrant solutions on test substrates are much lager than DI water. Since commercial ink contains 2 - 5% of penetrants, maximum areas of inks are larger than water and smaller than penetrant solutions. Alkylene glycol type penetrants such as Diethylene glycol monobutyl ether (DEGMBE), Diethylene glycol diethyl ether (DEGDEE) are to show large maximum wicking area and fast wicking rate. Alcohol type penetrants including Ethyl alcohol (EtOH) and Isopropyl alcohol (IPA) indicate fast drying rate at 100 and 50% concentration; however, drying rate of both alcohol type and alkylene glycol type penetrants at low concentrations are close to drying rate of water. Alkylene glycol type penetrants show less effects of concentration on wicking ratio, while concentrations of alcohol type penetrants greatly affects to absorption.

Flow conveying and diagnosis with carbon nanotube arrays

Dense arrays of aligned carbon nanotubes are designed into strips, nanowicks, as aminiature wicking element for liquid delivery and potential microfluidic chemical analysisdevices. Liquid wicks away along the nanowicks spontaneously. This delivery function ofnanowicks enables novel fluid transport devices to run without any power input, movingparts or external pump. Flow around the opaque nanotubes can be detected either directlyor indirectly. Direct signals of the flow come out of dyed liquid or from the liquid–airinterface; indirect signals are detected through observing surface-tension-induceddeformation and dislocation of the nanotubes. Here we show that flow progression aroundand inside nanowicks is sensitive to liquid properties. Different flow progression leavesdifferent traces of liquid. These traces not only allow liquid diagnosis any time aftersampling, but also enable analysis of flow at a nanoscale resolution with scanning electronmicroscopy.

Development of a simplified heat pipe numerical model and case study/experimental validation using a long ?wicked? heat pipe

This paper describes existing numerical techniques used for simulating heat pipe operation, and the development of a simplified numerical model for normal wicked/wickless heat pipes based on the analysis of current modelling methods. Vapour flow was treated as a two-dimensional flow. Heat transfers through the liquid–wick region and wall region were computed by solving a one-dimensional heat conduction equation. Flow in the liquid–wick region was treated as a one-dimensional problem. The liquid and vapour flows were coupled using a set of governing equations, incorporating thermal compressibility, hydro-dynamical and capillary relationship, as well as geometrical correlation. The finite-difference method was employed to carry out the numerical analysis, and FORTRAN language was used to develop a computer program. The model was used to investigate the operating characteristics of a long ‘wicked’ heat pipe, including variation of cross-sectional area, axial/radial velocity, pressure and temperature of liquid/vapour flows with height position above the liquid level. To validate the modelling predictions, a test rig was constructed to carry out experimental testing. This included measurement of surface temperatures and heat flow associated with heat-pipe heat transfer. The results from tests were found to be in general agreement with the numerical predictions when the test conditions were close to the simulation assumptions. Copyright © 2004 John Wiley & Sons, Ltd.

Measurement of Wood Wettability by the Wilhelmy Method. Part 2. Determination of Apparent Contact Angles

Summary This work focuses on the determination of apparent contact angles on wood by the Wilhelmy method. In this method, the force acting on an object is measured during a test cycle involving immersion in and withdrawal from a probe liquid. Fresh and aged veneers of extracted and non-extracted heart- and sapwood of pine were investigated. The results indicate that wicking of the probe liquids, into and along the porous wood veneers, occurs during the test cycles and that this strongly affects the determination of contact angles. It is suggested that two different wicking phenomena occur. First, when the veneer contacts the liquid, an instantaneous ‘initial wicking’ occurs. It is suggested that this initial wicking is influenced primarily by the liquid density and structural properties of the specimen (such as porosity and surface roughness), and not by surface energetics. An initial wicking constant was therefore estimated for the different veneer samples based on measurements in octane. Second, after the initial wicking, a continuing ‘secondary wicking’ is observed. In some cases, this may result in zero contact angle after a certain immersion depth. Contact angles should, therefore, be estimated from the initial part of the immersion, where the secondary wicking can be neglected. This may also reduce any contamination of the probe liquids by extractives. The Wilhelmy method seems to be a valuable tool for estimating the wetting properties of wood, permitting reproducible measurements of apparent contact angles provided that there is efficient control of wicking and contamination effects.

Analytical modeling of the startup characteristics of asymmetrical flat-plate and diskshaped heat pipes

An analytical model is developed for the startup transient of asymmetrical flat-plate and diskshaped heat pipes. The model solves the proper transient heat conduction equations for the heat pipe wall and liquid wick regions. A quasi-steady state, pseudo three-dimensional approximation is used for the vapor transient behavior. The heat transfer within the wall and liquid-wick regions is coupled with the vapor phase at the liquid-vapor interfaces. Analytical solutions of temperature, vapor velocity, and vapor pressure distributions are obtained based on an in-depth integral method. Results covering the entire startup transient are presented for disk-shaped and flat-plate heat pipes

Synthesis of Ag sheathed, Bi-2212 tapes by a novel liquid wicking method

A novel liquid wicking process has been developed to produce silver-sheathed Bi-2212 samples with oxide core thicknesses of 10–20 μm, uniform oxide/silver interfaces, small non-superconducting phases and low porosity. This technique avoids many problems associated with oxide-powder-in-tube (OPIT) processing by exploiting the wicking behavior exhibited by BiSrCaCuO (BSCCO) liquid between silver surfaces. Critical current densities over 50 000 A/cm 2 at 4 K in self-field have been achieved with an isothermal melt process and Bi 2.1Sr 2Ca 0.9Cu 2O x composition powder.

Wicking of Spin Finishes and Related Liquids into Continuous Filament Yarns

Using a simple electronic method for measuring wicking times, we have shown that horizontal wicking of liquids into continuous filament yarns follows the Lucas-Wash burn equation. We have investigated the effects of the liquid properties, viscosity, and surface tension, and of the liquid-solid interaction parameter cos θa. We have found that transient effects due to surfactant adsorption play a significant role in wicking, and that cos θa values of ∼0.7 or higher are necessary for wicking to take place. Certain kinds of fluorosurfactants seem to have a considerable negative effect on the wicking of model finishes in yarns and on the distribution of these finishes on the surfaces of constituent fibers.

A Heat Pipe Concept for Cooling a Liquid-Pool Blanket of a Tandem Mirror Fusion Reactor

The performance potential of a heat pipe designed specifically to operate in the high magnetic fields of a fusion reactor is investigated analytically. The heat pipe has a thin, flat cross section aligned parallel to the magnetic field so as to reduce the eddy currents and the resultant magnetohydrodynamic pressure drops in the liquid wick flow. The flat heat pipes are used to cool a pool of liquid lithium (or lithium-lead eutectic) in the blanket that surrounds the central-cell plasma of a tandem mirror fusion reactor. Calculations indicate that this new heat pipe design may be able to transport up to about6800 W/cm/sup 2/ of condenser cross-sectional area in a 2-T magnetic field. This is considerably higher than the 420 W/cm/sup 2/ capability of a conventional cylindrical heat pipe of similar dimensions employing a channel wick and operating in the same 2-T field.

Use of thermocapillary migration in a controllable heat valve

In accordance with the Marangoni effect, immiscible droplets in a host fluid in which a temperature gradient exists move in the direction of increasing temperature. It is proposed that this thermocapillary migration could be used to construct a ‘‘liquid wick’’ that would return the condensed vapor at the condenser end of a heat pipe back to the evaporator, thus completing the fluid circuit. The droplets would be formed by capillary pressure forcing the condensate through a perforated diaphragm whose temperature would control the droplet flux, and hence the heat flux between the two ends of the heat pipe, thus making it a controllable heat valve.

A wicking method for measuring wetting properties of carbon yarns

A dynamic method for measuring the wettability of carbon yarn has been devised which is based on the rate of wicking of a test liquid by a bundle of the yarn. An equation has been derived which relates the wicking rate data to the change in surface free energy of the yarn caused by wetting. Contact angles are calculated from the free energy values. This method has the advantages of being fast, independent of operator judgment, and only requires a sample size of about 1 g. Since all of the surface area of the sample is involved in the measurement, the average wetting characteristic of about 1 m 2 of carbon yarn surface is determined conveniently in a test.