Interstitial Fluid Properties Research Articles

Experimental study of contacting surfaces microgeometry and gas gap impact on thermal contact conductance of metallic joints

Thermal contact resistance is an important phenomenon in heat transfer and impacts many fields of technology. The interrelated influences of many factors—such as geometry and microgeometry of contacting surfaces, their mechanical and thermal properties, apparent contact pressure, type and properties of interstitial fluid—make prediction of this resistance problematic and necessitate both theoretical and experimental research. The paper reports an experimental study of thermal contact conductance (the reciprocal of thermal contact resistance) of joints created by flat, conforming metallic surfaces in static contact. The measurements were performed for samples made of mild steel and stainless steel with relatively low roughness (σ = 0.5 - 2.14 µm) and large slope of asperities (m = 0.4 – 1.3), resulting in values of σef/mef = 1.25 - 1.96 µm that are distinctly lower than reported in the majority of experimental research on thermal contact conductance. The apparent contact pressure was changed from 1.5 to 11 MPa and for some cases up to 19 MPa. Analysis of the results obtained showed that the correlations available in the literature, for greater values of roughness and smaller asperity slope, mostly overestimated the predicted thermal contact conductance. The elasticity indices values for samples used in this study indicated plastic deformation of asperities, but it was concluded that the smoothest surfaces of both kinds of steel underwent elastic deformation. A new experimental correlation for contact of mild steel surfaces (σ = 0.5 - 2.14 µm, σef/mef = 1.25 - 1.96) was proposed. The results of this study indicate the need for further investigation of thermal contact conductance, especially for this range of surface microgeometry parameters, which is not dealt with in the correlations available in the literature. There is also a need to study the impact of asperity curvature on contact conductance. The results of this study proved the important role that air gaps play in the transfer of heat across a joint. The gap conductance values were predicted correctly for low mechanical loads and rough surfaces.

Comparison of laboratory and field electrical resistivity measurements of a gypsum rock for mining prospection applications

Geophysical surveys are frequently applied in mining prospection to detect the presence and volume of ore bodies of different nature. Particularly, in gypsum ore bodies exploitation, electrical resistivity measurements are usually the most used methodology. However, it has been observed that different electrical resistivity values can be obtained depending on geometrical features and composition of gypsum. Indeed, electrical resistivity of gypsum rocks depends on several parameters, such as gypsum purity, nature of secondary minerals, porosity, saturation and interstitial fluid properties. Saturation and hydrogeological setting, in particular, were recognized as the most influencing parameters. Hydrogeological conditions of gypsum rock masses are also very relevant for exploitability, safety conditions and economic feasibility and should be accurately known during the prospection and planning phases of the quarries. In this work, a relationship between electrical resistivity and saturation degree of gypsum is proposed. The possibility to estimate gypsum porosity with the use of this relationship is also investigated. The reliability of laboratory measurements is finally verified in comparison with field and modelled resistivity data. The reported results underline the potentiality of the proposed approach to obtain a reliable characterization of the studied ore body.

Numerical and analytical study of rate effects on drilling forces under bottomhole pressure

The scope of this paper is to investigate rate effects on rock cutting process at bottomhole pressure. The solution of the cutting problem is derived in the framework of the theory of poroelastoplasticity. The problem is firstly solved analytically using some assumptions derived from the literature review. Then, a numerical resolution of the fully coupled problem is performed based on the finite element method. These two different approaches show that pore pressure in shear-dilatant rocks decreases as a function of the cutting velocity depending on rock permeability and interstitial fluid properties. Pore pressure change has a hardening effect leading to an increase of the rock drilling resistance.

An in vivo study with an MRI tracer method reveals the biophysical properties of interstitial fluid in the rat brain

The nature of brain interstitial fluid (ISF) has long been a subject of controversy. Most of the previous studies on brain ISF were carried out in vitro. In the present study, a novel method was developed to characterize ISF in the living rat brain by magnetic resonance (MR) imaging using gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA) as a tracer. Sprague Dawley rats (n=8) were subjected to MR scanning before and after the introduction of Gd-DTPA into the caudate nucleus. A one-way drainage of brain ISF was demonstrated on the dynamic MR images. According to the traditional diffusion model, the diffusion and clearance rate constants of the tracer within brain extracellular space (ECS) were derived as (3.38+-1.07)×10(-4) mm(2) s(-1) and (7.60±4.18)×10(-5) s(-1). Both diffusion and bulk flow contributed to the drainage of ISF from the caudate nucleus, which demonstrated an ISF-cerebrospinal fluid confluence in the subarachnoid space at the lateral and ventral surface of the brain cortex at 3 h after the injection. By using this newly developed method, the brain ECS and ISF can be quantitatively measured simultaneously in the living brain, which will enhance the understanding of ISF and improve the efficiency of drug therapy via the brain interstitium.

Full waveform inversion of seismic waves reflected in a stratified porous medium

SUMMARY In reservoir geophysics applications, seismic imaging techniques are expected to provide as much information as possible on fluid-filled reservoir rocks. Since seismograms are, to some degree, sensitive to the mechanical parameters and fluid properties of porous media, inversion methods can be devised to directly estimate these quantities from the waveforms obtained in seismic reflection experiments. An inversion algorithm that uses a generalized least-squares, quasi-Newton approach is described to determine the porosity, permeability, interstitial fluid properties and mechanical parameters of porous media. The proposed algorithm proceeds by iteratively minimizing a misfit function between observed data and synthetic wavefields computed with the Biot theory. Simple models consisting of plane-layered, fluid-saturated and poro-elastic media are considered to demonstrate the concept and evaluate the performance of such a full waveform inversion scheme. Numerical experiments show that, when applied to synthetic data, the inversion procedure can accurately reconstruct the vertical distribution of a single model parameter, if all other parameters are perfectly known. However, the coupling between some of the model parameters does not permit the reconstruction of several model parameters at the same time. To get around this problem, we consider composite parameters defined from the original model properties and from ap rioriinformation, such as the fluid saturation rate or the lithology, to reduce the number of unknowns. Another possibility is to apply this inversion algorithm to time-lapse surveys carried out for fluid substitution problems, such as CO2 injection, since in this case only a few parameters may vary as a function of time. We define a two-step differential inversion approach which allows us to reconstruct the fluid saturation rate in reservoir layers, even though the medium properties are poorly known.

Spatially periodic suspensions of convex particles in linear shear flows. I. Description and kinematics

Preparatory to a subsequent dynamical study in Part II, aimed at calculating the rheological properties of geometrically-ordered models of concentrated suspensions, a purely kinematical study is here presented of the motion of a mobile spatially periodic array of identical convex particles, typically spheres, participating in a macroscopically homogeneous linear shear flow to which the suspension as a whole is subjected. The geometrical configuration of such particle-lattice suspensions is shown to evolve temporally in a manner dependent upon the initial lattice configuration and the specific bulk shearing motion to which the suspension is subjected. Under certain circumstances the particle-lattice system is found to reproduce itself periodically in time—or, less stringently—“almost” periodically. Precise circumstances under which this occurs are exhaustively delineated for the entire class of two-dimensional isochoric spatially homogeneous shearing motions, parametrized by a scalar λ expressing the relative amounts of shear and vorticity present in the flow. This investigation is performed for both two- and three-dimensional lattices. (Eventual time averaging of the local, instantaneous, dynamical, interstitial fluid properties of these almost self-reproducing systems in Part II furnishes the rheological properties of the suspension.) Using concepts borrowed from Minkowski's geometry of numbers, calculations are outlined for establishing the maximum volume fraction of suspended particles that is kinematically possible for each shearing motion. This is observed to be always less than would obtain in a comparable static system.