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Purpose In the present study, laminar steady flow of nanofluid through a trapezoidal channel is studied by using of finite volume method. The main aim of this paper is to study the effect of changes in geometric parameters, including internal and external dimensions on the behavior of heat transfer and fluid flow. For each parameter, an optimum ratio will be presented. Design/methodology/approach The results showed that in a channel cell, changing any geometric parameter may affect the temperature and flow field, even though the volume of the channel is kept constant. For a relatively small hydraulic diameter, microchannels with different angles have a similar dimensionless heat flux, while channels with bigger dimensions show various values of dimensionless heat flux. By increasing the angles of trapezoidal microchannels, dimensionless heat flux per unit of volume increases. As a result, the maximum and minimum heat transfer rate occurs in a trapezoidal microchannel with 75° and 30 internal’s, respectively. In the study of dimensionless heat flux rate with hydraulic diameter variations, an optimum hydraulic diameter (Dh) was observed in which the heat transfer rate per unit volume attains maximum value. Findings This optimum state is predicted to happen at a side angle of 75° and hydraulic diameter of 290 µm. In addition, in trapezoidal microchannel with higher aspect ratio, dimensionless heat flux rate is lower. Changing side angles of the channels and pressure drop have the same effect on pressure drop. For a constant pressure drop, if changing the side angles causes an increase in the rectangular area of the channel cross-section and the effect of the sides are not felt by the fluid, then the dimensionless heat flux will increase. By increasing the internal aspect ratio (t_2/t_3), the amount of t_3 decreases, and consequently, the conduction resistance of the hot surface decreases. Originality/value The effects of geometry of the microchannel, including internal and external dimensions on the behavior of heat transfer and fluid flow for pressure ranges between 2 and 8 kPa.

Please cite this article as: Raheem AM, Vipulanandan C, Joshaghani MS, Non-destructive experimental testing and modeling of electrical impedance behavior of untreated and treated ultra-soft clayey soils, Abstract: The characterization of ultra-soft clayey soil exhibits extreme challenges due to low shear strength of such material. Hence, inspecting the non-destructive electrical impedance behavior of untreated and treated ultra-soft clayey soils gains more attention. Both shear strength and electrical impedance were measured experimentally for both untreated and treated ultra-soft clayey soils. The shear strength of untreated ultra-soft clayey soil reached 0.17 kPa for 10% bentonite content, while the shear strengths increased to 0.27 kPa and 6.7 kPa for 10% bentonite content treated with 2% lime and 10% polymer, respectively. The electrical impedance of the ultra-soft clayey soil has shown a significant decrease from 1.6 kΩ to 0.607 kΩ when the bentonite content increased from 2% to 10% at a frequency of 300 kHz. The 10% lime and 10% polymer treatments have decreased the electrical impedances of ultra-soft clayey soil with 10% bentonite from 0.607 kΩ to 0.12 kΩ and 0.176 kΩ, respectively, at a frequency of 300 kHz. A new mathematical model has been accordingly proposed to model the non-destructive electrical impedance-frequency relationship for both untreated and treated ultra-soft clayey soils. The new model has shown a good agreement with experimental data with coefficient of determination (R 2 ) up to 0.99 and root mean square error (RMSE) of 0.007 kΩ.

In this study, a detailed review on the reported correlations of shear strength and physical properties of soft soil has been investigated. An ultra-soft soil has been prepared from 2% to 10% bentonite clay soil with high water content. The shear strength of the prepared ultra-soft soil has been tested using modified vane shear device. Based on collected data and experimental results, two new mathematical models for shear strength-water content relationship has been proposed for shear strength and water content ranged from 6 kPa to 0.1 kPa and 50% to 1100% respectively. The second proposed model was compared with several reported models from literature to demonstrate shear strength-water content relationship for ultra-soft soil with low shear strength and high water content. The second proposed model has shown a very good agreement with the experimental results with coefficient of determination (R 2 ) up to 0.91.Copy Right, IJAR, 2016, All rights reserved.

Many processes in nature (e.g., physical and biogeochemical processes in hyporheic zones, and arterial mass transport) occur near the interface of free-porous media. A firm understanding of these processes needs an accurate prescription of flow dynamics near the interface which (in turn) hinges on an appropriate description of interface conditions along the interface of freeporous media. Although the conditions for the flow dynamics at the interface of free-porous media have received considerable attention, many of these studies were empirical and lacked a firm theoretical underpinning. In this paper, we derive a complete and self-consistent set of conditions for flow dynamics at the interface of free-porous media. We first propose a principle of virtual power by incorporating the virtual power expended at the interface of free-porous media. Then by appealing to the calculus of variations, we obtain a complete set of interface conditions for flows in coupled free-porous media. A noteworthy feature of our approach is that the derived interface conditions apply to a wide variety of porous media models. We also show that the two most popular interface conditions -the Beavers-Joseph condition and the Beavers-Joseph-Saffman condition -are special cases of the approach presented in this paper. The proposed principle of virtual power also provides a minimum power theorem for a class of flows in coupled free-porous media, which has a similar mathematical structure as the ones enjoyed by flows in uncoupled free and porous media. PROBLEM STATEMENTLet us consider a domain which consists of two non-overlapping regions: a porous region and a free flow region. The interface is the surface that demarcates these two regions. Fig. 1 provides a pictorial description. Now consider the situation in which an incompressible fluid flows in this domain with the porous solid to be rigid. The central question pertaining flows in coupled freeporous media is:Given the domain, free flow and porous regions, boundary conditions on the external boundaries, properties of the incompressible fluid (e.g., the coefficient of dynamic viscosity, true density), and properties of the rigid porous medium (e.g., porosity, permeability), what is the set of conditions appropriate at the interface?

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