Abstract: This paperreportstheresultsofanexperimentalinvestigationonthethermophysical,chemicaland dielectric propertiesofthreevarietiesofdatepalmwood(Phoenix dactylifera L.) fromBiskraoasisin
Algeria. Thegoalistousethisnaturalmaterialinthemanufactureofthermalinsulationforbuildings. Scanning electronmicroscopy(SEM)andenergydispersivespectroscopy(EDS)analysisofthedatepalm
wood wereinvestigatedtocharacterizethemicrostructureandthechemicalcompositionofthesamples. Asimultaneousdeterminationofthethermalconductivityandthediffusivitywasachievedusing a periodicmethod.Therelativepermittivitywasobtainedfromcapacitancemeasurementsperformed at roomtemperature.Theresultshaveshownthatthesurfacesofthesamplesareirregularwithmany
filaments, impurities,cellsandpores.Theeffectofthefibersorientationwassignificantontherelative permittivity whencomparedtothethermalconductivityofthedatepalmwood.Furthermore,thether-
mal conductivitymeasuredinvacuumandatatmosphericpressureshowedthatthematerialremains, in bothcases,withgoodproperties.Thisresultwasconfirmedcomparingtothethermalconductivityof
other naturalinsulatingmaterials.Hencethedatepalmwoodisagoodcandidateforthedevelopment of efficientandsafeinsulatingmaterials.
Abstract: This article presents the results of the first experimental investigation of the performance of solar air flat plate collector at Biskra (latitude 34480N and longitude 5°44'E), Algeria. The thermal efficiency between absorber plate and air in flat plate solar collector has been enhanced by introducing obstacle rows in the dynamic air vein of the collector. For this objective, a flat plate solar collector, of 1.73m2 area and 25mm air gap, has been designed and constructed. These obstacles formed with two parts: first part is perpendicular to fluid flow and the second part is inclined, they are mounted in a staggered pattern, oriented perpendicular to the fluid flow and soldered to the back plate. The solar air heater was mounted on a stand facing south at inclination angle, and it was tested under the environmental conditions. Moreover, a theoretical approach is employed for determination of the thermal performances of this collector where the temperatures of all components of the collector and outlet air are predicted. Comparisons among the experimental and theoretical results considered are reported.
Abstract: In this article, the rheological properties of bentonite suspensions at different concentrations, with and without anionic polymer additives, are investigated. The clay used is a drilling bentonite from Maghnia (west of Algeria) and the additives are sodium carboxymethylcellulose and xanthan gum. Experimental flow measurements, obtained by a controlled-stress rheometer, were used to highlight the effect of the additives on the rheological properties of the bentonite suspension. The Herschel-Bulkley and the Ostwald models were used to fit the rheograms. It has been shown that the presence of carboxymethylcellulose in the bentonite suspension has helped to remove the yield stress and to increase the viscosity of the mixture. On the other hand, the xanthan induced an increase in the yield stress and a high increase in viscosity of the bentonite-polymer mixtures.
Abstract: This paper presents the results of an experimental investigation of the
performance of a flat plate air solar collector outfitted with artificial roughness of
different forms and different arrangements. A complete collector test facility equipped
with data acquisition system has been assembled and tested for this purpose. A flat plate
solar collector, of 1.74 m2 area has been designed and constructed. The adapted artificial
roughness unit is structured from fin galvanized metal. Four configurations with two
forms (model-1 and model-2) of artificial roughness and two arrangements (A and B) are
combined (A1, A2, B1 and B2) and tested. The flat plate air solar collector was mounted
on a stand facing south at an inclination angle, and they were tested in the environmental
conditions. The experimental setup was instrumented for the measurement of solar
radiation, ambient temperature, outlet and inlet air temperature, air flow rate and wind
velocity.
Abstract: The rheological properties of aqueous solutions of poly(ethylene oxide) (PEO) of different molecular
weights (100, 400, 1000 and 4000 kg/mol) and concentrations were investigated using shear
viscosity and dynamic rheological measurements. It was found that the aqueous solutions of PEO do not
exhibit a yield stress and that, above a critical shear rate, all PEO solutions exhibit shear-thinning behavior,
well described by the Cross model, except for the solutions made by the lowest molecular weight
(100 kg/mol) which were almost Newtonian. The parameters of the Cross model, namely the zeroshear
rate viscosity and reciprocal of the time constant, allowed the determination of the critical concentrations
c* and c** (respectively, the transition to semi-dilute network solution and concentrated solution).
At concentrations higher than c** and below a critical shear rate, solutions made of PEO of high molecular
weight exhibited a clearly shear-thickening behavior at very low shear rates. In addition, the dynamic
tests showed that PEO solutions exhibit concentration-dependent viscoelastic properties, with a dominant
viscous behavior at PEO concentrations lower than c** and a dominant elastic behavior at PEO concentrations
greater than c**.
Abstract: In this study, we investigated the way of predicting two critical concentrations of Sodium Carboxylmethylcellulose (CMC) solutions using simple experimental procedures with a rotational rheometer. It was found that, above a critical shear rate, all CMC solutions (0.2 to 7wt.%) exhibit shear-thinning behavior and the flow curves could be described by the Cross model. A first critical CMC concentration c*, transition to semi-dilute network solution, was determined using the following methods i) study of the flow curve shapes, ii) Cross model parameters, iii) plot of the specific viscosity vs the overlap parameter and iv) empirical structure-properties relationships. Furthermore, both creep and frequency-sweep measurements showed that the solutions behaved as viscoelastic materials above a second critical CMC concentration c** (transition to concentrated solution). The characterization of CMC solutions was completed with a time-dependent viscosity study that showed that the CMC solutions exhibited strong thixotropic behavior, especially at the highest CMC
Abstract: Three different experimental measurements, namely rheology, particle sizing and X-Ray Diffraction, were used to study the effect of anionic additives on the properties of bentonite suspensions. The three additives were Sodium Carboxyl Methyl Cellulose (CMC), Xanthan gum and Sodium Dodecyl Sulfate (SDS). Flow curves were obtained from shear stress-shear rate measurements and the viscoelastic properties were determined from oscillatory and transient measurements. Mineralogical data were evaluated by X-ray diffraction (XRD) and the particle size analysis performed by light scattering technique. The presence of the surfactant modifies the face-to-face interactions and yields changes of the mixtures rheological behavior at low deformation rates. Polymers act by coating each clay particle and prevent their agglomeration. Therefore, the additives are responsible for the mechanisms of destructuration and structure reorganization as well as the mixtures viscous and viscoelastic behavior.
Abstract: The thixotropic behavior of bentonite suspensions was studied using different experimental procedures. It was found that the bentonite dispersions exhibit a time-dependent non-Newtonian behavior. In addition to the major factors affecting the rheological properties in the dispersion were the shearing value and duration, the rest time preceding the measurements and the structural state of the dispersion. The Herschel–Bulkley model was found to correlate well with the behavior of bentonite suspensions. The time evolution of the shear stress at constant shear rates was correlated by the Bird–Leider equation. In order to take into account structural evolution of the suspensions, the rheological law was modified by the introduction of the phenomenological model of Tiu and Boger derived from Moore's kinetics evolution. It was observed that at short rest times and low shearing conditions, this model describes satisfactorily the time-dependent behavior of the bentonite suspensions. The behavior laws and kinetics evolution were established through the determination of structure destructuration and reorganization rates values. The structure parameters were found to be dependent on the clay concentration, providing evidence that the scale characteristic times of the buildup and breakdown processes are also concentration dependent.
Abstract: The aim of the present work is to establish a bibliographical synthesis on the microstructure, the colloidal and rheological characterization of bentonite suspensions with and without polymer/surfactant addition; to lead to a rheological characterization of clay-additive mixtures and to understand the interaction between the clay particles and polymer/surfactants. Different experimental measurements: rheology, particle sizing, and x-ray diffraction were used to study the rheological character of the water-bentonite-anionic additive mixtures (CMC, SDS, xanthane) as well as the nature of the particle-particle interactions and particle-additive. The modeling part led to the adoption of Tiu and Boger's model to predict the thixotropy of the bentonite suspensions without additive. Thus, a new model is proposed with physical parameters for a better correlation of the rheological behavior of the various studied mixtures.
