Search

We present here some elements in order to improve the non-destructive procedures for the measurement of the local heat transfer coefficient between a plate uniformly heated and an air-flow. We use the pulsed photothermal method which consists of analysing the transient temperature on the front face of a wall, initially subjected to a convective flow, after a sudden deposit of luminous energy. For the examination of the experimental thermograms, two models are used: in the first one the heat coefficient is assumed to remain constant during the pulsed experiment, and we take into account its variation in time in the second one. The temporal variation law of the heat transfer coefficient used in the second model is obtained by extension of the differential method to the unsteady laminar boundary-layer due to a finite duration excitation. We compare the results of the two models in transient state with those given in steady state by multi-layered heat flux sensor. [Copyright &y& Elsevier]

In the present paper a numerical study of natural turbulent convection in a tall cavity filled with nanofluids. The cavity has a heat source embedded on its bottom wall, while the left, right, and top walls of the cavity are maintained at a relatively low temperature. The working fluid is a water based nanofluid having three nanoparticle types: aluminum, Cu, and CuO. The influence of pertinent parameters such as Rayleigh number, the type of nanofluid, and solid volume fraction of nanoparticles on the cooling performance is studied. Steady forms of 2-D Reynolds- аveraged-Navier-Stokes equations and conservation equations of mass and energy, coupled with the Boussinesq approximation, are solved by the control volume based discretisation method employing the SIMPLE algorithm for pressurevelocity coupling. Turbulence is modeled using the standard k-ε model. The Rayleigh number is varied from 2.491009 to 2.491011. The volume fractions of nanoparticles were varied in the interval 0 ≤ φ ≤ 6%. Stream lines, isotherms, velocity profiles, and temperature profiles are presented for various combinations of Rayleigh number, the type of nanofluid, and solid volume fraction of nanoparticles. The results are reported in the form of average Nusselt number on the heated wall. It is shown that for all values of Rayleigh number, the average heat transfer rate from the heat source increases almost linearly, and monotonically as the solid volume fraction increases. Finally, the average heat transfer rate takes on values that decrease according to the ordering Cu, CuO, and Al2O3. [ABSTRACT FROM AUTHOR]

The use of natural resources in composite materials becomes more frequently, as they are low-cost and lightweight materials. In addition, industrial trends tend towards Eco-products, hence the importance of integrating natural products that are recyclable and easily degradable. Aim of this study is prepared polymer composites of polyvinyl chloride (PVC) using palm fibers at different loading (10 and 30 % by weight). Improving the interfacial adhesion between matrix- filler interfaces using chemical modification of date palm fibers (DPF) by two types of treatments (acetylation, alkali). The effect of chemical treatment and fiber content on morphological, thermal, mechanical and water absorption properties of composites have been studies. It was found that the use of treated fibers in PVC composites improves the mechanical properties and decomposition temperature, and reduce water absorption of the composites. [ABSTRACT FROM AUTHOR]

This article deals with the influence of both morphology and amount of Typha on hygrothermal behavior of a Typha–clay composite for building application. An agromaterial containing the fiber mix of Typha Australis and clay was made in three samples: three fiber mixtures were prepared with different amounts Typha and cut type (transversal or longitudinal). The physical properties of these materials were studied in terms of porosity, apparent and absolute density, thermal conductivity, and hygric properties. Results show a real impact of the Typha fraction type and its volume content on hygrothermal properties of the studied material due to the porosity. The transversal fraction of Typha (80% in volume weight) seems to be the optimal composition for a better hygrothermal behavior. [ABSTRACT FROM AUTHOR]

This paper presents a study on energy performance of an earth air heat exchanger (EAHE) for buildings in Maghreb climatic context (Oran, Bechar and Adrar cities in Algeria). In order to check the influence of the material, two air conducts (one of galvanized sheet metal and the other in polyvinyl chloride–PVC) are considered under the same geometric conditions (a 20 m conduct length, 120 mm diameter and 2 m burial depth). They are used separately for the ventilation in simple current flow of two adjoining rooms constituting a test cell located at the university campus IGCMO-USTOMB (Oran, Algeria). An experimental device has been set up to measure the temperature at different points (air inlet/outlet air duct). Measurements were run in August 2015, and the monitoring of both exchangers allowed us to evaluate their cooling performance: 35.41% for the Zinc pipe and 58.42% for the PVC pipe. Experimental results were compared to those obtained from the simulation (under the Trnsys 16) and a fair similarity is obtained. In order to optimize the energy performance of the exchanger (EAHE), numerical simulations are carried out by varying different parameters: climate, burial depth, length and diameter of the duct. Other simulations have shown that the energy supplied by the cooling exchanger (EAHE) is more significant in the south of the country (Adrar and Bechar) than in the north (Oran). [ABSTRACT FROM AUTHOR]