Asymmetrical Hot Plate Research Articles

Thermal and mechanical properties of light-weight concrete utilizing Moroccan Pozzolan

Today, the poor adaptation of construction in Morocco to climatic conditions increases by 7% per year in demand for electricity. Hence the increase in demand for new, more energy-efficient buildings that are comfortable and environmentally friendly. In this study, new material was produced using natural pozzolan elaborated with concrete based on pozzolanic aggregates. For the thermal characterization, the asymmetrical hot plate method in a steady-state regim was applied. For the mechanical investigation, the flexural and the compressive strengths of developed samples are tested. The experimental results of dry thermal characteristics are interesting. Thermal conductivity of concrete samples is varied between 1.5 W m−1 K−1 and 0.78 W m−1 K−1. A sample of concrete with 40% of pozzolanic aggregate demonstrates optimum mechanical strength and heat conductivity.

Investigation on mechanical and thermal properties related to hygroscopicity of two African hardwoods

ABSTRACT This paper aims to study the mechanical, thermal and hygroscopic behavior of Okan (Cylicodiscus gabunensis) and Ayous (Triplochiton scleroxylon), two African hardwood species grown in southern Cameroon. The mechanical characterization of wood at 10%, 15%, 20%, 25% and 30% was investigated using tensile and bending tests. The thermal parameters were measured at the same moisture content levels by using the asymmetrical hot plate method. Sorption isotherms were obtained using the static gravimetric method. Mechanical properties decreased with moisture content. Okan wood, which Guitard and Brazilian models was not suitable for, presented very good properties compared to Ayous wood. Its flexural strength varied between 100 and 140 MPa and was 2.5 times higher than Ayous wood. Thermal conductivity increased with moisture content and was ranged from 0.1 to 0.56 W/mK. There was no significant difference between the radial thermal conductivities of the two species. The volumetric heat capacity was not influenced by the heat flow and the species. Experimental data showed a good fitting with the GAB model concerning sorption isotherms. Okan wood was less hygroscopic than Ayous wood. The annual equilibrium moisture content of the two species was determined and the cities of Bafoussam and Douala presented the best stabilization trend.

Influence of moisture content on the thermophysical properties of tropical wood species

The aim of this work was to investigate the thermal behavior of solid wood used as building materials. Three tropical wood species namely Iroko (Milicia excelsa), Bilinga (Nauclea diderrichii), and Tali (Erythrophleum suaveolens) were chosen. The thermophysical properties in the longitudinal, radial and tangential directions were determined experimentally for different moisture contents. Asymmetrical hot plate method was used to measure the thermal conductivity and volumetric heat capacity. The influence of water content and the direction of the fibers on thermophysical properties of the species studied were investigated. The results show that thermal conductivity and volumetric heat capacity increase with moisture content, while the diffusivity decreases. In the wide range of moisture content considered, thermal conductivities varied between 0.1 and 0.6 Wm−1 K−1. The increase of moisture content by 1% induces a 0.2% increase in thermal conductivity for Bilinga, 0.4% for Tali and 0.3% for Iroko. Tali, whose density is the highest, presented high values of thermal conductivity in longitudinal direction but lowest values in radial and tangential directions compared to other species. Thermal conductivity is 2 to 3 times higher in the longitudinal direction than in the radial and tangential directions. The volumetric heat capacity was not influenced by the direction of the heat flow.

Thermal characterization of a new multilayer building material based on clay, cork and cement mortar

Developing construction materials with high thermal performance will reduce significantly energy consumption of the building. This research aims to characterize thermal insulation of a new multilayer building material using the asymmetrical hot plate in transient and steady state regime. This material based on the composite clay-cork consolidated with an internal and external layer of cement mortar. A comparison of the experimental results with theoretical models of equivalent thermal conductivity is established. Finally, an evaluation of cost/ effectiveness ration and of thermal transmittance for multilayer developed material was done compared with a classic hollow clay brick.

Modelling and experimental determination of thermal properties of local wet building materials

One of the greatest challenges in the construction sector throughout the world is the development of appropriate building materials that can reduce energy consumption. In this work, an investigation on the thermophysical properties of three wet composite building materials was carried out: the black pouzzolan, the red pouzzolan and sand cinder blocks. Experimental measurements were carried out on these three materials each with a water contentranging between 0 and 5%.Using an asymmetrical hot plate device, a transient method, the thermal effusivity and volumetric heat capacity were estimated experimentally with respect to water content. With the values of the mass specific heat capacity of pouzzolans, sand and cement separately measured by the Differential Scanning Calorimeter (DSC) method, the values of the volumetric heat capacity of these composite materials were evaluated according to their water content calculated from the theoretical developed model. The results obtained are in good agreement with those determined experimentally with the asymmetrical hot plate method (maximum standard deviations 5%). Results reveal that the thermal conductivity of red pouzzolan cinder blocks (e.g. λ=0.503Wm−1K−1 at 0% water content) and of black pouzzolan cinder blocks (e.g. λ=0.549Wm−1K−1 at 0% water content) are lower than that of sand cinder blocks (e.g. λ=0.875Wm−1K−1 at 0% water content). Results also show that pouzzolans cinder blocks have higher volumetric heat capacity than sand cinder blocks. These results further confirm that blocks based on pouzzolans are better insulator materials than sand blocks (usually uses) and can contribute significantly to the energy saving and thus reduce the GHG emission in the air-conditioning building.

Modeling and estimation of the thermal properties of clusters aggregates for construction materials: The case of clusters aggregates of lateritic soil, sand and pouzzolan

Most of the composite materials are manufactured by mixing several aggregates such as sand, cement, gravel and others. The aim of this paper was to present a method dedicated to the determination of the thermal effusivity and porosity for building material that is in aggregates granular form. A transient asymmetrical hot plate device was constructed to characterize the thermal effusivity. Experimental measurement of the specific heat capacity using the Differential Scanning Calorimeter (DSC) and measurement of apparent density enabled the estimation of the volumetric heat capacity of the aggregates. With these values and that of the thermal effusivity pre-estimated using the simplified 1D model, the study of the reduced sensitivity of the experimental temperature to parameter Eag and ρCag and ρCh is carried out. The thermal effusivity is then estimated from a complete 1D model by minimization of the quadratics errors between the experimental temperature curve and simulated one. Experimental results applied on clusters with maximum diameter aggregates 1.6mm; 1mm; 0.8mm, 0.4mm and 0.2mm show that for the same diameter, the black pouzzolan have higher thermal effusivity and thermal conductivity than the red pouzzolan (e.g. for D=1mm, EBPZ=418Jm-2K-1s-1/2, λBPZ=0.166Wm-1K-1, ERPZ=418Jm-2K-1s-1/2, λRPZ=0.135Wm-1K-1). Pouzzolan has the smaller value of porosity and lateritic the greater one.

Thermal Inertia and Thermal Properties of the Composite Material Clay-plastic

Improving insulation building materials with low energy consumption becomes an obligation so as to reduce the heat energy of houses. For this purpose, a series of experimental studies were performed on composite clay-plastic. The first step in this study is the chemical characterization of clay using the fluorescence X method. The second step is thermal characterization of clay alone and the composites clay-plastic using the asymmetrical hot plate and Flash methods. The third step in the work is the verification of thermal conductivity using different theoretical models. The fourth step in this study is the study of thermal Inertia of walls done from the composite clay-plastic. Finally a study of delay of temperature, heat flow and damping factor for a wall done from those composites were conducted. The obtained results indicate that this composite presents interesting characteristics in term of insulation and thermal Inertia.

Modeling and measuring of the thermal properties of insulating vegetable fibers by the asymmetrical hot plate method and the radial flux method: Kapok, coconut, groundnut shell fiber and rattan

This article presents two methods dedicated to the determination of the thermophysical properties of natural fibers grown in almost all countries of the world. Experimental measurements were carried out on four dry natural plant fibers of low density: kapok fibers; groundnut shell fibers; rattan fiber and coconut fibers. The thermal effusivity has been estimated by a transient method (the asymmetrical hot plate method). With experimental measurement of the specific heat capacity by Differential Scanning Calorimeter (DCS) which made it possible to deduce the thermal conductivity of such fibers. The thermal properties estimated by this method are then compared to the results obtained by radial flux flow method, a steady state method that directly measures the thermal conductivity. The experimental results compared by these two methods are in good agreement (relative error<5%). The thermal conductivities of kapok fibers (λ=0.045Wm−1K−1) and coconut fibers (λ=0.055Wm−1K−1) obtained all showing that they can be used as substitutes for synthetic insulating materials such as polyester fibers (λ=0.045Wm−1K−1) or glass wool (λ=0.04Wm−1K−1). Also the thermal conductivities of kapok and coconut fiber measured correspond with the results obtained by other measuring methods in the literature. This can then help us infer that the quadrupole 1D model developed to estimate the thermal properties of bulk fiber is valid and can allow a good estimation of thermo-physical properties. Therefore, the thermal conductivity of groundnut shell fibers and cane fibers is estimated in the order of λ=0.093Wm−1K−1 and λ=0.072Wm−1K−1 respectively.

Experimental Approach of Measuring Thermal Properties for Ecological Materials Based on Additives Cork or Wool and Illite

This work is a contribution to understand the thermal properties of Illite with ecological additives granular presented by cork or fiber by wool in order to use those composites in building construction, the composites are air dried. Knowing that the clay composites were studied before, a series of experimental studies confirmed by complete theoretical models were conducted using different methods such as the asymmetrical hot plate in transient, steady-state regime, and flash methods in order to determine the thermal properties of the composite clay with ecological additives. Also, an analysis of sensibility of thermal properties was studied. For this purpose, a thermal characterization using hot plate and flash methods confirmed by complete theoretical models was studied. Then an analysis of the physicochemical characterization of clay was done to determine its characteristics. Finally, a study of depth heat flow diffusion was conducted to see the effect of additives on penetrating exterior heat flow inside house.

Thermal inertia and thermal properties of the composite material clay–wool

Developing ecological insulation of unfired building materials will not only reduce energy consumption of bill houses but will assure also sustainability, especially for Bensmim region which is a poor area, cold and the main activity of its inhabitant is the elevation of sheep, so the wool is a very abundant and affordable material. For this purpose, a series of experimental studies were performed on the composite clay–wool in different percentage of wool. The first step in this work is the physic-chemical characterization of clay using the fluorescence X method. The second step is the thermal characterization of clay alone and the composite clay–wool using the asymmetrical hot plate and flash methods. The third step in the work is the verification of thermal conductivity using different theoretical models. The fourth step in this work is the study of thermal Inertia of different wall's thickness of the materials: clay, clay–3%wool and clay–5%wool. By asserting all of the depth of heat flow diffusion, the delay of temperatures, the delay of heat flow density and the damping factor for different wall's thickness for the three materials. The obtained results indicate that those developed composites show off interesting characteristics in term of insulation and thermal Inertia. Those results attend above 11h of delay on (temperature, heat flow density), 0.27 of damping factor and 0.19Wm−1k−1 of thermal conductivity. Also, a comparison of heating energy need was conducted to a whole building model demonstrating that the composite clay–wool presents the best energy efficiency of envelope building.

Measurement and modelisation of the thermal conductivity of a wet composite porous medium: Laterite based bricks with millet waste additive

Millet waste is traditionally and empirically mixed with laterite for bricks fabrication in Sahelian countries, particularly in Senegal. The aim of this paper was to characterize the thermal conductivity of these bricks as a function of their water and millet contents. Samples having five different millet mass contents Y (from 0 to 0.122kgmikgla−1) with dimensions 10×10×3cm3 were first fabricated. An original asymmetrical hot plate device was developed and modeled to measure the thermal conductivity of these samples, with their water content varying from 0 to a maximum value of 0.1kgwkgdm−1. An adapted device was developed to prevent water evaporation on the lateral faces of the samples. A new model based on a physical approach of the repartition of air and water inside the solid structure was built. It leads to a more accurate representation than other classical models of the measured variations of the thermal conductivity with the water and millet contents.

Water content dependence of the porosity, density and thermal capacity of laterite based bricks with millet waste additive

Millet waste is traditionally and empirically mixed with laterite for bricks fabrication in Sahelian countries, particularly in Senegal. The aim of this paper was to characterize the porosity, the density and the thermal capacities of these bricks as a function of their water and millet contents. Samples having five different millet mass contents Y (from 0 to 0.122kgmikgla-1) with dimensions 10×10×3cm3 were first fabricated. A pycnometer suited to the samples dimensions was constructed and calibrated. Then, it was used to measure the porosity of the five dried samples. An asymmetrical hot plate device was used to measure the thermal capacity of these samples with their water content varying from 0 to a maximum value of 0.1kgdmkgw-1. An adapted device was developed to prevent water evaporation on the lateral faces of the samples. Both density and thermal capacity were modeled and the experimental results were processed to evaluate separately the density and the thermal capacity of laterite and of millet. The models enabling the estimation of the density and of the thermal capacity of the samples as a function of the millet and water contents was found to be in good agreement with the experimental results.