This work deals with the influence of envelope thickness and solar absorption on the time lag and the decrement factor. For this, a test cell of 1 m3 of volume is built with a material commonly used in construction in Senegal, the compressed earth brick stabilized with cement. The ambient-air temperature inside and outside of test cell and solar direct normal irradiance is measured. The test cell is modeled using EnergyPlus software. The comparison of experimental and theoretical ambient-air temperature puts out a great linear showing the reliability of the model. The time lag and the decrement factor are calculated using the air-sol equivalent temperature of the test cell and the inside ambient-air temperature. The time lag and decrement factor of the compressed stabilized earth brick envelope are respectively 0.22 and 6.6 h showing the good thermal inertia of those bricks. A parametric study is performed to determine the effect of envelope thickness and solar absorptivity on the time lag and decrement factor. The results show that the decrement factor decreases with envelope thickness while the time lag increases linearly and that an envelope thickness of 32 cm has a decrement factor of around zero with a maximum time lag of about 12 h for this type of material. The envelope’s solar absorption has a moderate effect on the decrement factor and time lag.
Sun-drying is the oldest way to preserve, store and also to enhance the value of our agricultural production. Nowadays, several types of dryers have been developed but the greenhouse is an ideal solution for drying in our tropical countries because the sun is abundant. But the control of the greenhouse climate depends on several factors, namely the external climatic conditions but also the type of materials used in the greenhouse. The study was carried out in a greenhouse, tested under the climatic conditions of Dakar. It is in this context of sustainable development that this work, whose objective is to contribute to the improvement of drying conditions for agricultural products, is carried out and to achieve this, the distribution of temperatures and speeds in the greenhouse must be determined. For the three-dimensional CFD simulation, we added a discrete radiation model to solve the radiation transfer equation and the Solar Load Model which gives the position of the sun and its radiation. The simulated air temperatures give an average of 52.8°C with average air velocities that are around 0.114 m/s in the closed greenhouse and the results found can be used to improve the design and control of the greenhouse climate.
Sun drying is the oldest way to preserve but also to valorize and store surplus agricultural production. Nowadays, several types of dryers have been developed, but the solar greenhouse dryer is an ideal solution in our tropical countries because of its implicit and higher load capacity. The greenhouse climate depends on several factors, namely the outdoor climatic conditions (air temperature, wind speed, radiation, etc.) but also on the type of materials used to cover the greenhouse. The study was carried out on a parabolic greenhouse covered by a polyethylene film with a concrete base (absorber) which in turn is placed on the ground and will be tested under the climatic conditions of Dakar, Senegal. It is in this context of sustainable development that this work is carried out. The goal is to determine the distribution of temperatures and wind speeds in the greenhouse. The simulation was carried out using the three-dimensional computer fluid dynamics software (CFD). The turbulence method (k-ε) was used and to solve the radiation transfer equation (RTE) we introduce the discrete ordered method DO. We also add the “Solar Load Model” which gives the position of the sun and its radiations in relation to the layout of the greenhouse according to the date and time of the simulation. The simulation is carried out in a closed greenhouse and the results found can be used to improve the design and control of the greenhouse climate. Air temperatures and velocities simulation give an average of 325.95 K and 0.114 m/s respectively.
This study contributes to the valorization of typha as local materials of building for thermal insulation. We will examine the influence of the binder content and granulometry on the mechanical and thermal properties of typha -clay panels. The plant of typha is used in different granulometries such as powdered typha and defibrated typha. The results showed that compressive strength, thermal conductivity and effusivity depend on the particle size of the typha and also the binder. The panels of defibrated typha have a better thermal insulation performance (0.085 W.m -1 .K -1 for 66.66%), which is comparable with many of natural insulating materials. The panels also have low thermal effusivities which show that they have low thermal inertia.
New composite boards with low-thermal conductivity produced from a mixture of powder Typha leaves and a binder as gum arabic have been developed. The goal of this paper was to investigate the effect of binder content on compressive strength and thermal properties of typha panels. The results showed that the panels with a binder content of 33.33-50 % had the thermal conductivity values ranging from 0.055 to 0.083 W.m-1 .K-1 , which was close to that of many natural insulating materials. The compressive strength values obtained were comparable to those of the limehemp concrete. This study showed that typha possesses interesting capacities of insulating and its combination with gum arabic contributes to the improvement of thermal comfort, to the reduction of the energy consumption as well as to the emissions of CO2.
Earth is the main raw material most used in building construction in Africa and particularly in Senegal. It is a particularly malleable material, easy to handle, from which hard bricks (unfired or fired) can be made. Thus for a good prediction of the mechanical and thermal behavior of a material, it is important to determine its hygroscopic properties. This is why our study focuses on the hygroscopic characterization of earth materials based on laterite and clay. We are mainly interested in the study of adsorption and desorption isotherms by water vapor. The adsorption and desorption isotherm curves of the samples were determined by a volumetric method using the Belsorp Aqua3 apparatus. The measurement results showed that the earth materials are hygroscopic materials. Furthermore, unfired earth materials adsorb more moisture than fired earth materials.
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