Search

Converting solar energy efficiently into hydrogen is a promising way for renewable fuels technology. However, high-temperature heat transfer enhancement of solar thermochemical process is still a pertinent challenge for solar energy conversion into fuels. In this paper, high-temperature heat transfer enhancement accounting for radiation, conduction, and convection heat transfer in porous-medium reactor filled with application in hydrogen generation has been investigated. NiFe-Aluminate porous media is synthesized and used as solar radiant absorber and redox material. Experiments combined with numerical models are performed for analyzing thermal characteristics and chemical changes in solar receiver. The reacting medium is most heated by radiation heat transfer and higher temperature distribution is observed in the region exposed to high radiation heat flux. Heat distribution, O2 and H2 yield in the reacting medium are facilitated by convective reactive gas moving through the medium's pores. The temperature gradient caused by thermal transition at fluid-solid interface could be more decreased as much as the reaction chamber can store the transferred high-temperature heat flux. However, thermal losses due to radiation flux lost at the quartz glass are obviously inevitable.

Thermal reduction of the partial oxidation of CH4 NiFe2O4 followed by oxidation with H2O and CO2 was numerically investigated for H2 and CO production. P1 radiation model was used to account for radiative heat transfer. The synergistic effect of the reactivity of Fe/Ni exhibited a very promising strategy for producing 45% of syngas with 2.54 ratios of H2:CO at the first step and 55% of syngas with 2.34 ratios of H2:CO at the second step. The increase in incident radiation heat flux to 437.69 kW/m2 resulted in higher reduction kinetics of species conversion until the formation of oxygen carriers consisting of 65% of FeO, 35% of Ni Fe and 2.6% of carbon deposition. However, during the reduction process, the decrease in total pressure to 0.05 MPa enhanced the species reactivity and the production of H2 and CO while minimizing carbon deposition. Moreover, the oxidation temperature, operating pressure and the concentration of oxidizing species have strong impacts on the oxidation kinetics. Unlike high thermal reduction process, increasing the total pressure to 1 MPa has favorable effects on syngas production at oxidation step.

International audience; This paper presents a study of the hot plate method with two simultaneous temperature measurements, on the heated and unheated faces of a sample to characterize. The thermal properties of polyvinyl chloride, plaster and laterite were considered to be a representative range of building materials. A 1D quadrupolar model was developed to represent the temperature evolution on the two faces over time. Three-dimensional numerical modeling of a quarter of the testing device with COMSOL software allowed defining the domain of the 1D hypothesis validity. The analysis of estimation possibilities of materials’ thermal characteristics, with the developed method, revealed that thermal effusivity can be accurately estimated by using the temperature of the heated face at the beginning of heating. We showed that the simultaneous use of two temperatures enables the estimation of the thermal conductivity with a greater accuracy and over a shorter time interval than using the temperature of the heated face alone. We also demonstrated that under certain conditions (samples with a high ratio of thickness to width) the method with two temperature measurements enabled the estimation of the thermal effusivity and conductivity, while the method with one temperature allowed only the thermal effusivity to be estimated, because of 3D effects. This conclusion was confirmed by experimental results obtained with a mortar sample.

International audience; This paper dealed with the valorization of Benin natural resources through the development of new composite materials made of banana fibers-cement mortar which could be used as thermal insulator in building. The developed composites were formulated and made by substituting a mix of sand and cement, in mass fractions, with the banana trunk fibers previously washed with hot water and dried. Cement was dosed at 250 kg m-3 of mortar and the ratio W/C was equal to 0.7 for the samples. The effected thermal tests by the hot plate method using two temperature measurements had shown a decreasing of the thermal effusivity and conductivity when the proportion of fibers increased. One had obtained the respective relative deviations of 25.54%, 56.09% and 65.68% between the thermal conductivity of the reference sample, which was equal to 1.14 W m-1 K-1, and that of the composites. These results made the composites interesting thermal insulators in building with reduction of the normally used quantity of cement and sand and valorization of agricultural waste. The water absorption was also calculated for each sample.