An Experimental Study of the Drying of Papayes by Solar Panels

One of the major problems concerning the use of solar panels for heating is the low level of thermal interchange with air in the dynamic vein of the solar panel. This weakness in such systems does not enable an optimum performance or high level of thermal efficiency to be obtained from their use. There is, however, a very noticeable improvement to thermal transfer when baffles are placed in rows in the ducts. To conduct the experiments, solar energy was simulated, the aim being to improve the ratio between temperature and thermal efficiency of an air heating plane solar panel and to make use of the system to reduce the drying time of papayes

Real-time evaluation of the concentration of impurities during organic solution crystallization

International audienceATR FTIR spectroscopy was previously presented as a promising technique for measuring supersaturation on-line during crystallization operations, without requiring complex hardware developments. The present paper reports new experimental results where, in addition to the determination of the concentration of the main dissolved product, the real-time measurement of the concentration of impurities is shown to be feasible before the onset of primary nucleation. Using spectral data obtained with both clear solutions and suspensions, the calibration of the in situ infrared sensor was performed to relate the time variations of the concentrations of the main product and of its main impurity, in the presence of both pH and temperature variations. As far as the on-line monitoring of crystallizing slurries is concerned, it is shown that measuring the concentration of impurities is very difficult to perform. However, the quantitative evaluation of impurities present in the clear solution feeding the crystallizer is valuable and expected to allow further design of monitoring and control policies leading to the reduction of batch-to-batch variations of the final quality of the solid produced

Comportamento compressivo de um nitossolo: efeito do tamanho de agregados, do teor de água e da pressão aplicada Compression behaviour of a clay soil: effects of aggregate size, water content and applied pressure

A compactação do solo tem sido assunto de intensivas pesquisas nos últimos anos; no entanto, os mecanismos que implicam o processo de compactação dos solos agrícolas, ainda permanecem pouco conhecidos. A contribuição do tamanho de agregados do solo, bem como o efeito do teor de água e da pressão normal aplicada na compactação e pressão de pré-compactação do solo, foi investigada em um Nitossolo Vermelho eutrófico. Amostras de solo deformado, constituídas por agregados menores que 2,5 mm e de 9,3 a 19,4 mm, foram submetidas a ensaio de compressão uniaxial drenado. O índice de vazios e a pressão de pré-compactação foram avaliados. Os resultados obtidos mostram que o tamanho de agregados teve efeito no processo de compactação do solo. A mudança da compactação do solo pode ser prevista em função do estado inicial do solo, da pressão aplicada e do teor de água.<br>Soil compaction has been the subject of intensive researches in the last ten years, but the mechanisms involved in the soil compaction process remain a little known. The contribution of aggregate size of the soil as well as the effect of water content and normal pressure applied on soil compaction and pressure of pre-compaction were investigated in a Clay soil during this trial. Disturbed soil samples constituted by aggregates less than 2.5 mm and 9.3 to 19.4 mm were submitted to a drained compression uniaxial test. The void ratio and the pre-compaction pressure were also evaluated. The results obtained show that the size of the aggregates had effect on the process of soil compaction. The change of soil compaction can be predicted according to the initial state of soil, the applied pressure and the water content of the soil

Mass transfer inside oblate spheroidal solids: modelling and simulation

A numerical solution of the unsteady diffusion equation describing mass transfer inside oblate spheroids, considering a constant diffusion coefficient and the convective boundary condition, is presented. The diffusion equation written in the oblate spheroidal coordinate system was used for a two-dimensional case. The finite-volume method was employed to discretize the basic equation. The linear equation set was solved iteratively using the Gauss-Seidel method. As applications, the effects of the Fourier number, the Biot number and the aspect ratio of the body on the drying rate and moisture content during the process are presented. To validate the methodology, results obtained in this work are compared with analytical results of the moisture content encountered in the literature and good agreement was obtained. The results show that the model is consistent and it may be used to solve cases such as those that include disks and spheres and/or those with variable properties with small modifications