Estimates of Thermal Diffusivity and Heat Flow of a Soil in Agreste Pernambucano

Abstract

Conhecer as características térmicas do solo é de fundamental importância para entendimento de seus processos físicos. Este trabalho objetivou estimar o fluxo de calor do solo através da lei de Fourier para o transporte de calor e a difusividade térmica do solo utilizando seis métodos (fase, amplitude, logaritmo, condução-convecção, arco tangente e diferenças finitas) em um solo do agreste Pernambucano. Para isto, foram medidas temperaturas nas profundidades de 0,02; 0,08; 0,10; 0,20; 0,30; 0,40; 0,50 m por meio de termopares ao longo dos primeiros dez dias do ano. A eficácia dos métodos foi comprovada por meio de simulações do perfil de temperatura do solo onde os algoritmos arco tangente e condução-convecção apresentaram os melhores resultados e parâmetros estatísticos, enquanto o método das diferenças finitas destoou dos demais. Estimativas do fluxo de calor foram realizadas a partir das condições de fronteira dos dados medidos. Os melhores resultados ocorreram nas camadas superficiais, enquanto que os valores estimados não apresentaram resultados satisfatórios nas camadas mais profundas. Palavras-chave: temperatura do solo, capacidade térmica do solo, condutividade térmica no solo. Estimates of Thermal Diffusivity and Heat Flow of a Soil in Agreste Pernambucano A B S T R A C T Knowing the thermal characteristics of the soil is of fundamental importance for understanding their physical processes. This study aimed to determine soil heat flux through the Fourier's law for the transport of heat and thermal diffusivity of the soil using six methods (phase, amplitude logarithm conduction-convection, and finite differences arctangent) in a soil wild Pernambucano. For this, temperatures were measured at depths of 0.02; 0.08; 0.10; 0.20; 0.30; 0.40; 0.50 m by means of thermocouples during the first ten days of the year. The effectiveness of the methods has been proven through the soil temperature profile simulations where the algorithms arc tangent and driving-convection showed the best results and statistical parameters, while the finite difference method disagreed when compared the other. Heat flux estimates were made from the boundary conditions of the measured data. The best results observed in the surface layers, while the estimated values did not show satisfactory results in deeper layers.

Determinação da Difusividade Térmica de um Solo Multicamadas Através do Algoritmo Condução-Convecção (Determination of the Thermal Diffusivity of a Multi-layered Soil Through a Conduction-Convection Algorithm)

“…Soares et al (2014) compared six (6) methodologies to determine the diffusivity, where the conduction-convection method presented good results. In a study by Oliveira et al (2015), this algorithm more accurately represented the temperature profile before the others, for soil types similar to the one studied in this study.…”

“…The indicators showed that the simulations were very close to the one analyzed in the field. In comparison with the study carried out by Oliveira et al (2015), it is possible to observe the evolution of the simulations, when the thermal diffusivity of each layer is taken into account, and the method used has performed better than the others.…”

“…The method of conductionconvection (Gao et al, 2003) was used to determine the diffusivity during the soil stratification, and for obtaining coherent results (Oliveira et al, 2015). The temperature of the soil surface can be represented by a sine wave, described in:…”

“…To study other thermodynamic parameters associated with diffusivity, Kun and JieMin (2008) showed the direct dependence of the heat flux and the depth investigated for thermal energy of solar origin. Soares et al (2014) and Oliveira et al (2015) used six methodologies to calculate thermal diffusivity, highlighting in both studies the conduction-convection methodology. These algorithms are very attractive, since only temperature measurements are required.…”