The flash method is the most used technique to measure the thermal diffusivity of solid samples. It consists of heating the front face of an opaque slab by a short light pulse and detecting the temperature evolution at its rear surface, from which the thermal diffusivity is obtained. In this paper, we extend the classical flash method to be used with rods, tubes, and spheres. First, the temperature evolution of the back surface of solid cylinders, hollow cylinders, and spheres is calculated. Then, experimental measurements of the thermal diffusivity on a set of stainless steel samples confirm the validity of the method.

In this article, the solution of the periodic temperature fluctuation of an opaque material with buried spheres as a result of a modulated illumination is presented. The model includes the multiple scattering of the plane thermal wave, generated at the sample surface, when interacting with the spheres and with the sample surfaces. A series solution to the heat diffusion equation and a matrix formulation to solve the scattering coefficients are used. The solution is general in the sense that there are neither restrictions on the number of spheres, their size, and position inside the material nor on the thermal properties of spheres and sample. Measurements on calibrated samples using an infrared radiometric microscope validate our model. This theory is specially suited to the thermal characterization and nondestructive evaluation of particulate composites using photothermal techniques.

Abstract:The aim of this research is to identify, quantify and characterize the potential available forest biomass of Pinus radiata D. Don and Eucalyptus globulus Labill. across Biscay province in northern Spain. In order to do this, we have used information from the National Inventories of Spain to quantify the amount of carbon dioxide accumulated in the forests of Biscay by means of stratum-species-based forestry statistics. The total biomass and biomass fractions have been estimated using two different methods: allometric biomass equations (ABE) and biomass expansion factors (BEF). The second objective is to develop a methodology to quantify and produce a cartography of the prospective energy production of residual biomass from the most representative forest species of Biscay. For this purpose, we have used a Geographic Information System (GIS) computer tool. We have found that the stock of carbon accumulated in the main forest species in Biscay in 2014 amounts to 8.2 Tg (ABE) and 6.63 Tg (BEF) equivalent to 30 and 24.3 Tg of CO 2 , respectively. The quantity of forestry biomass residue (FBR) obtained has been estimated as 52,214 Mg·year −1 dry matter. This amount means a prospective energy supply of 947,000 GJ·year −1 .