Thermophysical Properties of Baled Switchgrass

Abstract

HighlightsThermal conductivity and thermal diffusivity of baled switchgrass were measured with a dual thermal probe.Specific heat of baled switchgrass was estimated based on other thermophysical parameters.Thermophysical parameters were modeled as functions of the material properties using multiple regression.Anisotropism was observed with different heat transfer rates occurring in each directional orientation.Abstract.Although the thermophysical properties of baled biomass play a critical role in developing postharvest quality models, these parameters have not been investigated for many bulk agricultural feedstocks including switchgrass. In this study, a dual thermal probe, consisting of a thermal conductivity probe and separate thermal diffusivity probe, was used to determine the thermal conductivity, thermal diffusivity, and specific heat of lab-scale rectangular bales of switchgrass (~10.16 × 10.16 × 30.48 cm). Thermal conductivity, thermal diffusivity, and specific heat ranged from 1.04E-2 to 6.10E-2 W m-1 °C-1, 0.863E-7 to 2.284E-7 m2 s-1, and 0.40 to 2.51 kJ kg-1 °C-1, respectively, depending on temperature (20.3°C, 30.2°C, and 40.1°C), moisture content (11.4%, 20.8%, 29.0%, and 42.3% on a wet basis), bulk density (157.2, 172.4, 197.2, and 230.1 kg m-3) and directional orientation (lateral or transverse). The results of this study promote a practical understanding of heat transfer within baled switchgrass while defining the dynamic relationship to material properties through multiple regression analysis. Anisotropism between the lateral and transverse bale orientations was observed with different heat transfer rates observed in both directional orientations. This anisotropism was attributed to the unique physical composition of the bulk material in the axial direction of bale compression (i.e., variation in porosity, discontinuous porous cavities, and material heterogeneity) compared to the composition of continuous stem material forming a layered flake of the rectangular bale. Keywords: Biomass, Bioprocessing, High solids, Thermal conductivity, Thermal diffusivity.