Explaining the heat capacity of wood constituents by molecular vibrations

Abstract

The heat capacity of wood and its constituents is important for the correct evaluation of many of their thermodynamic properties, including heat exchange involved in sorption of water. In this study, the dry state heat capacity of cellulose, hemicelluloses and lignin are mathematically described by fundamental physical theories relating heat capacity with molecular vibrations. Based on knowledge about chemical structure and molecular vibrations derived from infrared and Raman spectroscopy, heat capacities are calculated and compared with experimental data from literature for a range of bio-and wood polymers in the temperature range 5-370 K. A very close correspondence between experimental and calculated results is observed, illustrating the possibility of linking macroscopic thermodynamic properties with their physical nano-scale origin.

Computational study of the effects of density, fuel content, and moisture content on smoldering propagation of cellulose and hemicellulose mixtures

“…where γ is the parameter controlling the radiation heat transfer across pores [7,13,22]. The pore diameter (d p ), permeability (K), and the parameter controlling the radiation heat transfer across pores (γ) are calculated using equations 6 (17), (18), and (19), respectively, which were obtained from [7,22,23]:…”

“…The bulk density of the mixture in this model (ρ mix ) is calculated by taking into account the bulk density of cellulose and hemicellulose before mixing and mass fraction of those species (Y i ) in the mixture: Porosity (ψ i ) and effective thermal conductivity (k i ) are calculated using 3 , respectively, where γ is the parameter controlling the radiation heat transfer across pores [7,13,22]. The pore diameter (d p ), permeability (K), and the parameter controlling the radiation heat transfer across pores (γ) are calculated using equations ( 17), (18), and (19), respectively, which were obtained from [7,22,23]:…”

Smouldering combustion in cellulose and hemicellulose mixtures: Examining the roles of density, fuel composition, oxygen concentration, and moisture content

“…Table 2. Thermophysical properties of condensed-phase species, taken from the literature for water [10], cellulose [34], hemicellulose [35][36][37], char [10,38], and ash [10,38]. The effective thermal conductivity of a condensed-phase species is calculated using…”

Enhanced High Thermal Conductivity Cellulose Filaments via Hydrodynamic Focusing

“…The experimental results in Figure show that the thermal conductivity of filaments with higher CI increases steeply with the temperature up to 300 K. The thermal conductivity of filaments with lower CI also increases with a similar slope until 240 K, but then saturates to a constant value until 300 K. Based on the above discussion of the temperature dependence of thermal conductivity, the steep increase in thermal conductivity is due to the contribution of C i (ω) in eq , and the flattening observed for filaments with low CI is due to fewer and weaker interfibril bonds, which reduce the effective Debye temperature. The peaking or flattening temperatures in both cases are higher than that of polyethylene crystalline nanofibers owing to the high Debye temperature of bulk cellulose materials . For instance, the Debye temperature of cotton and wood cellulose is reported to be approximately 920 K, which is significantly higher than the Debye temperature of polyethylene (400 K) .…”

“…The peaking or flattening temperatures in both cases are higher than that of polyethylene crystalline nanofibers owing to the high Debye temperature of bulk cellulose materials . For instance, the Debye temperature of cotton and wood cellulose is reported to be approximately 920 K, which is significantly higher than the Debye temperature of polyethylene (400 K) . Debye temperature increases with enhanced interatomic force constant and lattice orderliness for materials with the same composition.…”