Heats for combustion, capacities, and evaporation of fresh leaves, and their relationships to leaf compositions

Abstract

Fundamental thermal properties of fresh leaves that are essential to CFD modeling of leaf pyrolysis and flammability are related to leaf composition and moisture content. The focus of this paper is on measuring and providing functional relationships for the heat of combustion, specific heat capacity, and heat of moisture desorption for fresh leaves as they vary with moisture content and composition. With the leaves typically being within a fraction of a millimeter thick and having internal structures of petiole, veins, and blades filled with active living moisture and organic compositions that can also naturally degrade, specialized methods of thermal measurements were required. Heats of combustion were derived from leaf elemental formula for each leaf based on composition from ultimate analysis testing and an in-depth composition analysis for several fresh leaf varieties. Heat capacity was derived for the cut up and dried fresh leaves as function of temperature and corrected for mass loss during pyrolysis up to 440°C utilizing a modulated Differential Scanning Calorimeter (DSC) and high resolution Thermogravimetric Analysis (TGA). Heat of evaporation was derived from the isoteric thermodynamic relationship with the leaf moisture desorption process obtained from a modern water activity meter with precise temperature and water activity measurements. The composition of a dozen and wide variety of leaf species from pine forests in the southern U.S. were recently determined for their content broken down into the following categories: lipid, fructose, glucose, protein, pectin, hemicellulose, starch, cellulose, phenols, lignin, and minerals. This summative analysis was recently completed and is currently being documented.

Citation

Dietenberger, Mark A.; Boardman, Charles R.; Weise, David R. 2019. Heats for combustion, capacities, and evaporation of fresh leaves, and their relationships to leaf compositions. In: Proceedings, 6th international fire behavior and fuels conference. Missoula, MT: International Association of Wildland Fire. 6 p.