Heat Transfer in Straw-Based Thermal Insulating Materials

Abstract

An analytic-empirical model was developed to describe the heat transfer process in raw straw bulks based on laboratory experiments for calculating the thermal performance of straw-based walls and thermal insulations. During the tests, two different types of straw were investigated. The first was barley, which we used to compose our model and identify the influencing model parameters, and the second was wheat straw, which was used only for validation. Both straws were tested in their raw, natural bulks without any modification except drying. We tested the thermal conductivity of the materials in a bulk density range between 80 and 180 kg/m3 as well as the stem density, material density, cellulose content, and porosity. The proposed model considers the raw straw stems as natural composites that contain different solids and gas phases that are connected in parallel to each other. We identified and separated the following thermal conductivity factors: solid conduction, gas conduction in stem bulks with conduction factors for pore gas, void gas, and gaps among stems, as well as radiation. These factors are affected by the type of straw and their bulk density. Therefore, we introduced empirical flatness and reverse flatness factors to our model, describing the relationship between heat conduction in stems and voids to bulk density using the geometric parameters of undisturbed and compressed stems. After the validation, our model achieved good agreement with the measured thermal conductivities. As an additional outcome of our research, the optimal bulk densities of two different straw types were found to be similar at 120 kg/m3.

Estimation of Thermal Properties of Straw-Based Insulating Panels

“…The density increase above 60 kg/m 3 caused a gradual and distinct increase of thermal conductivity, which was explained by the porosity decrease. A similar relation was found by Csanády et al [ 21 ] for insulating panels made of straw. The values of the thermal conductivity were determined with the guarded hot plate method and related to density of the panels.…”

Thermal insulation and mechanical characteristics of cement mortar reinforced with mineral wool and rice straw fibers

“…Hareedy, Nasr, and Sadek [22], who researched incorporating rice straw into cement bounded boarded also observed an increase in flexural strength, but flexural strength deteriorated with increasing addition. Other studies [23][24][25][26] have also dwelt on the thermal insulation properties of rice straw and mineral wool. Also, some applications of fibrous materials in mortar production have been reported [27][28][29][30].…”

Production of Particleboard Using Various Particle Size Hemp Shives as Filler

“…Research into the identification of energy loss, life cycle assessment for materials, improved durability standards, and the switch to more carbon-neutral materials is already in progress. [ 3 , 4 , 5 , 6 , 7 , 8 , 9 ]. The use of plant-based ingredients and green biomass is an imminent alternative to timber resources and soon will be explored even more than in the past [ 10 , 11 , 12 ].…”