PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu Radmanović et al. (2024). “ Beech & fir conductivity,” BioResources 19(3), 4104-4119. 4104 Determining Thermal Properties of Beech and Fir Wood Samples in Longitudinal Direction via Modified Transient Plane Source Method Kristijan Radmanović, Krešimir Balaško, Dario Pervan, Franko Lončar, Marin Dujmović, and Branimir Šafran * The increasing use of wood leads to the need for a better understanding of its thermal properties with the aim of quantitatively identifying the exchange of thermal energy between wood and the surrounding solar radiation as precisely as possible. Reliable and rapid measurement of thermal conductivity is one of the most important current industrial requirements. The aim of this study is to examine the validity of using the modified transient plane source method (MTPS), which uses the principle of one-sided heating of the sample, and is defined by the ASTM D7984-21 (2021) standard, for determining the thermal conductivity of complex biocomposite composite materials such as wood. The analysis of the available literature shows a lack of data on the thermal conductivity of the type of wood originating in Croatia. In this study, the thermal conductivities of beech and fir wood samples in the longitudinal direction was determined by the MTPS method depending on the temperature and moisture content in the samples. Measurements were made on samples with a moisture content of 0%, 10%, and 20% in the temperature range from 20 to 80 °C. DOI: 10.15376/biores.19.3.4104-4119 Keywords: Thermal effusivity of wood; Thermal conductivity of wood; Thermal resistance; Wood moisture content; Temperature Contact information: University of Zagreb, Faculty of Forestry and Wood Technology, Department of Process Engineering, Svetošimunska 25, 10 000 Zagreb, Croatia; * Corresponding author: bsafran@sumfak.hr INTRODUCTION Awareness of the benefits of green construction, wood, and wood-based materials gives preference to their use in many industrial branches. The production of wood and wood-based materials requires less energy and causes less CO2 emissions compared to the production of some other building materials (Wang et al. 2014), which makes it more environmentally friendly. In addition to the construction and furniture industry, wood is increasingly being researched in the energy industry. Jiao et al. (2020) investigated the influence of lignocellulosic and multichannel wood microstructure on the mass transfer of ionically conductive electrolytes for charging vanadium batteries. A thorough knowledge of thermal conductivity as a quantity that describes the ability of wood to heat transfer is extremely important. An example is when determining the influence of heat dissipation on the performance of wood products (Qiu 2023). Another example is when quantitatively determining the exchanged heat between wood and the environment, etc. As a result, there is a need for a faster and more precise determination of their thermal conductivity (TC).