Meysam Nazari

This work explores the elaboration of wood particle‐based composites incorporating bio‐based phase change materials, with epoxidized linseed oil or clay as a binder. Fire performance evaluation of the novel composites includes an assessment to determine the impact of the addition of boric acid as a fire retardant, as well as the incorporation of recycled paper fibres containing boric acid, and the application of trimethoxymethylsilane coating. The study employs thermogravimetric analysis and cone calorimetry under uniform external irradiance, with a T‐history method to analyse thermal behaviour. Results indicated that fire retardants do not compromise the energy functionality of bio‐based phase change material composites, exhibiting a latent heat of approximately 50 J/g. The density ranges from 750 to 875 kg/m³. The use of clay as a binder improves fire performance, leading to a 60% decrease in total heat release and 52% of the composite mass remaining after analysis. Although enhancing fire performance presents challenges, incorporating wood particles in clay demonstrates a promising potential approach for safe use in building applications, contributing to energy efficiency in indoor heating and cooling. The findings contribute valuable insights into these materials for creating safer and more efficient building solutions, particularly in terms of thermal regulation and fire safety.

This study investigated the impregnation of beech and thermally modified beech (TMB) with a ternary mixture of capric acid, palmitic acid, and stearic acid as a bio‐based phase change material (BPCM). Finite element method (FEM) was used to complement the experimental analysis by providing new insights into computational methods for simulating the behavior of BPCMs in untreated and TMB. The analyzed specimens namely beech and TMB were impregnated with BPCM; the TMB achieved 54% weight percentage gain (WPG) while untreated beech got 37%. Accordingly, a greater increase in the latent heat was obtained for TMB up to 90 J/g, while for untreated beech with BPCM up to 75 J/g. Impregnated specimens absorbed less moisture at relative humidity of air above 50%, likely caused by the high uptake and hydrophobic nature of the BPCM. The study highlights the research gap in performing mathematical simulations on wood samples with BPCM using material thermal properties derived from differential scanning calorimetry or T‐History analysis. It shows that the direct use of these values for simulations leads to unacceptable outputs that result in high errors. The root mean square error for untreated and TMB samples impregnated with BPCM was in the range from 1.06 to 3.1 while that for untreated samples was in the range from 0.57 to 0.87, indicating that the main challenge in simulating and characterizing the samples is due to the interaction of the phase change material with the wood structure.

The environmental impact of fossil-based materials in the building industry and significant energy consumption in residential buildings have urged new research areas in using bio-based, renewable and sustainable materials for production of energy smart bio-based envelopes for building applications. This can be achieved by incorporation of bio-based phase change materials (BPCMs) in wood materials for energy storage in residential buildings. In this thesis, an attempt was made to develop a new BPCM based on coconut oil (CO). The oil was converted into free fatty acids (CoFA) by alkaline saponification and mixed with oleic (OA) and linoleic (LA) acid in various proportions to obtain stable compositions with desirable working temperatures. The prepared mixtures were visually, chemically and thermally studied confirming that the combination of CoFA/LA 20:80 was the most suitable combination and used further as BPCM (xLA= 0.2). The new system melts uniformly at 24.8 ºC, and freezes at two points 18 and 22 ºC, with latent heat of fusion of 100 J/g, heat capacity of around 5 J/g K, thermal conductivity of 0.2 W/m K, in liquid and 0.35 W/m K in solid phase and a good thermal stability after 700 intensive cooling/heating cycles. BPCM (xLA= 0.2) was incorporated by impregnation in solid untreated Scots pine and beech and thermally modified pine (TMP), beech (TMB) and spruce (TMS) wood. The impregnability and intensive leakage tests revealed the positive effect of thermal modification on improving permeability and decreasing leakage. A microscopy study showed that rays in both pine and beech were the main pathway for impregnation. The specific heat capacity of unmodified and thermally modified samples before impregnation were similar at around 2 J/g K, which after impregnation, increased to 4-5 J/g K. The introduction of BPCM (xLA= 0.2) led to improved thermal mass and thermal conductivity of the impregnated samples. The latent heat of fusion for impregnated samples was proportional to the amount of BPCM (xLA= 0.2) in the samples. Mold tests showed that BPCM (xLA= 0.2) encapsulated in Chemical and physical incorporation of bio-molecules into wood materials for energy storage studied thermally modified wood species is less susceptible to mold discoloration compared to unmodified samples. A bio-composite consisting of wood particles impregnated with ethyl palmitate ester (EP) as BPCM and a bio-binder was studied. An optimal proportion of 25 % EP was used in the composite to minimize leakage. The composite was thermally stable to a temperature of 200 ºC. The composite thermal characteristics are similar to solid wood impregnated with BPCM. A benefit of the bio-composite was the added-value to less-valuable industrial bi-products involved in the production of energy smart bio-composite for building application, as well as possibility to produce different profiles.

Solid wood can serve multifunctionality for energy savings in buildings. The study reveals the results of biodeterioration and degradation of solid Scots pine wood used to incorporate single or multicomponent fatty acid mixtures as bio-based phase change materials (BPCMs). The sapwood samples were impregnated with capric acid (CA), methyl palmitate (MP), lauryl alcohol (LA) and a mixture of coconut oil fatty acids and linoleic acid (CoFA-LA). The samples were tested against subterranean termites by an Italian species (Reticulitermes lucifugus), the wood boring beetle Hylotrupes bajulus and mold through a discoloration test. Tested against termites, the impregnated samples were significantly less susceptible to the attack than the controls, i.e., the tested BPCMs were resistant to R. lucifugus. The only test with MP terminated at the moment against H. bajulus showed positive results with no larvae surviving. The mold discoloration test revealed that the wood impregnated with CoFA-LA was identically susceptible to mold discoloration when compared to the control, nonimpregnated samples. This pioneer study verifies that solid wood employed for the encapsulation of BPCMs for building purposes can serve identically or somewhat better than similar wooden building elements regarding attacks of the above microorganisms and insects. Such multifunctional building elements will be tested further in a pilot scale building to characterize better the durability aspects of the new materials.

Due to growing consciousness regarding the environmental impact of fossil-based and non-sustainable materials in construction and building applications, there have been an increasing interest in bio-based and degradable materials in this industry. Due to their excellent chemical and thermo-physical properties for thermal energy storage, bio-based phase change materials (BPCMs) have started to attract attention worldwide for low to medium temperature applications. The ready availability, renewability, and low carbon footprint of BPCMs make them suitable for a large spectrum of applications. Up to now, most of the BPCMs have been incorporated into inorganic matrices with only a few attempts to set the BPCMs into bio-matrices. The current paper is the first comprehensive review on BPCMs incorporation in wood and wood-based materials, as renewable and sustainable materials in buildings, to enhance the thermal mass in the environmentally-friendly buildings. In the paper, the aspects of choosing BPCMs, bio-based matrices, phase change mechanisms and their combination, interpretation of life cycle analyses, and the eventual challenges of using these materials are presented and discussed.

The present work investigates analytically the problem of forced convection heat transfer of a pulsating flow, in a channel filled with a porous medium under local thermal non-equilibrium condition. Internal heat generation is considered in the porous medium, and the channel walls are subjected to constant heat flux boundary condition. Exact solutions are obtained for velocity, Nusselt number and temperature distributions of the fluid and solid phases in the porous medium. The influence of pertinent parameters, including Biot number, Darcy number, fluid-to-solid effective thermal conductivity ratio and Prandtl number are discussed. The applied pressure gradient is considered in a sinusoidal waveform. The effect of dimensionless frequency and coefficient of the pressure amplitude on the system’s velocity and temperature fields are discussed. The general shape of the unsteady velocity for different times is found to be very similar to the steady data. Results show that the amplitudes of the unsteady temperatures for the fluid and solid phases decrease with the increase in Biot number or thermal conductivity ratio. For large Biot numbers, dimensionless temperatures of the solid and fluid phases are similar and are close to their steady counterparts. Results for the Nusselt number indicate that increasing Biot number or thermal conductivity ratio decreases the amplitude of Nusselt number. Increase in the internal heat generation in the solid phase does not have a significant influence on the ratio of amplitude-to-mean value of the Nusselt number, while internal heat generation in the fluid phase enhances this ratio.