This study investigates the effect of SiO₂ nanoparticles on the rheological and thermal behavior of soybean oil at 5–40°C, a low-temperature range of internal combustion engines. This investigation has been done for the concentrations of 0.05% to 1.0%. The results indicated that the dynamic viscosity reduced in all shear rates as the temperature rose. The significant change in the volume fraction’s viscosity was approximately 55% at 5°C from 0% to 1%. The maximum thermal conductivity coefficient obtained was 0.169 w/(m. K) at 30°C and 1.0% of volume fraction; indeed, it was 12% higher than that of the base oil. Statistical analysis has been performed with the Response Surface Method (RSM) using Design-Expert® v.11. The dynamic viscosity behavior, which has been provided in a mathematical correlation with the adj-R² of 0.9997, suggested a high consistency between the experimental and modeling output data.

Efficient thermal management is essential for the safety, performance, and lifetime of lithium-ion batteries, especially in high-power applications such as electric vehicles, where elevated temperatures and thermal non-uniformity accelerate degradation. Passive cooling by phase change materials (PCMs) offers a compact, energy-efficient solution. In this study, eleven paraffin wax/eicosane (PW/E) binary composite PCMs were prepared across the full composition range (S1–S11; 100/0 to 0/100 wt%) for the Molicel INR 21700 P42A battery module. Simultaneous thermal analysis (STA) under argon (10°C·min⁻¹) provided combined DSC and TGA/DTG data. Increasing eicosane content shifted the melting peak from 55.00°C (S1) to 40.26°C (S11); total phase-change enthalpy ranged from 135.03 J·g⁻¹ (S4) to 252.78 J·g⁻¹ (S11), a net +35.3 % from S1 to S11. A solid–solid rotator transition (24.98–31.50°C) contributed 4.8–22.4 % of the total latent heat and is critical for accurate BTMS simulations. TGA yielded onset decomposition temperatures of 170–222°C, exceeding the 60°C battery limit by more than 110°C. Coats–Redfern analysis identified D3–Jander diffusion as the rate-controlling mechanism (KCE-validated, R² = 0.957); effective activation energies were 107.43–145.07 kJ/mol after excluding the S2 encapsulation anomaly. Filippov-based k(T) coupled with DSC-derived tanh β(T) functions captured up to a 66.6 % conductivity drop across melting. Box–Cox RSM optimization (Stat-Ease 360) identified S6 (PW/E 50/50) as the global optimum (D = 0.861, β(40°C) = 0.07). The validated k(T), ρ(T), β(T), and Cp(T) correlations are directly deployable in passive and hybrid BTMS CFD.