Finite Volume Method and Statistical Analysis of Heat Transfer in Hybrid PCM Bricks Containing Paraffin, Zeolite, and Hydrogel Ice Pack

ABSTRACT: This study evaluates the daytime thermal-regulation performance of a hybrid composite brick integrated with a phase change material (PCM) core containing paraffin, natural zeolite, and a hydrogel ice pack. A one-dimensional finite volume method (1D FVM) model with a 10-node through-thickness grid and an effective heat-capacity formulation was used to represent transient conduction and was validated against outdoor measurements collected at 15-min intervals from 06:00 to 18:00 over six consecutive days. The measured exterior surface reached 45.52 °C at 12:15, whereas the brick core reached 44.58 °C at 13:45, giving a 90-min peak-temperature time lag. The maximum exterior-to-core temperature difference was 7.88 °C and the maximum exterior-to-interior thermal decrement was 4.65 °C. The calculated conduction heat flux reached 32.50 W/m² during heat absorption and −4.76 W/m² during heat release. Model validation yielded MAE = 0.577 °C, RMSE = 0.788 °C, and R² = 0.994. Because the maximum core temperature only approached the lower end of the reported paraffin melting interval (44–60 °C), a linear phase-fraction interpretation indicates only the onset of melting (approximately 3.6% at the core peak), rather than complete PCM melting. The results therefore support the hybrid brick as a thermal-buffering wall concept while defining the scope of the reduced-order model: radiation and free convection are not solved as separate field equations but are embedded in the measured surface-temperature boundary conditions.