Three dimensional computational assessments of nano-encapsulated phase change materials: Effects of endothermic and exothermic interactions

The present study investigates the thermal energy transport of heat exchangers, specifically in the cooling system of underground transmission lines. Four data transfer lines are assumed to generate heat during data transmission, and a cold line is inserted among them to extract and dissipate heat effectively. All these are enclosed within adiabatic cubical walls filled with water-based nano-encapsulated phase change materials (NEPCM). The influences of walls are neglected by assuming infinite depth enclosure. Here, the entropy generation equations are incorporated and nondimensionalized for the problem. A three-dimensional (3D) mathematical model is formulated under the assumptions of steady-state, incompressible, and laminar flow, incorporating the phase transition behavior of the NEPCM while neglecting any volume or shape variations. The finite element scheme is utilized and first validated with experimental and numerical results for computations. This analysis is based on the interplay between natural convection, the latent heat storage capabilities of phase change materials and volume fraction of NEPCM. The analysis demonstrates that an increase in thermal buoyancy strengthens fluid circulation and alters the primary mode of thermal transport from conduction to convection. Additionally, increasing the Darcy number (Da), the mean Nusselt number (Nu_m) increases from 7.5759 to 12.140, resulting in more efficient thermal distribution. The phase change materials exhibit distinct thermal storage behavior, marked by localized regions of elevated heat capacity, particularly near the melting zone. It is observed that increasing the concentration of nano-capsules enriches the suspension's overall heat capacity, resulting in more efficient energy storage and thermal regulation. As the Stefan number increases from 0.5 to 2, the Nu_m decreases slightly from 8.9422 to 8.7791. With an increasing Rayleigh number, the friction entropy exhibits a nonlinear rise. The mean heat entropy increases continuously as the particle concentration increases from 1 % to 5 % ,owing to the greater thermal storage capacity of the fluid.