Asymmetry in Heat Transfer and Phase Change Materials: A Review of Modeling, Simulation, and Applications in Energy Systems

Asymmetric heat transfer is an intrinsic and defining feature of phase change material (PCM) systems, arising from the nonlinear coupling between conduction, buoyancy-driven convection, interfacial motion, and geometric or operational non-uniformities. This review synthesizes the physical, numerical, and application-specific mechanisms through which asymmetry emerges and shapes the thermal behavior of PCM-based energy systems. We first examine the fundamental origins of asymmetry, highlighting how natural convection, material heterogeneity, and spatially uneven boundary conditions distort temperature fields and melt front evolution even in nominally symmetric enclosures. We then provide a comprehensive assessment of state-of-the-art modeling approaches—including full-domain CFD, advanced interface tracking methods, stability and bifurcation analysis, and reduced-order modeling—emphasizing their capacity to resolve asymmetric flow structures and capture the complex dynamics governing phase transition. Experimental observations from optical, infrared, and flow visualization techniques further validate the prevalence of asymmetric patterns and underscore the need for high-resolution multi-field datasets. Building upon these foundations, the review analyzes the implications of asymmetry across key energy applications such as thermal energy storage, building envelopes, solar receivers, electronics cooling, transportation systems, and industrial heat exchangers. We also provide a literature review on the importance of using multicriteria evaluation as a key tool in the design of multidimensional symmetric and asymmetric PCM systems. In this context, we address and analyze the performance criteria, evaluation metrics, case studies, and optimization strategies to be considered in the design of these systems. Finally, we identify critical research gaps—including multiphysics coupling, uncertainty quantification, CFD–machine learning integration, and the exploration of emerging asymmetric applications—and outline pathways toward next-generation PCM-based technologies that not only accommodate asymmetry but strategically exploit it for enhanced thermal performance.