Hybrid Phase Change Material–Heat Pipe Thermal Management of Electronics: A Comprehensive Review

The relentless miniaturization of electronic devices, together with the steep growth in transistor density and switching power, has pushed volumetric heat generation in modern chips, power modules, light-emitting diodes (LEDs), photovoltaic concentrators, and battery packs to levels at which conventional air cooling is no longer sufficient. Passive thermal management based on latent heat absorption in phase change materials (PCMs) offers high energy storage density and near-isothermal operation but is fundamentally limited by the low thermal conductivity of organic PCMs (typically 0.2 to 0.4 W/mK). Heat pipes (HPs), in contrast, provide extremely high effective thermal conductance (102 to 104 times that of copper) but possess negligible thermal storage capacity and are vulnerable to dry-out under transient overloads. The hybridization of these two complementary technologies—through approaches such as embedding heat pipes within PCM-filled heat sinks, wrapping PCM around heat pipe adiabatic sections, or coupling finned heat pipes, vapor chambers, metal foams, and nano-enhanced PCMs—has emerged over the last two decades as promising passive and semi-passive strategies for electronics cooling, particularly under intermittent duty. Its position relative to microchannel, spray, and thermoelectric cooling is assessed qualitatively and not through a systematic quantitative benchmark. This paper presents a comprehensive, critically structured review of PCM–heat pipe hybrid thermal management, synthesizing an original search-and-chaining corpus of 185 experimental, numerical, and analytical sources identified through four bibliographic databases and citation chaining, with the search and selection procedure and its limitations reported in profiled bibliometrically. Three additional studies recommended during peer review were incorporated, and one legacy uncited reference was removed, resulting in 187 references in the revised manuscript. The review covers (i) the classification, thermophysical properties, and selection criteria of solid–liquid, solid–solid, microencapsulated, and low-melting-point metal PCMs; (ii) heat pipe operating principles, typologies (conventional wicked, flat/micro, ultra-thin, loop, oscillating, and vapor chamber), and nanofluid-based performance enhancement; (iii) hybrid configuration taxonomies and their charging–discharging behavior, quantified through an enhancement ratio, reduction ratio, and overall effectiveness; (iv) advanced composite PCMs, including nano-enhanced, metal foam-embedded, and solid–solid variants; and (v) application domains spanning portable computing, high-power LEDs, photovoltaic and concentrator photovoltaic systems, thermoelectric hybrid panels, and lithium-ion battery packs. Comprehensive tables and figures bring together the reported operating conditions, geometries, materials, and quantitative performance improvements. Each primary section concludes with an in-depth analysis of methodological shortcomings and contradictory results. The synthesis concludes with a quantitative aggregation of reported improvements across studies, a comparison with both commercial and new cooling technologies, design guidelines supported by evidence featuring a six-step design process, and a standardized protocol for reporting. A qualitative techno-economic comparison of the five configuration types is also provided. Individual studies report peak or base temperature reductions of roughly 4% to 54%, depending on the configuration, heat load, and baseline; charging-time improvements of about 15% to 36% and discharging-time improvements of about 12% to 40% for heat pipe-embedded paraffin sinks relative to their declared baselines; thermal resistance reductions of up to 76% with nanofluid-charged heat pipes; and extensions of safe operating or working times by factors of about 1.4 to 2.4. These values come from studies that differ in heat load, ambient temperature, PCM, heat pipe type, geometry, and baseline definition. They are therefore indicative ranges and not pooled effect sizes. In conclusion, the ongoing issues of PCM leakage, long-term cyclic stability, nanoparticle agglomeration, orientation sensitivity, mass and volume penalties, lack of standardized figures of merit, limited system-level techno-economic data, and the lack of post-cycling enthalpy data for solid–solid PCMs in heat pipe hybrids are discussed. A detailed research roadmap is suggested, which includes digital twin and physics-informed machine learning techniques, reliability forecasting, multi-objective and techno-economic optimization, dynamic PCM concepts, and additively manufactured integrated wick–fin–PCM structures.