What micro pulsating heat pipes are — and why they matter now

Micro pulsating heat pipes (micro-PHPs), also termed micro oscillating heat pipes (micro-OHPs), are passive two-phase heat transfer devices comprising wickless serpentine capillary channels — typically with hydraulic diameters below 500 µm — in which self-sustained oscillatory flow of liquid slugs and vapor plugs drives highly efficient heat transport without any external power input. Unlike conventional wicked heat pipes, PHPs require no wick structure, reducing fabrication complexity and enabling flat-plate, flexible, and micro-channel form factors that conventional thermal solutions cannot match.

The technology exploits the inherent instability of two-phase flow in narrow capillary channels — specifically the competition between nucleate boiling, thin-film evaporation, and capillary pressure — to generate self-excited oscillatory fluid motion between heated (evaporator) and cooled (condenser) sections. The channel diameter relative to the capillary length, expressed as the Bond number criterion, is the critical design constraint: channels must be small enough that surface tension dominates gravity, ensuring slug-plug flow formation.

The technology has moved from laboratory curiosity to near-commercial deployment across data centers, aerospace, foldable electronics, and fuel cells, driven by escalating power densities that conventional thermal solutions can no longer address. According to the World Intellectual Property Organization (WIPO), thermal management technologies are among the fastest-growing patent categories linked to electronics miniaturisation — a trend that directly underpins the urgency of micro-PHP commercialisation. The dataset underpinning this report spans patent and literature records from 1998 through 2025 and should be read as a snapshot of innovation signals within that dataset, not a comprehensive view of the full industry.

From 1998 patent filing to 2025 commercial hardware: the innovation arc

The micro-PHP field has evolved through three clearly distinguishable phases over nearly three decades, each marked by a shift in the dominant type of innovation activity. The earliest filing in this dataset is a 1998 Japanese micro heat pipe patent from an Akachi-lineage inventor, describing a fine-tube container where two-phase working fluid transports heat solely through axial vibration — arguably the earliest micro-PHP concept in the dataset.

The development and characterisation period (2012–2019) accounts for the largest concentration of literature records in the dataset. Key milestones include mathematical modelling of PHP startup asymptotics (National Physical Laboratory, UK, 2012); experimental investigation of silicon-based micro-PHPs with HFE-7100 working fluid by the Industrial Technology Research Institute (ITRI), Taiwan (2014); cryogenic nitrogen PHP design at University of Wisconsin-Madison (2015); Tesla-type valve integration for PHP directional flow promotion (Eindhoven University of Technology, 2017); and the first systematic study of micro-PHP local thermal behaviour using infrared thermography (University of Parma, 2020).

“The most recent patent filing in this dataset — Global Cooling Technology Group’s Micro-channel pulsating heat pipe (EP, active, November 2025) — represents the frontier of commercial micro-PHP hardware, featuring internal wall obstructions for nucleation enhancement.”

The maturation and application deployment period (2020–2025) is defined by the transition from characterisation-phase research toward product-level engineering. ABB Schweiz AG filed a heat spreader embedding pulsating heat pipe multichannel tubes for power electronics (EP, 2019, active). Nokia Technologies filed an oscillating heat pipe for bendable consumer electronics (EP, May 2024, active). CEA Paris-Saclay published microgravity PHP simulations in 2019 using the CASCO numerical code, establishing a reference simulation framework. The field is now firmly transitioning toward commercial deployment.

Four technology clusters defining the competitive frontier

The micro-PHP patent and literature dataset organises into four distinct technology clusters, each representing a different structural approach and competitive dynamic. Understanding which cluster a given R&D programme sits within is essential for IP strategy and white-space identification.

Cluster 1: Micro-channel flat-plate PHPs with structured internal surfaces

This is the most commercially active cluster in the dataset, characterised by machined or etched channel arrays in flat metal substrates, with recent innovations focused on internal surface features to control nucleation and flow. Global Cooling Technology Group, LLC holds the dominant IP position here, with an EP filing active as of November 2025 and a JP counterpart from 2023 (priority from a 2019 US provisional application), both claiming closed-loop micro-channel PHPs with internal wall obstructions — ribs, protrusions, and surface features on bottom, side, and top walls — that increase surface area, add nucleation sites, and enhance fluid movement. External ribbing of thermally conductive material promotes convective air-side heat transfer. Provides Metalmeccanica S.r.l (2021) validated a flat-plate micro-channel PHP on actual 1-U server hardware, demonstrating gravity-independent operation.

Cluster 2: Tubular micro-PHPs — sub-millimeter bore metallic tubes

This cluster covers copper, stainless steel, and aluminum tube-based PHPs with inner diameters approaching and below 500 µm. The University of Parma is the most prolific academic assignee in experimental micro-PHP characterisation, contributing at least three papers from 2020 to 2022. Their 2022 study of a seven-turn stainless-steel micro-PHP (hydraulic diameter below 500 µm) in vertical bottom-heated configuration is the first systematic reporting of local — not just global — thermal behaviour in the micro-PHP regime. Earlier work from 2020 used extra-thin metallic pipes with inner diameter below 0.4 mm and HFC-134a working fluid, demonstrating that extreme miniaturisation couples flexibility and compactness while maintaining high performance, with space application relevance. ITRI Taiwan’s 2014 study of silicon-based micro-PHPs with channel widths 0.6–1.0 mm, depth 0.25 mm, and overall size 60 × 10 × 1.25 mm showed that non-uniform channel widths enable start-up at lower power thresholds — a key finding for low-power-budget applications such as those tracked by IEEE in its thermal management standards work.

Cluster 3: 3-D configuration and anti-gravity PHP architectures

Driven by the limitation of conventional serpentine PHPs in non-favourable orientations, this cluster introduces three-dimensional tube routing and non-uniform cross-sections to enable orientation-independent and anti-gravity operation. National Tsing Hua University’s 2018 3-D serpentine PHP achieved thermal resistance ranging from 0.148 K/W at 100 W to 0.0595 K/W at 1,000 W — demonstrating 1 kW handling capability. National Chin-Yi University of Technology (2020) used adiabatic sections with uneven inner diameters to induce asymmetric vapour/liquid distribution, generating unitary circulation capable of functioning against gravity using methanol working fluid at 38% filling ratio. ABB Schweiz AG’s EP 2019 patent embeds multichannel PHP tubes in parallel within a base plate for power electronics, combining heat spreading with PHP oscillatory transfer in a compact industrial module.

Cluster 4: Flexible and polymeric PHPs for emerging form factors

An emerging cluster addresses the constraint of rigid tubular geometry, targeting foldable consumer electronics, soft robotics, and cube satellites. Nokia Technologies Oy’s EP 2024 patent covers an oscillating heat pipe for bendable electronic devices with polymer tubing in the hinge-crossing bendable region, supported by a flexible helical structure, while rigid materials are used for condenser and evaporator zones. The Laboratory of Technical Physics (2022) evaluated polypropylene PHP prototypes (250 × 100 × 1.5 mm) at multiple bending angles and evaporator/condenser configurations, identifying them as promising for foldable portable electronics and deployable cube satellites. The University of Brighton and ESA (2019) designed a titanium–sapphire flat-plate PHP for International Space Station deployment, addressing the materials bonding challenge for space-rated flexible PHP hardware.

Application domains: where micro-PHP is winning

Micro pulsating heat pipes are gaining traction across four primary application domains, each driven by a distinct thermal challenge that conventional cooling cannot resolve at the required form factor or power density.

Consumer and enterprise electronics cooling

The most densely populated application domain in this dataset. Changchun Institute of Technology demonstrated a PHP radiator for CPU heat dissipation achieving minimum average thermal resistance of 0.19 K/W with no dryout up to 120°C. The University of Chinese Academy of Sciences reviewed passive cooling for high-power server CPUs, identifying PHP as the most promising candidate for data center deployment. Mini-scale flat-plate PHPs were validated on actual 1-U server hardware by Provides Metalmeccanica S.r.l (2021), and ABB’s embedded PHP power module targets high-density power electronics (EP, 2019). Fraunhofer IPM’s small-sized PHPs reported thermal resistances up to 90% lower than an equivalent solid copper plate — a performance differential that is difficult to match with any passive alternative at comparable form factors, as documented in thermal engineering standards bodies such as ASME.

Aerospace and microgravity applications

Microgravity behaviour is a distinct and active sub-domain. University of Pisa’s U-PHOS project tested large-diameter PHPs on REXUS 18 and REXUS 22 sounding rockets (2015, 2017). University of Pisa and CEA Paris-Saclay further studied transient startup of large-diameter PHPs designed for ISS experiments (2022). CEA Paris-Saclay built 3.7 m long large-scale cryogenic PHPs for accelerator magnet cooling (2017). Nokia’s flexible OHP (EP, 2024) also has deployment-system relevance for satellite applications. The European Space Agency’s involvement in the University of Brighton’s titanium–sapphire flat-plate PHP study (2019) signals that space agencies are actively evaluating PHP as a next-generation thermal control technology, consistent with ESA‘s published thermal control research roadmap.

Fuel cells and electric vehicles

Proton exchange membrane fuel cell (PEMFC) thermal management is an active growth area. Changchun Institute of Technology performed ANSYS Fluent VOF+PHMPC simulations showing PHP integration reduces PEMFC channel temperature by approximately 12°C. Tsinghua University investigated ultra-thin heat pipe internal structures for PEMFC cooling in urban air mobility applications (2023). Battery thermal management using micro-channel OHP was reviewed by Jinan University, reporting that proper micro-channel layout can increase PHP heat transfer limit by 44%. This domain is expected to see rapid growth as fuel cell power densities increase — a trajectory consistent with projections published by the International Energy Agency for hydrogen mobility adoption through 2030.

Cryogenic and scientific instrumentation

University of Wisconsin-Madison demonstrated helium-based PHPs operating at 2.9–5.19 K with effective thermal conductivity up to 50,000 W/m·K, and nitrogen PHPs achieving 32,000–96,000 W/m·K. CEA Paris-Saclay built 3.7 m long large-scale cryogenic PHPs for accelerator magnet cooling. Zhejiang University designed a hydrogen PHP for cryocooler spread-cooling. These performance levels represent a domain where PHP is already technically superior to alternatives but commercial IP is sparse — a strategic opportunity for parties serving accelerator magnet cooling, space telescope detector cooling, and quantum computing cryogenic chains.

Geographic and assignee landscape

The innovation landscape in this dataset is moderately distributed — no single assignee dominates across both academic and patent dimensions. Geographic concentration patterns are nonetheless clear and carry strategic implications for IP filing decisions.

China is the most represented jurisdiction by volume of literature assignees, with contributions from Changchun Institute of Technology, University of Chinese Academy of Sciences, Xi’an Jiaotong University, Zhejiang University, Jinan University, Tsinghua University, and Dalian Maritime University. Chinese institutions dominate review literature and simulation-based work on PHP thermal performance optimisation.

Taiwan contributes concentrated experimental innovation, particularly in 3-D PHP architectures: National Tsing Hua University, National Chin-Yi University of Technology, and ITRI are repeatedly represented. Europe shows the strongest patent activity in this dataset: ABB Schweiz AG (EP, 2019), Nokia Technologies Oy (EP, 2024), Global Cooling Technology Group (EP, 2025), and Fraunhofer IPM contribute the highest-density technical patent claims. University of Parma is the most prolific academic assignee in experimental micro-PHP characterisation, contributing at least three papers from 2020 to 2022.

United States: Global Cooling Technology Group, LLC holds the most recent and technically detailed micro-PHP patent in this dataset (EP 2025, JP 2023), with US provisional priority from 2019. Among the retrieved results, the dominant PHP utility patent activity is concentrated in EP and JP jurisdictions — suggesting that core micro-channel PHP architectures with nucleation-enhancing internal features may not yet be adequately claimed in US utility patents, representing a potential white space for North American electronics and data center cooling market entrants.

Five emerging directions shaping the next product generation

Based on the most recent filings and publications (2022–2025) in this dataset, five forward-looking directions are identifiable, each representing a distinct technical or commercial frontier for micro-PHP product development.

• Internal surface engineering for nucleation control (2023–2025): Global Cooling Technology Group’s EP and JP patents introduce deliberate wall obstructions — ribs, protrusions, surface features — inside micro-channels to control nucleation site density and enhance thin-film evaporation. This represents a shift from passive geometric optimisation toward active surface engineering within the PHP channel.
• Flexible and bendable PHPs for foldable devices (2022–2024): Nokia’s EP 2024 patent and the Laboratory of Technical Physics’s 2022 polypropylene PHP study both signal that flexible PHP form factors are approaching product-readiness. The key unresolved challenge cited in the dataset is maintaining working fluid compatibility with polymer tubing over operating lifetimes.
• 3D-printing of metal flat-plate OHPs (2022): Dalian Maritime University used AlSi10Mg powder-based metal additive manufacturing to fabricate aluminum flat-plate OHPs, enabling complex internal channel geometries impractical with conventional welding. This manufacturing approach could significantly reduce unit cost and enable geometries tailored to specific hotspot distributions.
• PHP integration into hydrogen fuel cells and EV powertrains (2022–2023): Two independent groups — Changchun Institute of Technology (2022) and Tsinghua University (2023) — targeted PEMFC cooling with PHP and ultra-thin heat pipe technologies respectively, driven by urban air mobility and EV market demand.
• PHP critical diameter design methods for vertical operation (2022): The Dalian Maritime University JP patent (2022) formalises a quantitative design method for determining the critical channel diameter required for startup in vertical PHPs, addressing one of the key engineering barriers to confident product specification. This type of design tool — moving from empirical rules to first-principles methods — signals the technology’s transition toward engineering standards maturity.

“Dalian Maritime University’s JP 2022 patent formalises a quantitative design method for critical PHP channel diameter — moving from empirical rules to first-principles methods, signalling the technology’s transition toward engineering standards maturity.”