Vapor Chamber Research Articles

Inspired biomimetic design for efficient fluid channel configuration based on leaf vein structures

Efficiency of heat and mass transfer is critical for vapor chambers (VCs), but conventional designs often encounter problems with heat transfer and liquid distribution. The hierarchical branch network and heat dissipation function of leaf veins share certain similarities with the wick structure employed in vapor chambers (VCs). Therefore, to explore the potential of biomimetic design for optimizing fluid channel configuration, we investigated the heat transfer and capillary flow performance of symmetric and asymmetric leaf vein (SLV and ALV) networks. Our investigation reveals that the SLV exhibits the best heat transfer and flow characteristics among the ALV and tree branch structure. Additionally, the relationship between the distribution patterns and natural structures of leaf veins was also elucidated. Our findings suggest that the leaf vein network may offer a promising template for designing more efficient liquid channels in VCs and other engineering applications.

A Patent Review and Current Status of Ultra-thin Vapour Chamber

Background: With the advent and rapid development of 5G technology, many electronic products have been developed in the miniaturized direction. However, excessive operating temperature generated by these electronic products in a small space results in serious runaway problems, such as battery failure and dead equipment. To solve the heat dissipation problem of small electronic products, ultra-thin vapour chambers are widely used in the heat dissipation field of these electronic products due to the characteristic of rapid heat conduction and thermal expansion. Therefore, optimizing the performance of ultra-thin vapour chambers is critical. Over the years, optimizing the performance of ultra-thin vapour chambers has piqued the industry's interest. Objective: This study aimed at exploring the structural features, optimization method, and development status of the ultra-thin vapour chambers. Methods: This study reviews various representative patents related to ultra-thin vapour chambers and discusses the problems existing in the process of achieving ultra-thinning to provide a reference for designers of ultra-thin vapour chambers in the future. Results: Through the investigation of a large number of patents on ultra-thin vapour chamber, some existing problems are summarized and analyzed. Finally, the future trend of ultra-thin vapour chambers is discussed. Conclusion: The optimization of ultra-thin vapour chambers benefits the heat dissipation of small electronic products and improves product safety. More related patents will be published in the future.

Characteristics of droplet transportation on feather-shaped superhydrophilic-superhydrophobic patterns

As a new structure, the Wick-free vapor chamber (WF-VC) breaks through ultra-thin and ultra-light technical difficulties. The convergence and dripping of droplet in the condensation section and the rapid diffusion of the working fluid at the evaporation section have become hot spots. In this research, a feather-shaped superhydrophobic-superhydrophilic pattern (SSP) was prepared for the droplet's directional wetting and rapid diffusion. The main path is responsiblefor transporting droplets over long distances, and the branch is designed to diffuse the droplet rapidly toward the end of the branch. The highest transportation velocity reaches 174 mm/s. After 29 orthogonal experiments and performing a response surface analysis of the four structural parameters, the optimal structural parameters were determined through multi-objective optimization of transportation time and mass point.

Numerical analysis on thermal hydraulic characteristics of mesh-type ultra-thin vapor chambers

The mesh-type ultra-thin vapor chamber (UTVC) is a highly cost-effective device that spreads heat efficiently and maintains good temperature uniformity, meeting the present trend and demand for compact system heat dissipation. To analyze the thermal behavior of the mesh-type UTVC, a three-dimensional transient numerical model involving the non-isothermal flow and phase change processes of the working medium was developed to solve the hydraulic and heat transfer performance of the mesh-type UTVC. The model was validated by experimental results with a maximum relative error of 1.98 %. The effects of the mesh parameter including the support coarse mesh and the fine mesh wick on the heat transfer performance of the mesh-type UTVC are analyzed, and the thickness of the fine mesh wick is determined to be the influencing factor of the thermal response performance of the UTVC. With the design of limited space, the wick space ratio of the UTVC is reduced from 0.565 % to 0.085 %, and the thermal response time can be reduced by 22.7 %, while it is beneficial to improve the heat transfer performance of the mesh-type UTVC.

Experimental and numerical investigation on thermal characteristics of the heat sink integrating 3D vapor chamber heat spreader and liquid cooling fins

The traditional vapor chamber/ heat pipe heat sink in high-power chip heat dissipation structures consists of two separate parts. The contact thermal resistance between these parts leads to an increase in thermal resistance during the heat transfer process. To mitigate the contact thermal resistance and improve the heat dissipation performance of vapor chamber heat sinks, this paper proposes a heat sink integrating a 3D vapor chamber heat spreader and liquid cooling fins. Experiments and simulations were carried out to analyze the heat transfer characteristics under different heating powers. The pressure drop and thermal resistance were calculated to analyze the internal phase-change heat transfer process and capillary heat transfer limit. The simulation results were in close agreement with the experimental data for heating powers ranging from 397 to 795 W, with the thermal resistance of the proposed heat sink of about 0.04℃/W. Compared to three traditional vapor chamber heat sinks operating under the same heat flux, the proposed type exhibited a noteworthy enhancement in the heat transfer performance, leading to a reduction in thermal resistance by approximately 44% to 67%.

Modelling ridge enhanced droplet jumping with varying mismatches and scales for vapor chamber performance estimations

The coalescence-induced jumping detachment of droplets during condensation on superhydrophobic surfaces proves to be a promising strategy for addressing critical issues in various phase-change related applications. Protruding structures such as ridges have been reported to enhance the jumping probability and jumping kinetic energy. However, there is a lack of comprehensive investigations into the coupling physics involved in this process, as well as a unified model for accurately predicting droplet jumping, which is presented in this work. The model can predict droplet jumping under varying ridge heights, mismatches and scales of droplets. With the aid of ridges, we achieve a maximum energy conversion efficiency of 43.1% for micro-droplets, which is 18 times of that on a planar surface. Our phase maps illustrate the critical conditions necessary for successful jumping detachments, validated by experimental data within a 20% margin of error. Applications of our model on the droplet-jumping-based vapor chambers are elaborated. It is found that mere detachment is inadequate. Furthermore, jumping needs to be fast enough to overcome air entrainment. By introducing ridges, we demonstrate that the upper limit of heat flux of vapor chamber at the hotspot can be expanded by an order of magnitude to 1000 W/cm2, corresponding to a vapor flow velocity of 1.48 m/s perpendicular to the condensing surface. Our model helps in the design and assessment of condensation equipment by providing the necessary parameter space required to realize valid condenser-to-evaporator jumping.

A Review on Cooling Systems for Portable Energy Storage Units

Achieving the global electricity demand and meeting the United Nations sustainable development target on reliable and sustainable energy supply by 2050 are crucial. Portable energy storage (PES) units, powered by solid-state battery cells, can offer a sustainable and cost-effective solution for regions with limited power-grid access. However, operating in high-dust and high-temperature environments presents challenges that require effective thermal management solutions. This paper is a comprehensive review of thermal management systems for PES units, with a specific focus on addressing the challenge of overheating in airtight designs. The review of various active and passive cooling systems is conducted through extensive study of the relevant literature, which is significant in providing insights into the operation, performance parameters, and design options for different cooling system technologies. The findings from this review show heat pipe (HP) technologies as key cooling-system solutions for airtight PES units. Specifically, loop and oscillating HPs, as well as the vapour chamber, offer desirable features such as compactness, low cost, and high thermal conductivity that make them superior to other alternatives for the cooling systems in PES. The insights and knowledge generated via this review will help facilitate the design and development of innovative, efficient, and reliable PES units, thereby contributing to the advancement of off-grid renewable energy applications and enabling sustainable power solutions worldwide. Furthermore, an appropriate design of PES units can help in reducing capital and maintenance costs.

Rice-inspired oriented copper fiber wick with excellent capillary performance for ultra-thin vapor chamber

In response to the current trend of thermal management systems for microelectronic products, ultra-thin vapor chambers (UTVCs) have become an emerging hotspot. Currently, there is an urgent challenge to design of high-performance capillary wicks for use in limited spaces for UTVCs. In this study, an ultra-thin copper fiber wick (UTCFW), inspired by rice plants, was proposed and prepared by the limited fiber sintering and hydraulic pressure methods. By simply varying the fiber length in the mould, it was possible to prepare an UTCFW with ordered orientation similar to the developed root system of the rice plant. A chemical treatment was used to develop micro- and nano-scale structure on the surface of the UTCFW, similar to hairs on roots of the rice plant, which makes the UTCFW exhibit superhydrophilic properties. After optimization, the capillary factor M of the most ordered sample with 80 mm fibers (L80) was 1.254 μm, which was 567 % times that of the poorly ordered with 5 mm fibers (L5). In short, the bioinspired UTCFW had both excellent wettability and capillary performance. This study demonstrated the preparation of a high-performance and cost-effective UTCFW for improving the thermal performance of UTVCs.

An improved vapor chamber with enhanced two-phase transport by using structured surfaces

The novel type of vapor chamber (VC) with combined superhydrophilic/superhydrophobic surface holds great potential in hot spot cooling. In this study, an improved VC was developed by implementing structured surfaces on both condenser and evaporator. The thermal resistance, condenser temperature uniformity, and gravity independence were discussed. It was found that sintering an appropriate copper mesh on condenser could reduce the thermal resistance but would cause a slight deterioration in the temperature uniformity of the condenser. On the evaporator, the thermal performance of VC was further improved by introducing micro grooves on the wick in order to enhance bubble discharge of the boiling working fluid. Moreover, to strengthen the liquid recirculation on the evaporator, pore size gradient was adopted in the evaporator wick. Compared to the axial gradient of pore size, the radial gradient of pore size was more efficient in accelerating the working fluid recirculation. Among all the results reported in this study, the combination of sintering copper mesh on the condenser and implementing micro-grooves and pore size gradient on the evaporator wick yields optimal results, with the minimum thermal resistance of the VC reaching 0.041 K/W and the critical heat flux exceeding 213.3 W/cm2, which shows excellent thermal performance.

Experimental Investigation on Thermal Performance of Vapor Chambers with Diffident Wick Structures

In this paper, a type of vapor chamber with a gradient pore size wick (VC-G) was developed, and its thermal performance was experimentally tested and compared with two types of VCs with uniform pore size wick (which can be defined as VC-U (200) and VC-U (50) as the powder size of the wick is 50-mesh and 200-mesh, respectively) and a VC without a wick (VC-N). In addition, a VC heat transfer ability experiment platform was built, and the thermal resistance, temperature distribution and thermal response time of the VC with different wick structures were experimentally investigated. The experiment results show that the capillary driving force provided by gradient pore size wick increases gradually from outside, which can not only promote the condensation fluid to gather in the central heat source but also facilitate the vapor to spread around. Therefore, compared with VC-U (200), VC-U (50) and VC-N, VC-G shows the best heat transfer performance, temperature uniform performance and start-up performance.

Isobutane Dehydrogenation on CrO<sub><i>x</i></sub>/Al<sub>2</sub>O<sub>3</sub> Nanoparticles, Prepared by Laser Synthesis in Various Gases

The catalytic properties of nCrOx/Al2O3 nanoparticles (n = 4.8 ± 0.05 wt %) tested in the isobutane dehydrogenation reaction which were obtained by laser synthesis in various gases are studied in detail for the first time. Laser synthesis of 4.8% CrOx/Al2O3 nanopowders was carried out by the vaporization of 5.0% Cr : α-Al2O3 ceramic targets using cw CO2 laser irradiation in an inert, oxidizing and reducing gaseous environment in a vaporization chamber: in an Ar medium; Ar with addition of O2, H2 and CH4 at concentrations of 20, 30, and 13 vol. %, respectively. The role of the gas medium during the synthesis of 4.8% CrOx/Al2O3 nanopowders in their catalytic properties (activity, selectivity, conversion, and stability in the reaction) was determined. A comprehensive study of the physicochemical properties of the obtained nanocatalysts was carried out using XRD, TEM, UV-Vis DRS, and Raman techniques. According to XRD data the phase composition is predominantly consists of γ-Al2O3 with the beginning of the transition to δ-Al2O3. According to the TEM results, the shape of nanoparticles is spherically symmetric with an average particle size dm = 15 nm. Using the UV-Vis DRS method, charge states of Crq+ (q = 3, 6) in different coordination (Cr6+(Td) and Cr3+(Oh)) and its different ratios depending on the gas atmosphere used in the process of laser vaporization were revealed in the obtained 4.8% CrOx/Al2O3 nanopowders. Nanosized 4.8% CrOx/Al2O3 catalyst prepared in an atmosphere (Ar + H2) demonstrated the highest values of isobutane conversion (39%) and isobutylene selectivity (90.7%); the lowest corresponding values of conversion (18.8%) and selectivity (85.6%) were typical for the sample obtained in the atmosphere (Ar + CH4). Thus, the most active and selective in the isobutane dehydrogenation reaction was the 4.8% CrOx/Al2O3 nanocatalyst synthesized in the (Ar + H2) medium, and the presence of methane during vaporization led to the initial surface carbonization, which prevents the access of reacting molecules to it.

Maximizing energy output of a vapor chamber-based high concentrated PV-thermoelectric generator hybrid system

Thermal management of triple-junction solar cell is crucial for enhancing electrical efficiency of a high concentrated photovoltaic (HCPV) system. In this paper, a HCPV system integrated with vapor chamber (VC) cooling and thermoelectric generator (TEG) is proposed to maximize the energy output. The VC as a passive cooling device can effectively extract the excessive heat from the triple-junction cell and the TEG module are used to convert the waste heat into electrical power thereby harvesting more energy. A detailed unsteady-state modeling of the VC based HCPV/TEG system is established in MATLAB. The effects of new VC structure, TEG type and concentration ratio on the dynamic performance of the system are discussed and a comparison with the CPV-TEG system without VC cooling is provided. Results reveal that effective cooling of the new VCs can maintain the sophisticated cell under 1000 suns at below 329 K and the average exergy efficiency of the system is 31.20%. It is observed that the appropriate selection of TEG module can improve the system performance. Using TEG5, the proportion of CPV power in total power for the proposed system reaches 99.02%, which increases by 2.81% compared with that of the reported CPV-TEG system without VC cooling.

Enhancing heat transfer performance in 3D-printed integrated vapor chamber using composite structures

The demand for lightweight heat dissipation devices in aerospace and various other fields has spurred the development of aluminum-based vapor chambers. However, the surface of the aluminum particles is covered by a dense alumina layer, which poses a challenge in preparing the aluminum-based porous wick structure by sintering aluminum powder. In this study, two aluminum-based vapor chambers (60 mm × 50 mm × 4 mm) with distinct wick structures were integrated with the container utilizing 3D technology. The wicks of the vapor chamber included an aluminum-based grooved wick structure (GVC) and an aluminum-based grooved-porous composite wick structure (GPVC). A comprehensive experiment was conducted to evaluate the heat transfer characteristics of the vapor chamber, including startup performance, temperature uniformity, and thermal resistance, under different filling ratios and wick structure parameters. The working fluid was acetone. The results indicated that the GPVC demonstrated excellent startup performance under both low and high heat loads. The startup time of the GPVC was found to be 230 s, 30.3% less than that of the GVC under a heat load of 80 W. Furthermore, at a 60% filling ratio, the GPVC demonstrated lower thermal resistance and better temperature uniformity compared to the GVC. The GPVC achieved a minimum thermal resistance of 0.033 K/W with a maximum temperature difference of only 4.51 °C. This resulted in a reduction of thermal resistance by 47.5% and an improvement in temperature uniformity by 69%. The findings of this study provide valuable insights to the application of 3D printing technology to the production of aluminum-based composite porous wick structures.

Experimental study of a passive thermal management system using vapor chamber for proton exchange membrane fuel cell stack

To mitigate the parasitic power consumption caused by conventional air and water cooling, this study proposes a novel passive cooling scheme that integrates vapor chambers into proton exchange membrane fuel cell stack for thermal management. A 1.32 mm thick vapor chamber is designed and fabricated, and its heat transfer performance is verified through tests conducted at different powers using a heating pad. After confirming that vapor chambers can meet the heat dissipation requirements, the output characteristics of the stack coupled with vapor chambers, are experimentally evaluated during both fast start-up and steady-state operation. Results demonstrate that the vapor chamber efficiently operates at a heat flux density of only 0.052 W/cm2 at evaporation section, while maintaining a maximum in-plane temperature difference of 2.6 °C at 48 W. During fast start-up loading of the stack from 0 A to 40 A, the vapor chamber exhibits rapid thermal response and excellent temperature uniformity, preventing stack performance degradation due to improper operating temperatures. Compared to a general air-cooled stack, the stack coupled with vapor chambers exhibits a significant 21.7% improvement in stack voltage. These results systematically demonstrate the feasibility of vapor chambers for the thermal management of air-cooled proton exchange membrane fuel cell stacks.

Enhancing capillary performance of copper wicks by electrodeposition of superhydrophilic dendritic structures

Capillary wick is a critical component that sustains working fluid circulation in heat-spreading vapor chambers. A preferred wick layer requires a porous structure of multiscale porosity to meet the requirements of high liquid permeability (K) and large capillary pressure (ΔP). In this study, we controlled the etched substrate topography to modulate the morphology and capillary dynamics of the electrodeposited porous films on a specifically treated Cu substrate. The effective pore radius (Reff) of porous Cu films depends on the size and density of the dendritic bushes grown on Cu substrates treated with sodium persulfate/sulfuric acid (SPS) solution. An analytical approach was used to quantitatively analyze the dendritic deposits grown on the SPS-treated Cu substrates. The surface profile and roughness of Cu substrates were investigated by alpha-step profilometer. Scanning electron microscopy, contact angle analyzer and x-ray diffractometer were used to characterize the surface morphology, wetting behavior and oxide formation of the electrodeposited Cu films, respectively. The capillary performance (K/Reff) of the electrodeposited Cu film was measured using the capillary rate-of-rise test. The effect of dendritic bush distribution on fluid transport properties was investigated. A high K/Reff value of 0.975 μm was obtained for the electrodeposited Cu film on a Cu substrate with an optimal SPS etching treatment.

Comprehensive optimization design of ultra-thin flat heat pipe based on pressure-bearing and heat transfer performance

With the development of high-power consumption and miniaturization of electronic devices, the high heat flux in limited space requires thinner thickness and better heat transfer performance of ultra-thin flat heat pipe (UFHP). Due to the decrease of UFHP thickness, the thickness of wall and vapor chamber, and the arrangement of support structure have completely different effects on pressure-bearing and heat transfer performance. Therefore, in order to reasonably design the structure of UFHP, it is necessary to consider both the pressure-bearing and heat transfer capacity. In this study, the deformation, thermal resistance and pressure drop of UFHP with support strips are analyzed. It is found that with the decrease of vapor chamber thickness, under the constraint of the maximum wall deformation, the rapid increase of thermal resistance and pressure drop caused by thin thickness could be reduced by optimizing the vapor chamber size. The size optimization model of UFHP based on pressure-bearing and heat transfer performance is established to guide the design of UFHP with support strips.

Evaporation of sulphur mustard (HD) from common matrices with comparison to nerve agents

ABSTRACT The use of chemical warfare agents (CWAs) in terrorist attacks remains a potential threat. Therefore, an updated wide-ranging database that contains details on the fate of CWAs on environmental surfaces is required, especially for the persistent blister agent sulphur mustard (HD). For this purpose, long-period evaporation rates measurements of HD from various common urban matrices were conducted from our specialised laboratory-designed wind tunnel. Small HD droplets were dispersed on each matrix surface, and then placed in the evaporation chamber. Samples of the target material were collected by continuous sampling on SPE (solid-phase extraction) tubes and analysed by GC (gas-chromatography) analytical method. Profiles of the air vapour concentrations as a function of time (up to four orders of magnitude) and the total mass balances were calculated at two temperatures. The results indicated fast clearance of HD together with a nearly full mass balance from stainless steel and smooth surface tiles, as these matrices are relatively inert. On the other hand, asphalt blocks relatively conserve HD, exhibiting a slow-release mode of action over 7–11 days until matching the GPL (General Population Limit) for HD. The concentration profile of commercial sidewalk bricks showed a moderate decay that characterises a semi-conserving matrix. These findings were compared to the evaporation profiles of the nerve agents sarin (GB) and VX from the same surfaces at the same experimental conditions. We can conclude that HD contamination can cause a secondary risk by a slow release into the atmosphere, especially from surfaces exhibiting conserving characteristics.

A coupled model and thermo-electrical performance analysis for flat heat pipe-based battery thermal management system

Power battery is one of the key components of the electric vehicles, and an efficient battery thermal management system (BTMS) is significant for improving power battery performance. Flat heat pipe (FHP) has lightweight structure and high thermal conductivity, receiving much more focuses in the field of BTMS. In this paper, an FHP-based BTMS configuration is proposed. A coupled model of FHP and batteries was established considering the vapor flow effect of the FHP working medium, which can calculate the battery electrochemical parameters, battery heat generation rate, FHP heat transfer capacity in real time. The coupled model was verified by experiment. Then, the battery thermo-electrical performance at different discharging conditions is simulated and analyzed, and the relationship between battery electrochemical parameters and discharge rate is reflected. Under 3C discharge rate, the battery maximum temperature can be limited under 50 °C, while the maximum temperature difference can be kept below 2.26 °C. Finally, the influence mechanism of different FHP structural parameters including vapor chamber thickness, FHP total thickness, FHP total length on battery thermo-electrical characteristics is investigated. The results show that the decrease of FHP vapor cavity thickness or FHP total thickness will not only increase the vapor thermal resistance, but also aggravate the uneven distribution of FHP heat transfer capability, worsening the battery thermal performance on this occasion. The uneven battery module temperature distribution will further lead to non-uniformity of battery electrical performance. The change of FHP total length will result in the change of the total FHP heat transfer thermal resistance and affect the battery overall performance.

Enhanced capillary performance of hierarchical dendritic copper surface for ultrathin heat-spreading devices

High-performance electronic systems require efficient heat dissipation devices. Vapor chambers (VCs) are practical thermal solutions for lightweight portable electronics that have limited heat dissipation space. A functional VC requires an interior wick to sustain the capillary circulation of the condensed fluid back to the heated region. The capillary wick performance can be indexed by the ratio of liquid permeability to the effective pore size of the wick structure. This study describes the capillary behavior of a thin hierarchical dendritic copper film (<100 μm thick) prepared by electrodeposition and thermal sintering. The effects of the electrodeposition current density, deposition time, and sintering temperature on the capillary performance of the dendritic copper films were investigated. The relationship between the wicking capability and dendritic morphology, tailored by the electrodeposition process, was explored. A post-deposition sintering treatment was found to be beneficial for improving the structural integrity, adhesion, and capillary performance of dendritic copper wicks. A very high capillary performance (0.81 μm) was realized on a 30-μm-thick dendritic copper wick that matches the need for ultrathin VCs used in highly compact electronic systems.

Experimental Study and Visual Observation of a Loop Heat Pipe with a Flat Disk-Shaped Evaporator under Various Orientations

In this study, visualization treatment was applied to the flat disk-shaped evaporator of a loop heat pipe. By observing the liquid/vapor behavior inside the evaporator and compensation chamber, the effects of orientation on the performances during startup and during a step-increase in heat load were investigated. With water as the working fluid, the loop heat pipe was tested under three typical orientations of φ = −90°, φ = 0°, and φ = +90°. The startup time was the shortest for the φ = −90° orientation but there could be a slight temperature overshoot, resulting in an unsmoothed startup process. The startup speeds under the φ = 0° and φ = +90° orientations were similar, both without any significant temperature overshoot. The orientation could significantly change the heat leak and, therefore, the operating temperature and the heat-transfer limit. For the φ = +90° and φ = −90° orientations, the heat-transfer limits were about 71% and 157% of the value at the φ = 0° orientation, respectively. Based on visual observations, for the loop heat pipe operating in gravity-driven mode, there could be two different paths for the working fluid to return to the evaporator, namely, along the vapor line for low heat loads and along the condenser and liquid lines for relatively large heat loads, respectively.