Vapor Chamber Research Articles

Molecular dynamics simulation of heat and mass transfer in a nano-grooved heat pipe: Focusing on filling ratios' effect.

Managing the heat generated in microprocessors and other similar heat-generating devices requires the design and construction of superconductors with high reliability. For this purpose, heat pipes (HPs) are a very good option. Nano-grooved micro flat plate heat pipes (FPHPs), which are in the group of vapor chambers (VCs), have received attention due to their suitable structure. In this research, an FPHP with a length of 1050nm is investigated using molecular dynamics (MD) simulation. The effects of using three metals for walls including platinum (Pt), copper (Cu), and aluminum (Al) as well as three working fluids including argon (Ar), water (H2O), and ethanol (EtOH) were investigated. Focusing on the filling ratio of the interior space, mass and heat transfer inside the HP has been fully investigated. Evaporation rate, condensation rate, temperature, density, and velocity distribution as well as heat flux have been studied. The results show that although Ar shows better mass transfer results (due to its monoatomic nature), EtOH has better thermal performance. Among the three metals used, Cu has the best thermal performance. The maximum heat flux is obtained by using Cu and EtOH and is equal to 1819 W/cm2. The optimal filling ratio is reported in different states. The maximum mass transfer rate relates to Ar and at FR = 0.3; which equals 32.5%. The highest phase change rate is obtained using platinum and water, which is equal to 74%.

Experimental study on heat transfer performance of mesh-type ultra-thin vapor chamber for large-area pouch battery

Ultra-thin vapor chambers (UTVCs) with high heat transfer characteristics in tight spaces are ideal for the heat dissipation needs of compact, high-energy-density battery systems for electric vehicles (EVs). This has also led to the expansion of the UTVC area to accommodate the battery size. In this study, a large-area (197 mm × 215 mm) UTVC with cost-effective flat meshes as the internal structure was designed for LiNi1-x-yCoxMnyO2 (NCM) pouch battery. Different from traditional mesh-type UTVCs, the vapor core is designed with multiple partially-through vapor channels to reduce vapor flow resistance. Experimental methods were used to investigate the impact of the UTVC placement and the position of the vapor channel in the vapor core on the heat transfer performance, as well as to examine the actual heat dissipation effect on the battery. The results show that gravity affects the performance of UTVC through placement. The UTVC under gravity-assisted placement has an advantage in both heat transfer performance and maximum heat dissipation power, reaching 0.142 °C/W and 144 W, respectively. And it is beneficial to reduce the thermal resistance of the UTVC by locating the vapor channel deeper into the evaporation section. The heat dissipation of the large-area battery by UTVC reduces the maximum temperature of the battery at the rate of 2.4C charging and 3C discharging by 22.3 and 23.8 °C, and the temperature difference is reduced by 62.31 % and 67 %, respectively.

Thermal Performance Investigation of Vapor Chamber Under Partial Heating and Different Heat Flux Conditions: Effects of Inclination Angle

Abstract The need for cooling technologies increases tremendously with raising demand on the powerful and compact electronics. There, it pushes the research and technology to the new investigations on varying heat transfer mechanisms and devices. While one of these devices is vapor chamber (VC), an experimental study has been carried out to investigate the heat transfer performance of a VC under partial heating, varying heat fluxes, and different inclination angles for different temperatures, in the current study. For this purpose, a VC with a dimension of 90 mm × 90 mm × 3 mm is evaluated via its resulting thermal resistance, performance, and the temperature distribution over the VC surface. There, the limited effect of inclination angle is observed on the performance, while the highest change is obtained with decreasing local heating surface area, thus increasing heat fluxes. Moreover, this trend is seen almost similar with a reasonable shift up or down according to the different temperature differences.

Effect of small inclination angle on heat transfer performance of Ω-grooved bending heat pipe

Grooved bending heat pipe may operate at small inclination angle caused by practical installation errors. Previous researches mainly focused on large inclination angles of straight heat pipes, but fewer experiments were conducted at small inclination angle of bending heat pipe where liquid accumulation and gravity effect on liquid–vapor transport varies along the pipe. This paper experimentally studied the effect of small inclination angle (±3°) on heat transfer of aluminum-ammonia Ω-grooved bending heat pipe with total length of 650 mm, vapor chamber diameter of 4 mm and grooved wick diameter of 1.24 mm. The results showed that small inclination angle significantly affect the heat transfer performance of bending heat pipe with heat transfer limit changed by 9 times from 20 W to 180 W and thermal resistance changed by 8 times from 0.04 K/W to 0.32 K/W. Effect of negative and positive angles in bending heat pipe is complex than that in straight heat pipe. Positive condensation end inclination enhances heat transfer due to gravity-driven liquid reflux. Negative condensation end inclination inhibits heat transfer due to anti-gravity reflux and liquid accumulation suppressing gas condensation. Positive evaporation end inclination weakens heat transfer due to anti-gravity reflux. Negative evaporation end inclination also weakens heat transfer due to thick liquid film, increasing thermal resistance and potentially blocking vapor channels. Attributed to coupling effect of liquid accumulation at bending section and capillary force dominant at tiny incline, maximum heat transfer limit of 180 W is achieved at both end inclination of −0.5°.

Experimental study of the design and performance optimisation of a self-heating methanol on-board reforming reactor for hydrogen production

There is an increasing research on efficient and compact on-board reformer, based on which a serpentine plate type self-heating reformer integrating preheating, reforming and combustion has been designed and fabricated, which can be disassembled and assembled flexibly. In this paper, experiments on the self-heating reformer have been carried out to optimise the differential structure of different chambers. It can be found that: the combustion chamber needs to be partitioned and the resistance loss is small and stable for a long time when the number of partitions is 3. The combustion chamber with O2/CH3OH = 1.5 has the highest wall temperature of 240 °C. Hydrogen yield can be increased to more than two times after optimising the evaporation chamber. The catalyst in the reforming chamber must be uniformly distributed, and the methanol conversion rate is stable at 75 % with a mass of 110 g and Weight Hourly Space Velocity (WHSV) = 8 h−1. The optimum operating conditions of the reactor is WHSV = 8 h−1 with air flow rate of 25 L/min, at which the reactor starts up within 20 min, the hydrogen yield stabilises within 40 min, and the hydrogen yield is 9.8 L/min and remains stable for 120 min.

Enhancing heat dissipation for laser illumination by utilizing the phosphor in metal combined with vapor chamber (PiMCVC)

Laser-driven illumination has unique advantages in high-power applications. However, the low thermal conductivity of the phosphor converter and high-power density of the laser result in a serious heat dissipation problem. Although the thermal conductivity has been improved in the previous work, the heat transferred from the facula cannot be further dissipated. Herein, a phosphor in metal combined with vapor chamber (PiMCVC) was proposed. A copper foam skeleton structure (CFSS) coated with boron nitride (BN) was welded to an ultra-thin vapor chamber (UTVC). The heat dissipated from the facula can be transferred through the CFSS. The heat dissipation area is significantly enlarged by the UTVC. The facula central temperature of PiMCVC can be maintained below 107.0 °C under a load of 4.92 W while that of the reference sample is 530.18 °C. Even at a laser load of 11.58 W, the PiMCVC can still work normally with a luminous flux of 1568.37 lm. Due to the superior thermal management, under the laser power of 9.20 W, the PiMCVC sample can be stably operated for 720 min with a luminous flux of approximately 1150 lm and a CCT of about 4000 K. This work provides a new approach to the thermal management of high-power laser-driven illumination.

Design of 3D vapor chamber for thermal management of permanent magnet synchronous motors

The vapor chamber is a high thermal conductivity device with significant potential for enhancing the power density of permanent magnet synchronous motors. Practical installation requirements and the heat curing process of thermal conductive adhesive impose strict demands on vapor chambers, such as precise 3D profiles and resistance to expansion. This paper presents a novel 3D wave vapor chamber with high thermal conductivity, a design not previously reported. Special internal support structures are engineered to ensure the vapor chamber with performances of thermal conductivity, anti-expansion, and bendability. Simulation results show an anti-expansion deformation of 6.28 % at 125 °C. Heat transfer experiments demonstrate that the 3D vapor chamber achieves an effective thermal conductivity of 4426.73 W/m·K and a thermal resistance of 0.136 °C/W under a 100 W heating load. Furthermore, the 3D vapor chamber-based cooling strategy manages a heat load of 143.93 W at a cutoff temperature of 90 °C, marking an 82.1 % improvement over traditional cooling methods.

Experimental study on the thermal performance of a novel vapor chamber manufactured by 3D-printing technology

Vapor chamber holds great application potential in the field of heat dissipation for high-power electronic devices. This study developed a novel vapor chamber using 3D-printing technology to enhance heat dissipation for compact electronic devices. The vapor chamber was constructed from aluminum alloy with a structural dimension of 60×60×30mm3. In this work, the extended condensation structure of the vapor chamber was combined with an external cooling structure, resulting in a 729 % increase in the external heat dissipation area compared to the evaporation area in a limited space. Extensive experiments were conducted using deionized water as the working fluid under various cooling conditions and heat loads. The results showed that the vapor chamber was capable of maintaining a low thermal resistance at high power and high heat flux conditions, with a minimum thermal resistance of 0.087 °C/W when the heat load was 1000 W. At a cooling water flow rate of 0.1 L/s, the vapor chamber demonstrated the capacity to withstand a critical heat load of up to 1600 W, with the heat flux of 326 W/cm2. Compared to conventional vapor chambers, this novel vapor chamber is better able to achieve stable and efficient heat dissipation under high power and high heat flux conditions, especially in a limited space.

Heat dissipation enhancement of PiGF converter with vapor chamber radiator for high-brightness laser lighting

Laser illumination is widely believed to have great development potential in high-brightness lighting and display. In order to realize high-power laser illumination, an efficient heat dissipation method was proposed for phosphor-in-glass film (PiGF) color converter. The heat dissipation of PiGF converter was enhanced by the vapor chamber radiator (VC). The VC-PiGF converter demonstrates great optical-thermal performances due to its excellent heat dissipation capability. The maximum luminous flux of VC-PiGF converter (3699.3 lm) is 38.2 % higher than that of traditional fin-PiGF converter (2677.1 lm). The VC-PiGF converter has higher laser power saturation threshold (maximum 34.51 W) than the fin-PiGF converter (maximum 29.12 W). As the laser power is 24.82 W, the operating temperature of VC-PiGF converter (128 °C) is 41.8 % lower than that of fin-PiGF (220 °C). In addition, the VC-PiGF converter exhibits stable optical performances and a low surface temperature with the continuous excitation of 15.78 W for 60 min. The VC-PiGF converter packaged in a lighting module has an excellent outdoor test result. The efficient heat dissipation method with high reliability has great application prospects in high-brightness laser lighting.

Enhanced heat transfer performance in vapor chambers via fabrication of novel regular composite porous wick structures using selective laser melting

The composite structure wick has been proven to significantly enhance the heat transfer performance of vapor chambers. Aluminum vapor chambers offer advantages such as being lightweight and cost-effective, meeting the requirements for lightweight cooling in fields like aviation. This study presented two novel composite porous wick structures with regular-shaped pores, designed and controlled via selective laser melting (SLM): the vertical square pore composite wick structure and the round-vertical square pore composite wick structure. A water-cooling test platform was built to investigate the effects of parameters such as wick structure thickness, round pore diameter, and round pore depth on the heat transfer performance and thermal resistance of the vapor chambers. The results indicate that the optimal thickness for the vertical square pore composite wick structure was 1.5 mm, yielding a minimum thermal resistance of 0.04 K/W. When the thickness was below 1.5 mm, it caused a reduction in the density of the vaporized core and insufficient liquid transport capacity. Conversely, when the thickness exceeded 1.5 mm, the primary limiting factor for heat transfer shifts to vapor-liquid flow resistance. Furthermore, the round-vertical square pore composite wick structure can provide further improvements in vapor-liquid transport within the structure.

Visualization experimental study on the boiling characteristics of vapor chamber evaporator surface with different heat sources

The effective functioning of vapor chambers depends on the phase change of the working fluid at the wick surface. Given the prevalent role of vapor chambers in thermal management in the electronics industry, it is critical to study the boiling characteristics and thermal performance of vapor chambers, as well as the effect of heat source conditions. In this work, to observe phase change at the wick surface, the visualization confined chamber with wick (VCCW) is proposed and fabricated, which features a side window and a 2 mm thick wick sintered with aluminum powders. The working fluid used is acetone. The heat source is designed in three different sizes to heat the VCCW in either the middle or right position. The experimental results show that the boiling curve is divided into four stages. In the stage Ⅰ, the boiling curve is linear, and the visualization results reveal that the phase change phenomenon on the wick surface is evaporation. The Ⅱ stage is defined as ONB (Onset of Nucleate Boiling) for the vapor chamber evaporator surface. The boiling curve shows a turning, and bubbles were observed to appear and spread by visualization. In the Ⅲ and Ⅳ stages, the boiling curve remains linear. The stable nucleate boiling and intermittent local dryout is observed before and after the DNB (Departure from Nucleate Boiling). The slope of the boiling curve increases as the size of the heat source enlarges, which contributes to greater superheat and evaporation of the working fluid at smaller heat fluxes. Moreover, the position and size of the heat sources affect the ONB and DNB due to heat diffusion and capillary-driven supply of fluid.

Biomimetic fractal pillars for the thermal–hydraulic enhancement of a vapor chamber

Owing to their remarkable thermal–hydraulic performance, vapor chambers have diverse applications, especially for cooling electronic devices. However, the performances of circular and noncircular pillars throughout the entire vapor chamber under identical wick volume conditions have been compared in very few studies. In this study, a series of noncircular pillar arrays featuring biomimetic tree-like fractal networks is introduced. The incorporation of fractal pillars significantly enhances the thermal–hydraulic performance of the vapor chamber because the gas–liquid interface area is extended. Compared to a vapor chamber with circular pillars, the maximum condensation surface temperature difference, total thermal resistance, and liquid pressure drop of this vapor chamber with fractal pillars are reduced by up to 57.8 %, 13.8 %, and 10.9 %, respectively. In particular, with large branch levels and pillar diameters, the fractal structure is pivotal for boosting the overall performance. When the number of pillars is increased, the fractal structure's impact on the thermal performance reaches a limit, whereas its boosting effect on the flow performance weakens. This study is a pioneering exploration of the application of stretched geometries in pillar-type vapor chambers, with fractal pillars utilized in showcase demonstrations.

Experimental investigation on the thermal performance of a large-size aluminum vapor chamber for multi-point heat sources

Abstract With the development of electronic information technology, the integration and power of electronic equipment continue to increase. As an efficient heat transfer element, vapor chambers are widely used in the field of heat dissipation of electronic devices. However, greater challenges have been posed in terms of higher heat dissipation capacity, larger size, and lighter weight. Therefore, a large-scale aluminum vapor chamber with a size of 340 mm×295 mm ×7.5 mm is designed for the heat dissipation of multi-point array heat sources. Multiple parallel porous ribs are sintered to form capillary wicking channels and vapor diffusion paths, which efficiently transfer the heat from the middle of the vapor chamber to the cold plate on the two sides. The transient working characteristics and heat dissipation performance under different working conditions are experimentally investigated. The results show that there is obvious temperature instability, which can be suppressed by the tilt of the vapor chamber and the increase of the heating power. Under the tilt condition, the temperature rises in the vertical direction due to the influence of gravity, while the inclination angle has basically no effect. The vapor chamber can work stably at the total heating power of 2100 W with the smallest thermal resistance 0.03 °C/W. The single-point heat flux can reach 7.3W/cm2 for the 128 heat sources. Compared to a traditional vapor chamber, the proposed aluminum vapor chamber provides a thermal management solution for large-size electronic devices with multiple heat sources.

Visualization investigation on heat and mass transfer of Al2O3 nanofluid in vapor chamber

As the vapor chamber (VC) moves towards ultra-thinness to meet the thermal management of microelectronic devices, achieving efficient heat transfer within a limited space poses severe challenges. In this study, a visualization VC with a thickness of only 0.9 mm was designed to investigate the heat transfer effect and boiling behavior of nanofluid applied on VC. The influences of Al2O3-deionized water (Al2O3-DW) with different mass concentrations and filling ratios on the heat transfer characteristics and flowing behavior were explored. The results indicated that the addition of nanoparticles improved the temperature uniformity and startup performance of VC. At 0.3 wt%, nanofluid promoted bubbles generation and growth, enhancing the phase-change process. The minimum thermal resistance was 1.46 K/W, representing a 13.6 % reduction compared to that of DW. However, at 0.6 wt% and under high filling ratios or heat load, excessive nanoparticles tended to accumulate on the surface of bubbles by surface tension during the boiling process and were pushed to the gas–liquid interface under the pressure gradient, resulting in deteriorated heat transfer. The results also found that deposition of nanoparticles further enhanced heat transfer. Nonetheless, the nanoparticles were detached from the substrate as the bubbles boiled, and the enhancement effect gradually diminished. The relevant research findings provide guidance for the application of nanofluids in ultra-thin VC.

Pilot-scale testing of a multi-tube type falling film distillation column equipped with a biphasic thermosyphon as a new alternative for the desalination of brackish water and seawater

This paper proposes an innovative technology for desalinating brackish water and seawater using a multi-tube type falling film distillation column integrated with a biphasic thermosyphon. Based on the literature survey, this proposal has not been previously explored. In this study, the viability of the pilot-scale application of this technology for desalination was tested, and the process performance was evaluated in terms of distillate flow rate, salinity removal, and energy consumption, considering different experimental conditions. Synthetic solutions containing 10.0 and 35.0 g/L of sodium chloride were used to simulate brackish water and seawater salinities, respectively. The thermal desalination pilot plant integrating a compact falling film distillation column and a biphasic thermosyphon demonstrated high effectiveness, consistently producing desalinated water with a conductivity below 10 μS cm−1. Considering both concentrations, the optimal condition for desalinated water production was a feed temperature of 85 °C, a vapor chamber temperature of 121 °C, and an energy consumption of 16 kW. This new technological option’s energy consumption is approximately 33 % lower than that of a simulated flash distillation column operating under similar conditions. In conclusion, this study presents promising results, establishing falling film distillation technology as a viable alternative for desalinating brackish water and seawater.

Performance analysis and optimization of an annular thermoelectric generator integrated with vapor chambers

To overcome the structural barriers of conventional annular thermoelectric generators (ATEGs), a new ATEG integrated with vapor chambers (VCs) is proposed in this paper, where the use of VCs enables a large hot-end contact area and a high temperature uniformity for traditional planar thermoelectric modules. Besides, a numerical model for the ATEG is built to conduct performance analysis and optimization under different parameters. Results suggest that the heat absorption of the ATEG increases with the increase of the number of VCs, thereby boosting the output power of the system. When the flow rate is lower than 35 g/s, the optimal number of VCs for the ATEG is 12, with the highest output power, conversion efficiency, net power, and net efficiency of 287.3 W, 5.36 %, 214.1 W, and 3.99 %, respectively, at the exhaust temperature of 800 K. Besides, the exhaust temperature does not affect the optimal result, while the ATEG should be designed with fewer VCs when applied to the waste heat recovery with a larger flow rate. The increase in the VC thermal conductivity is not related to heat absorption but can improve temperature uniformity, and the thermal conductivity of 4000 W m−1 K−1 already meets performance requirements. This study provides new perspectives on the structure design of ATEGs.

Heat transfer performance of the vapor chamber with spiral support-composite wick

Inefficient heat dissipation in vapor chambers (VCs) is a major challenge for their development and application. To investigate the effect of supports on VCs’ maximum thermal power and thermal resistance, the relationship between the number of supports and the vapor channel pressure drop is studied through pressure drop measurement. Composite Wick Vapor Chambers (CWVCs) with various supports are fabricated and tested with a constructed thermal performance test platform. The results indicate that the heat transfer performance of CWVC is related to the number of supports and the liquid filling ratio. The optimum filling ratio of the composite wick with 3-6 spiral supports (SS3-SS6) is 60%, 70%, 90%, and 70%, with corresponding maximum thermal power of 19.25 W, 25.61 W, 25.97 W, and 21.22 W. The thermal resistance of SS4-CWVC is lower overall. Additionally, when the power is 21 W, the surface temperature difference of the condenser of SS3-CWVC and SS6-CWVC is 2.3 °C and 1.3 °C, respectively. However, the condenser surface temperature difference of SS4-CWVC is 66.5% lower than that of SS3-CWVC and 40.8% lower than that of SS6-CWVC at the same power. Therefore, SS4-CWVC exhibits better temperature uniformity and has better heat transfer performance.

A filling rig for liquid and gas working fluids for two-phase thermal management systems

Two-phase cooling devices are used to remove and dissipate heat from high power-density electronic systems to maintain them within their operating temperature limits. The manufacture of these devices, such as heat pipes, thermosyphons or vapour chambers, involves firstly removing any internal air or non-condensable gases before charging with the required volume of working fluid. This paper presents detailed designs and operating instructions for a single bench-top station for use in a laboratory environment for the vacuum evacuation, degassing and charging of these devices. Two configurations allow for the filling of fluids which are either liquids or gases at standard temperature and pressure conditions. For liquids, the dispensed volume can be measured directly on an integrated burette, while the method of vapour transfer is used for gases.The hardware was demonstrated by filling multiple thermosyphon devices with a number of common working fluids used in two-phase systems, including water, acetone and ammonia. It was shown to deliver precise and repeatable filling volumes with average differences compared to target volumes of 1.7% and 10.5% for liquids and gases respectively. The design is intended to be highly customisable where its size can be modified to accommodate filling volume requirements for different applications.

Superspreading Surface with Hierarchical Porous Structure for Highly Efficient Vapor-Liquid Phase Change Heat Dissipation.

Superspreading surfaces with excellent water transport efficiency are highly desirable for addressing thermal failures through the liquid-vapor phase change of water in electronics thermal management applications. However, the trade-off between capillary pressure and viscous resistance in traditional superspreading surfaces with micro/ nanostructures poses a longstanding challenge in the development of superspreading surfaces with high cooling efficiency in confined spaces. Herein, a heat-treated hierarchical porous enhanced superspreading surface (HTHP) for highly efficient electronic cooling is proposed. Compared with the single porous structures in nanograss, nanosheets, and copper foam, HTHP with hierarchical honeycomb pores effectively resolves the trade-off effect by introducing large vertical through-pores to reduce viscous resistance, and connected small pores to provide sufficient capillary pressure synergistically. HTHP exhibits excellent capillary performance in both horizontal spreading and vertical rising. Despite a thickness of only 0.33mm, the as-prepared ultrathin vapor chamber (UTVC) fabricated to exploit the superior capillary performance of HTHP achieved effective heat dissipation with outstanding thermal conductivity (12121 Wm-1K-1), and low thermal resistance (0.1 KW-1) at a power of 5W. This regulation strategy based on hierarchical honeycomb porous structures is expected to promote the development of high-performance superspreading surfaces with a wide range of applications in thermal management.

Comparison of Maximum Heat Transfer Rate of Thin Vapor Chambers with Different Wicks under Multiple Heat Sources and Sinks

In this paper, we present a new analytical model to investigate the maximum heat transfer rate of a thin vapor chamber (TVC) with multiple heat sources and sinks. The model can specifically consider different heat flux conditions for each heat source. Both capillary limitations and allowable maximum temperature constraints were employed to determine the maximum heat transfer rate. The liquid and vapor pressure distributions within the TVC were analytically derived using the Brinkman-extended Darcy equation and the Hagen–Poiseuille equation, respectively. Additionally, the theoretical wall temperature distribution was calculated based on the 3D energy equation, considering different heat flux conditions for multiple heat sources with a weighting factor. Our results demonstrate that the heat flux conditions applied to the heat sources significantly impact the internal flow pattern of the TVC. These changes in flow patterns influence the pressure distributions of the liquid and vapor, thereby affecting the maximum heat transfer rate. Furthermore, the effects of wick parameters on the maximum heat transfer rate under various heat flux conditions were examined.