Ultrathin vapor chambers have great potential in cooling compact and portable electronics due to their unique advantages including adjustable cooling surface and good temperature uniformity. However, ...minimizing the thickness of the vapor chambers while maintaining high thermal conductivity could be mutually exclusive. Here, we develop an ultrathin vapor chamber that enables thermal conductivity of more than 10000 W/mK at an overall thickness of only 0.27 mm. Our ultrathin vapor chamber employs the vapor-liquid coplanar arrangement structure that minimizes the vapor flow pressure drop, the superhydrophilic hybrid mesh wicks that strengthen the capillary performance, and superhydrophilic orthogonal microgrooves that absorb the condensed liquid film and smooth the vapor channels. The heat transfer capability and thermal resistance are theoretically modelled to better understand the heat transfer mechanism of the ultrathin vapor chamber. The proposed extremely thin vapor chamber shows good superiority and great impetus in the thermal management of practical compact applications. This extremely ultrathin vapor chamber and the experimental results may guide the new directions for minimized thermal control devices.
•A high thermal conductive vapor chamber with a thickness of 0.27 mm is achieved•Vapor-liquid coplanar structure optimizes the vapor flow pressure drop•Hybrid mesh wicks and orthogonal microgrooves facilitate the liquid flow•The theory model may guide for design of minimum thermal control devices•The developed vapor chamber shows great impetus in cooling compact electronics
•A novel vapour-liquid channel-separated ultra-thin vapour chamber was designed.•A mathematical model of heat transfer limit was established.•The effects of different etching structures on the ...thermal performance were studied.•The cooling modules with and without ultra-thin vapour chamber were compared.
In this work, a novel vapour-liquid channel-separated ultra-thin (0.4-mm-thick) vapour chamber fabricated via etching and diffusion bonding was designed for cooling electronic devices. The heat performance of ultra-thin vapour chamber was tested under five states, and micropillar arrays were etched into the chamber to study their effect on heat transfer. Additionally, infrared thermal imaging was performed to investigate the heat dissipation of cooling modules with and without the ultra-thin vapour chamber. The maximum heat transfer capacity of the ultra-thin vapour chamber in the horizontal state was 4.50 W, and the temperature difference was 4.75 °C. The experimentally measured values were very close to the theoretical capillary limit. Under normal and reverse gravities, the maximum heat transfer capacity changed by less than 11%. The effective thermal conductivity of the ultra-thin vapour chamber was 12000 W/(m·K), which is 30 times higher than that of pure copper. The cooling module with the ultra-thin vapour chamber exhibited better heat dissipation, thermal uniformity and thermal response properties. When the heating input power was 6 W, the heating block temperature, maximum surface temperature difference and equilibrium time of the cooling module with the ultra-thin vapour chamber were 8%, 54% and 32% lower, respectively, than those of the module without the ultra-thin vapour chamber. The proposed cooling solution is promising for heat dissipation problems in high-power portable electronic devices.
•Thermophysical properties of surfactant free CuO/DI water nanofluids are evaluated.•Surface and vapor temperature distributions of heat pipes are measured.•Characterization of mesh wick structures ...are carried out and analyzed.•Mechanisms for the thermal performance enhancement of heat pipes are analyzed.
The present work analyzes the thermal performance of a cylindrical copper mesh wick heat pipe using water based CuO nanofluids. The studies are extended further by varying the heat pipe inclination angle and heat input. Thermophysical properties of CuO/DI water nanofluids are also effectively analyzed. The reduction in thermal resistance ratio is about 23.83% and 10.43% respectively for 1.0 and 1.5wt.% of CuO nanofluid compared with low concentration. Evaporation and condensation heat transfer coefficient ratios are improved by the use of CuO nanofluid and the maximum enhancement obtained is 30.50% and 23.54% respectively for an optimum tilt angle of 60°. Thermal efficiency of heat pipe tends to increase with the heat load and inclination angle and an improvement of 33.34% is observed for 120W heat load at 60° inclination angle compared with the horizontal heat pipe. After the experimentation, characterizations of mesh wick structures are carried out. It is found that the deposition of CuO nanoparticles creates a thin coating layer on the wick surfaces in evaporator section. This increases the surface wettability and enhances the thermal performance of heat pipe.
With the rapid development of microelectronic devices, efficient thermal management in narrow spaces faces significant challenges. Two-phase heat transfer technology is proposed as a breakthrough in ...this field; however, big challenges, especially in designing a high-performance wick within limited space, are urgent to be addressed before ultrathin two-phase heat transfer devices (TPHTDs) can be further applied. In this study, a multilayer composite micromesh wick (MCMW), comprised of coarse and fine meshes with different layer combinations, is proposed to enhance the wicking capability, which is promising to further enhance the thermal performance of ultrathin TPHTDs. Capillary rise rate experiments are conducted to evaluate the comprehensive wicking capability. The results show that MCMW structures yield a significant wicking capability enhancement when compared with multilayer single mesh wick (MSMW) structures. The MCMW, consisted of 3 layers of 100-mesh and 3 layers of 300-mesh, exhibits an optimum volumetric flow rate of 14.44 mm3/s and an equilibrated wicking height at 55.98 mm. MCMW structure provides a convenient and effective alternative in enhancing the wicking capability of mesh wicks and the thermal performance of ultrathin TPHTDs.
•Multilayer composite micromesh wicks exhibit a significant enhancement in wicking capability.•Optimum layer number combination parameters of multilayer composite micromesh wicks were obtained.•Multilayer composite micromesh wicks are highly promising for ultrathin two-phase heat transfer devices.
•Silica coatings were enveloped on nylon mesh by the sol-gel method and endowed it with superhydrophilicity.•Superhydrophilic nylon mesh wicks (SNMWs) yielded good capillary performances.•SNMWs with ...the maximum volumetric flow rate of 1.19 mm3/s were promising wicks for flexible heat pipes.•SNMWs maintained good capillary performances even after 10,000 bending cycles.
The rapid development of flexible electronic devices brings the demand for flexible thermal management systems. Nylon mesh with excellent flexibility is ideal for flexible thermal management systems, especially acting as wicks in flexible heat pipes (FHPs). In this study, novel superhydrophilic nylon mesh wicks (SNMWs) with enhanced capillary performance are fabricated by the sol-gel method. Silica coating is formed on the surface of nylon mesh and endowed the mesh with superhydrophilicity. Capillary rise tests and cyclic bending reliability tests are conducted to evaluate the capillary performance and bending fatigue resistance of the SNMWs. The results show that the SNMWs yield excellent capillary performance, the maximum equilibrated wicking height of the SNMWs reaches 87.38 mm and the largest wicking coefficient is 5.91 mm/s0.5. The average volumetric flow rate proportional to wicking velocity and wetted volume is taken as a comprehensive index to evaluate the feasibility of applying SNMWs in FHPs and the maximum average volumetric flow rate reaches 1.19 mm3/s. Simultaneously, the SNMWs maintain good capillary performance even after 10,000 bending cycles, which means strong bending fatigue resistance. This study provides a high-performance, high-reliability, and cost-effective flexible wick for enhancing the thermal performance of FHPs.
With the rapid development of high-power electronic devices, phase change heat transfer has attracted much attention for efficient and lightweight thermal management. However, the mesh structure ...design for aluminum-based pool boiling enhancement still lacks experimental investigation and theoretical analysis. Herein, an aluminum gradient mesh wick is developed for efficient heat transfer performance. The optimized gradient mesh wick is comprised of a large-hole rhombus flat punching structure on the top and a small-hole 2D screen woven mesh on the bottom, providing sufficient active nucleation density sites, timely liquid supply, and rapid bubble departure. The gradient mesh design for pool boiling enables to achieve a high critical heat flux (CHF) of 1095.46 kW/m2 and a high heat transfer coefficient (HTC) of 46.20 kW/m2·K at a wall superheat of 23.70 °C, which is 167.06% and 240% that of Al plate, respectively. The visualization of bubble behaviors and theoretical analysis reveals that the CHF of the gradient mesh wick mainly depends on the bubble departure and liquid supply, and the bubble departure accounts for a greater proportion. Such aluminum gradient mesh wick provides a strategy for efficient thermal management of lightweight and high-power electronic devices.
•An aluminum gradient mesh wick for pool boiling enhancement is proposed.•A high CHF and HTC of 1095.46 kW/m2 and 46.20 kW/m2·K at a wall superheat of 23.70 °C are achieved.•The visualization of bubble behavior and theoretical analysis are proposed for the mechanistic explanation of pool boiling.
Minimisation of electronics requires increased cooling capacity, and research on heat pipes packed with nanofluid is ongoing. In the open literature, comparative study in heat pipe performance and ...nanofluid stability has attracted much attention. A cylindrical-shaped heat pipe with a copper screen mesh typed wick construction is improved using new experimental data for water-based nanofluids. Al
2
O
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(Aluminum Oxide), CuO (Copper Oxide), and ZnO (Zinc Oxide) nanoparticles have been dispersed to the base fluid at a concentration of 1.0 wt %t. The influence of several nanofluids on heat transfer capabilities of heat pipes was compared with the experimental results, especially in the context of heat load (continued to rise in a range of 60-160W with a 20 W distinction) and inclination angle (fluctuated from 0° to 90° with a 15° difference). At a 60° angle, the CuO nanoparticles dispersed nanofluids showed higher thermal enhancement than other working media. Compared to Al
2
O
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/DI water, ZnO/DI water, and based fluid, the retardation in the form of thermal resistance for CuO/DI water was 27.51%t, 36.21%t, and 57.58%t, respectively. Furthermore, increased heat load causes a delay in thermal enrichment.
•Permeability and effective pore radius measured for mesh-groove wick and mesh wicks.•Heat pipes tests conducted for composite mesh-groove wick and two-layer mesh wick.•Heat pipes tests compared for ...both wicks under different inclinations.•Maximum heat loads of mesh-groove wick 4 times higher than same-thickness mesh wick.•Qmaxs calculated using measured wick properties agree well with measurements.
After the thermal performance of a flat-plate heat pipe with sintered composite copper mesh-groove wick has been shown to be superior in our previous study, the capillary properties, namely the permeability (K) and effective pore radius (reff), are characterized in this work using the capillary rate-of-rise method. The composite mesh-groove wick consists of a layer of 200-mesh copper screen sintered over parallel semi-elliptic grooves with a width of 0.18 mm and a depth of 0.075 mm. While the measured reff for the composite mesh-groove wick agrees well with the prediction by a literature formula, the measured K is about a half of the theoretical prediction available in the literature, which does not account for mesh layer. A new formula of K calculation for the composite mesh-groove wick is proposed with the mesh layer accounted for. The new theoretical K agrees excellently with our measurement. Also investigated is a sintered two-layer 200-mesh (2 × 200 mesh) wick for comparison. Our measured K and reff of it also agree well with the experimental values in the literature. The experimental K/reff value for the composite mesh-groove wick is about 4 times as large as that of the 2 × 200 mesh wick. Then, visualization experiments for flat-plate heat pipes adopting either of these two wicks are conducted under different inclinations. The maximum heat loads (Qmaxs) measured for the composite mesh-groove wick are about 4 times as large as those for the 2 × 200 mesh wick, in agreement with the ratios of the K/reff values of these two wicks. In addition, the measured data of K and reff are used to calculate the Qmaxs of the heat pipes with either wick under various orientations. The theoretical Qmaxs compare well with the experimental measurements.
•Thermal performance of a mLHP using graphene nanofluid was studied.•Very low concentrations of nanofluid gave improvement in heat transfer.•A reduction of 10.3°C in evaporator interface temperature ...was obtained.•A 29.9% decrease in thermal resistance and 42.8% increase in Keff were obtained.•Different diameter transport lines prevented reverse flow.
The heat transfer performance of miniature loop heat pipe with graphene–water nanofluid is experimentally analysed. The miniature loop heat pipe used in the study consisted of a square flat evaporator having a size of 20mm×20mm, a compensation chamber placed above the evaporator and transport lines having different diameters. The difference in diameter prevents reverse flow of vapour through liquid line and also increases the flow rate of condensed liquid through liquid line. An optimum filling ratio of 30% of the total volume of the heat pipe is used in all the experiments. The experiments are conducted for a heat load range of 20–380W using water and graphene–water nanofluid in vertical orientation. The graphene nanosheets having 1–5nm thickness with very low volume fractions of 0.003%, 0.006% and 0.009% are mixed with distilled water to prepare nanofluid. The experimental results indicate that the nanofluids improve the thermal performance of the miniature loop heat pipe and lower the evaporator interface temperature compared to distilled water. An optimum concentration of 0.006% provides the maximum improvement in heat transfer. The lowest thermal resistance value (0.083K/W at 380W) is observed for the optimum concentration and it is 21.6% below the value of distilled water. The evaporator interface temperature reached only 106.3°C at 380W which shows a decrease of 10.3°C compared to distilled water. The experimental results confirm suitability of miniature loop heat pipe filled with graphene–water nanofluid for cooling applications.
•The UTFHP with striped super-hydrophilic wick structure was developed.•The mesh number of N = 200 and passage width of P = 1.5 mm is the best wick structure.•The UTFHP could tolerate 8 W heating ...load with the minimum thermal resistance of 0.26 K/W.
The development of high-performance electronic devices requires high heat transfer components with small thickness and high thermal performance. This paper presented an ultra-thin flat heat pipe (UTFHP), and the total thickness and inner height is respectively 0.68 mm and 0.48 mm. The striped-channel structure was developed to withdraw the deformation of UTFHP and reduce the flow resistance. In order to improve the capillary performance of mesh wick, the oxidation treatment was finished by the thermal oxidation method. The thermal performance of UTFHPs was investigated under natural convection cooling condition. The effects of mesh structure, passage width and filling ratio on the thermal resistance and temperature distribution were analyzed. It is found that the UTFHP with mesh number of N = 200 and passage width P = 1.5 mm showed the best thermal performance under the filling ratio of φ = 57%. The minimum thermal resistance was 0.26 K/W with a maximum temperature of 74.07 °C at 8 W heating load, indicating that the proposed UTFHP was able to be a reliable candidate for the thermal management of electronic devices with high heat transfer rates.
