Performance Of Vapor Chamber Research Articles

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.

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.

Enhancing heat transfer performance of aluminum-based vapor chamber with a novel bionic wick structure fabricated using additive manufacturing

Given the lightweight nature and excellent thermal conductivity of aluminum, it offers significant potential for light-weighting of phase-change cooling components. To further enhance the thermal performance of aluminum-based vapor chambers, this study utilized selective laser melting (SLM) to design and integrally manufacture the slightly oleophilic wick for the condenser of the aluminum-based vapor chamber, along with three different superoleophilic wick structures for the evaporator: the gyroid bionic composite porous wick vapor chamber (GBCPVC), the groove composite porous wick vapor chamber (GCPVC), and the uniform porous wick vapor chamber (UPVC). A water-cooling experimental setup was established, and the effects of wick structure, cooling water flow rate, and cooling water temperature on the maximum heat load, temperature uniformity, and thermal resistance of vapor chambers were systematically investigated. The results indicated that the gyroid bionic porous wick structure significantly enhanced the thermal performance of the vapor chamber. Under the same conditions, GBCPVC exhibited lower thermal resistance and superior temperature uniformity, achieving a higher heat load than GCPVC and UPVC. When the cooling water temperature was decreased, its maximum heat load significantly increased. Specifically, at 15 °C, the maximum heat load for GBCPVC reached 300 W, an increase of 33.33 % and 53.33 % compared to 25 °C and 35 °C, respectively. Conversely, a rise in cooling water temperature enhanced the temperature uniformity and reduced thermal resistance of CBCPVC. At 35 °C and a heat load of 120 W, GBCPVC achieved a minimum thermal resistance of 0.034 K/W and a maximum temperature difference of 1.46 °C. Additionally, an increased flow rate enhanced the maximum heat load of GBCPVC, and under high heat loads, it could also reduce the thermal resistance and improve temperature uniformity. This study provides new insights and solutions for the thermal management of phase-change cooling components in aerospace electronic devices.

Experimental study on ultra-thin silicon-based VC for chip-level heat dissipation

The trend towards miniaturization and integration of integrated circuits has led to the emergence of local hotspots with high heat flux and high temperature frequently. Integrating vapor chamber (VC) directly on the surface of semiconductor electronic devices, can effectively address the problem of overheating on the chip surface, and is therefore considered as a promising thermal management solution. However, the challenge of reducing the size of the VC while improving its heat transfer performance cannot be ignored. To address this, a silicon-based VC with thickness of 0.6 mm is designed and fabricated in this study. Structural optimization is carried out, including the design of three types of wicks using square micropillar arrays and two types of support columns including solid and porous and an experimental system is built to study the influence of these structures on the heat transfer performance of VC. The results indicate that the VC can still function normally under the highest heat flux of 123.6 W/cm2, resulting in lowest thermal resistance of 1.54 °C/W. For wicks, the thermal resistance of VC with characteristic size of 10 μm is reduced compared with that of 20 μm. The introduction of gradient wick, that is, using small-size (10 μm) micropillar arrays in heating area and big-size (20 μm) micropillar arrays in non-heating area, can effectively reduce the thermal resistance of VC. Moreover, the solid support columns are found being advantageous in reducing the thermal resistance of VC, while porous support columns improve the surface temperature uniformity of VC. This work provides a feasible path to optimize silicon-based VC.

A dual-height wick to improve capillary performance of vapor chambers

The wick performance is a crucial metric for ensuring the reliable and efficient operation of vapor chambers (VCs) away from dry-out. To enhance the performance of VC, a pitcher plant inspired enhanced wick characteristic dual-height microgrooves (DHMW) was fabricated on 6063 aluminum alloy by one-step picosecond laser texturing without chemical modification. This study describes the two-step capillary behavior of DHMW by high-speed camera and infrared camera. The effects of minor rib number, groove height ratio, length scale, and test liquids (water, acetone, ethanol) on the capillary performance were investigated. When using water as the working fluid, the DHMW achieved a K/Reff of 1.182 µm, which was about 71.3 % larger than that of normal microgroove wicks due to the liquid propagation effect and the flow resistance reduction effect. Furthermore, the maximum K/Reff could reach 1.819 µm of the sample with a minor rib depth of about 70 μm. However, the wetting results showed that the droplets of acetone and ethanol tend to spread laterally after contact with the surface, which is unfavorable for the formation of hierarchical transport in the DHMW. This study demonstrates that laser texturing is an effective and controllable method for the complex shaping of grooved aluminum wicks, with the potential to improve the heat transport capability of VCs.

Influence of transient heat pulse on heat transfer performance of vapor chamber with different filling ratios

Influence of transient heat pulse on heat transfer performance of vapor chamber with different filling ratios

Sensitivity and optimization analysis of pillar arrangement on the thermal–hydraulic performance of vapor chamber

A vapor chamber with pillar columns is imperative for heat management in high-powered electronic devices. Previous investigations presented a trade-off between the thermal transfer and flow pressure drop within the parameters of the pillar arrangement. However, the parameters of pillar arrangement at millimeter scale are not thoroughly considered, and this trade-off has yet to be addressed in the complete VC-P device. In this work, we optimized the parameters of pillar arrangement at millimeter scale within the complete VC-P, which was conducted by ANSYS Workbench with optiSLang. The multi-objective minimization strategy was the maximum temperature difference on the condenser surface (ΔTc,max), total thermal resistance (R), and total pressure drop (ΔPtotal). The three key parameters of optimizing pillar arrangement were the horizontal (X) and vertical (Y) pitch of pillar columns, and the diameter of pillar columns. First, a prediction model utilizing a response surface methodology derived from a central composite design was established. The results found that a critical pitch of pillar columns is approximately 15 mm. High sensitivity value (0.84) indicate that the diameter of pillar columns has a crucial impact on ΔTc,max and R. Using strength Pareto evolutionary algorithm 2, Part of these optimized VC-P exhibits reduce ΔPvc significant up to 40–60 %, while incurring a marginal increase in R and ΔTc,max higher less than 4–13 % and 1–8 % compared to the vapor chamber without pillar columns. Finally, the final optimal solution has been selected using the TOPSIS analysis method. The case study presented can offer valuable insights into the application of the same methodologies for the analysis of scenarios involving non-circular pillars.

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.

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.

Analytical and experimental on the capillary rise of aluminum multi-scale microgroove wick structures

Ultrathin vapor chambers (VCs) are the most typically used heat-sink components in the development of thin and light electronic products. In this study, microgrooved aluminum wicks with multi-scale structures fabricated by two-step laser processing are developed to enhancing the performance of ultrathin VCs. The multi-scale microgroove wick is composed of the main groove and the multi-scale microstructures that include cluster particles, the gradient structure, and holes formed between cluster particles. The effects of the second step laser processing scan interval and the scan number on the surface morphology, wettability, capillary rise rate, and capillary performance parameters of the multi-scale microgroove structured wicks are investigated. The second-step laser processing changes the morphology of the main groove surface, which affects the wettability of the multi-scale microgroove structure. When the scan interval of second step laser processing is 0.05 mm and the scan number is 1, the droplets on the surface of the multi-scale microgrooves are completely immersed within 23.5 ms, which is 80.6% less than all the time of A1. In addition, the capillary rise velocity of the two-step laser processing multi-scale microgroove structure in the initial 3 s is 150% higher than that of the one-step laser processed microgroove wick, and the capillary performance parameters K/Reff improves by 114.15%.

Thermal performance of a vapor chamber with synergistic effects of droplet jumping and pillared-wick capillarity

• Thermal performance of jumping-droplet vapor chamber was experimentally studied. • The number of auxiliary wick columns shows nonmonotonic effect on the performance. • Increased inner chamber height reduces thermal resistance and gravity dependence. • Jumping droplets may not directly reach the evaporator surface. • The minimum thermal resistance of the vapor chamber reaches 0.064 K/W. When condensate droplets coalesce on a superhydrophobic surface, the released surface energy may yield the merged droplet to jump off the substrate. Based on such principle, jumping-droplet vapor chamber (JDVC) has been proposed as a novel type of heat spreader for hot spot cooling, while the internal working mechanism is rather complicated and still remains inadequately understood. In the present work, the thermal performance of JDVC with auxiliary capillary pillars were experimentally studied, with particular interest on understanding the synergistic effects of droplet jumping and pillared-wick capillarity. Five JDVC samples were fabricated (with a fixed diameter of 97.6 mm, three different overall chamber heights of 3.4 mm, 3.9 mm and 4.4 mm, and a fixed heating area of 1.5 cm 2 ) to investigate the effect of filling ratio, number of auxiliary wick columns and inner chamber height on performance. Results show that, the thermal resistance shows a non-monotonic variation of “decrease-increase” with increasing filling ratio, with a higher heat flux favoring a higher optimal filling ratio. The temperature homogeneity is improved under bottom heat mode compared to under top heat mode, which could be possibly attributed to the improved efficiency of droplet removal. The number of auxiliary wick columns shows non-monotonic effect of “enhance-suppress” on the thermal performance, suggesting that a moderate number of auxiliary wick columns helps to gather the jumped-off droplets in space and facilitates stable capillary-driven working fluid circulation. Increasing the inner chamber height yields reduced thermal resistance and improved gravity independence, indicating that direct arrival of jumping droplets on the evaporator surface may not be the primary way of working fluid recirculation, otherwise the thermal performance should degrade since less jumping droplets are able to reach a higher evaporator surface. Among the results, the minimum thermal resistance of the vapor chamber reaches 0.064 K/W and the critical heat flux exceeds 253.2 W/cm 2 .

A parametric study on the performance of vapor chamber in association with pillar distribution

The performance of vapor chamber is significantly affected by the wick structure, height of the vapor cavity, pillar structure, working fluid, filling ratio, and heat source area. Besides, it can also be influenced by the pillar distribution, which has not been extensively studied in prior literature. Therefore, the present study investigates the influence of pillar distribution on the vapor chamber performance. Totally 11 different vapor chamber models are fabricated and tested, and water is selected as a working fluid for all the samples. The examined geometric features include different mesh layers, mesh sizes, wick structure in condenser surface, pillar distributions, and vapor core space. The results showed that the evaporator with a single-layered mesh provided the thermal resistance of 0.19 K W−1, while triple-layered mesh yielded a thermal resistance of 0.24 K W−1. Moreover, the 2 × 200 mesh offered a maximum heating load of 161 W with a thermal resistance of 0.18 K W−1 against the maximum heating load of 120 W and 75.6 W by the 2 × 150 and 2 × 100 mesh, respectively. The experimental results showed that increasing the pillar numbers alone may not always reduce the thermal resistance, a better pillar distribution can help to direct the vapor flow and improve the performance of the vapor chamber. The proposed vapor chamber with a novel X-wing patterned pillar distribution can offer a thermal resistance of 0.19 K W−1 at a heating load of 146.6 W.

Investigation of boiling behaviors in vapor chambers in response to transient heat input profiles

Vapor chambers are being increasingly utilized as passive heat spreaders in various high-power density thermal management architectures. Particularly, in applications involving power electronics packaging, there is a need to understand and predict thermal performance of vapor chambers under different transient heat loads. It is known that boiling could occur in the wick structure of a vapor chamber at the location of heat input if sufficiently high heat fluxes are directly imposed on the chamber wall. Prior experimental studies that characterize the steady state thermal resistance of vapor chambers versus input power can only identify the behavior before and after the transition to boiling. However, because the initiation of boiling is a discrete event that occurs during the transient powering up, it is critical to understand how boiling behaviors will affect the performance of the vapor chamber in response to the transient heat input profile characteristics. Furthermore, currently available transient vapor chamber modeling efforts do not consider the occurrence of nucleate boiling, precluding their usage for applications where boiling is likely to occur. In this paper, we experimentally characterize the occurrence and effect of nucleate boiling in a vapor chamber coupled with an air-cooled heat sink, subject to various transient heat input profiles. The long-time step response behaviors are first studied for ten on–off cycles, at different on-powers, to illustrate the complete temperature response to a steady state in each cycle. For a range of intermediate powers, an interesting phenomenon is observed, where boiling occurs in every alternate cycle; we identify this range as the transition regime of boiling incipience in the vapor chamber. We further investigate the transient response to a pulsed heat input for various on-times ranging three orders of magnitude from 0.1 s to 400 s, and with two duty cycles (0.25 and 0.5), while keeping either the on-power or the average power constant. For a fixed on-power, lower on-times (0.1 s – 2 s) do not cause any boiling, but for longer on-times (≥ 20 s), cases with lower duty cycles led to occurrences of boiling incipience. Furthermore, for a fixed average power, a higher on-power at a lower duty cycle is more likely to cause boiling, which interestingly leads to an even lower mean steady temperature compared to cases with lower on-power and larger duty cycle. These studies provide insights into the nature of boiling incipience in vapor chambers for their usage under realistic transient input powers mimicking power electronics.

Thermal performance of copper vapor chamber with double-sided uniform radial micro-grooved wicks by laser fabrication

In order to ensure the reliability of high heat-flux electronic devices, vapor chambers with double-sided uniform radial micro-grooved wicks (DURM) are developed. The driving force model of the working liquid inside the DURM vapor chamber is established. To enhance the driving force of the working liquid, the condensation micro-grooves and evaporation micro-grooves of the DURM vapor chamber are fabricated using an ultraviolet laser and an infrared laser, respectively. In addition, the startup characteristics and temperature uniformity of the DURM vapor chamber and the effect of the depth–width ratio and radiation angle of the micro-grooves and the filling ratio of the DURM vapor chamber on its thermal performance are also investigated. The results indicate that the DURM vapor chamber could maintain good temperature uniformity. Both the evaporation micro-grooved and condensation micro-grooved wicks facilitate the enhancement of the thermal performance of the vapor chamber. The double-sided micro-grooved wick with a larger depth–width ratio and a smaller radiation angle improves the thermal performance of the DURM vapor chamber. However, when the radiation angle is lower than 4°, further reducing the radiation angle has little effect on improving the thermal performance. In addition, an appropriate filling ratio helps reduce the thermal resistance of the vapor chamber under a certain heat load.

Heat dissipation performance of grooved-type and copper foam-type vapor chambers

Both grooved-type and copper foam-type vapor chambers are explored and investigated. The overall performance of vapor chamber depends on both axial and spread thermal resistance mutually. The copper foam-type vapor chambers achieved the lowest axial thermal resistance less than 0.2 K/W. The grooved-type sample presented the lowest spread thermal resistance, indicating better temperature uniformity. The visual experiment demonstrated that the evaporating surface of the copper-foam vapor chamber was dominated by the thin film evaporation mechanism at low charging ratio while dominated by the pulsed pool boiling mechanism at large charging ratio. For the grooved-type vapor chamber, the pool boiling mode was observed at any charging ratio.

Vapor chamber with two-layer liquid supply evaporator wick for high-heat-flux devices

Modern electronic devices with high heat flux increasingly exceed the capability of thermal management method. Two-phase thermal dissipation devices such as vapor chambers offer effective method for high heat flux cooling. Various new structural designs of vapor chambers are used as effective thermal control methods for high heat flux devices. However, the optimization criteria for the capillary wick structures are different. The combinations between the structural surface parameters and pore size of the capillary wick are different, while their influence on the heat transfer performance need to be studied. In this work, it is reported that the fabrication and thermal performance of vapor chambers with multi-layer sintered wicks and multi-artery wick design for liquid supply. We numerically and experimentally characterize the two types of sintered multi-artery wick for replenishing liquid and escaping vapor effectively with high heat flux. Three kinds of combinations of different copper particle sizes were applied to the sintered wicks in order to balance the liquid collecting rate and flow resistance. The copper particles of large particle size (60 μm/100 μm/150 μm) in the upper layer wick and copper particles of small particle size (30 μm/50 μm/100 μm) the lower layer wick were applied in the vapor chambers. In the present study, as an evaluation criteria for capillary wick designs, the relationship between surface porosity, surface area and critical heat flux was analyzed to obtain the experimental optimization of structural design and pore size combination as 50/100 μm. It was found that with similar multi-artery structure wicks, higher surface area porosity can effectively increase the critical heat flux of the vapor chambers. Judging from the experiment results, the minimum through-plane direction heat transfer resistance of the vapor chamber is 0.1426 K/W, the minimum in-plane direction heat transfer resistance is 0.016 K/W, while the critical heat flux of the vapor chamber is 262 W/cm2.

Experimental investigation on the thermal performance of vapor chamber in a compound liquid cooling system

To develop an efficient and practicable liquid cooling system for battery thermal management, a compound liquid cooling system combining a grooved aluminum vapor chamber with a one-through flow cold plate was proposed and its thermal performance experimentally was studied. The heating power, coolant flow rate, filling ratio and tilting angle of the vapor chamber were investigated, which had an impact on the thermal resistance and temperature difference on the heating surface. The results showed that the vapor chamber with a 20%~30% filling ratio had the smallest thermal resistance and preferable temperature uniformity in horizontal configuration. Due to the heat and mass transport of phases along the longitudinal direction inside the vapor chamber, the temperature difference of the heating surface arising from the temperature rise of the coolant could be suppressed effectively. To evaluate the suppressed effect on the temperature difference of the heating surface, the suppression ratio was proposed. The suppression ratio on the heating surface rose with the increase in heating power and the decrease in flowing rate. The thermal resistance and temperature uniformity of the vapor chamber deteriorated in tilting configuration. The vapor chamber at a positive tilting angle configuration performed better compared with that at a negative tilting angle configuration. At 20%~30% filling ratio, the suppression ratio of the temperature difference on the heating surface could be achieved at 0.78 under positive tilting angle configuration.

Experimental Investigation on the Vapor Chambers with Sintered Copper Powder Wick

High power electronics units generate high-density heat flux, which poses a significant threat to the reliability of these devices. The vapor chamber (VC) has a very high heat transfer rate and has a wide range of applications in the heat dissipation of electronic products. VCs with sintered copper powder wicks sized as irregular shape copper powder 50 µm (I-50 µm), I-75 µm, I-110 um, I-150 µm were studied in this paper. The effect of liquid filling ratio was discussed. The results indicated that the thermal resistance of all VCs decreased with the increase of heating power. The capillary performance of wick was the dominant factor for the heat transfer performance of VCs with different kinds of wick. A capillary performance factor was proposed to evaluate the capillary performance of VCs. The capillary performance factor of VC with the wick of I-75 µm was much higher than that of the other types of VC in this study. The heat source surface temperature of VCs could be affected by filling ratio and wick structure. But, it should be insensitive to the filling ratio when a better capillary performance factor was obtained. With the same heating area and similar structure, the maximum heat flux density of the VC would decrease as the height of vapor cavity decreased.