Thermal Performance Of Vapor Chamber Research Articles

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.

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.

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 .

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.

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 analysis of thin vapor chamber with composite wick structure under different cooling conditions

In this work, two types of thin vapor chambers, namely, copper foam vapor chamber (CFVC) and copper mesh vapor chamber (CMVC), are developed to enhance the thermal performance of vapor chambers for cooling high heat flux electronic devices. The evaporator wick is a composite wick of sintered copper powder-mesh with multi-artery structures made of several sintered powder bars on a thin evaporator zone. The condenser wicks for CFVC and CMVC are copper foam wick and 3-layer 200 mesh wick, respectively. A water-cooled testing system is set up to investigate the thermal performance of the vapor chamber. The characteristic parameters, including the temperature distribution, thermal resistance, filling ratio and critical heat flux (CHF) of vapor chambers are studied. The results indicate that the thermal performance of the vapor chamber is significantly affected by the cooling water temperature. At cooling water temperatures of 50 and 30 °C, the CHF of the CFVC can reach 180 W/cm2, which is increased by 100–200% compared to that of the CMVC. The CFVC exhibits a better heat transfer performance and adaptability to the cooling water temperature, given that the copper foam wick has a larger capillary performance parameter and a smaller contact thermal resistance.

Analysis on thermal and hydraulic performance of a T-shaped vapor chamber designed for motorcycle led lights

Experiment and numerical analyses were conducted to study the thermal performance and circulation characteristic of the working fluid of a T-shaped vapor chamber special designed for the motorcycle LED light. The influences of heat loads and cooling magnitude were experimentally investigated. Results show that both the heat loads and cooling conditions have strong influences on the thermal performance of the vapor chamber, and the thermal resistance in the extended section occupies over 75.8% of the overall thermal resistance of the vapor chamber. Simulation results indicate that large pressure drop occurs along the extended section of the vapor chamber, and causes large temperature difference along the extended section.

A Review of Vapor Chambers

ABSTRACTFuture developments in electronic industries will require efficient cooling systems to dissipate large amount of heat produced over a small area. In recent years, interest has grown in extending the use of vapor chambers to high heat flux electronics cooling because of their low thermal resistance values and uniform temperature distribution abilities. A detailed overview of vapor chambers is presented in this paper including their principle of operation, types of performance characteristics, and various applications. Recent developments in improving the thermal performance of vapor chambers are also presented in this article.

Multi-scale thermal modeling of glass interposer for mobile electronics application

Purpose – The functionality of personal mobile electronics continues to increase, in turn driving the demand for higher logic-to-memory bandwidth. However, the number of inputs/outputs supported by the current packaging technology is limited by the smallest achievable electrical line spacing, and the associated noise performance. Also, a growing trend in mobile systems is for the memory chips to be stacked to address the growing demand for memory bandwidth, which in turn gives rise to heat removal challenges. The glass interposer substrate is a promising packaging technology to address these emerging demands, because of its many advantages over the traditional organic substrate technology. However, glass has a fundamental limitation, namely low thermal conductivity (∼1 W/m K). The purpose of this paper is to quantify the thermal performance of glass interposer-based electronic packages by solving a multi-scale heat transfer problem for an interposer structure. Also, this paper studies the possible improvement in thermal performance by integrating a fluidic heat spreader or vapor chamber within the interposer. Design/methodology/approach – This paper illustrates the multi-scale modeling approach applied for different components of the interposer, including Through Package Vias (TPVs) and copper traces. For geometrically intricate and repeating structures, such as interconnects and TPVs, the unit cell effective thermal conductivity approach was used. For non-repeating patterns, such as copper traces in redistribution layer, CAD drawing-based thermal resistance network analysis was used. At the end, the thermal performance of vapor chamber integrated within a glass interposer was estimated by using an enhanced effective thermal conductivity, calculated from the published thermal resistance data, in conjunction with the analytical expression for thermal resistance for a given geometry of the vapor chamber. Findings – The limitations arising from the low thermal conductivity of glass can be addressed by using copper structures and vapor chamber technology. Originality/value – A few reports can be found on thermal performance of glass interposers. However thermal characteristics of glass interposer with advanced cooling technology have not been reported.

Effect of sintering columns on the heat transfer and flow characteristics of the liquid cooling vapor chambers

The results of the heat and flow characteristics of working fluid inside the vapor chamber with different sintering columns of 20, 81, 225 are presented. The vapor chambers with one inlet port and four outlet ports are tested by using water as coolant. Parametric studies including different heat fluxes, number and size of wick columns, and flow rate of coolants on the cooling performance are considered. A three-dimensional heat and mass transfer model for vapor chamber with wick and without sintering plate and sintering columns are developed. The numerical simulation results show the velocity and pressure distribution of liquid and vapor phases of the working fluid inside the vapor chamber. It is found that the number of wick column have an important influence to the velocity and pressure phenomena of working fluid which results in thermal performance of vapor chamber. Reasonable agreement is obtained from the comparison between the measured data and the predicted results.

On the Thermal Performance of the Vapor Chamber with Micro-channel for Unmixed Air Flow Cooling

Numerical and experimental results on the thermal performance of vapor chamber with and without micro-channel under constant heat flux are presented. The mathematical model of the vapor chamber is a two-phase closed chamber with wick sheet and a wick column. A finite volume method with structured uniform grid method system is applied to solve the model. Effects of micro-channel on the temperature distribution of the vapor chamber are considered. The results obtained from the model are verified with those from the measured data. The experimental tests are carried out and good agreement is obtained with the numerical results. These numerical results are useful for the design to improvement thermal performance of the vapor chamber and also diminished the expense and time of the real test.

Application of Al<sub>2</sub>O<sub>3</sub> Nanofluid on Sintered Copper-Powder Vapor Chamber for Electronic Cooling

The development of electronic devices pushes manufacturers to create smaller microchips with higher performance than ever before. Microchip with higher working load produces more heat. This leads to the need of cooling system that able to dissipate high heat flux. Vapor chamber is one of highly effective heat spreading device. Its ability to dissipate high heat flux density in limited space made it potential for electronic cooling application, like Central Processing Unit (CPU) cooling system. The purpose of this paper is to study the application of Al2O3 Nanofluid as working fluid for vapor chamber. Vapor chamber performance was measured in real CPU working condition. Al2O3 Nanofluid with concentration of 0.1%, 0.3%, 0.5%, 1%, 2% and 3% as working fluid of the vapor chamber were tested and compared with its base fluid, water. Al2O3 nanofluid shows better thermal performance than its base fluid due to the interaction of particle enhancing the thermal conductivity. The result showed that the effect of working fluid is significant to the performance of vapor chamber at high heat load, and the application of Al2O3 nanofluid as working fluid would enhance thermal performance of vapor chamber, compared to other conventional working fluid being used before.

Copper foam based vapor chamber for high heat flux dissipation

A copper foam based vapor chamber was designed, built and tested in this paper. The vapor chamber consists of a top and bottom copper foam pieces which are sintered on the two copper plates. Several copper foam bars directly contact the tip of the condenser and evaporator wicks. The surface temperature non-uniformity was defined to characterize the temperature distribution on the condenser and evaporator surfaces. It is found that the water and ethanol based vapor chambers have the best and worst thermal performance, respectively, among the three working fluids of water, acetone and ethanol. The surface temperature non-uniformity on the bottom (evaporator) surface are 3–5 times of those on the top (condenser) surface. Generally thermal resistances of vapor chambers are decreased with increases in heating powers. Charge ratios and inclined angles are combined to influence the thermal performance of vapor chambers. The maximum heating power attains 170W, corresponding to the heat flux of 216W/cm2 without the capillary or boiling limits reached. The minimum thermal resistance is 0.09K/W. The significantly extended operation range of heat flux is due to the distinct nature of high porosity and multiscale pore sizes of copper foams.

Analysis for Diving Regulator of Manufacturing Process

Diving regulator converts the compressed air in a tank into atmosphere air for divers and plays a very important role of SCUBA diving apparatus. The article analyzes its manufacturing process of injection mold in order to enhance the strength after insert molding through the good thermal performance of vapor chamber. The insert molding process is that the metal insert is firstly put into the cavity and then composed an embedded metal-plastic product by injection molding. These results proved that the product strength can be improved significantly with a yield rate up to 100% through this manufacturing process.

Analysis for diving regulator applying local heating mechanism of vapor chamber in insert molding process

This paper aims to use the local heating mechanism, along with the excellent thermal performance of vapor chamber, to analyze and enhance the strength of products formed after insert molding process. In the insert molding process, the metal insert is firstly placed into the mold, and then formed into an embedded plastic product named diving regulator by injection molding. These results indicate that, the product formed by the local heating mechanism of vapor chamber can reduce the weld line efficiency and achieve high strength, which passed the standard of 15.82 N-m torque test, with a yield rate up to 100%.

Evaporative Thermal Performance of Vapor Chambers Under Nonuniform Heating Conditions

This paper reports the test results of vapor chambers using copper post heaters and silicon die heaters. Experiments were conducted to understand the effects of nonuniform heating conditions (hot spots) on the evaporative thermal performance of vapor chambers. In contrast to the copper post heater, which provides ideal heating, a silicon chip package was developed to replicate more realistic heat source boundary conditions of microprocessors. The vapor chambers were tested for hot spot heat fluxes as high as 746 W/cm2. The experimental results show that evaporator thermal resistance is not sensitive to nonuniform heat conditions, i.e., it is the same as in the uniform heating case. In addition, a model was developed to predict the effective thickness of a sintered-wick layer saturated with water at the evaporator. The model assumes that the pore sizes in the sintered particle wick layer are distributed nonuniformly. With an increase of heat flux, liquid in the larger size pores are dried out first, followed by drying of smaller size pores. Statistical analysis of the pore size distribution is used to calculate the fraction of the pores that remain saturated with liquid at a given heat flux condition. The model successfully predicts the experimental results of evaporative thermal resistance of vapor chambers for both uniform and nonuniform heat fluxes.