The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Zhixin Zeng - One of the best experts on this subject based on the ideXlab platform.
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thermal performance of ultra thin flattened heat pipes with composite Wick structure
Applied Thermal Engineering, 2016Co-Authors: Wenjie Zhou, Yuying Yan, Zhixin ZengAbstract:This study proposes three composite Wick structures (copper power or mesh sintered on grooved tube), namely, single arch-shaped sintered–grooved Wick (SSGW), bilateral arch-shaped sintered–grooved Wick (BSGW), and mesh–grooved Wick (MGW), to improve the thermal performance of ultra-thin heat pipes (UTHPs). Phase-change flattening technology is employed to fabricate UTHPs. The morphologies of the Wick structures after flattening are observed. An experimental apparatus is setup to investigate the thermal performance of UTHP samples under incremental heat loads. The heat transfer limits of UTHP are theoretically and experimentally analyzed. Capillary limit is found to be the main heat transfer limit, and the theoretical values of the samples with SSGW and BSGW are in good agreement with the experimental results. Results indicate that the maximum heat transport capacities are 12 W, 13 W and 14 W, under the corresponding optimum filling ratios of 70%, 70%, and 80%, for the SSGW, BSGW and MGW UTHPs, respectively. Evaporation and condensation thermal resistances of UTHP samples increase with the increase in the filling ratio before the occurrence of dry-out. UTHPs with SSGW have the least evaporation thermal resistance whereas UTHPs with MGW have the least condensation thermal resistance.
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Investigation of ultra-thin flattened heat pipes with sintered Wick structure
Applied Thermal Engineering, 2015Co-Authors: Yuying Yan, Zhixin ZengAbstract:Abstract This study proposes a novel sintered Wick structure called bilateral arch-shaped sintered Wick (BASSW) for the improvement of the ultra-thin heat pipes (UTHPs). The bilateral arch-shaped Wick was sintered at the middle of its copper container and the vapor flow channels are located on both sides. The sintered Wick was manufactured with several paramount parameters including maximum Wick thickness, flattened thickness, and copper powder particle size fully controlled. An experimental apparatus was set up to investigate the thermal performance of the UTHP samples under the impacts of incremental heat loads. The effects of each processing parameter on the thermal performance of the UTHP samples were analyzed and compared with a mathematical model incorporating effects of the evaporation and condensation heat transfer in a copper-water Wick. Results indicate that the most critical factor for thermal performance of UTHP is flattened thickness, as it decreases, the heat transport capability drastically decreases and the thermal resistance increases. The maximum Wick thickness affects the evaporation thermal resistances by the variation of evaporation area of the liquid–vapor interface, and particle size affects the heat transport capability by the variation of the porosity of the Wick structure. The thermal resistances of the evaporator and condenser sections are consistent with the mathematical model before dry out occurs. The total thermal resistances of the UTHP samples range from 0.02 K/W to 0.60 K/W, and the maximum heat transport capability can reach as high as 25 W.
Wenjie Zhou - One of the best experts on this subject based on the ideXlab platform.
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a novel ultra thin flattened heat pipe with biporous spiral woven mesh Wick for cooling electronic devices
Energy Conversion and Management, 2019Co-Authors: Wenjie Zhou, Zhaoshu Chen, Liqiang Deng, Yunhua GanAbstract:Abstract In this work, a novel biporous spiral woven mesh Wick is developed to enhance the thermal performance of an ultra-thin flattened heat pipe for cooling high heat flux electronic devices. The biporous Wick with different sized pores is hybrid woven using 0.05 and 0.04 mm diameter copper wires in every strand. Three different structures are designed to study the effect of the characteristic parameters of the Wick on the thermal performance of the ultra-thin flattened heat pipe. The working fluid flow characteristics of the Wick are analyzed theoretically. The capillary rate-of-rise experiment with deionized water using the infrared camera method is carried out to characterize the capillary performance of the Wick. The thermal performance of the ultra-thin flattened heat pipe is experimentally investigated. The results indicate that the biporous Wick combines the advantages of high permeability due to the large pores and large capillary force due to the small pores. The optimal biporous Wick has 22% fewer copper wires than the monoporous Wick, but the maximum heat transport capacity of the ultra-thin flattened heat pipe is able to approach 24 W, which realizes the demands of both low production cost and high thermal performance using the biporous Wick.
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thermal performance of ultra thin flattened heat pipes with composite Wick structure
Applied Thermal Engineering, 2016Co-Authors: Wenjie Zhou, Yuying Yan, Zhixin ZengAbstract:This study proposes three composite Wick structures (copper power or mesh sintered on grooved tube), namely, single arch-shaped sintered–grooved Wick (SSGW), bilateral arch-shaped sintered–grooved Wick (BSGW), and mesh–grooved Wick (MGW), to improve the thermal performance of ultra-thin heat pipes (UTHPs). Phase-change flattening technology is employed to fabricate UTHPs. The morphologies of the Wick structures after flattening are observed. An experimental apparatus is setup to investigate the thermal performance of UTHP samples under incremental heat loads. The heat transfer limits of UTHP are theoretically and experimentally analyzed. Capillary limit is found to be the main heat transfer limit, and the theoretical values of the samples with SSGW and BSGW are in good agreement with the experimental results. Results indicate that the maximum heat transport capacities are 12 W, 13 W and 14 W, under the corresponding optimum filling ratios of 70%, 70%, and 80%, for the SSGW, BSGW and MGW UTHPs, respectively. Evaporation and condensation thermal resistances of UTHP samples increase with the increase in the filling ratio before the occurrence of dry-out. UTHPs with SSGW have the least evaporation thermal resistance whereas UTHPs with MGW have the least condensation thermal resistance.
Yunhua Gan - One of the best experts on this subject based on the ideXlab platform.
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a novel ultra thin flattened heat pipe with biporous spiral woven mesh Wick for cooling electronic devices
Energy Conversion and Management, 2019Co-Authors: Wenjie Zhou, Zhaoshu Chen, Liqiang Deng, Yunhua GanAbstract:Abstract In this work, a novel biporous spiral woven mesh Wick is developed to enhance the thermal performance of an ultra-thin flattened heat pipe for cooling high heat flux electronic devices. The biporous Wick with different sized pores is hybrid woven using 0.05 and 0.04 mm diameter copper wires in every strand. Three different structures are designed to study the effect of the characteristic parameters of the Wick on the thermal performance of the ultra-thin flattened heat pipe. The working fluid flow characteristics of the Wick are analyzed theoretically. The capillary rate-of-rise experiment with deionized water using the infrared camera method is carried out to characterize the capillary performance of the Wick. The thermal performance of the ultra-thin flattened heat pipe is experimentally investigated. The results indicate that the biporous Wick combines the advantages of high permeability due to the large pores and large capillary force due to the small pores. The optimal biporous Wick has 22% fewer copper wires than the monoporous Wick, but the maximum heat transport capacity of the ultra-thin flattened heat pipe is able to approach 24 W, which realizes the demands of both low production cost and high thermal performance using the biporous Wick.
Yuying Yan - One of the best experts on this subject based on the ideXlab platform.
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thermal performance of ultra thin flattened heat pipes with composite Wick structure
Applied Thermal Engineering, 2016Co-Authors: Wenjie Zhou, Yuying Yan, Zhixin ZengAbstract:This study proposes three composite Wick structures (copper power or mesh sintered on grooved tube), namely, single arch-shaped sintered–grooved Wick (SSGW), bilateral arch-shaped sintered–grooved Wick (BSGW), and mesh–grooved Wick (MGW), to improve the thermal performance of ultra-thin heat pipes (UTHPs). Phase-change flattening technology is employed to fabricate UTHPs. The morphologies of the Wick structures after flattening are observed. An experimental apparatus is setup to investigate the thermal performance of UTHP samples under incremental heat loads. The heat transfer limits of UTHP are theoretically and experimentally analyzed. Capillary limit is found to be the main heat transfer limit, and the theoretical values of the samples with SSGW and BSGW are in good agreement with the experimental results. Results indicate that the maximum heat transport capacities are 12 W, 13 W and 14 W, under the corresponding optimum filling ratios of 70%, 70%, and 80%, for the SSGW, BSGW and MGW UTHPs, respectively. Evaporation and condensation thermal resistances of UTHP samples increase with the increase in the filling ratio before the occurrence of dry-out. UTHPs with SSGW have the least evaporation thermal resistance whereas UTHPs with MGW have the least condensation thermal resistance.
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Investigation of ultra-thin flattened heat pipes with sintered Wick structure
Applied Thermal Engineering, 2015Co-Authors: Yuying Yan, Zhixin ZengAbstract:Abstract This study proposes a novel sintered Wick structure called bilateral arch-shaped sintered Wick (BASSW) for the improvement of the ultra-thin heat pipes (UTHPs). The bilateral arch-shaped Wick was sintered at the middle of its copper container and the vapor flow channels are located on both sides. The sintered Wick was manufactured with several paramount parameters including maximum Wick thickness, flattened thickness, and copper powder particle size fully controlled. An experimental apparatus was set up to investigate the thermal performance of the UTHP samples under the impacts of incremental heat loads. The effects of each processing parameter on the thermal performance of the UTHP samples were analyzed and compared with a mathematical model incorporating effects of the evaporation and condensation heat transfer in a copper-water Wick. Results indicate that the most critical factor for thermal performance of UTHP is flattened thickness, as it decreases, the heat transport capability drastically decreases and the thermal resistance increases. The maximum Wick thickness affects the evaporation thermal resistances by the variation of evaporation area of the liquid–vapor interface, and particle size affects the heat transport capability by the variation of the porosity of the Wick structure. The thermal resistances of the evaporator and condenser sections are consistent with the mathematical model before dry out occurs. The total thermal resistances of the UTHP samples range from 0.02 K/W to 0.60 K/W, and the maximum heat transport capability can reach as high as 25 W.
Suresh V Garimella - One of the best experts on this subject based on the ideXlab platform.
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simultaneous Wick and fluid selection for the design of minimized thermal resistance vapor chambers under different operating conditions
International Journal of Heat and Mass Transfer, 2019Co-Authors: Kalind Baraya, Justin A Weibel, Suresh V GarimellaAbstract:Abstract The thermal resistance of a vapor chamber is primarily governed by conduction across the evaporator Wick and the saturation temperature gradient in the vapor core. The relative contributions of these two predominant resistances can vary dramatically with vapor chamber operating conditions and geometry. In the limit of very thin form factors, the contribution from the vapor core thermal resistance dominates the overall thermal resistance of the vapor chamber; recent work has focused on working fluid selection to minimize overall thermal resistance in this limit. However, the Wick thermal resistance becomes increasingly significant as its thickness increases to support higher heat inputs while avoiding the capillary limit. It therefore becomes critical to simultaneously consider the contributions of the Wick and vapor core thermal resistances in the development of a generalized methodology for vapor chamber working fluid selection. The current work uses a simplified thermal-resistance-network-based vapor chamber model to explore selection of working fluids and Wick structures that offer the minimum overall thermal resistance as a function of the vapor chamber thickness and heat input. An illustrative example of working fluid selection, for cases with and without the contribution of Wick thermal resistance, is first used to demonstrate the potential significance of the Wick thermal resistance on fluid choice. This influence of the Wick on working fluid selection is further explained based on the Wick properties (effective pore radius, permeability, and effective thermal conductivity). The ratio of effective pore radius to Wick permeability is found to be the most critical Wick parameter governing the overall vapor chamber resistance at thin form factors where minimizing the Wick thickness is paramount; the Wick conductivity becomes an equally important parameter only at thicker form factors. Based on this insight, a new approach for vapor chamber design is demonstrated, which allows simultaneous selection of the working fluid and Wick that provides minimum overall thermal resistance for a given geometry and operating condition.
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experimental investigation of boiling regimes in a capillary fed two layer evaporator Wick
International Journal of Heat and Mass Transfer, 2019Co-Authors: Srivathsan Sudhakar, Justin A Weibel, Suresh V GarimellaAbstract:Abstract Vapor chambers with transformative evaporator Wick designs capable of passively dissipating high heat fluxes over large areas, while maintaining low thermal resistances, can meet the thermal management needs of next-generation power semiconductor devices. Our prior work proposed a two-layer evaporator Wick structure to enhance the performance of vapor chambers operating at high heat fluxes. The current study experimentally characterizes the capillary-fed boiling heat transfer behavior in such a two-layer evaporator Wick, compared to a homogeneous (single-layer) Wick, over a 1 cm2 evaporator area. The two-layer design comprises a thin base Wick layer that is fed with liquid from a thick cap Wick layer above using an array of vertical posts. The two-layer Wick is fabricated using a sequence of sintering and laser-machining steps to form the base Wick layer (200 µm), array of liquid-feeding posts, and cap Wick layer (800 µm) using 90–106 µm copper particles. A test facility is constructed to replicate the conditions that exist at the evaporator of a vapor chamber; the novel facility design uses a physical restriction to prevent flooding of the Wicks during testing. Two-layer Wicks having 5 × 5 and 10 × 10 arrays of liquid feeding posts are characterized, along with a 200 µm-thick single-layer evaporator Wick. The 10 × 10 array provides a >400% enhancement in the dryout heat flux compared to the single-layer Wick. High-speed visualizations are used to identify the characteristic regimes of boiling operations for the Wicks. The single-layer Wick exhibits a partial dryout mode of operation, where a dry spot formed in the center of the heated evaporator area causes an increase in the thermal resistance with heat flux. In contrast, the distributed feeding provided by the two-layer Wicks mitigates the development of this partial dryout regime and maintains a constant low resistance (∼0.1 K/W) during capillary-fed boiling until a complete dryout event occurs. This study demonstrates the significant enhancement in dryout heat flux offered by the liquid-feeding approach realized in the two-layer evaporator Wicks characterized here.
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area scalable high heat flux dissipation at low thermal resistance using a capillary fed two layer evaporator Wick
International Journal of Heat and Mass Transfer, 2019Co-Authors: Srivathsan Sudhakar, Justin A Weibel, Feng Zhou, Ercan M Dede, Suresh V GarimellaAbstract:Abstract A two-layer sintered porous evaporator Wick for use in vapor chambers is shown to offer very high performance in passive high-heat-flux dissipation over large areas at a low thermal resistance. The two-layer Wick has an upper cap layer dedicated to capillary liquid feeding of a thin base layer below that supports boiling. An array of vertical posts bridges these two layers for liquid feeding, while vents in the cap layer provide an unimpeded pathway for vapor removal from the base Wick. The two-layer Wick is fabricated using a combination of sintering and laser machining processes. The thermal resistance of the Wicks during boiling is characterized in a saturated environment that replicates the capillary-fed working conditions of a vapor chamber evaporator. Thermal characterization tests are first performed using conventional single-layer evaporator Wicks to analyze the effect of sintered particle size on capillary-fed boiling of water. Of the particle size ranges tested, Wicks sintered from 180 to 212 μm-diameter particles provided the best combination of high dryout heat flux and a low boiling resistance. A two-layer evaporator Wick comprising particles of this optimal size and a 15 × 15 array of liquid feeding posts yielded a maximum heat flux dissipation of 485 W/cm2 over a 1 cm2 heat input area while also maintaining a low thermal resistance of only ∼0.052 K/W. The thermal performance of the two-layer Wick is compared against various hybrid and biporous evaporator Wicks previously investigated in the literature. While previous Wick designs are typically restricted to small areas and low power levels or high surface superheats when dissipating such heat fluxes, the unique area-scalability of the two-layer Wick design allows it to achieve an unprecedented combination of high total power and low-thermal-resistance heat dissipation over larger areas than were previously possible.
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Wicking and thermal characteristics of micropillared structures for use in passive heat spreaders
International Journal of Heat and Mass Transfer, 2012Co-Authors: Ram Ranjan, Suresh V Garimella, Abhijeet Patel, Jayathi Y MurthyAbstract:The thermal and hydrodynamic performance of passive two-phase cooling devices such as heat pipes and vapor chambers is limited by the capabilities of the capillary Wick structures employed. The desired characteristics of Wick microstructures are high permeability, high Wicking capability and large extended meniscus area that sustains thin-film evaporation. Choices of scale and porosity of Wick structures lead to trade-offs between the desired characteristics. In the present work, models are developed to predict the capillary pressure, permeability and thin-film evaporation rates of various micropillared geometries. Novel Wicking geometries such as conical and pyramidal pillars on a surface are proposed which provide high permeability, good thermal contact with the substrate and large thin-film evaporation rates. A comparison between three different micropillared geometries – cylindrical, conical and pyramidal – is presented and compared to the performance of conventional sintered particle Wicks. The employment of micropillared Wick structure leads to a 10-fold enhancement in the maximum heat transport capability of the device. The present work also demonstrates a basis for reverse-engineering Wick microstructures that can provide superior performance in phase-change cooling devices.
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a numerical model for transport in flat heat pipes considering Wick microstructure effects
International Journal of Heat and Mass Transfer, 2011Co-Authors: Ram Ranjan, Suresh V Garimella, Jayathi Y Murthy, Unnikrishnan VadakkanAbstract:A transient, three-dimensional model for thermal transport in heat pipes and vapor chambers is developed. The Navier-Stokes equations along with the energy equation are solved numerically for the liquid and vapor flows. A porous medium formulation is used for the Wick region. Evaporation and condensation at the liquid-vapor interface are modeled using kinetic theory. The influence of the Wick microstructure on evaporation and condensation mass fluxes at the liquid-vapor interface is accounted for by integrating a microstructure-level evaporation model (micromodel) with the device-level model (macromodel). Meniscus curvature at every location along the Wick is calculated as a result of this coupling. The model accounts for the change in interfacial area in the Wick pore, thin-film evaporation, and Marangoni convection effects during phase change at the liquid-vapor interface. The coupled model is used to predict the performance of a heat pipe with a screen-mesh Wick, and the implications of the coupling employed are discussed.
