Copper Wick Research Articles

Experimental and numerical investigations of a diffusion bonded flat-type loop heat pipe for passive thermal management

Previous diffusion bonded loop heat pipes have been researched due to the benefits of this manufacturing technique, which includes direct sealing and maintaining material properties. The previous single-material diffusion bonded loop heat pipes were made of copper, leading to a high heat leak due to high thermal conductivity, causing a reduction in efficiency. This research used a new approach that separated the evaporator from the loop heat pipe while using diffusion bonding to manufacture a loop heat pipe using two materials, copper and stainless steel. This separation allowed for lower thermal conductivity materials to be used to help reduce the heat leak. Two evaporators with different wicks were tested, one made of copper and the other made of polytetrafluoroethylene. Both designs were tested in multiple orientations and operated for a range of 15 W to 45 W with an evaporator to condenser thermal resistance ranging from 2.18 °C/W to 0.004 °C/W. Additionally, a numerical model was developed to predict the performance of both evaporators, with an average temperature difference ranging from 5.5 °C to 6.6 °C for all thermocouple locations. The heat leak ratio was analyzed using the model, and a heat leak ratio of 7.6% to 8.0% and 13.6% to 16.0% for the copper wick and polytetrafluoroethylene wick loop heat pipe was calculated, respectively. This research demonstrates that diffusion bonding copper with a lower thermal conductivity material and using low thermal conductivity sealing material can help reduce the heat leak within diffusion bonded loop heat pipes.

The Effect of Wick Permeability and Porous Radius on Capillary and Entrainment Limit in A Heat Pipe Reactor

For heat extraction in nuclear systems, interest in the design of nuclear reactors with heat pipes has increased. The determination of heat limitations is one of the remarkable factors for safety when heat pipes are used for nuclear systems. In this study, capillary and entrainment limit values for the heat pipe were calculated in a heat pipe reactor with potassium working fluid operating at 650 K. Five different effective porous radii (10.1x10-6, 10.225x10-6, 10.35x10-6, 10.425x10-6 and 10.6x10-6 m) and five different wick permeability (4.75x10-12, 5x10-12, 5.25x10-11, 5.5x10-12 and 5.75x10-12 m2) is considered for sintered copper wick heat pipe. While the effects of effective porosity radius, wick permeability, and wick radius on the capillary barrier were studied, only the effects of effective porosity radius were studied. While the effects of effective porosity radius, wick permeability, and wick radius on the capillary barrier are studied, only the effects of effective porosity radius are studied. The highest values of the capillary and entrainment limits are obtained when the porosity radius is 10.1x10-6 m. Besides, maximum capillary limits are achieved when the wick permeability is 5.75x10-12 m2 and the effective porosity radius is 10.1x10-6. This study aims to determine the optimum effective porous radius and wick permeability for this reactor and investigate the effect of effective porous radius and wick permeability on the heat pipe limitations.

Development of Electrodeposited Hierarchical Dendritic Wick Structure for Ultra-Thin Vapor Chamber Applications

Compact and light-weight electronic systems have posed stringent dimensional criteria for heat-dissipation components such as heat pipes and vapor chambers. An ultra-thin vapor chamber (UTVC) with an overall thickness below 1 mm requires an interior capillary wick structure less than 100 μm. The capillary wick layer provides a flow path for fluid circulation in an operational UTVC. The maximum UTVC heat transfer rate normally depends on liquid permeability (K) and capillary pressure (∆P) of the wick structure. Large K and ∆P values are rarely realized in typical homogeneous porous structure. In this study, a novel hierarchical dendritic copper wick was prepared to achieve large K and ∆P simultaneously by one-step electrodeposition and thermal sintering process. The effects of electrodeposition parameters, such as current density, deposition time, and solution conditions on the capillary performance of the dendritic copper wicks were investigated. The results indicate that the wicking capability is modulated by the dendritic morphology of Cu deposits. Moreover, a post-deposition sintering process can improve further the structural integrity of the Cu dendrites and the capillary performance of the electrodeposited wicks. An optimal dendritic copper wick of 30 μm in thickness possesses a promising capillary performance K/R eff of 0.811 μm, which is the thinnest wick reported in the literature.

Enhancing capillary performance of copper wicks by electrodeposition of superhydrophilic dendritic structures

Capillary wick is a critical component that sustains working fluid circulation in heat-spreading vapor chambers. A preferred wick layer requires a porous structure of multiscale porosity to meet the requirements of high liquid permeability (K) and large capillary pressure (ΔP). In this study, we controlled the etched substrate topography to modulate the morphology and capillary dynamics of the electrodeposited porous films on a specifically treated Cu substrate. The effective pore radius (Reff) of porous Cu films depends on the size and density of the dendritic bushes grown on Cu substrates treated with sodium persulfate/sulfuric acid (SPS) solution. An analytical approach was used to quantitatively analyze the dendritic deposits grown on the SPS-treated Cu substrates. The surface profile and roughness of Cu substrates were investigated by alpha-step profilometer. Scanning electron microscopy, contact angle analyzer and x-ray diffractometer were used to characterize the surface morphology, wetting behavior and oxide formation of the electrodeposited Cu films, respectively. The capillary performance (K/Reff) of the electrodeposited Cu film was measured using the capillary rate-of-rise test. The effect of dendritic bush distribution on fluid transport properties was investigated. A high K/Reff value of 0.975 μm was obtained for the electrodeposited Cu film on a Cu substrate with an optimal SPS etching treatment.

Enhanced capillary performance of hierarchical dendritic copper surface for ultrathin heat-spreading devices

High-performance electronic systems require efficient heat dissipation devices. Vapor chambers (VCs) are practical thermal solutions for lightweight portable electronics that have limited heat dissipation space. A functional VC requires an interior wick to sustain the capillary circulation of the condensed fluid back to the heated region. The capillary wick performance can be indexed by the ratio of liquid permeability to the effective pore size of the wick structure. This study describes the capillary behavior of a thin hierarchical dendritic copper film (<100 μm thick) prepared by electrodeposition and thermal sintering. The effects of the electrodeposition current density, deposition time, and sintering temperature on the capillary performance of the dendritic copper films were investigated. The relationship between the wicking capability and dendritic morphology, tailored by the electrodeposition process, was explored. A post-deposition sintering treatment was found to be beneficial for improving the structural integrity, adhesion, and capillary performance of dendritic copper wicks. A very high capillary performance (0.81 μm) was realized on a 30-μm-thick dendritic copper wick that matches the need for ultrathin VCs used in highly compact electronic systems.

Mixed phase hierarchical Ni9Se6/Cu4O4/Cu4O2/Cu4 core-shell architectures via surfactant-free approach using waste copper wicks for hybrid supercapacitors

Recently, for energy storage materials, various surfactant-less synthesis methods have been attaining extensive attention from researchers. Herein, we utilized the wasted desoldering copper wicks (E-waste) as the base substrate to synthesize hierarchical core–shell maze-corn-like nickel selenide/copper oxide (NiSe/Cu4Ox) architectures by a facile two-step synthesis process. Initially, the Cu4Ox nanorods (NRs) were grown directly over the surface of the flat braided E-waste copper wicks by thermal oxidation, followed by a facile electrodeposition method to coat the pre-existing Cu4Ox NRs with NiSe nanoparticles. The optimized NiSe-120/Cu4Ox-3 electrode exhibited superior electrochemical characteristics (138.27 µAh cm−2 at 4 mA cm−2) compared to the other electrodes, owing to the contribution of core and shell materials, and sustained an ultra-long cycling test of 50,000 charge/discharge cycles with an excellent capacity retention of 98.7%. Inspired by commercially available AA battery, the as-synthesized working electrode was coupled with activated carbon-coated nickel foam to fabricate a cylindrical-type (C-type) hybrid supercapacitor (HSC) device, with an areal capacitance of 233.1 mF cm−2 accompanied by an extraordinary cycling efficiency of 99.1%. Furthermore, the C-type HSC device exhibited maximum energy and power densities of 70.9 µWh cm−2 and 14,000 µW cm−2, respectively and it was tested by powering portable electronics for real-time application.

High-performance electrodeposited copper wicks for heat-spreading vapor chambers

A capillary wick structure is a key component for producing the capillary pressure that drives two-phase circulation in phase-change heat transfer devices such as heat pipes and vapor chambers. This study examines the capillary performance of a porous Cu wick structure fabricated using a new electrodeposition process. This Cu wick exhibits large channels generated by hydrogen bubbles and small pores in the dendritic Cu deposits resulting from high-current electrodeposition. The capillary wick performance can be effectively enhanced by adjusting the morphology of the dendritic Cu deposits. Dendritic Cu wicks with different porous features are prepared using different electrodeposition current densities and Cu sulfate concentrations in the electrolyte. A capillary rate-of-rise method is used to assess the liquid permeability (K), effective pore radius (Reff), and capillary performance (K/Reff) of dendritic Cu wicks with deionized wateras the working fluid. The Cu wick is then thermally treated at 700 °C in ambient N2 for 90 min to improve its structural integrity. Despite partial welding occurring between the fine Cu dendrites, the Cu wick shows a superior K/Reff of 1.5 ± 0.06 μm and excellent structural stability. The high capillary performance can enhance the mass transport rate and effective transport distance of the working liquid in vapor chambers for high-density and large-area heat dissipation applications. A vapor chamber integrated with an electrodeposited Cu wick demonstrates excellent heat-spreading characteristics, with a vapor thermal conductivity of up to 6500 W/m⋅K.

A novel non-destructive methodology for the analysis of deformed heat pipes

This paper presents a non-destructive methodology to analyze the influence of bend angle on the thermal performance of a sintered copper wick heat pipe. A calorimeter-based technique is used to characterize the thermal performance of a concentric tube sintered wick heat pipe under bending deformation, for a range of bend angles. It is seen that the thermal resistance of this heat pipe increases by up to 31% as the pipe was bent by 90° while its maximum heat input reduces by 29%. X-ray tomography (µ-CT) is used to obtain geometric (pipe diameter, vapor channel, etc.) and morphological (porosity, pore size distribution) data for the pipe and wick at the bend site, and this data is utilized in a thermo-fluidic model of the pipe. The methodology quantifies the local vapor and liquid pressure drops caused by deformations to the wick and vapor channel of the pipe, and their influence on the capillary pressure limit. The X-ray method revealed that, when the heat pipe was bent to 90°, there was a 23% reduction in the vapor core area, a 7% increase in the wick area, and a 48% reduction in permeability at the bend site. These geometric changes accounted for a 12% increase in the vapor phase pressure drop and a 70% increase in the liquid phase pressure drop at the bend site. When compared to the overall capillary limit the increase in liquid pressure drop demonstrated a greater contribution (12 %) in comparison to the vapor pressure drop (0.5%). In spite of the fact that the methodology presents results for a heat pipe under a specific bending case, µ-CT inspection represents a novel diagnostic tool that can underpin the optimization of heat pipe manufacture, in order to mitigate the influence of bending deformations.

Dependence of Particle Size and Geometry of Copper Powder on the Porosity and Capillary Performance of Sintered Porous Copper Wicks for Heat Pipes

Permeability and capillary performance are the most important parameters relating to the thermal performance of heat pipes. These parameters are deeply linked to pore structure, which has been influenced by the starting powder utilized. In this paper, the effect of particle size and geometry of copper powder on the porosity and capillary performance of porous wicks were systematically studied. Sintered porous wicks were made from different-sized spherical (58 μm, 89 μm, 125 μm) and dendritic (59 μm, 86 μm, 130 μm) Cu powders. The results demonstrated that the porosity and capillary performance of both types of copper powder increase with particle size due to an increase in the connectivity between internal pores. In comparison to the spherical powder, the dendritic powder demonstrated superior capillary efficiency as well as greater porosity. Additionally, a model was proposed for the capillary performance and permeability of sintered porous copper. The predicted results were quite comparable to the experimental data, demonstrating the effect of the starting powder. These findings suggest that porosity and capillary performance of porous wicks are strongly related to powder geometry as well as particle size.

Low-profile heat pipe consisting of wick-lined and non-adiabatic wickless wettability-patterned surfaces

Heat pipes are metal-wick equipped systems that circulate a phase-changing liquid and transfer heat more effectively than solid-metal compact heat spreaders. Metal wicks are effective fluid transporters, but they can face capillary limits due to significant pressure drops and pore clogging. Wettability-patterned (WP) surfaces, on the other hand, are not limited by these constraints and, as demonstrated in this work, may offer a viable supplement for metal wicks in heat pipes, which come in many shapes and sizes. The use of WP surfaces facilitates the collection and efficient transport of condensate, thus improving heat transfer from the hot (evaporator) to the cold (condenser) side of the device. Most commonly, flat heat pipes consisting of a fully wick-lined plate opposed to a wickless surface, are evaluated considering a uniform adiabatic condition on the wickless plate, which does not promote condensation. However, in a practical scenario, the heat pipe portions in contact with an external heat sink could induce condensation on the wickless side, thus affecting the heat pipe’s operation and thermal resistance. To explore this scenario, a flat heat pipe of 10 cm operating length with axially graded copper-wick evaporator and non-adiabatic wickless WP surface is designed, fabricated and tested. A wettability pattern is imparted on the wickless surface to control the maximum droplet size of the condensate and condensation mode via spatially designed superhydrophilic/hydrophobic juxtaposed areas to regulate both Dropwise Condensation (DwC) and Filmwise Condensation (FwC) towards enhanced heat transfer with reduced overall system thermal resistance. Low capillary pressure domains are allocated in this design to collect condensate on the wickless plate and return it to the evaporator’s wick. On the evaporator side of the system, variable-porosity copper wicks are being used to improve liquid conveyance from the cold to the hot domains. Four heat-transfer fluid charging ratios are examined with the best thermal resistance 0.27 K/W achieved at 105 W. The effect of wettability patterning on the wickless surface and the wick characteristics of the wick-lined evaporator are investigated. • Low-profile hybrid heat pipe comprised of wick-lined and wickless components. • Three distinct wick structures and wettability patterns investigated and compared. • Axially-graded wick structure outperforms uniform wicks. • Wettability-patterned wickless plate lowers thermal resistance. • Highest-performing system’s thermal resistance below 0.3 K/W.

Copper wick based loop heat pipe for thermal management of a high-power LED module

Contemporary high-power LED modules are subjected to severe thermal management challenges due to continuing miniaturization and increased heat flux levels. The thermal loads need to be effectively dissipated to improve module reliability by maintaining the junction temperature below 120 °C. The viability of a Loop Heat Pipe (LHP), with copper as the wick material, as a potential thermal management solution for a 200 W high-power LED module is demonstrated in this work. The investigation is conducted in two stages. Firstly, the thermal performance of the LHP is characterized by using different working fluids, and sink temperatures, to obtain the optimum working conditions, using a heater assembly mimicking the LED module. Subsequently, the LHP is integrated with an actual high-power LED module, and this thermo-mechanical demonstrator is then characterized under different real-time operating conditions. Complimentary 3D computational heat transfer simulations are carried out to estimate the LED junction temperature and visualize the thermal fields generated in the LED module. The results demonstrate the efficacy of the copper-methanol LHP design for successful thermal management of the high-power LED module dissipating over 100 W/cm2 (maintaining junction temperature below 120 °C for the 200 W nominal power LED module).

Effect of wick oxidation on the thermal performance of a copper-acetone loop heat pipe

Loop Heat Pipe (LHP) is a passive phase-change heat transfer device. Among other factors, its performance largely depends on the heat leak from the evaporator to the compensation chamber (CC). For copper wick LHP, a high heat leak creates a problem in successful LHP start-up and can adversely affect its operation. The present study focuses on reducing the heat leak through manipulation of the copper wick properties. The effect of fluid charging, overall pressure drop, and wick oxidation on thermal performance is investigated. A cylindrical copper-acetone LHP is tested in favorable orientation for two cases with (1) oxygen-free, or pure copper wick and (2) oxidized copper wick in its evaporator. For Case #1, LHP is filled with acetone at different Charging Ratios (CR) of 50%, 60%, and 70%. For Case #2, the charging ratio is kept constant at 50%. For the pure copper wick, a charging ratio of 50% provides the best thermal performance, and it decreases with an increase in charging ratios. At CR = 50%, LHP can transfer a heat load of 90 W (hEvp = ∼900 W/m2K) and 180 W (hEvp = ∼2500 W/m2K) at the evaporator temperature below 100 °C for the pure copper and oxidized wick, respectively. The significant improvement in LHP thermal performance of the latter is attributed to a decrease in heat leak because of the low thermal conductivity of the oxidized porous wick. The heat leak for pure and oxidized wick is found ∼18% and ∼7% of input heat loads, respectively. This can be an effective methodology to pave the way for the usage of commercial copper-based LHPs for the thermal management of terrestrial devices.

THERMAL PERFORMANCE OF SINTERED COPPER WICK HEAT PIPE USING WATER-BASED HYBRID NANOFLUIDS: AN EXPERIMENTAL STUDY

Relatively stable titania and silica-distilled water-based hybrid nano fluid along with surfactant are proved to be more efficient in thermal performance enhancement of heat pipes which are used for efficient cooling in electronic industry. In the current research, sintered copper wick heat pipe is utilized due to its high level of capillary action and low thermal resistance of copper wick. In this article, the vertically mounted copper sintered heat pipe containing hybrid nano fluids is investigated to measure the wall temperature as well as thermal resistance through force convection. The experimentation was carried out at heat loads of 4W, 8W, 12W, 16W and 20W by using water, titania-distilled water nano fluids and titania-silica/distilled water hybrid nano fluid filled in heat pipe in order to compare the results. By increasing the input power, the wall temperature increases from evaporator to condenser section. Maximum reduction in average vapor temperature of titania-silica hybrid nano fluid filled heat pipe and titania-distilled water nano fluid filled heat pipe was observed to be 35.74% and 31.10% as compared to water filled heat pipe at 20 W respectively. The maximum decrement in thermal resistance of titania-silica/distilled water hybrid nano fluid filled heat pipe and titania-distilled water nano fluid was observed to be 30.66% and 17.33% in comparison with water based filled heat pipe at 8 W respectively. The highest enhancement in heat transfer coefficient of titania-silica hybrid nano fluid filled heat pipe and titania-distilled water nano fluid filled heat pipe was achieved to be 29.73% and 16.21% compared to water filled heat pipe at 8 W respectively. A vi

Design, fabrication, investigation and analysis of a novel flat evaporator loop heat pipe for cooling high heat flux server chips

• A novel LHP with a flat evaporator has been proposed and tested. • SEM, porosity, and capillary rise of different sintered powder size are measured. • The heat transfer performance of the novel LHP is studied at heat loads from 50 to 750 W. • The performance comparison of the novel LHP is presented. A novel loop heat pipe (LHP) with a flat evaporator has been proposed to meet the heat dissipation requirement of high heat flux server CPU. The sintered porous copper wick was provided with a double arrayed vapor channels to increase the evaporation area. And a 1 mm thick smaller particle size copper powder embedded with two 0.5 mm thick stainless steel rings was sintered on the inner surface of the compensation chamber to enhance the strength, and increase the working fluid into the porous wick such that the liquid saturation was enhanced and the dry zone was reduced at high heat flux. Additionally, a dual layer structure condenser was presented to increase the cooling area of the condenser. In this study, the systematic experimental studies were carried out mainly focusing on the optimization of powder size, heat transfer performance of the novel LHP and performance comparison of the novel LHP. The results demonstrated that the sintered copper powder of the 106–150 μm particle size shown the best capillary performance in comparison with other powder sizes. More importantly, in the heat load range of 500–750 W, the novel LHP of filling ratio of 46.1% exhibited better operating thermal characteristics. The minimum values of the LHP thermal resistance and the total system thermal resistance at the heat load of 750 W were 0.040 °C/W and 0.090 °C/W, respectively. Compared with the conventional LHP and the simple water block, the novel flat evaporator LHP was a more promising option when the heat load was higher than 250 W.

Experimental Investigation of a Loop Heat Pipe With R245fa and R1234ze(E) as Working Fluids

Abstract Two kinds of new refrigerant R1234ze(E) and R245fa were discussed as substitutes or supplements to traditional working fluids of loop heat pipes (LHPs) based on their favorable thermophysical properties and characteristics such as being safe and environmentally friendly. Thermal characteristics of a loop heat pipe with sintering copper wick at different charging ratios were experimentally investigated under variable heat loads. The results showed that the optimal charging ratio in the loop heat pipe range from 65% to 70%, and at this charging level, the R1234ze(E) system had better start-up response, while the R245fa system presented a stronger heat transfer capacity. The characteristic temperature of R1234ze(E) system was below 35 °C, and the corresponding thermal resistance was 0.08 K/W–1.62 K/W under heat loads ranging from 5 W to 40 W. The thermal resistance of the R245fa system was 0.18 K/W–0.91 K/W under heat loads of 10 W–60 W, and the operating temperature was below 60 °C. The loop heat pipes charged with the proposed new refrigerants exhibit superb performance in room temperature applications, making them beneficial for enhancing the performance of electronics and could provide a distinctive choice for the cooling of small-sized electronics especially.

Effect of coated mesh wick on the performance of cylindrical heat pipe using graphite nanofluids

Thermal performance evaluation of TiO2-coated copper mesh wick in a cylindrical heat pipe with graphite nanofluid is experimentally analyzed at various inclinations, nanoparticle concentrations and power levels. Boiling heat transfer from the evaporator of a heat pipe depends on both thermal conductivity of the nanoparticle and suspension stability of the nanofluid. The lower the density of the nanoparticle, the better the suspension stability. Spherical graphite nanoparticles having lower density and good thermal conductivity quicken the heat transfer rate and hence the vaporization of base fluid. A hydrophilic coating of TiO2 is done on the copper wick structure to reduce the contact angle of graphite nanofluid. Results showed that the heat pipe worked well at 60° inclination compared to the other tested orientations. For this optimum condition, a reduction in 168.75% of thermal resistance is obtained compared with DI water with uncoated wick at horizontal position and also an improvement in thermal efficiency of 94.07% for 1.0 mass% particle loading. The enhancement in equivalent thermal conductivity is 90.87% for 1.0 mass% compared with DI water. Results from the repeatability test also confirm that the hydrophilic coating over the wick is stable, and results are repeatable.

Performance study of flat heat pipe with metallic copper hierarchical structure as a wick

Flat plate heat pipes (FHP) can transport high heat fluxes liberated by electrical and electronic equipment. Wick structure plays an essential role in the performance of the heat pipe. The wick structures are made of materials like sintered metal powder, foam, screen mesh, different shapes of grooves, or any material capable of producing capillary force. Generally, wick structures can be inserted or fixed easily inside the heat pipe enclosure. There are cases where one cannot insert or fix the wick structure, such as tubes with several bends and varying cross-sections. Therefore, this study directed to develop a wick structure inside the enclosure through an electrochemical process. As a preliminary study, a hierarchical wick structure is formed at the inner side of the flat heat pipe, and the performance is studied. This method can be applied to create dendrite copper wicks with the required porosity, pore size, and wick thickness by adjusting the electrolyzing conditions. In this study, a flat heat pipe is fabricated with copper hierarchical wick structure, and the performance analyzed over another heat pipe without wick and with screen wick.

Effect of the working fluid transportation in the copper composite wick on the evaporation efficiency of a flat loop heat pipe

An excellent heat transfer performance of the loop heat pipe (LHP) was not only dependent on the efficient evaporation in the evaporating zone, but also on the working fluid transportation in the wick. A double-layered composite copper wick for both efficient evaporation and high permeability was proposed to eliminate the vapor trap in the wick at high heat loads. The transportation layer was 2 mm in thickness near the compensation chamber, and the evaporation layer was 3 mm in thickness facing the evaporating zone. It was experimentally found that vapor trap and dry-out in the wick at high heat loads were relieved, because the balance between high flow rate of working fluid supply and efficient evaporation was achieved. The optimized composite wick with the particle sizes ranging from 96–180 μm and 48–96 μm was ideal for the liquid transportation and evaporation in the wick, respectively. The LHP could start in 120 s stably at a low heat load of 20 W (2.83 W/cm2), and a maximum heat load of 140 W (19.80 W/cm2) was achieved at the allowable evaporator wall temperature of 90 °C. The highest heat transfer coefficient was 30,794 W/m2K, and the lowest evaporator thermal resistance and LHP thermal resistance were only 0.046 °C/W and 0.143 °C/W, respectively, at a heat load of 140 W.

A novel ultra-large flat plate heat pipe manufactured by thermal spray

An ultra-large flat plate copper heat pipe (180 × 180 mm2) was constructed using a thermal spray technique, and it was then thermally characterized. A porous copper wick was fabricated by using a flame spray torch to deposit a mixture of copper and aluminum particles onto the target substrate. A stainless-steel wire mesh acts as a mask so that the coating deposited is in the form of an array of microstructures with channels between them. After spraying, the aluminum deposit is leached away by immersing the plate in a dilute NaOH solution to produce a porous structure. A second copper plate was placed on top of the coated surface, and their edges were vacuum brazed to form a sealed enclosure. The enclosed volume was evacuated and partially filled with water to form a heat pipe. The heat pipe was centrally heated from its bottom and cooled along its top outer edge. Three liquid filling ratios and six heat fluxes from 2.5 W/cm2 to 15 W/cm2 were investigated. A decreasing lateral thermal resistance for an increasing applied heat flux was noted for all filling ratios until central dry-out. Central dry-out corresponds to the point where the evaporation rate outpaces the wicking of the working fluid at the centre of the heat pipe. Dry-out of the central wick results in a large thermal resistance compared to the pre-dry-out condition. Delayed dry-out onset was noted for increasing working fluid filling ratios. In the pre-dry-out condition, a peak average radial thermal conductivity of 920 W/m K was noted for a 65% filling ratio, and 7.5 W/cm2 applied heat flux. A model was generated to calculate dry-out of the thermally sprayed porous wick for a given filling ratio and applied heat flux. The present research represents two highly novel advances in heat pipe technology. The first is the development of a new innovative manufacturing technique for the generation of a porous wick structure within a heat pipe. This new manufacturing technique enables the production of large metal vapour chambers with complex 3D geometries. When applied in conjunction with copper compatible working fluids, this techniques facilitates the realization of skin thermal conductors. Second, the fabrication of an ultra-large flat plate heat pipe that is significantly larger than that previously reported in the literature is demonstrated.

Experimental and Numerical Analysis of Composite Wick Heat Pipes using Ethanol

Warmth pipes come convenient now-a-days as they work with most noteworthy warmth conductance contrasted with some other method of warmth move and accessible over wide scope parameters. In the present investigation de-ionized water stream in plain thermo siphon, Sintered Copper wick and Helical scored heat pipes with synchronous vanishing, adiabatic and buildup wonder are contemplated utilizing Heat pipe test gear. In this hardware warmth pipe exposed to foreordain heat load an obstruction radiator at its evaporator end water coat with controlled progression water is utilized disperse warmth vitality at condenser end. Every one temperatures are estimated necessary computations are done get rate efficiencies at different stream rates warmth inputs. The exhibition warmth funnels correlation between their efficiencies is done. The sintered copper wick structure pipe have been found capable when stood out from other two with heat inputs beginning from 50 to 800 watts evaporator 30, condenser 72, adiabatic 110, flate heat pipe width 7.6mm, thickness 3.4 mm, first dia 6mm warmth pipe holder thickness in 0.5mm working liquid ethanol wick in view prevailing Capillarity property. The varieties of evaporator and condenser surface temperatures are plotted for changing warmth information sources and stream rate changes at condenser water coat. ANSYS programming is utilized for computational investigation and exploratory outcomes are in great concurrence with the examination.