Porous Wick Research Articles

Developing of an open-source toolbox for liquid-vapor phase change in the porous wick of a LHP evaporator based on OpenFOAM

The deep understanding of characteristics and mechanism of liquid-vapor phase change and capillary pumping in porous wick is necessary for the optimal design of efficient heat transfer devices such as loop heat pipes. This paper develops a toolbox based on OpenFOAM for simulating the two-phase flow and phase change heat transfer in the hybrid domain using the micro-continuum model, which can asymptotically converge to Darcy model in porous domain and NS equation in solid-free domain. The toolbox also provides choices for the phase change model, capillary pressure model, and specific boundary conditions. The toolbox is validated by comparing the simulation results with analytical solutions or published results through several example problems. The simulation of the LHP evaporator indicates the receding of liquid-vapor interface into the porous wick with the increasing of heat flux, and its thermal performance is in good agreement with previous experimental studies. The developed toolbox can be anticipated to do theoretical and optimized studies on phase change heat transfer in porous media.

Experimental investigation on the start-up performance of a novel flat loop heat pipe with dual evaporators

Thermal management for multiple heat sources has been becoming increasingly important, especially under high heat flux conditions. As a passive heat transfer device, loop heat pipes (LHP) with multiple evaporators does not consume extra energy, demonstrating a great potential in thermal management. This paper proposed a flat plate LHP with dual evaporators for the first time. Two flat plate evaporators were adopted, and both of them had their own porous wick, compensation chamber (CC) and vapor line. The condensed liquid converged, then moved along the main liquid line. The CC of two evaporators was joined by a tube, which can ensure the sharing of the returning liquid. To verify the performance of novel flat plate LHP, the start-up test was investigated under different heat load arrangements, involving only a single evaporate was applied heat load, two evaporators were applied with the equal or unequal heat load. Meanwhile, the operation stability was determined by testing the performance with the successionally variable heat load. This system has been shown to operate successfully at heating source temperature below 100 °C with heat load ranging from 10 W–10 W to 130 W–130 W (corresponding to the maximum heat flux of 13.52 W/cm2).

Theoretical analysis of bubble nucleation in liquid film boiling

Many industrial applications such as electronic cooling and thermal desalination have adopted the heat dissipation technologies of capillary evaporation and liquid film boiling, with bubble nucleation being the transition criterion between them. In this paper, a theoretical model for bubble nucleation in liquid film boiling is developed, which mainly considers three aspects: transient heat conduction inside the liquid film supported with porous wick, evaporation at the liquid-vapor interface, and superheat requirement for the stable existence of a bubble nucleus. The criterion for the onset of nucleate boiling (ONB) in liquid film boiling is established, and size range of active microcavities for bubble nucleation is obtained, as well as comparisons being made with that during pool boiling and flow boiling. The results indicate that the size range of active microcavities in liquid film boiling is narrower with the minimum size being several times larger, and bubble nucleation in liquid film boiling is much more difficult. Although superhydrophilic surface with small contact angle is disadvantageous to bubble nucleation, it will decrease the minimum size of effective microcavities radius within the size scope of a few micrometers, which is beneficial for ONB in liquid film boiling. Moreover, critical thickness to trigger ONB in liquid film boiling is found to decrease with increasing contact angle, augmenting superheat and strengthening effective thermal conductivity of the wick, and its theoretical prediction is validated with experimental data in the literature. Our model offers a new avenue for understanding the ONB in liquid film boiling, and therefore can serve as a guideline for future enhancement design.

Computational comparison and experimental performance analysis on heat pipes using concentrating solar parabolic trough collector

The heat pipes in solar applications uses are important and it is significantly growing nowadays. Capable of meeting the world’s challenges with a threat to the climate; a shortage of conventional energy sources, usually fossil fuels, high electricity costs, and it is inexpensive; therefore, the renewable energy of solar energy is an excellent source, reaching total amount of energy is 34,00,000 EJ in each year, all over the world. This is between 7000 and 8000 times the annual global primary energy consumption. Thereby, a Concentrating Solar Parabolic Trough Collector is suggested in this paper, which can be used to analyze the performance of various heat pipes. Using solar parabolic trough collector to analyze the performance of different heat pipes rather than considering the supply of electric power input. Using a parabolic trough collector that concentrates solar energy on an evacuated tube heat pipe, which converts radiation energy into electrical energy heat, the experimental work demonstrates the use of solar energy. Condensers, evaporators, and three heat pipes consisting of aluminum galvanized iron, and stainless steel materials are the main components. A porous wick structure and an ammonia solution-filled working fluid consist of each heat pipe. Continuously recirculating the working fluid through temperature variation. The readings are taken using connected thermocouples on three heat pipes by continuously varying the mass flow rate. The vacuum pressure gauge to maintain the heat pipes generates the vacuum inside space. At various mass flow rates of heated water from the parabolic trough collector, experimentation was also performed. The result of this study calculates the mass flow rate at the end of the process of the different heat pipes used here. Furthermore, different inclinations are estimated in a variety of situations, such as at temperatures of 15°, 30°, 45°, and 60°. In the experimental analysis, outlet temperatures of heat pipes are measured and the temperature distribution contours are evaluated using the analysis of computational fluid dynamics.

Investigation of interface profiles in meshed wicks and related evaporation characteristics

The porous wick in a heat pipe determines the working fluid capillary replenishment ability and heat transfer process. To study the evaporation characteristics of meshed wicks fabricated with wires of micron-scale, a mathematical model based on the augmented Young-Laplace equation and molecular kinetic theory to predict the evaporation interface profile is developed, and the Marangoni effect and slip velocity in the boundary are considered. The evaporation interface can be divided into the thin-film region and intrinsic meniscus region according to the ratio of capillary pressure and disjoining pressure. A new solution method considering the constraints at the intersection of the two regions to obtain the interface profile is proposed and validated. Based on the two-dimensional results, the area and heat transfer rates of the two regions formed in the meshed wicks are calculated by integrating along the four side wires. Then, the evaporation characteristics of the thin-film region, including the pressure and thermal resistance distribution, are studied. Finally, the influence of the Marangoni effect, superheat, wire spacing, interface pressure difference and slip velocity on the interface profile and heat transfer of these two regions are discussed.

Vapor generation via porous nanochannel wicks

Vapor generation rate in nano/microstructured-based interfacial vapor generation devices is limited by water supply. Here, we report an innovative design for enhancement in vapor generation using porous nanochannel wicks. Vapor generation rate of 1.18 kg m − 2 h -1 is achieved in a dark environment (without heat input) and of 17.12 kg m − 2 h -1 is achieved with a heat input of 5.08 W at low temperature of 62°C, significantly higher than a typical vapor generation rate reported for interfacial solar vapor generation systems. We also demonstrate our wick’s performance under solar heat flux of 1.25 sun and attain a vapor generation rate of 4.87 kg m − 2 h -1 at surface temperature below 35°C. Thus, we present an unconventional approach of separating surfaces of vapor generation and heat supply that would provide additional flexibility in the choice of energy source, such as solar energy and waste heat from exhaust gases. This approach can be consequential in low-grade waste heat recovery. • Wick made of cross-connected buried nanochannels with micropores at intersections • Capillary-induced passive water supply with simultaneous evaporation at micropores • Thin film evaporation causes high vapor generation rate at low surface temperature Vapor generation rates are limited in passive nano/microstructure-based interfacial vapor generation devices. Ranjan et al. report the performance of a porous nanochannel wick design that can achieve high vapor generation rate with solar heat flux, with waste heat, and even in the absence of heat supply.

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.

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.

Multiobjective Optimization of Graded, Hybrid Micropillar Wicks for Capillary-Fed Evaporation.

As electronic device power densities continue to increase, vapor chambers and heat pipes have emerged as effective thermal management solutions for hotspot mitigation. A crucial aspect of vapor chamber functionality depends on the properties of the microporous wick that drives heat and mass transport within the device. While many prior studies have focused on the optimization of these porous structures to increase the maximum capillary-limited dryout heat flux, an equally important aspect of porous wick design is the minimization of the thermal resistance above heated areas. Segmented wicks with geometries that vary along the length of the wick are attractive candidates that can potentially be used to fulfill these simultaneous design goals. Previous studies on bisegmented wicks with only two distinct adiabatic and heated region geometries, however, have shown mixed results regarding the degree of performance benefit over homogeneous wicks. In this work, we present a systematic modeling approach to investigate the optimal composition of segmented micropillar wicks comprising multiple, discrete regions of graded geometry. Using a genetic algorithm, we generate Pareto fronts of optimal segmented wick distributions that maximize the dryout heat flux and minimize the thermal resistance for a given heating configuration. We find that optimal, graded segmented wicks are capable of dissipating dryout heat fluxes more than 200% higher than baseline homogeneous wicks with significantly lower thermal resistance. The sensitivity of the wick performance to the total number of geometry segments is found to vary depending on the desired heat flux and thermal resistance operating regimes.

Performance analysis for single slope solar still enhanced with multi-shaped floating porous absorber

In this study, the performance of the single slope solar still is improved by floating the porous wick material with different geometries in the basin. The jute cloth is used as the porous wick absorber, which is floated in the basin by the thermocol material. Three modified solar stills (named by MSS) with three absorber’s geometries are considered. The porous wick layers with flat, triangular-shaped, and semicircular-shaped tooth are used as the absorber surface in MSS-1, MSS-2, and MSS-3, respectively. The productivity and performance of these modified solar stills are compared to the conventional single slop solar still (named by CSS). The theoretical method is used to perform the performance analysis of these solar stills. The results showed that all three MSS devices produce more than 0.6 kg.m−2.hr-1 of freshwater during most of its operating hours, while the CSS device produces this amount of freshwater in only the last few hours of its operation. MSS-3 device produces the most daily yield among the other modified stills, which produces 65% more daily yield in comparison with the CSS device.

Experimental Study on the Heat Transfer Performance of Pump-Assisted Capillary Phase-Change Loop

To overcome the two-phase flow instability of traditional boiling heat dissipation technologies, a porous wick was used for liquid-vapor isolation, achieving efficient and stable boiling heat dissipation. A pump-assisted capillary phase-change loop with methanol as the working medium was established to study the effect of liquid-vapor pressure difference and heating power on its start-up and steady-state characteristics. The results indicated that the evaporator undergoes four heat transfer modes, including flooded, partially flooded, thin-film evaporation, and overheating. The thin-film evaporation mode was the most efficient with the shortest start-up period. In addition, heat transfer modes were determined by the liquid-vapor pressure difference and power. The heat transfer coefficient significantly improved and the thermal resistance was reduced by increasing liquid-vapor pressure as long as it did not exceed 8 kPa. However, when the liquid-vapor pressure exceeded 8 kPa, its influence on the heat transfer coefficient weakened. In addition, a two-dimensional heat transfer mode distribution diagram concerning both liquid-vapor pressure difference and power was drawn after a large number of experiments. During an engineering application, the liquid-vapor pressure difference can be controlled to maintain efficient thin-film evaporation in order to achieve the optimum heat dissipation effect.

The Influence of Loop Heat Pipe Evaporator Porous Structure Parameters and Charge on Its Effectiveness for Ethanol and Water as Working Fluids.

This paper presents the results of experiments carried out on a specially designed experimental rig designed for the study of capillary pressure generated in the Loop Heat Pipe (LHP) evaporator. The commercially available porous structure made of sintered stainless steel constitutes the wick. Three different geometries of the porous wicks were tested, featuring the pore radius of 1, 3 and 7 µm. Ethanol and water as two different working fluids were tested at three different evaporator temperatures and three different installation charges. The paper firstly presents distributions of generated pressure in the LHP, indicating that the capillary pressure difference is generated in the porous structure. When installing with a wick that has a pore size of 1 μm and water as a working fluid, the pressure difference can reach up to 2.5 kPa at the installation charge of 65 mL. When installing with a wick that has a pore size of 1 μm and ethanol as a working fluid, the pressure difference can reach up to 2.1 kPa at the installation charge of 65 mL. The integral characteristics of the LHP were developed, namely, the mass flow rate vs. applied heat flux for both fluids. The results show that water offers larger pressure differences for developing the capillary pressure effect in the installation in comparison to ethanol. Additionally, this research presents the feasibility of manufacturing inexpensive LHPs with filter medium as a wick material and its influence on the LHP’s thermal performance.

A wicked heat pipe fabricated using metal additive manufacturing

Additive Manufacturing (AM) has emerged as a high-potential manufacturing technology for fabricating all-in-one heat exchange devices that incorporate embedded two-phase heat transport and spreading systems. A key enabler of this technology is the capacity for AM to fabricate porous wick structures. To this end, this work experimentally investigates a simple AM-fabricated aluminum structure with an inner cavity. Within the cavity, a single-sided wick heat pipe is fabricated, again by aluminum AM. To facilitate capillary wicking within the embedded heat pipe, while being amenable to the direct metal laser sintering (DMLS) AM process, a novel cross-hatched porous wick structure is introduced. The wicks were fabricated by printing layered rows of fine wire-like features at different angles to one another in successive layers, creating a porous 3D structure. The resulting 3D wick structure was varied by controlling the hatch distance between neighboring printed wires in each layer, resulting in different wick properties. In this investigation, the capillary performance of three wicks were interrogated using the Rate of Rise technique, which also facilitated estimation of important wick properties such as permeability and effective pore radius. By varying the hatch distance between 0.6 mm and 1.0 mm, the permeability ranged between 35.6 and 39.6μm 2 with a corresponding range of 127–88 μm for the effective pore radius and 43–59% for the porosity. The efficacy of the proposed metal AM heat pipe concept was then verified by enclosing the wicks within a lid casing, creating two-part flat heat pipes, and experimentally characterizing them with acetone used as the working fluid. This study includes performance indicators such as overall thermal resistance, effective wick thermal conductivity, and effective thermal conductivity of the heat pipe cavity region.

Analytical steady-state model based on Fourier integral transforms for cylindrical heat pipes under axisymetric conditions

A thermohydraulic analytical model of a capillary cylindrical heat pipe in steady-state is proposed in this article. It is based on an original representation by thermal quadrupoles to describe heat transfer in the wall and in the porous wick, via the use of Fourier integral transforms. Thanks to a validation from literature results, this model provides two-dimensional axisymetric thermal fields and one-dimensional pressure and velocity profiles of both liquid and vapour flows. Different developments and solutions are introduced according to the kind of boundary conditions at evaporator and at condenser, and with a more or less strong thermohydraulic coupling at the liquid/vapour interface. For the simple case with imposed uniform heat fluxes, intrinsic properties of the heat pipe are originally defined. The introduced model offers a generalisation of analytical models of standard heat pipe as a design or optimisation tool. Wider developments of analytical models for more complex three-dimensional geometries of heat pipe and in transient regime can be expected.

Three-dimensional lattice Boltzmann investigation on pore scale liquid–vapor distribution patterns and heat transfer performance of a loop heat pipe heterogeneous porous wick evaporator

The pore scale numerical simulations on evaporation of a three-dimensional heterogeneous porous wick capillary evaporator used in a loop heat pipe (LHP) are realized through using a lattice Boltzmann method with liquid–vapor phase change. The dynamic liquid–vapor interface characteristics are obtained. The steady-state wick state and heat transfer performance as well as the influences of wick porosity and surface wettability are discussed. It is found that as heat flux increases, the wick state changes from the fully saturated state at low heat fluxes, to the partial dryout state at medium heat fluxes, and finally to the complete dryout state at high heat fluxes. The effective heat transfer coefficient of evaporator firstly grows slowly for the saturated wick, then increases rapidly and reaches a maximum value at partial dryout wick state, but afterwards drops sharply when the wick starts to be complete dryout. With the decreasing of wick porosity and contact angle, the heat flux to achieve the maximum effective heat transfer coefficient is increased and the complete dryout state is postponed. In the present range of parameters, the maximum effective heat transfer coefficient is improved by reducing wick porosity, while it is barely affected by contact angle.

Experimental Study on Preparation and Heat Transfer of Nickel-Based Ammonia Loop Heat Pipe

Abstract The loop heat pipe (LHP) is a passive heat sink used in aerospace and electronic devices. As the core component of the LHP, the physical property parameters of porous wick directly affect the overall performance of the LHP. In this paper, the performance of the porous wick is improved by adjusting the pore size, thereby improving the performance of the LHP. The nickel-based double-pore porous wicks are prepared by T225 nickel powder and NaCl particles, and the pore size of the porous wicks can be changed by different cold pressing force (30 kN, 40 kN, 50 kN, and 60 kN). The effects of different cold pressing force on the porosity, permeability, and other physical property parameters are studied when the ratio of pore former is 20 wt.%. In the end, we select the cold pressing force of 30 kN to prepare the porous wick of the LHP. Then the effects of constant load and variable load of the heat transfer performance under different placement elevations are studied. The results show that the heat load range is 10 W–100 W, the minimum evaporator thermal resistance is 0.424 K/W, and the minimum LHP thermal resistance is 0.598 K/W. When β = 0 deg, there is a “backflow” phenomenon at the initial stage of low thermal load. With the increase of thermal load, the “backflow” duration decreases until it disappears, and the startup time becomes shorter. The thermal resistances of the evaporator and LHP decrease rapidly and then slowly increase. When β = –90 deg, the LHP appears to demonstrate “reverse startup” phenomenon.

Pore scale study on capillary pumping process in three-dimensional heterogeneous porous wicks using Lattice Boltzmann method

Quartet structure generation set (QSGS) method is improved to numerically reconstruct three-dimensional heterogeneous porous wicks with uniform pore size distribution. The capillary pumping processes of the reconstructed random porous wicks are simulated at pore scale by using a three-dimensional two-phase lattice Boltzmann model. The evolutions of two-phase interface and the variations of the imbibed liquid volume fraction with time are analyzed under the conditions of different porosity, pore structure, and surface wettability. The comparisons between the LBM results and those predicted by a macroscopic scale homogenous model are also conducted. It is found that due to the pore scale effects, the two-phase interface in a random porous media is very irregular, especially at the earlier stages of capillary pumping process when the liquid penetration is faster, and the imbibed liquid does not increase exponentially with time as predicted by the macroscopic scale model. Meanwhile, the liquid penetration rate does not decrease monotonously, but exhibits different degrees of fluctuations. The pore scale effects are more prominent in the cases of lower porosity, smaller pore size and better surface wettability. In the parametric range of the present study, the capillary performance increases with the decreasing of porosity, average pore radius (when porosity is fixed) and contact angle.

Experimental Study of a Loop Heat Pipe with Direct Pouring Porous Wick for Cooling Electronics

A pouring silicate wick was manufactured to explore the influence of process and physical properties on the production and performance of loop heat pipes (LHP). This paper theoretically analyzed the advantages of pouring porous wick and introduced the technology of pouring silicate directly on evaporator. Based on this, the heat transfer performance of copper-methanol LHP system with pouring porous wick was tested under different positions. The results showed that with the input of multiple heat sources, the LHP could start up and maintain a stable temperature from 40 W to 160 W. When the vapor grooves were located above the compensation chamber, it was difficult to start up positively. By adding gravity assistance, the system could obtain more stable liquid supply and vapor flow, so as to realize start up. In the variable heat load test, the LHP showed good adaptability to the change of heat load. The thermal resistance of the system decreased with the increase of heat load. The thermal resistance of the evaporator almost unchanged and was always lower than 0.05 °C/W, which indicated that the pouring porous wick in the evaporator had good heat load matching.

Numerical investigation on transient and steady phase change heat transfer in the evaporator of a loop heat pipe

The dynamic evolution of vapor-liquid distribution in a porous wick coupled with the heat conduction in the evaporator casing of a loop heat pipe is numerically solved. The mathematical model is validated based on the experimental results issued from the literature. Both the transient and steady-state thermal behaviors of the evaporator are focused on, with the self-adjusting ability, evaporator temperature, thermal resistance, and parasitic heat leakage analysis as the evaluation indexes. The gradual invasion of the vapor region into the wick over time and the robust response of the evaporator temperature to varying heat loads are tracked. Additionally, the steady-state performance is explored to optimize the structural parameters, namely, the location of grooves, wick material and porosity, casing material, and fin ratio, through which the specific influences of each parameter are figured out. It is found that locating grooves in wick yields a 7.63°C lower evaporator temperature and a more uniform temperature distribution on the evaporator with a difference of 0.75°C than in casing at 140 W. Additionally, a 0.9 mm thick nickel layer with a porosity of 0.4 combined with a 4.1 mm nickel stainless steel layer with a porosity of 0.75 constitutes an optimized layered wick, which exhibits a 7.04°C lower evaporator temperature and a 0.05°C/W smaller thermal resistance than a single-structured stainless steel wick with a porosity of 0.75. Considering the heat transfer and flow pressure drop, the counterbalanced fin ratio range of 0.5~0.6 and the better thermal performance of copper casing are identified. The numerical results are expected to provide references for the evaporator structure optimization, laying a solid foundation for applying loop heat pipes to thermal control fields.

Experimental investigation on wettability and capillary performance of ultrasonic modified grooved aluminum wicks

The grooved wick has a promising potential in the field of ultra-thin flat heat pipes, and the porous structure can improve the capillary performance of grooved wicks significantly. In this paper, an environmentally friendly method, named as ultrasonic modification, was developed to fabricate porous microstructures on grooved aluminum wick. The effects of ultrasonic modification times on the morphology, wettability and capillary performance of the porous grooved wick were investigated. The results indicate that appropriate ultrasonic modification times can realize an excellent distribution of porous microstructures throughout the groove surface. After ultrasonic modification, the modified surface became hydrophobic since the porous microstructures were covered with a low-surface-energy coating. However, in case of aluminum heat pipes with acetone as working liquid, the wettability and capillary performance of the modified grooved wick can still be enhanced significantly. The maximum capillary rise height and the capillary performance parameter of the modified grooved wicks were increased for a factor of 3 and an order of magnitude, respectively. This study provides a new idea for the fabrication of porous aluminum wicks, which is beneficial to promote the development of ultra-flat aluminum heat pipes.