Performance Of Heat Pipe Research Articles

Experimental study on the heat transfer performance of loop heat pipe with different particle morphology and wettability of porous wick

Particle morphology and wettability of porous wick affect the movement and distribution of the working fluid in wicks, which further affects the phase change heat transfer. So the heat transfer performance will be significantly different for loop heat pipe (LHP) with different porous wicks. To study the effects of particle morphology and wettability of porous wick on the heat transfer performance of LHP from the perspective of phase separation, four types of porous wicks were fabricated and applied in LHP. Porous wicks were sintered with spherical and dendritic particle copper powder, respectively. Superhydrophilic wicks can be obtained by H2O2 oxidation. The results showed that capillary performance of dendritic particle wick was better than that of spherical particle wick. At t = 470 s, the climbing height of distilled water in the hydrophilic dendritic and spherical particle wicks were 19.8 and 18.1 cm, respectively. Compared with hydrophilic wick, superhydrophilic wick has a maximum 2.0 cm enhancement in climbing height at present experiments. The particle morphology of porous wicks had great effects on the heat transfer performance of LHPs. For LHPs with spherical or dendritic particle wick before H2O2 oxidation, their operating temperatures were 73.5 and 68.9 °C under θ = 90°, Q = 220 W situation. The latter has a lower operating temperature. For LHP with superhydrophilic dendritic particle wick, it had the best heat transfer performance among four kinds of LHP. The minimum thermal resistance can reach 0.07 K/W at Q = 300 W. Two diffusion modes of liquid in porous wicks were found in the visualization experiment, the distribution of the working fluid in dendritic particle wick was more uniform than that of spherical particle wick, which can explain well that the temperature of evaporator bottom surface is more uniform for LHP with dendritic particle wick. These results have a good guiding role for the preparation of high-performance LHP.

Fabrication and Thermal Performance of a Polymer-Based Flexible Oscillating Heat Pipe via 3D Printing Technology.

As flexible electronic technologies rapidly developed with a requirement for multifunction, miniaturization, and high power density, effective thermal management has become an increasingly important issue. The oscillating heat pipe, as a promising technology, was used to dissipate high heat fluxes and had a wide range of applications. In this paper, we reported the fabrication and heat transfer performance evaluation of a polymer-based flexible oscillating heat pipe (FOHP) prepared using 3D printing technology. The 3D-printed inner surface presented excellent wettability to the working fluid, which was beneficial for the evaporation of the working fluid. Ethanol was selected as the working fluid, and the influence of the filling ratios range of 30-60% on heat transfer performance was analyzed. It was found that a 3D-printed FOHP with a filling ratio of 40% presented the best heat transfer performance with the lowest thermal resistance, and the fabricated heat pipes could be easily bent from 0° to 90°. With the best filling ratio, the thermal resistance of the FOHPs increased with larger bending angles. In addition, the 3D-printed FOHP was successfully applied for the thermal management of flexible printed circuits, and the results showed that the temperature of flexible printed circuits was kept within 72 °C, and its service life was guaranteed.

Experimental Study on the Effect of Water as a Working Fluid in Aluminium Heat Pipes

Thermal management of machines and electronic devices is a matter of high importance. Cooling of electronics becomes much more sensitive in applications related to space because of the difficult constraints and environment. The weight and size are very important parameters as well as the efficiency of the cooling method and heat pipes are considered a very suitable option because of its passive operation and light weight. Different working fluids can be used in a heat pipe but the compatibility of the casing material with the working fluid is a very important parameter. Water aluminum heat pipes are not a common option because they react at temperatures starting from 294 K. In this research the effect of water in the degradation of the performance of aluminum heat pipes is studied. A suitable operation range for the heat load is considered. It is found that at higher loads, the performance of the heat pipe decreased but with the addition of nano particles the performance was compensated by a large measure

Review of effective techniques for surface engineering material modification for a variety of applications

<abstract> <p>The status of current advances in modifying surfaces for the protection of materials is reviewed in this research. The main goal of material selection is to improve and reinforce surface functionalities. A few examples of surface modification techniques include sol-gel, cladding, electroplating, plasma and thermal spraying, physical deposition of vapors (PVD), vapor chemical deposition (CVD) and beam electron physical vapor deposition (EB-PVD). Strengthening by flame, induction, laser or electron beam is one type of surface modification procedure. Other types include plasma-immersed ion implantation and ion implantation at high energies, as well as diffusion treatments like carburizing and nitriding. Friction control, improved surface corrosion and wear resistance and changes to a component's mechanical or physical qualities are all possible using surface modification methods. The study also contains contemporary research in laser therapy, PVD, EB-PVD, thermal spraying and ion implantation. Additionally, magnetron sputtering (MS) is a widely used and successful approach for thin film coating in the current study. It is crucial to remember that each approach has a distinct set of restrictions, and the method's parameters might change based on the one that is selected, such as deposition targets, overall vacuum substrate temperature, reactive or mixed gas type, pressure percentage and bias voltage, which all have impacts on the PVD technique's layer qualities. Phase formation, change in phase, hardness and film structure of monolayer and multilayer films formed on the substrate under various circumstances also cause variations in the characteristics. Additionally, ion implantation enhances the surface characteristics of layers by implanting ions such as N<sup>+</sup>, B<sup>+</sup>, C<sup>+</sup>, etc. The study shows that the higher layers of multilayer enhance the degree of hardness and lower friction coefficients. To enhance the protection of thermal resistance, a thermal spraying barrier coating was coated on substrate nickel-base alloys, and the surface materials' texture, hardness and wear rate were altered by laser beam. Additionally, a heat pipe's performance was improved by a factor of 300 by adding a tiny coating of gold.</p> </abstract>

Performances of a Cylindrical Heat Pipe Using Ferrofluid as the Working Liquid at Different Inclination Angles

Performances of a Cylindrical Heat Pipe Using Ferrofluid as the Working Liquid at Different Inclination Angles

Comparison of heat-transfer performance of a flat-plate pulsating heat pipe based on heating orientation and cross-sectional shape of the pipe

Comparison of heat-transfer performance of a flat-plate pulsating heat pipe based on heating orientation and cross-sectional shape of the pipe

Review of the effect of foldability and working fluid on the performance of flexible pulsating heat pipe for foldable applications

Pulsating Heat Pipe (PHP) is the most successful device used for thermal management in different application areas. Although it is having complex thermo-hydrodynamics, many researchers carried out theoretical as well as experimental investigations and reported important information regarding its operational phenomenon like a start-up, flow pattern, thermal performance, etc. To date, the majority of PHPs are built with rigid materials such as aluminum, glass, steel, and copper because of the simplicity of fabrication, high thermal conductivity, and of course good workability. However, foldable electronic devices have recently seen an increase in demand due to their flexibility, confined space, lesser weight, and also durability, where rigid PHP may not be compatible. This in turn leads to develop a PHP that fulfills the demand for foldability. Therefore, the present paper attempts to review the developments of flexible PHPs especially made of polymer materials over the last decade. Moreover, this paper also highlights the problems associated with flexible PHPs like flexibility limitation, the high gas permeability of base material, and reduced thermal performance. The paper also tried to suggest possible solutions to such problems. The present paper will help future researchers to fabricate and design flexible thermal management systems for foldable applications.

DESIGN AND HEAT TRANSFER PERFORMANCE OF FLAT-PLATE HEAT PIPE WITH LEAF VEINS

Inspired by the principle of heat dissipation of plant leaves, a bionic flat-plate heat pipe with fractal grooves was designed according to the veins of leaves. The working principle of the bionic flat-plate heat pipe is described, and the three-dimensional model of the bionic flat-plate heat pipe is established. Based on the volume of fluid (VOF) multiphase flow model and the continuum surface force (CSF) surface tension model, the steady-state numerical simulation of its working process is carried out. The experimental pieces of leaf veins flat-plate heat pipe were made and the heat transfer performance was studied. The results show that the working principle of the bionic flat-plate heat pipe is feasible, the flat-plate heat pipe with bionic structures developed in this study can be successfully start-up. The bionic flat-plate heat pipe has high heat transfer efficiency and working fluid reflux efficiency, which can effectively reduce the maximum temperature of the flat-plate heat pipe within a certain heating power range. However, when the heating power is 100 W, the heat pipe appears to be dried out. The height of the vapor chamber will affect the maximum temperature of the heat pipe. The optimal height of the vapor chamber of the heat pipe is 3-5 mm, and the specific value needs further discussion.

Experimental investigation on thermal performance of pulsating heat pipe by using Dowtherm – A

Experimental investigation on thermal performance of pulsating heat pipe by using Dowtherm – A

Experimental investigation and a new predictive tool for thermal performance of pulsating heat pipes

Experimental investigation and a new predictive tool for thermal performance of pulsating heat pipes

Hydrothermal performance of a stepped heat pipe

Hydrothermal performance of a stepped heat pipe

Experimental Studies of Metal Oxide Suspended Nanofluids on the Enhancement of the Thermal Performance of Heat Pipes

Experimental Studies of Metal Oxide Suspended Nanofluids on the Enhancement of the Thermal Performance of Heat Pipes

Influence of filling rate and working fluid on thermal performance of heat pipes using nanoparticle layer as wick

Influence of filling rate and working fluid on thermal performance of heat pipes using nanoparticle layer as wick

Sustainable dropwise condensation enabled ultraefficient heat pipes

AbstractHeat pipes play a critical role in determining the operations, safety, and energy efficiency of electronics. The main focus to improve the heat pipe performance is on the evaporator design or wicking structures. However, the intrinsic limitation comes from the condenser, which is fundamentally constrained by inefficient filmwise condensation (FWC). In this study, we successfully achieved a peak effective thermal conductivity (keff) of ~140 kW/(m·K) on widely used groove heat pipes by implementing sustianble dropwise condensation (DWC) and integrating with enhanced evaporator. To better understand the working mechanisms of the ultraefficient heat pipe, both the evaporator and condenser of the heat pipes have been modified accordingly. Our results show that up to 296% enhancements on the keff can be achieved under various inclination angles by only inducing DWC in the condenser section. The drawback of temperature fluctuations induced by DWC in smooth heat pipes appears to be effectively solved using the grooves‐wicking structure. Furthermore, by integrating the nanostructured evaporator, the keff of the heat pipe can be boosted up to 517% compared to conventional groove heat pipes. This study, for the first time, demonstrates the huge potential of engineering both the condenser and evaporator simultaneously in developing ultraefficient heat pipes.

Experimental and numerical investigation of solid-solid phase change material assisted heat sink with integrated heat pipe for electronic cooling

Advancements in phase change materials (PCM) technology offer adaptable solutions for challenging high heat dissipation problems in electronic devices. In this work, the influence of Neopentyl Glycol (NPG) as PCM having solid-solid phase transition on the functioning of heat pipe assisted heat sink is studied. Experimental and numerical investigation was performed on the transient thermal performance of heat pipe integrated PCM-assisted heat sink application with forced air cooling. The heat pipe's evaporator section is in contact with PCM- assisted heat sink, while condenser section is exposed to the ambient. Investigations were carried out at power levels of 9–13 W, corresponding to an equivalent heat flux range of 2.5–3.5 kW/m2 and with PCM filling of 33, 66 and 99 % of the heat sink volume where without integration of PCM and heat pipe in heat sink as the reference configuration. PCM-assisted heat sink and heat pipe configurations outperformed other configurations based on charging period for all experimental parameters with a maximum enhancement ratio of 3.29. Heat sink assembly comprising 99 % PCM with heat pipe gives the most significant results on comparison with all other configurations, whereas the assembly without heat pipe showed the best results for 66 %.

Experimental investigation, CFD and theoretical modeling of two-phase heat transfer in a three-leg multi-channel heat pipe

Muti-channel flat heat pipe is an innovative technology recently used at the rear of photovoltaic cells to absorb and reuse the wasted heat. To better understand the fundamentals of two-phase heat transfer (boiling and condensation) taking place inside multi-channel heat pipes, a unique three-leg heat pipe has been built. This one-of-a-kind heat pipe was used to develop both computational fluid dynamic (CFD) and theoretical models of a multi-channel heat pipe. To simulate the heat pipe operation with ANSYS Fluent, the Volume of Fluid (VOF) approach and Lee model were investigated. Different types of Lee models using user defined function (UDF) were compared and the influence of the condenser's boundary condition, saturation temperature, and mass transfer coefficient on the simulations was studied. For the first time, major limits of the Lee model for the simulation of heat pipes are identified. It is concluded that the available Lee model cannot predict the heat pipe temperature as it shows low physical meaning and can easily be manipulated to adjust the simulation's results. Based on the three-leg heat pipe experimental data, a new multi-channel theoretical model was developed that uses the thermal-electrical resistance analogy to predict the three-leg heat pipe thermal resistance. By selecting the optimum correlations for pool boiling and filmwise condensation, the developed iterative theoretical model was able to predict the three-leg heat pipe thermal resistance with an error of 8.2%.

Theoretical and experimental investigations on the supercritical startup of a cryogenic axially Ω-shaped grooved heat pipe

The successful supercritical startup of a cryogenic grooved heat pipe is the premise for its normal operation, and the startup time determines the working efficiency of the payload. Based on this demand, a supercritical startup model of grooved heat pipe is established in the paper. The model applies more practical boundary conditions of the condensation section, without the need of knowing the temperature change of condenser in advance. With known performance curve of the cryocooler, the startup performance of heat pipe can be predicted, including the temperature distribution, startup time, etc. The predicted results by the model showed good agreement with the startup experiment results of the cryogenic grooved heat pipe. Additionally, the effects of different condenser lengths and structural parameters on the startup of heat pipe were analyzed by using the model. The results show that longer condenser length, larger groove diameter can accelerate the flow rate of condensate and the startup process. The influence of the groove depth to width of an Ω-shaped grooved heat pipe and a trapezoidal grooved heat pipe was also compared. This model provides a theoretical basis for the design and optimization of cryogenic grooved heat pipe.

Thermal Characterization of Potassium Heat Pipe Using High-Temperature Calorimetry Method Based on Evaporative Weighing

In the characterization of high-temperature heat pipes, the measurement of heat transfer is a key technical issue that needs attention. In the present experimental research on high-temperature heat pipe using potassium as the working fluid, it was noted that the gas-gap-based calorimeters have some problems, such as difficulty in experiment, low test performance, and irreversible damage to the measured high-temperature heat pipe. In this study, a high-temperature calorimeter based on evaporation weighing method was designed and built to solve the aforesaid issues. Further, the heat transfer performance of potassium heat pipe under different heating power, inclination angles and cooling methods were tested. In the experiment, a 1000 mm long potassium heat pipe was heated at a heating power of 0-3000 W, the inclination angle was changed, to test the heat transfer performance of the heat pipe. The results showed that the high-temperature calorimeter method based on evaporation weighing would provide simple and convenient way for heat pipe evaluation without destroying the structure or system of the heat pipe.

Experimental study on performances of flat-plate pulsating heat pipes coupled with thermoelectric generators for power generation

Waste heat recovery for thermoelectric power generation is an important way to achieve carbon peaking and carbon neutrality goals. In this paper, the performances of flat-plate pulsating heat pipe (PHP) coupled with thermoelectric generators (TEGs) under constant heating temperature and constant heating power conditions were comparatively studied. It investigated the effects of type, number and layer number, connection mode, and installation mode of TEGs on the performances of the coupling system. Results indicate that there are different optimal types of TEGs in the coupling system under different conditions. The effects of connection mode, installation mode and cooling water flow rate on the maximum output power of the coupling system appear to be negligible. Under constant heating power conditions, the increase in the number of TEGs reduces the maximum output power and conversion efficiency. Three-layer TEGs can optimize the performances of the coupling system, and the maximum output power and open-circuit voltage can reach 4.115 W and 22.3 V at the heating power of 160 W. However, under constant heating temperature conditions, the effects of number and layer number on output power are completely opposite to those at constant heating power conditions. The maximum conversion efficiency of the coupling system is 4.40% at the heating temperature of 100 ℃. For thermal performances of the coupling system, the effective thermal conductivity can be up to 873 W/(m·K) and the thermal resistance is only about 0.1 ℃/W. The coupling system has broad application prospects in the fields of driving LED lamps and producing hydrogen by water electrolysis.

Comprehensive three-dimensional hydrodynamic and thermal modeling of steady-state operation of a flat grooved heat pipe

Mathematical modeling of grooved heat pipes is a challenging task since multiple coupled physical phenomena such as phase change, free-surface flow and heat transfer are involved. Moreover, the fact that the shape of the liquid–vapor interface in the heat pipe is unknown a priori requires simultaneous determination of the interface variation as a part of the solution procedure, a capability currently not addressed in commercially available engineering CFD tools. In this study, a multi-dimensional and multi-scale computational model is presented to gain a comprehensive understanding of the underlying physics of grooved heat pipes. The computational model is based on an iterative scheme for the solution of 3D heat transfer and liquid flow, interface phase change heat transfer (evaporation and condensation) and shape of the interface. The model is implemented using three different methodologies two of which utilize commercial engineering CFD software. The results are verified for a problem previously studied in the literature which indicates the robustness of our computational approach.