Cylindrical Heat Pipe Research Articles

Passive Cooling of PV Modules Using Heat Pipe Thermosiphon with Acetone: Experimental and Theoretical Study

The effect of heat pipe thermosiphon in reducing the operating temperature of a photovoltaic panel has been analyzed theoretically and experimentally in this paper. Copper heat pipe thermosiphon with acetone as a working fluid was used. The theoretical study involved a heat balance analysis of the panel with cylindrical heat pipe with surface contact with the panel bottom. The experimental study involved recording temperature variations, with and without a heat pipe, which had very good agreement with the theoretical results of 2.61%. Additionally, the optimum quantity of acetone was 50 mL, with a maximum reduction in panel temperature of 10 °C.

Вплив форми гравітаційної теплової труби з різьбовим випарником на її теплопередавальні характеристики

The modern development of electronics is associated with the problem of reducing the mass and size of the equipment while increasing its power. This leads to an increase in the temperature of both individual elements and the device as a whole, which contributes to a decrease in equipment reliability. This makes the development of inexpensive yet efficient cooling systems an urgent task. One of the ways to solve this problem is to use heat pipes of a new simplified design in cooling systems. This article compares the thermal characteristics of a cylindrical copper gravity heat pipe with a threaded evaporator before and after flattening. The working fluid used in the experiment was R141b. Experimental studies were conducted at two tilt angles relative to the horizontal under the conditions of forced convection cooling of the condensation zone. The influence of the change in the shape of the body from cylindrical to flat on the temperature in the heating zone of the heat pipe, thermal resistance, and heat transfer coefficients in the evaporation and condensation zones was shown in the range of heat power from 5 to 70 W. The choice of the heat pipe is justified based on the maximum thermal loads of electronic components and the orientation of the cooling system in space. Changing the shape of heat pipe from cylindrical to flat leads to a decrease in the maximum thermal power transmitted, but a flat heat pipe shape is more technologically feasible for use in cooling systems of electronic equipment.

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

Comparative Performance Analysis of Exhaust Air Heat Recovery Devices Based on Microchannel heat pipe

In response to the problem of low recovery efficiency of sensible heat recovery devices, this paper designs a microchannel heat pipe heat recovery device (MHPHRD) and compares its heat transfer performance during summer use through experiments and simulation calculations. The experimental results show that the microchannel heat pipe (MHP) has strong temperature uniformity, and the temperatures of the evaporation and condensation sections are basically the same. When the inlet temperature of fresh air changes between 32°C and 40°C, the recovery efficiency of the device varies between 67%-80%, and the linear relationship between the two is obvious. The established calculation model has high accuracy, with a maximum error of 0.7% between measured and simulated values. Simulation calculations show that the cooling capacity recovery efficiency of the MHPHRD is 4%-16% higher than that of the cylindrical heat pipe heat recovery device (CHPHRD), and 24%-30% higher than that of the plate heat recovery device (PHRD). The research in this article can provide reference for the practical application of the device.

Surface treatment on metal foam wick of a ferrofluid heat pipe

In this current investigation, two metal foams (stainless steel) were treated and cleaned to be modified into superhydrophilic and superhydrophobic surfaces. The surface modifications of the metal foams were prepared using acetone cleaning and superhydrophobic coating methods. The two metal foam samples were then characterized to analyze the morphology, physical properties, wettability and capillary. The superhydrophilic metal foam was chosen as the wick structure in cylindrical heat pipe because of high wettability, and capillary behavior as characterized previously. In the cylindrical heat pipe, ferrofluid was used as the working liquid. The cylindrical heat pipe was tested at two heat input variations of 3 and 5 W in a horizontal direction. The heat pipe's performance test proposed that the optimum thermal resistance is 2.47 °C/W at a heat input of 5 W.

Investigation of the Thermal Performance of a Nanofluid-filled Grooved Cylindrical Heat Pipe for Electronics Cooling

Thermal management of electric and electronic components is a critical issue and needs to consider enhanced cooling systems such as heat pipes. This study deals with the theoretical modeling of a nanofluid-filled copper cylindrical heat pipe for electronics cooling applications. The heat pipe includes helicoidal and trapezoidal capillary grooves. The model can predict the capillary limit as well as the heat transfer in the different sections of the heat pipe. The thermal resistances of the evaporation and condensation sections are calculated based on correlations for heat transfer, which are determined from experiments. Two working nanofluids are considered: water/CuO and water/Al2O3. The thermal performances are predicted for different concentrations and heat sink temperatures, and the heat pipe is positioned horizontally. For both nanofluids, the results indicate that augmenting the concentration of the nanoparticles leads to a capillary limit increase reaching up to 14 % and 25 % for water/Al2O3 and water/CuO, respectively, and an overall thermal resistance decrease reaching up to 51 % and 68 % for water/Al2O3 and water/CuO. Moreover, decreases up to 24 %, and up to 18 % in the evaporator wall temperatures are obtained for water/CuO and water/Al2O3 nanofluids, respectively. The nanofluid water/CuO gives the best thermal performance whatever the nanoparticle concentration and heat sink temperature.

Manyetik Alan Altinda Nanoakişkanlarin Akiş Karakteristiklerinin İncelenmesi

The existence/application of an externally induced magnetic field, like in satellite cooling applications, causes a decrement in heat transfer when used with nanofluids. This study investigates the flow characteristics and velocity profile of distilled water, alumina nanofluid, and cobalt ferrite ferrofluid in a horizontal cylindrical heat pipe flowing in a laminar regime and being exposed to an external magnetic field. All of the simulations were performed with ANSYS Fluent MHD module, for a concentration of 2%, Reynolds number of 10, and Hartmann numbers of 25, 50, and 150. The velocity profiles, pressure drops, and flow characteristics are examined by varying the magnetic field intensity while keeping all other parameters constant. It is concluded that an external magnetic field causes a deterioration in the velocity profiles of the nanofluid, especially in cobalt ferrite, while it does not have a significant effect on water. When the magnitude of the magnetic field is increased by 2 times, it is seen that the velocity of the fluid decreases by 6% and increasing the magnetic field from 0 to 50 Tesla causes a deceleration rate of 9%, which leads to the conclusion that application of a magnetic field for the first time has a more significant slowing effect when comparing it to increasing the magnetic field. In addition, when a magnetic field of 50 Tesla is considered, the maximum velocity of alumina is lower than that of water by 5.10%, and the maximum velocity of cobalt ferrite is lower by 28.57%.

Experimental investigation of thermal characteristics of a cylindrical heat pipe under varied system parameters and operating conditions

Abstract A heat pipe transfers heat effectively between two solid surfaces by incorporating the principles of the transition of phase and thermal conductivity. The study aims to investigate the thermal characteristics of a cylindrical heat pipe and the various factors affecting its performance. The effect of different working fluids, i.e., water, ethanol, and methanol, wick material, i.e., copper and stainless steel, and angle of inclination varied from varied between 0° and 90°. The fill volume is also varied from 20 to 40% to analyze the thermal resistance and effective thermal conductivity of the heat pipe. The optimum value of angle of inclination is found to be 60° at 30% fill volume of working fluid irrespective of the wick material.

The effect of operating parameters on the heat transfer in the heat pipe

Heat pipes are a good solution for temperature stabilization, for example, of microelectronics, because these kinds of systems are without any moving parts. Experimental research of the effect of operating parameters on the heat transfer in a cylindrical heat pipe has been conducted. The effect of the working fluid properties and the porous layer thickness on the heat flux and temperature difference in the heat pipe has been investigated. The temperature field of the heat pipe has been investigated using the IR-camera and K-type thermocouples. The data obtained by IR-camera and K-type thermocouples have been compared. It is demonstrated the power transferred from the evaporator to the condenser is a linear function of the temperature difference between them.

Experimental and theoretical investigation of heat transfer characteristics of cylindrical heat pipe using Al2O3\u2013SiO2/W-EG hybrid nanofluids by RSM modeling approach

Nanofluids are emerging two-phase thermal fluids that play a vital part in heat exchangers owing to its heat transfer features. Ceramic nanoparticles aluminium oxide (Al2O3) and silicon dioxide (SiO2) were produced by the sol-gel technique. Characterizations have been done through powder X-ray diffraction spectrum and scanning electron microscopy analysis. Subsequently, few volume concentrations (0.0125–0.1%) of hybrid Al2O3–SiO2 nanofluids were formulated via dispersing both ceramic nanoparticles considered at 50:50 ratio into base fluid combination of 60% distilled water (W) with 40% ethylene glycol (EG) using an ultrasonic-assisted two-step method. Thermal resistance besides heat transfer coefficient have been examined with cylindrical mesh heat pipe reveals that the rise of power input decreases the thermal resistance and inversely increases heat transfer coefficient about 5.54% and 43.16% respectively. Response surface methodology (RSM) has been employed for the investigation of heat pipe experimental data. The significant factors on the various convective heat transfer mechanisms have been identified using the analysis of variance (ANOVA) tool. Finally, the empirical models were developed to forecast the heat transfer mechanisms by regression analysis and validated with experimental data which exposed the models have the best agreement with experimental results.

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.

Thermal performance of a cylindrical shell-like thin networked pulsating heat pipe

The cylindrical vapor chamber with its interior vapor–liquid circulation facilitated by the pulsating heat pipe network at the 50% filling ratio of distilled water was proposed. The total heating area of the two annular evaporators at both axial ends is identical with the middle condenser cooling area. With the equal heat flux emitted from each evaporator, the measurements of the overall thermal resistance, the Nusselt numbers of evaporator and condenser, the temporal pressure variation and the skin temperature uniformity over the condenser were carried out with the total heating power in the range of 30–90 W at the inclination angles of 0 (horizontal), π/6, π/3, π/2 (vertical) and six cooling airflow rates for each heating power tested. The thermal resistances of the two evaporators were both decreased as the heater power increased but their difference was systematically enlarged by tilting the vapor chamber from horizontal to vertical orientations. The power spectrum of the time-domain pressure signal revealed two dominant frequencies in association with the vapor bubble agitations in the pulsating heat pipe network at all the test conditions. These frequencies and the heating power dominated the thermal performances of the vapor chamber after demonstrating that the responses of the dominant frequencies to the changes in heating and cooling conditions correlated well with the corresponding variations in the overall thermal resistance and the temperature uniformity of the condenser. Referring to the results measured from the planar vapor chambers in the literature, the comparative thermal performances of the cylindrical thin vapor chamber were disclosed. A set of empirical correlation was developed to permit the evaluation of the overall thermal resistances of the two evaporators for relevant applications.

Thermal performance of U-shaped and L-shaped heat pipes

A comprehensive three-dimensional numerical model is developed to evaluate the effects of bending on the performance of both low temperature and high temperature heat pipes. The model solves for wall, wick, and vapor regions and includes the compressibility effects of the vapor. The proposed model can calculate the operating pressure and temperature of the heat pipe based on the operational and physical conditions. The effects of one 90-degree bend (L-Shaped) and two 90-degree bends (U-Shaped) are evaluated based on the hydrodynamics and thermal performance of the cylindrical heat pipes. The effects of bending on the heat pipe wall temperature are more significant for a high temperature heat pipe at a lower operating temperature range compared to a low-temperature heat pipe. The effects of bending on heat pipe is not significant if the wick of the heat pipe is not damaged due to bending and the blockage of liquid flow does not occur. In addition, if the heat pipe is operating in a horizontal plane where the evaporator and condenser are at the same level, the liquid pressure drop in the wick is not affected significantly by bending. Furthermore, the effects of gravity can be important when bending heat pipes and consideration should be given for this factor.

Modelling of a screen mesh wick heat pipe using Al2O3 nanofluids

In this work, a phenomenological model that considers the interaction of nanoparticles of a Al2O3/water nanofluid within a cylindrical mesh wick heat pipe has been developed. The model is based on Navier-Stokes equations and it uses population balance as a method to account for the interaction of nanoparticles. The model predicted values of capillary limit with nanofluids up to 32% higher than that of the heat pipe using DI water. Those values were in agreement with the values found experimentally. Although the better performance of the capillary limit in the model was a consequence of the reduction of the pore radius which increases the capillary pressure, that was not the main cause for better capillary limit in experimental conditions at lower nanofluid concentrations. On the other hand, it was found that exists an optimum concentration of nanoparticles which decreases the effective thermal resistance of the heat pipes. In this work, that concentration was 0.5% w/w.

An accurate calorimeter-based method for the thermal characterization of heat pipes

This study presents a method that can be used to accurately determine the thermal performance of a cylindrical heat pipe. In the method, the heat pipe is placed between two stainless steel 304 cylindrical blocks, configured as radial calorimeters that achieve thermal contact with the evaporator and condenser sections of the pipe. A flexible isothermal electrical heater mat surrounds the evaporator block, and a liquid-cooled copper pipe wrapped around the condenser block is used to remove heat. High precision thermistors (±0.01 K) positioned at fixed radial locations within the calorimeters are used to measure the heat supplied to the evaporator and the heat extracted from the condenser. One-dimensional radial conduction is assumed to occur within each calorimeter, and this enables the quantification of heat flows from the temperature readings. This assumption is verified by a steady-state analysis of the radial, axial and circumferential temperature differences within the evaporator calorimeter, based on data recorded for the lowest and highest heat inputs. Furthermore, a numerical model is used to confirm that end effects have a negligible influence on radial conduction within each calorimeter. This study concludes that the most commonly used characterization techniques for heat pipes can greatly overestimate thermal performance (15–32% for input powers of 7.5–25 W respectively) due to inaccurate quantification of heat flows into the evaporator and from the condenser. The calorimetric technique reported here achieves uncertainties in thermal resistance of <7.5% for low thermal loads (<12.5 W) and <6% for higher loads (>12.5 W). Moreover, the method achieves a significant improvement in the experimental thermal efficiency, with values of >75% recorded for all heat inputs in this study. The use of radial calorimeters in the current study obviates the requirement for calculating the losses from the heater to ambient, hence achieving low uncertainties in thermal resistance and effective thermal conductivity for a range of heat inputs.

Combined effects of filling ratio and wick surface coating on thermal performance of cylindrical heat pipes

Growing technological developments to improve the thermal efficiency of heat pipes resulted in many innovative techniques. The use of nanofluids with superior thermophysical properties compared to conventional fluids is one such technique. However, the service life of nanofluid driven heat pipes is affected by agglomeration and stability issues, demanding an alternate solution. Boiling heat transfer rate of a heat pipe depends on the availability of working fluid at the evaporator, which is decided by the wick wettability and filling ratio. Wick wettability is improved with a hydrophilic coating using sol-gel dip coating process. Coating improves wick capillarity at the expense of wick permeability. Hence, an accurate balance of wick coating thickness and evaporator filling ratio are essential for the enhanced performance. The present work aims to demonstrate the benefits derived from optimal wick coating over these issues posed by nanofluids and to provide a better understanding on device level thermal performance. Thermal performance of coated mesh wick cylindrical heat pipe is experimentally studied for various coating thicknesses, evaporator filling ratios and inclinations. The existence of an optimum evaporator filling ratio for each coating thickness in boosting the limits of heat transfer is established. For the optimized values of inclination, coating thickness and evaporator filling ratio, a maximum reduction of 38.49% in thermal resistance and an improvement of 25% in thermal efficiency are obtained at 150 W heat input. The results from the repeatability test confirms coating stability.

Numerical simulation of flattened heat pipe with double heat sources for CPU and GPU cooling application in laptop computers

Abstract An investigation of the effect of the thermal performance of the flattened heat pipe on its double heat sources acting as central processing unit and graphics processing unit in laptop computers is presented in this work. A finite element method is used for predicting the flattening effect of the heat pipe. The cylindrical heat pipe with a diameter of 6 mm and the total length of 200 mm is flattened into three final thicknesses of 2, 3, and 4 mm. The heat pipe is placed under a horizontal configuration and heated with heater 1 and heater 2, 40 W in combination. The numerical model shows good agreement compared with the experimental data with the standard deviation of 1.85%. The results also show that flattening the cylindrical heat pipe to 66.7 and 41.7% of its original diameter could reduce its normalized thermal resistance by 5.2%. The optimized final thickness or the best design final thickness for the heat pipe is found to be 2.5 mm.

Syntheses of ferrofluids using polyethylene glycol (PEG) coated magnetite (Fe3O4), citric acid, and water as the working liquid in a cylindrical heat pipe

Ferrofluids were synthesized from magnetite (Fe3O4) nanoparticles coated with three different base fluids: polyethylene glycol (PEG), citric acid (CA), and water. Each of the fluids act as the working liquid in a cylindrical heat pipe. The ferrofluids were synthesized using a two-step method with varied concentrations; 0.04 g/ml and 0.06 g/ml for PEG, and 5, 10, 15, 20 % weight for CA, respectively. Ferrofluid with the most optimal condition was used as the working liquid in a cylindrical heat pipe. Heat inputs of 5, 10, and 15 W were then applied to test its performance. From the x-Ray diffraction (XRD) analysis, the formation of Fe3O4 phase has been confirmed. Fourier transform infrared (FTIR) spectroscopy was able to identify the occurrence of a new absorption at a wavenumber of 1029.70 cm−1. This result gives a clear indication of the existence of PEG molecules on the surface of Fe3O4 nanoparticles. The magnetic properties measured by vibrating sample magnetometer (VSM) suggest that with the PEG addition, the value of saturation magnetization is reduced from 55.36 emu/g Fe3O4/PEG-a to 53.24 emu/g Fe3O4/PEG-b. Thermal conductivity and specific heat analyses revealed that the values are within specified ranges of 0.58–0.6​ W/m.K and 4055–4085 J/kg.K. The investigation of the heat pipe filled with ferrofluid demonstrates that the optimal thermal resistance is 3.2 °C/W at heat input of 15 W.

Parametric optimization for better thermal performance on Heat Pipe using Taguchi method

Heat pipes are hollow cylindrical form devices filled with a small amount of operational fluid and are used to transfer heat, which alters its phase. In contrast to standard heat exchange systems, the heat transfer rate in heat pipes is higher. Different heat pipes are being built depending on the heat transfer applications. The aim of the current work is to optimize the process parameters of heat pipe using Taguchi technique. The control factors like heat input (Q), inclination angle (θ), fill ratio (ϕ) and mass flow rate (M) were considered to evaluate the thermal performance in terms of thermal resistance and thermal conductivity. Using a L9 orthogonal array, a total of nine experimental runs were performed and the optimal combination of control parameter levels for the responses was calculated. The Taguchi technique is utilized by using MiniTab-17 software to find the level of importance and optimal independent parameter for the cylindrical mesh wick heat pipe using DI-water as the working fluid.

Mathematical model of a heat transducer with a cylindrical heat pipeline and with a focused heat source

The mathematical model of heat converters with a homogeneous extended cylindrical heat pipe is considered. Based on the developed mathematical models, the main characteristics of thermal converters are analyzed.