Closed Loop Pulsating Heat Pipe Research Articles

CFD Analysis of Copper Closed Loop Pulsating Heat pipe

Pulsating heat pipes (PHPs) are passive heat transfer devices where the heat transfer is much higher as compared to the general heat transfer devices such as metal fins. The main reason for this is the two phase phenomenon happening inside PHPs with the oscillatory motion of the bubbles. It can be used in various applications, space satellites, laptops or any other place where you want heat transfer to be very high in a small temperature drop. CFD analysis for the PHP is tested with different working fluids binary mixtures like water-methanol and water-ethanol for 50% fill ratio viz., for different inner diameters of 2mm and 3mm. At evaporator boundary, heat flux that is equivalent to 10W to 70W is supplied and the condenser boundary is set as heat flux of range 1000w/m2 and in the adiabatic section heat flux is zero. A CFD modelling is done in ANSYS CFX with two turns of PHP. The temperature distribution across the heat pipe was measured. The performance parameters such as temperature difference between evaporator and condenser, thermal resistance evaluated. CFD results demonstrate the heat transfer characteristics observing the performance of PHP is a numerical approach. The obtained CFD results are compared with the experimental paper [1].The CFD analysis is performed and the outputs of the simulations are plotted in graphs and contours.

Thermal Analysis of Closed Loop Pulsating Heat Pipe

Thermal Analysis of Closed Loop Pulsating Heat Pipe

Thermal performance of a vertical closed loop pulsating heat pipe and analysis using dimensionless numbers

Thermal performance of a vertical closed loop pulsating heat pipe and analysis using dimensionless numbers

Numerical Analysis of Closed Loop Pulsating Heat Pipe Using CFD

Numerical Analysis of Closed Loop Pulsating Heat Pipe Using CFD

Experimental study of Large-scale cryogenic Pulsating Heat Pipe

Pulsating Heat Pipes (PHP) are passive two-phase heat transfer devices consisting of a long capillary tube bent into many U-turns connecting the condenser part to the evaporator part. They are thermally driven by an oscillatory flow of liquid slugs and vapor plugs coming from phase changes and pressure differences along the tube. The coupling of hydrodynamic and thermodynamic effects allows high heat transfer performances. Three closed-loop pulsating heat pipes have been developed by the DACM (Department of Accelerators, Cryogenics and Magnetism) of CEA Paris-Saclay, France. Each PHP measures 3.7 meters long (0.35 m for the condenser and the evaporator and 3 m for the adiabatic part), being almost 20 times longer than the longest cryogenic PHP tested. These PHPs have 36, 22 and 12 parallel channels. Numerous tests have been performed in horizontal position (the closest configuration to non-gravity) using nitrogen as working fluid, operating between 75 and 90 K. The inner and outer diameters of the stainless steel capillary tubes are 1.5 and 2 mm respectively. The PHPs were operated at different filling ratios (20 to 90 %), heat input powers (3 to 20 W) and evaporator and condenser temperatures (75 to 90 K). As a result, the PHP with 36 parallel channels achieves a certain level of stability during more than thirty minutes with an effective thermal conductivity up to 200 kW/m.K at 10 W heat load and during forty minutes with an effective thermal conductivity close to 300 kW/m.K at 5 W heat load.

Numerical investigation on pulsating heat pipes with nitrogen or hydrogen

With flexible structure and excellent performance, pulsating heat pipes (PHP) are regarded as a great solution to distribute cooling power for cryocoolers. The experiments on PHPs with cryogenic fluids have been carried out, indicating their efficient performances in cryogenics. There are large differences in physical properties between the fluids at room and cryogenic temperature, resulting in their different heat transfer and oscillation characteristics. Up to now, the numerical investigations on cryogenic fluids have rarely been carried out. In this paper, the model of the closed-loop PHP with multiple liquid slugs and vapor plugs is performed with nitrogen and hydrogen as working fluids, respectively. The effects of heating wall temperature on the performance of close-looped PHPs are investigated and compared with that of water PHP.

An experimental investigation of thermal performance of pulsating heat pipe with alcohols and surfactant solutions

An experimental investigation was conducted to determine the thermal performance of Pulsating Heat Pipe (PHP) with different concentrations and fill ratios (FRs) of Methanol, Ethanol and Cetyltrimethyl ammonium chloride, C19H42ClN (CTAC) and compared with that of Deionized (DI) water. In this study, effects of thermo-physical properties of these working fluids on progression of temperature at different regions of the PHP and thermal resistance at varying thermal loads ranging from 15 W to 80 W were investigated. The closed-loop pulsating heat pipe was bottom heated and kept at vertical position for the entire period of study. 35%, 50% and 65% FRs of DI water were used and it was observed that the thermal resistance was lowest when the PHP was filled with 50% FR. The lowest thermal resistance achieved with DI water was 0.34 K/W at higher heat load. Methanol and Ethanol have lower specific heat capacity and performed almost no better than DI water. Larger (dP/dT)sat values of Methanol and Ethanol produced greater fluctuations in the flow and rapid movement of the fluid was induced within the pipe because of their relatively lower surface tension and viscosity. But these properties were not dominating factors for the thermal performance at higher heat loads. Lower specific heat capacity and latent heat of vaporization of these alcohols dominated the thermal resistance. When 50 ppm, 100 ppm, 1000 ppm and 2000 ppm of CTAC surfactant solutions were used, the experimental results showed that the heat transfer capability of the PHP is highly dependent on FR. It was observed that surface tension and viscosity are dominating factor in the performance of the PHP, when CTAC surfactant solution is used, and their degree of dominance varies with FR and heat loads. Lower surface tension of CTAC solution was advantageous for lower FR and heat load. Lower viscosity offered greater advantage at higher FR and heat load. The lowest thermal resistance achieved with surfactant solution was 0.30 K/W for 35% and 50% FR with 2000 ppm CTAC solution at higher heat load which are lower than that of DI water.

Thermal performance of rotating closed-loop pulsating heat pipes: Experimental investigation and semi-empirical correlation

A rotating closed loop pulsating heat pipe (RCLPHP) was experimentally investigated as a passive heat sink for rotary equipment cooling. The effects of heat input, rotational speed, filling ratio, and working fluid on the thermal resistance of RCLPHP were studied. Pure water and ethanol were used as working fluids with filling ratios of 30%, 50%, and 70% by volume, and the RCLPHP was tested at four rotational speeds: 200, 400, 600, and 800 rpm. The results showed that the best filling ratio for both water and ethanol is 50% and proved that the RCLPHP is able to work efficiently in a wide range of rotational speed. Moreover, it was observed that at the optimum filling ratio for ethanol and water, which is 50%, the decrease in thermal resistance at 800 rpm compared to 200 rpm was 5.4% and 13%, respectively. Such an enhancement in thermal performance indicates that these types of heat pipes are applicable for the purpose of cooling rotating devices. Moreover, a correlation is presented to estimate the amount of heat flow in RCLPHP with a maximum estimated error of 20%.

Thermal characterization and optimization of pulsating heat pipes operating in a circulation mode

In the present study, thermodynamic characterization and thermal optimization of pulsating heat pipes (PHPs) operating in a circulation mode are conducted experimentally and analytically. A series of experiments is performed to identify the thermodynamic state of the vapor plugs inside the PHPs. Two-turn closed-loop PHPs are made of glass capillary tubes with inner diameters of 1.2, 1.7, and 2.2mm. Temperature, internal pressure, and high-speed flow visualization data are obtained for PHPs at various input powers in a vertical orientation inside which the flow in the steady state exhibits a circulating motion with a sporadic pulsating motion. It is experimentally found that when a PHP is operating in a circulation mode, the vapor plugs in the PHP exist in a saturation state and the saturation pressure of each vapor plug is nearly identical. This physically means the phase changes can be treated to occur at a constant saturation temperature corresponding to the system pressure along the entire tube. On the basis of the experimental findings, a one-dimensional numerical model is developed to predict the thermal performance of PHPs operating in a circulation mode. The numerical results are shown to be in close agreement with the experimental data within an error of 7%. Finally, thermal optimization is conducted using the proposed model. The number of turns (Nturn) is optimized under the given three-dimensional space (200×190×6 mm3) for various lengths of the condenser section (20, 40, and 60mm). According to the numerical results, there is an optimum number of turns at which the thermal performance is maximized in the case of PHPs with condenser length of 20mm, while the thermal performance of PHPs with condenser length of 40 and 60mm is monotonically enhanced as the number of turns increases. The optimum thermal performance results from the combined effect of the mass flux of circulating flow and the condensation area.

A Comprehensive Experimental Investigation of the Performance of Closed-Loop Pulsating Heat Pipes

Closed-loop pulsating heat pipes (CLPHPs) are a new type of two-phase heat transfer devices that can transfer considerable heat in a small space via two-phase vapor and liquid pulsating flow and work with various types of two-phase instabilities so the operating mechanism of CLPHP is not well understood. In this work, two CLPHPs, made of Pyrex, were manufactured to observe and investigate the flow regime that occurs during the operation of CLPHP and thermal performance of the device under different laboratory conditions. In general, various working fluids were used in filling ratios of 40%, 50%, and 60% in horizontal and vertical modes to investigate the effect of thermo-physical parameters, filling ratio, nanoparticles, gravity, CLPHP structure, and input heat flux on the thermal performance of CLPHP. The results indicate that three types of flow regime may be observed given laboratory conditions. Each flow regime exerts a different effect on the thermal performance of the device. There is an optimal filling ratio for each working fluid. The increased number of turns in CLPHP generally improves the thermal performance of the system reducing the effect of the type of the working fluid on the aforementioned performance. The adoption of copper nanoparticles, which positively affect fluid motion, decreases the thermal resistance of the system as much as 6.06–42.76% depending on laboratory conditions. Moreover, gravity brings about positive changes in the flow regime decreasing thermal resistance as much as 32.13–52.58%.

A robust pulsating heat pipe cooler for integrated high power LED chips

This paper presents a closed loop pulsating heat pipe (CLPHP) with specific pipe arrangement for high power LED cooling. Two CLPHPs were fabricated and charged with DI water and methanol, respectively. The effects of gravity force and working fluid on the heat transfer performance were investigated carefully. Results show that the water-CLPHP performed better than the methanol-CLPHP, with a minimum thermal resistance of 0.06 °C/W at a 220 W heat load under air natural convection situation. In addition, the gravity force can help the CLPHP starting up and enhance the robustness of the thermal transportation at steady state. Finally, the real application to cooling a 100 W LED chip indicates that the proposed CLPHP can meet the thermal control requirement for integrated high power LEDs. Nevertheless, the low cost and light weight of the proposed CLPHP heat sink are very suitable for the LED lighting devices.

Analysis of chaotic flow in a 2D multi-turn closed-loop pulsating heat pipe

Numerical study has been conducted for the chaotic flow in a multi-turn closed-loop pulsating heat pipe (PHP). Heat flux and constant temperature boundary conditions have been applied for heating and cooling sections respectively. Water was used as working fluid. Volume of Fluid (VOF) method has been employed for two-phase flow simulation. Volume fraction results showed formation of perfect vapour and liquid plugs in the fluid flow of PHP. Non-linear time series analysis, power spectrum density, correlation dimension and autocorrelation function were used to investigate the chaos. Absence of dominating peaks in the power spectrum density was a signature of chaos in the pulsating heat pipe. It was found that by increasing the filling ratio and evaporator heating power the correlation dimension increases. Decreasing of the autocorrelation function with respect to time showed the prediction ability is finite as a result of chaotic state. An optimal filling ratio of 60% and minimum thermal resistance of 1.62°C/W were found for better thermal performance of the pulsating heat pipe. It is notable that two dimensional simulations in current study lead better understanding of the mechanism and validating the numerical method for full three dimensional modeling.

Thermal resistance of rotating closed-loop pulsating heat pipes: Effects of working fluids and internal diameters

The objective of this study was to experimentally investigate the effects of working fluids and internal diameters on the thermal resistance of rotating closed-loop pul?sating heat pipes (RCLPHP). The RCLPHP were made of a copper tube with internal diameters of 1.50 mm and 1.78 mm, bent into the shape of a flower petal, and arranged into a circle with 11 turns. The evaporator section was located at the outer end of the tube bundle. R123, ethanol, and water were filled as the working fluids. The RCLPHP was rotated at centrifugal accelerations 0.5, 1, 3, 5, 10, and 20 times of the gravitational acceleration considered at the connection between the evaporator and the condenser sections. The heat input was varied from 30 W to 50 W, and then to 100 W, 150 W, and 200 W. It can be concluded that when the latent heat of evaporation increases, the pressure difference between the evaporator and the condenser sections decreases, and the thermal resistance increases. Moreover, when the internal diameter increases, the driving force increases and the frictional force proportionally decreases, or the Karman number increases, and the thermal resistance decreases.

Effect of Centrifugal Acceleration on Heat Transfer Characteristics of Rotating Closed-Loop Pulsating Heat Pipes

The objective of this paper is to qualitatively study the effect of centrifugal acceleration on heat transfer characteristic of a rotating closed-loop pulsating heat pipe (RCLPHP). RCLPHP can be applied to cool rotating devices, such as disc brake or steam turbine. It improves the lifetime and reduces the wear of the device. In recent studies, effects of several parameters on thermal performanceof CLPHP have been investigatede.g. inner diameter, length of evaporator section, meandering of turn and working fluid. Some researchersderivedthese parameters in dimensionless form, and then established correlation to predict thermal performance of CLPHP at specified inclination angles. Another parameter that affects rotating or moving heat pipe is centrifugal acceleration. The induced internal centrifugal acceleration of the RCLPHP affects the circulation of working fluid. When flow direction of condensate is in the same direction as the acceleration,the centrifugal acceleration is defined to be positive. In turn,thecondensate is in thecounter-flow direction to the acceleration, if centrifugal acceleration is negative. This acceleration affectsthe circulation of liquid phase. Because of heavier mass of the liquid, most of itaccumulatedat the end part of evaporator section. When the RCLPHPis heated, working fluid in this section changes from liquid to vapor phase. Then it circulates to condenser section, or another end, and condensed. When centrifugal acceleration is increased, thermal resistance decreases. The condensate can quickly circulate to evaporation sectionbecause working fluid velocityis higher than those at lower acceleration. In the future, researches to quantitatively study on the effects of centrifugal and parameters which related to the thermal performance of RCLPHP will be further conducted.

Experimental Investigation on Thermal Performance of a Closed Loop Pulsating Heat Pipe without Fin and with Fin Structure

Pulsating Heat Pipe (PHP) is a new and emerging cooling technique in the field of thermal management especially in microelectronics. To fulfill the increasing demand of power electronic applications, PHP is a proven technology which works on principle of self-oscillation of the working fluid and phase change heat transfer phenomenon in a capillary tube. In this paper, the thermal performance of a closed loop pulsating heat pipe (CLPHP) without fin and with fin at the condenser section by using Acetone and Water as working fluid has been investigated experimentally. The effects of different parameters include the filling ratios (from 40% to 70% in steps of 10%), the inclination angles ( 0°, 30°, 45°, and 60°), and at various heat input (10 to 10W in the steps of 10W) has been investigated thoroughly. In this study CLPHP is made from long capillary copper tube with inner diameter of 2.0 mm and outer diameter of 3.0 mm. The heat pipe is bent into eighth number of U-turns and divided into three sections, evaporator section (50 mm), adiabatic section (120 mm) and condenser section (80 mm). Adiabatic section is maintained by using aluminum foil surrounded by appropriate insulation. The result shows that, the thermal resistance decreases as heat input increases. But at low heat input i.e. up to 60W, the thermal resistance decreases rapidly and the PHP performance is more sensitive to the inclination angle whereas high heat input i.e. above 60W, the thermal resistance decreases slowly and comparatively less independent to the inclination angle. Evaporator dry out is occurred for acetone at low filling ratio with 40% and 50% at heat input 40W and 50 W respectively. CLPHP with fin structure shows better performance than the CHPHP without fin structure at high heat input. Acetone with 70% filling ratio and water with 50% filling ratio shows the best performance at 0° inclination angle for both structures.

Influence of working fluids on startup mechanism and thermal performance of a closed loop pulsating heat pipe

Development of efficient cooling system is a tricky and challenging task in the field of electronics. Pulsating heat pipe has a great prospect in the upcoming days for an effective cooling solution due to its excellent heat transfer characteristics. Experimental investigations are reported on a Closed Loop Pulsating Heat Pipe (CLPHP). The influence of working fluids on startup mechanism and thermal performance of a CLPHP are carried out on 2mm, nine turn copper capillary. Total eleven (11) working fluids are prepared and investigated. Deionized (DI) Water (H2O), ethanol (C2H6O), methanol (CH3OH) and acetone (C3H6O) are used as pure fluids. The water-based mixture (1:1) of acetone, methanol and ethanol are used as binary fluids. Sodium Dodecyl Sulphate (SDS, NaC12H25SO4) is used as a surfactant to prepare the water-based surfactant solutions of 30PPM, 45PPM, 60PPM and 100PPM. The filling ratio is kept as 50%. The vertical bottom heating position of a CLPHP is considered. Heat input is varied in the range of 10–110W. Significant influence is observed for water-based binary fluids and surfactant solutions on startup mechanism and thermal performance of a CLPHP compared to DI water used as the pure working fluid.

Artificial Neural Network Modeling of a Closed Loop Pulsating Heat Pipe

Artificial Neural Network Modeling of a Closed Loop Pulsating Heat Pipe

Particle size and type effects on heat transfer enhancement of Ferro-nanofluids in a pulsating heat pipe

The present study evaluated the effect of γ (gamma) and α (alpha) Fe2O3/Kerosene nanofluids for a closed loop pulsating heat pipe under the magnetic field. The nanoparticles had a size ranged from 10nm to 30nm. The heat transfer rate and the temperature distribution of the heat pipe were examined with and without the magnetic field. Likewise, the Fe2O3 base nanofluids were exposed to a magnetic field to measure the vapor temperature at the center of the pulsating heat pipe directly. The results showed that both heat transfer coefficient and thermal performance of the pulsating heat pipe are enhanced by the addition of Fe2O3 nanoparticles, especially when the magnetic field is present. The increased input heat flux rises the heat transfer coefficient of the condenser and the evaporator. Lower evaporator heat transfer coefficient and higher temperature difference between condenser and evaporator were seen because of α-Fe2O3 nanoparticles as compared to γ-Fe2O3 nanoparticles. Among six nanoparticles investigated in this research, the optimum type and size of Iron oxide nanoparticles under similar conditions for attaining the best heat transfer performance was 20nm γ-Fe2O3 nanoparticles.

Nonlinear Analysis of Chaotic Flow in a Three-Dimensional Closed-Loop Pulsating Heat Pipe

Numerical simulation has been conducted for the chaotic flow in a 3D closed-loop pulsating heat pipe (PHP). Heat flux and constant temperature boundary conditions were applied for evaporator and condenser sections, respectively. Water and ethanol were used as working fluids. Volume of fluid (VOF) method has been employed for two-phase flow simulation. Spectral analysis of temperature time series was carried out using power spectrum density (PSD) method. Existence of dominant peak in PSD diagram indicated periodic or quasi-periodic behavior in temperature oscillations at particular frequencies. Correlation dimension values for ethanol as working fluid were found to be higher than that for water under the same operating conditions. Similar range of Lyapunov exponent values for the PHP with water and ethanol as working fluids indicated strong dependency of Lyapunov exponent on the structure and dimensions of the PHP. An O-ring structure pattern was obtained for reconstructed 3D attractor at periodic or quasi-periodic behavior of temperature oscillations. Minimum thermal resistance of 0.85 °C/W and 0.88 °C/W were obtained for PHP with water and ethanol, respectively. Simulation results showed good agreement with the experimental results from other work under the same operating conditions.

Thermal Resistance of a Rotating Closed-Loop Pulsating Heat Pipe: Effect of Centrifugal Accelerations

Objective of this study is to experimentally investigate the effect of centrifugal accelerations on thermal resistance of the rotating closed-loop pulsating heat pipe (RCLPHP). The RCLPHPs were made of a copper tube with internal diameter of 1.50 and 1.78 mm and bent into flower’s petal-shape and arranged into a circle with 11 turns. The evaporator section located at the outer end of the bundle while the condenser section placed around the center of the RCLPHP with no adiabatic section. Both sections had an identical length of 50 mm. R123, and ethanol was filled as working fluid respectively. The RCLPHP was installed on the test rig and it was rotated by the DC motor at the centrifugal acceleration of 0.5, 1, 3, 5, 10, and 20 times of the gravitational acceleration considering at the connection between the evaporator and condenser section. Heat input was generated by electrical annular-plate heaters and varied from 30 to 50, 100, 150, and 200 W. Ceramic papers, wooden plate, and insulation sheet were consecutively attached on the outer side of the heaters in order to prevent the heat loss from the heater. It can be concluded that when the centrifugal acceleration increases, the thermal resistance continuously decreases since the condensate flows back to the evaporator section more rapidly.