Open Loop Pulsating Heat Pipe Research Articles

Analysis of Entropy Generation of a Magneto-Hydrodynamic Flow Through the Operation of an Unlooped Pulsating Heat Pipe

The aim of the study is the analysis of a uniform magnetic field effect on fluid flow, heat transfer, and entropy generation through the operation of a pulsating heat pipe (PHP). An open loop PHP with three neighboring vapor plugs and two liquid slugs has been considered. The governing equations such as momentum, energy, and mass equations are solved using an explicit method except for the energy equation of liquid slugs. For each case study, Bejan number has been derived to find the heat transfer share in entropy generation. According to the results, the performance of the oscillating heat pipe decreases by applying uniform magnetic field. Moreover, the obtained results illustrate the effects of the applied magnetic field position on the heat transfer and the entropy generation. The latent and sensible heat transfer into the PHP enhance as a result of increase in the pipe diameter, so that the liquid slugs oscillate with high amplitudes. In addition, the entropy generation value increases with an augmentation in the value of the pipe diameter. The evaluated Bejan numbers indicate that the viscous effects in entropy generation decrease as the pipe diameter increases. Furthermore, the results depict that the heat transfer performance of PHP improves by increasing temperature difference between evaporator and condenser sections. With an increase in the value of the evaporator temperature, the Bejan number will increase, as a result, this phenomenon reveals the inconsiderable role of viscous impacts in high evaporator temperatures. In order to validate the calculations, the calculated results have been compared with the previous studies which show good agreement.

自励振動型ヒートパイプの熱輸送特性におよぼす作動流体の影響

Recently, electronics thermal management faces problems in the wake of component miniaturization, which has led to higher demands on heat flux dissipation. Pulsating heat pipe (PHP) can be used for cooling devices of electronics because of its potential for removing high heat flux. It is well known that various parameters affect the performance of the pulsating heat pipe. Therefore, many researchers have done research on the improvement of performance. This paper presents heat transfer characteristics of the open-loop pulsating heat pipe (OLPHP) using a self-rewetting fluid as working fluids. The heat transfer characteristic results were obtained by PHP that was made of copper tubes of internal diameters 1.8 mm. On the other hand, flow visualization tests were conducted by the use of a PHP that was made of Pyrex-glass tubes with the dimension of the copper tubes PHP. The experimental results indicate that OLPHP using self-rewetting fluid as working fluids can be observed anomalous liquid film behavior in adiabatic section. Especially, it was found that the liquid film was strong wavy when liquid slug moved to cooling section from heating section. The findings showed that the wavy liquid films and liquid slug behavior contributed to the thermal performance improvement.

Experimental Investigation on Heat Transfer Characteristics of an Open Loop Pulsating Heat Pipe(OLPHP) with Fin

This paper presents an experimental investigation of an open loop pulsating heat pipe of 2mm inner diameter and 2.5mm outer diameter with fin in condenser section to study the heat transfer performance. The setup is an open loop closed end pulsating heat pipe creating a total of 8 loops with total length of 25cm. The performance characterization will be done for methanol as working fluid with 50% filling ratio. The evaporator section is 5cm in length and the condensation section is of 8cm with an adiabatic section of 12cm. The evaporator section is heated by electrical input using Ni-Chrome wire and the condenser section is cooled by fan. The effects of fin in PHP for open loop will be analyzed for heat transfer characteristics and the results are compared with that of without fin keeping constant the other parameters. The results explore the possibility of using the open loop pulsating heat pipe as an integrated structure to achieve higher thermal conductance to the host substrate. Effect of gravity, pressure differential in the system, temperature, heat input etc. may have influence in this fact due to which 45˚ inclined position of finned structure shows the best performance.

Effect of Fin and Insert on the Performance Characteristics of Open Loop Pulsating Heat Pipe (OLPHP)

The pulsating heat pipe, a serpentine tube of capillary dimension with many turns, has great impact on today's successful thermal management. It is an ascending technology to satisfy present requirement of increasing thermal performance. Focusing on this, an experiment has been done on the open loop pulsating heat pipes (OLPHP) to observe their performance characteristics by using two types of working fluid by varying inclination angles. The experiment is performed on 2.5mm inner diameter and 3mm outer diameter OLPHP with an insert of copper wire of 1mm diameter and fins are added on the condensation section. This investigation is done using methanol and ethanol with 50% filling ratio in OLPHP with 8 loops. In this experiment the effects on the performance of using fins with insert with two different fluids (methanol and ethanol) and the variation of inclination angles are investigated. The results show that the performance characteristics in all the circumstances are better for setup with fin and insert than the normal setup. As higher thermal resistance indicates better performance, so we can say that setup with methanol performs better than ethanol. This performance is best at 45˚ inclination angle. It can be seen that, higher the inclination angle, better the performance and this performance is best at 45˚ inclination angle for this experiment.

An Open Loop Pulsating Heat Pipe for Integrated Electronic Cooling Applications

Increasing trends toward integrated power electronic systems demand advancements in novel, efficient thermal management solutions to cope with the increasing the power density. This paper investigates the performance of a novel open loop pulsating heat pipe embedded in an FR4 organic substrate. The heat pipe is comprised of 26 parallel minichannels, 13 turns with an average hydraulic diameter of 1.7 mm and maximum surface roughness of 2.5 μm. The bulk thermal performance of three saturated working fluids—Novec 649, Novec 7200 and Ethanol (99.8%)—is investigated in terms of fill ratio, three angles of orientation, and applied heat fluxes ranging from 0.4 to 2.5 W/cm2 at subambient pressures. Novec 649 achieved quasi-stable pulsations at lower heat fluxes compared to Novec 7200 and Ethanol (99.8%). In addition, the dielectric Novec 649 fluid showed significant potential for integrated heat spreading applications demonstrating heat transfer of up to 176 W and thermal resistances as low as 0.25 °C/W for a filling ratio of 30%—16 times greater than that of a standard dry FR4 substrate

Ferrofluidic Open Loop Pulsating Heat Pipes: Efficient Candidates for Thermal Management Of Electronics

Thermal management of electronic devices is presently a serious concern. This article investigates the thermal performance of a five-turn open-loop pulsating heat pipe in both start-up and steady thermal conditions. The effects of working fluid, namely water and ferrofluid, heat input, charging ratio, ferrofluid concentration, orientation, as well as application of magnetic field, are explored. Experimental results show that using ferrofluid enhances the thermal performance in comparison with the case of distilled water under certain conditions. In addition, applying a magnetic field on the open-loop pulsating heat pipe charged with ferrofluid improves its thermal performance. Charging ratios that lead to lower thermal are mentioned. Optimum concentration of ferrofluid in steady-state performance is 2.5 g/L. This study helps to design electronic cooling devices more efficiently.

Open-Loop Pulsating Heat Pipes Charged With Magnetic Nanofluids: Powerful Candidates for Future Electronic Coolers

The present research proposes an effective method to enhance the heat transport capability of conventional electronic coolers and improve their thermal management. Pulsating heat pipes (PHPs) are outstanding heat transfer devices in the field of electronic cooling. In the present study, two sets of open-loop pulsating heat pipes (OLPHPs) for two different magnetic nanofluids (with and without surfactant) were fabricated and their thermal performance was experimentally investigated. Effects of working fluid (water and two types of magnetic nanofluids), heating power, charging ratio, nanofluid concentration, inclination angle, application of a magnetic field, and magnet location are described. Experimental results showed that magnetic nanofluids can improve the thermal performance of OLPHPs. Application of a magnetic field reduces the thermal resistance of OLPHPs charged with magnetic nanofluids. The optimum charging ratio and nanofluid concentration are reported. The best thermal performance of OLPHPs was observed when oriented 67.5° relative to the horizontal axis. The variation in magnet location in OLPHPs charged with magnetic nanofluids resulted in a heat pipe with variable thermal performance at a fixed heating power, charging ratio, and orientation. OLPHPs that are charged with magnetic nanofluids provide a path toward considerable improvement in electronic cooling technology.

H224 ブタノール水溶液を用いた自励振動型ヒートパイプの可視化に関する研究 : 水平姿勢の場合(一般講演(11))

This paper presents flow visualization results obtained by using open-loop pulsating heat pipe made of pyrex glass tubes. The tubes have internal and external diameter of 1.8mm and 3.0mm, and the number of turns was 10. The PHP was tested at horizontal orientation. The working fluids employed were water and 1-Butanol aqueous solution (so-called self-rewetting fluids). Flow visualization results indicate that 1-Butanol aqueous solution showed anomalous liquid film behavior when liquid slug moved from heating section to cooling section. And the interface between the liquid film and vapor plug was unsteadily ruffled. Similar tendency was observed at vertical bottom heat mode.

Overall thermal performance of ferrofluidic open loop pulsating heat pipes: An experimental approach

Pulsating heat pipes (PHPs) are simple, cheap, and efficient heat transfer devices. They have applications in electronic cooling. In the present research, an experimental investigation is conducted on startup and steady thermal performances of open loop pulsating heat pipes (OLPHPs). Effects of working fluid, heat input, non-condensable gases (NCGs), ferrofluid concentration, magnets location, and inclination angle on the thermal performance of OLPHPs have been considered. Obtained results show that using ferrofluid can improve the thermal performance in steady state condition. Furthermore, applying a magnetic field enhances the heat transfer characteristics of ferrofluidic OLPHPs in both startup and steady state conditions. At 20 W heating power and startup condition, higher NCGs have the best performance in the presence of magnetic field. However, in the absence of magnetic field opposite trend is observable. In the case of steady thermal performance in both presence and absence of magnetic field, lower amounts of NCGs lead to better thermal performance. Best heat transfer capability is achieved at around 67.5° inclination angle relative to the horizontal axis for all of the working fluids. With the application of magnetic field in different locations of the OLPHPs, one can adjust their thermal performance to the desired value.

Thermal performance of an open loop closed end pulsating heat pipe

This paper presents an experimental study of an open loop pulsating heat pipe (OLPHP) of 0.9 mm inner diameter. The performance characterization has been done using four working fluids at vertical and horizontal orientations. Water, Methanol, 2-Propanol and Acetone has been employed as the working fluid with 50% fill ratio. The experimental results indicate a strong influence of gravity and thermo physical properties of the working fluids on the performance of OLPHP. Considering all the working fluids used, Water has shown better thermal performance in vertical orientation while Methanol has shown better performance in horizontal orientation. All the working fluids perform better at horizontal orientation.

Water-copper nanofluid application in an open loop pulsating heat pipe

Abstract Several investigations have pointed the operational behavior of passive thermal control devices such as loop heat pipes (LHPs) and pulsating heat pipes (PHPs) in the past, which have cleared many points related to their design. However, an interesting aspect related to passive thermal control devices that operate by means of capillary forces to pump the working fluid have gained attention during the last years, is in regard to the use of nanofluids on such devices. Nanofluids are known as regular fluids with addition of solid nanoparticles with sizes (diameter) below 40 nm, which are used to enhance the working fluid’s thermal performance by enhancing its thermal conductivity. Previous works have demonstrated that the liquid’s thermal conductivity can be enhanced by 20% if nanoparticles are added on a concentration of 5% by mass. PHPs operate by the dynamics of slug/plug formation, removing heat from a high temperature source and dissipating in a low temperature sink, and are highly influenced by the bubble critical diameter related to a specific working fluid. Thus, an experimental open loop PHP (OLPHP) was tested with water-copper nanofluid, with an addition of 5% by mass of copper nanoparticles. Improvements on the overall device’s operation have been observed when using the nanofluid with lower temperatures, as well as a direct influence on the thermal conductances throughout the PHP.