Pulsating Heat Pipe Research Articles

Characteristics of pulsating heat pipe with variation of tube diameter, filling ratio, and SiO2 nanoparticles: Biomedical and engineering implications

Pulsating heat pipe (PHP) is an implicit technique through a passive two-stage heat transfer system. This paper presents the experimentations on PHP contrived using copper with different inner tube diameters of 1, 1.5, 2, and 2.5 mm, respectively. The PHP is accused of acetone as a functional liquid with filling proportions varying from 50 to 90% of its volume with an increment of 10%. The effects of filling proportion and tube diameter on the thermal performance of PHP were investigated. The evaporator zone is electrically heated using a mica heater in the range of 20–80 W, and the condenser area is kept cool by the water circulation method. The results show that a 2 mm inner tube diameter performs best compared to other tube diameters, with a lower rate of thermal resistance of 0.49 K/W. Also, the performance of PHP is enhanced at a filling proportion of 60% for all the tube diameters. Further, CFD analysis was carried out for different filling ratios for a 2 mm diameter pipe at a constant heat input of 80 W, and it revealed that test outcomes were in line with CFD results. The deviation between the experimental and numerical studies was 10%. Considering the optimized parameters, i.e., tube diameter and filling ratio, the work was extended by adding SiO2 nanoparticles to the base fluid with 1–5 % mass concentration. The results showed a lower thermal resistance value of 0.3 W/K and a higher heat transfer coefficient of 828.64 W/m2 °K was obtained at 2% mass concentration of SiO2. Also, the proportional rise in heat transfer coefficient at 60 W is 11.46, 17, 14, 4.15, and 1.94% for 1, 2, 3, 4, and 5% mass concentration of SiO2 nanoparticles, respectively. Hence, the PHP operates better at a 2 mm diameter with a 60% filling ratio and 2% mass concentration of SiO2 nanoparticles.

Performance of Pulsating Heat Pipe with a stimulus of auxiliary heat load for Battery Thermal Management System

Stimulus strategy is proposed to enhance the heat dissipation performance of Pulsating Heat Pipe (PHP) at low heat load for local hot spot regression in Battery Thermal Management (BTM). An auxiliary heat load is applied to stimulate the start-up of PHP. The performances of PHP with and without stimulus are compared and the properties of PHP after stimulus are discussed. It is concluded that the application of auxiliary heat load is able to stimulate the start-up of PHP in experiments. The strategy is mainly based on the phase-change mechanism as well as the hysteresis of working medium. Thermal resistance and the evaporator temperature are significantly reduced, if PHP starts operation after stimulus. Long period of stimulus and strong auxiliary heat load are favored for the reduction of thermal resistance and the shortening of period for start-up. The thermal resistance may be reduced by 29.1 ∼ 69.6 % and the temperature may be regressed by around 8 °C. However, PHP may suffer from temperature uplift and overshot to the maximum evaporator temperature. Therefore, high interference temperature coupled with weak auxiliary heat load and long period of stimulus are suggested as the optimal strategy. The verified strategy offers a new method for local hot spot regression and a possible way to mitigate the risk of thermal runaway, since the heat dissipation is enhanced at the initial stage of damage or destruction.

Heat transfer performance study of a separated pulsating heat pipe

In order to study the heat transfer performance of the pulsating heat pipe (PHP) under the separation arrangement of evaporating and condensing ends, this paper designs a separated PHP for experimental investigation, and describes its heat transfer capability in terms of the wall temperature oscillation performance, the heat transfer temperature difference and the heat transfer thermal resistance. Under different heating powers, the effects of different placement inclinations and their structures on the heat transfer performance of the in-line and bent separated PHP are analyzed. The study shows that in the low heat transfer power scenario, the performance of the in-line type separated PHP is more excellent, and with the increase of the placement of the inclination of the heat transfer situation is further optimized, 90 ° placement of the inclination of the optimal performance of the heat transfer; bent type separated PHP condensing end of a certain level of inclination is conducive to low-power startup and operation, the condensing section of the 15 ° horizontal angle of the optimal performance; and in the high heat transfer power, the two performances are similar, but the arrangement of flexible bent type separated PHP is more suitable for the changing heat transfer scenarios.

Experimental Investigation on the Thermal Performances of a New Design of Pulsating Heat Pipe With Two Condensers

Abstract In this paper, for the first time, a novel design of pulsating heat pipe (PHP) with one evaporator and two condensers located on both sides of the evaporator at an angle to the horizon was proposed, manufactured, and experimentally investigated for the purpose of use in cooling systems for electronic devices operating in a tilted position. The PHP body is made of a copper capillary tube with an inner diameter of 1.5 mm. The working fluid is methanol. The number of turns is 4. The heating zone dimensions are 60 mm × 36 mm, and the cooling zone dimensions are 200 mm × 35 mm. The РНР condensers were cooled by aluminum radiators blown by two fans with an air flowrate of 5.2 m3 h–1. The launch of the РНР began with a power of 30 W at all positive tilt angles and in a horizontal position. The dependences of the temperature in the heating and cooling zones and the PHP thermal resistance both on the power input (from 30 W to 200 W) and on the orientation in space (at tilt angles of 0 deg, 15 deg, 30 deg, 60 deg, 90 deg) were obtained. It is shown that when the evaporator is located below the condensers, the РНР works stably. Moreover, in the power range from 120 W to 200 W, the tilt angle practically does not affect the thermal resistance of the PHP. A comparison of the thermal resistance of the developed РНР with known РНРs filled with methanol showed the high efficiency of the developed РНР: at power input from 120 W to 200 W, the thermal resistance was from 0.2 °С W–1 to 0.18 °С W–1. The developed РНР design is promising for use in air cooling systems, for instance, of radar transmit/receive modules and high-power LED lighting systems.

Thermo-Fluidic Analysis of Pulsating Heat Pipes Charged with Water-Based Immiscible Fluid Pairs

Immiscible fluids may provide operational flexibility for pulsating heat pipes (PHPs) due to thermo-hydrodynamic diversity lead by each pure component. In this regard, present paper focuses on the thermo-fluidic analysis of non-uniform pulsating heat pipes charged with water-based immiscible fluid pairs. Research parameters cover gravity effect via the inclination angles (IA) of 0o and 90o, and fluid pair effect via two different water-based immiscible binary fluids as Water (W) – Hexane (H), and Water (W) – Pentane (P). The volumetric mixing ratios are W:H=1:1, 1:4, 4:1, 1:0, 0:1, and W:P=1:1, 1:4, 4:1, 1:0, 0:1; and the non-uniform flat plate type pulsating heat pipe (FP-CLPHP) has alternating-sequence parallel channels. The experiments are performed at the filling ratio of 40% (FR=40%), and flow phenomena is visualized. As some conclusions; at vertical orientation, the FP-CLPHPs having binary fluids of water-pentane show better thermal performance compared to the pure counterparts. Especially, the heat transfer characteristics of W:P=1:1 are the best ones among all the pure and binary fluids. On the other hand, as a conclusion of combination of non-uniform design and suitable thermophysical properties, the FP-CLPHPs charged with pure pentane, pure hexane or binary fluid of W:P=1:4 can work independent from gravitational force.

Wrap-around loop pulsating heat-pipe heat exchanger for enhancing the energy efficiency of high-tech cleanroom HVAC systems

Abstract To maintain strict temperature, humidity, and cleanliness requirements, the cleanrooms of high-tech semiconductor fabrication plants have heating, ventilation, and air conditioning (HVAC) systems, which require substantial amounts of energy. To reduce energy consumption, this study proposes using a wrap-around loop pulsating heat pipe (WLPHP) heat exchanger comprising a pulsating heat pipe for precooling high-temperature outdoor air to reduce relative humidity. The heat absorbed by the heat-pipe evaporator is then transferred to the condenser and released, reducing the energy required to subsequently reheat the air with an HVAC system. The experimental results reveal that the system reduces the required reheating energy and increased the moisture removal rate per unit energy consumption by an average of 24.8% and 33% compared with a typical heat exchanger. Hence, using the WLPHP heat exchanger in HVAC systems could provide large energy savings.

Research on performance test and evaluation of thermal management system of power battery module under harsh conditions

Under harsh conditions, the battery module (BM) used for Ev’s power system has issues of local overheating, continuous high temperature, and spontaneous combustion causing thermal accidents. This problem is directly related to the safety of life and property of drivers and passengers. What’s more, it also seriously restricts the high-quality development and promotion of Evs. To solve the limitations and drawbacks of the BM. this paper designs the thermal management structure with TiO2 nanofluids closed loop pulsating heat pipe (TiO2-CLPHP) as the key component and constructs the thermal management system with TiO2-CLPHP (TiO2-CLPHP TMS). On the basis, the temperature optimal thermal management strategy (TOS) and energy consumption optimal thermal management strategy (ECOS) is proposed. To investigate the performance response of TiO2-CLPHP TMS, the performance test of TiO2-CLPHP TMS is carried out. The results show that in terms of thermal management performance, the TiO2-CLPHP TMS with TOS and ECOS (TOS-TiO2-CLPHP TMS, ECOS-TiO2-CLPHP TMS) can effectively suppress the highest temperature, temperature rise and improve temperature uniformity of the PM. Of these, the minimum improvement rates of TOS-TiO2-CLPHP TMS can reach 29.41%, 78.37%, 65.88%, 58.82%, and 64.95%. The minimum improvement rates of ECOS-TiO2-CLPHP TMS can reach 27.24%, 72.65%, 64.71%, 55.88%, and 68.04%, respectively. In terms of the thermal management economy, compared with TOS-TiO2-CLPHP TMS, ECOS-TiO2-CLPHP TMS has lower energy consumption. The efficiency values of the ECOS-TiO2-CLPHP TMS are not less than 87.72%. It can be concluded that the proposed TiO2-CLPHP TMS has excellent thermal management performance. The ECOS-TiO2-CLPHP TMS can maximize the dual requirements of the thermal management performance and thermal management economy. This study innovatively proposed a thermal management method for nanofluids PHP used in BM. Compared with previous studies, the proposed TiO2-CLPHP TMS reduced the temperature difference from the traditional 5.00 °C to less than 3.40 °C, greatly improving the temperature uniformity of the BM. The completion of this research provides a new idea of battery thermal management based on metal oxide nanofluids PHP, and the constructed performance evaluation method provides a referral scheme for the performance test and evaluation of thermal management technology.

A novel fabrication method for polymeric flat plate pulsating heat pipe via additive manufacturing

Advancements in material development and fabrication techniques have led to the production of a new generation of electronic devices that are flexible, compact, small-scale, and lightweight. Effective thermal control management is crucial to ensure their performance, reliability, and durability. This paper proposes the fabrication of a polymeric pulsating heat pipe (PPHP) using a common stereolithography technology. The heat transfer performance of three PPHPs with different channel configurations was compared at heating powers ranging from 5 to 30 W and at a constant filling ratio of 50 %, using FC-72 as the working fluid due to its compatibility with the solid material. All three PPHPs have eight turns and length, width, and thickness of 185 mm, 85 mm, and 2 mm, respectively. All experiments were conducted for four thermal hysteresis cycles. The findings revealed that pressure and temperature distributions displayed similar patterns and fluctuations in response to heating power for all the PPHPs. Despite the simple technique and the use of a standard plastic material, the thermal resistance ranged from 2.5 to 1.7 °C/W, i.e., the effective thermal conductivity was already more than one thousand times higher than the conductivity of a solid plastic sheet for a 30 W heat input. The non-uniform channel configurations in PPHPs offered the potential of better heat transfer performance, fluid distribution, and operational stability. The present overture investigation paves the way for a more extended development of plastic 3D printing technologies for prototyping flexible PHPs and for teaching purposes.

Surface wettability modifications and applications in wickless heat pipes

Proper methods of surface fabrication and characterization are essential for various applications. For example, wickless heat pipes, such as flat plate pulsating heat pipes (FPPHP) and a compact flat thermosyphon (CFT), have massive potential for commercialization owing to simple construction, flexibility in using different working fluids, and better thermal contact with flat heat sources. In this work, various surface treatment methods such as chemical etching, electrochemical deposition, and laser texturing on a copper sample are investigated to prepare superhydrophilic or superhydrophobic surfaces, and the thermal durability of the as-prepared surfaces is tested through heating and boiling experiments for 15 days. The wettability modification methods are implemented on the surfaces of the FPPHP and CFT, with the different wettability combinations as either bare evaporator and condenser, completely superhydrophilic (that is, all surfaces including that of evaporator, condenser, and adiabatic section) or completely superhydrophobic or hydrophilic evaporator and superhydrophobic condenser. The thermal performance of the FPPHP and CFT subjected to different wettability combinations on the surface is investigated. Results of FPPHP are reported for water as the working fluid at 60 % filling ratio with power inputs given from 40 to 200 W. Similarly, for CFT, the results are reported for water filled at 50 % filling ratio with heat flux input from 2 to 20 W/cm2. On the FPPHP, the best thermal performance and lowest resistance were obtained when the entire surface was superhydrophilic with a maximum reduction of 60 % at 200 W. The CFT gives the best thermal performance with a bare evaporator and superhydrophobic condenser with a maximum decrease in thermal resistance of 42 % at 20 W/cm2. The best-performing wettability combination for FPPHP and CFT is contrasting and has to be chosen appropriately depending on the heat transfer device.

Estimation of Internal Heat Flux on Pulsating Heat Pipes using Kalman Filter: Numerical and Experimental Results

Pulsating Heat Pipes (PHPs) are two-phase passive thermal devices characterized by the presence of significant fluid oscillations inside the tubes that permit to fast and efficiently transfer heat from a hot region to a cold one. They are present in many engineering applications, e.g., electronics, sustainable energies, aerospace. They are very attractive due to their high heat removal capability, flexibility, and low manufacturing cost. Although they have been widely studied their working principles are still not fully understood. To better comprehend their thermal behaviour recent works presented different approaches to assess the internal heat flux in PHPs. However, all the adopted approaches are based on whole-domain techniques that require a higher computational cost compared with sequential estimations. Therefore, to allow heat flux estimation with lower computational effort, in this work a procedure based on the Kalman filter has been adopted. The heat flux has been estimated by solving the inverse heat conduction problem in the PHP’s wall adopting as input data the temperature measurement on the external surface of the pipe acquired by an infrared camera. Firstly, the procedure has been validated adopting synthetic data. Then, experimental data referring to actual operating conditions have been employed to estimate the internal heat flux. The Kalman filter has been adopted as technique to solve the classical instability intrinsically present in inverse problems. It is relatively simple to implement and requires only previous time information, requiring low computational costs. Moreover, the Kalman filter allows the real time estimation of the heat flux: assessing the heat flux on PHPs during operation could be a useful instrument to provide information about on-time working conditions and thus avoid any possible malfunctioning.

The DEPLOY! Project: Development of a Deployable Pulsating Heat Pipe experiment on a parabolic flight

DEPLOY! Project aims at analysing the behaviour of Deployable Pulsating Heat Pipe (PHP) shaped as a helicoidal torsional spring in the adiabatic section on board a Parabolic Flight platform. A PHP is a passive thermal control device where the heat is efficiently transported by means of the self-sustained oscillatory fluid motion driven by the phase change phenomena. The microgravity environment allows to eliminate the buoyancy force contribution in the liquid phase momentum. Consequently, it is possible to isolate the contribution of the pressure drop caused by the 3D arrangement and infer on their effect on the PHP performance. As a result, a proper design based on the previous considerations would increase the flexibility of the PHP for use in space applications without significant reductions in efficiency. The goal of DEPLOY! is to demonstrate the functionality of a Deployable Pulsating Heat Pipe in various unfolding configurations by analysing its thermal-hydraulic response throughout a Parabolic Flight. The presented Deployable PHP is composed of an aluminium tube (inner/outer diameters 1.6mm/2.6 mm) and filled with HFE-7000. It is heated at the evaporator using a flat heater and cooled at the condenser with a water-cooled cold plate. T-type thermocouples are used to measure the wall temperature in several locations, while two pressure transducers (one located in the evaporator section and another in the condenser section of the same pipe) measure the local fluid pressure. Additionally, an IR Camera will be used to observe a section of the pipe for further analysis of the flow frequency. The device operation will be tested on ground and 0-g at different heat loads (24W, 34W), in multiple static positions corresponding to different opening angles (0°, 45°, 90°, 135°, 180°) and during its dynamic opening from 0° to 180°, thanks to a remotely controllable motion system.

Study on heat transfer characteristics of pulsating heat pipe heat exchanger with asymmetric structure

The Pulsating Heat Pipe (PHP), lauded for its efficacy in heat transfer, is distinguished by its uncomplicated architecture, economical production, diminutive form, and robust adaptability to environmental conditions. This study delineates the design of an asymmetric PHP heat transfer apparatus, achieved through the alteration of select conduit lengths within the comprehensive circulation system. The thermal transfer efficacy of this apparatus was empirically scrutinized under dual dissipation modalities: natural and forced convection. It was observed that the asymmetric PHP, when devoid of oscillatory activity, maintained a heat source temperature of 25∘C, whereas the temperature escalated to 26∘C upon the initiation of pipe vibration. Under the regime of forced convection, the asymmetric PHP demonstrated expedited activation, reduced initiation temperature, and heightened oscillatory behavior compared to its natural convection counterpart, thereby facilitating the phase change condensation within the condensation segment and ensuring efficient, sustained heat dissipation. Consequently, this bolstered the PHP’s heat transfer capabilities. The thermal resistance exhibited a declining trajectory under both dissipation strategies, with forced convection consistently yielding lower thermal resistance than natural convection. Nonetheless, the decrement in thermal resistance was gradual near the critical startup juncture and throughout the initiation phase. The PHP’s equivalent thermal conductivity displayed an upward trend in tandem with the escalation of the heat source’s temperature under both dissipation methods. Despite the superior heat transfer performance at elevated heat source temperatures, the efficiency of natural convection dissipation remained suboptimal, necessitating the application of forced convection to the condensation segment to further enhance the PHP’s thermal transfer proficiency and the overall device performance.

Experimental study on collaborative enhancement of led heat dissipation characteristics by pulsating heat pipe and heat pipe

The objective of this research is to experimentally evaluate the specific impact of a collaborative heat sink composed of gravity heat pipes (GHP) and pulsating heat pipes (PHP) on the thermal efficiency of LED light sources. The heat sink developed in this experiment is designed to improve the thermal management system, ensuring that LED operate within a safe temperature range, which is crucial as the performance of LED is directly affected by their junction temperature. An HP-PHP collaborative heat sink was employed in the experiment, where PHP served as heat dissipating fins to enhance its thermal performance, while HP handles the majority of the heat transfer tasks. The results showed that under forced convection conditions, the HP-PHP collaborative heat sink can increase the maximum thermal power capacity of LED to 192 W. The HP-PHP collaborative heat sink can reduce the substrate?s temperature to below 70.5 ?C in passive mode when the LED input power does not exceed 96 W. Additional experimental results show that the minimum thermal resistance of the collaborative heat sink is 0.19 K/W under natural-convection conditions, under forced convection conditions, this value drops to 0.15 K/W, which still lower than the non-collaborative heat sink. These results demonstrate that the contact thermal resistance between HP and PHP significantly enhances the thermal performance of the collaborative heat sink. Therefore, this collaborative type of heat sink is an effective method for cooling high power LED.

Infrared measurements of fluid temperature in a polymeric Pulsating Heat Pipe

Pulsating heat pipes are two-phase passive heat transfer devices partially filled with a working fluid in saturation conditions. During operation, supplying heat to one end of the system (named evaporator) results in a local increase in temperature and pressure, which drives the fluid through a transport section (named adiabatic section) towards the cooled, opposite end (named condenser) for effective heat dissipation. The local thermo-fluid dynamic state of the working fluid is sometimes assessed by means of non-intrusive techniques, such as infrared thermography. In this case, the radiative properties of the systems in the infrared spectrum must be known a priori. Nevertheless, since pulsating heat pipes may be manufactured with different materials, wall thicknesses and channel geometries, the radiative properties of the walls and the confined flow are not always known or assessable by means of the available literature. Hence, the work proposes to design a straightforward calibration procedure for quantitative infrared fluid temperature measurements in a polymeric pulsating heat pipe charged with FC-72 and having unknown radiative properties. The emissivity and transmissivity of the walls and confined fluid are estimated with good accuracy. The results will allow repeatable and reliable fluid temperature measurements in future experimentations on the mentioned device.

Visualized investigation of a nitrogen pulsating heat pipe

This paper presents the results of a visualization study of a cryogenic pulsating heat pipe (PHP). The impact of radiation heat leakage was reduced by minimizing optical windows. Visual images of the adiabatic section of a 2-turn PHP with nitrogen as working fluid were obtained at a filling ratio of 50 % and an inclination angle of 90°. The lengths of the evaporator, adiabatic section, and condenser were 50 mm, 100 mm, and 50 mm, respectively. The adiabatic section was made of quartz, whereas the evaporator and condenser were made of stainless-steel capillaries soldered onto copper plates. The flow channel of PHP was 1 mm. The fluid characteristics of the PHP under quasi-steady state conditions at different heat inputs were captured using a high-speed camera. Based on the experimental results, the evolution of flow patterns and fluid motion characteristics, and the coupling relationship between flow and heat transfer were illustrated and discussed.

Combined effect of the magnetic field, orientation, and filling ratio on cylindrical pulsating heat pipe using distilled water and distilled water/Fe3O4 nanofluid

To investigate the effect of the magnetic field, a pulsating heat pipe was made in the shape of a cylinder and Fe3O4 nanoparticles (%0.1 wt) were used with the base fluid of distilled water as the working fluid. (Tetramethyl ammonium hydroxide) TMAH surfactant was used as a stabilizer. To investigate the effect of gravity on the performance of the pipe, the device was tested at different angles from zero to 90 degrees. In this research, the effect of different variables, including the type of working fluid (distilled water vs. nanofluid), filling ratio, slope, and amount of heat input to the evaporator (30–300 W), in two different states, once without the influence of the magnetic field and once again with the application of a magnetic field was investigated. The results of the tests showed that the performance of the device at 50 % filling ratio is better than 60 % filling ratio. The use of nanoparticles improved the performance of the device. Inclining the device increases the thermal resistance so that the device performs poorly in the horizontal mode in all modes except when it is under the influence of a magnetic field. The use of nanofluid as well as the application of a magnetic field makes the start-up time of the device decrease by 37 % and 30 %, respectively, compared to distilled water. The temperature of the start of fluctuations also decreases by 24 % and 32 %, respectively.

A BUBBLE SIZE CHANGE IN A PULSATING HEAT PIPE DEPENDING ON ITS POSITION

In this paper, we present the visualization results obtained on the liquid flow in a pulsating heat pipe. Relative to their position in the condenser section, we measured the volume variations of bubbles as they moved through capillary tubes. For small heat fluxes, the bubble volume weakly depended on the distance. However, with an increase in the supplied power, the bubble volume changed significantly as the bubbles moved through the evaporator part due to evaporation of the liquid inside these bubbles. In addition, we employed an infrared scanner to perform a temperature distribution analysis and demonstrate the heat transfer processes.

Experimental Analyses of Flow Pattern and Heat Transfer in a Horizontally Oriented Polymer Pulsating Heat Pipe with Merged Liquid Slugs

Experimental Analyses of Flow Pattern and Heat Transfer in a Horizontally Oriented Polymer Pulsating Heat Pipe with Merged Liquid Slugs

A Novel Integrated Photovoltaic System with a Three-Dimensional Pulsating Heat Pipe

A Novel Integrated Photovoltaic System with a Three-Dimensional Pulsating Heat Pipe

Effect of heat load fluctuation on heat transport characteristics of three-dimensional pulsating heat pipe

Effect of heat load fluctuation on heat transport characteristics of three-dimensional pulsating heat pipe