Performance Of Pulsating Heat Pipe Research Articles

Experimental investigation on the ethane pulsating heat pipe under asymmetric heating

A three-dimensional cylindrical copper pulsating heat pipe (PHP) with ethane as the working fluid is designed. Experiments are conducted to study the thermal performance of the ethane PHP under the asymmetric heating mode. The evaporation section is divided into two parts: the left part and the right part. The left and right evaporators are provided with different heat inputs to study the temperature oscillation and heat transfer performance. Three cases are carefully studied: no heat input on the left evaporator, the fixed heat input on the left evaporator, and the fixed total heat input. Experiments are also conducted on the PHP operated in the temperature range of −100 ∼ −20 °C. Results demonstrate that when no heating on the left evaporator, the minimum right heat input to form the circulating flow is 40 W. The maximum allowable heat flux is 88419.41 W/m2, which is the 200 W heat input. When there is no heating on the left evaporator, as the heat input on the right side increases, the temperature oscillation experiences: small oscillation, severe fluctuation, stable operation, slight fluctuation, stable operation, and intermittent fluctuation. The heating on the left evaporator relieves the stagnation caused by the movement lag of the working fluid and promotes the flow motion. When the total heat input is fixed, the overall thermal resistance of the PHP is little influenced by the exchange of the heat input of the left and right evaporators, instead, it is decided by the amount of the total heat input. The decrement of the working temperature improves the amplitude of the temperature oscillation but also results in the degradation of the thermal performance of the PHP. The optimal working temperature is discovered to be −40 °C.

Comparative analysis of CLPHP working with binary mixtures in different concentrations

The advanced technologies in design and manufacturing of electronic components have resulted considerable heat flux through component miniaturization. For highly performing microelectronic devices production, thermal management has the priority. Other applications also like material science, fabrication technology, solar applications etc. which directly impact cost, reliability and performance. When it comes to overcome these problems efficient cooling approaches development and use will come into play. The best solution for this is Pulsating heat Pipe (PHP). A simple PHP is a two-phase heat transfer device consists of a tube with a suitable working fluid, along with an evaporator (heating)section, adiabatic section and a condenser (cooling)section. In the present work multi turn Closed Loop Pulsating Heat Pipe (CLPHP) is chosen with capillary dimensions. The experimentation is carried out with different working fluids viz. water, water-based mixtures (75%-25%) at different volumetric fill ratios 50%,60% and 75%. The heat inputs of20W, 40 W, 60 W, 80 W, 100 W applied. At various heat inputs for all the working fluids the variation of thermal resistance is plotted and observed that upon increasing heat input, thermal resistance of fluid decreases. Comparative study is also presented for same experimental setup when the binary mixtures are considered in 50%-50% as mixture concentration. This gives the better understanding of Closed Loop Pulsating Heat Pipe performance when operated at different fill ratios and concentrations for different working fluids considered.

Influence of Cooling Water Flow Rate on Start and Heat Transfer Performance of Pulsating Heat Pipe at Different Inclination Angles

Pulsating heat pipe (PHP) is an efficient heat transfer technology applied in the fields of heat dissipation and energy utilization. There are many factors affecting the heat transfer of PHP, including working fluid, filling ratio, inclination angle, etc. The cooling capacity of the cooling water system at the condensing section to the working fluid is also an important factor affecting the starting and operating of PHP. The research on PHP at different cooling water flow rates is of great significance for enhancing the operating performance. An experimental investigation of starting and running performance is carried out on a closed loop PHP with ultrapure water under different inclination angles of 90°, 60° and 30°. The starting and heat transfer performance of PHP with a filling ratio of 50% is obtained by adjusting the heat input in the range of 30–210 W at different cooling water flow rates of 6.7 g/s, 9.7 g/s and 13.9 g/s. The temperature and heat transfer resistance are used for analyzing the heat transfer performance. The results show that the starting mode, initial pulsating temperature and different heat transfer effects are brought about by different cooling water flow rates. It is observed that the cooling water flow rate has no obvious influence on the starting mode of PHP and that the starting mode of PHP is temperature progressive, starting with the increase in cooling water flow rates at a heating input of about 30 W. The influence of cooling water flow rates on the heat transfer performance of PHP is affected in a different way by inclination angles. The heat transfer performance of PHP with an inclination angle of 90° is similar at 6.7 g/s, 9.7 g/s and 13.9 g/s but, under the condition of 60° and 30°, the heat transfer resistance drops within a certain range effectively with an increasing cooling water flow rate from 6.7 g/s to 9.7 g/s and the heat transfer performance does not change significantly with the cooling water flow rate increasing to 13.9 g/s. Thus, there is an optimal value for the cooling water flow rate during the operating of PHP. The inclination angle also has an important effect on the temperature pulsating, and the temperature of PHP affected by gravity is stable with an inclination angle of 90°. However, the reduced influence of gravity on the backflow of the working fluid drops when the inclination angle decreases from 90° to 30°, and the wall temperature increases due to local overheating when the high heat input occurs.

Lorenz-like equation of two-phase flow in a single closed loop pulsating heat pipe

The pulsating heat transfer characteristics of pulsating heat pipes are often obtained through a large number of experiments and numerical simulations, and the results have certain errors and uncertainties. In order to deal with this situation, the theoretical model of pulsating heat pipe was studied. Based on the governing equation of a single closed loop pulsating heat pipe with two-phase flow containing latent heat, the theoretical model of Lorenz-like equation was derived firstly, and the variation rules of chaotic characteristic such as attractor and Lyapunov index were obtained. On the basis, the parameters of a single closed loop pulsating heat pipe were optimized. The results show that the model of a single closed loop pulsating heat pipe approach to chaos when the Rayleigh number reaches about 3, and the chaos characteristic increases gradually with the increase of heating power. At the same time, the optimal structure parameters and liquid filling rate of a single closed loop pulsating heat pipe under specific conditions were predicted, which provides a theoretical basis for further exploring the optimal heat transfer performance of pulsating heat pipe.

Investigation into the effects of passive check valves on the thermal performance of pulsating heat pipes

A passive check valve without a subsidiary channel that effectively increases the thermal performance of pulsating heat pipes (PHPs) is proposed. To realize this, topology optimization is employed to maximize the diodicity (Di) of the check valve. The proposed passive check valve consists of a pair of hook-shaped structures and has a Di value of 2.2. PHPs with overall dimensions of 53.5×80×1.5 mm3 are fabricated to investigate the effects of the passive check valve on the thermal performance and the flow behaviors of PHPs. A ten-turn closed-loop serpentine square channel with a height and an average width of 0.6 mm and 2 mm is engraved on a silicon plate and then covered with a glass plate for flow visualization. A total of twenty passive check valves are implemented into the entire channel at the locations where the condenser section and the adiabatic section meet. HFE-7000 is used as the working fluid and the filling ratio is fixed at 48% by volume. The experimental results on PHPs with the single-diameter channel show that the proposed passive check valves significantly improve the thermal performance of PHPs: 48% and 81% reduction in the thermal resistance in the vertical orientation and the horizontal orientation, respectively. Also, the experimental results on PHPs with the dual-diameter channel show that the passive check valves effectively improve the thermal performance over the wide operating range regardless of the orientation of PHPs: 33% and 34% reduction in the thermal resistance in the vertical orientation and the horizontal orientation, respectively. It is found through high-speed photography that this enhanced performance occurs because the passive check valves significantly increase the time-averaged volumetric fraction of vapor in the condenser section by 5 times from 0.09 to 0.45. This stems from the fact that the passive check valves effectively make the working fluid flow 3.5 times more preferentially in one direction over the other.

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

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

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

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

Local heat flux estimation inside tubes through conjugate gradient method with adjoint operator: application to the pulsating heat pipes case

PurposeThe purpose of this paper is to apply the conjugate gradient (CG) method, together with the adjoint operator (AO) to the pulsating heat pipe problem, including some quite interesting experimental results. The CG method, together with the AO, was able to estimate the unknown functions more efficiently than the other techniques presented in this paper. The estimation of local heat transfer coefficients, rather than the global ones, in pulsating heat pipes is a relatively new subject and presenting a robust, efficient and self-regularized inverse tool to estimate it, supported also by some experimental results, is the main purpose of this paper. To also increase the visibility and the general use of the paper to the heat transfer community, the authors include, as supplemental material, all numerical and experimental data used in this paper.Design/methodology/approachThe approach was established on the solution of the inverse heat conduction problem in the wall by using as starting data the temperature measurements on the outer surface. The procedure is based on the CG method with AO. The here proposed approach was first verified adopting synthetic data and then it was validated with real cases regarding pulsating heat pipes.FindingsAn original fast methodology to estimate local convective heat flux is proposed. The procedure has been validated both numerically and experimentally. The procedure has been compared to other classical methods presenting some peculiar benefits.Practical implicationsThe approach is suitable for pulsating heat pipes performance evaluation because these devices present a local heat flux distribution characterized by an important variation both in time and in space as a result of the complex flow patterns that are generated in this type of devices.Originality/valueThe procedure here proposed shows these benefits: it affords a general model of the heat conduction problem that is effortlessly customized for the particular case, it can be applied also to large datasets and it presents reduced computational expense.

Experimental Study of Pulsating Heat Pipes Filled with Nanofluids under the Irradiation of Solar Simulator

Developing renewable energy technologies, especially solar technology, is of vital importance to cope with increasing energy consumption. The existing solar thermal systems have the disadvantages of capturing solar energy inefficiently and needing additional pumping power to circulate the working fluid. A concept of a direct absorption pump-free solar thermal system that combines the advantages of nanoparticles and pulsating heat pipes (PHP) is proposed in this work. The effects of a variety of parameters including nanoparticle types, nanoparticle concentration, and nanofluid filling rate on the performance of PHP were studied. It was found that PHP has the best filling rate (80–90%) making the best heat transfer performance and minimizing the thermal resistance. The concentration of nanoparticles affects the input power of the pulsating heat pipe and thus the operation of the PHP. The nanofluid with relatively low concentration cannot absorb enough solar energy to drive the PHP to operate normally. Experimental research shows that the new solar thermal system can absorb solar energy efficiently and transfer the heat into the targeted area spontaneously, which may be an approach for future solar thermal utilization.

Experimental Investigation of Aluminum Oxide Nanofluid on Closed Loop Pulsating Heat Pipe Performance

This paper discusses the experimental studies performed on a single closed loop pulsating heat pipe (CLPHP) to evaluate its thermal performance. The pulsating heat pipe is brass which has a single closed loop. Aluminium oxide (Al2O3) and deionized (DI) water nanofluid were utilized as working fluids, with different volume concentrations of aluminium oxide nanoparticles of 0.05 %, 0.5 % and 1%. The aluminium oxide particles are mixed with water in the two-step method to produce a stable suspension. Experiments are carried out in the horizontal mode with watt loads of heat inputs ranging from 10 w to 100 w. The temperature differences between the evaporator and condenser portions, thermal resistance, heat transfer coefficient and thermal conductivity are the parameters used to determine thermal performance. The thermal resistance of aluminium oxide and DI water nanofluid was the lowest, having 48 % less than that of water. The effective thermal conductivity of the heat pipe improves as the concentration of nanoparticles increases. The comparison between experimental results and computational fluid dynamics (CFD) simulation results CLPHP was carried out under the same condition.

Experimental investigation and semi-empirical correlations for a pulsating heat pipe filling with hybrid nanofluids applied for low-grade energy recovery

Pulsating heat pipe (PHP) is a high-efficiency thermal transportation technology being utilized in the low-grade energy fields. In current work, the novel-hybrid working fluid - graphene oxide nanoplatelets (GO nanofluid) and surfactant solution were jointly utilized to reduce flow resistance and enhance overall thermal performance of PHPs. Sodium Dodecyl Sulfate (SDS) was employed as a surfactant to prepare the water-based surfactant solutions of 500 PPM. The charge ratio was maintained at 60%, vertical bottom heating position of PHP was applied with the power range of 10–100W. Our experimental results illustrated that the oscillation frequency of temperature fluctuation was higher than that with charged GO-SDS hybrid nanofluid in comparison with DI water and pure GO nanofluid. Additionally, maximum average improvement rate of thermal performance 8.55% was successfully achieved in 0.03 wt% GO-SDS hybrid nanofluid than that with pure GO-nanofluid. Furthermore, multiphase fluid flow inside PHP has been comprehensively analyzed, and its flow regimes such as formation of foam and slug, coalescence and breakup of bubbles, and annular flow were observed. On site visualization results illustrated that a fast nucleation of vapor bubbles could be promoted in the evaporator section due to lower surface tension. Specially, a series of bubbles were expected to form cluster for GO-SDS hybrid nanofluid, which further enhanced the oscillation circulation inside PHP. This experimental research and its results could contribute to the optimization and application of PHP.

Fluid flow and thermal performance of the pulsating heat pipes facilitated with solar collectors: Experiments, theories and GABPNN machine learning

Solar energy could be effectively exploited and transferred by the solar collectors, where thermal transport efficiency was inhibited by actual operations and applications. In present research, solar collector combined with pulsating heat pipes (PHP) was proposed to enhance solar energy conversion and management. Fluid temperature oscillation, flow patterns and motions, heat transfer mechanisms inside present facility were comprehensively investigated, which aimed to suitably determine the flow stability of working fluid for PHPs, such that the whole system performance could be fully optimized. Firstly, an experimental investigation was comprehensively conducted to obtain the flow motions, temperature oscillation, and thermal resistance of PHPs, under multi-parameter conditions. Our results indicated that heat transfer performance was promoted with an increase in thermally driven force, accompanied by which low frequency with “small amplitude” transformed to high frequency with “bulk amplitude”. In addition, filling ratio of 25% even a minimum input power generally results in dry-out phenomena, superior liquid-vapor patterns and heat transfer performance were observed as filling ratio was 60%. Following that, theoretical modeling results confirmed that, within the critical pipe diameter, larger saturated vapor pressure and lower surface tension were significantly beneficial for the application of PHPs-solar collector. Considering dimensionless parameters and experimental data, Genetic Algorithm-Back Propagation Neural Network (GA-BPNN) was further built to predict the heat transfer performance of PHPs, which was in great agreement with the experimental data. Optimal filling ratios were further confirmed depending on the best Ku performance, within average deviation being no more than 10%. Present theoretical and experimental researches could facilitate the optimization and application of PHP- solar collectors, greatly exploiting solar energy for buildings.

Experimental investigation of pulsation behaviour and performance of pulsating heat pipe

This paper focuses on the experimental study of a closed-loop pulsating heat pipe with water. The unsteady state experiment was conducted to understand the role of different evacuation pressure, variable heat input and filling ratio on the PHP behaviour. The DAQ system did temperature measurements of the pipe at 13 locations for variable heat inputs, evacuation pressure, and filling ratio. PHP thermal behaviour is evaluated in terms of temperature variation with time, thermal resistance, effective thermal conductivity, and pulsation frequency. The strong pulsating effect is observed at 0.0799 bar. The thermal resistance of the heat pipe declines with the decrease in evacuation pressure. The lowest thermal resistance 0.05,786 K/W is observed at 0.0799 bar evacuation pressure with 30% FR, 6 times lower than 90% FR. Effective thermal conductivity rises with the decrease in evacuation pressure. The highest effective thermal conductivity of 10,233.32 W/mK is found at 30% FR and 0.0799 bar evacuation pressure, 7.5 times higher than atmospheric pressure. So, better performance is observed at low evacuation pressure of 0.0799 bar and 30% FR. This study benefits the heat transfer of integrated circuit technology and electronic devices because of its high effective thermal conductivity.

Numerical investigation of slug flow in pulsating heat pipes using an interface capturing approach

The thermal performance of pulsating heat pipes is based on a self-sustained fluid motion in presence of phase change phenomena. To study this complex coupling of pressure and temperature, the volume-of-fluid method is a widely used approach to capture the phase distribution and interface dynamics, while the Lee model is employed to account for phase change. However, no consensus can be found in literature regarding the film resolution requirements, turbulence or an optimal choice of the mass transfer intensity parameter. In this study, the influence of these factors on pulsating heat pipe simulations is systematically investigated. A closed interface-tracking CFD-VOF method is presented, whereby phase change is only assumed to occur in computational cells within the phase boundaries. First, the model is successfully validated on the one-dimensional analytic sucking interface problem to proove the preservation of supersaturated states and the correct calculation of momentum and energy sources due to phase changes. Subsequently, as a basic reference for the flow in a pulsating heat pipe, the impact of model parameters on a Taylor bubble expanding due to evaporation within a micro-channel is investigated. It has been observed that both, the near wall film discretization and choice of the mass transfer intensity factor are significantly influencing the transferred latent heat and thus, the expansion velocity of the bubble. Finally, the model is extended to account for flow phenomena in an experimental two-turn pulsating heat pipe. The simulation results revealed that it is crucial to adjust the mass transfer intensity factor of condensation in order to achieve viable pressure levels within the closed system. The proposed model was demonstrated to be easily implemented, numerically efficient, and capable of performing in depth two-phase studies.

Novel flat plate pulsating heat pipe with ultra sharp grooves

• Diffusion bonding was applied for the fabrication of flat plate PHPs. • Ultra-sharp grooves in the evaporator improved the heat transfer capacity of a PHP. • The proposed PHPs perform effectively for heat fluxes up to 1200 W (20.9 W/cm 2 ). • The gravity influence becomes negligible for powers beyond 600 W (10.4 W/ cm 2 ). • The PHPs appear to be a good alternative for temperature control of electronics. Pulsating heat pipe (PHP) is a very efficient solution for electronics cooling. Several strategies can be applied to improve the thermal performance of PHPs. In this context, the heat transfer enhancement of a flat plate pulsating heat pipe with a channel modification in the evaporator region, resulting in ultra sharp lateral grooves, was investigated experimentally. Chamfers were machined in the lateral walls of thirteen semi-circular cross section U-turn channels, drilled in flat copper plates. To form the sharp-grooved circular channels, two plates were faced against each other and diffusion bonded, resulting in a monolithic piece with high quality channels. The ultra sharp grooves had an angle of 29.1 ± 2.9°. The lateral grooves work as artificial nucleation sites, helping in the bubble formation, and act as a capillary medium, spreading the liquid over the evaporator region, delaying the dry-out. Therefore, the device could be less dependent on gravity, enabling it to be considered for applications in microgravity environments. To ascertain the efficiency of the proposed device, its performance was compared with another similar PHP with the same external geometry and with round ordinary cross-section channels of the same 2.5 mm channel diameter. Distilled water was selected as the working fluid, which, as predicted by literature models, worked at confinement conditions. As usual, the thermal behaviors of PHPs were characterized by their temperatures and pressures, depending on the operation conditions. The best filling ratio for each PHP was experimentally determined, considering heat loads from 20 up to 350 W (from 0.35 up to 6.1 W/cm 2 ). The influence of the ultra sharp grooves on the thermal performance of the PHP was investigated for a large range of power inputs, reaching up to 1200 W (20.9 W/cm 2 ), for the best filling ratio. The gravity influence in the PHP operation was evaluated by tests in three orientations: gravity-assisted, horizontal and against-gravity. Both cross-section profile PHPs performed effectively well for heat fluxes up to 20.9 W/ cm 2 , even in the against-gravity position, showing that the devices are suitable for temperature control of electronics, including those with high heat fluxes. Besides, the gravity effect could be neglected for heat powers beyond 600 W (10.4 W/ cm 2 ), which make them adequate for microgravity applications. The presence of ultra sharp grooves in the evaporator section of the PHP reduced by 2.1 °C the average evaporator temperature, decreased the temperature variations among sections and improved the thermal performance by 12% in the horizontal and gravity-assisted orientation.

Numerical study to recover low-grade waste heat using pulsating heat pipes and a comparative study on performance of conventional pulsating heat pipe and additional branch pulsating heat pipe

To understand the low-grade waste heat recovery ability of a pulsating heat pipes (PHPs) with water as working fluid. A two-dimensional conventional pulsating heat pipe (C-PHP) and an additional branch pulsating heat pipe (AB-PHP) were simulated using computational fluid dynamics and the volume of fluid method. Results revealed that based on the wall heat flux at condenser walls the waste heat recovery capability of the AB-PHP is 11% more than that of the C-PHP. Current work also presented the outcomes of a numerical simulation that compared the performance of AB-PHP with C-PHP. The comparison is made based on the flow and thermal performance by maintaining constant wall temperature at various filling ratios (FR) and tilt angles (TA). To understand the flow performance of PHP’s mean fluid flow velocity is used. Owing to the additional driving force provided by the additional branch the maximum mean flow velocity of AB-PHP is 1.16 times that of C-PHP. To understand the thermal performance of PHP’s temperature gradient of working fluid is used. In AB-PHP, the minimum fluid temperature gradient is observed at 50% FR and 90° TA. AB-PHP had a 21.6%, 11.5%, 9.3%, and 6% lower temperature gradient than C-PHP at 90°, 60°, 45°, and 30° TA, respectively.

Effect of Different Cooling Methods on Thermal Performance of Single Loop Pulsating Heat Pipe

A pulsating heat pipe (PHP) is a promising two-phase passive thermal device that consists of a capillary tube meandering between an evaporator and a condenser. Heat is transferred from the evaporator to the condenser by the self-excited oscillation of vapor and liquid. The complete knowledge of the heat transport mechanisms, particularly at the operating limit of PHPs, is far from satisfactory. In PHP, the phase-change acts as a driving force of the self-excited oscillation of the fluid. In this context, the condensation highly affects the performance of PHPs, while few studies have investigated the effect of the sink temperature or the cooling methods. In this study, a single metallic loop is tested to understand the local phenomena focusing on the impact of cooling methods of the condenser section: natural convection and forced air convection. Regardless of the cooling methods, the PHP showed the intermittent and unstable oscillation at low power input just after the start-up, and then continued to operate stably until the heater turned off after the evaporator temperature exceeds 140 °C. The resistance of natural convection cooling is more than 1 K/W lower than that of forced convection cooling, for the same heat input conditions. However, the resistance of both cooling methods at the same evaporator temperature shows a good agreement. The resistance is inversely proportional to the evaporator temperature as well as the heat input.

Experimental study on a hydrogen pulsating heat pipe in different heating modes

In practical applications, the heat load changes caused by various factors require the pulsating heat pipe (PHP) to have good heat transfer performance and temperature response characteristics in different heating modes. In order to understand the heat transfer performance of a hydrogen PHP in different heating modes, the temperature curves of the PHP in two heating modes (stepwise heating and sudden heating) are obtained experimentally. The experimental results show that for a given heat load, the differences of the quasi-steady-state temperatures and the effective thermal conductivities between two heating modes are negligible. It’s concluded that the stable heat transfer performance of the PHP is reproducible in the two different heating modes.

A review on the heat transfer performance of pulsating heat pipes

ABSTRACT The miniaturisation of systems has widely attracted researchers to contribute to the thermal performance enhancement utilising efficient heat transfer devices. Pulsating heat pipe (PHP) is an inimitable passive two-phase energy conversion/transport device capable of transferring extensive heat energy by oscillating liquid slugs and vapour plugs from hot to cold areas suitable for the management of generation of heat in electronics. Several theoretical, experimental and visualisation studies are made on PHP to understand operational mechanisms and to arrive at optimal conditions. Although PHP has potential application in the field of heat management, its effective utilisation is limited due to complex operational mechanisms.It is observed that PHPs are effective and reliable devices for utilisation in numerous energy systems. It is observed that PHPs are effective and reliable devices for utilisation in numerous energy systems. Advanced research is directed towards numerical simulations on the evaluation of PHP performance with non-conventional working fluids. It is found that the use of ternary hybrid nanofluid in PHP has scope for research work. The objective of this paper is to review the existing methodologies for enhancing the PHP overall performance and its applications.

Advancing Cryogenic Technologies Through Pulsating Heat Pipes

Comprising thin tubes that contain ultra-cold liquids and vapours, ‘cryogenic pulsating heat pipes’ can transport heat far more rapidly than even the most conductive metals. Logan Kossel and John Pfotenhauer at the University of Wisconsin-Madison are exploring the unique capabilities of this technology in unprecedented levels of detail. Through their research, they hope to boost the performance of pulsating heat pipes even further – potentially leading to new breakthroughs in many technologies that rely on cryogenic temperatures.