Closed Loop Pulsating Heat Pipe Research Articles

Detailed visualization experiments on the start-up process and stable operation of pulsating heat pipes: Effects of dividing boards

To broaden the applicable orientation for the existing closed loop pulsating heat pipe (CLPHP) with a relatively large tube (internal diameter of 6 mm), this work fabricated a novel quartz CLPHP inserted with a dividing board in the straight section of each tube. The dividing board forms two semi-circles with an effective hydraulic diameter (Dh) of 3.09 mm. This method amplifies the surface tension effect with almost no change in the mass inventory of working fluid. Through a series of visualization experiments, the effect of filling ratio (FR) on the pulsation in the boarded model are first revealed by comparing with the original non-boarded CLPHP under the vertical and the horizontal orientations. The four longitudinal corners generated by dividing board are found not only accelerated the drain down of the liquid slugs but beneficial to the onset of nucleate boiling, prompting the threshold of pulsation motion for 10 - 20 W. Also, the visualization results for the vertical orientation show that the sealing between the dividing boards and the inner tube had a great impact on the performance and heat transfer behavior. The thermal resistance can be improved by 22 - 43 % without leakage between the semi-circles. Under the horizontal orientation, the boarded CLPHP with only three number of turns can be incited with pulsation motion successfully. The boarded design provides additional vapor channels and avoids the liquid slug trains being pushed away from the evaporator during the initial heating period. Also, the un-balanced capillary force due to the hydraulic diameter difference can sustain subsequent pulsation motion. However, the success under only FR = 50 % indicates that an appropriate FR was also necessary.

Optimizing Closed Loop Pulsating Heat Pipes (CL-PHPs) using Taguchi method enhancing thermal performance and operational parameters

Closed Loop-Pulsating Heat Pipes (CL-PHPs) are a promising heat transfer technologies known for their efficient and versatile thermal management capabilities. This study presents a comprehensive analysis of CL-PHPs employing Taguchi method. It's a statistical technique to optimization enhance their performance. The research involves the utilizing an 8-turn pulsing heat pipe and a variety of working fluids aqueous mixtures, including Water with acetone, methanol, ethanol and water. An optimal CL-PHP performance was achieved while incorporation of optimization techniques for the selected operational parameters such as thermal resistance, heat supply, angle of orientation, type of fluid and filling ratio. The optimization process aims to improve various operational parameters impact such as the thermal resistance performance of CL-PHPs were examined, including fill ratio, heat input, angle of inclination, working fluid, etc. to attain optimal CL-PHP performance. The performance parameters orthogonal array were studied using ANOVA and analysis of variance. Experiments with changing the input parameters were carried out using the Taguchi L27 orthogonal array. The performance of CL-PHP was mostly effected by heat supply along with inclination angle and fill ratio to some extent. The optimization results indicate that the most important element affecting CL-PHP performance is heat input, which is followed by fill ratio and angle of inclination. This research contributes to the advancement of thermal management technologies and underscores the potential benefits of CL-PHPs in various engineering applications A maximum deviation of with ±8 % divergence from the anticipated values is obtained among the test runs that are considered random.

Effect of evaporating-condensing length ratio and heat flux on starting and operating characteristic of pulsating heat pipe

Pulsating heat pipe is an efficient heat transfer technology applied in the fields of electronic cooling and energy utilization. There are many factors affecting the starting and operating characteristic, such as structure, working fluid, filling ratio and so on. In order to investigate the effect of heating length and heat flux, a series experiment was carried out on a closed loop pulsating heat pipe with six different length ratios of 0.3, 0.4, 0.6, 0.8, 1.0, 1.2. The results show that the length ratio and heat flux jointly affect the characteristic of PHP. The starting process of PHP experiences no pulsating, unstable pulsating and then stable pulsating at different length ratios with heat flux increasing. Starting heat flux drops firstly and then tends to be flat and stable near a certain value with increasing evaporating-condensing length ratio. The continuous increase of heating flux can lead to the transition of PHP from stable operating to unstable operating, and the transition occurs on the pulsating heat pipe with length ratio of 0.4 on the condition of heat flux increasing to 7.64 W/cm2. Working heat flux region of pulsating heat pipes varies with the variation of length ratios. The higher heat flux area is for the pulsating heat pipe with smaller length ratio, but the lower heat flux area is better for the PHP with larger length ratio. The optimal operating characteristic was obtained by pulsating heat pipe with length ratio of 0.8, and the thermal resistance reach to the lowest of 2.5 °C/W at heat flux of about 4.5 W/cm2.

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.

Segmented thermal resistance model of flat-plate CLPHP based on PEMFC cooling

As a passive heat transfer superconductor for proton exchange membrane fuel cell (PEMFC) cooling, the heat transfer performance and temperature uniformity of flat-plate closed loop pulsating heat pipe (CLPHP) are the key factors to determine its application efficiency. Based on the geometric structure and working medium thermophysical properties of flat-plate CLPHP, this study establishes segmented and integral thermal resistance theoretical models for the heat transfer properties of each section of the flat-plate CLPHP. The calculation accuracy of the segmented and integral thermal resistance models is compared through experimental verification. The results show that the segmented thermal resistance model's temperature variation and temperature uniformity are more accurate than that of the integral thermal resistance model when the flat-plate CLPHP is started, operated stably, or at higher heating power. However, the model calculation error is relatively large when the heating power is relatively high at 400 W, but the calculation accuracy of the segmented thermal resistance model in temperature and temperature uniformity is 2.32 and 5.99 times that of the integral thermal resistance model. The segmented thermal resistance model provides a theoretical basis for improving the calculation accuracy of flat-plate CLPHP coupled PEMFC cooling.

Chaotic index analysis of ethanol-based graphene nanofluid pulsating heat pipe

Pulsating heat pipes utilizing ethanol-based graphene nanofluids hold significant promise for cooling large electronic devices. However, traditional methods fall short in fully characterizing their properties due to internal phase transitions, latent heat, multiphase flow, and multi-field coupling. To address this, nonlinear chaotic analysis methods are introduced. This study constructs a vertical closed-loop pulsating heat pipe platform and applies Takens embedding theorem, phase space reconstruction theory, mutual information recursive selection method, and associative dimensionality algorithm to analyze ethanol-based graphene nanofluids with various concentrations. The investigation focuses on correlation dimensions and Kolmogorov entropy to provide numerical feedback on nanofluid concentration. Notably, ethanol-based graphene nanofluids concentrations between 0.04 wt% and 0.07 wt% exhibit an average heat transfer thermal resistance of approximately 0.74 K/W, corresponding to correlation dimension and Kolmogorov entropy values of 1.36 and 0.035, respectively. Additionally, reconstructed three-dimensional Singular Attractor phase diagrams offer morphological feedback on the pulsating heat pipe's working conditions. As the ethanol-based graphene nanofluids concentration reaches 0.35 wt%, an increase in the number of free vector points within the three-dimensional coordinate Attractor indicates localized unstable conditions in the heat pipe. Employing a wavelet noise reduction method with a soft threshold of 80 preserves the macroscopic vector flow pattern while eliminating irrelevant local information. Overall, this paper introduces novel approaches for analyzing heat transfer characteristics of graphene nanofluids in pulsating heat pipes.

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.

Partial visualization study on flow, startup and heat transfer characteristics of closed-loop pulsating heat pipe with R1336mzz(Z)

R1336mzz(Z), as a non-flammable, low-toxicity and environmentally friendly refrigerant, with relatively high boiling temperature and critical temperature among the existing HFOs refrigerants, has a great potential to be applied as the working fluid of pulsating heat pipes (PHPs). To evaluate the application of R1336mzz(Z) in PHPs, a partially visual experiment on the startup, flow and heat transfer characteristics of the R1336mzz(Z)- PHP with 0.3–0.7 filling ratios was carried out, and compared with the experimental results of a distilled water-PHP. The research results showed that within the experimental range, the startup time of the R1336mzz(Z)-PHP and the maximum evaporation temperature (Ts,max) before the startup were both lower than those of the distilled water-PHP, which meant that the R1336mzz(Z)-PHP had better startup performance. During the stable operation of the PHP, the R1336mzz(Z)-PHP presented a better hydrodynamic behavior than the distilled water-PHP. With the better hydrodynamic behavior, at the low heat input, the R1336mzz(Z)-PHP presented a lower thermal resistance compared with the distilled water-PHP. As the heat input increased, the heat transfer performance of the R1336mzz(Z)-PHP became inferior to that of the distilled water-PHP. Meanwhile, the flow patterns for the R1336mzz(Z)-PHP and the distilled water-PHP were further compared and discussed. In general, the PHP with R1336mzz(Z) showed predominance in the startup and heat transfer at low heat input.

An Innovative Design for a Solar Water Heating System Utilizing a Flat-Shaped Heat Pipe

Abstract In this work, an innovative design for a solar water heating system using a flat-shaped heat pipe as a heat transfer device is presented to pave the way for a substantial increase in the thermal performance of these systems. An analytical study is utilized to investigate the thermal performance of the solar water heating system. The analytical results of the flat-shaped heat pipe system are compared with the results of the evacuated tube solar water heating system with a U-tube, thermosyphon, and closed-loop pulsating heat pipe. It is found that the water temperature difference between the inlet and outlet of the flat-shaped heat pipe system is substantially higher than the U-tube, thermosyphon, and closed-loop pulsating heat pipe system by as much as 31.4, 22.5, and 18.5 °C, respectively, at a nominal 0.6 l/min mass flowrate. Furthermore, utilizing the flat-shaped heat pipe in the solar water heating system optimizes the thermal conductivity of the solar setup due to a reduction in the condenser section length. These reductions also lead to a large reduction in the weight and cost of the system.

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.

Computational study on the thermal properties of a closed loop pulsating heat pipe

Pulsating Heat Pipes (PHPs) are passive heat transfer devices, where heat transfer is higher than that in common heat transfer devices such as metal fins and heat pipes. The main reason for this is the two-phase phenomenon occurring inside the PHPs with oscillatory motion of the bubbles. The flow in the pipe is a multiphase flow, where vapor plugs and liquid slugs are created in PHPs due to capillary action. In this study, a CFD analysis was conducted on a two-turn PHP using the Analysis of Systems (ANSYS) Fluent software. The adiabatic section and overall height of the pipe were kept constant, whereas the height of the evaporation region varied at 32, 37, 42, 47, and 52 mm from the bottom. This study aims to investigate the performance of PHP and how heat transfer is affected. It also observed variations in the volume fraction and thermal resistance, considering other factors. The study was conducted under previously researched conditions with an inner diameter of 2.0 mm and an outer diameter of 3.0 mm. The PHP was made of copper, and the working fluid was methanol, which filled 50% of the volume. Heat inputs of 80 W, 85 W, 90 W, and 95 watts were supplied to the PHP. The simulation was performed, and the output results are presented in graphical and contour plots.

Thermal performance of a single loop pulsating heat pipe with asymmetric adiabatic channel

The thermal performance of an asymmetric single-turn closed-loop pulsating heat pipe (aCLPHP) has been investigated experimentally. In an asymmetric closed-loop, the working fluids may exhibit a consistent two-phase oscillatory-circulatory flow as a direct consequence of the capillary pressure difference. The adiabatic channels of different cross-sections will cause a pressure difference, boosting the flow of heated vapor and liquid. So, a novel aCLPHP of 208 mm with an evaporator of 35 mm length was fabricated from 2.4 and 3.4 mm inner diameter copper capillary tubes. The setup was subjected to gradual and abrupt heat loads (in vertical bottom heating mode) to find out the effects of inclination angles (0°, 30°, 60°, and 90°), working fluids, and filling ratios (FR) on the thermal performance. A constant supply of coolant in the condenser chamber through a bath assisted in dissipating the heat from the heat pipe. The simultaneous temperature and pressure signals at 10 Hz were recorded through a data acquisition system to analyze the thermal performance and flow characteristics. The average thermal resistance is mapped to different operating conditions to compare the conventional (uniform cross-section) and asymmetric adiabatic channel configurations. The pseudo-steady state operation was obtained up to 100 W power supply at 60% FR of pure water in the vertical orientation. Due to asymmetry, the heat carrying capacity was increased by 75% and 50% for working fluid water and acetone, respectively. The heat pipe was operating at lower inclination angles, except horizontal orientation only with pure water. Hence, introducing an asymmetric adiabatic section is a simple, reliable, and cost-effective approach to improve the capability of a single-turn CLPHP for the thermal management of various electronic components.

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.

Parametric Investigation of Closed Loop Pulsating Heat Pipe with Cerium Oxide Nanofluid

In this study, a closed-loop pulsating heat pipe experimental investigation was done with 1% wt concentration of cerium oxide/EG-water (60-40) nanofluid. The unsteady state measurement was done to determine the effect of heat input, filling ratio and evacuation pressure on the thermal performance of the closed-loop pulsating heat pipe. The thermal performance is assessed in terms of temperature variation, thermal resistance and effective thermal conductivity of the pulsating heat pipe. The most appropriate behaviour is observed at 0.0799 bar evacuation pressure with 50% FR. The lowermost thermal resistance of 0.116598K/W was observed at 0.0799 bar evacuation pressure and 50% FR. The effective thermal conductivity value was observed as 5078.34 W/mK at 50% FR, 0.0799 bar for 80W heat input which is 12 to 13 times better than pure copper. The pulsation action inside the pulsating heat pipe is verified with the power spectral density analysis. This study supports the better performance of the heat pipe at 50% FR with a lower evacuation pressure of 0.0799 bar.

A Capillary Tube Pulsating Heat Pipe With Asymmetric Adiabatic Channels for Thermal Management

The two-phase flow passive thermal management device, an asymmetric (adiabatic channel) closed-loop pulsating heat pipe (aCLPHP), has been investigated experimentally. The thermo-hydrodynamic behavior of a pulsating heat pipe (PHP) strongly depends on various operating and geometric parameters. In this effort, asymmetry has been adopted to promote the unidirectional two-phase oscillatory motion of the working fluid. In the present study, simultaneous pressure and temperature variations under gradual and sudden heat loads are monitored to estimate thermal performance. The effects of inclination angles (IAs), heat loads, working fluids, and filling ratios (FRs) on thermal performance have been demonstrated using average thermal resistance. In a two-turn (four-channel) aCLPHP in bottom heating mode, acetone and water were used as working fluids within 50%–70% of FRs. The results show that the startup phenomena of two-phase flow and pseudo-steady-state temperature were achieved using acetone at a 60% FR up to 30° angle from a horizontal orientation. In the vertical orientation, the working fluid water at 60% FR performed well under a sudden heat load of 50 W. Adding asymmetric adiabatic channels to a PHP can be a simple and inexpensive way to improve its thermal performance.

Experimental Study on Thermal Performance of Dual Diameter Closed Loop Pulsating Heat Pipe Using ZnO/water Nanofluid

Abstract: In this paper, experimental study on the thermal performance of closed loop pulsating heat pipe (CLPHP) with single diameter and dual-diameter structure is investigated. The CLPHP with dual-diameter configuration is made of copper capillary tubes with two diameters; greater in the condenser section (inner diameter of 3mm) and smaller in the evaporator and adiabatic sections (inner diameter of 2mm). Experiment was conducted in vertical orientation with bottom heating mode having two-turns and 50% filling ratio (FR). The water and zinc oxide (ZnO/water) nanofluid with 0.25% and 0.5% w/v used as working fluids. The heat power was supplied from 8 W to 80 W, in the steps of 8 W. The various temperatures were recorded on the outer wall of the evaporator and condenser section of single diameter and dual diameter CLPHP. The thermal performance is measured in terms of thermal resistance. The thermal resistance at different heat inputs was measured. It is concluded that, the thermal performance of the dual-diameter configuration is better than the single-diameter.

Thermal characteristics of rotating closed-loop pulsating heat pipe designed for rotating-type energy storage devices

This research was aim to investigate the thermal characteristics of the rotating closed-loop pulsating heat pipe (RCLPHP) designed for integrating onto rotating-type energy storage devices. The thermal characteristics beginning from the start-up state to the post-critical state were thoroughly observed. The RCLPHP was made from 1.78-mm inner diameter copper tube and it was bent to be 11 meandering turns. The evaporator section length was 50 mm, which was the same as of the condenser section. Working fluid was distilled water. Filling ratio was 50% of total volume. It was installed on a rig and oriented in vertical plane. Annular plate electrical heaters were used to supply heat input. The heat released from the condenser section to the ambient air at constant temperature of 25 ± 1 °C. The rotational speed was 70 rpm. It could be found that when the RCLPHP worked in the normal operating state, the evaporator and the condenser section temperatures fluctuated with obvious frequency and amplitude, and the internal phenomena of the working fluid could be implied as the slug-train. When the RCLPHP has reached the critical state, the condenser section temperature subsequently decreased. This is because the condensate is strongly pushed by the centrifugal force against the vapor flow direction, then the vapor plugs cannot flow to transfer the heat to the condenser section as usual.

Thermal performance of various adiabatic section lengths of closed-loop pulsating heat pipe designed for energy recovery applications

This experimental study aims to emphasize on thermal performance and temperature variation of the closed-loop pulsating heat pipe (CLPHP) affected by various adiabatic section lengths. A capillary copper tube has been bent to have 10 and 20 meandering turns to form the CLPHPs with 1.78 mm internal diameter. The evaporator section length was 150 mm, which was the same as of the condenser section length. The adiabatic section length was varied from 75 to 150, 300, and 450 mm. Ethanol, R123, and water was selected to be working fluid with the volumetric filling ratio of 50%. Hot water was pumped through the heating jacket for supplying the heat input to the evaporator section. Heat flux selected as the thermal performance in this study was measured by means of the calorific method across the cooling jacket enveloping the condenser section. It could be concluded that effect of the adiabatic section length has two different trends that are: (i) When the adiabatic section length increases, the heat flux continuously increases until the evaporator section length exceeds a certain value, the heat flux then decreases. And (ii) when the adiabatic section length increases, the heat flux continuously increases. The different effects between both trends are depended on the working fluid’s flow velocity, surface tension, density, and viscosity.

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.