Filled Heat Pipe Research Articles

Evaluation of innovative thermal performance augmentation techniques in heat sinks & heat pipes: Electronics & renewable energy applications

Heat sinks and heat pipes have vast applications including industrial domains requiring high heat flux. Due to numerous uses of these heat transfer devices, there have been great advancement in this area through innovation. This study focuses use of nanofluids and hybrid nanofluids for thermal performance enhancement of heat pipes and heat sinks. There are five different arrangements finless sintered copper wicked heat pipe, water based TiO2 filled heat pipe, TiO2 and SiO2 based hybrid nanofluid filled heat pipe, water cooled cylindrical pin finned heat sink and Fe2O3 and TiO2 hybrid nanofluid cooled heat sink. There are two test rigs one for testing heat pipe configurations and other for heat sinks. All the five elements are tested at constant heat flux ranging from 900 W/m2 to 3600 W/m2, in four equal steps. It’s observed that nanofluids play a very significant role in thermal performance augmentation, the affect is even more significant in heat pipes compared to heat sinks. Interestingly, nanofluids based heat pipes are proved more significant for high heat flux applications, although, nanofluid cooled heat sinks have slight better performance compared to the said but at a higher expense of weight, auxiliaries, space and cost. At 3600 W/m2 nanofluid based heat pipes have 33 % lower thermal resistance compared to water cooled heat sink. Therefore, nanofluid based heat pipes are primarily significant unless use of heat sink deemed dire. Nusselt number of heat sink is calculated at various heat flux and at variable mass flux conditions and found increasing with both parameter.

Experiment study on dryout characteristics and thermal resistance analysis of two-phase closed thermosiphon

This study aims to explore the dryout characteristics of two-phase closed thermosiphon. It involves the design and experimentation on low-liquid filled heat pipes. We investigated the effects of different fill ratios, heating water temperatures, and cooling water flow rates on the start-up characteristics of two-phase closed thermosiphon. Based on the network model, we proposed an analytical expression for the thermal resistance, R, of two-phase closed thermosiphon, and provided an explanation of the various thermal resistance components. This research expands our understanding of dryout and provides insights for optimizing heat pipe design and addressing heat conduction issues with low fill ratios.

Stability issues and operating limitations of nanofluid filled heat pipe: A critical review

It has been proved by researchers that nanofluids are good alternatives to conventional fluids in heat pipes. Typically, application of nanofluids in heat pipes results in improved thermal performance but some contradictions were also reported by the researchers. Although nanofluids are widely used in heat pipes some issues are yet to be resolved like the stability of nanofluids and operational limitations. The stability problem is a big issue for researchers either before or after the operational cycle. Therefore, it is important to enhance the nanofluid stability for the commercialization of the heat pipe. In this regard, this paper aims to study and summarise the outcomes of applications of nanofluids in different heat pipes. The authors emphasized on stability problems of nanofluids in heat pipes. Moreover, the impacts of operating limitations are also reviewed in this article.

THERMAL PERFORMANCE OF SINTERED COPPER WICK HEAT PIPE USING WATER-BASED HYBRID NANOFLUIDS: AN EXPERIMENTAL STUDY

Relatively stable titania and silica-distilled water-based hybrid nano fluid along with surfactant are proved to be more efficient in thermal performance enhancement of heat pipes which are used for efficient cooling in electronic industry. In the current research, sintered copper wick heat pipe is utilized due to its high level of capillary action and low thermal resistance of copper wick. In this article, the vertically mounted copper sintered heat pipe containing hybrid nano fluids is investigated to measure the wall temperature as well as thermal resistance through force convection. The experimentation was carried out at heat loads of 4W, 8W, 12W, 16W and 20W by using water, titania-distilled water nano fluids and titania-silica/distilled water hybrid nano fluid filled in heat pipe in order to compare the results. By increasing the input power, the wall temperature increases from evaporator to condenser section. Maximum reduction in average vapor temperature of titania-silica hybrid nano fluid filled heat pipe and titania-distilled water nano fluid filled heat pipe was observed to be 35.74% and 31.10% as compared to water filled heat pipe at 20 W respectively. The maximum decrement in thermal resistance of titania-silica/distilled water hybrid nano fluid filled heat pipe and titania-distilled water nano fluid was observed to be 30.66% and 17.33% in comparison with water based filled heat pipe at 8 W respectively. The highest enhancement in heat transfer coefficient of titania-silica hybrid nano fluid filled heat pipe and titania-distilled water nano fluid filled heat pipe was achieved to be 29.73% and 16.21% compared to water filled heat pipe at 8 W respectively. A vi

Heat Transfer Performance of Microgroove Back Plate Heat Pipes with Working Fluid and Heating Power

Micro heat pipes (MHP) cooling is one of the most efficient solutions to radiate heat for high heat flux electronic components in data centers. It is necessary to improve heat transfer performance of microgroove back plate heat pipes. This paper discusses about influence on thermal resistance through experiments and numerical simulation with different working fluids, filling ratio and heat power. Thermal resistance of the CO2 filled heat pipe is 14.8% lower than the acetone filled heat pipe. In the meantime, at the best filling ratio of 40%, the CO2 filled heat pipe has the optimal heat transfer behavior with the smallest thermal resistance of 0.123 K/W. The thermal resistance continues to decline but the magnitude of decreases is going to be minor. In addition, this paper illustrates methods about how to enhance heat pipe performance from working fluids, filling ratio and heat power, which provides a theoretical basis for practical applications.

Harvesting Waste Heat Energy from Automobile Engine Exhaust Using Teg with Heat Pipes

This research investigates how the heat from car exhaust pipe line can be recovered as power using passive Thermo electric generator (TEG) using heat pipes. In this research the heat pipes are place on the cold side of TEG to remove the rising temperature and hot side of TEG is placed on the circumference of exhaust pipe line of car engine. The heat pipes with and without nano-fluids were placed on cold side of TEGs to investigate heat removal from increasing temperature and too maintain constant temperature on cold side. On the basis of results from 3D finite element simulations and experiments in the setup, the heat flow, voltage, and current were measured. The method presented in this paper gives detailed insight into how TEG modules perform in general, and also enables prediction of potential improvement in module performance by using different nano-fluids as coolants and Preliminary results were obtained. The results of Finite Element Analysis are analogous with the experimental results of TEG with water filled heat pipes with minimal possible errors. Therefore, the performance of nano-fluids in heat pipes are numerically evaluated and proposal are made for the enhancement of Module power outputs in Harnessing exhaust heat energy.

Material Selection, Manufacturing and Performance Test of Ceramic High‐Temperature Heat Pipes Using Liquid Metals as Working Fluids

Heat exchange applications at high temperatures of greater than 800 °C under corrosive or abrasive conditions require heat exchangers based on ceramic materials instead of conventionally used metals. Heat exchangers based on heat pipes are exceptionally suitable since temperature gradients and correspondent thermal stresses are inherently low for this design. At high temperatures greater than 800 °C, the structural material SSiC and working fluids sodium or zinc appear to be the most promising options. Encapsulating the working fluid in ceramic heat pipes with a sealing joint ensuring long term stability and high temperature resistance is particularly challenging. A nickel‐based alloy has been identified as solder material for SSiC heat pipes using sodium as working fluid and a glass solder was used in case of zinc filled heat pipes. Manufactured heat pipes were tested in a hot‐gas test rig at temperatures up to 1000 °C.

Thermal performance of heat pipe with suspended nano-particles

Nanofluids are employed as the working medium for a conventional cylindrical heat pipe. A cylindrical copper heat pipe of 19.5 mm outer diameter and 400 mm length was fabricated and tested with two different working fluids. The working fluids used in this study are DI-water and Nano-particles suspension (mixture of copper nano particle and DI-water). The overall heat transfer coefficient of the heat pipe was calculated based on the lumped thermal resistance network and compared with the heat transfer coefficient of base fluid filled heat pipe. There is a quantitative improvement in the heat transfer coefficient using nano-particles suspension as the working medium. A heat transfer correlation was also developed based on multiple regression least square method and the results were compared with that obtained by the experiment.

Investigation of heat pipe heat exchanger effectiveness and energy saving in air conditioning systems using silver nanofluid

The present study attempts to use the methanol–silver nanofluid filled heat pipe heat exchanger and compares the effectiveness as well as the energy saving with pure methanol. A heat pipe heat exchanger has been tested in a test rig under steady-state conditions. The lengths of both the evaporator and the condenser sections of the heat exchanger were 700 mm, and its central adiabatic section had a length of 160 mm. The heat exchanger had 36 plate finned copper thermosyphons arranged in three rows. The inlet air temperature across the evaporator section was varied in the range of 33–43 °C while the inlet air temperature to the condenser section was nearly constant to be 13 °C. First, pure methanol was used as the working fluid with a fill ratio of 50 % of the evaporator section length, and then dilute dispersion of silver nanoparticles in methanol was employed as the working fluid. The nanofluid used in the present study is 20 nm diameter silver nanoparticles. The experiments were performed to compare the heat pipe heat exchanger effectiveness and energy saving, using nanofluid and pure methanol. The inlet air relative humidity across the evaporator section was varied between 35 and 80 %. The sensible effectiveness of the heat pipe heat exchanger obtained from experiments varied about 5–22 % for pure methanol and 9–32 % for methanol–silver nanofluid. Based on these experimental results, using methanol–silver nanofluid leads to energy saving around 8.8–31.5 % for cooling and 18–100 % for reheating the supply air stream in an air conditioning system.

Experimental investigation of nanofluids on sintered heat pipe thermal performance

Dilute dispersion of silver nano-particles in pure water was employed as the working fluid for conventional 1 mm wick-thickness sintered circular heat pipe. The nanofluid used in present study is an aqueous solution of 10 and 35 nm diameter silver nano-particles. The experiment was performed to measure the temperature distribution and compare the heat pipe temperature difference using nanofluid and DI-water. The tested nano-particle concentrations ranged from 1, 10 and 100 mg/l. The condenser section of the heat pipe was attached to a heat sink that was cooled by water supplied from a constant temperature bath maintained at 40 °C. At a same charge volume, the measured nanofluids filled heat pipe temperature distribution demonstrated that the temperature difference decreased 0.56–0.65 °C compared to DI-water at an input power of 30–50 W. In addition, the nanofluid as working medium in heat pipe can up to 70 W and is higher than pure water about 20 W.

Experimental investigation of silver nano-fluid on heat pipe thermal performance

Nano-fluid is employed as the working medium for a conventional 211 μm wide × 217 μm deep grooved circular heat pipe. The nano-fluid used in this study is an aqueous solution of 35 nm diameter silver nano-particles. The experiment was performed to measure the temperature distribution and to compare the heat pipe thermal resistance using nano-fluid and DI-water. The tested nano-particle concentrations ranged from 1 mg/l to 100 mg/l. The condenser section of the heat pipe was attached to a heat sink that was cooled by water supplied from a constant-temperature bath maintained at 40 °C. At a same charge volume, the measured nano-fluid filled heat pipe temperature distribution demonstrated that the thermal resistance decreased 10–80% compared to DI-water at an input power of 30–60 W. The measured results also show that the thermal resistances of the heat pipe decrease as the silver nano-particle size and concentration increase.

Performance of a Heat Pipe Solar Collector

This paper presents a comparative study between theoretical predictions and experimental results of a flat-plate solar collector with heat pipes. The theoretical model for the heat pipe solar collector is based upon the method by Duffie and Beckman(1980), modified to use heat pipes for energy transport. The methanol filled heat pipes are self-contained devices whose evaporators are inserted under pressure in the flat plate of the solar collector and the heat exchange is carried out at their condensers. The evaporators contain a wick of one mesh layer to ensure a better distribution of the working fluid. The condensers are wickless and inclined 15 deg more than the inclination of the evaporators to facilitate the return of the condensate to the evaporators. The time constant of the heat pipe solar collector was calculated and found to be about 23 minutes. Also presented in this paper are comparative experimental results of the proposed solar collector and a conventional commercial solar collector. The two collectors were tested simultaneously. The instantaneous efficiencies of the heat pipe solar collector are lower than the conventional collector in the morning and higher when the heat pipes reach their operating temperatures.

The inclination effect on the performance of water-filled heat pipes

Heat pipes have been used in wide ranges of applications today including solar engineering. During this research study, the inclination dependent performance of water filled heat pipes was investigated both theoretically and experimentally for solar energy applications. The results showed that the performance of water-filled heat pipes are strongly dependent on the inclination and the heat source temperatures. As a general result, the heat transfer capability of water filled heat pipes is reduced dramatically below a 45° tilt angle.