Performance Of Thermosyphon Research Articles

Role of impregnated lubricant in enhancing thermosyphon performance

We report on the optimal configuration for enhanced heat transfer performance of a two-phase closed thermosyphon (TPCT), incorporating a superhydrophilic (SHi) evaporator with a slippery lubricant-infused porous surface (SLIPS) condenser (TPCT-SHiSL). For the conditions examined, the overall heat transfer performance of the TPCT-SHiSL was enhanced by as much as 28.9% compared to the other configurations proposed. This enhancement is attributed to the use of SLIPS as the condenser, which promotes the condensation heat transfer and the overall heat transfer performance. Moreover, we illustrate the importance of pairing the SLIPS condenser with a SHi evaporator, in order to minimize lubricant absorption at the evaporator. Additionally, the heat transfer performance of the TPCT-SHiSL was evaluated over time and consistent results were observed even after 16 experimental runs (192h in 90days), demonstrating good durability of the TPCT-SHiSL.

Modeling of natural convection and radiative heat transfer in inclined thermosyphon system installed in the roof of a building

AbstractSome construction laws require the integration of an open thermosyphon system having multiple functions to the building roof. In order to analyze the efficiency of this system, a numerical model was developed. This model is based on the study of the natural convection coupled with radiative heat transfer in an inclined air channel. Two configurations are studied, the first one is a simple channel formed by two parallel plates and the second one is equipped with fin blades joined to the upper plate. The air flow in the channel which is due to the buoyancy forces is fully turbulent and the turbulence was modeled using the k‐ε model. Some numerical results obtained were validated using the experimental ones of Khedari et al. (2002) and those of Nouanégué and Bilgen (2009). The effect of the radiative heat transfer on the mean Nusselt number was shown. Correlations for Nusselt numbers were obtained for the two configurations as functions of the geometric parameters and the Rayleigh number. The main objective of this study is to use these correlations in other models to facilitate the operation of this system

Experimental Study of Copper Nano-fluid on Thermosyphons Thermal Performance

A new way to remove the intense heat by developing and implementing an innovative low cost compact loop thermosyphon has been widely observed. Especially, it was concluded that nano-fluids are potential heat transfer fluids to be used as working fluid in thermosyphon. Therefore, the thermophysical or transport properties of nano-fluids in thermosyphon need to be discussed. In present work was to experimental study the thermal performance of thermosyphon using a copper nano-fluid as a working fluid. The experiment was performed in order to measure the temperature distribution and compare heat transfer rate of the thermosymphon with nano-fluid and with pure water. The concentration of copper nano-particle was 10, 30 and 50 ppm. The tested working temperature was 60, 70 and 80C. Results shown that the concentration of 50 ppm of copper nano-fluid improved thermal performance compared with the case of pure water. The optimum and behavior of copper nano-fluid in thermosyphon is presented, which highlights all of the beforehand mentioned advantages.

Loop thermosyphon performance study for solar cells cooling

The loop thermosyphon was used in the heat dissipation of concentrating solar cells, to solve the problem of the high temperature of solar cells and their low efficiency. In this paper, a loop thermosyphon heat exchanger was designed and the effect of working fluid on heat transfer performance of loop thermosyphon was studied through experiments and the best working fluid was selected. The results show that the heat transfer effect of acetone as the working medium is better than that of water and ethanol. Acetone loop thermosyphon can be used for 7 times concentrating photovoltaic cells cooling, while the ethanol loop thermosyphon can be used for 3 times and the water loop thermosyphon only used for 1 time. The heat transfer characteristics of the fin with natural convection were studied by numerical calculation, and the fin structure was optimized. The influencing factors were analyzed by orthogonal analysis.

The effects of bend angle and fill ratio on the performance of a naturally aspirated thermosyphon

An experimental investigation is carried out on a fully passive cooling system for possible application in cooling tower top remote radio heads (RRHs). Specifically, the system implements a reflux thermosyphon to transport the heat from simulated power amplifiers to a natural convection cooled remote heat exchanger. In this work, the thermosyphon performance is investigated with changing evaporator orientation, rotating from vertical to horizontal in increments of 30 degrees. Of course the condenser remains vertical as it is being cooled by buoyant natural convection. Furthermore, the combined influence of fluid loading and bend angle is considered. For the vertical evaporator orientation and low applied power and high fill volumes the unsteady geyser boiling regime is apparent which tends to adversely influence the effectiveness of the two phase heat transfer in both the evaporator and condenser. Increasing the thermal loading and increasing the bend angle tend to mitigate geyser boiling and improve the heat transfer. For moderate to high heat inputs the thermosyphon is fairly insensitive to both bend angle and fluid loading and it is hypothesised that this is because pool boiling and film condensation are the mechanisms of heat transfer in the evaporator and condenser sections respectively. However, the failure power was found to have a strong dependence on bend angle and fluid loading and the mechanisms for this are discussed. It is concluded that the overall thermal system is appropriate for its target application with the thermosyphon taking up a very small portion of the overall thermal budget.

Heat transfer and thermal storage performance of an open thermosyphon type thermal storage unit with tubular phase change material canisters

A novel open thermosyphon-type thermal storage unit is presented to improve design and performance of heat pipe type thermal storage unit. In the present study, tubular canisters filled with a solid–liquid phase change material are vertically placed in the middle of the thermal storage unit. The phase change material melts at 100°C. Water is presented as the phase-change heat transfer medium of the thermal storage unit. The tubular canister is wrapped tightly with a layer of stainless steel mesh to increase the surface wettability. The heat transfer mechanism of charging/discharging is similar to that of the thermosyphon. Heat transfer between the heat resource or cold resource and the phase change material in this device occurs in the form of a cyclic phase change of the heat-transfer medium, which occurs on the surface of the copper tubes and has an extremely high heat-transfer coefficient. A series of experiments and theoretical analyses are carried out to investigate the properties of the thermal storage unit, including power distribution, start-up performance, and temperature difference between the phase change material and the surrounding vapor. The results show that the whole system has excellent heat-storage/heat-release performance.

Effect of anodization on the heat transfer performance of flat thermosyphon

This paper presents the thermal performance of a flat thermosyphon with and without anodized inner surface. Anodization is performed to prepare a uniform coating on the inner side of the thermosyphon. Both non-anodized and anodized thermosyphons charged with acetone and tested in the heat input range of 50–300W. Experiments are conducted for anodized and non-anodized flat thermosyphons at various inclination angles (0°, 45°, 90°) and fill ratios (40%, 60% and 100%). It is found that fill ratio and inclination angle has a significant effect on the performance of the thermosyphon. The total thermal resistance of the anodized thermosyphon is reduced by 20% when compared to the non-anodized thermosyphon. The pore density of the anodized surface has increased almost 90% than the pore density of non-anodized surface. Both evaporator and condenser heat transfer coefficient of anodized thermosyphon is enhanced, when compared to that of non-anodized thermosyphon. The maximum enhancement in heat transfer coefficients of the evaporator and condenser in the anodized thermosyphon is 9% and 27% respectively, when compared to non-anodized thermosyphon at a heat flux of 49kW/m2. The performances of flat and cylindrical anodized thermosyphons are compared and it is found that the flat thermosyphon performed better than the cylindrical one. The heat transfer coefficient in evaporator and condenser of flat thermosyphon is enhanced to 69% and 56% respectively when compared to the cylindrical one at a heat flux of 50kW/m2.

열사이펀의 형상비와 충전율에 따른 열전달 성능 해석

Thermal-fluid analysis is performed numerically to figure out the characteristics of heat transfer in a thermosyphon varying with the aspect ratio of geometry and the filling ratio of working fluid. The computational results are reasonable compared with the experimental data and visualized. The thermal resistance and the convective heat transfer coefficients are evaluated with the aspect ratio of thermosyphon and the filling ratio of working fluid, respectively. In conclusion, the thermal resistance decreases as the length of evaporator increases. However, the variation of a condenser length is nearly independent on the thermal resistance. In order to raise the performance of thermosyphon, the working fluid needs to be filled over 75%. In addition, Nusselt numbers in the evaporator and the condenser show 275 and 304, respectively.

Role of nanofluid fouling on thermal performance of a thermosyphon: Are nanofluids reliable working fluid?

This paper focuses on fouling formation of nanofluid in a gravity-assisted thermosyphon equipped with a mesh screen wick. A transient study has been established on the fouling resistance of water-based TiO2 nanofluids at different operating conditions comprising the applied heat flux, mass concentration and inclination of thermosyphon. Nanofluids were prepared using prolonged sonication, stirring, and pH control. Triton X-100 was utilized as a dispersant. The thermosyphon is a copper made tube, which is dimensionally 10.7 mm and 12 mm for inner and outer pipe diameters respectively and total length of 280 mm. Transient results over the extended time reveal a considerable deterioration of heat transfer coefficient and thermal performance as a result of fouling formation inside the wick at evaporator section. According to the results, rate of fouling can be enhanced by increasing the nanofluid mass concentration. Intensification of fouling on wick structure and internal wall of evaporator causes instabilities in thermal performance of thermosyphon over the time, which eventually causes the thermosyphon failure. This point has been ignored by most of previous researchers, which has a considerably negative impact on thermal performance of thermosyphon at longer operating time and higher heat loads. Therefore, a new fouling resistance model has been re-developed combining the microfluidic typical models. This model can predict the fouling resistance of nanofluid inside the thermosyphon with approximate deviation of 30%.

Utilization of Fly Ash Nanofluids in Two-phase Closed Thermosyphon for Enhancing Heat Transfer

This study investigates how fly ash nanofluids affect the thermal performance of a two-phase closed thermosyphon at various states of operation. The utilization of nanofluids obtained from X2O3-type oxides, such as Al2O3, Fe2O3, or CuO, on the improvement of two-phase closed thermosyphon performance was reported in a number of studies in the literature. The present study experimentally demonstrated the effect of using a nanofluid obtained from fly ash comprised of various types of metal oxides in varying ratios on improving the performance of a two-phase closed thermosyphon. The fly ash was obtained from the flue gas that was captured in the cyclones of the Yatagan thermal power plant (Turkey). Triton X-100 (Dow Chemical Company) dispersant was used in the study to produce the 0.2% (wt) fly ash/water nanofluid via direct synthesis. A straight copper tube with an inner diameter of 13 mm, outer diameter of 15 mm, and length of 1 m was used as the two-phase closed thermosyphon. The nanofluid filled 33.3% (44.2 ml) of the volume ofthe two-phase closed thermosyphon. Three heating power levels (200, 300, and 400 W) were used in the experiments with three different flow rates of cooling water (5, 7.5, and 10 g/s) used in the condenser for cooling the system. A increase of 26.39% was achieved in the efficiency of the two-phase closed thermosyphon when 4% (wt) fly ash containing nanofluid was used to replace deionized water at a heat load of 200 W and with a cooling water flow rate of 5 g/s.

열사이펀의 열성능 산정을 위한 수치해석 연구

동토지역에서는 계절변화에 상관없이 항시 영하상태로 동결되어 있는 영구동토층과, 그 위로 동결융해가 반복되는 활동층으로 구성되어있다. 일반적으로 대기온도 변화에 따라 동결융해가 반복되는 활동층은 얼음과 물의 상변화 작용이 반복되기 때문에 지반의 융기현상과 침하현상, 그리고 영구동토층의 온도상승을 초래할 수 있다. 열사이펀이란 구조체 내부에 충전된 냉매의 자가적인 열순환을 이용하여 지반의 온도를 영하상태로 제어하는 지반 안정화 공법 중 하나이다. 열사이펀은 대기중에 냉매의 열을 방출하는 응축부와 지중에 열을 흡수하는 증발부로 구성되어 있으며 대기의 온도가 영하의 상태일 때 지반의 온도를 영하상태로 제어한다. 본 연구에서는 열사이펀의 지반 열전달성능을 분석하기 위해 모형지반에 단열재를 배치하여 열사이펀을 통한 지반동결실험을 수행하였다. 단열재의 열차단성 및 열사이펀 길이를 고려하여 단열재 및 열사이펀의 성능실험을 수행하였으며, 실험에서 얻어진 물성치를 상용수치해석 프로그램인 TEMP/W에 반영하였다. 본 연구에서 제시된 실내실험과 수치해석 방법을 통해 열사이펀의 열성능을 산정할 수 있었다. The ground in cold region consists of active and permafrost layers. The active layer at the unstable state may cause ground corrosion and uplift, when the temperature of frozen ground increases due to seasonal changes. The thermosyphon is one of the stabilization methods to maintain the ground stability in the frozen ground. The thermosyphon is a closed two-phase convection device that extracts heat from the ground and discharges it into the atmosphere. In this study, ground freezing experiment using a thermosyphon and simulated ground with the isolation material was conducted to evaluate the thermal performance of the thermosyphon. In order to consider the thermal performance of the thermosyphon, commercial numerical program (TEMP/W) was adopted. Likewise, the thermal performance of thermosyphon and thermal properties of ground were applied in the numerical model. In a series of comparisons with experiment results and numerical study, thermal performance of thermosyphon can be evaluated.

Experimental and numerical study on the self-balancing heating performance of a thermosyphon during the process of oil production

The thermosyphon has been widely used in various industries due to its high heat transfer efficiency and large heat flux density, it has the significant value and wide application foreground. In this paper, an experimental rig was established to test the self-balancing heat transfer performance of the thermosyphons with three diameters in an unsteady temperature field, which exists in the actual oil production process. The experimental rig was also able to demonstrate how certain factors can impact on the heat transfer performance of thermosyphon. These factors include the diameter of the pipe, angle, with or without working medium and so on. Based on experimental results, a long thermosyphon made of several hollow sucker rods was designed and manufactured, which has been used in the Su 28 Well situated in the Huabei oilfield in China. Experimental results further indicated that the thermosyphon can effectively transfer the required heat of the fluid from wellbore bottom to wellbore top, causing the temperature of wellhead fluid to increase from 22 °C to 39 °C. In addition, a mathematical model is established to simulate the heat transfer process of this thermosyphon. The positive correlation between the simulated results and the experimental data demonstrated the effectiveness of the model. With this model, the heat transfer process of thermosyphon during oil production is simulated, with results indicating that the fluid temperature at the wellhead would increase when the production of oil increases, given a linear tendency pump setting.

Effect of electric field on thermal performance of thermosyphon heat pipes using nanofluids

In the present study the effect of electric field on thermal performance of two-phase closed thermosyphon as external modifications has experimentally investigated. Internal modifications applied by using two different water based nanofluids as working fluids. Nanofluids prepared by adding Al2O3 and CuO nanoparticles into the pure water using ultrasonic vibration system without adding any dispersant or stabilizer to prevent any possible change of chemical properties of the nanofluid. Results show that the thermal performance, and the Nusselt number ratio of thermosyphon gradually increase by increase in electric field intensity and nanofluids concentration. These values decrease by increasing in input power. Results also show that Al2O3/water nanofluid improves thermal performance of thermosyphon more than CuO/water nanofluid. Also, the experimental results indicate that the effect of nanoparticles on thermosyphon thermal performance is higher than the electric field. Maximum enhancement of Nusselt number ratio is about 43% that observed at 60W input power and 2.5% by volume of Al2O3 nanoparticles in the work fluid under 20V electrical field strength. Enhancement value is 39% for CuO/water nanofluid.

Effects of inclination angles on heat transfer performance of a loop thermosyphon for CPU cooling

A loop thermosyphon is known that it has higher heat transfer performance without a pump. Thus, we have applied new loop thermosyphon to cool CPUs of a rack mount server. Thermosyphon uses gravity to return refrigerant from the condensation part to the evaporation part. Therefore, when it is working, the water level in the condenser side should be higher than the evaporator side. In addition, the height of the new loop thermosyphon is designed low with 67.4mm to put it on a rack mount server. Hence, when the surrounding system and the loop thermosyphon incline, it is thought that water surface exists inside of the condenser. It causes decrease of heat transfer performance of loop thermosyphon. Hence, it is important to make clear how the performance changes by inclination angle of the system. To this purpose, the heat transfer performance of the loop thermosyphon has been measured as a function of inclination angles. As the result, it is found that thermal resistance of the condensing part and sub-cool degree at out-let of the radiator increase with increase of inclination angle. And the sub-cool degree has a correlation with vapor temperature of the loop thermosyphon. In addition, we confirmed the tendency of this correlation can be predicted by thermal circuit model of the radiator. These results show the thermal resistance changes of the loop thermosyphon by inclination angle are caused by water surface level changes in the condensing part.

Improvement of thermosyphon performance by employing nanofluid

The presented study aims to make nanofluids applicable for thermosyphons. Experiments employing a vertical thermosyphon are carried out utilising deionised water, water based titanium dioxide and gold nanofluids with different concentrations as working fluids. A maximal reduction of the thermal resistance of about 24% can be achieved when nanofluids are employed. An optimum is reached at concentrations between 0.2 vol. % and 0.3 vol. %, whereas at higher concentrations the thermal resistance remains either unchanged or increases again. A nanoparticle layer on the evaporator surface seems to cause the found changes. Experiments with the gold nanofluid indicate that no nanoparticles are transported with the vapour phase and deposited on the condenser surface. Long term experiments carried out with 0.3 vol. % indicate a massive aging of the porous layer built of nanoparticles on the evaporator surface.

Thermal performance of an open thermosyphon using nanofluid for evacuated tubular high temperature air solar collector

A novel evacuated tubular solar air collector integrated with simplified CPC (compound parabolic concentrator) and special open thermosyphon using water based CuO nanofluid as the working fluid is designed to provide air with high and moderate temperature. The experimental system has two linked panels and each panel includes an evacuated tube, a simplified CPC and an open thermosyphon. Outdoor experimental study has been carried out to investigate the actual solar collecting performance of the designed system. Experimental results show that air outlet temperature and system collecting efficiency of the solar air collector using nanofluid as the open thermosyphon’s working fluid are both higher than that using water. Its maximum air outlet temperature exceeds 170°C at the air volume rate of 7.6m3/h in winter, even though the experimental system consists of only two collecting panels. The solar collecting performance of the solar collector integrated with open thermosyphon is also compared with that integrated with common concentric tube. Experimental results show that the solar collector integrated with open thermosyphon has a much better collecting performance.

Heat transfer characteristics of thermosyphon with N2–Ar binary mixture working fluid

The N2–Ar binary mixture is adopted as the working fluid of a cryogenic thermosyphon and the heat transfer performance of such thermosyphon is studied in the present research. The heat transfer of the binary mixture in the thermosyphon is discussed theoretically by considering the mass transfer of the components. Meanwhile, an experimental setup for investigating the heat transfer performance of the cryogenic thermosyphon is built. The condenser is cooled by the liquid nitrogen on the top and the evaporator is heated circumferentially by the resistive wire. The N2–Ar binary mixture is charged into the cryogenic thermosyphon in different compositions, including pure N2 and pure Ar. It is found that the N2–Ar binary mixture can widen the operational temperature range of the cryogenic thermosyphon and it can work in the range of 64.0–150.0K. The dry-out limit appears in the experiments for the cases with Ar fraction below 0.503. The heat transfer rate of the dry-out limit increases with the increase of Ar molar fraction until film boiling appears on the top of the condenser. The heat transfer rate limited by the film boiling can be determined based on the empirical correlations that are used to estimate the critical heat flux of liquid nitrogen boiling on the plate. The heat transfer processes in the evaporator and the condenser are discussed, and the thermal resistances are calculated by empirical correlations. The calculated results agree well with the experimental results.

Comparison between a Heat Pipe and a Thermosyphon Performance with Variable Evaporator Length_ENG

Heat pipes and two phase thermosyphons are heat transfer devices whose operating principles are based on the evaporation/condensation of a working fluid using the capillary pumping forces (in the case of heat pipe) and gravity forces (in the case of two phase thermosyphons) to ensure the fluid circulation. The two systems were designed and constructed to investigate the performance and the affecting parameters, using ethanol as a working fluid. The affecting parameters which were studied are power input (200≤Q≤700) W, working fluid filling ratios (35% and 85%) and aspect ratio, the ratio of evaporator length to inner diameter, (4.0, 7.8 and11.5) . The experimental results showed that the best performance of heat pipe obtained at aspect ratio (7.8) and (85%) filling ratio at (500) W where the maximum heat transfer coefficient was (9950) W/m2.oC, while for the two phase thermosyphon the best performance was obtained at aspect ratio (4.0) for (35%) filling ratio and power input (600) W with maximum heat transfer coefficient equals to(4590) W/m2.oC. The overall comparison between the two systems showed that the performance of the heat pipe is better than that of the two phase thermosyphon. The experimental results of heat pipe was compared with theoretical and empirical correlations showing reasonable agreement especially with immura with percent 70%. KEY WORDS: heat pipe, two phase thermosyphon, aspect ratio, filling ratio

H123 CPU冷却用ループ型熱サイホン向け沸騰面の性能比較(OS-3:電子機器・デバイスの熱課題(2))

For energy saving of the servers, we applied the loop-type thermosyphon to CPU cooling. It is necessary to choose the high-performance boiling surfaces to enhance the performance of thermosyphon. Therefore, we have compared the pin-fin and TE-E as high-performance boiling surfaces in condition that they have , been put in real thermosyphon. As a result, the performances of both are equal in the condition that liquid level enough. In addition, they can cool the CPUs in degree of superheat less than half of the flat plate. However, the pin-fin has not worked enough performance in a condition with a little quantity of water.

Effects of Non-Condensable Gases on Heat Transfer Performance of Loop Thermosyphon for CPU Cooling

We have developed a loop thermosyphon for cooling electronics devices. Non-condensable gases (NCG) in a loop thermosyphon increase by leakage from outside, release of the gas dissolved in the refrigerant, and chemical reaction in the inside. Hence, it is necessary to know how the heat transfer performance changes when the amount of NCG in a loop thermosyphon increases. The effect of NCG's amount was measured for each component of the loop thermosyphon while changing the amount of heat input. The overall thermal resistance of a loop thermosyphon increased with the amount of NCG. The thermal resistance of the condensing part particularly increased with the NCG. The effect of NCG on the boiling part should be considered only by steam temperature which was raised by increase in the amount of NCG. The thermal resistance of the air cooling part is not affected by NCG, but the temperature difference of the air cooling part becomes smaller because heat-leakage increases with steam temperature.