Performance Of Thermosyphon Research Articles

Prediction of Al2O3/R134a nanorefrigerant based modified thermosyphon performance using random forest algorithm

Performance of Al2O3/R134a nanorefrigerant based modified thermosyphon predicted by random forest algorithm is presented in this paper. Three types of thermosyphon namely conventional, thermosyphon with internal fin and thermosyphon with internal fin and internal cut were used in the study. The input parameters to the random forest algorithm are heat input, surface area, cooling water temperatures and the working fluid; while the output are in terms of truepositive rate, false positive rate, positive predictive value and accuracy. The results of the analysis indicate that accuracy of 95% has been obtained with regard to the experimental studies carried out. The predicted output is observed to be in good agreement with the experimental results. The temperature obtained at each section of the thermosyphon provides the true positive rate greater than 96% with less fault occurrence using random forest algorithmic approach.

Numerical and experimental analysis of effect of working fluid amount on the thermal performance of thermo-syphon system

The thermal performance enhancement of a thermo-syphon system has been studied by many researchers. However, according to the best knowledge of the authors, the impact of the amount of the working fluid on the performance of thermo-syphon has not hitherto been studied. In the present work the impact of inserting a closed tube inside the riser pipe and effect of increase and decrease the amount of the working fluid on the thermal performance have been investigated. Several cases have been considered and tested. To ensure the validity of the theoretical results, an experimental work has been conducted and results compared with numerical results. The results show good match between numerical and experimental results. In particular, the maximum difference between experimental and numerical results is found 14.52% and 11.23% for water temperature inside tank and working fluid at outlet of the riser pipe respectively. As well as, the numerical results have been demonstrated that the amount of the working fluid within the thermos-syphon loop has a noticeable impact on the thermal performance of the regarding system. Furthermore, it is found that the (case-A-) is the best case among all cases under consideration regarding system the thermal performance of thermos-syphon. Moreover, a correlation equation to predict water temperature within the storage tank has been established. The accuracy of this equation around 95.6%.

EXPERIMENTAL INVESTIGATION OF AN ALUMINIUM THERMOSYPHON AT NORMAL OPERATING CONDITIONS

The paper presents experimental investigation of an aluminium thermosyphon charged with acetone as working fluid. The effect of filling ratio on steady state performance of thermosyphon is experimentally investigated. Experimentation is performed at three different ratios namely 30 %, 60 % and 100 %. The effect of heat input and mass flow rate of water is also investigated. The heat input is varied between 50 to 300 W and mass flow rate is maintained in the range 30 lph to 60 lph. A condenser section of thermosyphon is surrounded by two pass aluminium cooling block for effective condensation. The cooling block is design in such a way that water will absorbs maximum heat from working fluid in condenser section. The temperature at outer surface of thermosyphon is recorded with the help of temperature sensors. The temperature distribution at outer surface of evaporator and condenser observed to be almost uniform for all mass flow rates and filling ratios. The heat transfer limitations are not encountered for any of thermosyphon. The filling ratio has significant effect on outer surface temperature of evaporator. The surface temperature of evaporator increases by 20 % with increasing the filling ratio at 150 W heat input and 30 lph mass flow rate. The results also indicate that mass flow of cooling water has significant effect on total thermal resistance of thermosyphon at lower input. For 50 W heat input, minimum thermal resistance is recorded as 0.269 °C/W at 60 % filling ratio and 50 lph mass flow rate. While for a same heat input, maximum thermal resistance is recorded as 1.077 °C/W at 100 % filling ratio and 60 lph mass flow rate.

Fabrication and thermal performance of a novel roll-bond flat thermosyphon

In this work, a novel wickless heat pipe fabricated using the roll-bond process and called the roll-bond flat thermosyphon was proposed for electronic component cooling due to its slim and large-size configuration, low-cost, and mass-production capable. The thermal performance of roll-bond flat thermosyphon was investigated through the tests in terms of 3 typical structures (stagger, cross and align) and 4 filling ratios (5%, 10%, 20%, and 40%) under the increasing heat power, and evaluated with the effective thermal conductivity and the maximum heat transfer capacity. The phenomena of boiling regime evolution, geyser effect, liquid entrainment and dry-out, can be found through the temperature responses in the cases of progressive filling ratios and heating powers. The cross-structured sample was found to behave the worst among the three structures due to its blocked up-flowing inflated circuits. The highest effectivity thermal conductivity of 22404 (W/K·m) was found in the 5%-align sample, however, accompanied with early dry-out. The heat transfer capability is positive correlated to the filling ratio, and maximum heat transfer capacity of 100 W (heat flux of 14.9 (kW/m2)) was recorded in the stagger-40% sample. The 20%-stagger sample is recommended as the optimum design, due to its more stable and relative high thermal conductivity, which is peaked to 16019 (W/K·m), and averaged at 12616 (W/K·m) in the range of 0–90 W.

A review of experimental studies on cylindrical two-phase closed thermosyphon using refrigerant for low-temperature applications

Abstract A comprehensive review of cylindrical two-phase closed thermosyphon for low-temperature applications is presented in this paper. The review of literature based on the experimental studies of two-phase closed thermosyphon is categorized according to the utilization of refrigerants, nanofluids, external parameters, surface coating and modifications in the design of two-phase closed thermosyphon to provide a useful reference to the researchers in the field of cylindrical two-phase closed thermosyphon. The effect of geometrical parameters, power input, working fluid, inclination angle and fill ratio on the performance of thermosyphon has been studied thoroughly. The outcome of this review paper would help the research community to enhance the thermal efficiency of cylindrical two-phase closed thermosyphon. It would emphasize the need for utilization of environment-friendly refrigerants in two-phase closed thermosyphon, powered by a solar photovoltaic system, as these two would not affect the environment.

Experimental investigation of the characteristics of thermosyphon with flat evaporator and micro-pillar arrays

This study experimentally investigated the cascaded start-up performance of thermosyphon with a flat evaporating surface combined with different sizes of micro-pillars. The thermosyphon was composed of a condenser section and an evaporator section. Different sizes of micro-pillar were processed on the surface of the evaporator bottom plate to enhance the heat transfer. A smooth flat surface was used as the standard reference for comparison with the micro-pillar surfaces. Deionized water was used as the working fluid to cool the condenser section of the thermosyphon. The operating pressure of thermosyphon was measured using a pressure sensor. Additionally, the evaporator section wall temperature and the temperature and flow rate of the cooling water were measured at nine different heat fluxes. The start-up performances of the thermosyphon with a smooth evaporator bottom plate (THSE) and thermosyphon with a micro-pillar in the evaporator bottom plate (THMPE) were compared. The THSE had a longer start-up time and a higher start-up temperature than the THMPE. When the heat flux was 68.6 W/cm2, the start-up time of the THMPE with a micro-pillar width of 0.2 mm and a height of 0.8 mm was reduced by 57.1% compared to THSE, and the start-up temperature was reduced by 28%. Thermosyphons with different micro-pillar widths showed various start-up performances for different heat fluxes. For a narrow micro-pillar width, THMPEs with larger micro-pillar heights had a lower start-up temperature and a shorter start-up time. As the micro-pillar width increased, the micro-pillar height had a different and more complex effect on the start-up performance of the thermosyphon. When the micro-pillar heights were 0.2 mm and 0.4 mm, the thermosyphon with wider micro-pillars had a longer start-up time with a lower heat flux but a shorter start-up time with a higher heat flux. When the micro-pillar heights were 0.6 mm and 0.8 mm, varying the micro-pillar width had a smaller influence on the start-up performance of the thermosyphon, but was dependent on the heat flux.

Charging procedures: effects on high temperature sodium thermosyphon performance

In this work, the influence of the charging procedures on the performance of two-phase thermosyphons operating with sodium as working fluid is studied experimentally. Solid charging and liquid charging, both in controlled and uncontrolled environments, with a non-condensable gases purge process after the thermosyphon closing were the methods employed. A charging apparatus for liquid sodium was designed and constructed, taking into consideration the operator safety, industrial applicability, cost of implementation, minimization of sodium contamination and, most importantly, the thermosyphon performance. Before charging, all thermosyphons experimentally studied were subjected to standard fabrication processes: cleaning, preparation, leak checking, tube vacuuming, sodium handling and case closure. The results show that the thermosyphon charged with sodium in liquid state under controlled environment and with non-condensable gases purging after closing presented the best performance among all. Therefore, the developed charging apparatus, in spite of its low cost of implementation, showed to be adequate for the manufacturing of sodium thermosyphons, as the sodium handling is quite safe and the resulting devices present excellent performance.

Thermal Performance of Loop Thermosyphon Charged by Nanofluid for Cooling Electronic Component

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Effect of working fluid inventory and heat input on transient and steady state behavior of a thermosyphon

The effect of working fluid inventory and heat input on the performance of thermosyphon is investigated in this paper. First, a thermosyphon with diameter of 16 mm made of steel with toluene as working fluid and the length of the evaporator, adiabatic and condenser section 10, 23 and 17 cm was considered, respectively. The working fluid inventory was considered 0.1, 0.14, 0.18 and 0.24 of total volume of thermosyphon and in each case 54–235 W of heat input applied to the evaporator area also. In order to evaluate the transient behavior of the thermosyphon, in any amount of working fluid, 28 W of heat input was considered and temperature of the evaporator area were recorded at different times. The results showed that in startup, in the values of the working fluid equal to 0.14, 0.18 and 0.24, the evaporator temperature has fluctuated behavior that is indicative of the occurrence of geyser boiling phenomenon. When the volume of the working fluid was more than 0.24, thermosyphon performance was associated with vibration, indicating a high fluidity and a lack of proper functioning of the thermosyphon. The amount of optimal working fluid with respect to the total thermal resistance of thermosyphon is equal to 0.18 that in this case, the efficiency of thermosyphon at different levels of heat input is between 73 and 78%. In addition, in any amount of working fluid, increase of heat input leads to increment in the evaporator and condenser heat transfer coefficient increases and reduction in the total thermal resistance of thermosyphon.

Experimental studies on thermosyphon using low global warming potential refrigerant HFE7000 and nanorefrigerant HFE7000/Al2O3

Thermosyphon is used in numerous applications such as permafrost, cooling building and structures, Alaska pipeline, electronic cooling, and other applications. Improving the performance of thermosyphon is essential for technology advancement. Therefore, experimentation is conducted to improve the efficiency of thermosyphon with the natural refrigerant hydrofluoroether (HFE) and Al2O3/HFE7000 nanorefrigerant. The Al2O3 nanoparticle is chosen based on its economic feasibility and better thermo-physical properties with the refrigerants. Firstly, the preparation of Al2O3/HFE7000 nanorefrigerant is carried out specifically at different volume concentrations of the nanoparticle to check the long-term stability. Secondly, the heat transfer characteristics of the thermosyphon charged Al2O3/HFE7000 nanorefrigerant of 0.025%, 0.05%, and 0.075% volume concentration and pure HFE7000 is investigated experimentally. The nanorefrigerant charged thermosyphon experimented for different inclinations and different volume concentrations as the working fluid. It was observed that the two-phase closed thermosyphon charged with Al2O3/HFE7000 nanorefrigerant enhanced its evaporator heat transfer performance also decreased the thermal resistance of 57.5% compared with the pure HFE7000 and was at its peak for 0.05% volume concentration. The heat transfer of nanorefrigerant Al2O3/HFE7000 0.025%, 0.05%, and 0.075% volume concentration is increases 41.61%, 88.414%, and 74.362% than HFE7000. In conclusion, the results of the experiments suggest that the use of Al2O3/HFE7000 nanofluid produce a significant thermal enhancement in thermosyphon. This research also discloses the effect of dimensionless parameters such as the Bond number of the boiling phenomenon, Prandtl and condensation number of conduction phenomenon, and Ohensorge number of buoyancy phenomenon in thermosyphon with Al2O3/HFE7000 nanorefrigerant. It is identified that the volume concentration of 0.05% Al2O3/HFE7000 has a considerable effect on nondimensional parameters.

Heat and mass transfer for a small diameter thermosyphon with low fill ratio

Abstract Thermosyphons of smaller dimensions are more commonly sought after as electronics cooling devices. The interactions of the tube wall and working fluid become more significant as the dimension of a thermosyphon is reduced, particularly for high surface tension fluids such as water. This paper aims to experimentally investigate a water-charged, small diameter (8 mm) thermosyphon as it operates with a low (25%) filling ratio for a relatively long evaporator length of 200 mm. High speed videography provides in-situ flow pattern visualization at different heat input power. The boiling regimes for each level of heat flux are determined by analyzing the flow patterns from the high-speed video footage. The interdependence of the flow regimes and the heat and mass transfer mechanisms is evaluated using the measured wall temperature variations and derived thermosyphon performance metrics, such as the average heat transfer coefficients and thermal resistances. It was observed that the heat and mass transport was dominated by Geyser-type boiling at lower heat fluxes with associated low heat transfer coefficients in the evaporator and condenser. With increasing thermal power, less liquid was observed to return to the evaporator resulting in more aggressive boiling events which improved the heat transfer coefficients in both the evaporator and condenser. For all power levels tested, the dominant thermal resistance was found to be that associated with the condenser. The ultimate failure of the thermosyphon was a result of liquid hold-up in the condenser section and subsequent falling liquid film and evaporator dryout.

Thermal performance of thermosyphon with flat evaporating surface combined with different sizes of micro pillars

In this paper, the thermal performance of thermosyphon with a flat evaporating surface combined with different sizes of micro pillars was investigated by experimental method. Micro pillars with different sizes were fabricated on the surface of the evaporator bottom plate to enhance heat exchange. An experimental platform was designed and constructed to test the heat transfer performance of the thermosyphon. Deionized water was chosen as the working fluid and the condenser section of the thermosyphon was cooled using water cooling. The operating pressure of the thermosyphon was measured by a pressure sensor to obtain the corresponding saturated temperature. The wall temperature of the evaporator section, the operating pressure of the thermosyphon, as well as the temperature and flow rate of the cooling water were detected for different heat flux. The evaporator section wall temperature (ESWT) and evaporator section wall superheat (ESWS) of the thermosyphon with a smooth evaporator bottom plate (THSE) or micro pillars on the evaporator bottom plate(THMPE)were comparatively studied. ESWT and ESWS of the thermosyphon with micro pillars were much lower than those of THSE. Generally, when the micro-pillar width was constant, heat transfer was intensified with increasing micro-pillar height. When the micro-pillar width was 200 μm, ESWT of the thermosyphon with a micro-pillar height of 200 μm was 12.1 °C higher than that of thermosyphon with a micro-pillar height of 800 μm at a heat flux of 68.6 W/cm2. When the micro-pillar heights were 200 μm and 400 μm, the variations of micro-pillar width evidently reduced ESWT. However, when the micro-pillar height was 600 μm and 800 μm, the variations of micro-pillar width barely affected ESWT due to the capillarity and disturbance of bubbles motion caused by micro-pillar changes. At a smaller micro-pillar width, the thermosyphon with higher micro pillars had lower ESWS. When the heights of micro pillars were 200 μm and 400 μm, the increase of micro-pillar width was conducive to reducing ESWS. When the heights of micro pillars were 600 μm and 800 μm, a smaller micro-pillar width better reduced ESWS of the thermosyphon.

Experimental investigation of a novel type of two-phase closed thermosyphon filled with functionalized carbon nanotubes/water nanofluids for electronic cooling application

Two-phase closed thermosyphon as a gravity-assisted heat pipe is an efficient heat transfer device in which heat transmits by evaporation and condensation of a working fluid. Nanofluids are suspensions of nano-sized solid particles in a base fluid which can be used as heat transfer media in the thermosyphon. In the present study, thermal performance of functionalized multi-walled carbon nanotubes/water nanofluids was investigated in a novel type of thermosyphon which was made of an evaporator with square frustum shape, and a condenser composed of two connected tubes. To prepare nanofluids, multi-walled carbon nanotubes were first functionalized using two oxidant agents (potassium persulfate and sodium persulfate) to improve the cooling performance of nanofluids. The prepared nanofluids were characterized by Fourier transform infrared spectroscopy, inductively coupled plasma optical emission spectroscopy, zeta potential, and thermal conductivity analyzer. The results of characterization showed that the nanofluid with sodium functional group had higher stability as well as higher thermal conductivity. Thermal efficiency and thermal resistance were calculated to evaluate the thermal performance of thermosyphon. Using nanofluid with sodium functional group in the thermosyphon showed better performance in terms of higher thermal efficiency and lower thermal resistance. Experimental results also showed that the thermosyphon could perform at higher input powers (up to 90 W) using the nanofluid compared to water (up to 70 W). Furthermore, the results of the temperature distribution of thermosyphon during the test confirmed that two connected tubes in the condenser section could provide pathways for both condensate liquid and vapor. In other words, this behavior indicated that this type of thermosyphon can be considered between a tubular thermosyphon and a loop thermosyphon.

Examining the Impact of Different Thermosyphon Diameters and Working Fluids on Their Performance

This work was designed to examine the effect of various thermosyphon diameters and working fluids on the thermosyphon performance. A thermosyphon made from copper tubes with three different external diameters 7, 13 and 22mm with thickness of 1mm is used in this work. The length of evaporator and condenser were 120 and 300 mm respectively. Working fluids were water, acetone and Freon R11 working fluids are tested. The obtained results have shown that the temperature gradient was decreased when increasing the thermosyphon diameter. Also, the results showed that the Merit for water had the highest value than the other working fluid at the operating range of temperature. The results were shown the heat dissipation by the thermosyphon increased when increasing the thermosyphon diameter for all working fluids. Also the heat dissipation from the thermosyphon with working fluid of water had a highest value of heat dissipation than the others working fluids. The percentage decreased in the temperature gradient by using thermosyphon with diameter of 22mm for water, acetone and Freon R11 were 73.53 %, 68,53 % and 52.35 % respectively compared with that without using thermosyphon.

Experimental study on visualization of U-shaped array thermosyphon

U-shaped array thermosyphon has no capillary core structure, which can be used for power battery thermal management. In this paper, we performed a visualization experiment about U-shaped array thermosyphon. Its fluid flow and heat transfer mechanism and the influencing factors are studied. With input of heat power, the thermosyphon underwent stages of cold start-up, heat energy storage, transition and circulation flow stage. Before the start-up of the thermosyphon, there would be three kinds of vapor-liquid states of the working fluid, namely vapor tube, liquid tube and vapor plug liquid slug tube. After the start-up, the corresponding change were slug flow, annular flow or liquid cylinder oscillation. Slug flow and annular flow relative to liquid cylinder oscillation can enhance heat transfer. The main factors affecting the performance of the U-shaped array thermosyphon are the filling rate and working fluid. The liquid filling rate affects the stage of the working fluid at the stationary state and the flow pattern at the circulation flow state. Taking the temperature difference of start-up and the stability of circulation flow as the evaluation criterion, the performance of the thermosyphon of R134a is better than that of R113.

Mathematical model of a thermosyphon integrated storage solar collector

Abstract Thermosyphon solar collectors are popular in warm climates since their initial and operating costs are lower compared to forced-circulation units. Recently new types of thermosyphon collector with integrated storage, without any external tank, to meet law requirements about solar applications in restricted areas (e.g. old town of particular architectural significance) are put in the market. Such a collector is modelled in this paper using the software MATLAB Simulink. This model is able to describe the transient behavior of the natural circulation phenomenon and it requires a much lower computational effort compared to CFD codes. The present mathematical model has been validated using ad-hoc experimental tests and numerical simulations. The validated model has been run varying the tilt angle, the geometry and the working conditions to analyze the solar thermosyphon performance. It can predict the minimum inclination and solar radiation that is needed to promote the flow circulation.

Effect of nano-structure coating on thermal performance of thermosyphon boiling in micro-channels

A novel micro-channel thermosyphon technology for passively cooling 3D stacked chips was provided, and the thermosyphon boiling characteristics in vertical and inclined micro-channels with two open ends which simulate the specific stacked structure of actual 3D chip were experimentally carried out. In order to improve the heat transfer of micro-channel thermosyphon by surface treatment technology, four kinds of nanoparticles (CuO, Cu, Al2O3, SiO) were added to the base fluid to make nano-structure coatings on the heater surfaces by using a long time pool boiling treatment. Then, micro-channel thermosyphon boiling experiments were carried out with four kinds of working liquids: two kinds of pure fluids (deionized water and R113) and two kinds of moist fluids (deionized water+surfactant and R113+surfactant). The gaps and heights of micro-channels tested were in the range of 30–60 μm and 30–90 mm, respectively. Experimental results show that nano-structure coatings can significantly enhance both the maximum heat flux and heat transfer coefficient of thermosyphon boiling in micro-channels, and exist both the optimal nanoparticle kind and nanoparticle concentration in the base fluids. The experimental results provided some meaningful technology support for 3D stacked chip cooling.

Investigation of two-phase thermosyphon performance filled with modern HFC refrigerants

Two-phase closed thermosyphons (TPCTs) are widely utilized as heat exchanger elements in waste heat recovery systems and as passive heating/cooling devices. They are popular because of their high thermal conductivity, simple construction and reliability. Previous researches indicate that refrigerants are performing better than typical TPCT working fluids like deionized water or alcohols in the low temperature range. In the present study three HFC (Hydrofluorocarbons) refrigerants were tested: R134a, R404A and R407C. The total length of the investigated TPCT is 550 mm with equal length (245 mm) condenser and evaporator sections. Its outer diameter is 22 mm with 1 mm wall thickness. The evaporator section was heated by hot water with varying inlet temperature by 5 K step in the range of 288 K – 323 K. The condenser was cooled by cold water with inlet temperature kept at a constant value of 283 K. It was found that using R134a and R404A as working fluids heat transfer rates are the highest. For both refrigerants 10% is optimal filling ratio. They can be utilized interchangeably because the differences between their throughputs are within uncertainty bands. R407C performance was 50% lower. Other disadvantages of using this refrigerant are relatively high working pressures and higher optimal filling ratio (30%).

Thermal Performance of a Vertical U-Shaped Thermosyphon Containing a Phase-Change Material Suspension Fluid

This study investigated the thermal performance of a vertical U-shaped thermosyphon containing a phase-change material (PCM) suspension fluid via experimentation. The heating and cooling sections were located at the top and bottom of the loop, respectively. The lengths of the heating and cooling sections each accounted for one fifth of the height of the loop. Pure water and a PCM (octadecane) suspension fluid were used to fill the loop to compare the thermal performance of the thermosyphon under different heating power, cooling temperature, and PCM suspension concentration conditions. The results showed that, when the PCM suspension concentration was higher than a critical value, the addition of the PCM suspension had no positive effect on reducing the highest temperature of the fluid in the loop but instead resulted in an increase in fluid temperature. More detailed experiments are needed to observe the phenomena and decide critical values under different experimental parameters.

Efficiency enhancement of a loop thermosyphon on a mixed-wettability evaporator surface

This study presents an experimental investigation of the heat transfer performance of a two-phase loop thermosyphon with an enhanced mixed-wettability evaporator surface at sub-atmospheric pressures. For central-processing-unit (CPU) cooling applications, a lowering of the saturation temperature (pressure) is essential when water is used as the working fluid. Compared with copper mirror surfaces, up to over 100% enhancement of high heat transfer coefficient (HTC) was observed using surfaces with spotted wettability patterns, which consists of hydrophobic spots with contact angle ranged from 145° to 150°. The results revealed that the boiling behaviors changed drastically with the application of hydrophobic spots coating by artificially increasing the nucleation site density. Parametric tests with a variety of operating conditions, including different filling ratios, condenser temperatures, and heat loads revealed the minimum thermal resistance (i.e., the optimum thermosyphon performance) to be 0.03K/W on the boiling side.