scholarly journals Heat Transfer Enhancement of Small-Diameter Two-Phase Closed Thermosyphon Using Cellulose Nanofiber and Hydrophilic Surface Modification

Nanomaterials ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 647
Author(s):  
Dongnyeok Choi ◽  
Gyosik Jun ◽  
Woonbong Hwang ◽  
Kwon-Yeong Lee
Keyword(s):  
Surface Modification ◽  
Thermal Resistance ◽  
Natural Circulation ◽  
Small Diameter ◽  
Cellulose Nanofiber ◽  
Working Fluid ◽  
Hydrophilic Surface ◽  
Two Phase ◽  
Total Thermal Resistance ◽  
Internal Working

In this study, we observed the Geyser phenomenon that occurs in a small-diameter two-phase closed thermosyphon (confinement number of 0.245). This phenomenon interferes with the natural circulation of the internal working fluid and increases the thermal resistance of the system. This study attempts to improve the thermal performance of the system using cellulose nanofiber as the working fluid and hydrophilic surface modification at the inner surface of the evaporator section. As a result, the total thermal resistance showed average reduction rates of 47.51%, 36.69%, and 22.56% at filling ratios of 0.25, 0.5, and 0.75, respectively.

Numerical Investigation of Regular and Hybrid Nanofluids Application as the Working Fluids on Thermal Performance of TPCT

2019 ◽  
Vol 11 (4) ◽  
Author(s):  
Roozbeh Vadi ◽  
Kamran Sepanloo
Keyword(s):  
Numerical Simulation ◽  
Thermal Resistance ◽  
Natural Circulation ◽  
Industrial Applications ◽  
Input Power ◽  
Working Fluid ◽  
Hybrid Nanofluid ◽  
Distilled Water ◽  
Two Phase ◽  
Working Fluids

Two-phase closed thermosyphon (TPCT) is a cost-effective heat transfer device with high thermal efficiency owing to extensive interphase heat and mass transfer. Thus, TPCT has found many industrial applications. Proper selection of the working fluid could further improve efficiency of TPCT, and nanofluids with superior thermal properties are suitable choices. Numerical simulation of boiling and condensation, natural circulation, and hybrid nanofluid modeling in a closed space is a notable challenge and current study is devoted to this subject. In this study, a novel methodology for incorporating the effects of compressibility and thermal expansion into all thermophysical properties of both phases is developed and programmed into a validated computational fluid dynamics (CFD) code. Distilled water, a regular nanofluid, Al2O3/water, and a hybrid nanofluid, TiSiO4/water are selected as the working fluids. Experimental data for wall thermal profile are employed to validate the numerical simulation. Then, overall thermal resistance is evaluated in terms of nanoparticles concentration and input power variations. Results indicate that the numerical methodology developed in this study could evaluate the optimum state of TPCT in an efficient and accurate manner and the optimum state for regular and hybrid nanofluid demonstrates 48% and 54% improvement over distilled water, respectively. Furthermore, a subtle relation between the thermal resistance and the height to which fluid column rises in TPCT has been discerned and quantified, which is used as a supplement to the conventional qualitative method of reasoning to justify the somewhat controversial behaviors of nanofluid application in TPCT.

A Comprehensive Experimental Investigation of the Performance of Closed-Loop Pulsating Heat Pipes

2017 ◽  
Vol 139 (9) ◽  
Author(s):  
M. Halimi ◽  
A. Abbas Nejad ◽  
M. Norouzi
Keyword(s):  
Thermal Resistance ◽  
Flow Regime ◽  
Thermal Performance ◽  
Closed Loop ◽  
Heat Pipes ◽  
Filling Ratio ◽  
Working Fluid ◽  
Physical Parameters ◽  
Two Phase ◽  
Laboratory Conditions

Closed-loop pulsating heat pipes (CLPHPs) are a new type of two-phase heat transfer devices that can transfer considerable heat in a small space via two-phase vapor and liquid pulsating flow and work with various types of two-phase instabilities so the operating mechanism of CLPHP is not well understood. In this work, two CLPHPs, made of Pyrex, were manufactured to observe and investigate the flow regime that occurs during the operation of CLPHP and thermal performance of the device under different laboratory conditions. In general, various working fluids were used in filling ratios of 40%, 50%, and 60% in horizontal and vertical modes to investigate the effect of thermo-physical parameters, filling ratio, nanoparticles, gravity, CLPHP structure, and input heat flux on the thermal performance of CLPHP. The results indicate that three types of flow regime may be observed given laboratory conditions. Each flow regime exerts a different effect on the thermal performance of the device. There is an optimal filling ratio for each working fluid. The increased number of turns in CLPHP generally improves the thermal performance of the system reducing the effect of the type of the working fluid on the aforementioned performance. The adoption of copper nanoparticles, which positively affect fluid motion, decreases the thermal resistance of the system as much as 6.06–42.76% depending on laboratory conditions. Moreover, gravity brings about positive changes in the flow regime decreasing thermal resistance as much as 32.13–52.58%.

scholarly journals Thermal Resistance and Pressure Drop Minimization for a Micro-gap Heat Sink with Internal Micro-fins by Parametric Optimization of Operating Conditions

CFD Letters ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 100-112
Author(s):  
Shugata Ahmed ◽  
Erwin Sulaeman ◽  
Ahmad Faris Ismail ◽  
Muhammad Hasibul Hasan ◽  
Zahir Hanouf
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Thermal Resistance ◽  
Void Fraction ◽  
Heat Sink ◽  
Operating Conditions ◽  
Superior Performance ◽  
Pumping Power ◽  
Two Phase ◽  
Total Thermal Resistance

In recent years, researchers are investigating several potential applications of two-phase flow in micro-gap heat sinks; electronic cooling is one of them. Further, internal micro-fins are used to enhance the heat transfer rate. However, the pressure drop penalty due to small gap height and fin surfaces is a major concern. Hence, minimization of thermal resistance and pressure drop is required. In this paper, effects of operating conditions, e.g., wall heat flux, pumping power, and inlet void fraction, on total thermal resistance and pressure drop in a micro-gap heat sink with internal micro-fins of rectangular and triangular profiles have been investigated by numerical analysis for the R-134a coolant. Furthermore, optimization of these parameters has been carried out by response surface methodology. Simulation results show that rectangular micro-fins show superior performance compared to triangular fins in reducing thermal resistance. Finally, for an optimum condition (7.1202×10-5 W pumping power, 1.2×107 Wm-2 heat flux, and 0.03 inlet void fraction), thermal resistance and pressure drop are reduced by 56.3% and 87.2%, respectively.

Experimental Characterization of Two-Phase Cooling of Power Electronics in Thermosiphon and Forced Convection Modes

2021 ◽  
Vol 143 (3) ◽  
Author(s):  
Fabio Battaglia ◽  
Farah Singer ◽  
David C. Deisenroth ◽  
Michael M. Ohadi
Keyword(s):  
Heat Flux ◽  
Thermal Resistance ◽  
Power Electronics ◽  
Forced Convection ◽  
Heat Removal ◽  
High Heat ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Two Phase ◽  
Total Thermal Resistance

Abstract In this paper, we present the results of an experimental study involving low thermal resistance cooling of high heat flux power electronics in a forced convection mode, as well as in a thermosiphon (buoyancy-driven) mode. The force-fed manifold microchannel cooling concept was utilized to substantially improve the cooling performance. In our design, the heat sink was integrated with the simulated heat source, through a single solder layer and substrate, thus reducing the total thermal resistance. The system was characterized and tested experimentally in two different configurations: the passive (buoyancy-driven) loop and the forced convection loop. Parametric studies were conducted to examine the role of different controlling parameters. It was demonstrated that the thermosiphon loop can handle heat fluxes in excess of 200 W/cm2 with a cooling thermal resistance of 0.225 (K cm2)/W for the novel cooling concept and moderate fluctuations in temperature. In the forced convection mode, a more uniform temperature distribution was achieved, while the heat removal performance was also substantially enhanced, with a corresponding heat flux capacity of up to 500 W/cm2 and a thermal resistance of 0.125 (K cm2)/W. A detailed characterization leading to these significant results, a comparison between the performance between the two configurations, and a flow visualization in both configurations are discussed in this paper.

Thermal Characteristics of a Circular Finned Thermosyphon Using Different Working Fluids

2014 ◽  
Vol 575 ◽  
pp. 322-328 ◽  
Author(s):  
Narayanan Alagappan ◽  
Narayanan Karunakaran
Keyword(s):  
Experimental Study ◽  
Ethylene Glycol ◽  
Thermal Resistance ◽  
Thermal Performance ◽  
Heat Input ◽  
Base Fluid ◽  
Thermal Characteristics ◽  
Working Fluid ◽  
Two Phase ◽  
Evaporation And Condensation

The two-phase closed thermosyphon (TPCT), which is essentially a gravity-assisted wickless heat pipe, utilizes the evaporation and condensation of the working fluid inside the TPCT to transport heat. This experimental study was carried out to understand the thermal performance of circular finned thermosyphon using nanofluid with alcohol and was analyzed, compared with alcohol and base fluid DI water. The concentration of nanoparticle used in this setup was 110mg/lit of TiO2combined with 0.2 ml of ethylene glycol. The heat input (Q) were 10W, 12W, 14 W and 16 W and the orientation 30°, 45°, 60° and 90°.The results demonstrate that TiO2nanofluid with 0.2 ml of ethylene glycol improves the performance through reduction in thermal resistance by 85.86%.

scholarly journals Experimental study on heat transfer characteristics of a modified two-phase closed thermosyphon

2017 ◽  
Vol 21 (6 Part A) ◽  
pp. 2481-2489 ◽  
Author(s):  
Babak Aghel ◽  
Masoud Rahimi ◽  
Saeed Almasi
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Experimental Study ◽  
Thermal Resistance ◽  
Thermal Performance ◽  
Working Fluid ◽  
Heat Transfer Characteristics ◽  
Two Phase ◽  
Transfer Characteristics ◽  
Adiabatic Section

This study investigated the heat transfer characteristics of modified two-phase closed thermosyphon (TPCT) using water as the working fluid. In the modified TPCT, to reduce thermal resistance, a small TPCT was inserted inside the adiabatic section. For both the plain and modified thermosyphons the performances were determined at various heat inputs from 71-960 W. The results showed that the modified TPCT had less temperature difference between the evaporator and condenser sections than the plain one. According to the experimental data, in the modified TPCT, the thermal performance increased up to 20% over that of the unmodified one.

An Experimental Study of Closed Loop Two-Phase Thermosyphon for Spent Fuel Pool Passive Cooling

2016 ◽  
Author(s):  
Minglu Wang ◽  
Mingguang Zheng ◽  
Cheng Ye ◽  
Zhongming Qiu ◽  
Zhenqin Xiong
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Heat Transfer Coefficient ◽  
Thermal Resistance ◽  
Transfer Coefficient ◽  
Closed Loop ◽  
Working Fluid ◽  
Spent Fuel ◽  
Two Phase ◽  
Spent Fuel Pool

The study reported here examined a closed loop two-phase thermosyphon (CLTPT) of evaporator length 7.6m and internal diameter 65mm used to cool the spent fuel pool. This experimental study investigates the thermal performances and heat and mass transfer characteristic of CLTPT by examining the thermodynamic cycles and overall thermal resistances with ammonia, R134a and water as the working fluid. Measurements of temperature and pressure distributions of the fluid around the loop were made under various conditions. Results show that this loop operates with low filling ratio, low mass flow rate, and high heat-transfer coefficient and the CLTPT has the ability to cool the spent fuel pool. The working fluid flowing through the heat pipe evaporator section generally experienced a subcooled zone, pool boiling zone and high gas quality two-phase region. The average heat transfer coefficient of evaporator reaches 450 W/m2•°C using R134a as working fluid. The thermal resistance of R134a is always smaller than ammonia but the thermal resistance of water is largest at small temperature difference while is smallest when temperature difference is large.

Research on Thermal Resistance of Micro Heat Pipe with Sintered Wick

2013 ◽  
Vol 589-590 ◽  
pp. 552-558
Author(s):  
Xi Bing Li ◽  
Xun Wang ◽  
Yun Shi Ma ◽  
Zhong Liang Cao
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Heat Pipe ◽  
Heat Transfer Performance ◽  
High Heat ◽  
Working Fluid ◽  
Transfer Performance ◽  
Total Thermal Resistance ◽  
Vapor Cavity ◽  
Micro Heat Pipe

As a highly efficient heat dissipation unit, a micro heat pipe is widely used in high heat flux microelectronic chips, and its thermal resistance is crucial to heat transfer capacity. Through analyses of the structure and heat transfer performance of a circular heat pipe with sintered wick, the theoretical model of total thermal resistance was established on heat transfer theory, and then simplified, finally a testing platform was set up to test for total thermal resistance performance. The testing results show that when the micro heat pipe is in optimal heat transfer state, its total thermal resistance conform well with that from the theoretical model, and its actual thermal resistance is much lower than that of the rod made of the material with perfect thermal conductivity and of the same geometric size. With the increment of heat transfer capability, the total thermal resistance of a micro heat pipe with sintered wick decreases first, then increases and reaches the minimum when it is in the optimal heat transfer state. The greater total thermal resistance in low heat transfer performance is mainly caused by too much working fluid accumulating in evaporator and the lower velocity in vapor cavity, and the greater total thermal resistance in high heat transfer performance is mainly due to the working fluid drying up in condenser. Total thermal resistance is related to many factors, such as thermal conductivity of tube-shell material, wall thickness, wick thickness, copper powders grain size and porosity, the lengths of condenser and evaporator, and the diameter of vapor cavity etc.. Therefore, the structure parameters of a micro heat pipe with sintered wick should be reasonably designed according to the specific conditions to ensure its heat transfer capacity and total thermal resistance to meet the requirements.

Modeling and Testing a Cold Plate

2006 ◽  
Author(s):  
Bryan R. Wilcox ◽  
Donald W. Mueller ◽  
Hosni I. Abu-Mulaweh
Keyword(s):  
Numerical Model ◽  
Thermal Resistance ◽  
Cover Plate ◽  
Maximum Temperature ◽  
Working Fluid ◽  
Water Mixture ◽  
Heat Flow Rate ◽  
Cold Plate ◽  
Maximum Temperature Difference ◽  
Total Thermal Resistance

The objectives of this work were to build and test a liquidcooled cold plate, and then to develop a numerical model to describe the thermal characteristics of the cold plate. An important parameter of interest was the total thermal resistance of the cold plate which is defined as the maximum temperature difference divided by the net heat flow rate. A cold plate was constructed by machining nine parallel, rectangular channels into an aluminum base (1.65 cm × 7.6 cm × 40 cm) upon which an aluminum cover plate was then welded. Twelve thermocouples were used to measure the temperature of the plate (surface and fin tip) and the circulating fluid at the inlet, outlet, and mid-plane. The working fluid was a 50/50 ethylene glycol-water mixture. Three heater blocks were mounted to the cold plate, and the assembly was insulated so that heat loss to the surroundings was minimized. Four runs were performed with flow rates ranging from 56 g/s to 95 g/s, and after steady-state conditions were reached the temperatures were recorded. Using these temperature measurements, the total thermal resistance was calculated. The thermal resistance of the cold plate was also calculated using a one-dimensional numerical model; agreement between the experimental measurements and model predictions is good. The methods described and results presented in this paper are useful to applied thermal engineers.

scholarly journals Integration of a Multiple-Condenser Loop Heat Pipe in a Compact Air-Cooled Heat Sink

2013 ◽  
Author(s):  
H. Arthur Kariya ◽  
Daniel F. Hanks ◽  
Wayne L. Staats ◽  
Nicholas A. Roche ◽  
Martin Cleary ◽  
...  
Keyword(s):  
Thermal Resistance ◽  
Heat Pipe ◽  
Heat Sink ◽  
High Performance ◽  
Ambient Air ◽  
Optimal Operation ◽  
Working Fluid ◽  
Air Cooling ◽  
Loop Heat Pipe ◽  
Total Thermal Resistance

We present the characterization of a compact, high performance air-cooled heat sink with an integrated loop heat pipe. In this configuration, heat enters the heat sink at the evaporator base and is transferred within the heat pipe by the latent heat of vaporization of a working fluid. From the condensers, the heat is transferred to the ambient air by an integrated fan. Multiple condensers are used to increase the surface area available for air-cooling, and to ensure the equal and optimal operation of the individual condensers, an additional wick is incorporated into the condensers. We demonstrated with this design (10.2 cm × 10.2 cm × 9 cm), a total thermal resistance of less than 0.1 °C/W while dissipating a heat load of 500 W from a source at 75 °C. Furthermore, constant thermal resistance was observed in the upright as well as sideways orientations. This prototype is a proof-of-concept demonstration of a high performance and efficient air-cooled heat sink design that can be readily integrated for various electronics packaging and data center applications.

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