Effect of silver nano-fluid on pulsating heat pipe thermal performance
Introduction
New type with high efficiency of the heat dissipation device and pulsating heat pipe has become one of the most serious challenges in many technologies because of constant demands in the industrial world at present.
The benefit of the fluid in the heat transfer occupies a high and important status. So the innovation heat transfer fluid (nano-fluid) is placed in the pulsating heat pipe and analyzed the improvement of the whole efficiency. Heat pipe and the PHP are applied in the phase change to take away the heat. Because of the phase change, it will cause to absorb a large amount of latent heat. So the heat from the heat source can be rapidly excluded from the condenser. The temperature of the heat source will not increase and influence the whole working efficiency.
The heat transfer benefit is according to the transformed latent heat and the phase change theory of the heat pipe in comparison to the forced air cooling is more than 50 times and PHP not only dissipates the latent heat of the vapor phase, but also will take away the sensible heat from the liquid phase. Hence, the pulsating heat pipe can operate at higher heat fluxes than the traditional heat pipes. Nano-fluid is quite a new developing topic in recent years, which put the nano-particle in a liquid. Therefore, we can call as the fluid of suspended nano-particle. Also invest and endure the research that the nano-fluid uses actively in the laboratory. The result shows the performance of using the silver nano-fluid to improve the heat pipe.
In 2004, Tsai et al. [1] found that some of the gold particle solution could be used in the application of heat pipes. At a same charge volume, there is a significant reduction in thermal resistance of heat pipe with nano-fluid as compared with DI water. The measured results also show that the thermal resistance of a vertical meshed heat pipe varies with the size of gold nano-particles.
In 2006, Kang et al. [2] discusses the thermal enhancement of heat pipe performance using silver nano-fluid as the working fluid. The higher thermal performance of nano-fluids indicates nano-fluid potential as a substitute for conventional pure water in grooved heat pipes. This finding survey makes nano-fluid much more attractive as a cooling fluid for devices with high energy density. Ma et al. [3], [4] showed the investigation of pulsating heat pipe charged with diamond nano-fluids can reach a thermal resistance of 0.03 °C/W at a power input of 336 W. They also applied diamond nano-fluid in pulsating heat pipe this experiment shows the working fluid of diamond nano-fluid, making the thermal conduction coefficient increases from 0.5813 W/m K to 1.0032 W/m K.
In 2007, Park and Ma [5] pointed out the oscillating heat pipe charged with nano-fluids has drawn researcher’s attention, due to the heat transfer enhancement of strong oscillating motion of the working fluid and higher effective thermal conductivity of nano-fluid. Chiang et al. [6] applied the nano-fluid that had a nano-diamond concentration of 0.5 wt% in PHP. It was found that the optimum fluid fill ratio depends on the PHP structure, with 50% and 20% being the best values for the 36-port and 26-port PHPs, respectively. Also, the 36-port design was able to dissipate a higher power input of 80 W vs. 60 W for the 26-port case, and keep the heat source temperature under 110 °C.
According to the high thermal conductivity, the advantages of nano-fluids and the pulsating heat pipe have never used the silver nano-fluid as working fluid. Therefore, this present study tries to use the silver nano-fluid water solution in different concentrations, filled ratio and heating power to compare the thermal performance with the pure water.
Section snippets
PHP set-up
The experiments were conducted with closed loop type pulsating heat pipe, serpentine and joined with the same pipe with internal diameter 2.45 mm and external diameter 3 mm. We can consult the experimental apparatus (Fig. 2), the under part is the evaporator and the upper part is the condenser. Heating was supplied for five turns and the interval is about 2 mm, working fluid are pure water and silver nano-fluid. About the tube design, the most important condition of PHP is the production of the
Results and discussion
The PHP depends on the bubble pulsation, and pushes the liquid slug to the condensation which results the heat dissipation, too high filled ratio will make the bubble not easy to drive, showing not good pulsating and the efficiency result. Too low filled ratio is rather easier to make the bubble pulsation and get easier to make it dry out.
Summary and conclusions
The PHP makes use of bubbles to pulse and promote the liquid slug and dispel the heat to the condensation section. In PHP, considerably high filled ratio will hinder the pulsation of the bubble and the efficiency of the heat transfer will not be favorable enough. The low filled ratio will get pulsation of the bubble easily, but it is extremely easy to dry out. So the most proper filled ratio is between 40% and 60%, the results will be enable to explain, maybe in these two filled ratio at high
Acknowledgement
This research work was supported by the National Science Council of Taiwan, Republic of China under Contract No. NSC 95-2221-E-032-040-MY2.
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Effect of structural character of gold nano-particles in nano-fluid on heat pipe thermal performance
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Experimental investigation of silver nano-fluid on heat pipe thermal performance
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An experimental investigation of heat transport capability in a nano-fluid oscillating heat pipe
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