Abstract
Problem statement: The purpose of this research was to determine the effects of aspect ratios and number of meandering turns on performance limit of an inclined closed-loop oscillating heat pipe. Approach: The Closed-Loop Oscillating Heat Pipe (CLOHP) was made of a long copper capillary tube. The geometrical sizes, which were t he variable parameters of this study, were as follows; the internal diameter of 0.66, 1.06 and 2. 03 mm, the evaporator section length of 50, 100 and 150 mm, the adiabatic and condenser section length of each set was equaled to the evaporator length and the numbers of meandering turn of 5, 10 and 15 turns. The experiments were conducted by setting the inclination angles at 0-90° adjusted by 10°, th ere totally were 9 sets and each set was tested wit h R123 as working fluid. The adiabatic temperature was controlled at 50±5°C. The low-voltage and high-current power transformer was used as the heat source and heat transfer rate was obtained by using calorific method at the condenser section. Results: It was found from the experiments that, in case of the CLOHP with 10 turns and the internal di ameter of 2.03 mm, the maximum heat flux increases from 10-35.5 kW m -2 when the aspect ratio decreases from 151.5-49.26 a nd the highest maximum heat flux occurs at inclination angle about 70-90°.Conclusion: The result indicated that the aspect ratio, the ratio of evaporator length by int ernal diameter and number of meandering turns significantly affect the maximum heat flux and incl ination angle.
Highlights
New inventive technologies consist of smaller electronic devices for sustainable well-being
The adiabatic and condenser section length of each set was equaled to the evaporator length in order to eliminate the effect of heat flux transformation
In case of the Closed-Loop Oscillating Heat Pipe (CLOHP) with meandering turns of 5, 10 and 15 turns, evaporator length of 100 mm, internal diameter of 2.03 mm and R123 as working fluid (Fig. 6), it can be seen that, when the inclination angle increases from 090°, the maximum heat flux rather increases from 028.4 kW m−2 for 5 turns, 10-35.5 kW m−2 for 10 turns and 9.3-35.2 kW m−2 for 15 turns respectively
Summary
New inventive technologies consist of smaller electronic devices for sustainable well-being. The working fluid, which is in liquid plug and vapor bubble form, will evaporate, expand and move toward to cooler section. Since the evaporation and collapsing of vapor bubble as mentioned above is the main mechanism by which the working fluid can circulate and continuously transfer the heat in cycle. (Soponpongpipat et al, 2006) It is clearly known that the working fluid is able to form itself into liquid plug alternates with vapor bubble for entire tube if the diameter of the capillary tube used to make the oscillating heat pipe does not exceed the critical diameter in Eq 1. When the CLOHP is supplied with heat, higher evaporation rate of the working fluid and its vapor velocity and pressure can be realized.
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