TY - JOUR
T1 - Experimental studies of surface modified oscillating heat pipes
AU - Leu, Tzong Shyng
AU - Wu, Cheng Han
N1 - Funding Information:
The study was supported by the funding from Ministry of Science and Technology, Taiwan under the contract of MOST 105-2221-E-006-122 and NSC 102-2221-E-006-091-MY3. On behalf of all authors, the corresponding author states that there is no conflict of interest.
Funding Information:
Acknowledgements The study was supported by the funding from Ministry of Science and Technology, Taiwan under the contract of MOST 105-2221-E-006-122 and NSC 102-2221-E-006-091-MY3.
Publisher Copyright:
© 2017, Springer-Verlag Berlin Heidelberg.
PY - 2017/11/1
Y1 - 2017/11/1
N2 - Oscillating heat pipe (OHP) is a two-phase heat transfer device which has the characteristics of simple construction, high heat flux capability and no need of wicking structures for liquid transport. There are many studies in finding the ways how to improve the system performance OHP. In this paper, studies of the effects of contact angle (θc) on the inner wall of OHP system have been conducted first. Glass OHP systems with unmodified (θc = 26.74°), superhydrophobic (θc = 156.2°), superhydrophilic (θc < 10°) and hybrid (superhydrophilic within evaporator region and superhydrophobic within condensation region) surfaces, are studied. The research results indicated that thermal resistance of these four OHP systems can be significantly affected by different surface modification approaches. Although superhydrophobic OHP system can still work, the thermal resistance (Rth) is the highest one of the four OHP systems, Rth = 0.36 °C/W at 200 W. Unmodified pure glass and superhydrophilic OHP systems have similar performance. Thermal resistances are 0.28 and 0.27 °C/W at 200 W respectively. The hybrid OHP achieves the lowest thermal resistance, Rth = 0.23 °C/W at 200 W in this study. The exact mechanism and effects of contact angle on OHP systems are investigated with the help of flow visualization. By comparing the flow visualization results of OHP systems before and after surface modification, one tries to find the mechanism how the surface modified inner wall surface affects the OHP system performance. In additional to the reason that the superhydrophobic dropwise condensation surface inside the hybrid OHP system, hybrid OHP system shows more stable and energetic circulation flow. It is found that instead of stratified flow, vapor slug flows are identified within the evaporator section of the hybrid OHP system that can effectively generate higher pressure force for two phase interfacial flow. This effect is attributed to be the main mechanism for better performance of the hybrid OHP system.
AB - Oscillating heat pipe (OHP) is a two-phase heat transfer device which has the characteristics of simple construction, high heat flux capability and no need of wicking structures for liquid transport. There are many studies in finding the ways how to improve the system performance OHP. In this paper, studies of the effects of contact angle (θc) on the inner wall of OHP system have been conducted first. Glass OHP systems with unmodified (θc = 26.74°), superhydrophobic (θc = 156.2°), superhydrophilic (θc < 10°) and hybrid (superhydrophilic within evaporator region and superhydrophobic within condensation region) surfaces, are studied. The research results indicated that thermal resistance of these four OHP systems can be significantly affected by different surface modification approaches. Although superhydrophobic OHP system can still work, the thermal resistance (Rth) is the highest one of the four OHP systems, Rth = 0.36 °C/W at 200 W. Unmodified pure glass and superhydrophilic OHP systems have similar performance. Thermal resistances are 0.28 and 0.27 °C/W at 200 W respectively. The hybrid OHP achieves the lowest thermal resistance, Rth = 0.23 °C/W at 200 W in this study. The exact mechanism and effects of contact angle on OHP systems are investigated with the help of flow visualization. By comparing the flow visualization results of OHP systems before and after surface modification, one tries to find the mechanism how the surface modified inner wall surface affects the OHP system performance. In additional to the reason that the superhydrophobic dropwise condensation surface inside the hybrid OHP system, hybrid OHP system shows more stable and energetic circulation flow. It is found that instead of stratified flow, vapor slug flows are identified within the evaporator section of the hybrid OHP system that can effectively generate higher pressure force for two phase interfacial flow. This effect is attributed to be the main mechanism for better performance of the hybrid OHP system.
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U2 - 10.1007/s00231-017-2051-2
DO - 10.1007/s00231-017-2051-2
M3 - Article
AN - SCOPUS:85018302316
SN - 0947-7411
VL - 53
SP - 3329
EP - 3340
JO - Heat and Mass Transfer/Waerme- und Stoffuebertragung
JF - Heat and Mass Transfer/Waerme- und Stoffuebertragung
IS - 11
ER -