Influence of Inclination Angle on the Start-up Performance of a Sodium-Potassium Alloy Heat Pipe

ABSTRACT

Alkali metal heat pipes play significant role in various high-temperature engineering applications because of their excellent heat transfer capacity. Inclination angle is one of major factors which significantly affect start-up and heat transfer characteristics especially for thermosiphons. A sodium-potassium alloy (Na-K) gravity-driven heat pipe (GHP), in which the content of potassium in Na-K is wt. 55%, was fabricated to study the effect of inclination angle on start-up and heat transfer capacities of high-temperature GHPs. The Na-K GHPs was fixed by the adjusting bracket in 9 inclination angles (0°, 10°, 20°, 30°, 40°, 50°, 60°, 70° and 80°). Outside wall temperature was measured by eleven thermocouples which calibrated by the China Institute of Metrology prior to using them in the experiments. Results show that inclination angle has a significant impact on start-up and heat transfer performances of the Na-K GHP because of the impact of gravity on the two-phase flow inside the heat pipe and effective heating area in the evaporator. Start-up and heat transfer characteristics are dramatically improved and temperature difference significantly decreases as the inclination angle increases from 0° to 50°, but slightly decreases when the inclination angle exceeds 60°.

Acknowledgements

The authors express their gratitude to the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China for the financial support (Grant No. 2012QK357).

Nomenclature

De	=	external diameter of heat pipe, m
Di	=	internal diameter of heat pipe, m
g	=	gravitational acceleration, m/s2
G	=	gravity, N
G1	=	axial component of gravitational force of the gaseous working fluid, N
G2	=	normal component of gravitational force of the gaseous working fluid, N
GHP	=	gravity-driven heat pipe
L	=	total length of gravity-driven heat pipe, m
La	=	length of adiabatic section, m
Lc	=	length of the condenser, m
Le	=	length of the evaporator, m
Na-K	=	sodium-potassium alloy
PCM	=	phase-change material
Pi	=	measurement placement of the point i (= 1, 2,…, 11)
S	=	superficial area of the liquid working fluid in the evaporator, m2
T	=	outside wall temperature, °C
TPi	=	average temperature in the Pi, °C
Ttr	=	theoretical transition temperature, °C
ΔT	=	temperature difference ($=T_{P_9}-T_{P_{11}}$), °C
V	=	volume of the liquid working fluids in the bottom of the evaporator, m3

Greek symbol

Φ

=

inclination angle, measured against vertical, °

Additional information

Notes on contributors

Qing Guo

Qing Guo is a Ph.D. student of the College of Environmental and Energy Engineering, Beijing University of Technology, Beijing, China. She received her M.S. of Power engineering in 2014 from Beijing University of Technology, where she investigated the performance enhancement of the start-up of the high temperature heat pipe.

Hang Guo

Hang Guo is a Professor of the College of Environmental and Energy Engineering, Beijing University of Technology, Beijing, China. He received his Ph.D. in 2003 from Xi'an Jiaotong University. His main research interests are clean energy applications, advanced power technologies, heat pipes and their applications.

Xiao Ke Yan

Xiao Ke Yan is a Professor of the division of thermophysics and process measurements of the National Institute of Metrology, Beijing, China. He received his Ph.D. in 2009 from Beijing University of Technology, Beijing, China. His main research interests are three-phase point of water, contact thermometry, and heat pipe and its applications.

Fang Ye

Fang Ye is an Associate Professor of the College of Environmental and Energy Engineering, Beijing University of Technology, Beijing, China. She received her Ph.D. in 2008 from Beijing University of Technology. Her main research interests are heat and mass transfer enhancement, and thermal fluids management of electrochemical cells.

Chong Fang Ma

Chong Fang Ma is a Professor of the College of Environmental and Energy Engineering, Beijing University of Technology, Beijing, China. He received his M.S. in 1967 from Institute of Mechanics, Chinese Academy of Sciences, Beijing, China. His main research interests are enhanced heat transfer and energy conservation, renewable energy technology.