TY - JOUR
TI - Visual study on two-phase flow in a horizontal closed-loop oscillating heat pipe
AU - Charoensawan Piyanun
AU - Terdtoon Pradit
JN - Thermal Science
PY - 2019
VL - 23
IS - 2
SP - 1055
EP - 1065
PT - Article
AB - Two-phase flow boiling of working fluid within a closed-loop oscillating heat  pipe in the horizontal orientation (HCLOHP) was studied visually. The HCLOHP  was made of Pyrex glass tubes with an inside and outside diameter of 2 and 7  mm, respectively. The evaporator, adiabatic and condenser of the HCLOHP were  50 mm in length. The internal flow phenomena was carefully investigated for  various number of turns, evaporator temperatures and filling ratios of the  two working fluids, i.e. distilled water and absolute ethanol. The HCLOHP was  installed on cooling and heating copper plates and the two-phase flow  patterns were recorded by digital still and video cameras. The rate of heat  transferred to the cooling water at the condenser was evaluated. The fluid  motion characteristics may be separated into two main conditions viz., the  oscillating slug flow and the standstill condition. The thermal performance  improved when the number of turns reached the critical value of 10 turns at  which the vapor fraction was small and the time fraction of oscillating flow  was long. For both working fluids, the time fraction of oscillating flow was  longest for 50% filling ratio, which led to the lowest thermal resistances.  The wavy vapor-liquid interface which induced the vapor/liquid slug train  formation was only found for water. Nucleate boiling followed by oscillating  flow was discovered in the evaporator part only at the 50% and 80% filling  ratios of water. At these filling ratios the thermal resistance of water  tended to be lower than that of ethanol.