Visualization of refrigerant behaviors in a variable conductance heat pipe by neutron radiography

Variable Conductance Heat Pipes (VCHP) are used as a cooling device which can passively keep the evaporating temperature by enclosing non-condensable gas (NCG) with refrigerant. The VCHP has often a bend section between evaporating and condensing area, since the condensation section should be placed vertically above the evaporation section. It is known that the bend may disturb a liquid flow to the evaporation section. The effect of the VCHP orientation, filling ratio of the refrigerant, amount of the charged NCG have been examined. A thin plate was inserted to more the effects of the bend. In this study, the refrigerant behaviors in the VCHP with the bend were diagnosed based on flow visualization by neutron radiography. It was observed that liquid plugs formed at the bend and suppressed the condensed liquid supply to the evaporating section without the thin plate. It was also shown that the thin plate inserted in the bend was effective to avoid the liquid plug formation. (author)