The Research On Heat Transfer Of Gravity Heat Pipes With Different Diameter

In recent years,China’s energy consumption has increased rapidly,but the energy intensity is still keep a high level.A lot of thermal equipment are inefficient.Gravity heat pipe,an efficient heat exchange element,which the application scope of is continuously expanding.However,the internal heat transfer mechanism of gravity heat pipe is very complicated,so it is urgent to study the thermal characteristics of gravity heat pipe deeply.Therefore,theoretical and experimental studies on the phase change heat transfer mechanism and key parameters affecting geyser boiling are carried out.The main contents are included in two parts.First,a experimental platform for stainless steel-water two-phase closed thermosyphon was established.An experimental investigation has been carried out to study on heat transfer characteristics and geyser boiling of two-phase closed thermosyphon.Three stainless steel pipes of 1000 mm length with 8,16 and 24 mm inside diameter and water as the working fluid were employed.Parameters such as pipe diameter(d),evaporation section length(Le),heat input(Q)and the coolant mass flow rate(m)affect the thermosyphon’s thermal performance,period of geyser boiling and geyser boiling instability.The experimental results show that the thermal resistance of the 8mm inner diameter thermosyphon is low at low heat loads.After the heat input exceeds 150 W,its thermal resistance is higher than that for the inner diameter of the 24 mm.The diameter and the evaporation section length have a significant effect on geyser boiling at low heat loads.Choosing a larger pipe diameter and a shorter evaporation section length can effectively reduce the geyser boiling intensity at low heat loads.An experimental equation was offered to correlate the data for the period of geyser boiling.Secondly,a visual experimental platform was established.Quartz glass two-phase closed thermosyphon was used to observe the bubble behavior.The experimental results show that the instability of geyser boiling is largely determined by the location of bubble generation.Bubbles generated at the lower part will strong impact on the top of the heat pipe.When the filling height became less then 80 mm,geyser boiling of 24 mm diameter thermosyphon disappers.Finally,a method to suppress geyser boiling intensity by changing the density of vaporization core and controlling the bubble generation position is proposed.