Flow restriction and heat transfer in liquid helium cooling channels

Heat transfer characteristics in vertical liquid-helium cooling channels have been examined to understand the effect of restriction of liquid and vapor flows. Simulated channels were made to examine the steady-state and transient heat-transfer characteristics. The channel had a foil heater of stainless steel, and a movable block for hindering coolant flow was located just above or below the channel. The results indicated that the critical heat flux was considerable influenced by the hydrodynamic situations if the channel was sealed at the top or bottom. The cooling capacity of the top-sealed channels was significantly reduced. In the case of buttom-sealed channels, the critical heat flux was reduced due to vapor locking when the channel was small. These phenomena are explained in terms of the flow restriction of the updrafting vapor. The transient heat transfer was almost independent of the flow restriction.