Self-purging thermosiphon

Abstract

A thermosyphon system is provided that enables passive startup and sustained operation in configurations where geometric constraints or flexible tubing introduce local low points in the vapor tube. Embodiments of the invention include a vapor tube and a liquid return tube fluidly coupling an evaporator to a condenser, and may further include an accumulator and a liquid-vapor separator with a purge tube. During startup, the system facilitates passive purging of entrained liquid from the vapor tube through phase separation and gravity-driven drainage into the accumulator. Configurations may feature submerged liquid tube inlets and strategically placed purge tube low points to control pressure head relationships, enabling stable initiation of vapor flow and return of condensed liquid. The invention eliminates the need for mechanical pumping, enhances startup reliability, and improves thermal performance in compact or variably-oriented systems.

We claim: 
     
         1 . A thermosyphon system, comprising:
 an evaporator thermally coupled to a heat-generating device;   a condenser;   a vapor tube fluidly coupling the evaporator to the condenser; and   a liquid return tube fluidly coupling the condenser to the evaporator;   wherein the liquid return tube enters the evaporator at an upper portion; and   wherein the liquid tube includes at least one localized low point positioned below the upper portion of the evaporator.   
     
     
         2 . The thermosyphon system of  claim 1 , further comprising an accumulator fluidly connected between the condenser and the evaporator via the liquid return tube, configured to receive and store liquid during system startup. 
     
     
         3 . The thermosyphon system of  claim 1 , wherein the condenser is positioned at an elevation above the evaporator to promote gravity-assisted return of liquid. 
     
     
         4 . The thermosyphon system of  claim 1 , wherein the vapor tube includes at least one local minimum that imposes an adverse hydrostatic pressure head during system startup. 
     
     
         5 . The thermosyphon system of  claim 1 , wherein a terminal end of the liquid return tube extends into the evaporator but does not extend below the upper portion of the heat-generating device, such that the terminal end of the liquid return tube stabilizes liquid in the evaporator during initial vapor formation. 
     
     
         6 . The thermosyphon system of  claim 1 , wherein the system is configured such that the favorable pressure head from the liquid return tube exceeds an adverse pressure head in the vapor tube during startup. 
     
     
         7 . A thermosyphon system, comprising:
 an evaporator fluidly coupled to a vapor tube and a liquid tube;   a condenser fluidly coupled to the vapor tube;   an accumulator fluidly coupled to the liquid tube;   a liquid-vapor separator fluidly connected to the vapor tube; and   a purge tube fluidly coupled between a lower portion of the liquid-vapor separator and the accumulator;   wherein the liquid-vapor separator is configured to receive a two-phase mixture from the evaporator and to separate liquid from vapor; and   wherein the purge tube includes a vertical low point defining a purge pressure head that exceeds a favorable pressure head in the liquid tube under steady-state conditions.   
     
     
         8 . The thermosyphon system of  claim 7 , wherein an upper portion of the vapor tube is fluidly coupled to the top of the liquid-vapor separator and the condenser. 
     
     
         9 . The thermosyphon system of  claim 7 , wherein the purge tube is hydraulically inactive during steady-state operation due to the elevation of its low point relative to the accumulator. 
     
     
         10 . The thermosyphon system of  claim 7 , wherein the system is configured to initiate passive startup flow by allowing vapor pressure to displace liquid from the evaporator through the vapor tube and the liquid tube. 
     
     
         11 . The thermosyphon system of  claim 7 , wherein the condenser includes sufficient volume to serve as an integrated accumulator. 
     
     
         12 . The thermosyphon system of  claim 7 , wherein the liquid-vapor separator is positioned at approximately the same elevation as the accumulator to facilitate gravitational return of separated liquid.