A thermosiphon cooling assembly includes a refrigerant disposed in a lower portion of a housing for undergoing a liquid-to-vapor-to-condensate cycle. A mixing device is disposed within the lower portion of the housing for increasing the transfer of heat from the electronic device during the liquid-to-vapor-to-condensate cycle. The mixing device may include a vapor stirrer disposed above the liquid of the refrigerant and/or a liquid stirrer disposed in the liquid of the refrigerant for moving the liquid of the refrigerant over a boiler plate.