Tham khảo tài liệu 'underwater vehicles part 14', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Autonomous Underwater Gliders 509 derived from harnessing the energy of the thermal gradient between the ocean s surface and bottom for use as the vehicle s propulsion. In missions with electric-powered gliders 60-85 of the energy consumed goes into propulsion so a thermal-powered glider may have a range 3 4 times that of a similar electric-powered vehicle. Except for its thermal buoyancy system and using roll rather than a movable rudder to control turning Slocum Thermal is nearly identical to Slocum Battery Griffiths 2002 . The Slocum Thermal glider uses the change in volume from a material s ethylene glycol freezing and melting as the means of vehicle propulsion. The vehicle begins to descend by venting the external bladder into an internal bladder using the pressure difference between the two chambers . the hull internal bladder filled with Nitrogen is slightly below atmospheric pressure . As the vehicle passes through the freezing point of the material during its descent the contraction of the material causes the fluid in the internal reservoir to be drawn out into a heat exchanger. To ascend the pressurized material in the heat exchanger is transferred to the external bladder causing the vehicle to switch from negative to positive buoyancy. As the vehicle ascends the warming of the ocean waters cause the material to melt and expand further increasing its buoyancy. The vehicle arrives at the surface with the same conditions it had at the start . in a stable thermal equilibrium with the external bladder inflated the material expanded and the internal bladder at a slightly negative pressure. The material and pressurized nitrogen is at a slightly greater pressure than the external ocean pressure. The thermodynamic stages of the system can be seen in Figure 10. Slocum Thermal Webbresearch 2008b Weight Hull Diameter 60 kg cm Vehicle Length m Wing Span 120 cm Depth Range 4 - 2000 m Payload 2kg Speed m sec horizontal projected Energy Thermal engine
