CHARACTERISTICS AND FLOW VISUALIZATION OF A THERMOSYPHON IN MELTS INSIDE A COMPOSITE HEAT EXCHANGER TUBE

The characteristics of a thermosyphon in molten aluminum inside the annulus of a composite heat exchanger tube has been studied. The physical system consists of two concentric, hollow, carbon steel cylinders press-fitted with a hollow aluminum cylinder in the annulus. It is heated by a helical electric heater wound around the outer surface and is cooled by air flowing through the inner tube. The lower half of the heater surface is insulated to create enough temperature difference to initiate thermosyphon action in the molten aluminum. The orientation of the composite structure is varied from the horizontal to an inclined, to a vertical position. The temperature-time history of the aluminum is monitored at strategic locations to determine the characteristics and mechanisms of thermosyphoiting. flow instability is manifested in the form of temperature fluctuations. The phenomenon have also been studied by means of flow visualization in a transparent composite heat transfer tube with one-half of the outer surface wound with a sheet heater. A molten paraffin wax mixed with an aluminum pigment as the tracer confined in the annulus is cooled by a water stream flowing through the inner tube.