EXPERIMENTAL INVESTIGATION ON FLOODING IN A FLUTED TUBE WITH AND WITHOUT A TWISTED INSERT

Experimental flooding data were obtained for a smooth tube and a flute d tube with and without a twisted insert. Fluted tubes have been used to enhance both heat and mass transfer for many thermal systems includ ing absorption heat pump systems. A plastic auger (twisted insert) was inserted in the fluted tube to increase heat and mass transfer. The e ffects of the twisted insert and angle of inclination on the flooding were examined. A water and ethyl alcohol solution (simulating an ammon ia-water solution) flows downward in the fluted tube while air flows c ounter current in an upward direction. The onset of flooding and the f looding mechanism were analyzed at variable angles of inclination by v isual observation, The experimental results showed that the effect of the twisted insert on the flooding curve decreased as the inclination angle varied from a horizontal to a vertical position. The effect of t he enhanced surface was not affected by the inclination angle. The flo oding velocity was the highest between the inclination angle of 20 deg rees and 50 degrees depending on the liquid mass flow rates for the sm ooth tube, between 20 degrees and 55 degrees for the fluted tube witho ut the insert, and between 40 degrees and 60 degrees for the superfici al liquid velocities of 42.4 m/hr and lower for the fluted tube with a n insert. The enhancement factor for the flooding velocity was obtaine d for the fluted tubes with/without inserts. Flooding correlations wer e developed as a function of inclination angle for the smooth tube, an d the fluted tube with/without a twisted insert with an error band of +/-8.5%, +/-5.0% and +/-10.0%, respectively.