Experimental study of heat transfer and flow characteristics of liquid falling film on a horizontal fluted tube

The aim of the present study is to investigate experimentally the effect of the fluted surface tube on the heat transfer and flow characteristics of liquid falling film. Experiments have indicated that, when a liquid falling film falls on a horizontal fluted surface tube, the transition starts at low Reynolds number than that of the plain tube. The value of the film thickness has been slightly decreased by decreasing the fluted pitch. A reduction of the film thickness was observed at about 9% for tube number 4, which has lower pitch, at Reynolds number of 485. A clear reduction of the dimensionless wavelength, lambda*, has occurred at low fluted pitch tube. The use of enhanced surfaces can provide heat transfer coefficients higher values than those obtained from plain tube. Heat transfer enhancement was noticed due to the use of fluted tube surface. An improvement of the Nusselt number reached about 45% for tube 4. However, the low values of the fluted pitch increased the heat transfer enhancement than that of the high values.