Experimental and Numerical Study of Hydrodynamic and Heat Transfer Characteristics of Falling Film Over Metal Foam Layered Horizontal Tube

A novel non-intrusive technique based on air-coupled ultrasonic transducer was used to study the hydrodynamic behaviour of falling film over a metal foam layered horizontal tube. Copper foam having a porosity of 90.5%, brazed over a copper tube of 25.4 mm diameter was used in this study. Falling film thickness distribution in the circumferential direction and the dynamic characteristics of falling film were studied in the falling film Reynolds number range of 356 to 715, and at a tube spacing of 5 mm and 15 mm. The falling film characteristics over metal foam layered horizontal tube were compared with that over a plain horizontal tube surface. Heat transfer studies of falling film over metal foam layered tube were studied in an evaporator of a multi-effect desalination system by experiment. It was observed that the falling film heat transfer coefficient was enhanced 2.7 times by the application of metal foam over the plain horizontal tube. The measurements obtained from hydrodynamic and heat transfer studies were compared with the predictions made by a computational model and were found to be in good agreement. Metal foam properties required for the computational model were obtained using a micro-computed tomography based study.