Parameters and stability of surface waves for single and double layer liquid flows : an experimental and computational study

In modern technology flows of thin liquid films play a major role in fine liquid coating processes, such as the production of photo film and magnetic tape. The principle of such processes is the application of one or more thin layers of coating liquids to a solid substrate. The quality of the products and the efficiency of the coating operation depend to a large extent on the mechanics of the thin film flow. The flow of thin liquid film is known to frequently develop surface waves due to its instability. In liquid coating industry they lead to defective products, when the wavy film is dried with a non-uniform thickness. This work is an experimental and numerical study of the instability and the wave parameters of the free-surface wave of thin liquid film flow. An experimental procedure employing optic-electric transformation and digital signal processing techniques is designed, and used to obtain the frequency information about waves on the surface of a single layer flow and a double layer flow. Also, the criteria for onset of waves and the transit distance information are experimentally determined for a single layer flow. A computer model employing finite difference and numerical grid generation techniques is developed and used to simulate the single layer film flow subjected to a minute disturbance