Characteristics of a Falling Liquid Film Flow Using Periodic Jetting Flow

Abstract

This work tried to form a falling thin film by supplying liquid to the disk attached to the upper part of the device, rotating the disk and jetting liquid onto the wall surface in order to develop a new falling film evaporator without contamination. Heat transfer enhancement is expected by the surface renewal effect of unsteady and/or periodical flow due to the rotating disk with ditches. The influence of the shape and rotation speed of the disk on the flow of the falling thin film was investigated. Four kinds of rotating disk having small two or four ditches with a depth of 1 mm were used. The apparatus consists of a rotating disk, a cylindrical glass tube and a reservoir. An aqueous solution of uranine is supplied from the reservoir to the upper part of the rotating disk by a pump. The flow rate of the aqueous solution was 88 L/h, and the rotation speed of the disk was set at 200 or 300 rpm. The time-dependent flow condition was observed by irradiating a UV lamp from the side of the apparatus and photographing the front test section with the vertical length of 200 mm by a digital camera. The correlation between film thickness distribution and heat transfer characteristics suggested that thinner film thickness, nonuniform film thickness distribution with higher intensity due to large-scale waves, and higher circumferential velocity of liquid film were three major factors to enhance heat transfer.