Effects of Jet Arrangement and Jet Height on Flow Characteristics of Air Impingement

摘要

Air impingement is a cooling technology which applies to freezing, cooling and plastics industries. An air impingement device was set up to investigate the flow characteristics of air jets. The influences of the arrangement and jet height on air flow characteristics were investigated experimentally. An oil film technique was used to visualize the jet flow on the surface of the impingement plate, and a hot-wire anemometer was used to measure the air velocity between the orifice plate and impingement plate in order to study the vertical velocity distribution of air jets. In the experiments, the specific value of jet height (H) and orifice diameter (D) was adjusted in the range of 4 to 7, and the pressure of the plenum chamber was adjusted in the range of 50 to 200 Pa. The vertical velocities were measured at different specific value of the distance (Z, between measuring point and orifice plate) and orifice diameter (D) when H/D was 7. Based on the patterns of oil film and the air vertical velocity distribution of the air jets, the airflows under an in-line orifice plate and in a staggered orifice plate were analyzed and compared with each other. The results indicate that the two jet arrangements have an identical initial state out of the orifices; however, the oil film of the staggered array has more crosses and less obstruction in the impingement plate. In addition, the fastest drop of air velocity under the orifice was in the Z/D range of 3 to 5 and the staggered array had higher velocity than the in-line array. Accordingly, airflow in the staggered array is better than in the in-line array.