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首页> 外文会议>7th Conference of Food Engineering (CoFE 2001) and A Topical Conference of 2001 AIChE Annual Meeting, Nov 5-9, 2001, Reno, NV >Air Impingement of Foods with Circular and Rectangular-shaped Jets
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Air Impingement of Foods with Circular and Rectangular-shaped Jets

机译：圆形和矩形喷嘴对食品的空气冲击

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摘要

Most of the impingement systems used in the food industry utilize jets with a circular opening. However, jet systems with a two-dimensional opening, and arranged parallel to each other, promise to have a more uniform convective heat transfer coefficient distribution. This may result in uniform cooking, freezing, or thawing characteristics of foods while applying impingement systems. In the present work, a comparative study of flow distribution patterns from circular-opening nozzles and a two- dimensional jet was conducted using flow visualization techniques. Single as well as double circular jets were used for the purpose. A Helium-bubble generation device in conjunction with a CCD camera system was used for the purpose of visualization. The relative spatial distribution of convective heat transfer from the two types of jets was studied at jet exit with airflow velocities of 15, 20 and 25 m/s. A previously described setup for measurement of spatial heat transfer coefficient was used for the temperature ranges of 25℃ to 80 ℃. For the same exit air velocities, the rectangular slot jets show a slightly lower convective heat transfer coefficient (averaged over the entire area) but a more uniform heat transfer coefficient distribution pattern as compared to the array of circular jets. The flow patterns indicate that the lower convective heat transfer may be attributed to the reduced turbulence in the boundary layer while using the two-dimensional jet as compared to the circular jets where the jets interact with each other to increase the turbulence effect. The results show that with a suitable optimization procedure, two-dimensional jets may give a much better product quality than conventional round jets due to uniform heat transfer coefficient distribution.
机译：食品工业中使用的大多数撞击系统都使用带有圆形开口的喷嘴。然而，具有二维开口并且彼此平行布置的喷射系统有望具有更均匀的对流传热系数分布。在施加冲击系统时，这可能导致食物的均匀烹饪，冷冻或解冻特性。在目前的工作中，使用流量可视化技术对圆形开口喷嘴和二维射流的流量分布模式进行了比较研究。为此目的，使用了单圆形和双圆形喷嘴。为了可视化，使用了氦气泡生成设备和CCD相机系统。在气流速度为15、20和25 m / s的射流出口处研究了两种射流对流传热的相对空间分布。在25℃至80℃的温度范围内使用先前描述的用于测量空间传热系数的设置。对于相同的出口空气速度，矩形缝隙射流显示的对流传热系数略低（在整个区域平均），但与圆形射流阵列相比，传热系数的分布方式更均匀。流动模式表明，与圆形射流彼此相互作用以增加湍流效果的圆形射流相比，使用二维射流时，较低的对流热传递可归因于边界层中减小的湍流。结果表明，采用适当的优化程序，由于均匀的传热系数分布，二维射流可以提供比常规圆形射流更好的产品质量。

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