Lee Jong Hwi, Shin Jong-Hyeon, Chang Se-Myong, Min Taegee
Department of Mechanical Engineering, Kunsan National University, Gunsan, Jeonbuk 54150, Korea.
G&D Co., Gunsan, Jeonbuk 54001, Korea.
Entropy (Basel). 2020 Mar 21;22(3):363. doi: 10.3390/e22030363.
In this research, unsteady three-dimensional incompressible Navier-Stokes equations are solved to simulate experiments with the Boussinesq approximation and validate the proposed numerical model for the design of a circular fin-tube heat exchanger. Unsteady time marching is proposed for a time sweeping analysis of various Rayleigh numbers. The accuracy of the natural convection data of a single horizontal circular tube with the proposed numerical method can be guaranteed when the Rayleigh number based on the tube diameter exceeds 400, which is regarded as the limitation of numerical errors due to instability. Moreover, the effective limit for a circular fin-tube heat exchanger is reached when the Rayleigh number based on the fin gap size ( Ra s ) is equal to or exceeds 100. This is because at low Rayleigh numbers, the air gap between the fins is isolated and rarely affected by natural convection of the outer air, where the fluid provides heat resistance. Thus, the fin acts favorably when Ra s exceeds 100.
在本研究中，求解非稳态三维不可压缩纳维 - 斯托克斯方程，以采用布辛涅斯克近似来模拟实验，并验证所提出的用于设计圆形翅片管换热器的数值模型。针对不同瑞利数进行时间扫描分析，提出了非稳态时间推进法。当基于管径的瑞利数超过400时，所提出的数值方法能够保证单个水平圆形管自然对流数据的准确性，这被视为由于不稳定性导致的数值误差的限制。此外，当基于翅片间隙尺寸的瑞利数（Ra s）等于或超过100时，圆形翅片管换热器达到有效极限。这是因为在低瑞利数下，翅片之间的气隙是孤立的，很少受到外部空气自然对流的影响，流体在其中提供热阻。因此，当Ra s超过100时，翅片的作用效果良好。
