Optimum Design of Two-Row Slotted Fin Surface with X-Shape Strip Arrangement Positioned by “Front Coarse and Rear Dense” Princple, Part I: Physical/Mathematical Models and Numerical Methods

Abstract

In this article, a comprehensive numerical investigation of the air-side fluid flow and heat transfer characteristics in a two-row finned-tube heat exchanger is conducted with a three-dimensional laminar conjugate model. Three groups including 15 types of slotted fin surface are studied. In the first group the strips are arranged in X shape with the principle of “front coarse and rear dense,” and the number of strips varies from three to six. The first series of the second group is formed by changing the strip length of slit fin 3 in the first group, and the second series of this group is formed by changing the strip lengths of slit 1 and slit 2 in the first group. The third group is formed by splitting one strip of slit fin 2 into two. The three groups are designed in order to enhance the values of j/f at the same Reynolds number and enhance the heat transfer at identical pumping power. The physical model/mathematical formulation and numerical methods are described. The authors' numerical experiences show that for the convergence criteria, apart from the relative variation of the key parameters, their variation trends versus some independent variables should also be taken into account. Reliable numerical solutions for the problem studied should possess consistency and smoothness in their variation trends. In Part II of this article, the specific flow and heat transfer characteristics of the 15 slotted fin surfaces and comparisons with a plain plate surface will be presented in detail.