轴向导热对逆流式板翅换热器传热性能的影响

Influence of Longitudinal Heat Conduction on a Counterflow Plate-Fin Heat Exchanger

为了确认轴向导热对复叠逆流式板翅换热器传热性能的影响,通过数学分析建立了一组控制方程,定义了无量纲轴向当量热扩散系数(φ).用φ来表示换热器的轴向导热能力可以使换热器的二维模型实现一维简化,使计算工作更加简单方便,并可采用差分法解出其数值解.计算结果表明,轴向导热对换热器性能的影响随着φ和传热单元数(NNtu)的增大而加剧,导致换热器换热性能的恶化.为了减少轴向导热损失,应尽可能减小换热器的横截面积.同时,高导热性能的换热器材料也会加大轴向导热损失.

A group of governing equations for a counter-flow plate-fin heat exchanger (HX) with double cold channels were put forward on the basis of theoretical analysis and eventually solved by finite difference method in order to confirm the longitudinal heat conductivity effects on cryogenic HX. A dimensionless longitudinal heat diffusion coefficient (φ) was proposed to indicate the effect of longitudinal heat conductivity in cryogenic HX, which could simplify the model from two dimensions to one dimension and be more convenient for calculation. The results show that the effect of the longitudinal heat conduction on HX increases along with the increase of φ and heat transfer unit, and degrades the performance of HX. The cross-sectional area should be reduced as small as possible for alleviating the heat loss. It is also revealed quantitatively that higher heat conductivity of solid walls enhances the heat loss according to this model.