对于 PCHE (通道直径, 通道倾斜角, 流向节距) 来说，由于流体无法在人字形热交换器中形成充分发展的流动，因此努塞尔数无法像在直通道热交换器中那样保持恒定值。因此，应针对人字形热交换器中的He-Xe提出新的准则关联式。然而，通道直径对热交换器的流动和传热也有重要影响。因此，需要在数值模拟的基础上拟合努塞尔数与D/σ、I_z/σ、α和Re的函数关系。PCHE热侧通道的不同相对通道直径比、相对节距长度比和之字形角度下的努塞尔数随Re的变化。努塞尔数最大的几何参数值，这表明人字形角度比人字形间距长度对努塞尔数的影响更大。此外，当Re值较小时，努塞尔数受几何参数的影响较小。这是因为Re值的增大会导致通道中流体速度的增大，可以看出PCHE的传热能力也会增强，因此努塞尔数会增大。在不同的Re条件下，通道直径的相同变化所引起的努塞尔数变化基本相同。

Since the fluid cannot form a fully developed flow in a zigzag PCHE, the Nusselt number cannot hold a constant value as in a straight PCHE. Therefore, a new correlation for HeXe in a zigzag PCHE should be proposed. Previous studies [13, 14] have developed correlations to account for the effects of zigzag angle and zigzag pitch length in PCHE, but their channel diameters are held at a constant value. However, the channel diameter also has an important impact on the flow and heat transfer of a PCHE. Therefore, it needs to fit the Nusselt number as a function of D/σ, I_z/σ, α, and the Re based on numerical simulation. This figure shows the variation of the Nusselt number with Re for different relative channel diameter ratios, relative pitch length ratios, and zigzag angles of PCHE hot-side channels. The line frames highlight the geometric parameter values in which the Nusselt number is the largest, which shows that the zigzag angle has a greater effect on the Nusselt number than the zigzag pitch length. In addition, when the Re is smaller, the Nusselt number is less affected by the geometric parameters. This is because the increase of the Re will cause the increase of the fluid velocity in the channel, and it can be seen that the heat transfer capacity of the PCHE will also be enhanced, so the Nusselt number will increase. With different Re, the variation of the Nusselt number caused by the identical variation of channel diameter is almost the same.