It is observed that the TEFs for the in-phase Z-baffles generally are found to be above unity and to be much higher than those for employing the out-phase Z-baffles at similar baffle and flow conditions. This indicates that the use of the in-phase Z-baffles leads to the advantage over that of the out-phase ones. The TEF tends to decrease with the increase of Re, e/H and P/H for all Z-baffles applied.