Passive techniques are more attractive because no power is required to facilitate the enhancement and among them treated surfaces, rough surfaces, displaced enhancement devices, swirl-flow devices, surface-tension devices, coiled tubes, or flow additives [1–3] are found. Moreover the simultaneous use of two or more of these techniques has been investigated in literature in order to verify if it is able to produce an enhancement larger than that produced by only one technique. This simultaneous use is termed compound enhancement [2].