Apparatus and methods are disclosed for uniformly mixing fluid phases entrained in a porous material. A mixer may have a vessel and at least one porous material held by the vessel. At least one actuator may be acoustically coupled with at least one wall of the vessel for generating a wave. The wave effects mixing of at least two fluids in the porous material. The actuator may be a linear motor actuated with a control signal of predetermined frequency. The actuator may have a number of actuator pairs each including respective first and second actuators at respective first and second sides of the vessel. The actuators may be hinged for reciprocal movement. The actuators may be actuated to form a compression-expansion wave to effect fluid motion in the porous material.