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 .