Processing devices that include one or more process arrays with thermal transfer structures that can be used alone or in conjunction with gravity/rotation to transport fluids within a microfluidic system. The thermal transport function can be accomplished by changing the temperature of one or more chambers to create a vacuum to draw fluids in selected directions within the process array. The methods and apparatus of the present invention may provide the ability to move fluids in a direction that is against the direction of gravity or any centrifugal forces generated by rotating a processing device using the thermal transfer structures. In other words, fluids may be moved against the direction of gravity or towards the axis of rotation using the thermally-activated vacuum.