English: A comparison between the operations and effects of a concurrent and a countercurrent flow exchange systems are depicted by the two diagrams. In both it is assumed (and indicated) that red has a higher value (e.g. of temperature) than blue and the property being transported in the channels therefore flows from red to blue. It is important to note that channels need to be contiguous for effective exchange to occur (i.e. there can be no gap between the channels).