A fluid processing unit having first and second interleaved flow paths in a cross flow configuration is disclosed. The first flow paths are substantially longer than the second flow paths such that the pressure drop in the second flow paths can be maintained at a relatively low level and temperature variations across the second flow paths are reduced. One or more of the flow paths can be microchannels. When used as a vaporizer and/or superheater, the longer first flow paths include an upstream liquid flow portion and a downstream vapor flow portion of enlarged cross sectional area. A substantial pressure drop is maintained through the upstream liquid flow portion for which one or more tortuous flow channels can be utilized. The unit is a thin panel, having a width substantially less its length or height, and is manufactured together with other thin units in a bonded stack of thin metal sheets. The individual units are then separated from the stack after bonding.