Provided is a process and apparatus for exchanging heat energy between three or more streams in a millichannel apparatus, which millichannel apparatus may comprise a heat exchanger which may be integrated with a millichannel reactor to form an integrated millichannel processing unit. The combining of a plurality of integrated millichannel apparatus to provide the benefits of large-scale operation is enabled. In particular, the millichannel heat exchanger enables flexible heat transfer between multiple streams and total heat transfer rates of about 1 Watt or more per core unit volume expressed as W/cc.