Abstract: A plate-fin-type heat exchanger for transferring heat from a hot fluid to a cold fluid includes stacked plates having fins therebetween that define alternate interdigitated first and second fluid passages, the fins defining the first fluid passages having a high coefficient of heat transfer and a large area of heat transfer and the fins defining the second fluid passages having a low coefficient of heat transfer and a small area of heat transfer. Either the hot fluid or the cold fluid is continuously passed through the first fluid passages and the other fluid is intermittently passed through the second fluid passages.