(57) The heat-exchanger comprises a set of parallel spaced apart heat-conducting plates (10) mounted in a frame member (2) surrounding and engaging the peripheries of the plates. The plates are so mounted to the frame member for example, in grooves (9) or in rubber mountings, that they are readily detached and removed for cleaning and/or replacement when a portion of the frame member is removed or opens upon a hinge. Two separate fluids are introduced into and exhausted from alternating sets of channels (12) formed between the plates through inlet (14, 16) and outlet (15, 17) passages in the frame member whereby heat-exchange takes place through the plates. The fluids may travel at right angles to each other, co-currently or in counter-current.