Abstract: A heat exchanger of the type having a tube assembly made up of a number of tubes through which a first medium flows and around and between which a second medium flows to accept heat from, or transfer heat to, the first medium. One of the media is constrained by baffles to follow a tortuous path through the heat exchanger. According to the invention, the baffles are completely separate from the tubes, so permitting them to be replaced or adjusted without the necessity of disassembling the tube assembly. The baffles can be carried releasably on rods which allow their spacing to be adjusted at will, with the result that heat exchangers according to the invention are more versatile than conventional heat exchangers where the baffles are fixed to the tubes.