Method of making heat exchangers

A method of making a plastic heat exchanger for transferring heat from one gas to another while maintaining a barrier between them to isolate one gas from the other,

• providing a plurality of panels of plastic material, each having a substantial thickness, and two opposed broad surfaces,
• pressure-forming at least one broad surface of selected ones of said panels to form at least one gas passage cavity in each,
• providing the others of said panels with elongated gas flow passages,
• interleaving said selected sheets with said others of said panels in a predetermined sequence, and
• securing said panels together with broad surfaces thereof contacting one another,
• said gas passage cavities, together with surfaces of adjacent panels, forming conduits for one of said gases, and said elongated gas flow passages forming conduits for the other of said gases.

A method of making a heat exchanger, said method comprising

• (a) providing a plurality of thermoplastic panels each having a plurality of internal gas flow conduits,
• (b) securing said panels together in spaced-apart relationship to one another using spacers between said panels, with the edges of said panels aligned with one another,
• (c) using said spacers to form gas flow passageways between said panels,
• (d) forming a housing for said heat exchanger around said panels and said spacers while leaving an inlet opening and an outlet opening for said gas flow conduits, and a separate inlet opening and a separate outlet opening for said gas flow passageways,
• (e) said forming step comprising the step of heating at least one length of said aligned edges and melting them to form a fused solid housing wall.