HEAT EXCHANGER

A heat exchanger comprises a first set of first conduits 80 for conveying a first fluid, and a second set of second conduits 90 for conveying a second fluid, the first and second conduits having a triangular cross-section portion (120, 120B, Fig.3A). Adjacent first conduits are interspaced by an intervening second conduit. The first and second conduits may be arranged in at least one tessellated row, with alternating adjacent first and second conduits. A first end of the first and second conduits may define a first aperture 110, (150, Fig.2B) having a triangular cross-section. The first and second conduits may have a narrowing portion (130, Fig.3A) together with an adjacent enlarging portion (140, Fig.3A) towards a second end which defines a second aperture 30, 100. A first void is defined between outer surfaces of the narrowing portions of the second set of second conduits. The first apertures of the first set of first conduits are positioned for fluid communication with the first void. In an alternative arrangement, the core of the heat exchanger may comprise a nest of triangular passages formed between coincident walls, each wall being a boundary between a forward (hot) flow and counter (cold) flow passage.