Abstract: A matrix of heat exchange tubes in a heat exchanger in which a first fluid flows in the heat exchange tubes and undergoes heat exchange with a second fluid flowing externally on the heat exchange tubes. The tubes have a teardrop shape and are arranged in the matrix in parallel relation in rows in which each tube has a rounded surface at one end and a tapered narrow surface at the other end. The tubes in each row all face in the same direction and the tubes in alternate rows face in opposite directions. The tubes have alternate unequal spacing of distances a.sub.1 and a.sub.2 in successive rows. The tubes can be bent to form a U-shape matrix or a semi-circular matrix. The tubes are each manufactured by filling the space between an inner channel and an outer shell of the tube with a ceramic or metal.

Abstract: A cooling arrangement for the cooling air of hypersonic jet engines comprises a heat exchanger in which the temperature of the cooling air is reduced by means of the fuel to be burnt in the engine. In order to keep the operating temperatures of the heat exchanger within controllable limits, a partial flow of the cooling air is branched off downstream of the heat exchanger and is admixed to the cooling air upstream of the heat exchanger for reducing the temperature.