Heat exchanger comprising: - a fluid circulation chamber comprising a fluid inlet and a fluid outlet intended to be supplied with a first fluid, referred to as outer fluid, brought to a first temperature, - a heat exchange matrix housed in said circulation chamber and formed by a plurality of heat exchange tubes each comprising at least one pair of ducts (32; 33) nested one inside the other, referred to as inner duct (32a; 33a) and outer duct (32b; 33b), respectively, extending along a direction, referred to as longitudinal direction, and defining: o a channel for the circulation of a fluid, referred to as inner channel (32c; 33c), delimited by said inner duct (32a; 33b), and suitable for being able to be supplied with a second fluid, referred to as inner fluid, brought to a second temperature, and o a channel for the circulation of a fluid, referred to as intermediate channel (32d; 33d), delimited by the inter-duct space between said inner duct (32a; 33a) and said outer duct (32b; 33b), and suitable for being able to be supplied with a third fluid, referred to as intermediate fluid, brought to a third temperature, different from said first temperature, characterized in that at least one heat exchange tube comprises at least two pairs of nested ducts (32; 33), said pairs being connected to each other by at least one transverse spacer. - a fluid circulation chamber comprising a fluid inlet and a fluid outlet intended to be supplied with a first fluid, referred to as outer fluid, brought to a first temperature, - a heat exchange matrix housed in said circulation chamber and formed by a plurality of heat exchange tubes each comprising at least one pair of ducts (32; 33) nested one inside the other, referred to as inner duct (32a; 33a) and outer duct (32b; 33b), respectively, extending along a direction, referred to as longitudinal direction, and defining: o a channel for the circulation of a fluid, referred to as inner channel (32c; 33c), delimited by said inner duct (32a; 33b), and suitable for being able to be supplied with a second fluid, referred to as inner fluid, brought to a second temperature, and o a channel for the circulation of a fluid, referred to as intermediate channel (32d; 33d), delimited by the inter-duct space between said inner duct (32a; 33a) and said outer duct (32b; 33b), and suitable for being able to be supplied with a third fluid, referred to as intermediate fluid, brought to a third temperature, different from said first temperature, characterized in that at least one heat exchange tube comprises at least two pairs of nested ducts (32; 33), said pairs being connected to each other by at least one transverse spacer. o a channel for the circulation of a fluid, referred to as inner channel (32c; 33c), delimited by said inner duct (32a; 33b), and suitable for being able to be supplied with a second fluid, referred to as inner fluid, brought to a second temperature, and o a channel for the circulation of a fluid, referred to as intermediate channel (32d; 33d), delimited by the inter-duct space between said inner duct (32a; 33a) and said outer duct (32b; 33b), and suitable for being able to be supplied with a third fluid, referred to as intermediate fluid, brought to a third temperature, different from said first temperature,