A tubular heat exchanger (10) comprising: a fluid circulation chamber (20) intended to be supplied with a first fluid, referred to as outer fluid, brought to a first temperature, a heat exchange matrix (30) housed in said circulation chamber and formed by a plurality of heat exchange tubes (31) each comprising at least one pair of ducts (32; 33) nested one inside the other, extending along a direction, referred to as longitudinal direction, and defining: a channel for circulating a fluid, referred to as inner channel (32c; 33c), suitable for being able to be supplied with a second fluid, referred to as inner fluid, brought to a second temperature, and a channel for the circulation of a fluid, referred to as intermediate channel (32d; 33d), 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.