The invention relates to a heat exchanger (1) for indirect heat transfer between a first medium (F1) and a second medium (F2), comprising: a shell (2) which has a shell space (3) for receiving the first medium (F1), a heat transfer block (4) which is disposed in the shell space (3) and which during correct operation is surrounded by the first medium (F1), wherein the heat transfer block (4) is designed to cool the second medium (F2) against the first medium (F1), such that a gaseous phase of the first medium (G1) forms in the shell space (3). According to the invention a collecting channel (5) located in the shell space (3) is provided for drawing off the gaseous phase of the first medium (G1) from the shell space (3).