Heat exchanger for the indirect heat transfer between a first medium and a second medium, with: - a shell which has a shell space for receiving the first medium, - at least one heat transfer block which is arranged in the shell space and enveloped by the first medium during a design-specified operation, wherein the heat transfer block is designed for cooling and/or for at least partially liquefying the second medium against the first medium so that a gaseous phase of the first medium is formed in the shell space, - wherein for extracting the gaseous phase of the first medium from the shell space, provision is made for a collecting channel which is located in the shell space and extends along a direction of extension which is oriented parallel to the longitudinal axis of the shell, - and wherein the at least one heat transfer block is a plate heat exchanger, - and wherein the collecting channel is connected to at least one outlet connector which is provided on the shell so that the gaseous phase of the first medium can be extracted from the shell space through the collecting channel via the at least one outlet connector, - and wherein the collecting channel has two end faces (11a, 11b) which lie mutually opposite along the direction of extension of the collecting channel, characterized in that - the collecting channel has a cross section transversely to the direction of extension which increases towards the outlet connector and - the collecting channel has a multiplicity of inlet openings (12, 13) for extracting the gaseous phase, wherein the spacings of adjacent inlet openings decrease towards the respective end face (11a, 11b) of the collecting channel. - a shell which has a shell space for receiving the first medium, - at least one heat transfer block which is arranged in the shell space and enveloped by the first medium during a design-specified operation, wherein the heat transfer block is designed for cooling and/or for at least partially liquefying the second medium against the first medium so that a gaseous phase of the first medium is formed in the shell space, - wherein for extracting the gaseous phase of the first medium from the shell space, provision is made for a collecting channel which is located in the shell space and extends along a direction of extension which is oriented parallel to the longitudinal axis of the shell, - and wherein the at least one heat transfer block is a plate heat exchanger, - and wherein the collecting channel is connected to at least one outlet connector which is provided on the shell so that the gaseous phase of the first medium can be extracted from the shell space through the collecting channel via the at least one outlet connector, - and wherein the collecting channel has two end faces (11a, 11b) which lie mutually opposite along the direction of extension of the collecting channel, - the collecting channel has a cross section transversely to the direction of extension which increases towards the outlet connector and - the collecting channel has a multiplicity of inlet openings (12, 13) for extracting the gaseous phase, wherein the spacings of adjacent inlet openings decrease towards the respective end face (11a, 11b) of the collecting channel.