Heat exchanger with build powder in barrier channels

A method for additively manufacturing a heat exchanger configured to transfer heat between a first fluid and a second fluid, the method comprising:

• providing an alternating plurality of hot layers and a plurality of cold layers, wherein each of the plurality of hot layers provides a flow path through the heat exchanger for the first fluid and is separated from each other of the plurality of hot layers by one of the plurality of cold layers and each of the plurality of cold layers provides a flow path through the heat exchanger for the second fluid, wherein:
• each of the plurality of hot layers comprises a plurality of hot flow assemblies, and each of the plurality of hot flow assemblies is built by a layer by layer process using additive manufacturing techniques that comprises the steps of:
• building an inner channel wall that defines an inner channel configured to port flow of the first fluid;
• and
• building a barrier channel wall surrounding the inner channel wall such that the barrier channel wall defines a barrier channel coaxially exterior to the inner channel and located between the inner channel wall and the barrier channel wall, wherein the barrier channel is configured to prevent mixing of the first fluid and the second fluid when one of the inner channel wall and the barrier channel wall ruptures;
• wherein the method further comprises leaving in the barrier channel unprocessed build powder used by the additive manufacturing techniques.