A counterflow heat exchanger configured to exchange thermal energy between a first fluid flow at a first pressure and a second fluid flow at a second pressure less than the first pressure, comprising: a first fluid inlet ; a first fluid outlet fluidly coupled to the first fluid inlet via a core section ; a second fluid inlet ; a second fluid outlet fluidly coupled to the second fluid inlet via the core section ; the core section including: a plurality of first fluid passages configured to convey the first fluid flow from the first fluid inlet toward the first fluid outlet ; a plurality of second fluid passages configured to convey the second fluid flow from the second fluid inlet toward the second fluid outlet such that the first fluid flow exchanges thermal energy with the second fluid flow at the core section; one or more drains disposed in the core section operably connected to the plurality of first fluid passages configured to remove condensation from an interior of the first fluid passages prior to the condensation reaching the first fluid outlet characterised in that the counterflow heat exchanger further comprises a water removal and air re-entrainment apparatus disposed between the plurality of second fluid passages and the one or more drains; wherein the water removal and air re-entrainment apparatus includes a water removal chamber including multi-passage tortuous flow channels to separate condensate from airflow; wherein the water removal and air re-entrainment apparatus includes one or more air re-entrainment holes in the outlet manifold to re-introduce airflow from the water removal chamber into the outlet manifold. a first fluid inlet ; a first fluid outlet fluidly coupled to the first fluid inlet via a core section ; a second fluid inlet ; a second fluid outlet fluidly coupled to the second fluid inlet via the core section ; the core section including: a plurality of first fluid passages configured to convey the first fluid flow from the first fluid inlet toward the first fluid outlet ; a plurality of second fluid passages configured to convey the second fluid flow from the second fluid inlet toward the second fluid outlet such that the first fluid flow exchanges thermal energy with the second fluid flow at the core section; one or more drains disposed in the core section operably connected to the plurality of first fluid passages configured to remove condensation from an interior of the first fluid passages prior to the condensation reaching the first fluid outlet characterised in that the counterflow heat exchanger further comprises a plurality of first fluid passages configured to convey the first fluid flow from the first fluid inlet toward the first fluid outlet ; a plurality of second fluid passages configured to convey the second fluid flow from the second fluid inlet toward the second fluid outlet such that the first fluid flow exchanges thermal energy with the second fluid flow at the core section; one or more drains disposed in the core section operably connected to the plurality of first fluid passages configured to remove condensation from an interior of the first fluid passages prior to the condensation reaching the first fluid outlet characterised in that the counterflow heat exchanger further comprises a water removal and air re-entrainment apparatus disposed between the plurality of second fluid passages and the one or more drains; wherein the water removal and air re-entrainment apparatus includes a water removal chamber including multi-passage tortuous flow channels to separate condensate from airflow; wherein the water removal and air re-entrainment apparatus includes one or more air re-entrainment holes in the outlet manifold to re-introduce airflow from the water removal chamber into the outlet manifold. <EOS>