TURBINE ENGINE WITH PREHEAT OF CRYOGENIC FUEL VIA INTERMEDIATE FLUID

A turbine engine has: a compressor; a combustor; a turbine; a gaspath (90) passing downstream from the compressor through the combustor and then through the turbine; a fuel source; a fuel flowpath from the fuel source to the combustor; and a heat exchanger for transferring heat from the gaspath (90) to the fuel flowpath. The heat exchanger has: an inner wall (250) in heat transfer relation with the gaspath (90); an outer wall (252); tubes between the inner wall (250) and the outer wall (252) bounding respective segments of the fuel flowpath; and a heat transfer fluid (140) between the inner wall (250) and the outer wall (252) and in heat transfer relation with the tubes and the inner wall (250).