Impeller backface cooled P3 passage through diffuser/reducing high temp exposure of cooled air

A gas turbine engine comprising:

• a combustor;
• a compressor impeller rotational coupled to a turbine by a shaft;
• a gas generator case comprising:
• an outer annular wall surrounding the combustor to form a combustor cavity and surrounding the compressor impeller to form a bleed air cavity;
• an inner annular wall extending radially inward from the outer annular wall to separate the combustor cavity from the bleed air cavity, wherein the inner annular wall and the outer annular wall are concentric with respect to an axis;
• and
• a diffuser integrally formed with the inner annular wall, the diffuser comprising:
• a plurality of tubes, each tube extending from an exterior surface of the diffuser to a distal end radially outward from the exterior surface;
• a plurality of diffuser pipes, each diffuser pipe joins with a different tube of the plurality of tubes and includes a first portion that extends in a radial direction and a second portion extending in an axial direction;
• and
• a plurality of diffuser passages, each diffuser passage extending from an inlet at an interior surface of the diffuser through one of the tubes and one of the diffuser pipes to an outlet at the distal end of the diffuser pipe;
• and
• a cooling tube assembly comprising:
• a first tube extending from a cooling inlet through the inner annular wall;
• a second tube extending through the inner annular wall to a cooling outlet;
• and
• a third tube joined with the first tube and the second tube,
• wherein the first tube and the second tube are joined with the inner annular wall, and
• wherein the first tube, the second tube, and the third tube define a cooling passage from the cooling inlet to the cooling outlet, and
• wherein the cooling outlet extends along a direction that is oblique to a longitudinal direction of the second tube and fluidly communicates with a back side surface of the compressor impeller.