Process for manufacturing gas flow unit

A process for manufacturing a gas flow unit comprising the steps of providing a passage-forming core made of metal with low melting point, attaching a metal on the passage-forming core by electrocasting to provide a primary metal layer, forming a plurality of longitudinally extending grooves on said primary metal layer, filling said grooves with low-melting-point filler, attaching a metal on said primary metal layer by electrocasting to provide a secondary metal layer, circumferentially machining said secondary metal layer adjacent to opposite ends thereof to provide openings communicating with said grooves, heating said filler to melt the same, discharging the melted filler out of the secondary metal layer through said openings to provide a plurality of coolant passages defined by said grooves and said secondary metal layer, filling each of said openings with a manifold-forming core made of low-melting-point filler, attaching a metal on said manifold-forming cores and on said secondary metal layer adjacent to said manifold-forming cores by electrocasting to provide tertiary metal layers, forming a through hole on each of said tertiary metal layers so as to lead from outside to the corresponding manifold-forming core, dissolving said passage-forming core, discharging the dissolved passage-forming core out of the primary metal layer to provide a gas passage inside the primary metal layer, heating the manifold-forming cores to melt the same, discharging the melted manifold-forming cores out of the tertiary metal layers through said through holes to provide coolant manifolds defined by said openings and said tertiary metal layers.