Screw compressor having a discharging passage with enlarged cross section area

A screw compressor comprising:

• a male rotor and a female rotor each including a rotor tooth section that has a plurality of helical teeth, the male rotor and the female rotor rotating in engagement with each other;
• a casing including a main casing having a bore formed in such a manner as to accommodate the male rotor and the female rotor, and a discharge-side casing closing a discharge side of the bore;
• and
• a discharge passage including a discharge port that opens in a rotational axis direction of the male rotor and the female rotor on a surface of the discharge-side casing close to the bore, compressed gas flowing from the discharge port circulating in the discharge passage, wherein
• the male rotor and the female rotor are each configured such that a discharge-side end surface of the rotor tooth section serves as a discharge-side distal end of the male rotor or the female rotor in the rotational axis direction,
• the discharge passage includes an enlarged flow passage section formed such that the enlarged flow passage section extends from the discharge port in the rotational axis direction of the male rotor and the female rotor and that a flow passage cross-sectional area of the enlarged flow passage section is gradually enlarged from the discharge port to a downstream side in a compressed gas flow direction,
• the discharge passage further includes branch flow passage sections that diverge the compressed gas flowing via the enlarged flow passage section into a plurality of flows,
• the branch flow passage sections are branched in such a manner as to spread outward, and
• the branch flow passage sections are branched in a spiral fashion.