A first part of the air stream which is admitted into the portion 23 is swirled by the member 40 to form a swirling stream having a ring shaped cross sectional outline and contacting the outermost layer of {HEAD ~ the flow} of {TAIL ~ liquid} issuing from the end portion of the section 31 
A first part of the air stream which is admitted into the portion 23 is swirled by the member 40 to form a swirling stream having a ring shaped cross sectional outline and contacting the outermost layer of { HEAD ~ the flow } of { TAIL ~ liquid } issuing from the end portion of the section 31
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