列管式固定管板换热器设有折流板，其主要作用是（ ）。

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SQL Error: select id,body,options from ***_enewstiku where sourceid='24911' and id < 2125226 and id<>'2125226' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='24911' and id > 2125226 and id<>'2125226' order by id asc limit 5