By offsetting the pedestals in the second row relative to the pedestals in the first row positioned upstream from the second row and by alternating the protrusions from the inner wall to the outer wall, or vice versa, {HEAD ~ a spiral flow} of gas may be created in {TAIL ~ the cavity} 
created in
By offsetting the pedestals in the second row relative to the pedestals in the first row positioned upstream from the second row and by alternating the protrusions from the inner wall to the outer wall , or vice versa , { HEAD ~ a spiral flow } of gas may be created in { TAIL ~ the cavity }
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