In {HEAD ~ other embodiments}, the rows 50 may be positioned generally orthogonal to a direction of {TAIL ~ an average flow} of a gas 51 through the cavity 14 
In { HEAD ~ other embodiments } , the rows 50 may be positioned generally orthogonal to a direction of { TAIL ~ an average flow } of a gas 51 through the cavity 14
OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH