The packed tower includes a packing arrangement including a lower bed of mobile packing elements, and {TAIL ~ an adjacent upper bed} of {HEAD ~ fixed packing elements} 
The packed tower includes a packing arrangement including a lower bed of mobile packing elements , and { TAIL ~ an adjacent upper bed } of { HEAD ~ fixed packing elements }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD