{HEAD ~ The cross section} of flow of the tube 20 in {TAIL ~ this region} is given a transition radius R, the size of which in principle depends on the flow inside the tube 20 
in
{ HEAD ~ The cross section } of flow of the tube 20 in { TAIL ~ this region } is given a transition radius R , the size of which in principle depends on the flow inside the tube 20
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH