The melt circulation through {TAIL ~ the conduits} is caused by the difference in the levels and densities of {HEAD ~ the melt} in these vessels 
The melt circulation through { TAIL ~ the conduits } is caused by the difference in the levels and densities of { HEAD ~ the melt } in these vessels
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH