A specular layer is secured to the support on the internal channel surface to provide {HEAD ~ a relatively highly reflective surface} over {TAIL ~ the region} of the support facing the tube 
over
A specular layer is secured to the support on the internal channel surface to provide { HEAD ~ a relatively highly reflective surface } over { TAIL ~ the region } of the support facing the tube
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH