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