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