This permits the tubing 18 to be of minimum area since heat exchange from the collector to {HEAD ~ the second fluid} will be conducted over {TAIL ~ a longer period} of time 
This permits the tubing 18 to be of minimum area since heat exchange from the collector to { HEAD ~ the second fluid } will be conducted over { TAIL ~ a longer period } of time
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH