A fresh supply of solution to {HEAD ~ the face} of the membrane is provided by {TAIL ~ a stirrer} 
A fresh supply of solution to { HEAD ~ the face } of the membrane is provided by { TAIL ~ a stirrer }
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL