Comparative study of working fluids for OTEC power plants

The effect of three different working fluids (ammonia, propane, and freon-114) on the size of OTEC heat exchangers is analyzed. Seven different combinations of shell-and-tube heat exchangers are considered. For each combination, a simple computer model of the OTEC power system is used to compare the three fluids. The comparison is made on the basis of A/W/sub net/, where A is the total heat transfer area (evaporator plus condenser) and W/sub net/ is the net power output of the plant. Overall, ammonia is shown to be the best fluid (i.e., it yields the lowest value of A/W/sub net/), although in some cases only by a small margin. The thermophysical property that gives ammonia its general superiority is its relatively high thermal conductivity. The report also discusses heat exchanger design problems associated with liquid entrainment and boiling liquid superheat