regenerative heater. The source water will flow down through a packed bed where it will
meet the heated air and a portion of the water will evaporate into the air stream. The
saturated air exiting the diffusion tower will enter a countercurrent flow oriented direct
contact condenser. The fresh water exiting the condenser will enter a fresh water storage
tank where a portion is the product and a portion is pumped through a heat exchanger to
be cooled and then cycled back to the condenser. For all calculations it is assumed that
the sink temperature is 15 oC.
Operation Conditions
Using the analysis described at the beginning of the chapter, Figure 4-12 shows the fresh
water production flux for varying diffusion tower liquid mass fluxes. For the analysis the
condenser air mass flux is 1.5 kg/m2-S and the fresh water mass flux is 3.0 kg/m2-S.
These values were determined by Li et al. [l l] to be the optimal operating conditions of
the direct contact condenser using the HD Q-PAC packing material. It is also assumed
that the surface areas of the condenser and diffusion tower are the same. The condenser
was analyzed using the model proposed by Li et al. [17]. As seen from Figure 4-12, there
is an optimal fresh water production flux for an inlet water temperature of 30 oC at a
liquid mass flux of about 0.20 kg/m2-S. Figure 4-13 depicts the total energy consumption
for the DDD process with varying diffusion tower liquid mass flux. From the graph the
total energy consumption for an inlet water temperature is optimal in the range of liquid
mass fluxes from 0.1-0.2 kg/m2-s. It is fortunate that the optimal total energy
consumption and maximum fresh water production occur in the same range. The optimal
diffusion tower liquid mass flux is therefore taken to be 0.15 kg/m2-s. It is worthy to
note that the energy consumption of the DDD process demonstrated is nearly five times