Performance assessment of a marine freshwater generator through exergetic optimization

Abstract

The objective of this study is to examine the effect of operating parameters on the freshwater generation capacity of a vacuum type and low-temperature single-stage freshwater generator and the exergy destruction of the condenser and evaporator sections. Evaporator and condenser, which are plate type heat exchangers, are modeled using the ε-NTU method. Energy and exergy analyses were applied to the control volume enclosing the condenser and evaporator to find the freshwater production rate and to investigate the system performance. A parametric study was performed to assess the effects of the jacket water mass flow rate, the seawater salinity, and the seawater temperature on the output parameters (fresh water production rate and specific exergy destruction). In addition, an optimization study was performed using the Taguchi method to maximize the freshwater production rate and minimize the exergy destruction rates of the condenser and evaporator. The results derived from the parametric study showed that the seawater temperature of 31.88 °C and jacket water mass flow rate of 72,000 kg/h are the required values to obtain the maximum freshwater generation capacity (30 m3/day). When the salinity increases from 3 g/kg to 41 g/kg (3000 to 41,000 ppm), the freshwater production rate increases by 2.18% and 5.06% under the constant seawater temperature (23 °C) and the jacket water mass flow rate (58,500 kg/h), respectively. The optimization results revealed the conditions to obtain the maximum fresh water production rate and the minimum exergy destruction.