Dynamical charging and discharging of a capacitive mixing blue engine

Abstract

Where river water flows in to the sea a lot of entropy is created. A blue engine harvests (blue) energy from this increase in entropy. A device to obtain this energy is a capacitive mixing engine. This engine consists of two supercapacitor-like porous carbon electrodes immersed in water connected to a voltage source. Brogioli designed an equilibrium cycle that extracts this energy by changing the potential and switching the salt and fresh water accordingly. Brogioli calculated that the work per liter of fresh water was 1.6 kJ, which equals the energy of waterfall of 160 m. Because this is an equilibrium cycle, which takes infinitely long, the power output is 0. This Thesis focusses on finding the maximum power output for a Brogioli-like cycle by modeling the dynamics of a pore-reservoir system and using the Poisson and Nernst-Planck equations. Also the equilibrium cycle is calculated and yields a work of 2 kJ per liter of fresh water, which is in agreement with the results of Brogioli. The maximum power output is found around a cycle time of 2.7 mu s at 304 W m2, but highly depends on the flushing times and the length of the pore. If the flushing times are determined the maximum power output can be calculated more accurately.