Research On Energy Conversion Of Salt Difference Energy Based On Single-Pore Membrane

Osmotic energy(salinity gradient energy)between river water and seawater is a potential renewable energy.Reverse electrodialysis technology can realize the diffusion of cations or anions in high concentration solution to low concentration side by using ion selective film to generate electric energy.It has the advantages of low investment cost,high energy density and high efficiency.However,the conversion and collection of permeation energy are restricted by the low power density and conversion efficiency in actual production.Based on the finite element analysis method,this paper aims to obtain high-performance salinity gradient energy conversion performance.Focusing on how to improve output power and efficiency,this paper studies and analyzes the conversion characteristics of osmotic energy when different wall modifications and external condition parameters change,and optimizes the structural parameters of nanopores to achieve efficient salinity gradient energy generation.The main research content is divided into the following three parts :Firstly,the enhancement effect of the charged surface on power and efficiency under different parameters is studied,and the corresponding optimal power charging region is explored.It is found that when the external surface charge passes through nanopores with shorter length,wider diameter and larger surface charge density or at higher salt concentration gradient,the promotion effect on the output power of osmotic energy conversion is more significant.The optimal charge width of the charged ring region near the nanopore is inversely proportional to the pore length,and linearly related to the pore size,salt concentration gradient and surface charge density.Secondly,considering the wall slip can reduce the viscous friction at the solid-liquid interface,thereby promoting ion diffusion and increasing power.In this paper,the slip effect of different walls of nanopores is considered to break the balance between ion selectivity and permeability.The results show that the low concentration side slip wall can simultaneously increase the ion permeability and selectivity of the nanopore,and significantly improve the power and energy conversion efficiency,while the effect of the high concentration side slip wall on the permeability energy conversion performance can be ignored.Moreover,the promoting effect of wall slip on the permeability energy conversion process of ultrashort nanopores is also explored in combination with the charged outer surface.Finally,based on the actual situation,the influence of trace high valence ions in real seawater and river water on the performance of osmotic energy conversion is considered.The results show that when the wall is negatively charged,trace divalent ions act as counterions to significantly inhibit power and conversion efficiency.When the pore length is 25 nm,the power and efficiency decrease by 57% and 56%,respectively.The main reason for the decrease of the permeability performance is the valence state of the ions and the lower diffusion coefficient.Moreover,the divalent ion as the same ion has a weak effect on the permeability performance.At the same time,combined with the charged outer surface,the permeation energy conversion process of ultra-short nanopores was explored.It was found that when the charged width of the outer wall of the membrane was about 200 nm,it reached the commercial standard,which was not related to the presence of divalent ions.