EDI electric desalination equipment achieves deep water desalination through electric field drive and the selective permeability of ion exchange membranes. Its core mechanism relies on the directional migration of ions under the influence of an electric field. Temperature fluctuations, as a key environmental parameter, directly affect ion migration rates by altering the physical and chemical properties of water, thereby affecting the equipment's water quality and operational stability.
Water viscosity is the direct mediator through which temperature influences ion migration. When the temperature decreases, hydrogen bonds between water molecules strengthen, resulting in a significant increase in water viscosity. This increased viscosity directly hinders Brownian motion of ions, increasing the resistance to ion migration within the membrane. For example, the viscosity of water at 5°C is 70% higher than at 25°C. At low temperatures, ion migration rates decrease, requiring increased voltage to compensate for the power. At high temperatures, ion activity increases, but excessively high temperatures can reduce the exchange efficiency of ion-selective membranes and even induce ion leakage.
The relationship between ion migration rate and temperature can be described by the Arrhenius equation: for every 1°C increase in temperature, the module resistance decreases by approximately 2%. In EDI electric desalination equipment, this change manifests as follows: Under high temperature conditions, ion kinetic energy increases, accelerating migration rates, but product water quality may decline due to ion leakage. Under low temperature conditions, ion kinetic energy decreases, migration rates slow, and product water quality may deteriorate due to ion retention. For example, when the temperature drops from 25°C to 15°C, product water quality declines due to reduced ion migration efficiency. Furthermore, when the temperature exceeds 35°C, the amount of ions adsorbed onto the ion exchange resin decreases, resulting in similar deterioration in product water quality.
Voltage regulation is a key measure for addressing temperature fluctuations. At low temperatures, water viscosity increases, increasing resistance to ion migration. In this case, increasing voltage is necessary to enhance the electric field driving force to maintain ion migration rate. Industry practice shows that when the water temperature drops below 25°C, the voltage should be increased by 10% for every 10°C decrease in temperature to compensate for power loss caused by increased viscosity. At high temperatures, ion activity increases, and excessively high voltages can lead to increased ion polarization and diffusion, resulting in reduced product water quality. Therefore, voltage regulation must dynamically match temperature changes to achieve optimal control of ion migration rate.
The impact of temperature fluctuations on EDI electric desalination equipment is also reflected in changes in module resistance. Under given voltage conditions, rising temperature reduces module resistance, resulting in an increase in current; falling temperature increases module resistance, resulting in a decrease in current. This resistance-temperature relationship requires real-time monitoring of resistance changes during equipment operation and voltage adjustment to maintain current stability. For example, if module resistance increases due to falling temperature, maintaining the same voltage will reduce current, resulting in insufficient ion migration momentum and reduced product water quality. Conversely, excessively high voltage may cause electrode corrosion and membrane degradation.
Production water quality is the ultimate reflection of temperature fluctuations. At low temperatures, reduced ion migration rates can lead to a decrease in product water resistivity, potentially failing to meet ultrapure water standards. At high temperatures, ion leakage can cause a sudden drop in product water resistivity and increase the content of weak electrolytes (such as silicon dioxide and boric acid) in the water. Therefore, EDI electric desalination equipment requires temperature compensation mechanisms (such as temperature correction for resistivity meters) and dynamic voltage regulation to ensure stable permeate quality under varying temperature conditions.
Coordinated control of pressure and flow is a key auxiliary measure for coping with temperature fluctuations. A decrease in temperature increases water viscosity, leading to a rise in system pressure. In this situation, the inlet and product pressures must be adjusted to maintain a pressure differential between the dilute and concentrate chambers within a range of 0.03-0.05 MPa to prevent membrane deformation and ion retention in the concentrate chamber. Furthermore, flow distribution must be dynamically adjusted based on temperature fluctuations to avoid mechanical damage to the membrane due to excessive flow or resin clogging due to insufficient flow.
The impact of temperature fluctuations on the ion migration rate of EDI electric desalination equipment is multidimensional and dynamic. Temperature compensation mechanisms, dynamic voltage regulation, and coordinated pressure and flow control can effectively offset the adverse effects of temperature fluctuations and ensure stable equipment operation under varying environmental conditions.
