Salinity-Dependent Volumetric Flow Rate of Aqueous NaCl Solutions (0-40 g L⁻¹) in a Pump-Driven System: Implications for Saline Irrigation

Rising sea levels are increasing the salinity of irrigation water in low-lying coastal regions such as Indonesia, which makes it important to understand how dissolved salt changes the way water flows. This study investigated how sodium chloride concentration, from 0 to 40 g L⁻¹ in 5 g L⁻¹ steps, affects the volumetric flow rate of an aqueous solution driven by a fixed-power submersible pump. Flow rate was recorded with a Vernier flow rate sensor, using five trials per concentration at a constant temperature of 25 °C. Flow rate fell steadily with increasing concentration, from 0.126 to 0.066 (a reduction of about 48%). Assuming flow rate is inversely proportional to dynamic viscosity, as in Poiseuille’s Law with constant pressure difference and geometry, the corresponding viscosity was inferred to rise from 0.890 mPa s to 1.70 mPa s. A plot of reciprocal viscosity against flow rate was linear (R² = 0.9999), with a gradient of 8.91 ± 0.54 found by the minimum–maximum method. The results show that flow rate decreases consistently with salinity, and they suggest that salinity-driven changes in fluid properties could affect the efficiency of irrigation systems. Limitations include the non-cylindrical flow geometry, the assumption of constant pump pressure, and the lack of a direct viscosity measurement.