Experimental Investigation of the Effect of Circular and Square Pipe Geometries on Flow Characteristics

Pipe cross-sectional geometry plays an important role in determining flow behavior, pressure losses, and hydraulic performance in piping systems. Although numerous studies have investigated pressure drop in circular pipes, experimental investigations on the influence of circular and square pipe geometries on flow characteristics under equivalent hydraulic dimensions remain limited. Therefore, this study experimentally investigates the effect of circular and square pipe geometries on flow characteristics using a laboratory-scale pressure drop test apparatus. Experimental testing was conducted using circular and square acrylic pipes with characteristic dimensions of 8 mm under identical operating conditions. The investigated parameters included pressure drop, shear stress, shear rate, apparent viscosity, Reynolds number, and friction factor. In addition, Computational Fluid Dynamics (CFD) simulations were performed using ANSYS Fluent to qualitatively visualize the pressure and velocity distributions within the test pipes and to support the interpretation of the experimentally observed flow behavior. The experimental results demonstrate that pipe cross-sectional geometry significantly influences internal flow characteristics. The square pipe consistently exhibits higher pressure drop, shear stress, and friction factor than the circular pipe under comparable flow conditions due to the non-uniform velocity distribution generated near the pipe corners. The friction factor decreases with increasing Reynolds number for both pipe geometries, while the apparent viscosity remains nearly constant throughout the investigated shear rate range, indicating fluid behavior that is close to Newtonian. The CFD pressure and velocity contours qualitatively support these observations by illustrating more pronounced pressure gradients and flow non-uniformity in the square pipe. These findings demonstrate that pipe cross-sectional geometry is an important factor affecting hydraulic behavior and energy losses in piping systems. The results provide experimental evidence that can support the evaluation and optimization of piping system performance in engineering applications Keywords : Flow Characteristics, Pressure Drop, Circular Pipe, Square Pipe, Computational Fluid Dynamics.