Experimental study on the effect of thrust bearing surface roughness on circulator pump performance

Purpose This paper presents an experimental investigation into the effect of thrust bearing surface roughness on the performance of a wet rotor circulator pump. The aim of this study is to clarify how different surface roughness levels influence the hydraulic and energy performance characteristics of the pump under controlled laboratory conditions. In contrast to the limited number of existing works addressing thrust bearing surface finish in circulator pumps, this study provides quantitative evidence of its influence on efficiency by explicitly evaluating the Energy Efficiency Index (EEI). Design/methodology/approach Thrust bearings with three distinct levels of surface roughness (Ra ≈ 0.79 µm for stainless steel, Ra ≈ 0.19 µm for alumina ceramic and Ra ≈ 0.08 µm for silicon carbide) were evaluated under consistent operating conditions using a certified test stand in accordance with EN 16297 and ISO 9906 standards. For each bearing type, the pump was operated for 1 h to achieve steady-state conditions, and the tests were repeated four times to minimize uncertainty. Findings The findings reveal that increased surface roughness leads to elevated friction losses between rotating and stationary elements, resulting in higher power demand and reduced overall pump efficiency. Bearings with smoother surfaces demonstrated improved hydraulic performance and lower energy usage. The average EEI values were 0.213 for stainless steel, 0.204 for alumina ceramic and 0.198 for silicon carbide, indicating a clear correlation between reduced surface roughness and improved efficiency. The results provide practical guidance for reducing energy consumption and extending pump lifespan. Research limitations/implications This study focuses on steady-state experimental tests conducted under controlled laboratory conditions to evaluate the effect of thrust bearing surface roughness on pump performance and EEI. While the results clearly demonstrate the influence of surface finish, long-term operation and progressive wear effects were beyond the scope of the present work. In addition, the investigation was performed on a single pump configuration and operating range. Future studies extending the analysis to long-term testing, different pump designs and varying operating conditions would further enhance understanding of the durability and energy performance implications. Originality/value This study offers original quantitative evidence on the effect of thrust bearing surface roughness on the performance of wet rotor circulator pumps by directly linking surface finish to the EEI. Unlike most existing studies focusing solely on lubrication theory or computational models, this work presents real-world performance data, including EEI measurements in accordance with EN 16297. The study isolates surface roughness as the dominant parameter under standardized test conditions, providing practical insights for pump designers and manufacturers on improving energy efficiency through surface finishing without altering pump geometry or materials.