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Pamitran, Agus Sunjarianto
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Automotive Engineering Control & Systems Engineering Engineering Materials Science & Nanotechnology Mechanical Engineering

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Effect of water temperature on flow regimes and reynolds number in a passive natural circulation cooling system Setiawan, Putut Hery; Pamitran, Agus Sunjarianto; Yuliaji, Dwi; Pamungkas, Adhika Enggar; Budiman, Arif Adtyas; Amelia, Almira Citra; Maryadi, Shendy Akbar; Irwansyah, Ridho; Juarsa, Mulya
Jurnal Polimesin Vol 23, No 3 (2025): June
Publisher : Politeknik Negeri Lhokseumawe

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.30811/jpl.v23i3.6665

Abstract

Natural circulation flow is an important phenomenon of passive cooling systems in nuclear reactor thermal management during accidents. This experimental study investigates the effect of varying water temperatures on flow regimes and Reynolds number within a passive natural circulation system. The research was conducted using a rectangular TP-loop (FASSIP-04 Ver.2) made of 1-inch SS304 pipe, 6 m high and 1.32 m wide. The water temperature setting was varied at 45°C, 55°C, 65°C, and 75°C, with a heating power of 4.2 kW, and the cooling tank was maintained at 10°C. Observations were made during transient heating, steady-state (for 3 hours), and transient cooling phases. Results show that increasing the heating tank temperature reduces fluid density and viscosity, thereby enhancing buoyancy-driven flow. This led to a transition in flow regimes from laminar to turbulent as the temperature increased. The Reynolds number increased by 169.38% when the water temperature was raised from 45°C to 75°C. Unstable flow behaviour, including fluctuating amplitudes and frequencies, was observed—characteristic of natural circulation dynamics. The study confirms a strong correlation between thermal variation and flow regime transition, providing insights into the performance of passive cooling systems under varying thermal loads.
Experimental investigation of the impact of non-uniform pipe diameters on natural circulation and dimensionless flow in in a rectangular loop Roswandi, Iwan; Pamitran, Agus Sunjarianto; Juarsa, Mulya; Budiman, Arif Adtyas
Jurnal Polimesin Vol 23, No 3 (2025): June
Publisher : Politeknik Negeri Lhokseumawe

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.30811/jpl.v23i3.6666

Abstract

This experimental study investigates the effect of non-uniform pipe diameters on natural circulation flow within a rectangular loop related to non-dimensional numbers, such as the Reynolds number and the Grashof number. The study aims to understand how variations in pipe diameters influence natural circulation, which is critical for thermal engineering applications, including passive cooling systems for nuclear reactors and thermal management in electronic devices. Previous research by Vijayan et al., Garibaldi et al., and Elton et al. explored the impact of loop geometry on flow stability and heat transfer efficiency. In this study, a loop system with varying pipe diameters operates without a pump at atmospheric pressure. Data on fluid flow and temperature distribution were recorded at different temperature settings. The results show that fluid flow increases with temperature, decreasing fluid density and enhancing buoyancy forces. This increases the Reynolds number, reaching turbulent flow at 70°C throughout the loop. However, the 2-inch diameter hot leg remains in the transition region up to 90°C. The experimental correlation shows higher Grashof numbers than previous models, highlighting the significant impact of pipe diameter variations on buoyancy forces and flow transitions. These findings emphasize the importance of non-uniform pipe geometries in influencing natural circulation flow and its transition from laminar to turbulent flow, providing valuable insights for designing systems with non-uniform pipe configurations.
Co-Authors Amelia, Almira Citra Budiman, Arif Adtyas Dwi Yuliaji Maryadi, Shendy Akbar Mulya Juarsa PAMUNGKAS, ADHIKA ENGGAR Putut Hery Setiawan Ridho Irwansyah Roswandi, Iwan