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Heat Transfer Characteristics Simulation Based on Power Input Variation in a Natural Circulation U-Top Rectangular Loop

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Abstract:

Increasing demand for reliable and passive thermal management in modern energy systems, particularly in nuclear reactors, has elevated interest in natural circulation loops. Among the influencing factors, loop geometry and heating power are critical in natural circulation systems. This study investigates the effect of heating power on heat transfer in a rectangular VHVC natural circulation loop with an enlarged upper elbow radius of 350 mm. The analysis was conducted using CFD under steady-state conditions, employing a pressure-based solver with the realizable k-epsilon turbulence model and energy equation to simulate buoyancy-driven flow. Three power inputs 750 W, 1100 W, and 1540 W were applied to evaluate their effect on temperature distribution and energy absorption. Results show that increasing the heating power enhances buoyancy forces, leading to higher mass flow rate and stronger natural circulation within the loop. The fluid temperature difference between the heating and cooling sections rises with power input, which directly increases the convective heat transfer coefficient. Consequently, the obtained Nusselt number increased from 25.69 at 750 W to 31.23 at 1540 W. This finding confirms that higher heating power significantly improves the loop heat transfer performance, providing insight into the optimization of passive cooling systems in nuclear safety applications.

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Periodical:

Defect and Diffusion Forum (Volume 453)

Pages:

165-175

DOI:

https://doi.org/10.4028/p-0Jwi7w

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Online since:

July 2026

Authors:

Shendy Akbar Maryadi, Deendarlianto Deendarlianto, Sunandi Kharisma, Mulya Juarsa*

Keywords:

CFD, Heat Transfer, Natural Circulation, Passive Cooling, Power Variation

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© 2026 Trans Tech Publications Ltd. All Rights Reserved

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