Simulation on Power Effect in Natural Circulation Flow using U-top Rectangular Loop

Abstract

The influence of geometry and heating power on the natural circulation process is a crucial consideration for the development of passive cooling systems. This study investigates the effect of varying heating power on the thermal and hydrodynamic behavior of a single-phase natural circulation in a rectangular loop with a U-shaped top. The simulations were performed using CFD, using a pressure-based solver with a realizable k-ε turbulence model and steady-state energy equations. The loop has a height of 2812 mm, a width of 950 mm, and a top elbow of radius 350 mm. Heating power was applied to the lower vertical section of the loop using direct contact heating elements, with varying power of 750 W, 1100 W, and 1540 W. A cooling section is located in the upper vertical section whit a constant temperature of 10°C.The simulation results show increasing heating power significantly enhances fluid temperature (from 48.39 °C to 80.95 °C), flow velocity (from 0.067 m/s to 0.0795 m/s), and mass flow rate (from 0.03352 kg/s to 0.04332 kg/s), indicating a stronger buoyancy effect. Furthermore, the flow regime transitions from laminar to transitional with higher power input. These findings underline the critical role of thermal input and geometric configuration in natural circulation systems.