Thermo-hydraulic performance of connected single-phase natural circulation loops characterized by two different inner diameters

Misale, Mario; Bocanegra, Johan Augusto; Marchitto, Annalisa

doi:10.1016/j.icheatmasstransfer.2021.105309

Cited by 17 publications

(8 citation statements)

References 30 publications

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“…Those relationships have been validated by comparison with experimental data from laboratories worldwide. In recent years experimental works validated the applicability of the analytical model to NCL with a small inner diameter connected in parallel [7], [8].…”

Section: Introductionmentioning

confidence: 91%

Lattice Boltzmann model of a square natural circulation loop with small inner diameter: working fluid effects

Bocanegra

Misale

2023

J. Phys.: Conf. Ser.

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Natural circulation loops are systems used to transport heat by the free convection of a working fluid in a closed thermo-hydraulic circuit. Many examples of the Lattice Boltzmann method applied to free convection can be found in the literature, but most of them are limited to model simple enclosures. This work is one of the first approaches to an engineering system as the Natural Circulation Loops using this numerical method. This study describes the implementation and validation of a numerical model of a rectangular loop characterized by a small inner diameter. This research is focused on the thermohydraulic response of the NCL varying the working fluid. We have obtained satisfactory results demonstrating that accepted analytical correlations for the steady-state behavior are reproduced by the thermal Lattice Boltzmann Method (double distribution function). Overall, these results suggest that the temperature and velocity oscillations during the transient increase directly with the fluid Prandtl number; instead, the temperature difference between the vertical legs is inversely correlated and decreases.

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Section: Introductionmentioning

confidence: 91%

Lattice Boltzmann model of a square natural circulation loop with small inner diameter: working fluid effects

Bocanegra

Misale

2023

J. Phys.: Conf. Ser.

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“…The loop considered here works with the fixed temperature at the heater (T H ) and cooler (T C ), also known as NCL with heat end exchangers [15]. Recently was shown that this kind of square mini-loops can work connected in parallel to convoy more thermal energy, and the thermohydraulic performance remains stable even if the heating power in one circuit changes [7,16].…”

Section: Ncl Descriptionmentioning

confidence: 99%

Thermal performance investigation of a mini natural circulation loop for solar PV panel or electronic cooling simulated by lattice Boltzmann method

Bocanegra¹,

Marchitto²,

Misale³

2022

Int. J. EQ

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The natural circulation loop (NCL) consists of a thermal-hydraulic system that convoys thermal energy from a heat source to a heat sink without a pump. Applications of those loops can be found in solar energy, geothermal, nuclear reactors, and electronic cooling. The lattice Boltzmann method is a numerical method that can simulate thermal-fluid dynamics, using a mesoscopic approach based on the Boltzmann equation for the density function. A square NCL model with fixed temperatures at the heater and heat sink sections was developed in a bi-dimensional lattice with double distribution dynamics, one distribution for the hydrodynamic field and the other for the thermal field. The different cooler-heater configurations (vertical or horizontal) were investigated. We found that by positioning the source or sink vertically, the flow direction can be controlled. In contrast, in a loop with symmetric horizontal heater -horizontal cooler configuration where both fluid directions are equally probable. The effectiveness of the loop was studied by calculating the heat sink temperature gradient. The lower value was obtained for the horizontal heater horizontal cooler orientation (0.71) and the higher value for the vertical heater vertical cooler configuration with an increment of 34%; simultaneously, the flow rate (Reynolds number) was reduced by 47%.

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“…The stability of an NCL is a primordial problem because, under some operational parameters and loop geometries, the flow direction can be inverted, and the system flow can become chaotic [5], an undesirable situation for critical engineering applications that require predictable heat flux removal. In recent years, experimental works have found that localized pressure losses can stabilize the loops [6], and it was also found that an NCL with a small inner diameter is stable and can work connected in parallel [7,8] with small disturbances even if the power provided to one parallel loop changes. 928 Previous works have evaluated the performance of rectangular-shaped, single-phase NCLs with end heat exchangers mainly by developing analytical models, simulations, or experiments.…”

Section: Introductionmentioning

confidence: 99%

Study of a Square Single-Phase Natural Circulation Loop Using the Lattice Boltzmann Method

Bocanegra,

Marchitto,

Misale

2023

Applied Mechanics

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Natural circulation loops are thermohydraulic circuits used to transport heat from a source to a sink in the absence of a pump, using the forces induced by the thermal expansion of a working fluid to circulate it. Natural circulation loops have a wide range of engineering applications such as in nuclear power plants, solar systems, and geothermic and electronic cooling. The Lattice Boltzmann Method was applied to the simulation of this thermohydraulic system. This numerical method has several interesting features for engineering applications, such as parallelization capabilities or direct temporal convergence. A 2D model of a single-phase natural circulation mini-loop with a small inner diameter was implemented and tested under different operation conditions following a double distribution function approach (coupling a lattice for the fluid and a secondary lattice for the thermal field). An analytical relationship between the Reynolds number and the modified Grashof number was used to validate the numerical model. Two regimes were found for the circulation, a laminar regime for low Reynolds numbers and a non-laminar regime characterized by a traveling vortex near the heater and cooler’s walls. Both regimes did not present flux inversion and are considered stable. The recirculation of the fluid can explain some of the heat transfer characteristics in each regime. Changing the Prandtl number to a higher value affects the transient response, increasing the temperature and velocity oscillations before reaching the steady state.

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Thermo-hydraulic performance of connected single-phase natural circulation loops characterized by two different inner diameters

Cited by 17 publications

References 30 publications

Lattice Boltzmann model of a square natural circulation loop with small inner diameter: working fluid effects

Lattice Boltzmann model of a square natural circulation loop with small inner diameter: working fluid effects

Thermal performance investigation of a mini natural circulation loop for solar PV panel or electronic cooling simulated by lattice Boltzmann method

Study of a Square Single-Phase Natural Circulation Loop Using the Lattice Boltzmann Method

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