Numerical analysis of boiling in a horizontal pipe flow of a non azeotropic mixed mass

Chao Huang; Xiaohu Liu; Lijiao Gong; Mingting Wu; Mingfei He; Chao Huang; Xiaohu Liu; Lijiao Gong; Mingting Wu; Mingfei He

doi:10.3934/energy.2025050

AIMS Energy

2025, Volume 13, Issue 5: 1347-1364. doi: 10.3934/energy.2025050

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Research article

Numerical analysis of boiling in a horizontal pipe flow of a non azeotropic mixed mass

1.
Xinjiang Tianfu Energy Co., Ltd., Xinjiang, Shihezi 832000
2.
School of Energy and Materials, Shihezi University, Shihezi, Xinjiang 832000, China
3.
Institute of Bingtuan Energy Development Research, Shihezi University, Shihezi, Xinjiang 832000, China

Received: 30 May 2025 Revised: 28 October 2025 Accepted: 06 November 2025 Published: 14 November 2025

Non-azeotropic mixtures have attracted wide attention because they can reduce irreversible losses in heat exchangers and improve energy utilization efficiency. In this study, the heat and mass transfer characteristics during the boiling process of a non-azeotropic binary working-fluid mixture R601/R601a (1/3) in a horizontal tube (considering gravitational effects) were numerically analyzed using computational fluid dynamics (CFD) based on the VOF and k-ε turbulence models. The results indicate that the flow boiling behavior of the working fluid is strongly influenced by the coupling between thermal and hydrodynamic loads. Within the simulated operating range, when the inlet mass flow rate is low, the heat transfer coefficient becomes highly unstable, showing large fluctuations and poor overall heat transfer. With an appropriate increase in flow rate and heat-flux density, the heat-transfer performance improves significantly, and the Nusselt number becomes higher and more stable. At low flow rates, R601 reaches its saturation temperature, allowing vapor bubbles to pass through the main stream and form a vapor film near the upper wall. In contrast, the higher-boiling R601a undergoes only subcooled boiling, where bubbles shrink or collapse within the subcooled liquid core and cannot reach the upper wall. The observed two-phase flow differences are dominated by the boiling points of the components and the degree of subcooling in the main flow.
- non azeotropic,
- binary mixed media,
- horizontal tube,
- flow boiling,
- numerical analysis
Citation: Chao Huang, Xiaohu Liu, Lijiao Gong, Mingting Wu, Mingfei He. Numerical analysis of boiling in a horizontal pipe flow of a non azeotropic mixed mass[J]. AIMS Energy, 2025, 13(5): 1347-1364. doi: 10.3934/energy.2025050

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Abstract

Non-azeotropic mixtures have attracted wide attention because they can reduce irreversible losses in heat exchangers and improve energy utilization efficiency. In this study, the heat and mass transfer characteristics during the boiling process of a non-azeotropic binary working-fluid mixture R601/R601a (1/3) in a horizontal tube (considering gravitational effects) were numerically analyzed using computational fluid dynamics (CFD) based on the VOF and k-ε turbulence models. The results indicate that the flow boiling behavior of the working fluid is strongly influenced by the coupling between thermal and hydrodynamic loads. Within the simulated operating range, when the inlet mass flow rate is low, the heat transfer coefficient becomes highly unstable, showing large fluctuations and poor overall heat transfer. With an appropriate increase in flow rate and heat-flux density, the heat-transfer performance improves significantly, and the Nusselt number becomes higher and more stable. At low flow rates, R601 reaches its saturation temperature, allowing vapor bubbles to pass through the main stream and form a vapor film near the upper wall. In contrast, the higher-boiling R601a undergoes only subcooled boiling, where bubbles shrink or collapse within the subcooled liquid core and cannot reach the upper wall. The observed two-phase flow differences are dominated by the boiling points of the components and the degree of subcooling in the main flow.

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