Providing design guidelines for improving efficiency in power transmission devices
Osaka, Japan – Researchers have clarified the mechanisms by which energy loss is locally maximized at a certain rotational speed in gas-liquid two-phase flows driven by rotors, providing fundamental insights for energy savings and optimal design and operation in complex industrial equipment. Using the supercomputer "SQUID", a joint team from The University of Osaka, The University of Tokyo, and RIKEN analyzed detailed data on fluid motions and revealed that torque maximization arises not only from rotor-liquid surface collisions but also from significant pressure imbalances. This phenomenon was observed when the gas-liquid interface wave was in a resonant state. The outcomes, published in Multiphase Science and Technology, deepen the understanding of fluid resistance and agitation losses in power transmission devices.
Rotor-driven gas-liquid two-phase flows, used in various industrial applications such as power transmission devices, cooling systems and chemical agitators, exhibit complex flow phenomena that depend on rotational speed and liquid fill ratio, significantly impacting performance and efficiency. The total energy loss is dominated by fluid agitation. Therefore, elucidating the mechanism and reducing losses have been long-standing challenges. When a rotating body periodically drives the flow, a sloshing phenomenon occurs, leading to significant oscillations of the gas-liquid interface. Such "time-varying" characteristics during resonance are important from the perspectives of mechanical failure risk and energy efficiency, and have been extensively studied. Recent studies have demonstrated that, under resonance conditions, the torque (a "time-averaged quantity") exhibits peaks, thereby maximizing losses. Although such a local maximization was observed at the natural frequency of interface waves, the underlying mechanism have been unclear.
Integration of experiments and numerical simulations uncovered the core principles of loss maximization. Twofold causes are identified as i) direct collisions between the rotor and the liquid surface and ii) pressure imbalances around the rotor, suggesting the relevance of the enhanced fluid motion drawn toward the front of the rotor and the intensified flow instability behind it.
The insights from this research are expected to generate the following benefits:
- Improving energy efficiency: Understanding the mechanism behind loss maximization enables avoiding the resonant state and optimizing the rotor shape. It achieves energy savings, contributing to a sustainable society.
- Enhancing reliability and longer lifespan: Torque maximization can impose excessive loads on mechanical components, potentially leading to failure and wear. Elucidating the mechanism enables preemptive assessment of mechanical failure risks, leading to more robust and longer-lasting designs.
- Providing new design guidelines: The knowledge of the significant pressure imbalance impacting energy loss offers novel design guidelines. It leads to the development of system configurations that optimize agitation, cooling and so on.
"Gas-liquid two-phase flows driven by rotors are commonly observed around us. However, their internal structures remain poorly understood. Large-scale numerical simulations complement experiments, enabling detailed spatiotemporal analysis and helping gain fundamental insights into the factors causing losses. We expect that our outcomes will pave the way for shifting from empirical rule-based to theory-based design and accelerate the development of energy-efficient machinery" affirmed Mayu Kawamura, the lead author of the study.
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The article, “Mechanisms of torque maximization in gas-liquid two-phase flows driven by a pressure-loss-dominant rotor in a stationary cylindrical container,” has been published in
Multiphase Science and Technology at DOI:
https://doi.org/10.1615/MultScienTechn.2025060620