How UVP-DUO Helps to Analyze Heat and Momentum Transfer in Low Prandtl Number Fluids

2 July 2024 by
How UVP-DUO Helps to Analyze Heat and Momentum Transfer in Low Prandtl Number Fluids
Met-Flow SA

Summary of the Experiment: 

The study conducted by Hokkaido University aimed to investigate the heat and momentum transfer characteristics in low Prandtl number (Pr) fluids using Ultrasonic Velocity Profiling (UVP). Liquid gallium, a low Pr fluid, was used to understand the behavior of thermal plumes and buoyant blobs. The experiments focused on two main scenarios: the injection of a thermally buoyant blob and the behavior of a starting plume cooled from above. The objective was to gain insights into the convective motions driven by thermal buoyancy, which are significant in both natural and industrial processes.

UVP-DUO Usage: 

The UVP-DUO system by Met-Flow was employed to capture detailed velocity profiles of the liquid gallium. The experimental setup included a thin acrylic container (150mm x 270mm x 15mm) filled with liquid gallium up to 205mm in height. Three 4 MHz ultrasonic transducers (A, B, and C) were positioned to measure vertical and horizontal velocity distributions. Key setup parameters included:

  • Ultrasonic Frequency: 4 MHz
  • Transducer Positions: A for vertical axis, B and C for horizontal axes
  • Measurement Particles: Fine powder of ZrB2 (50 μm diameter)
  • Temperature Control: Experiments conducted at various temperature differences (ΔT)

Result of the Experiment and How UVP-DUO Contributed: 

The experiments revealed important findings on the behavior of buoyant blobs and starting plumes in low Pr fluids. In the injection of a thermally buoyant blob, the UVP-DUO captured the formation of vortex structures and their decay, depending on the direction of buoyancy forces relative to the blob's advection. When the buoyant force opposed the blob's movement, the vortex structure decayed rapidly.

In the starting plume experiment, the UVP-DUO measured both heat and momentum transfer velocities. The results showed that the translational velocity of the thermal plume was slightly higher than the momentum transfer velocity, indicating faster heat transfer. The UVP-DUO provided high-resolution velocity profiles, allowing for detailed analysis of plume behavior and entrainment effects.

Overall, the UVP-DUO's precise measurements were crucial in visualizing and understanding the complex dynamics of heat and momentum transfer in low Pr fluids. This study demonstrates the effectiveness of UVP-DUO in advancing the knowledge of thermal convection processes in opaque fluids, contributing to both scientific research and industrial applications.

Read the full paper on the Digital Library here.

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