Insights into two-phase flow dynamics in closed-loop pulsating heat pipes utilizing Fe₃O₄/water: experimental...

Area of Science:

• Heat Transfer
• Fluid Dynamics
• Nanotechnology

Background:

• Pulsating Heat Pipes (PHPs) are efficient passive two-phase heat transfer devices.
• Understanding fluid behavior and phase change is crucial for optimizing PHP performance.
• Nanofluids offer potential for enhanced thermal conductivity and heat transfer characteristics.

Purpose of the Study:

• To visualize and analyze two-phase flow patterns in a PHP using a Fe3O4/water nanofluid.
• To investigate bubble formation, expansion, and phase change phenomena in the evaporator section.
• To develop a model for bubble generation and growth and assess the impact of heat load on flow dynamics.

Main Methods:

• Utilized a high-speed video camera for dynamic flow visualization.
• Employed Fe3O4/water nanofluid at 3 V/V% concentration as the working fluid.
• Varied heat inputs from 10 to 80 W to study evaporator section behavior.
• Assessed nanofluid stability over a 4-day period.

Main Results:

• Observed distinct bubble formation and expansion processes.
• Developed a model for bubble generation and growth.
• Noted self-adjusting flow patterns (slugs and plugs) with increasing heat load at a 50% filling ratio.
• Fe3O4/water exhibited more oscillatory flow than pure water, leading to faster annular flow.
• Confirmed Fe3O4/water nanofluid stability over 4 days.

Conclusions:

• The Fe3O4/water nanofluid demonstrates stable and effective two-phase flow characteristics in a PHP.
• Enhanced oscillatory behavior and faster annular flow attainment contribute to improved thermal performance.
• The developed bubble dynamics model provides a valuable reference for future PHP designs and optimizations.