Heat and Mass Transfer

, Volume 53, Issue 11, pp 3315–3327 | Cite as

Motion of liquid plugs between vapor bubbles in capillary tubes: a comparison between fluids

  • Rémi Bertossi
  • Vincent Ayel
  • Balkrishna Mehta
  • Cyril Romestant
  • Yves Bertin
  • Sameer Khandekar


Pulsating heat pipes (PHP) are now well-known devices in which liquid/vapor slug flow oscillates in a capillary tube wound between hot and cold sources. In this context, this paper focuses on the motion of the liquid plug, trapped between vapor bubbles, moving in capillary tubes, to try to better understand the thermo-physical phenomena involved in such devices. This study is divided into three parts. In the first part, an experimental study presents the evolution of the vapor pressure during the evaporation process of a liquid thin film deposited from a liquid plug flowing in a heated capillary tube: it is found that the behavior of the generated and removed vapor can be very different, according to the thermophysical properties of the fluids. In the second part, a transient model allows to compare, in terms of pressure and duration, the motion of a constant-length liquid plug trapped between two bubbles subjected to a constant difference of vapor pressure: the results highlight that the performances of the four fluids are also very different. Finally, a third model that can be considered as an improvement of the second one, is also presented: here, the liquid slug is surrounded by two vapor bubbles, one subjected to evaporation, the pressure in both bubbles is now a result of the calculation. This model still allows comparing the behaviors of the fluid. Even if our models are quite far from a complete model of a real PHP, results do indicate towards the applicability of different fluids as suitable working fluids for PHPs, particularly in terms of the flow instabilities which they generate.

List of symbols

Roman symbols


Capillary number, Ca = μu/σ (−)


Diameter (m)


Latent heat (J kg−1)


Length (m)


Mass (kg)


Pressure (Pa)


Heat power (W)


Radius (m)


Reynolds number, Re = ρuD/μ (−)


Specific gas constant, Rv = R/M (J kg−1 K−1)


Time (s)


Temperature (K)


Velocity (m s−1)


Volume (m3)


Location of the liquid plug/slug (m)

Greek symbols


Density (kg m−3)


Time constant (s)/viscous stress per unit volume (Pa m−1)


Surface tension (N m−1)


Kinematic viscosity (m2 s−1)


Dynamic viscosity (Pa s)





Heated zone











The authors wish to thank the French National Research Agency ANR in the frame of the TDM-AAP project ‘AARDECO’, who supported the experimental work presented in Sect. 1. The authors would also like to acknowledge the contribution of Indo-French Center for Promotion of Advanced Research (IFCPAR/CEFIPRA), New Delhi, in facilitating contacts and interactions between the research groups.


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Copyright information

© Springer-Verlag Berlin Heidelberg 2017

Authors and Affiliations

  1. 1.Direction de la Recherche et de l’Innovation de l’IPSAIPSAIvry-sur-SeineFrance
  2. 2.Pprime Institut, UPR 3346CNRS – ENSMA – Université de PoitiersFuturoscope-ChasseneuilFrance
  3. 3.Indian Institute of Technology GuwahatiGuwahatiIndia
  4. 4.Indian Institute of Technology KanpurKanpurIndia

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