Research Papers: Evaporation, Boiling, and Condensation

A Dynamic Film Model of the Pulsating Heat Pipe

[+] Author and Article Information
Vadim S. Nikolayev

ESEME, Service des Basses Températures, INAC/CEA-Grenoble, France; and ESEME, PMMH-ESPCI, 10 Rue Vauquelin, 75231 Paris Cedex 5, Francevadim.nikolayev@espci.fr

J. Heat Transfer 133(8), 081504 (May 04, 2011) (9 pages) doi:10.1115/1.4003759 History: Received November 08, 2010; Revised March 04, 2011; Published May 04, 2011; Online May 04, 2011

This article deals with the numerical modeling of the pulsating heat pipe (PHP) and is based on the film evaporation/condensation model recently applied to the single-bubble PHP (Das, 2010, “Thermally Induced Two-Phase Oscillating Flow Inside a Capillary Tube,” Int. J. Heat Mass Transfer, 53(19–20), pp. 3905–3913). The described numerical code can treat the PHP of an arbitrary number of bubbles and branches. Several phenomena that occur inside the PHP are taken into account: coalescence of liquid plugs, film junction or rupture, etc. The model reproduces some of the experimentally observed regimes of functioning of the PHP such as chaotic or intermittent oscillations of large amplitudes. Some results on the PHP heat transfer are discussed.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

(a) Sketch of the closed loop PHP with the default gravity direction. Evaporator is to the left. Topological transformations of the tube. (b) Unlooping. (c) Unbending and projection to the x axis. The splitting of the x axis to branches is shown.

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Figure 2

Vapor bubble i that extends over Ne,i evaporators and the liquid films inside it

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Figure 3

Computer representation of the instantaneous state of the PHP as a doubly connected list. Each of its node (an oval) contains the state of a bubble-plug pair and two pointers (circles) to the previous and to the next nodes.

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Figure 4

General scheme of the C++ program

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Figure 5

The screen of the PHP_VIEWER version 1.6 in the liquid temperature visualization mode. The liquid films partially cover the internal tube walls inside the vapor bubbles. The temperature is indicated with coloring of the liquid plugs.

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Figure 6

Examples of the chaotic oscillation regime within the linear PHP representation schematized in Fig. 1. Evaporator (E) and condenser (C) sections are shown with the background bars; adiabatic sections are in between. PHP is shown partially with evolution of only several menisci. (a) Short-time evolution. The bubble recondensation occurs at an early stage. The evolution of only two film edges is shown by dotted lines. (b) Long-time evolution for Te=45°C, Tc=25°C, ϕ=0.55, and δf=40 μm.

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Figure 7

Heat transfer curve and PHP regimes for Tc=25°C, ϕ=0.55, and δf=40 μm

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Figure 8

Examples of the PHP heat exchange rate evolution in condenser and evaporator for the same parameters as Fig. 6. (a) Total heat exchange. The time average ⟨Q⟩ is shown with a horizontal line. (b) Part of the sensible heat exchange. The average values are 0.18 for evaporator and 0.29 for condenser.

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Figure 9

Typical evolution of temperatures obtained for a bubble from Fig. 6. The evolutions of the left and right ends of this bubble correspond to the third and second curves from the top of Fig. 6, respectively. The horizontal dashed lines correspond to Tc and Te.



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