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Research Papers: Two-Phase Flow and Heat Transfer

Visualization of Two-Phase Flows in Nanofluid Oscillating Heat Pipes

[+] Author and Article Information
Qi-Ming Li, Jiang Zou, Yuan-Yuan Duan, Bu-Xuan Wang

Laboratory of Phase Change and Interfacial Transport Phenomena, Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Tsinghua University, Beijing 100084, China

Zhen Yang1

Laboratory of Phase Change and Interfacial Transport Phenomena, Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Tsinghua University, Beijing 100084, Chinayangzhen.athu@gmail.com

1

Corresponding author.

J. Heat Transfer 133(5), 052901 (Feb 02, 2011) (5 pages) doi:10.1115/1.4003043 History: Received December 23, 2009; Revised October 26, 2010; Published February 02, 2011; Online February 02, 2011

Two-phase flows in an oscillating heat pipe (OHP) charged with deionized (DI) water and a nanofluid (0.268% v/v) were experimentally investigated. The OHP was made of quartz glass tube (with an inner diameter of 3.53 mm and an outer diameter of 5.38 mm) and coated with a transparent heating film in its evaporating section. The internal two-phase flows at different heat loads were recorded by a charge-coupled device (CCD) camera. Only column flow was observed in the DI water OHP while in the nanofluid OHP the flow first was column, then slug and annular flows as the heat load was steadily increased. Heat transfer in the OHP was strongly related to the two-phase regime. The flow regime transitions effectively increased the operating allowable heat loads in the nanofluid OHP two- to threefold relative to the DI water OHP. The nanofluid OHP had a much lower thermal resistance than the DI water OHP with the most effective heat transfer in the nanofluid OHP occurring in the slug flow regime.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

A schematic of the experimental system (a): 1—OHP, 2—ac power supplier, 3—cooling tank, 4—cooling water inlet, 5—cooling water outlet, 6—computer, 7—high-speed CCD, and 8—infrared imaging system. The detailed geometry of the OHP is shown in (b): 1—evaporating section, 2—condensing section, and 3—adiabatic section.

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Figure 2

Heat transfer performance of the OHP: (a) average temperature of the evaporating and condensing sections at different heat loads and (b) effective thermal resistance at different heat loads

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Figure 3

Initial distribution of liquid and vapor phases in the evaporating section: (a) DI water and (b) nanofluid of 0.268% (v/v)

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Figure 4

Column flow in the evaporating section of the nanofluid OHP at Q=44 W

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Figure 5

Transition to the slug flow regime in the evaporating section of the nanofluid OHP: (a) small bubbles generated in the liquid columns (Q=57 W, 74°C on the outer wall) and (b) slug flow (Q=61 W, 98°C on the outer wall)

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Figure 6

Transition from the slug flow to the annular flow: (a) breakup of a short liquid column at Q=61 W, 98°C on the outer wall and (b) typical annular flow at Q=68 W, 104°C on the outer wall

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Figure 7

Strong boiling in the thick liquid film around a long vapor slug at Q=57 W

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