Oscillating (Pulsating) Heat Pipes
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Oscillating (Pulsating) Heat Pipes. An OHP consists of a capillary sized tube and a refrigerant. Most OHPs are formed in closed serpentine loops with multiple turns, but OHPs can operate in other configurations Closed End (serpentine but not looped) Open End

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Oscillating (Pulsating) Heat Pipes

  • An OHP consists of a capillary sized tube and a refrigerant.

  • Most OHPs are formed in closed serpentine loops with multiple turns, but OHPs can operate in other configurations

    • Closed End (serpentine but not looped)

    • Open End

  • The tube is evacuated then partially filled with the working fluid

  • Capillary forces create a natural separation of liquid slugs and vapor plugs.

Khandekar ‘04


Operating Regimes

Static Slug/Plug distribution, generation of small bubbles at high temps. similar to nucleate boiling

Critical Heat Flux

Oscillatory slug/plug flow develops in individual loops

Heat flux

‘Stable’ oscillations develop, amplitudes increase with increasing heat flux, and oscillations in multiple tubes come into phase with one another

-direction is arbitrary and periodically changes (more so with lower heat flux)

-local oscillations superimposed on system oscillation

Annular flow develops in fluid traveling from the evaporator to condenser

  • References

  • Khandekar, S., 2004, “Thermo-hydrodynamics of Closed Loop Pulsating Heat Pipes,” Institut fur Kernenergetik und EnergiesystemederUniversitat Stuttgart.

  • Ma., H. B., Borgmeyer, B., Cheng, P., Zhang, Y., 2008, “Heat Transport Capability in an Oscillating Heat Pipe,” Journal of Heat Transfer, 130(8), pp. 81501-1-7.

  • Borgmeyer, B., 2005, “Theoretical Analysis and Experimental Investigation of A Pulsating Heat Pipe for Electronics Cooling,” Master’s Thesis, University of Missouri-Columbia.


Modeling

  • OHP modeling has focused on the “simpler” slug/plug flow regime

  • Multiple modeling approaches have been tried

    • Chaos

    • Continuity, Momentum & Energy

    • Spring-Mass-Damper

    • Non-Dimensional Analysis

    • Artificial Neural Networks

  • Our model has its roots in the spring-mass-damper models presented by Ma, Borgmeyer, et al.2,3

    • EES/MATLAB based thermo-hydrodynamic model of an OHP operating in slug-plug flow.

Evaporator

Adiabatic Region

Condenser

.

Q

Tc

Vapor Plug

Liquid Slug


The OHP Advantage and Project Goals

  • Advantages

    • OHPs are simpler/lighter than other two-phase heat transfer devices

      • No wick

      • No additional fluid reservoir

    • OHPs may be more robust?

      • Dry-out problems, while not extensively studied, do not appear to be a major problem…OHPs may be able to handle higher heat fluxes (convective heat transfer vs. phase change)

    • May be used as a thermal switch

  • Disadvantages

    • Lower effective conductance than Capillary Pumped Loops and Loop Heat Pipes

Project Objective: Further the development of the technology/understanding required for successful implementation of an OHP in spacecraft thermal control applications.

Approach: theoretical and experimental

Deliverable: OHP design guidelines and a physics-based, but semi-empirical, model suitable for design


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