Transcript Thermophysical Properties of a Cryogenic Pulsating Heat Pipe

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
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3.
Khandekar, S., 2004, “Thermo-hydrodynamics of Closed Loop Pulsating Heat Pipes,” Institut fur Kernenergetik und Energiesysteme der Universitat
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
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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
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EES/MATLAB based thermo-hydrodynamic model of an OHP operating in
slug-plug flow.
d 2 x C  dx  K
B


x

cos 0   

 
2
dt
mtot  dt  mtot
mtot
Evaporator
Adiabatic Region
Condenser
.
Q
Vapor Plug
Liquid Slug
Tc
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