Thermophysical Properties of a Cryogenic Pulsating Heat Pipe

1
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
2
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 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, Masters Thesis,
  University of Missouri-Columbia.

3
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.

Condenser
Evaporator
Adiabatic Region
.
Q
Tc
Vapor Plug
Liquid Slug
4
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 problemOHPs 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