Session: 7.1 - Heat and Mass Transfer in multiphase flows

Paper Number: 170292

170292 - Numerical Investigation of Conjugate Heat Transfer in Oscillating Heat Pipes 

Abstract: 

We use a recently developed transient 1D-vapor/liquid, 2D-conduction model for oscillating heat pipes to explore the effects of conjugate heat transfer - that is, the fluid-sidewall thermal interaction of the OHP - in various aspects of device performance (startup, steady oscillation, and dryout).    The model has previously been validated/tuned to give agreement for the ASETS-II experiments. In particular, we seek to understand whether there are conditions under which sensible heat can be transferred over long distances using comparably shorter oscillation distances, and how sidewall interactions quench the oscillation mechanism.   In this investigation, we use the ASETS-II geometry and vapor/fluid properties, but vary the thermal properties (conductivity and heat capacity) of the OHP.   First, we vary the thermal conductivity from k = 12.5-1600 W/m-K while fixing heat capacity, tracking the startup time, conductance at steady oscillation (long time), the average liquid slug displacement & velocity magnitudes, frequency of oscillation.  For the ASETS-II "OHP1" case, a symmetric configuration with large heaters, the device oscillates stably at k=200 W/m-K but becomes increasing pulsatile with lower k and eventually dries out under nominal 40W conditions.  We observe that increasing the solid thermal conductivity relative to the baseline material (aluminum) produces moderately increasing performance of the overall OHP conductance.   Measuring in terms of sensitivity of the conductance, dG/G = 0.33 dk_s/k_s - a relatively weak effect - until pulsatile flow is observed at low values of thermal conductivity.  On the other hand, we don't find any statistically significant dependence of the steady conductance on the heat capacity of the solid for the ASET-II geometry over the range 1-4 MJ/m3-K.  Any conjugate heat transfer mechanism which does not depend on the heat capacity cannot be associated with the transient portion of the diffusion equation, and therefore we conclude that to the extent that conjugate heat transfer mechanisms are important in OHP dynamics, the effect must be quasi steady-state.

Presenting Author: Joseph Feser University of Delaware

Presenting Author Biography: Feser has 22 years of combined experience in the area of microscale thermal transport and fluid mechanics, with expertise in both experimental and theoretical aspects of interfacial thermal phenomena and phonon scattering in nanoparticle in alloy materials. He was a recipient of an NSF Career Award in 2017.