Session G36: Multiphase Flows: General I

Which Way Do We Go? Self-Induced Axis-Switching Periodic Swirl in Annular Liquid Sheets

The aim is to characterize the mechanism for self-induced swirl-switching in flow through a steam-assisted transonic pulsing banana puree heater/atomizer. As the cold puree and hot steam interact, a cycle of blockage and release occurs; deformation of the non-Newtonian puree produces a wave which impedes the motion of the steam. This results in an increase in heat and pressure until the buildup of steam exceeds the banana puree’s ability to contain its motion. At this point the steam is able to force through the puree, producing more deformation and propagating the cycle. Augmenting the cycle are the traditional Kelvin-Helmholtz instabilities (KHI) for streamwise disturbance amplification and Rayleigh–Tayler instabilities (RTI) for azimuthal amplification. However, what was revealed is an additional feature of the flow never before identified. The high blockage ratio of the steam, due to the thick deforming annular puree sheet, encourages fin-like puree protrusions into the steam. Once formed, both sides of these protrusions begin to exhibit KHI and RTI in a plane orthogonal to the original perturbations. The result is a periodic axis-switching in which the self-induced puree swirl spontaneously alternates in both directions.     

Modeling of a Microchannel Condenser using Volume-of-Fluid (VOF) Computational Fluid Dynamic (CFD) Simulations for Heat Pumps

The current industry standard for best-practices in the modeling of heat pump components is to use zero- and one-dimensional simulations to model and optimize heat pumps. There is an opportunity to further understand the performance of these components in extreme environments, such as cold climate operation, a task which is well-suited for utilizing detailed computational fluid dynamic (CFD) simulations to model and optimize the performance of heat pump components. A simplified parallel square micro-channel is modeled to investigate the condensation of Fluorinet FC-72. Qualitative flow map regimes, as well as quantitative data in the form of pressure-drop and heat-transfer coefficients, are utilized from experimental results for validation of the model setup. The liquid mass fraction measured at the outlet is dependent on the mass flow rate at the inlet, as well as the spatial boundary conditions for the heat flux on the side walls of the condenser. Results are shown for different operating conditions that correspond to different flow map regimes, as well as the effect of refrigerant properties on condenser performance. Long-term utilization of the CFD simulations to improve reduced-order models for system-level components for heat pumps are presented.   

Investigating the role of surface structures on flow boiling instabilities

Flow boiling in microchannels has proven to have a high potential for heat transfer applications, but it faces instabilities that must be addressed for secure practical applications. This study investigates the possibility of two-phase flow instability suppression using surface structures in microchannels. Using a 300 µm deep and 420 µm hydraulic diameter microchannel fabricated through Deep Reactive Ion Etching (DRIE) process, platinum microheaters deposited via e-beam evaporation mimic localized heat load. The channels are sealed on top with glass. Parameters including heat fluxes, mass fluxes, pressure, and temperature are measured and simultaneously visualized on a high-speed camera for a dielectric fluid 3M® Novec-7000. The insights gained will advance thermal management systems for high-heat-flux electronics, aerospace, and automotive applications.   

Thermodynamically consistent Cahn-Hilliard Navier-Stokes equations using the metriplectic dynamics formalism

The Cahn-Hilliard-Navier-Stokes  (CHNS) equations describe flows with two-phases, e.g., a liquid with bubbles.  Obtaining constitutive relations for general dissipative processes for such  a  system, which are thermodynamically consistent, can be a challenge.  We  show how the metriplectic formalism of [1-4] achieves this in a straightforward manner. First, from the noncanonical Hamiltonian formulation  for the ideal part of the CHNS system we obtain an appropriate Casimir to serve as the  entropy in the metriplectic formalism [1-3] that describes the dissipation (e.g. viscosity, heat conductivity and diffusion effects). General thermodynamics with the thermodynamic conjugates of concentration and chemical potential are included. The formulation leads naturally to the more general case that allows for anisotropic surface energy effects. 

[1] P. J. Morrison & M. Updike, arXiv:2306.06787v1 [math-ph] 11 Jun 2023.

[2] P. J. Morrison, Phys. Lett. A 100, 423 (1984).

[3] P. J. Morrison, Tech. Rep. PAM--228, Univ.  Cal.  Berkeley (1984).

[4] P. J. Morrison, Physica D 18, 410 (1986).