Abstract
For the present study numerical simulations of subcooled flow boiling of FC-72 in microgravity have been conducted to accompany boiling experiments performed in microgravity on the International Space Station (ISS). The numerical domain represents the geometry of the experimental test cell. For all simulations the open source framework OpenFOAM was employed, including extensions to the interFoam solver, which have been developed at the authors’ institute. A reference case has been defined applying intermediate values from the experimental parameter range as system parameters. This case has been examined thoroughly with regards to hydrodynamic phenomena and heat transfer during multiple, successive bubble cycles. Based on this reference case, the system parameters flow velocity, input heat flux, pre-heating time, and subcooling of the liquid bulk have been varied, and the impact of these quantities on bubble growth and movement as well as heat transfer have been studied. It was found, that an increased flow rate as well as increased subcooling lead to smaller bubbles and increased time between subsequent nucleations. A high input heat flux, an increased pre-heating time, and a decreased subcooling lead to a rapid cycle of bubble nucleation and coalescence.
Highlights
Nucleate boiling is a highly efficient process to transfer high amounts of heat at low wall superheats
First the reference case will be analyzed in detail in order to gain insight into the hydrodynamic behavior of single vapor bubbles in subcooled flow boiling in microgravity as well as into the connected heat transfer phenomena
Numerical simulations of subcooled, laminar flow boiling in microgravity have been performed employing a VOF approach implemented in the open source framework OpenFOAM combined with methods to cover phase change, contact line physics, and transient heat transfer with the
Summary
Nucleate boiling is a highly efficient process to transfer high amounts of heat at low wall superheats. Kunkelmann and Stephan (2010) employed a finite volume approach from the open source framework OpenFOAM and its VOF based solver interFoam to simulate pool boiling of refrigerants They implemented explicit reconstruction of the interface, a boiling model based on the work of Hardt and Wondra (2008), a subgrid model for contact line evaporation according to Stephan and Busse (1992), and transient heat transfer within the wall. Parallel to experimental research on boiling under microgravity conditions, numerical studies addressing the gravitational influence were published: Aktinol and Dhir (2012) made similar observations as Fischer et al (2014) They performed simulations of subsequent bubble cycles in pool boiling of water under variable gravitational conditions using the level-set method, taking contact line evaporation and transient heat conduction in the wall into account.
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