Subcooled boiling oscillations in natural circulation boiling loop at low pressure

Abstract

Flow instabilities in a natural circulation boiling loop at a low pressure are reported. The oscillations at boiling incipience are primarily chaotic and bifurcate to quasiperiodic ones depending on inlet subcooling ΔTsub and heater power Q. They also strongly depend on water volume Φ in the loop. We have presented power spectrums, attractor reconstructions, and Hurst exponents for the analysis of the experimental data. The analysis shows that the primary oscillations are very similar to geysering instability. Chaotic oscillations occur at low ΔTsub or high Q, whereas quasiperiodic oscillations occur at high ΔTsub or low Q. Our experiments also suggest that wall superheat exceeding a critical value triggers the instability. © 2013 American Institute of Chemical Engineers AIChE J, 60: 375–386, 2014

Experimental investigation of transition process from nucleate boiling to microbubble emission boiling under transient heating modes

“…Problems arising from rapid increase in the heat release of advanced devices and systems, such as electronic chips, inverters of electric vehicles, advanced lasers, and fusion reactors, prompt a search of enhanced heat transfer technologies to meet the increasingly cooling demand . Nucleate boiling is one of the attractive methods because it allows accommodation of high heat flux at relatively low wall superheat, while its application is still limited due to the risk of boiling crisis. In 1981, Inada et al observed an extremely intensive boiling process with heat flux much higher than critical heat flux (CHF) under high subcooled conditions.…”

Onset of Flow Oscillation in a Natural Circulation Boiling Loop—Role of Bubble Dynamics

“…OFI occurs at the minimum point. The pressure drop versus loop velocity curve and Δp H − loop velocity characteristics in NCBL is shown by the experiments of Karmakar et al 9 The conditions for this type of instability is given by…”

“…The NCBL − is a rectangular vertical loop containing distilled water as working fluid. The NCBL has six major partsheater section (HS), condenser, adiabatic riser, down comer (DC), upper plenum, and lower plenum.…”

“…The present study mainly considers the effect of bubble growth and collapse on the onset of flow oscillations. In particular, we extend the works of Karmakar et al − by visualizing bubble dynamics using a high-speed camera (HiSpec 5 of Fastec make) to study the effect of vapor bubble size on the flow oscillation and to find the critical bubble diameter which initiates the flow oscillation. The inception of subcooled boiling oscillation still remains a challenging area for research to clearly understand the onset of flow oscillation.…”

“…They observed OFI at a constant heat flux and at higher mass fluxes of inlet water saturated with dissolved air. Recently, Karmakar et al 9 experimentally observed subcooled boiling oscillations in NCBL and the effect of wall superheat and subcooling on the oscillations in which bubble dynamics (bubble growth and collapse) seemed to have a significant role in triggering flow oscillations in NCBL. Karmakar and Paruya 10 visualized the boiling flow structure for vapor−liquid jet flows, flow patterns and their transitions during geysering instability under varying inlet subcooling in an NCBL.…”