Multiphase heat transfer is a complex phenomenon, yet one of the most effective mechanisms for exchanging heat by employing the phase-change latent heat. Processes like melting, boiling, vaporization, and condensation exemplify this phenomenon. Nucleate boiling, in particular, stands out as a highly employed method in various industrial applications, e.g., electric cooling devices and nuclear reactors. Understanding its limitation, i.e., departure from nucleate boiling (DNB) or critical heat flux (CHF), is crucial for ensuring the safety and optimal functioning of engineering systems.
EXAMPLE: SUBCOOLED FLOW BOILING EXPERIMENTAL SET-UP & COMPUTATIONAL MODELING
A prototypical experimental flow loop system (Fig. 1) was designed and constructed to replicate the geometry and operating conditions of real-world engineering system: one of the cooling channels in the isotope production facility (IPF) and an Inconel target capsule. One side of the Inconel test section was heated using an induction heater with a pancake coil to induce volumetric heating whose shape and magnitude were as close as possible to the IPF proton beam. A high-speed video (HSV) camera was utilized to capture bubble dynamics and quantitatively characterize fundamental boiling parameters, which further assisted the development of a CFD model. The ability to reproduce the experimental conditions and predict boiling performance provided a basis for understanding the IPF target cooling system.
Fig. 1. Schematic of experimental set-up.
Fig. 2. Coupled experimental and computational modeling framework to predict subcooled flow boiling.
A framework was developed using ANSYS CFX to predict an entire boiling curve, i.e., single-phase heat transfer coefficient (HTC), onset of nucleate boiling (ONB), two-phase HTC, and CHF, for subcooled flow boiling (Fig. 2). A unique feature of this framework is that one uses experimental boiling parameters (obtained by VIRTUAL ALGORITHMS), rather than empirical correlations, measured from ONB to an intermediate heat flux level, so that this computational model can be used to predict subcooled flow boiling up to CHF. This framework can be further extended to more complicated infrastructure systems.
In actual IPF, in-beam monitoring of the target the extreme radiation environment and the Hence, development of the above ex-situ frameworks are crucial to understand the limitations of the cooling system. Fig. 3 shows results at the operating conditions at IPF. The model provides a large margin, ~1.8 times current IPF average operating proton beam target thickness and diameter.
Fig. 3. Boiling curve prediction
system is not possible due to necessarily significant shielding. experimental and computational high-power target performance and experimental data and simulational predicted CHF by computational higher, in comparison with the power for a typical production target
J. H. Seong, J. Morrell, B. Singh, K. Woloshun, E. Olivas, P. Lance, N. Kollatrik, E. O'Brien*, c. Vermeulen
Development of experimental and computational frameworks to predict subcooled flow boiling in the LANL Isotope Production Facility
International Journal of Heat and Mass Transfer (IJHMT), 203, 123836
34141 대전광역시 유성구 대학로 291 (구성동 한국과학기술원 373-1) 기계공학동 www.kaist.ac.kr