1,720,974 research outputs found
Nucleate pool boiling investigation on a silicon test section with micro-fabricated cavities
No full textThe basic mechanisms of nucleate boiling are still not completely understood, in spite of the many numerical and experimental studies dedicated to the topic. The use of a hybrid code allows reasonable computational times for simulations of a solid plate with a large population of artificial micro-cavities with fixed distribution. This paper analyses the guidelines for the design, through numerical simulations, of the location and sizes of micro-fabricated cavities on a new silicon test section immersed in FC-72 at the saturation temperature for different pressures with an imposed heat flux applied at the back of the plate. Particular focus is on variations of wall temperature around nucleation sites
Pool boiling heat transfer on a thin plate: features revealed by liquid crystal thermography
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1-D modelling and 3-D simulation of confined bubble formation and formation and pressure fluctuations during flow boiling in a microchannel with a rectangular cross-section of high aspect ratio
No full textCopyright @ 2009 ASMEA simple 1-D model with low requirements for computing time is required to investigate parametric influences on the potentially adverse effects of pressure fluctuations driven by confined vapour bubble growth in microchannel evaporative cooling systems operating at high heat fluxes. A model is developed in this paper for the particular conditions of a channel of rectangular cross-section with high aspect ratio with a constant inlet flow rate (zero upstream compressibility). (The model will later be extended to the conditions of finite upstream compressibility that lead to transient flow reversal). Some parametric trends predicted by the model are presented. The simplifying assumptions in the model are examined in the light of a 3-D simulation by a commercial CFD code, described in an accompanying paper by the same authors. The predictions of pressure changes are in reasonable agreement. It is suggested that the 1-D model will be a useful design tool.This work is supported by the UK Engineering and Physical Sciences Research Council (EPSRC) under grants EP/D500095/1 and EP/D500125/1
Saturated flow boiling in small- to micro- diameter metallic tubes: Experimental results and modeling
No full textSome results of a long-term study of flow boiling patterns, heat transfer rates and pressure drop of R134a at pressures of 6-14 bar in five vertical stainless steel tubes of internal diameter 4.26, 2.88, 2.01, 1.1 and 0.52 mm are presented in this paper. The flow regimes in the 4.26 mm to 1.1 mm tubes were identified as dispersed bubble, bubbly, slug, churn, annular and mist flows. As the diameter was reduced, progressively slimmer vapour slugs, a thinner liquid film around the vapour slug and a less chaotic vapour-liquid interface in churn flow were observed. Confined flow appeared first in the 2.01 mm tube. Dispersed bubble flow was not observed in the smallest tube (0.52 mm) for the range studied in runs in which wavy film flow occurred. The heat transfer coefficients in tubes ranging from 4.26 mm down to 1.1 mm increased with heat flux and system pressure, but did not change with vapour quality for low quality values. At higher quality, the heat transfer coefficients decreased with quality, indicating local dryout. The heat transfer characteristics of the 0.52 mm tube were different from those in the larger tubes. The data fell into two groups that exhibited different influences of heat flux below and above a heat flux threshold. The pressure drop and heat transfer results were compared with existing correlations but with some limited success. Recent progress on mechanistic models for heat transfer along with comparisons and recommendations are included in the paper
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