Impact Of Phase Change Research Articles

Main characteristics of the groundwater and permafrost interaction

An analysis of the groundwater and permafrost interaction is presented in this study. The analysis is based on an extensive review of scientific literature and our own investigations. The article specifically examines the significant impact of phase changes between liquid and solid states in groundwater, including the freezing of aquifers and the thawing of ice-rich permafrost. The discussion highlights the essential characteristics of groundwater interactions with frozen ground in permafrost regions.

The Impact of Phase Changes of Imidazolium Based Ionic Liquids on the Solubility of Hydrofluorocarbons

Project EARTH (Environmentally Applied Research Toward Hydrofluorocarbons) is focused on developing sustainable processes for selectively separating refrigerant mixtures with high global warming potentials. The initial focus of the project is R-410A which is widely used in both commercial refrigeration systems and residential air conditioning. It is an azeotropic mixture containing 50 wt.% HFC-32 (CH2F2) and 50 wt.% HFC-125 (CHF2CF3). The separation approaches being investigated include membranes, porous media, and the use of ionic liquids as entrainers for extractive distillation.This poster will describe the work being conducted using ionic liquids and will specifically focus on the impact of phase changes of imidazolium based ionic liquids that are solid at room temperature on the solubility of HFC-32 and HFC-125. The poster will include an overview of how we use specialized equipment including a High-Pressure View Cell and Hiden Isochema IGA gravimetric microbalance to build a comprehensive understanding of these solubility differences.

Investigations on the impact of phase change on single plume flash boiling radial expansion and drop-sizing characteristics

• Flash boiling plume expansion is primarily caused by the expansion of the vaporized fuel. • The volume fraction of the flash-boiling-vaporized fuel dominates the spray morphology. • The mass fraction of the flash-boiling-vaporized fuel shows a major impact on the spray SMD. • Flash boiling spray radial properties are firstly governed by near-field expansion, then far-field evaporation. • The measured SMD of flash boiling spray increases with axial position due to the strong evaporation during spray penetrating. Flash boiling atomization has been considered a promising approach to enhance spray atomization. Increasing the fuel temperature or reducing the ambient pressure can promote the phase-change of the spray, and boiling can be achieved during this process, so that spray atomization can be enhanced. However, the strong evaporative feature of flash boiling atomization induced a high vapor concentration in the plume thus changes spray characteristics. To understand the impacts of the vapor phase on spray properties in the aspects of radial expansion and drop sizing, this investigation is carried out based on a customized single-hole fuel injector with practical fuel injection settings. High-speed backlit imaging and Phase Doppler Interferometry are used to quantify the characteristics of flash boiling sprays under various boundary conditions. Macroscopic and microscopic spray morphologies were captured and it was shown that the geometry of the flash boiling spray plume was significantly impacted by the expansion of the compressed vapor phase. The evaporation of the droplets was studied by the single droplet evaporation model and the results were compared against drop sizing measurements. It was found that the evaporation and elimination of liquid droplets might affect the statistical interpretation of the drop sizing results, which is a notable feature for flash boiling sprays.

Updated analysis of gauge-based rainfall patterns over the western tropical Pacific Ocean

This work considers observed changes in tropical Pacific Ocean rainfall amounts and the influence of climate variability cycles upon them. Observations were taken from the Comprehensive Pacific Rainfall Database (PACRAIN), using strict data selection criteria of >99% data completeness from eight locations for the period 1971–2017. These data were used to analyze temporal and spatial rainfall patterns based on several indicators that considered rainfall amount and frequency, 95th percentile extreme rainfall events, and length of consecutive rain/drought events. These indicators were also computed using satellite-derived observations from the Global Precipitation Climatology Project (GPCP), as a means to compare gauge-based values with nearby estimates from the GPCP product. Results show a temporal pattern that tended towards a reduction in rainfall amounts and frequency across the tropical Pacific Ocean. The impact of phase changes of the Interdecadal Pacific Oscillation (IPO) was also examined. There was some evidence of the impact of the IPO, as well as of the El-Niño Southern Oscillation (ENSO), when seasonal and monthly trends in these indicators were analyzed. Comparison of the temporal patterns observed from the rain gauges with the trends computed using the GPCP estimates showed inconsistencies that varied considerably when comparing trends calculated at different island locations. Future work should consider further comparison of GPCP and gauge-based rainfall trends, as well as the attribution of climate change and other climate variability cycles to these trends.

Optimum insulation design for buried utilities subject to frost action in cold regions using the Nelder-Mead algorithm

Frost action in soils can cause detrimental damage to buried utilities, such as water and gas pipes. One of the promising approaches to protect buried utilities against frost damage and reduce the excavation cost is to install thermal insulation over and around the pipe. This paper considers two different conductive heat transfer models, with and without the effect of soil pore-water phase change, as well as a heat and mass transfer model for freezing soils to investigate the effectiveness of insulation systems for frost protection of buried pipes. It was found that the latent heat released during the phase change significantly affects the heat transfer process and that the impact of phase change on insulation design should not be overlooked. Furthermore, by comparing numerical results to field measurement data, it is found that the mass transfer has an insignificant effect on the temperature and unfrozen water content distribution in the frost-susceptible foundation soil.A parametric study was carried out to assess the effects of different factors such as the backfill materials, geometry, total length, thickness of insulation, distance between pipe and insulation as well as the burial depth of pipe on the thermal performance of insulation. Finally, the Nelder-Mead algorithm was implemented to determine the optimum insulation design so that the overall cost is minimized while the pipe is protected from freezing.

Buoyancy statistics in moist turbulent Rayleigh–Bénard convection

We study shallow moist Rayleigh–Bénard convection in the Boussinesq approximation in three-dimensional direct numerical simulations. The thermodynamics of phase changes is approximated by a piecewise linear equation of state close to the phase boundary. The impact of phase changes on the turbulent fluctuations and the transfer of buoyancy through the layer is discussed as a function of the Rayleigh number and the ability to form liquid water. The enhanced buoyancy flux due to phase changes is compared with dry convection reference cases and related to the cloud cover in the convection layer. This study indicates that the moist Rayleigh–Bénard problem offers a practical framework for the development and evaluation of parameterizations for atmospheric convection.

Effects of Phase Change of Pb-Free Flip-Chip Solders During Board-Level Interconnect Reflow

The impact of phase change (from solid to liquid) on the reliability of Pb-free flip-chip solders during board-level interconnect reflow is investigated. Most of the current candidates for Pb-free solder are tin-based with similar melting temperatures near 230 degC. Thus, Pb-free flip-chip solders melt again during the subsequent board-level interconnect reflow cycle. Solder volume expands more than 4% during the phase change from solid to liquid. The volumetric expansion of solder in a volume constrained by chip, substrate, and underfill creates serious reliability issues. The issues include underfill fracture and delamination from chip or substrate. Besides decreasing flip-chip interconnect reliability in fatigue, bridging through underfill cracks or delamination between neighboring flip-chip interconnects by the interjected solder leads to failures. In this paper, the volume expansion ratio of tin is experimentally measured, and a Pb-free flip-chip chip-scale package (FC-CSP) is used to observe delamination and solder bridging after solder reflow. It is demonstrated that the presence of molten solder and the interfacial failure of underfill can occur during solder reflow. Accordingly, Pb-free flip-chip packages have an additional reliability issue that has not been a concern for Pb solder packages. To quantify the effect of phase change, a flip-chip chip-scale plastic ball grid array package is modeled for nonlinear finite-element analysis. A unit-cell model is used to quantify the elongation strain of underfill and stresses at the interfaces between underfill and chip or underfill and substrate generated by volume expansion of solder. In addition, the strain energy release rate of interfacial crack between chip and underfill is also calculated

The impact of phase changes, alloying and segregation in supported rhpd catalysts during selective NO reduction by H2.

Illuminating complexity: Time-resolved, microreactor-based, EDE/mass spectrometry (EDE=energy dispersive extended X-ray absorption fine structure) was used to probe the behaviour of both Rh and Pd components of alloyed nanoparticles during NO reduction by H2. The picture shows the NO conversion as a function of temperature. This surface enrichment in Pd is shown to curtail rapid oxidation of the Rh component by NO and leads to a promotion of NO reduction.