Deviations from classical droplet evaporation theory

In this article, we show that significant deviations from the classical quasi-steady models of droplet evaporation can arise solely due to transient effects in the gas phase. The problem of fully transient evaporation of a single droplet in an infinite atmosphere is solved in a generalized, dimensionless framework with explicitly stated assumptions. The differences between the classical quasi-steady and fully transient models are quantified for a wide range of the 10-dimensional input domain and a robust predictive tool to rapidly quantify this difference is reported. In extreme cases, the classical quasi-steady model can overpredict the droplet lifetime by 80%. This overprediction increases when the energy required to bring the droplet into equilibrium with its environment becomes small compared with the energy required to cool the space around the droplet and therefore establish the quasi-steady temperature field. In the general case, it is shown that two transient regimes emerge when a droplet is suddenly immersed into an atmosphere. Initially, the droplet vaporizes faster than classical models predict since the surrounding gas takes time to cool and to saturate with vapour. Towards the end of its life, the droplet vaporizes slower than expected since the region of cold vapour established in the early stages of evaporation remains and insulates the droplet.

Elevated LNG Vapour Dispersion—Effects of Topography, Obstruction and Phase Change

The dispersion of vapour of liquefied natural gas (LNG) is generally assumed to be from a liquid spill on the ground in hazard and risk analysis. However, this cold vapour could be discharged at height through cold venting. While there is similarity to the situation where a heavier-than-air gas, e.g., CO2, is discharged through tall vent stacks, LNG vapour is cold and induces phase change of ambient moisture leading to changes in the thermodynamics as the vapour disperses. A recent unplanned cold venting of LNG vapour event due to failure of a pilot, provided valuable data for further analysis. This event was studied using CFD under steady-state conditions and incorporating the effect of thermodynamics due to phase change of atmospheric moisture. As the vast majority of processing plants do not reside on flat planes, the effect of surrounding topography was also investigated. This case study highlighted that integral dispersion model was not applicable as key assumptions used to derive the models were violated and suggested guidance and methodologies appropriate for modelling cold vent and flame out situations for elevated vents.

Sensitive determination of mercury by magnetic dispersive solid-phase extraction combined with flow-injection-cold vapour-graphite furnace atomic absorption spectrometry

The preconcentration of Hg through MDSPE and cold vapor (CV) resulted in an excellent LOD.

Simple mercury determination using an enclosed quartz cell with cold vapour-atomic absorption spectrometry

A simple method for determining total inorganic mercury (Hg) in solution using an enclosed quartz cell applying cold vapour-atomic absorption spectrometry (CV-AAS) can reduce sample volume, reductant, and cost compared with those of official methods.

Analisis Merkuri Pada Merk Krim Pemutih Wajah dengan Metode Spektrofotometri Serapan Atom

<p><em>Telah dilakukan penelitian “Analisis Merkuri (Hg) pada Beberapa Merek Krim Pemutih Wajah dengan Metode Spektrofotometri Serapan Atom (SSA)”. Tujuan penelitian yang dilakukan untuk mengidentifikasi dan mengukur kadar merkuri dalam beberapa merek krim pemutih wajah yang dijual di pasaran Kota Bukittinggi. Sampel diekstraksi dengan cara destruksi basah selama 3 jam pada suhu ±100°C sampai diperoleh larutan bening. Analisa kualitatif merkuri menggunakan KI 0,5 N dan NaOH 2 N. Kemudian, penentuan merkuri dalam sampel menggunakan Spektrofotometri Serapan Atom Uap Dingin. Dari hasil validasi metode diperoleh persamaan regresi Y = 0,0072x – 0,0089. Hasil penelitian menunjukkan bahwa dari kelima sampel yang diuji mengandung merkuri dengan rata-rata kadar sampel A = 0,00087 ppm, B = 0,00075 ppm, C = 0,00066 ppm, D = 1,66794 ppm, dan E = 0,00189 ppm. Sampel D mengandung merkuri di atas batas aman yang diperbolehkan BPOM RI yaitu tidak melebihi 1 mg/L atau 1 ppm.</em></p><p> </p><p><em>This research has been done Analysis of Mercury on Several Brands of Whitening Creams by using Atomic Absorption Spectrophotometry Method. The purpose of this research was to identify and measure mercury consentrations on five samples of whitening cream in the market Bukittinggi City. The samples was extracted by wet destruction for 3 hours at ± 100 °C until the solution clear. Qualitative analysis was performed using color test KI 0.5 N and NaOH 2 N. Then, the determination of mercury in the samples by using Cold Vapour Atomic Absorption Spectrophotometry. The regression equation obtained from the calibration curve is Y = 0,0072x – 0,0089. The results of the five samples showed that all samples contained mercury with average level samples A = 0,00087 ppm, B = 0,00075 ppm, C = 0,00066 ppm, D = 1,66794 ppm, dan E = 0,00189 ppm. Sample D contained mercury above the safe limit allowed by BPOM RI that is not more than 1 mg/L or 1 ppm.</em></p>