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Sample Preparation Techniques to Isolate and Recover Organics and Inorganics
Published in Paul R. Loconto, Trace Environmental Quantitative Analysis, 2020
The extractant from S-LSE must be concentrated. If a low boiling solvent such as methylene chloride is used to conduct S-LSE, it is straightforward to remove this solvent by use of either a Kuderna–Danish (K-D) evaporative concentrator or a rotary evaporator. More contemporary K-D designs provide a means to recover the spent solvent. Earlier designs did not include a means to recover the solvent, and because of this, most solvents, such as methylene chloride, were evaporated to the atmosphere usually via a fume hood. A few boiling chips are usually added to the receiving tube so as to prevent “bumping” during the vigorous boiling step. Suspending the K-D vessel above a large boiling water bath where steam can be in contact with the glass surface serves to rapidly remove solvent. Solvent is removed until a volume between 1 and 5 mL is reached. An extractant is obtained whose concentration of the analytes of interest has been greatly increased. A K-D evaporative concentrator is shown in Figure 3.7. The concentrated extract is further cleaned up, depending on what matrix interferences might be present.
Energy Conservation Measures for Wastewater Treatment
Published in Frank R. Spellman, Fundamentals of Public Utilities Management, 2020
The Aerostrip® diffuser provides many of the same advantages and disadvantages as panel diffusers; however, it appears to be less prone to tearing. Also, the smaller strips allow tapering of the diffuser placement to match oxygen demand across the basin. Aerostrips may be mounted at floor level or on supports above the floor. Manufacturer’s claims regarding the strip membrane diffuser include: Energy efficiencies between 10 percent and 20 percent greater than the traditional ceramic and elastomeric membrane diffuser configurationsUniform bubble release across the membrane surfaceBubbles resist coalescingMembranes not prone to cloggingDiffusers are self-cleaning, although Aerostrip panels have been reported to be susceptible to frequent fouling requiring bumping and flexing of the membrane to dislodge (USEPA 2010)
A Review of Inverted Annular and Low Quality Film Boiling
Published in G. F. Hewitt, J. M. Delhaye, N. Zuber, Post-Dryout Heat Transfer, 2017
The effect of subcooling on the film boiling heat transfer coefficient may be explained as follows: heat is transferred primarily by conduction across the vapor film to the interface (convection and radiation may also be significant). Here a fraction of the heat received is used for heating up the liquid core, while the remainder is used for evaporation. Higher subcoolings results in evaporation, and hence a thinner vapor film, which consequently increases h. During tests on heated bodies immersed in water, Bradfield (1967) observed that subcoolings less than 35°C tend to calm the interface to a wavelike motion compared to saturated boiling. At higher subcoolings, a bumping instability was observed where the stable vapor film was replaced momentarily by violent nucleate boiling. Sometimes, stable film boiling was reestablished and the cycle was repeated. A possible mechanism could be that the vapor layer thickness becomes less than the mean free path of the vapor. As in the case of heat transfer in rarefied gases (Marx and Davis, 1952), the effective thermal conductivity decreases as the film thickness decreases allowing the liquid to come into very close proximity to the wall.
Assessment and comparison of PHCs removal from three types of soils (sand, silt loam and clay) using supercritical fluid extraction
Published in Environmental Technology, 2019
Mahmoud Meskar, Majid Sartaj, Julio Angel Infante Sedano
The 500-mL evaporation flask was connected to the concentrator tube (10 mL graduated glass tube) by a clamp. The liquid extract which was collected in the silica gel column, was transferred to the K-D with an additional 20 mL of solvent, a mixture of acetone and hexanes with a ratio of 1:1. One or two boiling chips were added to the flask [33]. Boiling chips with approximately 10–40 mesh from VWR Scientific, Inc. (ON, Canada) were used. Boiling chips are added to liquids to make them boil more calmly and prevent bumping [34]. The (3-ball macro) Snyder column were joined to the flask with a clamp. Approximately 1 mL of solvent (acetone/hexane with a ratio of 1:1) was used to moisten the column. The whole K-D set-up was placed in a hot water bath in a fume hood. The flask was positioned at a level such that the lower surface of the flask could be bathed in steam. The temperature of water bath was adjusted to approximately 85°C so that it could vaporize solvents. Around 1 mL of exchange solvent (toluene) was added to the flask by removing the Snyder column instantly [33]. Toluene (C6H5CH3) was purchased from Fisher Scientific (ON, Canada) at an Optima-grade and also met the ACS specifications. The concentration rate can be modified with the water’s temperature compared with the boiling point of solvents. The final volume of extract around 2 mL can be reached after a few hours [28]. At the end, the K-D device should be removed from the water bath to be cooled down before collection of the final extract.