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Low Flow Rates (low + flow_rate)
Selected AbstractsMicro-electrospray with stainless steel emittersRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 14 2003Wenqing Shui The physical processes underlying micro-electrospray (micro-ES) performance were investigated using a stainless steel (SS) emitter with a blunt tip. Sheathless micro-ES could be generated at a blunt SS tip without any tapering or sanding if ESI conditions were optimized. The Taylor cone was found to shrink around the inner diameter of the SS tubing, which permitted a low flow rate of 150,nL/min for sheathless microspray on the blunt tip (100,,m i.d.,×,400,,m o.d.). It is believed that the wettability and/or hydrophobicity of SS tips are responsible for their micro-ES performance. The outlet orifice was further nipped to reduce the size of the spray cone and limit the flow rate to 50,150,nL/min, resulting in peptide detection down to attomole quantities consumed per spectrum. The SS emitter was also integrated into a polymethylmethacrylate microchip and demonstrated satisfactory performance in the analysis and identification of a myoglobin digest. Copyright © 2003 John Wiley & Sons, Ltd. [source] An Evaluation of Physicochemical Treatment Technologies for Water Contaminated with MTBEGROUND WATER MONITORING & REMEDIATION, Issue 4 2000Arturo A. Keller Treatment of methyl tertiary-butyl ether (MTBE) from contaminated surface and ground water supplies presents specific challenges due to the physicochemical properties of MTBE that depend strongly on its hydrophilic nature, and translate into a high solubility in water, and low Henry's constant and low affinity for common adsorbents. We evaluate four treatment technologies-air stripping, granular activated carbon (GAC), hydrophobic hollow fiber membranes, and advanced oxidation processes (AOP)-using ozone or ozone/hydrogen peroxide. Experimental work was carried out to generate parameter values necessary for the design of these processes. Ten different flow rates/concentration combinations were evaluated in our designs to cover the range from high flow rate/low concentration typical of surface water and ground water drinking water supplies to low flow rate/high concentration typical of ground water remediation sites. For all cases, the processes were designed to produce effluent water of 5 ,g/L or less. Capital costs and operation and maintenance costs were determined at the feasibility level by using standard engineering estimating practices. Air stripping is the lowest cost technology for high flow rales (100 to 1000 gpm) if no air treatment is required. Hollow fiber membranes are the lowest cost technology for flow rates of 10 to 100 gpm if no air treatment is required, which is typical at these low flow rates. GAC will be most costeffective at all flow rates if air treatment is required and the influent water has low levels of other organic compounds. AOP using ozone or ozone/hydrogen peroxide is in all cases more expensive than the alternative technologies, and there are sufficient uncertainties at this point with respect to byproducts of AOP to warrant further study of this technology. The cost of treating MTBE-contaminated water for conventional technologies such as air stripping and GAC is 40% to 80% higher than treating water contaminated only with other hydrocarbons such as benzene. [source] Comparing flow-reversal and inner recirculation reactors: Experiments and simulationsAICHE JOURNAL, Issue 7 2003Moshe Ben-Tullilah The operation of reactors with flow reversal operate similar to a reactor with internal recirculation, which the feed enters through one (say, inner) reactor and then turns around and flows out through (the outer) another, when the heat-transfer coefficient between the tubes is large. In this study, we compare the behavior of a packed-bed reactor operating in flow-reversal or internal-recirculation modes, using ethylene oxidation on Pt/Al2O3 as a model reaction. The reactor was built from two concentric tubes (with 28.5 and 42.5 mm in diameter), both packed with a 20 cm catalytic bed and 10 cm inert beds (of alumina-pellets) on each side. An adjustable opening between the tubes allowed for an internal recycle mode and the whole system could be operated with periodic flow reversal. The reactor can be employed then either as a simple once-through bed or as a bed with flow reversal in the inner tube or as bed with internal recirculation flowing from the inner to outer tube, or in the opposite direction, as well as an internal-recirculation reactor with flow reversal. Due to heat losses, the latter two modes were inferior to the others. The experiments, backed by simulations using a homogeneous model with independently determined parameters, showed that the technically-simpler inner-outer internal-recycle reactor operated better at low flow rates, than that with flow reversal, but the conclusion is reversed at high flow rates. The domain where the internal-recirculation reactor is superior depends on the heat-transfer coefficient between the streams. By lowering the feed concentration, the extinction point was determined for each mode highlighting again the conclusions drawn above that inner-recirculation operation may be superior to flow reversal at low flow rates. Simulations revealed also the existence of solutions with stationary fronts or oscillatory fronts. [source] Flow Structures of a Liquid Film Falling on Horizontal TubesCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 6 2005J. Mitrovic Abstract Patterns of a liquid film falling across a vertical array of horizontal tubes change from droplet mode at low flow rates to liquid sheet at high flow rates. Between these limits, liquid columns form as a further stable flow pattern. The transition from one flow mode to another occurs via unstable structures consisting simultaneously of droplets and columns or of merging columns. The boundaries of the flow modes can be obtained from relationships expressing the flow rate as a function of physical properties, that is, the Reynolds number as a function of the Kapitza number. Correlations for the pattern boundaries recommended in the literature are compared with each other and found to be in acceptable agreement for practical purposes. [source] Development and evaluation of a simple calorimeter for the measurement of resting metabolismCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue S4 2002Toshiyo Tamura Summary 1.,A simple calorimeter based on the measurement of oxygen uptake has been developed. 2.,A respiratory simulator was used to evaluate oxygen uptake at different flow rates. A known concentration of mixed gases flows into the calorimeter via the respiratory simulator. Oxygen concentration and flow rate were measured and stored to memory for further analysis. 3.,Results indicate that large errors occur at low flow rates, but that the error is less than 5% under normal conditions. 4.,This device can be used to measure oxygen uptake under resting conditions. [source] | ||||||||||