The volumetric liquid‐phase mass transfer coefficient, kLa, was determined by absorption of oxygen in air using six different carboxy‐methyl cellulose (CMC) solutions with different rheological values in three phase spout‐fluid beds operated continuously with respect to both gas and liquid. Three cylindrical columns of 7.4 cm, 11.4 cm, and 14.4 cm diameters were used. Gas velocity was varied between 0.00154–0.00563 m/s, liquid velocity between 0.0116–0.0387 m/s, surface tension between 0.00416–0.0189 N/m, static bed height between 6.0–10.8 cm, and spherical glass particles of 1.75 mm diameter were used as packing material. A single nozzle sparger of 1.0 cm diameter was used in the spouting line. The volumetric mass transfer coefficient was found to increase with gas velocity, liquid velocity, and static bed height and to decrease with the increase of the effective liquid viscosity of the CMC solution. A dimensionless correlation was developed and compared with those listed in the literature. 相似文献
A general method for optimizing ideal Claude cycles with multiple expansion engines is presented for two types of engine arrangements. In one case, the inlet temperature of one engine is equal to the outlet temperature of another engine. In the second case, inlet and outlet temperatures of adjacent engines are independent of each other, the more general case which is sometimes used in practice. The optimizing technique is especially adapted to superconductive systems in which some of the helium vapour is used to cool electrical leads and mechanical support systems. The helium fraction to be returned to the refrigerator-liquefier vs the fraction to be used for other purposes is conventionally entered as a parameter which becomes part of the optimization technique. 相似文献
This paper describes a method for the modification of quartz crystal surfaces to be used as a transducer in biosensors that allow recognition and quantification of certain biomolecules (antibodies, enzymes, proteins, etc). Quartz crystal sensors were modified by a plasma based electron beam generator in order to detect the level of the toxin histamine within biological liquids (blood, serum) and food (wine, cheese, fish etc.). Cysteamine and ethylenediamine were used as precursors in the plasma. After each modification step, the layers on the quartz crystal were characterized by frequency measurements. Modified surfaces were also characterized by contact angle, X-ray photoelectron spectroscopy and atomic force microscopy to determine the physical and chemical characteristics of the surfaces after each modification. Finally, the performance of the sensors were tested by the response to histamine via frequency shifts. The frequency shifts of the sensors prepared by plasma polymerization of ethylenediamine and cysteamine were approximately 3230 Hz and 5630 Hz, respectively, whereas the frequency change of the unmodified crystal surface was around 575 Hz. 相似文献
The effect of surface modification of laser-cut 316L cardiovascular stents by low-T plasma nitriding was evaluated in terms
of mechanical properties and biocompatibility of the stents. The plasma nitriding was performed at 400, 450 or 500 °C using
various ratios of nitrogen–hydrogen gas mixtures. The flexibility and radial strength were measured in crimped and expanded
state of the stents, respectively. The mechanical properties could be adjusted and improved by plasma nitriding conducted
at temperatures lower than 450 °C and/or nitrogen content less than 10% in the treatment gas. An osteoblast cell culture model
system was utilized to investigate the effect of plasma nitriding of the stents on the biological response towards the stents,
using biological criteria such as cell viability, alkaline phosphatase and nitric oxide production. In terms of cell viability
and alkaline phosphatase production, the plasma nitriding procedure did not appear to negatively affect the biocompatibility
of the 316L steel stents. However, in terms of nitric oxide production that was slightly increased in the presence of the
plasma-nitrided stents, an indirect improvement in the biocompatibility could possibly be expected. 相似文献
Whilst carbon dioxide is water soluble the system is somewhat complex and results in the presence of carbonate anions which interact with cations such as Ca2+ and Mg2+ present in seawater to form insoluble carbonates, especially at high temperatures. In multistage flash (MSF) desalination plants CO2 gas becomes less soluble in the brine as a result of the brines high temperature and high salinity which causes the pH to be in the range of 8–9. The presence of these conditions causes the release of CO2, simultaneous to the formation of scale deposits since its solubility is a function of the solution pH.
The formation of scale deposits, such as CaCO3 causes fouling in the MSF distillers which has previously been studied by many researchers. A great amount of work has been carried out and more is yet to come in order to fully understand the role of various components and their interaction including the effectiveness of scale control techniques. The deposits may serve as an adsorbing film raising the speed of the loss of crystals or promoting the formation of scale deposits and therefore further adhesion on the wall surfaces of the MSF distillers and other process plant equipment leading to deterioration in the performance and efficiency of the whole desalination plant.
This paper shows direct quantification of the adhesion forces between CaCO3 crystals and different process equipment surfaces under different conditions. This was carried out using an atomic force microscope (AFM) with an attached CaCO3 crystal as a colloid probe to bring the CaCO3 directly into and out of contact with the surfaces and measuring the resultant adhesion. This involved using surfaces different grades of roughness and carrying out measurements in synthetic sea water solutions of differing ionic strengths as well as with real seawater samples. Furthermore, the effect on measured adhesion of adding anti-scalant to the solutions was examined. 相似文献
The efficiency of crossflow microfiltration processes is limited by membrane fouling and concentration polarization leading to permeate flux decline during operation. The experiments that were carried out in the laboratory were conducted to determine and investigate the performance, behaviour and the fouling susceptibility of new ceramic tubular microfiltration membranes during the crossflow filtration of yeast suspensions. The tubular membranes of nominal pore size 0.5 microns were fouled over a varied range of concentration, temperatures, pH, crossflow velocities and system pressures. The typical filtration conditions were at a temperature of 25°C, a system pressure of 1.5 bar and a concentration of 0.03 g/L yeast suspension. These parameters varied during subsequent investigations. After each experiment, the membrane and the rig were cleaned using a three stage cleaning process and was reused in order to replicate industrial filtration conditions. The effects of repeated fouling and cleaning cycles upon membrane flux over time and cleaning efficiency are investigated and their influence over time is also documented. For every experiment, the flux data was recorded over a 50 min period and the membrane was changed after the PWF declined considerably due to excessive fouling over time. Chemical cleaning consisted of a sequential application of a 1% caustic solution through the rig followed by a 2% hypochlorite solution and a 2% nitric solution, all at 50°C. The permeate flux was shown to decrease with filtration time during the development of the fouling layer. Once the fouling layer was developed and established, there appeared to be a leveling of permeate flux. The experimental results are presented in the report and the flux values at different conditions are presented. 相似文献
This study investigates the effect of calcium, alginate, fibrous cellulose, and pH on the flocculation dynamics and final properties of synthetic activated sludges. A laboratory-scale batch reactor, fed with standard synthetic sludges was used. The effects of varying calcium concentration (5-25 mM), alginate concentration (25-125 mg/L), fibrous cellulose concentration (0.2-0.8 g/L) and pH (3-9) on the sludge characteristics were studied by varying one parameter whilst keeping the others constant. The results from experiments indicated that the calcium, alginate, fibrous cellulose, and pH had the critical effect on the aggregation rate, flocs size, and made the improvement of the final properties of sludge. Dynamic measurements have established the optimum conditions for floc formation and can accurately reflect the state of formation of the synthetic activated sludge flocs. These correlate well with measurements of settleability and turbidity of the synthetic activated sludge. The results of this study support the bonding theory and indicate that formation of cations-polymer complexes and polymer gelation are important means of flocculation. The development of synthetic activated sludges is suggested also to be a possible surrogate for studying the final properties of activated sludge. 相似文献
This paper addresses solitons in nonlinear directional couplers in non-Kerr law media, with spatio-temporal dispersion. Both twin-core couplers as well as multiple-core couplers are studied. The nonlinearities studied are Kerr law, power law, parabolic law, dual-power law and log law. Bright, dark and singular soliton solutions of the governing equation are studied. 相似文献
Five muscles from USDA Select beef carcasses were cooked on an electric belt grill at three temperatures (93, 117, and 163°C), in a forced-air convection oven, and on an electric broiler to determine effects of cooking treatment and muscle on Warner-Bratzler shear force values, cooking traits (cooking loss, cooking time, and endpoint temperature), and repeatability of duplicate measurements. All cooking treatments allowed shear force differences to be detected (P<0.05) among the five muscles, although the differences were inconsistent. Neither longissimus lumborum nor semitendinosus shear values differed among the five cooking treatments; however, shear values for biceps femoris, deep pectoralis, and gluteus medius differed (P<0.05) among cooking treatments. Belt grill cooking resulted in the highest shear force repeatability (R=0.70 to 0.89) for the longissimus lumborum. All cooking methods provided acceptable repeatability (R?0.60) of shear values for the biceps femoris and semitendinosus. The electric broiler was the only cooking treatment that resulted in acceptable repeatability of shear force measurements for all five muscles. It is not recommended to use the gluteus medius to test treatment effects on shear force values. Belt grill or electric broiler cooking are recommended for shear force evaluations. 相似文献
The MP2 and DFT/B3LYP methods at 6-311++G(d,p) and aug-cc-pdz basis sets have been used to probe the origin of relative stability preference for eclipsed acetaldehyde over its bisected counterpart. A relative energy stability range of 1.02 to 1.20 kcal/mol, in favor of the eclipsed conformer, was found and discussed. An NBO study at these chemistry levels complemented these findings and assigned the eclipsed acetaldehyde preference mainly to the vicinal antiperiplanar hyperconjugative interactions. The tautomeric interconversion between the more stable eclipsed acetaldehyde and vinyl alcohol has been achieved through a four-membered ring transition state (TS). The obtained barrier heights and relative stabilities of eclipsed acetaldehyde and the two conformers of vinyl alchol at these model chemistries have been estimated and discussed. 相似文献