Binding and hydrodynamic properties of muscarinic receptor subtypes solubilized in 3-(3-cholamidopropyl)dimethylammonio-2-hydroxy-1-propanesulfonate

The muscarinic receptor from the cerebral cortex, heart, and lacrimal gland can be solubilized in the zwitterionic detergent 3-(3-cholamidopropyl)dimethylammonio-2-hydroxy-1-propane sulfonate (CHAPSO) with retention of high affinity [3H]N-methyls-copolamine binding. However, in this detergent there are significant differences in the binding properties of the receptors, compared with those observed in membranes and digitonin solution. Some agents retain a degree of selectivity. In the heart and cortex, agonists can bind with high affinity to a receptor-GTP-binding protein complex. A second, lower affinity, agonist binding state is also present, which resembles a class of sites seen in membranes but not in digitonin solution. The high affinity agonist binding state has been resolved from the lower affinity state on sucrose density gradient centrifugation. Hydrodynamic analysis suggests that the high affinity state is approximately 110,000 Da larger than the lower affinity state. The binding properties of the receptor in CHAPSO can be altered to those seen in digitonin by exchanging detergents after CHAPSO solubilization.

Hydrodynamic modeling of mineral wool fiber suspensions in a two-dimensional flow

A consequence of a loss of coolant accident is that the local insulation material is damaged and maybe transported to the containment sump where it can penetrate and/or block the sump strainers. An experimental and theoretical study, which examines the transport of mineral wool fibers via single and multi-effect experiments is being performed. This paper focuses on the experiments and simulations performed for validation of numerical models of sedimentation and resuspension of mineral wool fiber agglomerates in a racetrack type channel. Three velocity conditions are used to test the response of two dispersed phase fiber agglomerates to two drag correlations and to two turbulent dispersion coefficients. The Eulerian multiphase flow model is applied with either one or two dispersed phases.

Hydrodynamic characteristics of a plate heat exchanger

This thesis describes a detailed investigation of the hydrodynamic characteristics of a commercially-available three-dimensional plate heat exchanger.

The hydrodynamic behaviour and mass transfer characteristics of single droplets in a pulsed sieve plate column

The literature relating to the performance of pulsed sieve plate liquid-liquid extraction columns and the relevant hydrodynamic phenomenon have been surveyed. Hydrodynamic behaviour and mass transfer characteristics of droplets in turbulent and non-turbulent conditions have also been reviewed. Hydrodynamic behaviour, i.e. terminal and characteristic velocity of droplets, droplet size and droplet breakup processes, and mass transfer characteristics of single droplets (d≤0.6 cm) were investigated under pulsed (mixer-settler & transitional regimes) and non-pulsed conditions in a 5.0 cm diameter, 100 cm high, pulsed sieve plate column with three different sieve plate types and variable plate spacing. The system used was toluene (displaced) - acetone - distilled water. Existing photographic techniques for following and recording the droplet behaviour, and for observing the parameters of the pulse and the pulse shape were further developed and improved. A unique illumination technique was developed by which a moving droplet could be photographed using cine or video photography with good contrast without using any dye. Droplet size from a given nozzle and droplet velocity for a given droplet diameter are reduced under pulsing condition, and it was noted that this effect is enhanced in the presence of sieve plate. The droplet breakup processes are well explained by reference to an impact-breakup mechanism. New correlations to predict droplet diameter based on this mechanism are given below.vskip 1.0cm or in dimensionless groups as follows:- (We)crit= 3.12 - 1.79 (Eo)crit A correlation based on the isotropic turbulence theory was developed to calculate droplet diameter in the emulsion regime.vskip 1.0cm Experimental results show that in the mixer-settler and transitional regimes, pulsing parameters had little effect on the overall dispersed phase mass transfer coefficient during the droplet formation and unhindered travel periods.

Hydrodynamic modeling of mineral wool fiber suspensions in a two-dimensional channel flow

A consequence of a loss of coolant accident is the damage of adjacent insulation materials (IM). IM may then be transported to the containment sump strainers where water is drawn into the ECCS (emergency core cooling system). Blockage of the strainers by IM lead to an increased pressure drop acting on the operating ECCS pumps. IM can also penetrate the strainers, enter the reactor coolant system and then accumulate in the reactor pressure vessel. An experimental and theoretical study that concentrates on mineral wool fiber transport in the containment sump and the ECCS is being performed. The study entails fiber generation and the assessment of fiber transport in single and multi-effect experiments. The experiments include measurement of the terminal settling velocity, the strainer pressure drop, fiber sedimentation and resuspension in a channel flow and jet flow in a rectangular tank. An integrated test facility is also operated to assess the compounded effects. Each experimental facility is used to provide data for the validation of equivalent computational fluid dynamic models. The channel flow facility allows the determination of the steady state distribution of the fibers at different flow velocities. The fibers are modeled in the Eulerian-Eulerian reference frame as spherical wetted agglomerates. The fiber agglomerate size, density, the relative viscosity of the fluid-fiber mixture and the turbulent dispersion of the fibers all affect the steady state accumulation of fibers at the channel base. In the current simulations, two fiber phases are separately considered. The particle size is kept constant while the density is modified, which affects both the terminal velocity and volume fraction. The relative viscosity is only significant at higher concentrations. The numerical model finds that the fibers accumulate at the channel base even at high velocities; therefore, modifications to the drag and turbulent dispersion forces can be made to reduce fiber accumulation.

Concurrent multiscale modelling of atomistic and hydrodynamic processes in liquids

Fluctuations of liquids at the scales where the hydrodynamic and atomistic descriptions overlap are considered. The importance of these fluctuations for atomistic motions is discussed and examples of their accurate modelling with a multi-space-time-scale fluctuating hydrodynamics scheme are provided. To resolve microscopic details of liquid systems, including biomolecular solutions, together with macroscopic fluctuations in space-time, a novel hybrid atomistic-fluctuating hydrodynamics approach is introduced. For a smooth transition between the atomistic and continuum representations, an analogy with two-phase hydrodynamics is used that leads to a strict preservation of macroscopic mass and momentum conservation laws. Examples of numerical implementation of the new hybrid approach for the multiscale simulation of liquid argon in equilibrium conditions are provided. © 2014 The Author(s) Published by the Royal Society.

Hydrodynamic phenomena in the downcomer during flow rate transients in the primary circuit of a PWR

Mixing phenomena observed when the flow rate in a single loop of the primary circuit is changed can influence the operation of pressurized water reactor (PWR) by inducing local gradients of boron concentration or coolant temperature. Analysis of one-dimensional Laser Doppler Anemometry (LDA) measurements during the start-up and shutdown of pump on a single loop of the ROCOM test facility has been performed. The effect of a step change and a ramped change in the flow rate on the axial and azimuthal velocities was examined. Numerical simulations were also performed for the step change in the flow rate that gave quantitative agreement with the axial velocities. Phenomenological agreement was made on the turbulent kinetic energy; however, observed values were a factor of 2.5 less than the turbulent kinetic energy derived from the measurements. © 2007.

A CFD study of biomass pyrolysis in a downer reactor equipped with a novel gas-solid separator - I:hydrodynamic performance

This study presents the first part of a CFD study on the performance of a downer reactor for biomass pyrolysis. The reactor was equipped with a novel gas-solid separation method, developed by the co-authors from the ICFAR (Canada). The separator, which was designed to allow for fast separation of clean pyrolysis gas, consisted of a cone deflector and a gas exit pipe installed inside the downer reactor. A multi-fluid model (Eulerian-Eulerian) with constitutive relations adopted from the kinetic theory of granular flow was used to simulate the multiphase flow. The effects of the various parameters including operation conditions, separator geometry and particle properties on the overall hydrodynamics and separation efficiency were investigated. The model prediction of the separator efficiency was compared with experimental measurements. The results revealed distinct hydrodynamic features around the cone separator, allowing for up to 100% separation efficiency. The developed model provided a platform for the second part of the study, where the biomass pyrolysis is simulated and the product quality as a function of operating conditions is analyzed. Crown Copyright © 2014 Published by Elsevier B.V. All rights reserved.

Purification of phosphoric acid by solvent extraction

This work follows a feasibility study (187) which suggested that a process for purifying wet-process phosphoric acid by solvent extraction should be economically viable. The work was divided into two main areas, (i) chemical and physical measurements on the three-phase system, with or without impurities; (ii) process simulation and optimization. The object was to test the process technically and economically and to optimise the type of solvent. The chemical equilibria and distribution curves for the system water - phosphoric acid - solvent for the solvents n-amyl alcohol, tri-n-butyl phosphate, di-isopropyl ether and methyl isobutyl ketone have been determined. Both pure phosphoric acid and acid containing known amounts of naturally occurring impurities (Fe P0 4 , A1P0 4 , Ca3(P04)Z and Mg 3(P0 4 )Z) were examined. The hydrodynamic characteristics of the systems were also studied. The experimental results obtained for drop size distribution were compared with those obtainable from Hinze's equation (32) and it was found that they deviated by an amount related to the turbulence. A comprehensive literature survey on the purification of wet-process phosphoric acid by organic solvents has been made. The literature regarding solvent extraction fundamentals and equipment and optimization methods for the envisaged process was also reviewed. A modified form of the Kremser-Brown and Souders equation to calculate the number of contact stages was derived. The modification takes into account the special nature of phosphoric acid distribution curves in the studied systems. The process flow-sheet was developed and simulated. Powell's direct search optimization method was selected in conjunction with the linear search algorithm of Davies, Swann and Campey. The objective function was defined as the total annual manufacturing cost and the program was employed to find the optimum operating conditions for anyone of the chosen solvents. The final results demonstrated the following order of feasibility to purify wet-process acid: di-isopropyl ether, methylisobutyl ketone, n-amyl alcohol and tri-n-butyl phosphate.

The effect of selected water-soluble excipients on the dissolution of paracetamol and ibuprofen

The purpose of this investigation was to study the dissolution behavior of paracetamol and ibuprofen in the presence of a range of selected potential excipients. First, a pH-solubility profile was generated for both drugs, and the effect of changing hydrodynamic conditions on the intrinsic dissolution rate was investigated. It was established that both drugs dissolved according to the diffusion-layer model. Paracetamol solubility (approximately 20.3 mg mL -1) did not vary from pH 1.2-8.0, corresponding to the in vivo range in the gastrointestinal tract. Ibuprofen had an intrinsic solubility of approximately 0.06 mg mL-1, and pKa was calculated as 4.4. Second, the effects of selected potential excipients (lactose, potassium bicarbonate, sodium bicarbonate, sodium chloride, and tartaric acid) were evaluated by measuring the effect of the inclusion of each additive in the dissolution medium on drug solubility, drug intrinsic dissolution rate, and solution viscosity. The results were evaluated using the diffusion-layer model, and it was determined that for paracetamol, the collected data fitted the model for all the excipients studied. For ibuprofen, it was found that there were differences between the excipients that raised the solution pH above the pK a to those that did not. For the excipients raising the pH above the pKa, the effect on intrinsic dissolution rate was not as high as that expected from the change in drug solubility. It was postulated that this might be due to lack of penetration of the excipient into the drug boundary layer microenvironment. Formulators may calculate the effect of adding an excipient based on solubility increases but may not find the dissolution rate improvement expected. Copyright © 2005 Taylor & Francis Inc.

The development and optimisation of a fast pyrolysis process for bio-oil production

A two-tier study is presented in this thesis. The first involves the commissioning of an extant but at the time, unproven bubbling fluidised bed fast pyrolysis unit. The unit was designed for an intended nominal throughput of 300 g/h of biomass. The unit came complete with solids separation, pyrolysis vapour quenching and oil collection systems. Modifications were carried out on various sections of the system including the reactor heating, quenching and liquid collection systems. The modifications allowed for fast pyrolysis experiments to be carried out at the appropriate temperatures. Bio-oil was generated using conventional biomass feedstocks including Willow, beechwood, Pine and Miscanthus. Results from this phase of the research showed however, that although the rig was capable of processing biomass to bio-oil, it was characterised by low mass balance closures and recurrent operational problems. The problems included blockages, poor reactor hydrodynamics and reduced organic liquid yields. The less than optimal performance of individual sections, particularly the feed and reactor systems of the rig, culminated in a poor overall performance of the system. The second phase of this research involved the redesign of two key components of the unit. An alternative feeding system was commissioned for the unit. The feed system included an off the shelf gravimetric system for accurate metering and efficient delivery of biomass. Similarly, a new bubbling fluidised bed reactor with an intended nominal throughput of 500g/h of biomass was designed and constructed. The design leveraged on experience from the initial commissioning phase with proven kinetic and hydrodynamic studies. These units were commissioned as part of the optimisation phase of the study. Also as part of this study, two varieties each, of previously unreported feedstocks namely Jatropha curcas and Moringa olifiera oil seed press cakes were characterised to determine their suitability as feedstocks for liquid fuel production via fast pyrolysis. Consequently, the feedstocks were used for the production of pyrolysis liquids. The quality of the pyrolysis liquids from the feedstocks were then investigated via a number of analytical techniques. The oils from the press cakes showed high levels of stability and reduced pH values. The improvements to the design of the fast pyrolysis unit led to higher mass balance closures and increased organic liquid yields. The maximum liquid yield obtained from the press cakes was from African Jatropha press cake at 66 wt% on a dry basis.

Solvent extraction of phosphoric acid

This work investigated the purification of phosphoric acid using a suitable organic solvent, followed by re-extraction of the acid from the solvent using water. The work consisted of practical batch and continuous studies and the economics and design of a full scale plant, based on the experimental data. A comprehensive literature survey on the purification of wet process phosphoric acid by organic solvents is presented and the literature describing the design and operation of mixer-settlers has also been reviewed. In batch studies, the equilibrium and distribution curves for the systems water-phosphoric acid-solvent for Benzaldehyde, Cyclohexanol and Methylisobutylketone (MIBK) were determined together with hydrodynamic characteristics for both pure and impure systems. The settling time increased with acid concentration, but power input had no effect. Drop size was found to reduce with acid concentration and power input. For the continuous studies a novel horizontal mixer~settler cascade was designed, constructed and operated using pure and impure acid with MIBK as the solvent. The cascade incorporates three air turbine agitated, cylindrical 900 ml mixers, and three cylindrical 200 ml settlers with air-lift solvent interstage transfer. Mean drop size in the fully baffled mixer was correlated. Drop size distributions were log-normal and size decreased with acid concentration and power input and increased with dispersed phase hold-up. Phase inversion studies showed that the width of the ambivalent region depended upon rotor speed, hold-up and acid concentration. Settler characteristics were investigated by measuring wedge length. Distribution coefficients of impurities and acid were also investigated. The following optimum extraction conditions were found: initial acid concentration 63%, phase ratio of solvent to acid 1:1 (v/v), impeller speed recommended 900 r.p.m. In the washing step the maximum phase ratio of solvent to water was 8:1 (v/v). Work on phosphoric acid concentration involved constructing distillation equipment consisting of a 10& spherical still. A 100 T/d scale detailed process design including capital cost, operating cost and profitability was also completed. A profit model for phosphoric acid extraction was developed and maximised. Recommendations are made for both the application of the results to a practical design and for extensions of the study.

Coalescence of secondary dispersions in fibrous beds

SUMMARY A study has been made of the coalescence of secondary dispersions in a fibrous bed. The literature pertaining to the formation, hydrodynamic behaviour and methods of separation of droplets less than one hundred micrometres in diameter has been reviewed with particular reference to fibrous bed coalescers. The main operating parameters were identified as inlet drop size distribution, phase ratio, superficial velocity and the thickness and voidage of the bed . A recirculatory rig with interchangeable fibrous bed pads was designed and operated with toluene-water dispersions generated by a combination of centrifugal pumps . Inlet drop sizes were analysed using a Coulter Counter and outlet drops were sized photographically. A novel technique, involving conductivity measur ements at different planes in the bed, was developed to measure hold up distribution. Single phase flow and two phase flow pressure drops were correlated by a Blake-Kozeny type equation. Exit drop size was independent of inlet drop size distribution and phase ratio but a function of superficialvelocity and packing thickness. Average bed hold up was independent of inlet drop size distribution and phase ratio, but decreased with increase in superficial velocity. Hold up was not evenly distributed in the bed, the highest value occurred at the inlet followed by a sharp -2 drop at approximately 1.2 x 10 m. Hold up remained constant throughout the rest of the bed until the exit plane, where it increased. From the results, a mechanism is postulated involving: (a) Capture of the inlet drops followed by interdrop coalescence until an equilibrium value is reached. (b) Equilibrium size droplets flowing as rivulets through the intermediate portion of the bed, and (c) Each rivulet forms droplets at the exit face, which detach by a 'drip point' mechanism.

Fast pyrolysis of biomass in a circulating fluidised bed reactor

The objective of this work was to design, construct, test and operate a novel circulating fluid bed fast pyrolysis reactor system for production of liquids from biomass. The novelty lies in incorporating an integral char combustor to provide autothermal operation. A reactor design methodology was devised which correlated input parameters to process variables, namely temperature, heat transfer and gas/vapour residence time, for both the char combustor and biomass pyrolyser. From this methodology a CFB reactor was designed with integral char combustion for 10 kg/h biomass throughput. A full-scale cold model of the CFB unit was constructed and tested to derive suitable hydrodynamic relationships and performance constraints. Early difficulties encountered with poor solids circulation and inefficient product recovery were overcome by a series of modifications. A total of 11 runs in a pyrolysis mode were carried out with a maximum total liquids yield of 61.50% wt on a maf biomass basis, obtained at 500°C and with 0.46 s gas/vapour residence time. This could be improved by improved vapour recovery by direct quenching up to an anticipated 75 % wt on a moisture-and-ash-free biomass basis. The reactor provides a very high specific throughput of 1.12 - 1.48 kg/hm2 and the lowest gas-to-feed ratio of 1.3 - 1.9 kg gas/kg feed compared to other fast pyrolysis processes based on pneumatic reactors and has a good scale-up potential. These features should provide significant capital cost reduction. Results to date suggest that the process is limited by the extent of char combustion. Future work will address resizing of the char combustor to increase overall system capacity, improvement in solid separation and substantially better liquid recovery. Extended testing will provide better evaluation of steady state operation and provide data for process simulation and reactor modeling.