Identical Flow Rate Research Articles

Breast Lesion Detection and Characterization at Contrast-enhanced MR Mammography: Gadobenate Dimeglumine versus Gadopentetate Dimeglumine

To prospectively and intraindividually compare equivalent (0.1 mmol per kilogram of body weight) doses of gadobenate dimeglumine and gadopentetate dimeglumine for accuracy of detection and characterization of breast lesions at contrast material-enhanced magnetic resonance (MR) mammography. Ethics committee approval and informed consent were obtained. Twenty-six consecutive women (mean age, 47.8 years) suspected of having a breast tumor at mammography and sonography underwent two identical MR examinations at 1.5 T; examinations were separated by more than 48 hours but less than 72 hours. A T1-weighted three-dimensional gradient-echo sequence was used, and images were acquired before and at 0, 2, 4, 6, and 8 minutes after randomized injection of gadopentetate dimeglumine or gadobenate dimeglumine at an identical flow rate of 2 mL/sec. Separate and combined assessment of unenhanced, contrast-enhanced, and subtracted images was performed blindly by two readers in consensus. Accuracy for lesion detection was determined against a final diagnosis based on findings at conventional mammography, sonography, and surgery. Sensitivity, specificity, positive and negative predictive values, and overall accuracy for malignant lesion identification were determined against histologic results. Data were analyzed with the McNemar test, proportional odds models, and analysis of variance. MR mammography with gadobenate dimeglumine depicted significantly (P = .003) more lesions (45 of 46) than did that with gadopentetate dimeglumine (36 of 46), and detected lesions were significantly (P < .001) more conspicuous with gadobenate dimeglumine. Confidence for characterization was significantly (P = .031) greater with gadobenate dimeglumine. Comparison of the contrast agents for their ability to help identify malignant lesions revealed significant (P = .02) superiority for gadobenate dimeglumine: Sensitivity, specificity, positive predictive value, negative predictive value, and overall accuracy for malignant lesion identification were, respectively, 94.7%, 100%, 100%, 80.0%, and 95.6% with gadobenate dimeglumine and 76.3%, 100%, 100%, 47.1%, and 80.4% with gadopentetate dimeglumine. Quantitative evaluation of signal intensity-time curves revealed significantly (P < .001) greater lesion enhancement with gadobenate dimeglumine. Detection of breast lesions and accurate identification of malignant lesions at MR imaging are significantly superior with gadobenate dimeglumine in comparison with gadopentetate dimeglumine.

Ammonia large scale atmospheric dispersion experiments in industrial configurations

A programme of large-scale experiments for atmospheric dispersion was carried out by INERIS over a period extending from December 1996 to April 1997. The objectives of the test campaign were to measure anhydrous ammonia concentrations in a range of few meters to 2 km from the release, in order to generate data to be used to improve 2-phase discharge and dispersion modelling. The discharges were released from a 6-tonne storage tank of pressurised liquid ammonia and through a discharge device with an outlet diameter of 2 in. Fifteen trials were carried out with various release configurations corresponding to industrial situations (impinging jets on the ground and on a wall at various distances, release through a flange without seal…). The quantity of ammonia discharged from the liquid phase varied according to the tests, from 1.4 to 3.5 tons for durations between 7 and 14 min and, therefore, at flow rates between 2 and 4.5 kg/s. Approximately 200 sensors were settled downwind to measure ammonia concentrations and temperature in the plume. These tests showed that for discharges with identical flow rates the distances corresponding to the same concentration vary a lot according to the configurations. These distances tend to be reduced by the presence of obstacles or retention dikes that collected liquid ammonia. In the paper, the main experimental results are presented. In order to enable the comparisons with numerical predictions, more detailed information are given in [Bouet R. (1999). Ammoniac—Essais de dispersion atmosphérique à grande échelle. INERIS rapport, ref INERIS-DRA-RBo-1999-20410 (available at http://www.ineris.fr/recherches/recherches.htm).

Effects of die geometry on cell nucleation of PS foams blown with CO2

AbstractThis paper investigates the effect of varying the geometry of the die on the cell nucleation behavior of extruded PS foams blown with CO2. Three interchangeable groups of carefully calibrated filamentary dies have been used in the experimental study. The dies were deliberately designed to have either different pressure drop rates while having identical die pressures and flow rates, or different die pressures while having identical pressure drop rates and flow rates. The experimental results revealed that the geometry of the die governs the cell density of extruded PS foams, especially because of its significant effect on the pressure drop rate across the die. However, the effect of the die back pressure on the cell density was found to be marginal, whereas its effect on the cell morphology was found to be predominant. In addition, regardless of die geometry, the CO2 content proved to be a very sensitive parameter with respect to the cell nucleation behavior of extruded PS foams. On the other hand, the cell density was slightly improved by an increase of the tale content, especially at reduced concentrations of CO2.

UREA REDUCTION RATIOS MEASURED AT TWO DIFFERENT INTERDIALYTIC INTERVALS

Purpose of the study: In thrice weekly hemodialysis (HD), HD adequacy is usually measured during the first dialysis of the week, when the pre BUN is typically the highest and the interdialytic (ID) interval is the longest. We calculated urea reduction ratios (URR) at two different ID intervals to assess patterns of variability. Methods of study: 43 patients (pts) on maintenance HD were studied. All were on the same dialyzer and all had identical dialysate flow rates. URRs (slow pump sampling) were calculated on 2 different days after 72 and 48-hour ID intervals. Pts with a difference in blood flow rate (BFR) ± 50 ml/min or in duration of HD ± 30 min between the 2 sessions were excluded. 30 pts (19 arteriovenous graft/fistula [AVG/AVFl, 11 double lumen cuffed catheters) were included in the final analysis, with a mean HD duration of 3.85 hrs and mean BFR of 322 ml/min. Results: No significant difference in URR was noted when measured at 72 or 48-hr ID intervals. No specific pattern was seen when URRs were compared to the BUN gradient (pre BUN minus post BUN). On analysis according to access type, AVG/AVF or catheter, there was no significant difference in URR between the two ID intervals. Again, no significant difference was noted in a subgroup of 15 pts with identical BFR and identical duration in both sessions irrespective of type of access. Conclusion: No significant difference was seen in URR calculated at 72 or 48 hour ID interval.

Forced convective heat transfer and pressure drop of air flowing in a rectangle duct with cross-ribs on the opposite walls

Experiments were conducted to investigate the forced convective heat transfer and flow friction of turbulent airflow in a rectangular duct with cross-ribs attached at the two principal walls in the Reynolds number range from 5000 to 40000. The effect of the rib cross angle (45°, 60°, 75°) and the height (4 mm, 5 mm) of the cross-ribs on the forced convection and flow friction were tested. Non-dimensional correlations for the duct average Nusselt number and friction factor of cross-ribs duct were developed from the test data. Experiments were also conducted for the corresponding parallel ribs to compare their relative performance. The experimental results show that both of the convective heat transfer coefficient and friction factor were increased with cross-ribs, with 45° cross-ribs being the best. Compared with parallel ribs normal to the flow direction under identical flow rate and identical pumping power constraints, the cross-ribs can enhance heat transfer in the lower Reynolds number region, while in the high Reynolds number region, the heat transfer performance of the parallel ribs seems better.

Effect of inhaled indomethacin on distilled water-induced airway epithelial cell swelling.

We evaluated the mechanism of the anti-asthmatic effect of inhaled indomethacin (Indo) by using an animal model (guinea pigs) of airway inflammation. After being exposed to either ozone or room air at identical flow rates (5 l/min) for 2 h, guinea pigs were anesthetized, tracheostomized, and lung resistance (RL) was subsequently measured. Guinea pigs inhaled either saline or Indo (1.5 mg/ml) for 1 min before undergoing an ultrasonically nebulized distilled water (UNDW) inhalation test. RL increased significantly after 10 min of UNDW inhalation in the room air and ozone groups but more so in the ozone group. This increase in RL was significantly suppressed by pretreatment with Indo. In the morphometric assessment of airway mucosa, a significant swelling of the epithelial cells after UNDW inhalation was observed in both the room air and ozone groups but especially so in the ozone group. This increase was also suppressed with Indo pretreatment. These results suggest that the increase in RL and the swelling of airway epithelial cells induced by inhaled UNDW in ozone-exposed guinea pigs was suppressed by pretreatment of inhaled Indo and that this suppression may be one of the reasons for the anti-asthmatic effect of inhaled Indo.

Characteristics of droplets generated by bubble bursting from chromic acid solutions

The effects of electrolyte concentration and gas flow rate on the characteristics of droplets generated from bubbles bursting on the surface of CrO 3 solution were studied with an experimental bubbling system. The experimental conditions included two electrolyte concentrations, 125 and 250 g l -1 of CrO 3, and three flow rates of sparging air in the range of 4–8 l min -1. A cascade impactor collected droplet samples for chemical analysis. A laser aerosol spectrophotometer and an aerodynamic particle sizer were employed simultaneously to measure the number concentration and size distribution of the droplets. A layer of foam formed on the liquid surface under all experimental conditions studied except at the gas flow rate of 4 l min -1 in 125 g l -1 CrO 3 solution. Foams had a significant effect on the characteristics of droplets generated from bursting bubbles. At identical gas flow rate and electrolyte concentration, the formation of foams led to a reduction in number concentration of droplets larger than 10 μm in aerodynamic diameter and a lower concentration of airborne Cr(VI). In the ranges of gas flow rate and electrolyte concentration tested, the results showed that the airborne Cr(VI) mass concentration increased significantly with gas flow rate and slightly with electrolyte concentration in the presence of foams. The results obtained in the present study should have applications in the emission control of Cr(VI)-containing droplets in chromium electroplating processes.

Design of U-Column Microwave-Assisted Extraction System and Its Application to Pigment Extraction from Food

Amicrowave-assisted extraction (MAE) system for biological material was designed with a cylindrical cavity, a rectangular wave guide, a magnetron of 2450 MHz and a U-column made of two glass columns; one for heating solvent and the other for the packed bed. The central focusing, dipolar power mode in the cavity was simulated, and the actual mode when using the extraction column was verified with dummy food (agar containing 0−5% NaCl). The position and the alignment of the U-column in the cavity were examined using two design strategies. Firstly, the heating column was matched to the central focusing mode to achieve the highest heating rate of the solvent, and secondly, the packed column was positioned at a mild power mode to disrupt biological cells to increase the extraction rate. The set-up of the MAE system was applied successfully to the extraction of the edible yellow pigment from Cape Jasmine ( Gardenia Jasminoides Ellis ) and the extraction yield was 50% higher than the conventional extraction method on the basis of identical thermal energy input and flow rate. The extract from the MAE system showed a pulsating flow pattern with a nearly constant volume fraction. In spite of focused microwave irradiation to the heating column, the temperature of the extract was self-regulated in the range of 70−95°C.

ROLE OF GEOMETRIC PARAMETERS ON THE DROP SIZE CHARACTERISTICS OF LIQUID-LIQUID COAXIAL SWIRL ATOMIZERS

Measurements of drop size characteristics of liquid-liquid coaxial swirl atomizers used in bipropellant rocket engines are made for a range of flow and geometric parameters. The merging and separation process of liquid sheets which exhibits hysteresis leads to a drastic variation in the size characteristics which will have serious implications on the engine throttling. At identical flow rates through a given coaxial atomizer, the merged state may result in mean drop size nearly 40-50% larger than that in the separated state. For constant inner flow rate, the Sauter mean diameter (SMD) of the combined spray initially increases, reaches a maximum, and thereafter reduces with the outer jet flow rate. The inner jet influences the drop size distribution only at low outer flow conditions. The atomization quality of the combined spray can be improved specifically at high outer flow rate conditions by increasing the swirl intensity of the jets or by providing a positive offset to the inner orifice.

Minimum urine flow rate during water deprivation: importance of the nonurea versus total osmolality in the inner medulla.

Antidiuretic hormone leads to an increase in the permeability for water and urea in the inner medullary collecting duct. Hence, urea may not be an "effective" osmole in the inner medulla during maximal renal water conservation. Accordingly, the purpose of this study was to evaluate whether differences in the rate of urea excretion would influence maximum renal water conservation in humans. In water-deprived rats, the concentration of urea and total osmolality were somewhat higher in the urine exiting the inner medullary collecting duct than in interstitial fluid obtained from the entire papillary tip. Nevertheless, the "nonurea" (total osmolality minus urea in millimolar terms) osmolality was virtually identical in both locations. Chronically fasted human subjects that were water-deprived for 16 h had a lower rate of urea excretion (71 +/- 7 versus 225 +/- 14 mumol/min) and a somewhat lower urine osmolality (745 +/- 53 versus 918 +/- 20 mosmol/kg H2O). Nevertheless, they had identical urine flow rates (0.5 +/- 0.01 and 0.5 +/- 0.02 ml/min, respectively), and their nonurea osmolality also was similar (587 +/- 25 and 475 +/- 14 mosmol/kg H2O, respectively) to the water-deprived normal subjects. The composition of their urine differed in that the principal nonurea osmoles became NH4+ and beta-hydroxybutyrate rather than Na and C1. During water deprivation in normal subjects, the ingestion of urea caused a twofold rise in urine flow rate, a fall in the nonurea osmolality, and a rise in the rate of excretion of nonurea osmoles. The nonurea osmolality of the urine, and presumably the medullary interstitial fluid as well, was inversely related to the urea excretion rate. In chronic fasting, the nature, but not the quantity, of nonurea osmoles changed. The similar minimum urine volume was predictable from an analysis based on nonurea osmole considerations.

Efficacy and acceptability of different modes of oxygen administration in children: implications for a community hospital

Eighty under-five children admitted in the pediatric ward with acute respiratory distress requiring oxygen inhalation were prospectively studied. Oxygen was administered to all the children by head box, face mask, nasopharyngeal catheter, and twin-holed prenasal catheter in a predetermined sequence. Oxygen was delivered at a flow rate of 4 l/min in the head box and by face mask and at a rate of 1 l/min for nasopharyngeal catheter and twin-holed prenasal catheter. There was a significant rise in paO2 and SaO2 values with all the oxygen delivery methods. The number of children who achieved paO2 of > 90 mmHg with oxygen delivered by head box was 53 (69 per cent), with face mask 37 (57 per cent), with nasopharyngeal catheter 13 (26 per cent), and with twin-holed prenasal catheter 18 (25 per cent). In view of high acceptability of twin-holed prenasal catheter, a further pilot study involving 10 children was carried out to compare the efficacy of head box and twin-holed prenasal catheter at an identical oxygen flow rate of 4 l/min. The number of children achieving paO2 of > 90 mmHg were comparable, i.e. seven (70 per cent) and eight (80 per cent) when the oxygen was delivered by head box and twin-holed prenasal catheter, respectively. It is concluded that both head box and twin-holed prenasal catheter are equally effective, acceptable and safe methods for administration of oxygen to children with acute respiratory disorders. In view of the cost-effectiveness, and easy availability and affordability of twin-holed prenasal catheter, it should be popularized in the small hospitals in the community, while head box should be reserved for use in the referral hospitals.

Coupled chaotic chemical oscillators.

We present a model study of two mass-coupled reactors containing the Belousov-Zhabotinsky reaction under chaotic conditions. The critical coupling strength is estimated for symmetry breaking when two identical low flow rate chaotic modes are coupled. Our results confirm that the critical coupling strength is directly proportional to the maximum Lyapunov exponent of the uncoupled system. The constant of proportionality is found to be somewhat larger than the theoretical value. Direct integration reveals a rich structure of dynamical behavior when the coupling strength and the flow rate in one cell are varied. Our simulations reveal domains of oscillator death, in which a stable steady state coexists with limit cycle oscillations. We introduce a simple model for predicting the dynamics of the coupled system from the dynamical behavior of the uncoupled subsystems and the dependence on the coupling strength of the Hopf bifurcation of the coupled system. The model gives good estimates of the dynamical behavior of two coupled oscillators with a small difference in one parameter at intermediate and high coupling strengths. \textcopyright{} 1996 The American Physical Society.

Oxidation of ductile particle reinforced Ti-48Al composite

The oxidation behavior of a ductile TiNb particle reinforced Ti-48A1 (at. pct) system was studied at different temperatures. The objective of this work was to establish the role played by the TiNb reinforcement on the oxidation process. The activation energy for oxidation of Ti-48A1 was 324 kJ/mol and that of Ti-48Al-20 vol pct TiNb was 315 kJ/mol. The kinetics of oxidation of both the material systems are similar. At 982 °C, the outermost oxide layer in contact with air was always near stoichiometric TiO2. In all the alloys, a layer of porosity was created just below the outer TiO2 layer by the Kirkendall mechanism as a result of the rapid outward dif-fusion of Ti atoms. TiNb particles are more oxidation resistant than Ti-48A1. The boundary of the TiNb particles was oxidized to form TiO2. However, most of the TiNb particles were un-touched and existed as islands embedded within the Ti and Al oxides formed by oxidation of Ti-48A1. Oxidation in pure oxygen lowers the oxidation kinetics, as compared to oxidation in pure air for identical gas flow rates at 982 °C.

Sensitivity to ischaemic ATP breakdown in different models of cardiac hypertrophy in rats

To evaluate the sensitivity to ischaemia of rat hearts made hypertrophic by pressure overload [two-kidney, one clip (2-K,1C) rats], volume overload (aortocaval arteriovenous shunt), minoxidil or isoproterenol. Ischaemia was induced in the isolated perfused hearts by a stepwise lowering of the perfusion pressure; at each step the coronary effluent was assessed for the products of ATP breakdown. Hypertension increased cardiac weight by 35 and 56% after 2.5 and 12 weeks, respectively. Volume overload increased heart weight by 25 and 55% after 1 and 12 weeks, respectively. Minoxidil (for 5 weeks) or isoproterenol (for 1 week) increased cardiac weight by 22 and 16%, respectively. The hearts from 2-K,1C rats started to release ATP catabolites in the coronary effluent at a substantially higher perfusion pressure, and with significantly higher maximal levels, than the control hearts. In contrast, in volume overload cardiac ATP breakdown was similar to that in the controls, and isoproterenol administration caused significantly lower levels of ATP breakdown. At identical flow rates, normalized per gram dry tissue, the purine concentration in the coronary effluent was similar in all of the models of cardiac hypertrophy studied and in the respective controls, and was even lower in the long-term volume-overloaded and isoproterenol-induced hypertrophic hearts. We conclude that hearts from hypertensive rats are more sensitive to ischaemic ATP breakdown during lowering of perfusion pressure than hearts from volume-overloaded or control rats. This is independent of the duration of the hypertrophic process, and can be explained by a lower coronary flow per gram heart tissue at a given perfusion pressure. This conclusion is strengthened by the observation that hypertrophic hearts from volume-overloaded rats had similar amounts of cardiac hypertrophy to the hearts from the hypertensive rats, without a change in flow, coronary vascular resistance or ischaemic sensitivity, whereas the hearts from isoproterenol-treated rats had lower ischaemic sensitivity and coronary vascular resistance.

Ischaemia induced alternans of action potential duration in the intact-heart: dependence on coronary flow, preload and cycle length.

Clinical and experimental evidence relate action potential duration (APD) alternans to ischaemic heart disease and ventricular arrhythmias. The present investigation was performed to study the quantitative relationship between APD alternans and the degree of ischaemia, loading conditions and cycle length (CL) in an intact heart. Monophasic action potentials (MAP) were simultaneously recorded by contact electrodes from two left (LV) and one right ventricular (RV) sites in 20 Langendorff-perfused rabbit hearts. The preparations were subjected to global ischaemia at flow rates ranging from 40% of normal flow to complete cessation of flow. Pacing was performed at either constant or regularly changing CL. The magnitude of APD alternans was expressed as beat-to-beat differences in action potential duration of two consecutive MAPs. During normal perfusion, neither very fast pacing at a CL of 200 ms nor periodical rate switches resulted in persistent APD alternans. Pacing at a constant CL of 800 ms did not induce APD alternans at complete cessation of flow for 6 min. However, alternans developed progressively at a constant CL of 400 ms after 2.8 +/- 0.3 min of complete ischaemia at the pre-loaded LV, and after 4.6 +/- 0.4 min at the unloaded RV (P < 0.01). The reduction of preload at the LV from 15 to 5 mmHg end-diastolic pressure delayed development of APD alternans from 2.8 +/- 03 min to 4.3 +/- 0.4 min (P < 0.05) at 400 ms CL. Following graded underperfusion of 40%, 20% and 10% of initial flow, persistent APD alternans developed in relation to the degree of flow reduction and increased progressively with duration of ischaemia. APD alternans at the LV always preceded the onset of APD alternans at the RV. In experiments with identical flow rates the shortest CL of 200 ms resulted in the greatest and earliest initiation of APD alternans compared to the longer CL (P < 0.01, P < 0.001). An increase in CL from 400 to 800 ms immediately abolished APD alternans, generated by the shorter CL, at any time during the 6 min period of complete ischaemia. Similarly, increasing the cycle length from 200 or 400 to 600 ms eliminated APD alternans up to 6 min of ischaemia and significantly reduced its magnitude between 7 and 10 min within a few beats. We conclude that persistent APD alternans is a characteristic findings in the rabbit heart during global ischaemia4 It is a sensitive parameter of the severity of ischaemia and depends.(ABSTRACT TRUNCATED AT 400 WORDS)

Impact of impinging wall jet on color Doppler quantification of mitral regurgitation.

In clinical color Doppler examinations, mitral regurgitant jets are often observed to impinge on the left atrial wall immediately beyond the mitral valve. In accordance with fluid dynamics theory, we hypothesized that a jet impinging on a wall would lose momentum more rapidly, undergo spatial distortion, and thus have a different observed jet area from that of a free jet with an identical flow rate. To test this hypothesis in vivo, we studied 44 patients with mitral regurgitation--30 with centrally directed free jets and 14 with eccentrically directed impinging wall jets. Maximal color jet areas (cm2) (with and without correction for left atrial size) were correlated with mitral regurgitant volumes, flow rates, and fractions derived from pulsed Doppler mitral and aortic forward flows. The groups were compared by analysis of covariance. Mean +/- SD mitral regurgitant fraction, regurgitant volume, and mean flow rate averaged 37 +/- 17%, 3.06 +/- 2.65 l/min, and 147 +/- 118 ml/sec, respectively. The maximal jet area from color Doppler imaging correlated relatively well with the mitral regurgitant fraction in the patients with free mitral regurgitant jets (r = 0.74, p less than 0.0001) but poorly in the patients with impinging wall jets (r = 0.42, p = NS). Although the mitral regurgitant fraction was larger (p less than 0.05) in patients with wall jets (44 +/- 20%) than in those with free jets (33 +/- 15%), the maximal jet area was significantly smaller (4.78 +/- 2.87 cm2 for wall jets versus 9.17 +/- 6.45 cm2 for free jets, p less than 0.01). For the same regurgitant fraction, wall jets were only approximately 40% of the size of a corresponding free jet, a difference confirmed by analysis of covariance (p less than 0.0001). Patients with mitral regurgitation frequently have jets that impinge on the left atrial wall close to the mitral valve. Such impinging wall jets are less predictable and usually have much smaller color Doppler areas in conventional echocardiographic views than do free jets of similar regurgitant severity. Jet morphology should be considered in the semiquantitative interpretation of mitral regurgitation by Doppler color flow mapping. Future studies of the three-dimensional morphology of wall jets may aid in their assessment.

High-performance anion-exchange chromatography of sugars and sugar alcohols on quaternary ammonium resins under alkaline conditions

Ninety-three sugars and sugar alcohols of one to four monosaccharide units were subjected to high-performance anion-exchange chromatography on three quaternary ammonium columns of the same size and virtually the same composition under identical eluent flow rates (1 mL·min −1) and compositions (aqueous 0.1 n NaOH). Although the columns had very different histories of use, their different capacity factors for individual carbohydrates can be linearly correlated. Those for monosaccharides are lowest for sugar alcohols, and are higher and roughly similar for analogous aldoses and ketoses. There is a general trend, strongest with sugar alcohols, for capacity factors to increase withincreasing numbers of carbon atoms. Increasing numbers of hydroxyl groups on residues of similar structure lead to increasing capacity factors. For members of homologous oligosaccharides series, capacity factors increase in a regular and predictable manner with chain length. Peak areas for different sugars generated by a differential refractometer are roughly correlated with mass concentrations; with a pulsed amperometric detector, there are equally rough correlations with either molar or mass concentration.

Measuring kLa with randomly pulsed dynamic method

This reports on the determination of the overall oxygen transfer coefficient in a mechanically agitated vessel using a randomly pulsed dynamic method. This method consists in exciting the system by randomly switching the inlet gas stream with air or nitrogen with an identical volumetric flow rate. A pseudo-random binary sequence was used. This procedure is routinely used in process control for the identification of system's transfer function. The pulsed dynamic method gives good reliability (as compared with the traditional gassing-out method) and reproducibility in water. However, further improvement is needed before it can be used to monitor on-line the k(L)a during a fermentation.

Use of Ozone and Fluidized-Bed Biofilters for Increased Ammonia Removal and Fish Loading Rates

Abstract A water reuse system incorporating ozonation and a fluidized-bed, granular carbon biofilter supported approximately six times more fish than a conventional system of identical size and flow rate that incorporated oxygenation and a fixed-bed gravel biofilter. Increasing the hydraulic loading rate to 44 ML/cm2·s in an upflow granular carbon biofilter caused the carbon particles to become suspended in upflow currents (fluidized) and tripled ammonia removal. Ozonating the water prior to sedimentation, physical filtration, and biofiltration also increased ammonia removal, by reducing organic matter concentrations and favoring the growth of nitrifying bacteria over heterotrophic bacteria in the biofilter. Ozonation directly reduced nitrite concentrations by oxidation, and it reduced turbidity. Ammonia removal per unit volume was a more useful criterion for evaluating fluidized-bed biofilters than ammonia removal per unit of substrate surface area.

Evaluation of Tube Diameter and Fan Induced Swirl in Polyethylene Ventilation Tubes

ABSTRACT THE influence of flow swirl and tube diameter reduction have been examined for polyethylene ventilation tubes suitable for greenhouse applications. It was found that a conventional unmodified ventilation fan provided nearly identical flow rates from a 610 mm or 457 mm perforated ventilation tube, provided that swirl control was employed at the tube inlets. A six vane antiswirl device was installed that removed swirl for free fan exhaust. The antiswirl device can be made by a greenhouse operator or tradesman. Operation of the 457 mm tube without swirl control was found to be unacceptable, since the required contraction piece increased the fan induced swirl, causing tube vibration and poor flow distribution. Measurements of discharge from the ventilation holes were obtained along both tubes for flow with and without swirl control. The total discharge was found to be in good agreement with the measured flow into the fan in all cases. Friction factors were obtained for a nonperforated 610 mm tube. A cosine correction for swirl was included in the analysis to account for the actual length of flow path. The resulting friction factors were slightly lower than smooth pipe values in all cases. Polyethylene tubes can be reduced in size for a number of applications if flow swirl is controlled. Smaller tube sizes for overhead ventilation are of interest to greenhouse operators, because size reduction leads to less light blockage and hence to greater crop productivity.