Gas Holdup in a Trayed Cold-Flow Bubble Column

An Experimental Study Was Performed to Investigate the Effect of Sieve Trays on the Time-Averaged Gas Holdup Profiles and the overall Gas Holdup in a Cold-Flow Bubble Column that Was Scaled-Down from a Commercial Unit. Γ-Ray Computed Tomography (CT) Was Used to Scan the Column at Several Axial Locations in the Presence and Absence of Trays from Which the Local Variation of the Gas Holdup Was Extracted. the overall Gas Holdup Was Also Determined using the Same Configuration by Comparing the Expanded and Static Liquid Heights. Air and Water Were Used as the Gas-Liquid System. the Superficial Gas and Liquid Velocities Were Selected to Span the Range of the Commercial System using Gas Spargers Having Multiple Lateral Distributors that Were Also Scaled-Down from the Commercial Design. to Investigate the Impact of Sparger Hole Density on the Local and overall Gas Holdup, Two Difference Sparger Designs Were Used in Which the Hole Density Per Lateral Was Varied. the Gas Hole Velocity Was Maintained Constant at Ca. 245 M/s, Which Approached that Used in the Commercial Reactor. It is Shown that the Local Gas Holdup Determined by CT is Generally Higher in the Tray Down Comer Region and Exhibits an Asymmetric Pattern When Trays Are Present. the Use of Increased Sparger Hole Density at a Constant Gas Superficial Velocity Leads to Steeper Gradient in the Gas Holdup Near the Column Centerline and a Higher overall Gas Holdup. These Findings Suggest that the Performance of Bubble Column Reactors for Various Applications is Sensitive to Both Sparger and Tray Design. © 2001 Elsevier Science Ltd. All Rights Reserved

Clinical and echocardiographic predictors of mortality in acute pulmonary embolism

Purpose: The aim of this study was to evaluate the utility of adding quantitative assessments of cardiac function from echocardiography to clinical factors in predicting the outcome of patients with acute pulmonary embolism (PE). Methods: Patients with a diagnosis of acute PE, based on a positive ventilation perfusion scan or computed tomography (CT) chest angiogram, were identified using the Duke University Hospital Database. Of these, 69 had echocardiograms within 24–48 h of the diagnosis that were suitable for offline analysis. Clinical features that were analyzed included age, gender, body mass index, vital signs and comorbidities. Echocardiographic parameters that were analyzed included left ventricular (LV) ejection fraction (EF), regional, free wall and global RV speckle-tracking strain, RV fraction area change (RVFAC), Tricuspid Annular Plane Systolic Excursion (TAPSE), pulmonary artery acceleration time (PAAT) and RV myocardial performance (Tei) index. Univariable and multivariable regression statistical analysis models were used. Results: Out of 69 patients with acute PE, the median age was 55 and 48 % were female. The median body mass 2 index (BMI) was 27 kg/m . Twenty-nine percent of the cohort had a history of cancer, with a significant increase in cancer prevalence in non-survivors (57 % vs 29 %, p = 0.02). Clinical parameters including heart rate, respiratory rate, troponin T level, active malignancy, hypertension and COPD were higher among non-survivors when compared to survivors (p ≤ 0.05). Using univariable analysis, NYHA class III symptoms, hypoxemia on presentation, tachycardia, tachypnea, elevation in Troponin T, absence of hypertension, active malignancy and chronic obstructive pulmonary disease (COPD) were increased in non-survivors compared to survivors (p ≤ 0.05). In multivariable models, RV Tei Index, global and free (lateral) wall RVLS were found to be negatively associated with survival probability after adjusting for age, gender and systolic blood pressure (p ≤ 0.05). Conclusion: The addition of echocardiographic assessment of RV function to clinical parameters improved the prediction of outcomes for patients with acute PE. Larger studies are needed to validate these findings

New aspects in the pathogenesis, prevention, and treatment of hyponatremic encephalopathy in children

Hyponatremia is the most common electrolyte abnormality encountered in children. In the past decade, new advances have been made in understanding the pathogenesis of hyponatremic encephalopathy and in its prevention and treatment. Recent data have determined that hyponatremia is a more serious condition than previously believed. It is a major comorbidity factor for a variety of illnesses, and subtle neurological findings are common. It has now become apparent that the majority of hospital-acquired hyponatremia in children is iatrogenic and due in large part to the administration of hypotonic fluids to patients with elevated arginine vasopressin levels. Recent prospective studies have demonstrated that administration of 0.9% sodium chloride in maintenance fluids can prevent the development of hyponatremia. Risk factors, such as hypoxia and central nervous system (CNS) involvement, have been identified for the development of hyponatremic encephalopathy, which can lead to neurologic injury at mildly hyponatremic values. It has also become apparent that both children and adult patients are dying from symptomatic hyponatremia due to inadequate therapy. We have proposed the use of intermittent intravenous bolus therapy with 3% sodium chloride, 2 cc/kg with a maximum of 100 cc, to rapidly reverse CNS symptoms and at the same time avoid the possibility of overcorrection of hyponatremia. In this review, we discuss how to recognize patients at risk for inadvertent overcorrection of hyponatremia and what measures should taken to prevent this, including the judicious use of 1-desamino-8d-arginine vasopressin (dDAVP)

The Effect of Particle Dilution on Wetting Efficiency and Liquid Film Thickness in Small Trickle Beds

Partial Wetting in Small Scale Trickle Bed Reactors Results in Incorrect Determination of Intraparticle Apparent Kinetic Parameters as Well as in Erroneous Reactor Scale-Up. Although a Dilution of Catalyst Particles with Inert Fines Improves the Catalyst Wetting Efficiency, It Does Not Guarantee Full External Catalyst Wetting at All Superficial Liquid Mass Velocities. Int This Work, a Method is Presented to Relate the Wetting Efficiency Obtained at Different Operating Conditions and at Different Laboratories for Diluted and Non-Diluted Beds. Liquid Film Thickness in Diluted and Non-Diluted Beds is Estimated. the Effect of the Operating Conditions on Partial Wetting and Liquid Film Thickness is Discussed

Enhancement of CO2 Desorption from MEA-Based Nanofluids in Membrane Contactor: Simulation Study

As There is No Study Focusing on the Effect of the Presence of Nanoparticles on Enhancing Mass Transfer in Gas Desorption Systems. in This Study, a Two-Dimensional Mathematical Model Was Developed to Investigate the Effect of the Presence of SiO2 Nanoparticles on the Desorption of Carbon Dioxide from a Monoethanolamine (MEA) Solution in a Hollow Fiber Membrane Contactor (HFMC). the Developed Model Was Validated by Experimental Data Obtained from the Literature for a Similar System over a Range of Operating Conditions, Liquid and Gas Velocity, and MEA Concentration. the Numerical Data Agree Well with the Experimental Results with an Average Deviation (AD) of About 5%. the Numerical Data Also Showed that the Major Mass Transfer Resistance in the System Was in the Liquid Phase. the CO2 Desorption Flux Increased Dramatically with the Increase in the Liquid Velocity. Meanwhile, the Gas Velocity Showed Little Effect on the Desorption Flux. the Addition of Nanoparticles with Loading 0.6 G / L SiO2 to 3M MEA Solution Greatly Improved the Mass Transfer Rate in the Liquid Phase. the CO2 Desorption Flux Was Improved by 33 % at Liquid and Gas Velocities of 1.4 Cm S−1 and 10.0 Cm S−1, Respectively. the Desorption Flux Improved Significantly When the MEA Concentration in Nanofluid Was Increased. According to the Results of the Current Study, the Use of Nanoparticles Greatly Improves the Desorption Rate of CO2 and Can Contribute to Reducing Energy Consumption

Capsule Endoscopy in Left Ventricular Assist Device Patients: Retrospective Review of Efficacy and Necessity

Introduction: Capsule endoscopy (CE) is mainstream in the evaluation of obscure gastrointestinal bleeding (GIB) in the general population. However, the diagnostic and therapeutic impact of CE in LVAD patients susceptible to transient bleeding remains largely unexplored. This study aimed to assess the benefits of CE in the evaluation of LVAD associated GIB. Methods: Retrospective review of patients implanted with a continuous flow LVAD who underwent inpatient capsule endoscopy (CE) between January 2014 and May 2017 at our center. Identification of lesions with high bleeding potential or presence of frank blood were considered abnormal findings on CE study. Result: Twenty-five inpatients who underwent 41 CE were identified. All patients presented with GIB and had preceding negative upper endoscopy and colonoscopy in the past 4 weeks. On the first capsule in each patient, 19 had interpretable images, abnormal findings were detected in 5 patients (high risk lesion in 3, frank blood in 2), four of these underwent an enteroscopy and only 2 (8%) patients had confirmation of the capsule findings with APC treatment (true positive). Excluding patients with malfunction, LVAD interference and poor bowel prep, 14 patients had negative/equivocal CE, of which 4 underwent enteroscopy due to continued bleeding and 2 of these patients had treatable culprit lesions (false negative). A total of 17 (68%) patients were discharged without any therapeutic intervention irrespective of the success or findings on CE due to clinical stabilization. Twenty patients (80%) had recurrence in a mean 154 days. As expected, repeat capsules in the same admission increased the diagnostic yield (p=0.031) Only nine patients (36%) had capsule-image evidence of reaching the cecum while 4 patients (16%) had retention which had to be retrieved without further complication. Conclusion: This study demonstrated that evaluation of GIB with CE is feasible and safe but was associated with a low diagnostic yield and low conversion to therapeutic intervention. With a true positive yield of 4% in our cohort, the efficacy and cost-effectiveness of CE in the LVAD population is debatable. The role of CE in LVAD patients may need to be reevaluated. An identification of patients who would benefit from a capsule-first approach would allow optimum utilization of resources and reduce healthcare expenditure