Wax formation in oil pipelines: A critical review Aiyejina, Ararimeh; Chakrabarti, Dhurjati Prasad; Pilgrim, Angelus ...
International journal of multiphase flow,
09/2011, Letnik:
37, Številka:
7
Journal Article
Recenzirano
The gelling of waxy crudes and the deposition of wax on the inner walls of subsea crude oil pipelines present a costly problem in the production and transportation of oil. The timely removal of ...deposited wax is required to address the reduction in flow rate that it causes, as well as to avoid the eventual loss of a pipeline in the event that it becomes completely clogged. In order to understand this problem and address it, significant research has been done on the mechanisms governing wax deposition in pipelines in order to model the process. Furthermore, methods of inhibiting the formation of wax on pipeline walls and of removing accumulated wax have been studied to find the most efficient and cost-effective means of maintaining pipelines prone to wax deposition. This paper seeks to review the current state of research into these areas, highlighting what is so far understood about the mechanisms guiding this wax deposition, and how this knowledge can be applied to modelling and providing solutions to this problem.
Current therapies for pulmonary arterial hypertension have been adopted on the basis of short-term trials with exercise capacity as the primary end point. We assessed the efficacy of macitentan, a ...new dual endothelin-receptor antagonist, using a primary end point of morbidity and mortality in a long-term trial.
We randomly assigned patients with symptomatic pulmonary arterial hypertension to receive placebo once daily, macitentan at a once-daily dose of 3 mg, or macitentan at a once-daily dose of 10 mg. Stable use of oral or inhaled therapy for pulmonary arterial hypertension, other than endothelin-receptor antagonists, was allowed at study entry. The primary end point was the time from the initiation of treatment to the first occurrence of a composite end point of death, atrial septostomy, lung transplantation, initiation of treatment with intravenous or subcutaneous prostanoids, or worsening of pulmonary arterial hypertension.
A total of 250 patients were randomly assigned to placebo, 250 to the 3-mg macitentan dose, and 242 to the 10-mg macitentan dose. The primary end point occurred in 46.4%, 38.0%, and 31.4% of the patients in these groups, respectively. The hazard ratio for the 3-mg macitentan dose as compared with placebo was 0.70 (97.5% confidence interval CI, 0.52 to 0.96; P=0.01), and the hazard ratio for the 10-mg macitentan dose as compared with placebo was 0.55 (97.5% CI, 0.39 to 0.76; P<0.001). Worsening of pulmonary arterial hypertension was the most frequent primary end-point event. The effect of macitentan on this end point was observed regardless of whether the patient was receiving therapy for pulmonary arterial hypertension at baseline. Adverse events more frequently associated with macitentan than with placebo were headache, nasopharyngitis, and anemia.
Macitentan significantly reduced morbidity and mortality among patients with pulmonary arterial hypertension in this event-driven study. (Funded by Actelion Pharmaceuticals; SERAPHIN ClinicalTrials.gov number, NCT00660179.).
Registry data suggest that disease progression in pulmonary arterial hypertension (PAH) is indicative of poor prognosis. However, the prognostic relevance of PAH-related morbidity has not been ...formally evaluated in randomized controlled trials.
The purpose of these analyses was to assess the impact of morbidity events on the risk of subsequent mortality using the landmark method and data from the SERAPHIN and GRIPHON studies.
For each study, the risk of all-cause death up to the end of the study was assessed from the landmark time point (months 3, 6, and 12) according to whether a patient had experienced a primary endpoint morbidity event before the landmark. Each analysis was conducted using data from all patients who were available for survival follow-up at the landmark.
In the SERAPHIN study, on the basis of the 3-month landmark time point, patients who experienced a morbidity event before month 3 had an increased risk of death compared with patients who did not (hazard ratio HR: 3.39; 95% confidence interval CI: 1.94 to 5.92). In the GRIPHON study, on the basis of the 3-month landmark time point, there was also an increased risk with a HR of 4.48; (95% CI: 2.98 to 6.73). Analyses based on 6-month and 12-month landmarks also showed increased risk in patients who experienced morbidity events, albeit with a reduced HR.
These results demonstrate the prognostic relevance of PAH-related morbidity as defined in the SERAPHIN and GRIPHON studies, highlighting the importance of preventing disease progression in patients with PAH and supporting the clinical relevance of SERAPHIN and GRIPHON morbidity events. (Study of Macitentan ACT-064992 on Morbidity and Mortality in Patients With Symptomatic Pulmonary Arterial Hypertension SERAPHIN; NCT00660179; Selexipag ACT-293987 in Pulmonary Arterial Hypertension GRIPHON; NCT01106014)
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•Performance, combustion and emissions of a CRDI diesel engine were investigated.•HC and NOx have been decreased for lower FIP.•At SOI of 342.5 CA, lower exhaust gas temperature is observed.•The ...response surface methodology helps to find optimum factors.•‘Regression Model’ is best fit with standard deviation of 0.095, adjusted R2 of 0.972 and adequate precision of 18.482.
The operating mode of reactivity-controlled compression ignition appears as an effective technique for improving the engine's efficiency and emission reduction. This study investigates the emission and combustion characteristics of diesel engines operating under the reactivity-controlled compression ignition mode. The primary objective of this research is to examine the effect of fuel injection timings (7.5, 12.5 and 17.5 bTDC) and injection pressure (500 and 1000 bar), experimental testing is carried out on single cylinder water-cooled testing engines at constant speed of 1500 rpm with variable engine load (16, 20 and 24 Nm). In case of a fuel injection pressure of 1000 bar, the maximum brake specific fuel consumption of 0.42 kg/kWh is registered with a brake mean effective pressure of 3.2 bar. In this experimental study, Box-Behnken based response surface methodology was used to predict the optimal input parameters, resulting in the optimal combination of output and emission parameters. In addition, a statistically relevant test analysis of variance has been developed to obtain a 'regression model.' Results have shown that the proposed 'Regression Model' is ideally suited to 0.095 standard deviation, 0.972 modified R2 and 18.482 acceptable accuracy. This analysis also attempts to describe the application of the response surface methodology analysis to optimize the emission and performance parameters.
Critical-sized bone defects are augmented with cell free and cell loaded constructs to bridge bone defects. Improving the properties of three-dimensional scaffolds with multiple polymers and others ...is of growing interest in recent decades. Chitosan (CS), a natural biopolymer has limitations for its use in bone regeneration, and its properties can be enhanced with other materials. In the present study, the composite scaffolds containing CS, gelatin (Gn) and graphene oxide (GO) were fabricated through freeze-drying. These scaffolds (GO/CS/Gn) were characterized by the SEM, Raman spectra, FT-IR, EDS, swelling, biodegradation, protein adsorption and biomineralization studies. The inclusion of GO in the CS/Gn scaffolds showed better physico-chemical properties. The GO/CS/Gn scaffolds were cyto-friendly to rat osteoprogenitor cells, and they promoted differentiation of mouse mesenchymal stem cells into osteoblasts. The scaffolds also accelerated bridging of the rat tibial bone defect with increased collagen deposition in vivo. Hence, these results strongly suggested the potential nature of GO/CS/Gn scaffolds for their application in bone tissue regeneration.
•The influence of innovative multi strut with dual cavity on scramjet combustor is investigated.•Innovative strut aids in generating intense vorticity which helps in efficient mixing of fuel and ...oxidiser.•Combustion efficiency was higher with innovative strut in comparison with base strut.•Shear shock layer enhances the mixing rate by intensifying turbulence phenomena.•Total pressure loss in base strut is 10% lower than that of modified strut.
To analyze the influence of flow physics and operating parameters (i.e., injection pressure (2, 4, 6, and 8 bars), a simulation is performed on a scramjet combustor (modified) using the shear stress transport (SST) k- ω turbulence model and Reynolds Averaged Navier Stokes (RANS) equations. Wall pressures, the pattern of shock-wave, and static temperature of the combustor are three major parameters that have been analyzed in this study. An acceptable range of results indicates that the simulation approach adopted can be used for additional studies. According to the results of this study, the shock-wave position is destabilized when the hydrogen jet pressure is enhanced by varying the flame characteristics. Moreover, it was also observed that the shock wave travels upstream due to the pressure exerted by the main flow. A normal shock wave moves ahead of the strut as soon as the pressure in the hydrogen jet increases to 4 bar. According to this study, it is beneficial to have lower hydrogen jet pressures in supersonic flows for the geometry considered. The penetration depth of fuel in the axial direction increases, which deteriorates the combustion efficiency with an increase in the total pressure losses.
Emerging evidence suggests that the resistance of cancer stem cells (CSC) to many conventional therapies is one of the major limiting factors of cancer therapy efficacy. Identification of mechanisms ...responsible for survival and self-renewal of CSC will help design new therapeutic strategies that target and eliminate both differentiated cancer cells and CSC. Here we demonstrated the potential role of proapoptotic protein BAD in the biology of CSC in melanoma, prostate and breast cancers. We enriched CD44(+)/CD24(-) cells (CSC) by tumorosphere formation and purified this population by FACS. Both spheres and CSC exhibited increased potential for proliferation, migration, invasion, sphere formation, anchorage-independent growth, as well as upregulation of several stem cell-associated markers. We showed that the phosphorylation of BAD is essential for the survival of CSC. Conversely, ectopic expression of a phosphorylation-deficient mutant BAD induced apoptosis in CSC. This effect was enhanced by treatment with a BH3-mimetic, ABT-737. Both pharmacological agents that inhibit survival kinases and growth factors that are involved in drug resistance delivered their respective cytotoxic and protective effects by modulating the BAD phosphorylation in CSC. Furthermore, the frequency and self-renewal capacity of CSC was significantly reduced by knocking down the BAD expression. Consistent with our in vitro results, significant phosphorylation of BAD was found in CD44(+) CSC of 83% breast tumor specimens. In addition, we also identified a positive correlation between BAD expression and disease stage in prostate cancer, suggesting a role of BAD in tumor advancement. Our studies unveil the role of BAD in the survival and self-renewal of CSC and propose BAD not only as an attractive target for cancer therapy but also as a marker of tumor progression.
Graphene was prepared in a hydrocarbon oil medium through a mechano-chemical process. The resulting dispersion is a mixture of multilayer and single layer graphene as revealed by High Resolution ...Transmission Electron Microscopy (HRTEM) and Selected Area Electron Diffraction (SAED) studies. The dispersion yielded significant increase in the thermal conductivity with respect to the base oil. The inclusion of the graphene dispersion in grease instead of the traditionally used graphite improved the thermal conductivity value considerably, without deteriorating the tribological properties achieved from the pristine graphite system. A fully formulated lubricant inhibited with the said graphene dispersion showed excellent thermal dissipation and reduction in coefficient of friction over the neat lubricant. Spectro-analytical studies of the used test specimen of tribological test rig bear the signature peak of the graphene film, thus proving the lubrication efficiency of graphene in hydrocarbon medium.
The stable dispersion of graphene in formulated lubricating oils reduces the coefficient of friction and significantly improves heat dissipation from the system owing to its higher thermal conductivity.
Objectives This report characterizes a syndrome of granulomatous infiltration presenting as sustained monomorphic ventricular tachycardia (SMVT) with mediastinal adenopathy in patients with preserved ...ventricular function. Background Unlike truly idiopathic ventricular tachycardia, SMVT due to granulomatous infiltration responds poorly to radiofrequency ablation and has a poor prognosis. Methods Patients without obstructive coronary artery disease and with normal ventricular function presenting with SMVT other than posterior fascicular morphology were evaluated. Computed chest tomograms, cardiac magnetic resonance imaging, and 18-fluorodeoxyglucose positron emission tomographic scans (18 FDG PET-CT) were performed. Significant lymph nodes were evaluated for tuberculosis and sarcoidosis. Initial treatment included antiarrhythmic drugs ± radiofrequency ablation. Additionally, patients with evidence of tuberculosis received anti-tuberculosis therapy; the rest were treated as sarcoidosis. Results Mediastinal adenopathy with mid-myocardial scar and/or focal myocardial inflammation was observed in 14 patients; lymph nodes revealed noncaseating granulomas in all. Evidence of tuberculosis was present in 79%. During follow-up (median duration 25 months), SMVT recurred despite initial treatment in 92%. Addition of disease-specific therapy abolished further recurrences in 64% of them. Decrease in SMVT correlated with resolution of myocardial inflammation on serial18 FDG PET-CTs. Appropriate therapies occurred in 67% of patients receiving implantable cardioverter-defibrillators. Conclusions A subset of patients with SMVT with preserved ventricular function has a syndrome of arrhythmogenic myocarditis with granulomatous mediastinal adenopathy due to myocardial tuberculosis or cardiac sarcoidosis. This entity is optimally managed with a combination of disease-specific therapy and antiarrhythmic measures.
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