CFD Analysis of a Non-Newtonian Fluids Processing Pump

Abstract Pumps are among the most spread machines in industrial facilities. In this work a comparative CFD analysis using different software is presented. The three-dimensional flow in the semi-open impeller and volute of a centrifugal pump is numerically simulated. The main advantage of semi-open impeller centrifugal pump is its efficiency which can be considered constant thanks to the clearance adjustment. In addition this kind of impeller is less likely to clog with solid bodies (important in case of slurry-processing). The open impeller has all the parts visible, so it is easier to inspect for wear and damages. Eventually it is lighter than a shrouded impeller: it can spin faster. The stress due to centrifugal force is indeed a limit for the speed of this machines. On the other hand its main disadvantage if compared to a shrouded pump is its lower efficiency due to the heavier tip leakage. In addition it cannot be employed in case of explosive products: the risk of contact between impeller and volute causing sparks is not negligible. The simulations have been carried out using both open-source and proprietary software: OpenFOAM®, PumpLinx ® and ANSYS-CFX ®. The performance of the machine handling both Newtonian and non-Newtonian fluids are also investigated. The numerical models and the results of the different computational strategies were compared with the experimental data and the accuracy of different software is evaluated in the case of Newtonian model. It is well known that the performance of a centrifugal pump drops processing a viscous fluid. Even so the behavior during the pumping of non-Newtonian fluids has not been investigated so far. The non-Newtonian fluid processed is a shear-thinning fluid (the apparent viscosity decreases with an increase stress). The slurries which are usually processed in the food industries, chemical plants and oil&gas processes show a usual behavior which correspond to this kind of model

Experimental and Numerical Analysis of a Non-Newtonian Fluids Processing Pump

Abstract Centrifugal pumps are used in many applications in which non-Newtonian fluids are involved: food processing industry, pharmaceutical and oil/gas applications. In addition to pressure and temperature, the viscosity of a non-Newtonian fluid depends on the shear rate and usually is several orders of magnitude higher than water. High values of viscosity cause a derating of pump performance with respect to water. Nowadays, pumping and mixing non-Newtonian fluids is a matter of increasing interest, but there is still lack of a detailed analysis of the fluid-dynamic phenomena occurring within these machines. A specific design process should take into account these effects in order to define the proper pump geometry, able to operate with non-Newtonian fluids with specific characteristics. Only few approaches are available for correcting the pump performance based on the Hydraulic Institute method. In this work, an experimental and numerical campaign is presented for a semi–open impeller centrifugal pump elaborating non-Newtonian fluids. An on-purpose test bench was built and used to investigate the influence on pump performance of three different non-Newtonian fluids. Each pump performance test was accompanied by the rheological characterization of the fluid, in order to detect modifications of the rheological phenomena and allow a proper Computation Fluid Dynamics (CFD) modeling. The performance of the machine handling both Newtonian and non-Newtonian fluids are highlighted in relation with the internal flow field

Analisi Numerica e Sperimentale delle Prestazioni di Pompe Centrifughe per Fluidi Non-Newtoniani

Le pompe centrifughe sono utilizzate in molteplici applicazioni dove si trovano ad elaborare fluidi non newtoniani come ad esempio nell’industria alimentare e della carta, nel settore farmaceutico e nelle applicazioni oil&gas. In aggiunta alla pressione e alla temperatura, la viscosità di un fluido non newtoniano dipende dallo sforzo di taglio e solitamente risulta essere molto più elevata rispetto a quella dell’acqua. Per la correzione delle prestazioni di una pompa solo pochi metodi sono disponibili. Questi metodi si basano sulla stima di un valore rappresentativo di viscosità da utilizzare per correggere le performance come se la pompa elaborasse un fluido più viscoso (per esempio il metodo dell’Hydraulic Institute). Il progetto della pompa viene comunque eseguito con acqua e la correzione delle prestazioni della pompa viene fatta solamente a posteriori. Attualmente l’utilizzo di sistemi di pompaggio e di miscelazione di fluidi non newtoniani è di crescente interesse e recentemente sono stati fatti dei passi in avanti, anche se tuttavia esiste ancora una mancanza di dettagliate analisi dei fenomeni fluidodinamici che si verificano all’interno di queste macchine. In questa Tesi, viene riportato un avanzamento della conoscenza in questo campo. Partendo da una dettagliata analisi dello stato dell’arte presente in letteratura, per fornire un punto di vista globale relativo ai problemi legati alla stima delle prestazioni di pompe centrifughe operanti con fluidi non newtoniani, è stata realizzata un’analisi critica dei metodi principali per stimare il valore rappresentativo della viscosità. Parte dell’analisi è stata condotta realizzando delle simulazioni numeriche CFD per due pompe centrifughe: la prima pompa, di piccola taglia, è caratterizzata da una bassa velocità specifica e realizzata per operare con acque sporche mentre la seconda, di grande taglia, è caratterizzata da un’elevata velocità specifica e realizzata per lavorare nell’industria alimentare. I modelli numerici sono stati validati utilizzando risultati sperimentali ottenuti da numerose prove eseguite sulla pompa di taglia più piccola. Un sistema sperimentale, creato per lo scopo specifico, è stato utilizzato per investigare l’influenza sulle prestazioni della pompa di tre diversi fluidi non newtoniani realizzati con tre diverse concentrazioni di polvere di caolino in acqua. L’analisi sperimentale ha coinvolto anche la caratterizzazione reologica dei fluidi attraverso un viscosimetro a piatti rotanti. Ogni curva caratteristica della pompa è stata accompagnata dalla caratterizzazione reologica del fluido per individuare di tutte le possibili variazioni della reologia del fluido e permettere una migliore modellazione nel codice CFD. Le prestazioni delle pompe ottenute dalle analisi numeriche sono state comparate con quelle ottenute attraverso i metodi di correzione rispetto alle prestazioni con acqua, basati sul valore rappresentativo di viscosità del fluido. Infine è stata eseguita un’analisi dettagliata dei valori dello sforzo di taglio per permettere l’analisi dell’influenza della reologia del fluido sul calo delle prestazioni della macchina. L’analisi è focalizzata sulla transizione laminare/turbolenta e sull’influenza della diversa curva di flusso, rappresentata dalla legge di potenza che caratterizza il fluido non newtoniano, sulle prestazioni della pompa. Variazioni delle prestazioni della pompa, legate alla prevalenza, coppia e rendimento sono strettamente legate alla reologia del fluido elaborato. Per questa ragione, uno specifico processo di progettazione deve tenere in considerazione questi effetti per permettere la definizione di una geometria appropriata della pompa capace di operare con il fluido non newtoniano con le sue specifiche caratteristiche. Questa Tesi riporta numerosi spunti, utili in fase di progetto e rappresentano la base su cui sviluppare, nel futuro, nuove metodologie di progettazione.Centrifugal pumps are used in many applications in which non-newtonian fluids are involved: food processing industry, paper industry, pharmaceutical and oil/gas applications. In addition to pressure and temperature, the viscosity of a non-newtonian fluid depends on the shear rate and usually is several order of magnitudes higher than water. High values of viscosity cause a derating of pump performance respect to water. For the correction of the pump performance only few approaches are available. They rely on the estimation of a representative value of viscosity to be used with a high viscosity fluid performance correction (for instance the Hydraulic Institute method). The correction provided by these methods is applied a posteriori to the pump design developed with water as processed fluids. Nowadays pumping and mixing non-newtonian fluids is a matter of increasing interest, in the last years many progresses has been made, but there is still lack of a detailed analysis of the fluid-dynamics phenomenon involved inside these machines. In the present Thesis, an advance of knowledge in this field is attempted. Starting from a detailed literature review, that is carried out in order to give an overall point of view of the main centrifugal pump performance estimation problems with non-Newtonian fluids, a critical analysis of the most significant approaches for the estimation of the representative viscosity will be carried out. As part of the analysis, CFD numerical simulations will be carried out in two centrifugal pumps: a small size low specific speed pump for dirty water; and a large size high specific speed pump used in food processing industry. The numerical models were validated against experimental results obtained by means of several tests performed on the low specific speed pump. An on-purpose built test bench was used to investigate the influence in pump performance of three different non-newtonian fluids, which were mixtures of different concentration ratio of kaolin in water. The experimental analysis involved also the rheological characterization of the fluids by means of a rotating viscosimeter. Each pump performance test was accompanied by the rheological characterization of the fluid, in order to detected all modifications in the rheological phenomena of the fluid and allow the proper fluid modelization into CFD model. The performance obtained by using numerical simulations will be compared with the ones obtained through representative viscosity correction respect to water and finally a detailed analysis of the viscosity and shear rate distribution inside the pumps will be carried out in order to investigate the fluid-dynamics-rheological phenomenon involved in the performance derating. The analysis is focused on the laminar/turbulent transition and the influence of the viscosity index and consistency index of pseudo-plastic power law on the pump performance. Variations of the pump performance, related to the values of head, torque and efficiency are strongly related to the rheological behavior of the processed fluid. For this reason, a specific design process has to take into account these effects in order to define the proper pump geometry able to operate the non-newtonian fluid with specific characteristics. This thesis reports several hints useful during the design process and suitable for representing the basis on which future design methods will be based

Single vs double antiplatelet therapy in acute coronary syndrome: Predictors of bleeding after coronary artery bypass grafting

To investigate the contribution of anti-platelet therapy and derangements of pre-operative classical coagulation and thromboelastometry parameters to major bleeding post-coronary artery bypass grafting (CABG)

Thyroid Nodule Screening for Malignancy: A Prospective Study on Ultrasonographic/Clinical Profile, Cytology and BRAF V600E Mutation Evaluation

Ultrasound (US)-guided fine-needle aspiration biopsy (FNAB) is the most reliable nonsurgical test for distinguishing benign from malignant thyroid nodules. However, there is no consensus on which nodules should undergo FNAB, yet. The aim of our study is therefore to assess the diagnostic sensitivity of FNAB in a series of unselected thyroid nodules and to investigate the additional diagnostic contribution of BRAF V600E analysis in the detection of differentiated thyroid cancer. To thjs aim, 1856 patients with thyroid nodules displaying at least one US feature suspicious of malignant lesion were submitted to FNAB, for a total of 2421 cytoaspirates submitted to cytological evaluation and to biomolecular analysis.We found that cytology has high positive predictive value and specificity for the diagnosis of malignant lesions. BRAF V600E mutation was found in 115 samples, 80 of which were also cytologically diagnosed as papillary thyroid cancer. BRAF mutation analysis significantly enhanced the diagnostic value of cytology, increasing FNAB diagnostic sensitivity for malignant nodules by 28%. Diameter was not a good predictor of thyroid nodule malignancy. Each investigated US/clinical characteristic of suspected malignancy correlated with the presence of a thyroid cancer in thyroid nodules with diameter of 4 mm or greater.These data indicate that all nodules with at least one US/clinical characteristic of suspected malignancy should undergo FNAB. The diagnostic sensitivity for thyroid cancer is significantly increased by BRAF V600E mutation analysis, indicating that the screening for BRAF mutation in FNAB samples has a relevant diagnostic potential and should always be performed

Cabergoline reduces cell viability in non functioning pituitary adenomas by inhibiting vascular endothelial growth factor secretion

Dopamine (DA) therapy of non-functioning pituitary adenomas (NFA) can result in tumor stabilization and shrinkage. However, the mechanism of action is still unknown. Previous evidence showed that DA can inhibit pituitary vascular endothelial growth factor expression (VEGF), that may be involved in pituitary tumor growth. The aim of our study was to clarify whether VEGF secretion modulation might mediate the effects of DA agonists on cell proliferation in human NFA. We assessed DA receptor subtype 2 (DR2) expression in 20 NFA primary cultures, where we also investigated the effects of a selective DR2 agonist, cabergoline (Cab), on VEGF secretion and on cell viability. All NFA samples expressed \uce\ub1-subunit and DR2 was expressed in 11 samples. In DR2 expressing tumors, Cab significantly reduced cell viability (-25%; P < 0.05) and VEGF secretion (-20%; P < 0.05). These effects were counteracted by treatment with the DA antagonist sulpiride. Cab antiproliferative effects were blocked by VEGF. Our data demonstrate that Cab, via DR2, inhibits cell viability also by reducing VEGF secretion in a selected group of NFA, supporting that DA agonists can be useful in the medical therapy of DR2 expressing NFA. \uc2\ua9 2012 Springer Science+Business Media, LLC

Trifecta results in Retzius-sparing robotic radical prostatectomy: results of a high-volume center

Aim: We aimed to evaluate trifecta outcomes after Retzius-sparing robot-assisted radical prostatectomy (rs-RARP).Methods: We evaluated 1488 patients who had undergone rs-RARP at our institution from 2011 to 2019. All patients filled out questionaries for functional outcomes before surgery, and only patients with baseline continence and IIEF-5 scores of &gt; 16 were included. Biochemical recurrence (BCR) was defined as two consecutive prostatic specific antigen levels of &gt; 0.2 ng/mL after rs-RARP. Postoperative continence was defined as the use of no pads. Potency was defined as the ability to achieve erections for sexual intercourse, with or without phosphodiesterase-5 (PDE-5) inhibitors. A multivariable logistic regression model was performed to identify predictors of trifecta outcome.Results: In total, 1240 patients were included in the analysis. During the 24-month follow-up time, 149 patients (11.9%) harbored BCR. Urinary continence was observed in 981 patients (79.5%), while 171 (13.8%) still used a safety pad daily after 24 months. Sexual potency was reported in 643 patients (51.9%), of whom 379 (30.6%) had spontaneous erections and 264 (21.3%) used a PDE-5 inhibitor. Overall, the trifecta outcome was reached by 42.1% of the study’s population. The trifecta outcome was easily reached by younger patients and patients who underwent a full nerve-sparing (NS) prostatectomy. In the multivariable model, age [odds ratio (OR) = 0.89; 95% confidence interval (CI): 0.84-0.90; P &lt; 0.01] and type of NS surgery [partial NS (OR = 3.34; 95%CI: 1.01-11; P = 0.04) full NS (OR = 4.57; 95%CI: 1.86-12; P &lt; 0.01)] resulted as independent predictors.Conclusion: rs-RARP is associated with optimal trifecta outcome rate. Age and NS technique are independent predictors of trifecta outcomes

PUDENDAL NERVE BLOCK AND PUDENDAL NERVE NEUROMODULATION IN THE TREATMENT OF CHRONIC PELVIC PAIN DUE TO PUDENDAL NEURALGIA

INTRODUCTION AND AIM OF THE STUDY Pudendal Neuralgia (PN) is a frequent cause of chronic pelvic pain (CPP) in the absence of an organic pathology. Its diagnosis remains still clinical and there is not a definitive cure for it. After medical therapy failure, second level techniques are reserved to drug-refractory patients. Among these, the most widely used technique is represented by pharmacological nerve blocks, which are usually performed under radiological guidance with variable success rates [1]. Another technique is the pudendal nerve neuromodulation, advised for pharmacological block refractory patients, with high success rates in small number series [2]. However, studies regarding these therapies are sparse. The aim of our study was to describe a new technique for performing nerve block procedure and to evaluate block short and long-term efficacy in women with chronic pelvic pain (CPP) secondary to pudendal neuralgia (PN). Moreover, we investigate if neurophysiological tests are predictive for treatment efficacy and risk of disease relapse. The second outcome was the evaluation of the efficacy and safety of pudendal nerve neuromodulation (PNM) for block-refractory patients. MATERIALS AND METHODS We performed a retrospective study on 110 women undergoing pudendal nerve block with ropivacain, heparin and desamethasone under neurophysiological guidance for pudendal neuralgia (PN). Treatment success was considered as a VAS scale improvement>50%. All the women underwent maximum 6 infiltrations and VAS pain was evaluated at baseline and at every infiltration, with a median follow up of 6 months. A multivariate analysis was performed to investigate the anal reflex and somatosensory evoked potentials (SEP) predictive value. Within this cohort, 4 women and one added man were recruited for the first stage of pudendal neuromodulation implant [3]. A descriptive data analysis was performed to evaluate the treatment effectiveness into this fist case series. RESULTS We evaluated 110 women affected by CPP due to PN; age ranged from 26 to 84 years. The neurophysiological guidance guaranteed precision during infiltration. Median follow up was 6 months (range 4\u201324). A positive response after the nerve block was obtained in 63% patients with a recurrence rate after a median follow up of 6 months of 9%; median VAS score reduced from 10 up to 4. The multivariate analysis did not show a predictive value for treatment effectiveness or for the risk of relapse after treatment of anal reflex and SEP. With regard to the neuromodulation group, 3 months after the implantation, median VAS scale value decreased from 9 to 2 (p\u2009=\u20090,001) and this improvement has maintained even after 12 months (with a median VAS of 3) and without complications. INTERPRETATION OF RESULTS Our results are overlapping to the results of the literature. Literature series are small, with a short follow up and with several approaches and technique. CONCLUSIONS Pudendal nerve block is an effective and safe option for the treatment of PN unresponsive to medical therapy and the neurophysiological guidance allows to inject drugs as closes as possible to the nerve. Chronic pudendal nerve neuromodulation is a feasible and effective procedure in the mid term treatment of refractory CPP

The vietnamese pig as a translational animal model to evaluate tissue engineered heart valves: Promising early experience

Several animal models are currently used for the surgical implantation of either biologic or biopolymeric scaffolds in order to provide in vivo assessment of tissue-engineered heart valves. The Vietnamese pig (VP) is herein proposed as a suitable recipient to test the function of novel bioengineered valve substitutes, in the reconstruction of the right ventricular outflow tract (RVOT). This review aims to provide a complete and exhaustive panel of physiological parameters and methodological information for preclinical studies of tissue-engineered heart valves in the VP animal model