Pressure Surge Research Articles

Research on the Law of Surge Pressure during Tripping of HTHP Wells under the Influence of Tool Joints

Accurate surge pressure prediction during tripping is significant to ensure drilling safety. Based on the theory of wellbore hydraulics and heat transfer, a surge pressure prediction model considering the influence of HTHP and joints is established in this paper. The finite difference method is used to solve the wellbore flow model. Compared with the measured surge pressure, it was found that the error between the predicted and measured values after considering the above factors was only 0.89%. The influence of dimensionless joint outer diameter, joint length and drill string tripping speed on the surge pressure was further analyzed. The results show that the existence of joints increases the surge pressure. When the dimensionless joint outer diameter was increased from 0.70 to 0.91, the surge pressure increased by 76%. Neglecting the effect of the joint will cause a large error in calculating the surge pressure. In addition, the surge pressure is positively correlated with the drill string tripping speed. However, with the decrease in drill string tripping speed, the surge pressure will gradually tend to a stable value. This study provides a theoretical reference for the hydraulic design of HTHP well tripping.

Improvement of reliability of dozers through taking into account hydrodynamic phenomena in fluid power systems

Improvement of reliability of mining machines and equipment is a complex challenge. It is required to take into account many specific operating conditions, as well as physical processes and phenomena running in such machines. Such phenomena include dynamic and hydrodynamic events. One of the factors to affect reliability of fluid power drives of mining machines is the hydrodynamic phenomena and processes in these systems. This article describes theoretically one of the hydrodynamic events, namely, a surge of pressure (overpressure) which appears in fluid power systems of mining machines in case of stop of the fluid flow while the pump keeps working and the emergency valve acts tardily, which is governed by settlement of resinous substances and power fluid decomposition products on the surface of parts of hydraulic equipment. The experimental studies into the time dependences of vibrational accelerations of the force main walls enable correlating these vibrations with pressure surges because of retar ded actuation of the emergency valve in the fluid power system of a dozer. The total level of vibrations of the force main walls in the dozers is measured by the parameter of the emergency valve series PIK during blade lifting, which agrees with the time dependences of the vibrational accelerations of the force main walls. The technical consequences of the pressure surges are described. The authors propose a diagnostic sign to judge about the behavior of emergency valves. The experimental nondestructive testing used a commercial vibration analyzer with a piezoelectric sensor.

α-Adrenergic blockade prevented environmental temperature reduction-induced transient portal pressure surge in cirrhotic and portal hypertensive rats.

Exposure to low temperatures has been associated with increased gastroesophageal variceal bleeding in patients with cirrhosis and portal hypertension; however, the mechanism remains unclear. Therefore, the aim of the present study was to evaluate the impact of environmental temperature reduction on portal hypertension and the role of adrenergic signaling pathways in this phenomenon. Male Sprague-Dawley rats underwent common bile duct ligation or partial portal vein ligation to induce liver cirrhosis and/or portal hypertension. The impacts of acute or chronic changes in environmental temperature were surveyed. The results showed that acute cooling from 25 to 15°C and 5°C increased the portal pressure by 10.6% and 15.5% in cirrhotic rats, and by 22.2% and 36.1% in portal hypertensive rats, respectively. The transient portal pressure surge started shortly after cooling, reached a peak within 5 min and returned to baseline after 10 min. Systemic vascular resistance, mean arterial pressure and splanchnic blood flow increased significantly at the same time. Plasma epinephrine and norepinephrine concentrations, phospholipase C, protein kinase C activity and myosin phosphorylation of peripheral arteries increased significantly in response to cooling. Phentolamine (an α-blocker) but not propranolol (a non-selective β-blocker) dose-dependently inhibited the transient portal pressure surge and aforementioned molecular changes. In conclusion, environmental temperature reduction induced peripheral vasoconstriction via α-adrenergic pathways, and redistribution of blood flow to the splanchnic system led to a surge in transient portal pressure. Treatment with α-adrenergic receptor antagonists may exert additional benefits in controlling portal hypertension, especially on exposure to low temperatures.

Numerical solution to binary quasi-linear partial differential equations for drilling surge pressures based on the characteristic-lines method

Accurately predicting surge pressures caused by tripping drill string or running casing string is fundamental to implementing Managed Pressure Drilling in areas with narrow safety mud density margin. In this work, the region of interest is divided into 3 coupled regions, i.e., inside moving pipe, annulus, and that below the moving pipe. Mass conservation equations and momentum conservation equations depicting the 3 regions are developed considering mud compressibility, pipe elasticity and wellbore wall elasticity. Applying the characteristic-line theory for partial differential equations, a series of discretized equations have been developed for the 3 regions, including internal nodes within uniform size pipe conduit, coupling nodes between two adjacent different size conduits, surface and bottom-hole nodes, and the conjunction node of the 3 regions. Based on the discretized equations, a computational flowchart is programmed to get numerical transient solutions. Both the transient surge pressure variation with time at the given interested point and the surge pressure variation with depth along the whole well axis can be depicted using this method. Two case studies show that computational values are in good consistent with the measurements with a relative error less than 10%.

Rectal Application of Lidocaine Reduces the Severity of Autonomic Dysreflexia following Experimental Spinal Cord Injury.

Spinal cord injury (SCI) results in devastating cardiovascular dysfunction. Noxious stimuli from the rectum during bowel routine often trigger life-threatening blood pressure surges, termed autonomic dysreflexia (AD). Rectal application of anesthetic lidocaine jelly has been recommended during bowel care to reduce AD severity by mitigating sensory input. However, clinical studies have reported contradicting evidence. We performed a pre-clinical study on the efficacy of rectal lidocaine in a standardized rodent T3 transection model. We found that 2% and 10% lidocaine significantly reduced AD severity by 32% and 50%, respectively, compared with control (p < 0.0001). Our pre-clinical experiments support the current recommendation of rectal lidocaine application during bowel care.

Water Hammer in Steel–Plastic Pipes Connected in Series

This paper experimentally and numerically investigates the water hammer phenomenon in serially connected steel and HDPE pipes with different diameters. The aim of the laboratory tests was to obtain the time history of the pressure head at the downstream end of the pipeline system. Transient tests were conducted on seven different pipeline system configurations. The experimental results show that despite the significantly smaller diameter of the HDPE pipe compared to the steel pipe, introducing an HDPE section makes it possible to suppress the valve-induced pressure surge. By referring to the results of the experimental tests conducted, the comparative numerical calculations were performed using the fixed-grid method of characteristics. To reproduce pressure wave attenuation in a steel pipe, Brunone-Vitkovský instant acceleration-based model of unsteady friction was used. To include the viscoelastic behavior of the HDPE pipe wall, the one-element Kelvin–Voigt model was applied. By calibrating the unsteady friction coefficient and creep parameters, satisfactory agreement between the calculated and observed data was obtained. The calibrated values of parameters for a single experimental test were introduced in a numerical model to simulate the remaining water hammer runs. It was demonstrated that using the same unsteady friction coefficient and creep parameters in slightly different configurations of pipe lengths can be effective. However, this approach fails to reliably reproduce the pressure oscillations in pipeline systems with sections of significantly different lengths.

Pressure characteristics of the fuel system for two-stroke diesel engines under different operational modes

In this study, the pressure characteristics of the fuel system for two-stroke diesel engines were investigated experimentally. The driving pressure, fuel pressure, injection pressure, and pressure amplification piston (PAP) displacement under different working conditions and modes were tested. The results show that the fluctuation degree of injection pressure is higher than those of fuel pressure and driving pressure despite of the working conditions and modes. The more obvious the injection pressure fluctuation is, the more complex the variation of the PAP displacement. Before the fuel injection starts, the injection pressure peak under different pulse widths of pressure amplification control valve (PACV) for single-valve operational mode is about 83 MPa. The peaks of fuel pressure and driving pressure are relatively low. The variation of PAP displacement is stable. For double-valve operational mode, the injection pressure peak is about 88 MPa before the injection control valve (ICV) is energized when the dwell time is 10 ms. When the dwell time is not less than 20 ms, the injection pressure peak is about 160 MPa. The longer the dwell time is, the more obvious the PAP displacement fluctuates. For a certain working condition, the peaks of fuel pressure and driving pressure are relatively low. For the stable fuel injection stage, the ratio of fuel pressure to driving pressure is closed to the design value of 2.85. The PAP displacement increases almost linearly with time. The fuel pressure is almost 10 MPa higher than the injection pressure because of the frictional loss. After the fuel injection, for single-valve operational mode, the injection pressure and fuel pressure fluctuate very little. The fluctuation of driving pressure varies depending on whether the PAP has reached its maximum position. For double-valve operational mode, the surge of injection pressure after fuel injection could reach about 55.5 MPa. The fluctuation forms after fuel injection of fuel pressure and driving pressure are basically the same as injection pressure, but the fluctuation amplitude decreases gradually. Besides, the moment at which the system pressure and PAP displacement begin to decrease is delayed as the increase of the dwell time.

Entropy generation of magnetohydrodynamic pulsating flow of micropolar nanofluid in a porous channel through Cattaneo–Christov heat flux model with Brownian motion, thermophoresis and heat source/sink

The current article is to address the entropy generation on pulsating hydromagnetic flow of a micropolar nanofluid in a porous channel with the effects of Cattaneo–Christov heat flux and Buongiorno nanofluid model. This model is significant in the field of pressure surges, food processing systems, biomedical engineering, cancer therapeutic, artificial kidney, brain tumors, and nano-drug delivery in the arteries. The governing partial differential equations are converted into the system of ordinary differential equations by deploying the perturbation process then solved numerically by employing the fourth-order Runge–Kutta scheme with the support of the shooting technique. The flow variables like velocity, microrotation, temperature, nanoparticle concentration, entropy generation, and Bejan number are graphically depicted for different values of physical parameters. The heat transfer and mass transfer rates are displayed through a table. The velocity is diminishing with the enhancement of coupling parameter and Hartmann number. The temperature of nanofluid is increasing with the rising values of thermal radiation, Brownian motion, thermophoresis, and heat source while it is reduced with an enhancement of magnetic field, thermal relaxation time, and heat sink parameter. The total entropy generation is diminished by increasing the values of Hartmann number and Brownian motion.

Effects of isometric resistance training and detraining on ambulatory blood pressure and morning blood pressure surge in young normotensives.

Isometric resistance training (IRT) has been shown to reduce resting and ambulatory blood pressure (BP), as well as BP variability and morning BP surge (MBPS). However, there are no data available regarding how long after cessation of IRT these effects are maintained. Therefore, the purpose of this study was to determine the effects of 8 weeks of detraining on resting BP, ambulatory BP and MBPS following 8 weeks of IRT in a population of young normotensive individuals and to further substantiate previously reported reductions in MBPS following IRT. Twenty-five apparently healthy participants with resting BP within the normal range (16 men, age = 23 ± 6 years; 9 women, age = 22 ± 4 years, resting BP: 123 ± 5/69 ± 7 mmHg) were randomly assigned to a training-detraining (TRA-DT, n = 13) or control (CON, n = 12) group. Resting BP, ambulatory BP and MBPS were measured prior to, after 8 weeks of bilateral leg IRT using an isokinetic dynamometer (4 × 2-min contractions at 20% MVC with 2-min rest periods, 3 days/week) and following an 8-week detraining period. There were significant reductions in 24-h ambulatory systolic BP (SBP) and calculated SBP average real variability (ARV) following IRT that were maintained after detraining (pre-to-post detraining, −6 ± 4 mmHg, p = 0.008, −2 ± 1.5 mmHg, p = 0.001). Similarly, the training-induced decreases in daytime SBP and daytime SBP ARV (pre-to-post detraining, −5 ± 6 mmHg, p = 0.001; −2 ± 1.2 mmHg, p = 0.001, respectively), MBPS (pre-to-post detraining, −6 ± 9 mmHg, p = 0.046) and resting SBP (pre-to-post detraining, −4 ± 6 mmHg, p = 0.044) were preserved. There were no changes in night-time or night-time SBP ARV across all time points (pre-to-post detraining, −1 ± 8 mmHg, p = 1.00, −0.7 ± 2.9 mmHg, p = 1.00). These results confirm that IRT causes significant reductions in resting BP, ambulatory BP, ambulatory ARV and MBPS. Importantly, the changes remained significantly lower than baseline for 8 weeks after cessation of training, suggesting a sustained effect of IRT.

Necessity and suitability of in-line inspection for corrosion resistant alloy (CRA) clad pipelines

ABSTRACT This paper outlines the necessity and suitability of in-line inspection (ILI) using intelligent pigging for Corrosion Resistant Alloy (CRA) subsea clad pipelines through an incident that occurred during a baseline survey performed on a 20-inch y CRA clad pipeline of 2.7 km long. In this incident, an ultrasonic (UT) intelligent pigging tool was impacted and resulted in damage to the pipeline's clad layer. This damage was due to the collosion of the sealing pigs with the rear of the UT intelligent pigging tool, resulting in the UT intelligent pigging tool to get stuck and stop at the end of the pipeline. Pressure surges were used to dislodge the UT intelligent pigging tool, but caused the UT pig to be crashed into the pig receiver, resulting in severe damage to the UT pigging tool. The analysis of the metal swarf recovered from the pig receiver revealed that the damage was limited to the pipeline's clad layer. It was also revealed that a bypass has occurred to the sealing pigs causing damage to the sensor carriers of the intelligent pigging tool.

Suppression of vortex rope formation and pressure fluctuation using anti-swirl fins in a Francis turbine model at part load condition with cavitation inception point

Vortex rope formation at part load (PL) with cavitation inception causes pressure fluctuations inside the draft tube (DT) of a Francis turbine which may fail the turbine due to resonance and erosion. The pressure surge can be minimized by using anti-swirl fins which ensure safe turbine operation. The present study examines the effect of fin sizes and locations on the internal flow characteristics of the Francis turbine and predicts its adverse effect on the pressure surge. Three cases are investigated in which internal flow physics are compared among DTs with longer fins, shorter fins, and no fins. At the cavitation inception point under PL conditions, the characteristics are thoroughly studied numerically using ANSYS-CFX with structured and unstructured grids. Cavitation and PL conditions are designated by Thoma number 0.266 and guide vane angle 16°. Numerical methodology is then verified by an experiment based on International Standard (IEC 60193). The vortex rope occurrence is suppressed using fins on the DT periphery and longer fins that are extended up to the elbow exhibit the lowest strength of the vortex rope. Maximum pressure recovery inside the DT is achieved using longer fins. The swirl intensity is remarkably reduced by about 94% with longer fins. The pressure peak of low frequency is about 60% suppressed using longer fins. The PL and cavitation-induced instabilities and vibrations are significantly mitigated by longer fins, while shorter fins also moderately minimize it. Hence, energy production is preferable with longer fins because of the safe and stable turbine function.

The HOPE Asia network 2022 up-date consensus statement on morning hypertension management.

Morning hypertension is an important clinical target in the management of hypertension for perfect 24‐h blood pressure (BP) control. Morning hypertension is generally categorized into two types: “morning surge” type and “sustained nocturnal and morning hypertension” type. The “morning surge” type is characterized by an exaggerated morning blood pressure surge (MBPS), and the “sustained nocturnal and morning hypertension” type with continuous hypertension from nighttime to morning (non‐dipper/riser type). They can be detected by home and ambulatory blood pressure measurements (HBPM and ABPM). These two forms of morning hypertension both increase the risk of cardiovascular and renal diseases, but may occur via different pathogenic mechanisms and are associated with different conditions. Morning hypertension should be treated to achieve a morning BP level of < 135/85 mmHg, regardless of the office BP. The second target morning BP levels is < 125/75 mmHg for high‐risk patients with morning hypertension and concomitant diseases. Morning hypertension is more frequently found in Asians, than in Westerners. Thus, the management of morning hypertension is especially important in Asia. The detection of morning hypertension and the individual home BP‐guided treatment approach targeting morning BP in combination with ABPM, and the optimal treatment of morning hypertension would reduce cardiovascular events in Asia.

Study of pressure surge during priming phase of start transient in an initially unprimed pump-fed liquid rocket engine

In this paper, transient phenomenon during start up process of a pump fed liquid rocket engine is investigated through numerical simulation. The engine studied in this work is designed such that engine systems are not wetted with propellant until the engine is commanded to start. This is achieved by positioning the valves for propellant admission at the interface of test stand/flight stage and the engine. To evaluate engine performance during start transient for such systems, unsteady flow simulation was conducted using Method of Characteristics and equations for priming. The same has been reported in this work. The results indicated a brief period of abrupt pressure rise at pump upstream after opening of the propellant admission valves, during the process of priming of engine systems at valve downstream. The peak pressure obtained was significantly higher than the propellant tank pressure as well as the steady state pump suction pressure. The transitory pressure rise was found to occur due to flow resistance at impeller inlet caused by formation of a forced vortex for orienting the flow through impeller blades during off design transient regime. The maximum pressure at pump upstream, as computed from start transient simulation, was used as a design input for pump inlet feed lines. The engine was realized and subsequently qualified in a ground test facility. Hot test data obtained for pressure and flow rate during transient regime were found to be in good agreement with the simulation results.

Hydroacoustic interaction between draft tube and penstock eigenmodes under Francis turbine full load instability

At high load, Francis Turbines may experience self-sustained pressure surge leading to significant power swing and pressure fluctuations along the waterway. The physical mechanism initiating this instability phenomenon has been the subject of much research. The development of the axisymmetric cavitating vortex rope at the runner outlet modifies the hydroacoustic properties of the draft tube waterway. Very low wave speed due to high cavitation volume combined with a high swirling number initiates the unstable axial pulsations of the cavitating vortex rope which frequency corresponds to a penstock’s eigenfrequency. The 15 MW power plant of Monceaux-la-Virole in France, composed of two units fed by a single penstock, experiences such full-load surge. On-site tests have been carried out to analyze the envelope of pressure fluctuations along the penstock once instability occurs. Combined with a 1D SIMSEN model of the power plant, these measurements have allowed to enhance the understanding of this instability phenomenon. To achieve this, an advanced draft tube modelling taking into account distributed wave speed, convective terms and divergent geometry is used and frequency analysis is carried out. Unstable draft tube eigenmodes and stable penstock eigenmodes are predicted. The key draft tube model parameters such as wave speed and second viscosity are calibrated to set the draft tube eigenmode frequency to the unstable measured frequency for different operating points. This frequency analysis concludes that high load instability occurs when a matching between the draft tube and the penstock eigenfrequencies is experienced. Moreover, it is shown that the unstable draft tube eigenmode is able to interact with different order penstock eigenmodes as function of the operating point of the unit.

Drill string’s axial force transfer law in slide directional drilling in underground coal mine

During the slide directional drilling with long directional near-horizontal drilling technology, the weight on bit (WOB) at the bottom of the hole is exerted by pushing the drill pipe with the power head of the orifice drill. With the increase of drilling depth, the friction resistance between drill string and hole wall also goes up, resulting in problems including insufficient WOB, low drilling efficiency, and surge of feeding pressure. If the orifice feeding pressure continues to rise, the drill string will buckle or fracture. In our study, the field test method is adopted to explore the drilling string’s axial pressure transfer law. By comparatively analyzing different stratigraphic characteristics of five directional boreholes with an average radius of deflection, the deep-hole drill string transmitting pressure model with nine curvature radiuses is set up for simulating the relationships between drill string friction, hole depth, and strata characteristics under different working conditions. The results show that when the hole is relatively shallow, the relationship between the friction resistance and the hole depth is basically linear, which gradually develops into an exponential one with the increase in the hole depth. For the borehole with a curvature radius less than 200 m, the friction resistance is greatly affected. The softer the formation is, the greater the linear range of friction resistance becomes with the increase in the hole depth, the latter the hole depth with an exponential growth occurs, and the longer the limit depth is. The findings reveal the axial pressure transfer law of the drill string, which will facilitate future design of the drilling hole, optimize the control of drilling trajectory, and matter a lot to engineering practices.

Study on pressure surge characteristics of reactor coolant pump shaft stuck accident condition based on wavelet analysis

In order to study the internal transient pressure surge law of the reactor coolant pump (RCP) during the shaft stuck transition. Based on HPR1000 reactor primary circuit closed system (RPCCS), the steam generator tube bundle area and the reactor pressure vessel core area are simplified. The hydraulic characteristics of the RCP can be matched with the resistance characteristics of the system pipeline. The transient numerical calculation of the RCP shaft stuck transition process is carried out by establishing a three-dimensional simplified model of RPCCS. The pressure surge characteristics of each monitoring point in the impeller, guide vane and volute passage under different shaft stuck mass flow periods (TQi) are obtained. The collected transient pressure surge data is analyzed by wavelet transform method (WTM). The results show that: in the stable operation state, the wavelet intensity value in the high frequency band in each flow passage change periodically and alternately. During the process of shaft stuck transition, the demarcation point (TN0) is taken when the impeller speed just drops to 0 r/min. The pressure of each monitoring point in the flow passage reaches the extreme value at this point, and then gradually tends to the reference pressure of 15.5 MPa. The regularity of high-band wavelet response in each flow passage of the RCP is gradually destroyed. Taking TN0 as the demarcation point, the low-band wavelet response firstly increases and then decreases. And the low-band wavelet response in the guide vane passage is generally higher than that in other flow passages at the same time. In this process, there is significantly different in the vortex structures on both sides of the impeller blade. The high vorticity magnitude regions appear in the impeller passage on the side of the blade working surface and in the guide vane passage. In this paper, by revealing the time–frequency characteristics of pressure surge in the RCP under shaft stuck accident (SSA), which provides a certain support for the dynamic safety evaluation of the reactor hydrodynamic system.

Cardiac Complications of Hypertensive Emergency: Classification, Diagnosis and Management Challenges.

While mortality in patients with hypertensive emergency has significantly improved over the past decades, the incidence and complications associated with acute hypertension-mediated organ damage have not followed a similar trend. Hypertensive emergency is characterized by an abrupt surge in blood pressure, mostly occurring in people with pre-existing hypertension to result in acute hypertension-mediated organ damage. Acute hypertension-mediated organ damage commonly affects the cardiovascular system, and present as acute heart failure, myocardial infarction, and less commonly, acute aortic syndrome. Elevated cardiac troponin with or without myocardial infarction is one of the major determinants of outcome in hypertensive emergency. Despite being an established entity distinct from myocardial infarction, myocardial injury has not been systematically studied in hypertensive emergency. The current guidelines on the evaluation and management of hypertensive emergencies limit the cardiac troponin assay to patients presenting with features of myocardial ischemia and acute coronary syndrome, resulting in underdiagnosis, especially of atypical myocardial infarction. In this narrative review, we aimed to give an overview of the epidemiology and pathophysiology of hypertensive emergencies, highlight challenges in the evaluation, classification, and treatment of hypertensive emergency, and propose an algorithm for the evaluation and classification of cardiac acute hypertension-mediated organ damage.

Relationship between morning peak phenomenon and early renal injury NGAL in H-type hypertension

Purpose To investigate the relationship between morning blood pressure surge (MBPS) and neutrophilgelatinase associated lipocalin (NGAL) in patients with H-type hypertension. Materials and Methods A total of 224 patients with diagnosed H-type hypertension [homocysteine (Hcy)≧10umol/L] were selected and underwent 24-hour ambulatory blood pressure monitoring (ABPM). In the morning peak group (115 cases), NGAL and serum cystatin C levels, -microglobulin levels were detected in each group, and general biochemical indicators were also detected. Results There was no significant difference in the course of hypertension, age, blood glucose, blood lipids, Hcy, BUN, Cr, and UA between the two groups (p > 0.05). CysC, -MG were higher than those in the nonmorning peak group, and the difference was statistically significant (p < 0.05).; Pearson correlation analysis showed that NGAL was moderately and highly correlated with CysC, systolic blood pressure morning peak, -MG, and high (p < 0.05), low-density lipoprotein (LDL-C), and Hcy were lowly correlated (p < 0.05).) and morning peak diastolic blood pressure (p > 0.05); multiple linear stepwise regression analysis indicated that morning peak systolic blood pressure, CysC,-MG, and FBG were the risk factors for NGAL. Conclusion The morning peak of systolic blood pressure in H-type hypertension is an important factor causing kidney injury. Paying attention to the ambulatory blood pressure monitoring and the control of morning peak blood pressure in patients with H-type hypertension, and early screening of NGAL has important clinical significance for the early prevention and treatment of renal injury in patients with H-type hypertension. PLAIN LANGUAGE SUMMARY The morning peak of blood pressure is closely related to target organ damage. There are few studies on the relationship between morning peak phenomenon and renal damage in patients with H-type hypertension at home and abroad. We investigated the relationship between MBPS and NGAL in H-type hypertensive patients with BUN, Cr and UA in the normal range to provide a clinical basis for early renal protection in hypertensive patients.

Concerning Dynamic Effects in Pipe Systems with Two-Phase Flows: Pressure Surges, Cavitation, and Ventilation

The risks associated with unsteady two-phase flows in pressurized pipe systems must be considered both in system design and operation. To this end, this paper summarizes experimental tests and numerical analyses that highlight key aspects of unsteady two-phase flows in water pipelines. The essential dynamics of air–water interactions in unvented lines are first considered, followed by a summary of how system dynamics change when air venting is provided. System behaviour during unsteady two-phase flows is shown to be counter-intuitive, surprising, and complex. The role of air valves as protection devices is considered as is the reasonableness of the usual assumptions regarding air valve behaviour. The paper then numerically clarifies the relevance of cavitation and air valve performance to both the predicted air exchanges through any installed air valves and their role in modifying system behaviour during unsteady flows.

Press coated Bioadhesive Pulsatile Tablet of Lisinopril for Chronotherapy of Cardiac Disorders: in-vitro Evaluation

The purpose of present investigation was to formulate bioadhesive pulsatile release tablet (BPRT) of lisinopril drug belong to antihypertensive category for chronotherapy of cardiac disorder. The concept behind this dosage form development is to investigate effect of coating polymer concentration on lag time and drug release from directly compressed tablet. The core tablets prepared by using various concentrations of disintegrants found suitable for complete release of drug in acidic medium indicating its solubility in gastric fluid. The FT-IR studies indicate that selected polymers are compatible with lisinopril since no interaction found in drug-excipient compatibility studies. The dissolution study clearly indicates that higher concentration of polymers which is HPMC K100M and Carbopol reduces free water volume and increase viscosity of the tablet coat causes reduction in drug release. The prepared Bioadhesive pulsatile release tablets showed desired hardness and good mucoadhesion strength. The obtained results showed capability of formulated bioadhesive pulsatile drug delivery system in a drug release for a programmable period of time to attain drug release after minimum 3 hr of Lag time. A stability results clearly indicate that developed pulsatile product was sufficiently stable under accelerated and controlled conditions. Thus, the developed pulsatile tablet can be considered to be a promising formulation for the relief of early morning surge in blood pressure and other cardiac disorders which follows a circadian rhythm.