Pressure Spikes Research Articles

A multigrid method for EHL line contact problem with Grease as lubricant

The paper presents an isothermal Elastohydrodynamic lubrication (EHL) of line contact problem with grease as a lubricant, described by Herschel-Bulkley model. The simulation of the governing problem is analyzed using Multigrid method with full approximation scheme (FAS) for varying load, speed and rheological index n Herschel-Bulkley model. The EHL problem considered comprises of Reynolds equation and film thickness understudy for different parameters of interest. The minimum film thickness and pressure spike decrease with a decrease in rheological index n. The present paper traces out the comparison of minimum film thickness with the standard results of Dowson and Higginson. The results obtained are comparable and are presented in terms of graphs and tables.

Jacobian free Newton-GMRES method for the solution of elastohydrodynamic grease lubrication in line contact using wavelet based pre-conditioners

Jacobian Free Newton-GMRES (JFN-GMRES) method is used in the present study for the analysis of isothermal, steady and incompressible elastohydrodynamic lubrication line contact problem. The lubricant is grease, described by Herschel–Bulkley constitutive equation. The problem is investigated for smooth surface as well as surface with asperity. Governing equations are discretized on uniform grid. The resulting system of algebraic equations is solved using JFN-GMRES method for wide range of parameters of interest. For the convergence of restarted GMRES wavelet based pre-conditioners are used. Pressure profiles, film shapes and details of Petrusevich pressure spikes are given for moderate to high load and speed. The proposed scheme is stable and fast converging. Results presented in tables and graphs confirm these findings. The minimum film thickness increases for decrease in n, a parameter characterizing grease lubricant, with other parameters held constant. There is a noticeable decrease (in height as well as spread) of pressure spike for small values of n, which arrests bearings fatigue life.

Intraocular Pressure Spikes within First Postoperative Hours following Standard Trabeculectomy: Incidence and Associated Factors

Purpose: To evaluate the incidence of intraocular pressure (IOP) spikes within the first postoperative hours following trabeculectomy (TRAB) and to determine possible associated factors. Methods: An observational study was carried out. We enrolled consecutive patients undergoing standard TRAB with mitomycin C. They were examined twice within the first few postoperative hours (hours 1-2 and 4-6) and 3 times after TRAB (on days 1, 7, and 30). Demographic and ocular data were collected. Main outcome measurements were postoperative IOP values at each time point and the frequency of IOP spikes, defined as IOP ≥25 mm Hg. Results: A total of 40 eyes of 40 patients were included (mean age 59.62 ± 13.37 years). Although IOP was significantly reduced to 11.14 ± 7.99 mm Hg at hours 1-2 (p < 0.01) and to 11.52 ± 7.30 mm Hg at hours 4-6 (p < 0.01), IOP spikes were documented in 3 patients (7.5%). In the group of patients with IOP spikes, we noted that there was a high incidence of black patients and that the surgeries had been performed by fellow surgeons. Conclusion: Although the majority of the cases (92.5% of the patients) did not present IOP spikes, 7.5% of our patients presented the event. In selected cases, such as those with advanced disease, fixation threat, and of black race, IOP should be monitored during the first few postoperative hours for the identification and adequate management of potential IOP spikes, preventing undesirable outcomes.

Cataract surgery after proton-beam irradiation for uveal tumors

To study the risks associated with cataract surgery in patientswith previous proton-beam irradiation (PBI), focusing on preoperative risk factors, intraoperative findings, and postoperative complications. Massachusetts Eye & Ear Infirmary, Boston, Massachusetts, USA. Retrospective case series. Electronic medical records of patients who had PBI and cataract surgery between January 1, 2006, and October 1, 2016, were reviewed. The study comprised 29 eyes of 29 patients. Preoperative evaluation found dry eye (72.4%), posterior synechiae (24.1%), peripheralanterior synechiae (13.8%), anterior capsule fibrosis (10.3%), and iris atrophy (10.3%). Intraoperative findings included poor red reflex requiring trypan blue capsule staining (37.9%), synechiaerequiring synechialysis (24.1%), evidence of previous inflammation prompting sub-Tenon triamcinolone injection (17.2%), and miosis (10.3%). Postoperative complications included posterior capsule opacification (PCO) by 1 year (48.3%), intraocular pressure spike of 23 mm Hg or greater at 1 day (24.1%), anterior chamber inflammation at 1 month (24.1%), and cystoid macular edema (CME) (17.2%). Proximity of the initial tumor to the posterior pole was associated with poor visual outcomes after cataract surgery. Compared with reference data, this cohort had higher rates of anterior chamber inflammation at 1 month, CME, fibrinous inflammation, PCO by 1 year, intraoperative requirement for trypan blue, and synechialysis. Complications after cataract surgery performed afterPBI were similar to those seen in patients with uveitis (prolonged inflammation, CME, fibrinous inflammation, early PCO). Steroid depot administration might be useful to prevent these complications, although further research is needed to determine an optimum regimen.

Variability of IOP following laser photocoagulation used in the treatment of diabetic retinopathy

Background: Diabetic retinopathy (DR) is the leading cause of blindness in most industrialized countries. This study was undertaken to assess the variability of IOP following laser photocoagulation used in the treatment of diabetic retinopathy.Methods: This study was conducted at Department of Opthalmology, B.R.D. Medical College, Gorakhpur from June 2015 to December 2016. This study was intended to see the onset and duration of intraocular pressure spikes in diabetic retinopathy patients after green laser photocoagulation (532 nm) (Nidek). Forty patients were followed for next 3 months. The data was analysed by using SPSS version 15.0. Chi-square test and T test was used.Results: Out of 40 patients, 2 (5%) had background Diabetic retinopathy (DR) with maculopathy, 10 (25%) having pre-proliferative DR, 28 (70%) having proliferative DR. Out of 2 BDR patients, 1 (50%) developed immediate post laser angle closure (Schaffer's grade 1) which persisted for 3 days and another had shown no change in angle structure. Out of 10 PPDR patients, no one developed post laser angle closure (0%). Out of 28 PDR patients, 6 (21.4%) had post laser angle closure which included 4 patients who had angle closure before laser, that means around 7% patients developed angle closure in this group. Among these 2 patients, 1 developed angle closure immediately (Schaffer's grade 1) and another developed the same 1 day later and this angle closure (Schaffer's grade 1) remained for 3 days.Conclusions: Laser photocoagulation in diabetic retinopathy patients can cause increase in IOP.

Study on the free edge effect on finite line contact elastohydrodynamic lubrication

Abstract This paper incorporated a recently developed algorithm, which directly gives the elastic deformation of loaded quarter-space (QS) bodies, into a finite line contact elastohydrodynamic lubrication (EHL) analysis. Half-space (HS) and QS models were adopted in the analysis and the results were compared with the data obtained from conventional optical EHL tests of steel rollers on a glass disc. This study found that contact deformation was dominated by glass disc deformation. Thus, the use of a steel roller on a glass disc in conventional optical EHL technique is not appropriate for studying the free edge surface effect. Free edge surfaces reduce the magnitude of pressure spikes near the ends of contact. Rollers with different end profiles were also evaluated.

The Efficacy of a Posterior sub-Tenon’s Capsule Triamcinolone Injection in Patients with Non-infectious Intermediate Uveitis and Posterior Uveitis

Abstract To investigate the efficacy of a posterior sub-Tenon’s capsule triamcinolone injection for treating eyes with non-infectious posterior and intermediate uveitis. A total of 31 eyes from 20 patients with non-infectious posterior uveitis and 18 eyes from 10 patients with non-infectious intermediate uveitis that inadequately responded to treatment with systemic corticosteroids and second-line immunosuppressive agents were enrolled in the study. All patients received a posterior sub-Tenon’s injection of 20 mg/ml triamcinolone. The parameters we examined included the following: best corrected visual acuity, central foveal thickness, fluorescein angiography score and intraocular pressure. The mean best corrected visual acuity was significantly improved from the control visit, 0.15±0.30 logMAR (Snellen equivalent 0.7), compared to the baseline measurements, 0.60±0.30 logMAR (Snellen equivalent 0.25; P&lt;0.05). The mean central foveal thickness (CFT) and the mean score for fluorescein angiography (FA) were significantly decreased from the baseline (CFT: 320±34 μm; FA mean score: 5.9±1.9) compared to the twelve-week control visit (CFT: 235±30 μm; FA mean score: 1.2±1.1; P&lt;0.001). Five eyes had intraocular pressure spikes that required a topical anti-glaucomatous treatment. A posterior sub-Tenon’s injection of triamcinolone can significantly improve visual acuity and decrease macular oedema in patients with non-infectious posterior and intermediate uveitis. Complications were minimal, and there were no eyes that required surgical treatment for elevated intraocular pressure. The results suggest that the posterior sub-Tenon’s injection of triamcinolone is an important form of therapy for non-infectious posterior and intermediate uveitis.

Real-time measurement of needle forces and acute pressure changes during intravitreal injections.

The purpose of this study was to use a physiological pressure transducer to measure real-time, continuous pressure changes in an ex vivo study model of porcine eyes to record the amount of force needed for scleral penetration and to measure acute intraocular pressure rise during intravitreal injections. A pressure transducer was inserted into the anterior chamber of 30 fresh porcine eyes, and intraocular pressure was measured 2s prior to intravitreal injection until 2s after. A force transducer plate was used to insert various gauge needles into the vitreous cavity and the amount of force in Newtons (N) required for scleral penetration was recorded. For scleral perforation, 32- and 30-gauge needles required 0.44N and 0.45N, significantly less than larger gauge needles (P<0.05). Similarly, 27- and 25-gauge needles required more force than smaller gauge needles but less than 19 gauge (P<0.05). Intraocular pressure increased an average of 64.5mmHg during intravitreal injection. Two seconds postinjection intraocular pressure readings showed a residual intraocular pressure increase of 11.1mmHg from pre-injection baseline. Real-time continuous recordings of pressure reveal that an instantaneous intraocular pressure spike occurs during intravitreal injection and appears to be separate from the intraocular pressure spike that occurs during needle insertion. This pressure spike is transient and has not been captured by previous methods of intraocular pressure measurement, which rely on single time point measurements. The clinical significance of this brief intraocular pressure spike is unclear and warrants further investigation.

Trabecular microbypass stent implantation with cataract extraction in pseudoexfoliation glaucoma

To evaluate the safety and efficacy of a trabecular microbypassstent (iStent) combined with cataract surgery in patientswith pseudoexfoliation glaucoma (PXG). Vance Thompson Vision, Sioux Falls, South Dakota, USA. Retrospective case series. Eyes with PXG had implantation of 1 stent. Data were collected preoperatively and postoperatively through 24months. Data included intraocular pressure (IOP), number of glaucoma medications, the incidence of postoperative IOP pressure spikes of 15mm Hg or higher at any timepoint, and the need for additional surgery. The series included 115 eyes. The mean preoperative IOP was 20.00mm Hg±6.95 (SD). One year postoperatively, the mean IOP was 15.54±3.83mm Hg (P<.01). At 2years, the mean IOP was 14.51±2.79 (P<.01). The mean number of glaucoma medications was 1.41±1.04 preoperatively and 0.71±0.94 2years postoperatively (P<.01), indicating a 50% reduction in medication use. Postoperatively, 7 eyes (6%) had anIOP spike of 15mm Hg or higher above the baseline IOP; the spikes responded to topical therapy. Ninety-eight percent of patients with an IOP of 20mm Hg or higher achieved a reduction in IOP at the last follow-up. Trabecular microbypass stent implantation during cataract surgery safely and effectively lowered IOP and medication use in patients with mild to severe PXG.

Effective water cooling of very hot surfaces during the LOCA accident

The quench front propagation in the case of the water emergency cooling of water cooled fusion nuclear components is studied during the LOCA accident. In the case of the LOCA accident, heat removal can be successful only when water rewetts the surface. The place where water meets the very hot surface is called the quench front. The quench front propagation depends on the initial wall temperature, coolant flow rate, and heat accumulated in the cooled components. Results of the quench front experiment in an annular 1.7m length channel with initial wall temperatures within the range from 250°C up to 800°C and coolant mass fluxes 100kg/m2s and 180kg/m2s are presented. From the results is concluded, that quenching velocities and rewetting temperatures are strongly dependent on the initial wall temperature as well as the pressure spikes. The behaviour of the heat transfer coefficient at the quench front is analyzed.

Wavelet preconditioned Newton-Krylov method for elastohydrodynamic lubrication of line contact problems

In this paper, wavelet preconditioned Newton-Krylov method is used for the solution of elastohydrodynamic lubrication line contact problem. A finite difference method is used for the solution of EHL equations. The method comprise the non-linear Newton iteration on the outer loop and a linear iteration on the inside loop where wavelet based preconditioned GMRES (Generalized Minimum Residual Method of Krylov subspaces) is used. In the scheme, the Jacobian matrix-vector product is approximated accurately with much ease (without forming Jacobian explicitly and requiring no extra storage). It overcomes the limitations of conventional schemes for the investigation of the EHL problems, for computing pressure and film thickness distributions, covering wide range of physical parameters of practical interest. Also, the sensitivity of height and spread of pressure spike on load and other parameters are presented. To confirm and validate the solutions obtained, by the present method, are compared with those obtained by full approximation scheme of multigrid method.

线接触弹流润滑状态下的油膜压力极值研究

用Newton-Raphson法求解线接触弹流润滑问题基本方程，研究了线接触弹流润滑状态下中心压力、二次峰压力及其位置的影响因素(载荷、速度及材料参数)。在大量数值解结果基础上，通过多元回归分析，给出了中心压力、二次峰压力及其位置关于载荷、速度、材料参数的拟合公式，并对拟合公式的显著性和精确性进行了检验。结果表明：在很宽的参数范围内，本文所提出的拟合公式具有高度的显著性，变量之间具有密切的相关性及交互性；同时，拟合公式具有很高的计算精度，完全可以满足工程应用的需要。 Based on Newton-Raphson Method for line contact EHL problem, the influence factors (dimensionless load, speed and materials parameters) of center pressure, pressure spike and the location of pressure spike of the line contact EHL state were investigated. A large amount of numerical solution of center pressure, pressure spike and the location of pressure spike corresponding to load, speed and material parameter were obtained, and by making multiple regression analysis of these data, this paper proposed fitting formulas of center pressure, pressure spike and the location of pressure spike on operating parameters (dimensionless load, speed, and material parameter), and made significance test and accuracy test of the formulas. The result shows that in a rather wide range of operating parameters, the fitting formulas proposed in this paper are highly significant, and the variables are closely related and interactive; and the accuracy of the formulas are satisfactory, which can completely meet the need of engineering application.

Clinical Experience with the M4 Ahmed Glaucoma Drainage Implant.

AimTo evaluate the safety and efficacy of the M4 (porous polyethylene plate) Ahmed Glaucoma Valve (AGV) drainage implant in a multicenter retrospective study.Materials and methodsA retrospective chart review of medical records of patients who had undergone the M4 Ahmed valve was performed from January 2013 to April 2015. The primary outcome measure was surgical failure defined as: Less than a 20% reduction in baseline intraocular pressure (IOP) to last follow-up visit, final IOP less than 5 mm Hg or greater than 18 mm Hg, reoperation for glaucoma, or loss of light perception vision. All eyes not meeting the above criteria were defined as success.ResultsA total of 291 eyes met all study inclusion criteria. The average follow-up in the study was 6 months (±7.6 months) with 112 patients achieving 12-month follow-up (38.5%). 208 eyes (71.5%) met the study success criteria at final follow-up. No statistically significant spikes in postoperative IOP at 1 and 4 months were detected. The average preoperative IOP was 26.0 on an average of 2.8 medications. At 6 months, the average IOP dropped to 16.7 on 0.9 medications and stayed relatively stable at 15.8 on 1.2 medications at 12-month follow-up.ConclusionThe M4 valve appears to have less of a hypertensive phase compared with the other Ahmed class valves with a similar safety profile. While 71.5% success rate was achieved at final follow-up, the failure rate steadily increased over time.Clinical significanceWhile the M4 production has been discontinued, the porous design of the M4 may avoid a pressure spike in the Ahmed valve class and warrants future investigation for valve design.How to cite this article: Sluch I, Gudgel B, Dvorak J, Ahluwalia MA, Ding K, Vold S, Sarkisian S. Clinical Experience with the M4 Ahmed Glaucoma Drainage Implant. J Curr Glaucoma Pract 2017;11(3):92-96.

Intraocular Pressure Spikes following Neodymium-doped Yttrium Aluminum Garnet Laser Capsulotomy: Current Prevalence and Management in Israel.

ABSTRACTAim The current treatment for posterior capsular opacification (PCO), neodymium-doped yttrium aluminum garnet (Nd:YAG) laser capsulotomy, may lead to increased intraocular pressure (IOP). Our aim was to survey routines in the management of IOP spikes and to identify the rate of IOP spikes following prophylactic apraclonidine treatment.Materials and methods A survey questionnaire among ophthalmologists and a retrospective registry review was used. Patients were administered apraclonidine 0.5% prior to capsulotomy. The IOP was measured before and 1 hour postprocedure.Results A total of 71% of responders (n = 45) routinely prescribe topical IOP-lowering medication and 82% routinely measure IOP before or after capsulotomy. The registry analysis included 87 eyes of 75 patients. Mean IOP decreased by 0.9 ± 3.3 mm Hg (p = 0.01, range: -6 to 10) following capsulotomy. No patient reached IOP values above 21 mm Hg following the procedure, with 3.4 and 1.1% of patients demonstrating an IOP elevation of more than 3 and 5 mm Hg respectively. No association was found between number of laser shots, mean laser power, or comorbid conditions, such as diabetes, hypertension, or glaucoma status with posttreatment IOP.Conclusion Most ophthalmologists surveyed routinely prescribe prophylactic IOP-lowering medication and measure IOP before or after capsulotomy. Mean IOP remained clinically stable following capsulotomy with prophylactic apraclonidine instillation, and no patient reached IOP values above 21 mm Hg. Differences in laser delivery or comorbid conditions were not associated with posttreatment IOP. Considering that no patient demonstrated a clinically significant IOP spike following prophylactic apraclonidine instillation, perhaps routine measurement of IOP following primary Nd:YAG laser may be reserved for high-risk patients only.Clinical significance In this work, we showed the prophylactic effect of apraclonidine 0.5% and suggest that measuring IOP after the procedure is necessary only in certain high-risk cases, possibly helping to reduce workload and patient waiting time and improving quality of service.How to cite this article Achiron A. Intraocular Pressure Spikes following Neodymium-doped Yttrium Aluminum Garnet Laser Capsulotomy: Current Prevalence and Management in Israel. J Curr Glaucoma Pract 2017;11(2):63-66.

Quantitative Analysis of Uveitis Macular Edema in Multiple Sclerosis Patients Receiving Deep Posterior Sub-Tenon Triamcinolone Acetonide Injection

Aim: We aimed to analyze the effects of adjunctive posterior sub-Tenon capsule triamcinolone acetonide injection in the treatment of intermediate uveitis macular edema in multiple sclerosis patients that could not be controlled by systemic corticosteroid medications and immunomodulators. Methods: The study included 30 eyes of 25 patients with multiple sclerosis who received a posterior sub-Tenon injection of 40 mg/mL triamcinolone acetonide. Parameters monitored for therapy efficiency were best-corrected visual acuity, intraocular pressure, central foveal thickness (CFT), and fluorescein angiography (FA) scores. Results: Mean best-corrected visual acuity was significantly improved at the control visit 0.15 ± 0.10 versus baseline 0.40 ± 0.20 logMAR (p < 0.05). Six eyes showed intraocular pressure spikes requiring topical antiglaucomatous treatment. Mean CFT and FA scores were significantly decreased versus baseline (CFT: 345 ± 50 μm; FA score: 3.4 ± 1.0) compared with the 12-week control visit (CFT: 219 ± 35 μm; FA score: 1.6 ± 1.1; p < 0.001). Conclusion: Posterior sub-Tenon injection of triamcinolone acetonide significantly improved visual acuity and decrease macular edema in patients with intermediate uveitis associated with multiple sclerosis.

Intracochlear Pressure Transients During Cochlear Implant Electrode Insertion.

Cochlear implant (CI) electrode insertion into the round window induces pressure transients in the cochlear fluid comparable to high-intensity sound transients. Many patients receiving a CI have some remaining functional hearing at low frequencies; thus, devices and surgical techniques have been developed to use this residual hearing. To maintain functional acoustic hearing, it is important to retain function of any hair cells and auditory nerve fibers innervating the basilar membrane; however, in a subset of patients, residual low-frequency hearing is lost after CI insertion. Here, we test the hypothesis that transient intracochlear pressure spikes are generated during CI electrode insertion, which could cause damage and compromise residual hearing. Human cadaveric temporal bones were prepared with an extended facial recess. Pressures in the scala vestibuli and tympani were measured with fiber-optic pressure sensors inserted into the cochlea near the oval and round windows, whereas CI electrodes (five styles from two manufacturers) were inserted into the cochlea via a round window approach. Pressures in the scala tympani tended to be larger in magnitude than pressures in the scala vestibuli, consistent with electrode insertion into the scala tympani. CI electrode insertion produced a range of pressure transients in the cochlea that could occur alone or as part of a train of spikes with equivalent peak sound pressure levels in excess of 170 dB sound pressure level. Instances of pressure transients varied with electrode styles. Results suggest electrode design, insertion mechanism, and surgical technique affect the magnitude and rate of intracochlear pressure transients during CI electrode insertion. Pressure transients showed intensities similar to those elicited by high-level sounds and thus could cause damage to the basilar membrane and/or hair cells.

One-day postoperative intraocular pressure spikes after phacoemulsification cataract surgery in patients taking tamsulosin

To evaluate the relationship between 1-day postoperative intraocular pressure (IOP) after phacoemulsification cataract surgery and tamsulosin use. University of Colorado Health Eye Center, Aurora, Colorado, USA. Retrospective cohort study. Registry data from men who had cataract surgery were used. Patients taking tamsulosin at the time of surgery were included as cases, while patients with no history of tamsulosin use were used as controls. The primary outcome was a 1-day postoperative IOP spike defined as an IOP increase greater than 10mm Hg compared with baseline or a 1-day postoperative IOP of 30mm Hg or higher. General estimating equations were used for analysis. The study comprised 584 men (864 eyes). An IOP increase greater than 10mm Hg or IOP 30mm Hg or higher after cataract surgery occurred in 12.4% and 9.3%, respectively, of eyes in the tamsulosin group versus 4.4% and 2.1%, respectively, in the control group (all P=.001). After adjusting for significant covariates, patients on tamsulosin were 2.6 times (95% confidence interval [CI], 1.2-5.7; P=.01] and 3.8 (95% CI, 1.3-10.9; P=.01) more likely to have a 1-day postoperative IOP increase greater than 10mm Hg or a 1-day postoperative IOP of 30mm Hg or higher. Patients on tamsulosin had an increased risk of a 1-day postoperative IOP spike after cataract surgery, showing the importance of identifying patients on tamsulosin preoperatively to better manage and potentially mitigate IOP spikes. None of the authors has a financial or proprietary interest in any material or method mentioned.

Tissue interface pressure and skin integrity in critically ill, mechanically ventilated patients

To describe tissue interface pressure, time spent above critical pressure levels and the effect on skin integrity at seven anatomical locations. Descriptive, longitudinal study in critically ill mechanically ventilated adults, from Surgical Trauma ICU-STICU; Medical Respiratory ICU-MRICU; Neuroscience ICU-NSICU in a Mid-Atlantic urban university medical centre. Subjects were enroled in the study within 24hours of intubation. Tissue interface pressure was measured continuously using the XSENSOR pressure mapping system (XSENSOR Technology Corporation, Calgary, Canada). Skin integrity was observed at all sites, twice daily, using the National Pressure Ulcer Advisory Panel staging system, for the first seven ICU days and at day 10 and 14. Of the 132 subjects, 90.9% had no observed changes in skin integrity. Maximum interface pressure was above 32mmHg virtually 100% of the time for the sacrum, left and right trochanter. At the 45mmHg level, the left and right trochanter had the greatest amount of time above this level (greater than 95% of the time), followed by the sacrum, left and right scapula, and the left and right heels. Similarly, at levels above 60mmHg, the same site order applied. For those six subjects with sacral skin integrity changes, maximum pressures were greater than 32mmHg 100% of the time. Four of the six sacral changes were associated with greater amounts of time above both 45mmHg and 60mmHg than the entire sample. Maximum tissue interface pressure was above critical levels for the majority of the documented periods, especially in the sacrum, although few changes in skin integrity were documented. Time spent above critical levels for mean pressures were considerably less compared to maximum pressures. Maximum pressures may have reflected pressure spikes, but the large amount of time above the critical pressure levels remains substantial.

Experimental study on steam chugging phenomenon in a vertical sparger

Unstable direct contact condensation called ``Chugging'' that occurs in certain conditions in the pressure suppression pool of Primary Containment Vessel of Boiling Water Reactors (BWRs) was studied experimentally. The mechanisms of every phase of the chugging was described, and experimental results useful for the development and validation of more accurate CFD models were provided. The experiment was conducted with a transparent pool and a transparent polycarbonate pipe or a stainless steel pipe with inner diameter of 27mm under the conditions of the steam mass flux of 5.5–19.5kg/m2s and the pool temperature of 19–46.5°C. Pressure pulses were measured and synchronized with a high speed video camera for images acquisition. It was identified that the bubble implosion occurred while the pressure in the bubble quickly decreased. This condition might establish instability in the interfacial area which grew abruptly causing the implosion. Moreover the transparent apparatus allowed to interpret and relate internal condensations, generating pressure spikes of around 1.2MPa because of the condensation-induced water hammer. Finally, the chugging condensation regime map was created from the experimental data.

HIFU-induced cloud cavitation control for kidney stone treatment

The shock wave lithotripter uses an order of microsecond pulse durations and up to a 100 MPa pressure spike triggered at approximately 0.5—2 Hz to fragment kidney stones through mechanical mechanisms. One important mechanism is cavitation. We proposed an alternative type of lithotripsy method that maximizes cavitation activity to disintegrate kidney stones using high-intensity focused ultrasound (HIFU). We designed a two-frequency wave (cavitation control (C-C) waveform); a high-frequency ultrasound pulse to create a cavitation cloud, and a low-frequency pulse following the high-frequency pulse to force the cloud into collapse. High-speed photography showed cavitation collapse on a kidney stone and shock wave emission from the cloud. We also conducted in-vitro erosion tests of model and natural stones. For the model stones, the erosion rate of the C-C waveform showed a distinct advantage with the combined high- and low-frequency waves over either wave alone. Natural stones were eroded and most of the resulting fragments were less than 1 mm in diameter. The small fragments were small enough to pass through the urethra. The results demonstrate that, with the precise control of cavitation activity, focused ultrasound has the potential to be used to develop a less invasive and more controllable lithotripsy system.