Analysis of high-pressure safety valves

In presently used safety valve sizing standards the gas discharge capacity is based on a nozzle flow derived from ideal gas theory. At high pressures or low temperatures real gas effects can no longer be neglected, so the discharge coefficient corrected for flow losses cannot be assumed constant anymore. Also the force balance and as a consequence the opening characteristics will be affected. In former Computational Fluid Dynamics (CFD) studies valve capacities have been validated at pressures up to 35 bar without focusing on the opening characteristic. In this thesis alternative valve sizing models and a numerical CFD tool are developed to predict the opening characteristics of a safety valve at higher pressures. To describe gas flows at pressures up to 3600 bar and for practical applicability to other gases the Soave Redlich-Kwong real gas equation of state is used. For nitrogen consistent tables of the thermodynamic quantities are generated. Comparison with experiment yielded inaccuracies below 5% for reduced temperatures larger than 1.5. The first alternative valve sizing model is the real-average model that averages between the valve inlet and the nozzle throat at the critical pressure ratio. The second real-integral model calculates small isentropic state changes from the inlet to the final critical state. In a comparison the most simple ideal model performs slightly better than the real-average model and the dimensionless flow coefficient differs less than 3% from the most accurate real-integral nozzle model. Benchmark validation test cases from which field data is available are used to investigate the relevance of the physical effects present in a safety valve and to determine the optimal settings of the CFD code ANSYS CFX. First, 1D Shock tube calculations show that strong shocks cannot be captured without oscillations, but the shock strength in a safety valve flow is small enough to be accurately computed. Second, an axisymmetric nozzle (ISO 9300) model is simulated at inlet pressures up to 200 bar with computed mass flow rate deviations less than 0.46%. Third, a supersonic ramp flow shows a dependency of the location of the separation and reattachment points on the turbulence model, where the first order accurate SST model gives the best agreement with experiment. Fourth, computations of a simplified 2D valve model by F¨ollmer show that reflecting shocks can be accurately resolved. Fifth, a comparison of mass flow rates of a pneumatic valve model results in deviations up to 5% which seems due to a 5% too high stagnation pressure at the disk front. Sixth, the computed safety valve capacities of T¨UV Rheinland Aachen overpredict the measured discharge coefficient by 18%. However, a replication of this experiment at the test facility re8 Summary duces the error to 3%. A clear reason for the large deviation with the reference data cannot be given. Lastly, the computed mass flow rates of a nozzle flow with nitrogen at pressures up to 3500 bar agrees within 5% with experiment. A high-pressure test facility has been constructed to perform tests of safety valves with water and nitrogen at operating pressures up to 600 bar at ambient temperature. The valve disk lift and flow force measurement systems are integrated in a modified pressurized protection cap so that the opening characteristics are minimally affected. The mass flow rates of both fluids are measured at ambient conditions by means of a collecting tank with a mass balance for fluids and through subcritical orifices for gases with inaccuracies of the discharge coefficient of 3 and 2.5%. Reproducible valve tests with water have been carried out at operating pressures from 64 to 450 bar. The discharge coefficient does not depend on the set pressure of the safety valve. The dimensionless flow force slightly increases with disk lift. CFD computations of selected averaged measurement points with constant disk lift show that for smaller disk lifts the mass flow rate is overpredicted up to 41%. Extending the numerical model with the Rayleigh-Plesset cavitation model reduces the errors of the mass flow rates by a factor of two. The reductions in the flow forces range from 35 to 7% at lower disk lifts. Also reproducible valve tests with nitrogen gas at operating pressures from 73 to 453 bar have been conducted. The discharge coefficient is also independent of set pressure. In contrast to the water tests, the dimensionless flow force continually decreases with disk lift. All computed mass flow rates agree within 3.6%. The computed flow forces deviate between 7.8 and 14.7%. An analysis shows that the effects of condensation, transient effects, variation of the computational domain or mechanical wear cannot explain the flow force deviation. The reason partially lies in a larger difference between the set pressure and the opening pressure of the test valve. The flow distribution around the valve spindle is sensitive to the inlet pressure and rounding of sharp edges due to mechanical wear. The cavity of the valve spindle probably causes valve chatter partially observed in the experiments and simulations. In safety valve computations with nitrogen at higher pressures up to 2000 bar and temperatures down to 175 K outside the experimentally validated region the discharge coefficient of all three valve sizing models varies less than 6% compared to the 7 bar reference value at ambient temperature. So the standardized ideal valve sizing model is sufficient for safety valve sizing. The dimensionless force, however, increases with pressure up to 34% so that the valve characteristic is affected. The influence of valve dynamics on steady state performance of a safety valve is studied by extending the CFD tool with deformable numerical grids and the inclusion of Newton’s law applied to the valve disk. The mass flow rate and disk lift are less affected, but a fast rise and collapse of the flow force due to redirection of the bulk flow has been observed during opening. Only dynamic simulations can realistically model the opening characteristic, because these force peaks have not been observed in the static approach. Furthermore, the valve geometry can be optimized without sharp edges or cavities so that redirection of the flow will result in gradual flow force changes. Then, traveling pressure waves will lead to less unstable valve operation

MOD/R : A knowledge assisted approach towards top-down only CMOS VLSI design

MOD/R models all views on the design space in relations. This is achieved by eliminating the package constraints, as are apparent in PCB oriented hardware description languages. Assisted by knowledge engineering it allows for a top-down, mostly hierarchical decomposition, virtually eliminating the need for bottom-up assembly

A cluster-randomized controlled trial evaluating the effect of culturally-appropriate hypertension education among Afro-Surinamese and Ghanaian patients in Dutch general practice: study protocol

<p>Abstract</p> <p>Background</p> <p>Individuals of African descent living in western countries have increased rates of hypertension and hypertension-related complications. Poor adherence to hypertension treatment (medication and lifestyle changes) has been identified as one of the most important modifiable causes for the observed disparities in hypertension related complications, with patient education being recommended to improve adherence. Despite evidence that culturally-appropriate patient education may improve the overall quality of care for ethnic minority patients, few studies have focused on how hypertensive individuals of African descent respond to this approach. This paper describes the design of a study that compares the effectiveness of culturally-appropriate hypertension education with that of the standard approach among Surinamese and Ghanaian hypertensive patients with an elevated blood pressure in Dutch primary care practices.</p> <p>Methods/Design</p> <p>A cluster-randomized controlled trial will be conducted in four primary care practices in Amsterdam, all offering hypertension care according to Dutch clinical guidelines. After randomization, patients in the usual care sites (n = 2) will receive standard hypertension education. Patients in the intervention sites (n = 2) will receive three culturally-appropriate hypertension education sessions, culturally-specific educational materials and targeted lifestyle support. The primary outcome will be the proportion of patients with a reduction in systolic blood pressure ≥ 10 mmHg at eight months after the start of the trial. The secondary outcomes will be the proportion of patients with self-reported adherence to (i) medication and (ii) lifestyle recommendations at eight months after the start of the trial. The study will enrol 148 patients (74 per condition, 37 per site). Eligibility criteria for patients of either sex will be: current diagnosis of hypertension, self-identified Afro-Surinamese or Ghanaian, ≥ 20 years, and baseline blood pressure ≥ 140/90 mmHg. Primary and secondary outcomes will be measured at baseline and at 3 1/2, 6 1/2, and eight months. Other measurements will be performed at baseline and eight months.</p> <p>Discussion</p> <p>The findings will provide new knowledge on how to improve blood pressure control and patient adherence in ethnic minority persons with a high risk of negative hypertension-related health outcomes.</p> <p>Trial registration</p> <p>ISRCTN35675524</p

Pilot study evaluating the effects of an intervention to enhance culturally appropriate hypertension education among healthcare providers in a primary care setting

Background: To improve hypertension care for ethnic minority patients of African descent in the Netherlands, we developed a provider intervention to facilitate the delivery of culturally appropriate hypertension education. This pilot study evaluates how the intervention affected the attitudes and perceived competence of hypertension care providers with regard to culturally appropriate care.Methods: Pre- and post-intervention questionnaires were used to measure the attitudes, experienced barriers, and self-reported behaviour of healthcare providers with regard to culturally appropriate cardiovascular and general care at three intervention sites (N = 47) and three control sites (N = 35).Results: Forty-nine participants (60%) completed questionnaires at baseline (T0) and nine months later (T1). At T1, healthcare providers who received the intervention found it more important to consider the patient's culture when delivering care than healthcare providers who did not receive the intervention (p = 0.030). The intervention did not influence ex

Psychosocial stressors among Ghanaians in rural and urban Ghana and Ghanaian migrants in Europe

Psychosocial stressors have significant health and socio-economic impacts on individuals. We examined the prevalence and correlates of psychosocial stressors among non-migrant and migrant Ghanaians as there is limited research in these populations. The study was cross-sectional and quantitative in design. A majority of the study participants had experienced stress, discrimination and negative life events. Increased age, female sex, strong social support and high sense of mastery were associated with lower odds of experiencing psychosocial stressors in both populations. Interventions should be multi-level in design, focusing on the correlates which significantly influence the experience of psychosocial stressor

Food consumption, nutrient intake, and dietary patterns in Ghanaian migrants in Europe and their compatriots in Ghana.

Background: West African immigrants in Europe are disproportionally affected by metabolic conditions compared to European host populations. Nutrition transition through urbanisation and migration may contribute to this observations, but remains to be characterised. Objective: We aimed to describe the dietary behaviour and its socio-demographic factors among Ghanaian migrants in Europe and their compatriots living different Ghanaian settings. Methods: The multi-centre, cross-sectional RODAM (Research on Obesity and Diabetes among African Migrants) study was conducted among Ghanaian adults in rural and urban Ghana, and Europe. Dietary patterns were identified by principal component analysis. Results: Contributions of macronutrient to the daily energy intake was different across the three study sites. Three dietary patterns were identified. Adherence to the 'mixed' pattern was associated with female sex, higher education, and European residency. The 'rice, pasta, meat, and fish' pattern was associated with male sex, younger age, higher education, and urban Ghanaian environment. Adherence to the 'roots, tubers, and plantain' pattern was mainly related to rural Ghanaian residency. Conclusion: We observed differences in food preferences across study sites: in rural Ghana, diet concentrated on starchy foods; in urban Ghana, nutrition was dominated by animal-based products; and in Europe, diet appeared to be highly diverse

Determinants of Adherence to Treatment in Hypertensive Patients of African Descent and the Role of Culturally Appropriate Education

In Western countries, better knowledge about patient-related determinants of treatment adherence (medication and lifestyle) is needed to improve treatment adherence and outcomes among hypertensive ethnic minority patients of African descent.To identify patient-related determinants of adherence to lifestyle and medication recommendations among hypertensive African Surinamese and Ghanaian patients with suboptimal treatment results (SBP≥140) living in the Netherlands and how culturally appropriate hypertension education (CAHE) influenced those determinants.This study analysed data of 139 patients who participated in the CAHE trial. Univariate logistic regression analysis was used to measure the association between patient-related determinants (medication self-efficacy, beliefs about medication and hypertension, social support, and satisfaction with care) and treatment adherence. We also tested whether CAHE influenced the determinants.Medication self-efficacy and social support were associated with medication adherence at baseline. At six months, more medication self-efficacy and fewer concerns about medication use were associated with improved medication adherence. Self-efficacy was also associated with adherence to lifestyle recommendations at baseline. CAHE influenced patients' illness perceptions by creating more understanding of hypertension, its chronic character, and more concerns about the associated risks.In this high-risk population, health care providers can support medication adherence by paying attention to patients' medication self-efficacy, the concerns they may have about medication use and patients' perceptions on hypertension. The CAHE intervention improved patients' perception on hypertension

Development of a Core Outcome Set and Minimum Reporting Set for intervention studies in growth restriction in the NEwbOrN (COSNEON): study protocol for a Delphi study.

BACKGROUND: Growth restriction in the newborn (GRN) can predispose to severe complications including hypoglycemia, sepsis, and necrotizing enterocolitis. Different interventions and treatments, such as feeding strategies, for GRN have specific benefits and risks. Comparing results from studies investigating intervention studies in GRN is challenging due to the use of different baseline and study characteristics and differences in reported study outcomes. In order to be able to compare study results and to allow pooling of data, uniform reporting of study characteristics (minimum reporting set [MRS]) and outcomes (core outcome set [COS]) are needed. We aim to develop both an MRS and a COS for interventional and treatment studies in GRN. METHODS/DESIGN: The MRS and COS will be developed according to Delphi methodology. First, a scoping literature search will be performed to identify study characteristics and outcomes in research focused on interventions/treatments in the GRN. An international group of stakeholders, including experts (clinicians working with GRN, and researchers who focus on GRN) and lay experts ([future] parents of babies with GRN), will be questioned to rate the importance of the study characteristics and outcomes in three rounds. After three rounds there will be two consensus meetings: a face-to-face meeting and an electronic meeting. During the consensus meetings multiple representatives of stakeholder groups will reach agreement upon which study characteristics and outcomes will be included into the COS and MRS. The second electronic consensus meeting will be used to test if an electronic meeting is as effective as a face-to-face meeting. DISCUSSION: In our opinion a COS alone is not sufficient to compare and aggregate trial data. Hence, to ensure optimum comparison we also will develop an MRS. Interventions in GRN infants are often complicated by coexisting preterm birth. A COS already has been developed for preterm birth. The majority of GRN infants are born at term, however, and we therefore chose to develop a separate COS for interventions in GRN, which can be combined (with expected overlap) in intervention studies enrolling preterm GRN babies. TRIAL REGISTRATION: Not applicable. This study is registered in the Core Outcome Measures for Effectiveness ( COMET ) database. Registered on 30 June 2017

Effects of dietary and physical activity interventions on the risk of type 2 diabetes in South Asians: meta-analysis of individual participant data from randomised controlled trials

Aims/hypothesis: Individuals of South Asian origin have a high risk of type 2 diabetes and of dying from a diabetes-attributable cause. Lifestyle modification intervention trials to prevent type 2 diabetes in high-risk South Asian adults have suggested more modest effects than in European-origin populations. The strength of the evidence of individual studies is limited, however. We performed an individual participant data meta-analysis of available RCTs to assess the effectiveness of lifestyle modification in South Asian populations worldwide. Methods: We searched PubMed, EMBASE, Cochrane Library and Web of Science (to 24 September 2018) for RCTs on lifestyle modification interventions incorporating diet and/or physical activity in South Asian adults. Reviewers identified eligible studies and assessed the quality of the evidence. We obtained individual participant data on 1816 participants from all six eligible trials (four from Europe and two from India). We generated HR estimates for incident diabetes (primary outcome) and mean differences for fasting glucose, 2 h glucose, weight and waist circumference (secondary outcomes) using mixed-effect meta-analysis overall and by pre-specified subgroups. We used the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) system to rate the quality of evidence of the estimates. The study is registered with the International Prospective Register of Systematic Reviews ([PROSPERO] CRD42017078003). Results: Incident diabetes was observed in 12.6% of participants in the intervention groups and in 20.0% of participants in the control groups. The pooled HR for diabetes incidence was 0.65 (95% CI 0.51, 0.81; I2 = 0%) in intervention compared with control groups. The absolute risk reduction was 7.4% (95% CI 4.0, 10.2), with no interactions for the pre-specified subgroups (sex, BMI, age, study duration and region where studies were performed). The quality of evidence was rated as moderate. Mean difference for lifestyle modification vs control groups for 2 h glucose was −0.34 mmol/l (95% CI −0.62, −0.07; I2 = 50%); for weight −0.75 kg (95% CI −1.34, −0.17; I2 = 71%) and for waist −1.16 cm (95% CI −2.16, −0.16; I2 = 75%). No effect was found for fasting glucose. Findings were similar across subgroups, except for weight for European vs Indian studies (−1.10 kg vs −0.08 kg, p = 0.02 for interaction). Conclusions/interpretation: Despite modest changes for adiposity, lifestyle modification interventions in high-risk South Asian populations resulted in a clinically important 35% relative reduction in diabetes incidence, consistent across subgroups. If implemented on a large scale, lifestyle modification interventions in high-risk South Asian populations in Europe would reduce the incidence of diabetes in these populations

Dietary and physical activity recommendations to prevent type 2 diabetes in South Asian adults:A systematic review

Intervention trials and guidelines for the prevention of type 2 diabetes (T2D) in populations of South Asian origin often include strategies to improve diet and physical activity that are based on those developed for other populations. These may be suboptimal for the South Asian target populations. We aimed to provide an overview of included recommended dietary and physical activity components, and to identify whether these were supported by evidence of their effectiveness. Databases were searched until September 2017 for intervention studies and guidelines with an adult South Asian population without T2D. The protocol was registered in PROSPERO, registration number: CRD42015207067. The quality of included studies and guidelines was assessed. Dietary and physical activity components, and effects on T2D incidence, glycemic status and adiposity measures, were summarized in tabular format and evaluated narratively. Eighteen intervention studies and four guidelines were identified. Dietary and physical activity components were similar to recommendations for the general population. Intervention studies and guidelines did not reference evidence to support the effectiveness of components included in the intervention for South Asian populations in particular. Moreover, we were unable to assess patterns of components to determine the effects of specific components. Evaluation of current and emerging components among South Asian populations and subgroups seems necessary to formulate more specific recommendations in future intervention studies and guidelines