Full conjugate heat transfer modelling for steam turbines in transient operations

Steam turbines are increasingly required to operate more flexibly, leading to a need for more detailed calculations and design considerations of the thermal conditions during transient operations. A major challenge in transient thermal designs is the time scale disparity. For the natural cooling of a turbine, the physical process is typically in hours or tens of hours, but on the other hand, the time step sizes typically usable tend to be very small, in seconds or sub-seconds, due to the numerical stability requirement for natural convection as often encountered. The present paper reports a validation and demonstration study of a new loosely coupled conjugate heat transfer (CHT) approach developed for efficient and accurate simulations of steam turbine transient operations (Shut-down/Natural cooling). The verification and validation have been carried out for a complex 3D geometry configuration with attributes of realistic but geometrically simplified full-scale steam turbines and compared with a well-established simplified working method backed up by experimental data. Further comparisons are made against a direct baseline CHT method. The present results demonstrate a generally good agreement with the simplified working method. The new loosely coupled method is shown to give a marked speed-up (by a factor of 240) compared to the baseline directly coupled method with the same accuracy. It thus offers the potential for significant improvement in predicting the long-duration transient natural convection conjugate heat transfer problems of steam turbines in terms of computational efficiency and accuracy

Stable solar-driven oxidation of water by semiconducting photoanodes protected by transparent catalytic nickel oxide films

Reactively sputtered nickel oxide (NiO_x) films provide transparent, antireflective, electrically conductive, chemically stable coatings that also are highly active electrocatalysts for the oxidation of water to O_2(g). These NiO_x coatings provide protective layers on a variety of technologically important semiconducting photoanodes, including textured crystalline Si passivated by amorphous silicon, crystalline n-type cadmium telluride, and hydrogenated amorphous silicon. Under anodic operation in 1.0 M aqueous potassium hydroxide (pH 14) in the presence of simulated sunlight, the NiO_x films stabilized all of these self-passivating, high-efficiency semiconducting photoelectrodes for >100 h of sustained, quantitative solar-driven oxidation of water to O_2(g)

"GINEXMAL RCT: Induction of labour versus expectant management in gestational diabetes pregnancies"

<p>Abstract</p> <p>Background</p> <p>Gestational Diabetes (GDM) is one of the most common complications of pregnancies affecting around 7% of women. This clinical condition is associated with an increased risk of developing fetal macrosomia and is related to a higher incidence of caesarean section in comparison to the general population. Strong evidence indicating the best management between induction of labour at term and expectant monitoring are missing.</p> <p>Methods/Design</p> <p>Pregnant women with singleton pregnancy in vertex presentation previously diagnosed with gestational diabetes will be asked to participate in a multicenter open-label randomized controlled trial between 38+0 and 39+0 gestational weeks. Women will be recruited in the third trimester in the Outpatient clinic or in the Day Assessment Unit according to local protocols. Women who opt to take part will be randomized according to induction of labour or expectant management for spontaneous delivery. Patients allocated to the induction group will be admitted to the obstetric ward and offered induction of labour via use of prostaglandins, Foley catheter or oxytocin (depending on clinical conditions). Women assigned to the expectant arm will be sent to their domicile where they will be followed up until delivery, through maternal and fetal wellbeing monitoring twice weekly. The primary study outcome is the Caesarean section (C-section) rate, whilst secondary measurement4s are maternal and neonatal outcomes. A total sample of 1760 women (880 each arm) will be recruited to identify a relative difference between the two arms equal to 20% in favour of induction, with concerns to C-section rate. Data will be collected until mothers and newborns discharge from the hospital. Analysis of the outcome measures will be carried out by intention to treat.</p> <p>Discussion</p> <p>The present trial will provide evidence as to whether or not, in women affected by gestational diabetes, induction of labour between 38+0 and 39+0 weeks is an effective management to ameliorate maternal and neonatal outcomes. The primary objective is to determine whether caesarean section rate could be reduced among women undergoing induction of labour, in comparison to patients allocated to expectant monitoring. The secondary objective consists of the assessment and comparison of maternal and neonatal outcomes in the two study arms.</p> <p>Trial Registration</p> <p>The study protocol has been registered in the ClinicalTrials.gov Protocol Registration System, identification number <a href="http://www.clinicaltrials.gov/ct2/show/NCT01058772">NCT01058772</a>.</p

Women Born Preterm or with Inappropriate Weight for Gestational Age Are at Risk of Subsequent Gestational Diabetes and Pre-Eclampsia

Introduction: Low birthweight, which can be caused by inappropriate intrauterine growth or prematurity, is associated with development of gestational diabetes mellitus (GDM) as well as pre-eclampsia later in life, but the relative effects of prematurity and inappropriate intrauterine growth remain uncertain. Methods: Through nation-wide registries we identified all Danish mothers in the years 1989–2007. Two separate cohorts consisting mothers born 1974–1977 (n = 84219) and 1978–1981 (n = 32376) were studied, due to different methods o

A review of phase change heat transfer in shape-stabilized phase change materials (ss-PCMs) based on porous supports for thermal energy storage

Latent heat thermal energy storage (LHTES) uses phase change materials (PCMs) to store and release heat, and can effectively address the mismatch between energy supply and demand. However, it suffers from low thermal conductivity and the leakage problem. One of the solutions is integrating porous supports and PCMs to fabricate shape-stabilized phase change materials (ss-PCMs). The phase change heat transfer in porous ss-PCMs is of fundamental importance for determining thermal-fluidic behaviours and evaluating LHTES system performance. This paper reviews the recent experimental and numerical investigations on phase change heat transfer in porous ss-PCMs. Materials, methods, apparatuses and significant outcomes are included in the section of experimental studies and it is found that paraffin and metal foam are the most used PCM and porous support respectively in the current researches. Numerical advances are reviewed from the aspect of different simulation methods. Compared to representative elementary volume (REV)-scale simulation, the pore-scale simulation can provide extra flow and heat transfer characteristics in pores, exhibiting great potential for the simulation of mesoporous, microporous and hierarchical porous materials. Moreover, there exists a research gap between phase change heat transfer and material preparation. Finally, this review outlooks the future research topics of phase change heat transfer in porous ss-PCMs

Risk of caesarean section after induced labour: do hospitals make a difference

Background: There is a well-known relationship between induced labour and caesarean rates. However, it remains unknown whether this relationship reflects the impact of more complex obstetric conditions or the variability in obstetric practices. We sought to quantify the independent role of the hospital as a variable that can influence the occurrence of caesarean section after induced labour. Methods: As part of the Portuguese Generation XXI birth cohort, we evaluated 2041 consecutive women who underwent singleton pregnancies with labour induction, at five public level III obstetric units (April 2005-August 2006). The indications for induction were classified according to the guidelines of the American and the Royal Colleges of Obstetricians and Gynaecologists. Poisson regression models were adjusted to estimate the association between the hospital and surgical delivery after induction. Crude and adjusted prevalence ratios (PR) and a 95% confidence interval (95% CI) were computed. Results: The proportion of women who were induced without formal clinical indications varied among hospitals from 20.3% to 45.5% (p < 0.001). After adjusting for confounders, the risk of undergoing a caesarean section after induced labour remained significantly different between the hospitals, for the cases in which there was no evident indication for induction [the highest PR reaching 1.86 (95% CI, 1.23–2.82)] and also when at least one such indication was present [1.53 (95% CI, 1.12–2.10)]. This pattern was also observed among the primiparous cephalic term induced women [the highest PR reaching 2.06 (95% CI, 1.23–2.82) when there was no evident indication for induction and 1.61 (95% CI, 1.11–2.34) when at least one such indication was present]. Conclusions:Caesarean section after induced labour varied significantly across hospitals where similar outcomes were expected. The effect was more evident when the induction was not based on the unequivocal presence of commonly accepted indications

Multi-scale time integration for transient conjugate heat transfer

The quasi-steady assumption is commonly adopted in existing transient fluid–solid-coupled convection–conduction (conjugate) heat transfer simulations, which may cause non-negligible errors in certain casesof practical interest. In the present work, we adopt a new multi-scale framework for the fluid domainformulated in a triple-timing form. The slow-varying temporal gradient corresponding to the time scalesin the solid domain has been effectively included in the fluid equations as a source term, whilst short-scale unsteadiness of the fluid domain is captured by a local time integration at a given ‘frozen ’ large scaletime instant. For concept proof, validation and demonstration purposes, the proposed met hodology has beenimplemented in a loosely coupled procedure in conjunction with a hybrid interfacing treatment for couplingefficiency and accuracy. The present results indicate that a much enhanced app licability can be achievedwith relatively small modifications of existing transient conjugate heat transfer met hods at little extra cos

Multi-scale time integration for transient conjugate heat transfer

The quasi-steady assumption is commonly adopted in existing transient fluid–solid-coupled convection–conduction (conjugate) heat transfer simulations, which may cause non-negligible errors in certain casesof practical interest. In the present work, we adopt a new multi-scale framework for the fluid domainformulated in a triple-timing form. The slow-varying temporal gradient corresponding to the time scalesin the solid domain has been effectively included in the fluid equations as a source term, whilst short-scale unsteadiness of the fluid domain is captured by a local time integration at a given ‘frozen ’ large scaletime instant. For concept proof, validation and demonstration purposes, the proposed met hodology has beenimplemented in a loosely coupled procedure in conjunction with a hybrid interfacing treatment for couplingefficiency and accuracy. The present results indicate that a much enhanced app licability can be achievedwith relatively small modifications of existing transient conjugate heat transfer met hods at little extra cos

On LES based conjugate heat transfer procedure for transient natural convection

Natural convection prediction closely relevant to flexible operations (e.g. fast and frequent startups and showdowns) of gas turbines and steam turbines presents considerable challenges. The strong inter-dependence between fluid and solid parts points to the need for conjugate heat-transfer (CHT) methods. However the long time scales of the practical operation processes of interest, and the fundamental fluid-solid time scale disparity raise general issues regarding the computational costs of the CHT methods. In particular, if a high fidelity flow model (e.g. LES) needing to resolve smaller time scales of turbulence is adopted, we also face an additional question regarding the consistency and accuracy of the fluid-solid interface treatment. In this paper, we address the issues by the means of a loosely coupled CHT procedure based on the multi-scale methodology recently proposed for transient conjugate heat transfer predictions. The multi-scale framework provides an efficient way for accurately solving problems with a huge scale disparity. A particular emphasis of the present work is on efficient and accurate transient CHT solutions in conjunction with the turbulence eddy resolved modelling (LES) for natural convection. A multi-scale flow decomposition associated with the corresponding time step split is adopted. The resultant triple timing formation of the flow equations can be solved efficiently for the fluid-solid coupled system with very disparate time scales. The methodology will be presented with case studies supported by a new interface analysis to underpin the problem statement and motivation of the present work, and to demonstrate the validity and effectiveness of the methodology and implemented procedure