The deterioration in heat transfer to fluids at super-critical pressure and high heat fluxes

Introduction: Several supercritical steam generators in the American Electric Power system have shown evidence of tube overheat in the lower furnance at the point where the water bulk temperature is about 670 0 F. The evidence is of two kinds. First thermal fatigue has occurred and caused tube failures long before a failure of any kindwas to be expected. Second, pairs of cordal thermocouples have shown very high wall temperatures and, extrapolating back to the inside of the tube, evidence reduced inside heat transfer coefficients. It was suspected that a possible cause of the high tube temperature was a supercritical "burnout". The primary purpose of this investigation is to determine the cause and conditions leading to a supercritical "burnout" such as might occur in a supercritical steam generator. Before focusing on this aspect of the problem it is worthwhile to mention several other possible causes for the high tube wall temperatures which have been observed. In this context high means higher than the design temperature. Let us just list these possibilities. 1. Scale inside the boiler tubes. 2. Hot spot factors in the design procedure which are too low. 3. Higher heat transfer from the combustion gases than expected. Better design procedures or better control of the water purity might be sufficient to cause the problem to disappear without changing the water flow conditions inside the tube. Because the three factors which are listed above are really rather vague, it appeared that the most promising approach is to eliminate the excessive temperatures inside the tube at supercritical pressure is to eliminate the "burnout". Therefore, only the burnout aspect of the problem has been studied here. The undesirable behavior of the Nusselt number, which is of interest, is indicated in Fig. 1. In particular we want to find out when the supercritical Nusselt number is less than one would expect from the affects of simple porperty variations alone.Sponsored by American Electric Power Service Corp

Data sciences and teaching methods—learning

Data Science (DS) is an interdisciplinary field responsible for extracting knowledge from the data. This discipline is particularly complex in the face of Big Data: large volumes of data make it difficult to store, process and analyze with standard computer science technologies. The new revolution in Data Science is already changing the way we do business, healthcare, politics, education and innovation. This article describes three different teaching and learning models for Data Science, inspired by the experiential learning paradigm

Computational fact checking from knowledge networks

Traditional fact checking by expert journalists cannot keep up with the enormous volume of information that is now generated online. Computational fact checking may significantly enhance our ability to evaluate the veracity of dubious information. Here we show that the complexities of human fact checking can be approximated quite well by finding the shortest path between concept nodes under properly defined semantic proximity metrics on knowledge graphs. Framed as a network problem this approach is feasible with efficient computational techniques. We evaluate this approach by examining tens of thousands of claims related to history, entertainment, geography, and biographical information using a public knowledge graph extracted from Wikipedia. Statements independently known to be true consistently receive higher support via our method than do false ones. These findings represent a significant step toward scalable computational fact-checking methods that may one day mitigate the spread of harmful misinformation

Familial hypercholesterolaemia: identification and management. Evidence reviews for case-finding, diagnosis and statin monotherapy

This guideline covers identifying and managing familial hypercholesterolaemia (FH), a specific type of high cholesterol that runs in the family, in children, young people and adults. It aims to help identify people at increased risk of coronary heart disease as a result of having FH. In November 2017, we reviewed the evidence for case finding and diagnosis, identification using cascade testing, and management using statins. We amended recommendations in sections 1.1, 1.2 and 1.3

Paediatric CT scan usage and referrals of children to computed tomography in Germany-a cross-sectional survey of medical practice and awareness of radiation related health risks among physicians

<p>Abstract</p> <p>Background</p> <p>Computed tomography (CT) is a major source of ionizing radiation exposure in medical diagnostic. Compared to adults, children are supposed to be more susceptible to health risks related to radiation. The purpose of a cross-sectional survey among office-based physicians in Germany was the assessment of medical practice in paediatric CT referrals and to investigate physicians' knowledge of radiation doses and potential health risks of radiation exposure from CT in children.</p> <p>Methods</p> <p>A standardized questionnaire was distributed to all paediatricians and surgeons in two defined study areas. Furthermore, the study population included a random sample of general practitioners in the two areas. The questionnaire covered the frequency of referrals for paediatric CT examinations, the medical diagnoses leading to paediatric CT referrals, physicians' knowledge of radiation doses and potential health risks of radiation exposure from CT in children.</p> <p>Results</p> <p>A total of 295 (36.4%) physicians responded. 59% of the doctors had not referred a child to CT in the past year, and approximately 30% referred only 1-5 children annually. The most frequent indications for a CT examination in children were trauma or a suspected cancer. 42% of the referrals were related to minor diagnoses or unspecific symptoms. The participants underestimated the radiation exposure due to CT and they overestimated the radiation exposure due to conventional X-ray examinations.</p> <p>Conclusions</p> <p>In Germany, the frequency of referrals of children to computed tomography is moderate. The knowledge on the risks from radiation exposure among office-based physicians in our sample varied, but there was a tendency to underestimate potential CT risks. Advanced radiological training might lead to considerable amendments in terms of knowledge and practice of CT referral.</p