Gotowe bibliografie tematyczne / Efficiency of Stratification

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Gotowa bibliografia na temat „Efficiency of Stratification”

Autor: Grafiati

Data publikacji: 8 września 2023

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Artykuły w czasopismach na temat "Efficiency of Stratification"

Rosengarten, G., G. Morrison i M. Behnia. "A Second Law Approach to Characterising Thermally Stratified Hot Water Storage With Application to Solar Water Heaters". Journal of Solar Energy Engineering 121, nr 4 (1.11.1999): 194–200. http://dx.doi.org/10.1115/1.2888166.

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This paper presents a method of characterising and evaluating the performance of hot water storage systems in terms of their temperature distribution. The change in exergy from the stratified state to the delivery state depends on the stored energy and the stratification. It can thus he used to define the storage efficiency for sensible heat storage devices. A new parameter that isolates the stratification component of the exergy is defined and called the stratification efficiency. The effect of temperature distribution, delivery temperature and tank cross-section on exergy and stratification efficiency is investigated. The advantage that stratification offers over a mixed tank is examined in terms of the storage efficiency and overall solar water heating system performance. Exergy is used to assess the operation of mantle heat exchangers in solar water heating systems and it is shown that exergy and stratification efficiency, as well as energy, should be used to ascertain the performance of such heat exchangers.

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Sadooghi-Alvandi, S. M. "A NOTE ON THE EFFICIENCY OF PROPORTIONAL STRATIFICATION". Australian Journal of Statistics 30, nr 2 (czerwiec 1988): 196–99. http://dx.doi.org/10.1111/j.1467-842x.1988.tb00850.x.

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Roberts, Scott D., James N. Long i Frederick W. Smith. "Canopy stratification and leaf area efficiency: a conceptualization". Forest Ecology and Management 60, nr 1-2 (sierpień 1993): 143–56. http://dx.doi.org/10.1016/0378-1127(93)90028-l.

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Myllymäki, Mari, Terje Gobakken, Erik Næsset i Annika Kangas. "The efficiency of poststratification compared with model-assisted estimation". Canadian Journal of Forest Research 47, nr 4 (kwiecień 2017): 515–26. http://dx.doi.org/10.1139/cjfr-2016-0383.

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Survey sampling with model-assisted estimation has recently gained popularity in forest inventory. Another option for utilizing the auxiliary information is to use poststratification, which is a special case of model-assisted estimation with class variables as explanatory variables. In this study, we compared the efficiency of poststratification with an increasing number of strata with model-assisted estimation. We carried out a study based on a simulated population. We considered four different types of poststratifications, namely (i) stratification based on predictions of a linear model, (ii) stratification based on a regression tree model, (iii) stratification based on the first principal component of the explanatory variables, and (iv) stratification based on the regression tree model with the first principal component as the only explanatory variable. Furthermore, we examined both the traditional poststratification mean and variance estimators and the difference estimator and its variance estimator for poststratification. Within the recommended range of number of strata, the model-assisted approach was more efficient than poststratification. With a large number of strata, poststratification produced smaller standard error of estimates, but problems such as empty strata were encountered with small sample sizes. Using the first principal component directly for stratification or as an explanatory variable was the most efficient approach.

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Xie, Bing, John D. Clark i David D. L. Minh. "Efficiency of Stratification for Ensemble Docking Using Reduced Ensembles". Journal of Chemical Information and Modeling 58, nr 9 (16.08.2018): 1915–25. http://dx.doi.org/10.1021/acs.jcim.8b00314.

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Ferrarini, Luca, Giancarlo Mantovani i Marta Pagliarini. "Improving Energy Efficiency in Large Buildings with Thermal Stratification". IFAC Proceedings Volumes 47, nr 3 (2014): 4885–90. http://dx.doi.org/10.3182/20140824-6-za-1003.02532.

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Trinuruk, Piyatida, Papangkorn Jenyongsak i Somchai Wongwises. "Comparative Study of Inlet Structure and Obstacle Plate Designs Affecting the Temperature Stratification Characteristics". Energies 15, nr 6 (10.03.2022): 2032. http://dx.doi.org/10.3390/en15062032.

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Temperature stratification between outgoing hot water and incoming cold water is a key factor in diminishing energy loss during the discharging process and maximizing the useful hot water delivered from the tank or enhancing the thermal efficiency of the heating device during the heating process. In this study, the inlet structure and the obstacle plate were designed and modified based on two main factors, the reduction of inlet water velocity and the stipulation of the water recirculation area, to develop temperature stratification through the computational fluid dynamics method. The simulation model’s accuracy was validated against the experimental results. The results showed that using the equalizer as an inlet pipe’s auxiliary device was the best approach for decreasing the inlet water velocity, which resulted in enhancing temperature stratification. The discharging efficiency improved from 77.3% for the original tank model to 86.1% for the tank with equalizer IV model, which meant an additional 45 L of useful hot water was gained from the good temperature stratification storage tank. The installation of the obstacle plate for controlling the turbulence zone could not improve temperature stratification significantly, which resulted in an increase in discharging efficiency by only 4% more than the original tank model.

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Han, Wang Kook, Jin Man Kim, Tae Hun Lim, Hae Eun Song i Young Chull Ahn. "Temperature stratification using an air-cooled heat pump system with a mixing valve". Advances in Mechanical Engineering 12, nr 12 (grudzień 2020): 168781402098465. http://dx.doi.org/10.1177/1687814020984653.

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The main factor determining the performance of a thermal storage method is the temperature stratification in the storage tank. At the ideal stratification, the energy efficiency of the storage tank is extremely high. However, when the heat pump is applied, the stratification is disrupted by heat exchange between the layers of the heat medium, and consequent convection in the tank. Therefore, this study analyzed the influence of stratification-related design factors in the water-piping facility area outside a tank heated by a heat pump. In particular, it assessed the thermal stratification and energy efficiency in the storage tank installed with a mixing valve. In the system using the mixing valve, hot water of constant temperature was supplied to the top of the storage tank, reducing the mixing effect of the hot and cold waters; consequently, the stratification index was maximized at 0.42. Comparing the times at which the temperature of the uppermost part reached 70°C in the systems with and without the mixing valve (30 and 75 min, respectively), we find that the mixing valve reduced the time of obtaining effectively hot water by approximately 60%.

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Wissink, Martin, i Rolf Reitz. "The role of the diffusion-limited injection in direct dual fuel stratification". International Journal of Engine Research 18, nr 4 (20.08.2016): 351–65. http://dx.doi.org/10.1177/1468087416661867.

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Low-temperature combustion offers an attractive combination of high thermal efficiency and low NO x and soot formation at moderate engine load. However, the kinetically-controlled nature of low-temperature combustion yields little authority over the rate of heat release, resulting in a tradeoff between load, noise, and thermal efficiency. While several single-fuel strategies have achieved full-load operation through the use of equivalence ratio stratification, they uniformly require retarded combustion phasing to maintain reasonable noise levels, which comes at the expense of thermal efficiency and combustion stability. Previous work has shown that control over heat release can be greatly improved by combining reactivity stratification in the premixed charge with a diffusion-limited injection that occurs after low-temperature heat release, in a strategy called direct dual fuel stratification. While the previous work has shown how the heat release control offered by direct dual fuel stratification differs from other strategies and how it is enabled by the reactivity stratification created by using two fuels, this paper investigates the effects of the diffusion-limited injection. In particular, the influence of fuel selection and the pressure, timing, and duration of the diffusion-limited injection are examined. Diffusion-limited injection fuel type had a large impact on soot formation, but no appreciable effect on performance or other emissions. Increasing injection pressure was observed to decrease filter smoke number exponentially while improving combustion efficiency. The timing and duration of the diffusion-limited injection offered precise control over the heat release event, but the operating space was limited by a tradeoff between NO x and soot.

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SON, HYO SEOK, JAE-WOOK KWON, SEONG HOON LEE, CHUL KIM i HIKI HONG. "THE EFFECT OF UPPER-HEATING SYSTEM IN SOLAR WATER STORAGE TANK". International Journal of Air-Conditioning and Refrigeration 22, nr 04 (grudzień 2014): 1450027. http://dx.doi.org/10.1142/s2010132514500278.

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Thermal stratification in the water storage tank of solar heating system is essential to increase the collection efficiency. We previously investigated the stratification performance of side-heating system, where the hot water returning from the collector heats up the side wall of storage tank. Subsequently, we studied an evolved heating system for further improvement, where we added an upper-heating to the side-heating. Here we thoroughly examine the stratification performance of the evolved heating system using TRNSYS-based simulation. As the essential result, contrary to expectation, evolved system does not show substantial improvement of collection efficiency compared to side-heating. However, we confirm that evolved system excels in the useful energy.

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Rozprawy doktorskie na temat "Efficiency of Stratification"

Lawrie, Andrew. "Rayleigh-Taylor mixing : confinement by stratification and geometry". Thesis, University of Cambridge, 2010. https://www.repository.cam.ac.uk/handle/1810/225125.

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Rayleigh-Taylor instability has been an area of active research in fluid dynamics for the last twenty years, but relatively little attention has been paid to the dynamics of problems where Rayleigh-Taylor instability plays a role, but is only one component of a more complex system. Here, Rayleigh-Taylor instability between miscible fluids is examined in situations where it is confined by various means: by geometric restriction, by penetration into a stable linear stratification, and by impingement on a stable density interface. Water-based experiments are modelled using a variety of techniques, ranging from simple hand calculation of energy exchange to full three-dimensional numerical simulation. Since there are well known difficulties in modelling unconfined Rayleigh-Taylor instability, the confined test cases have been sequenced to begin with dynamically simple benchmark systems on which existing modelling approaches perform well, then they progress to more complex systems and explore the limitations of the various models. Some work on the phenomenology of turbulent mixing is also presented, including a new experimental technique that allows mixed fluid to be visualised directly, and an analysis of energy transport and mixing efficiency in variable density flows dominated by mixing.

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Adua, Lazarus. "The Salience of Stratification, Lifestyle and Residential Energy Efficiency Improvement in the Climate Change Discourse and Policy: Implications for Environmental Justice". The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1243888108.

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Davies, Wykes Megan Sydney. "Efficient mixing in stratified flows : Rayleigh-Taylor instability within an otherwise stable stratification". Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708349.

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Ebert, Guenther Wolfgang. "The efficiency of turbulent mixing in stratified fluids". Thesis, 2010. http://hdl.handle.net/2152/ETD-UT-2010-08-1876.

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Mixing is a common feature of stratified fluids. In stratified fluids the density varies with the height. This is true for the most fluids in geophysical environments, like lakes, the atmosphere or the ocean. Turbulent mixing plays a crucial role for the overall energy budget of the earth and has therefore an huge impact on the global climate. By introducing the mixing efficiency, it is possible to quantify mixing. It is defined as the ratio of gain of potential energy to the injection of mechanical energy. In the ocean energy provided by tidal forces leads to turbulence and thus highly dense water is lifted up from the deep sea to the surface. For this process, a mixing efficiency of 0.2 is estimated. Until now it is not completely understood how this high value can be achieved. Thus we measured the mixing efficiency by using a Couette-Taylor system, which can produce steady-state homogeneous turbulence. This is similar to what we find in the ocean. The Couette-Taylor system consists of two concentric cylinders that can be rotated independently. In between a stratified fluid is filled using salt as a stratifying agent. In the laboratory experiment, we obtained mixing efficiencies in the order of 0.001 as a result. Moreover we found that the mixing efficiency decreases with decreasing stratification like previous laboratory experiments have shown. As this value is two orders of magnitude smaller than what we find in the ocean, further studies will be necessary.
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Książki na temat "Efficiency of Stratification"

Daniel, Rene, i Catriona M. Harrop, red. Medical Management of Neurosurgical Patients. Oxford University Press, 2019. http://dx.doi.org/10.1093/med/9780190913779.001.0001.

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Modern management of neurosurgical patients requires close cooperation between neurosurgeons and other specialists. The latter include internists, nurse practitioners, and physician assistants. This textbook aims to provide for these professionals a guide to the challenges associated with the medical management of these patients. It gives an overview of neurosurgical operations and procedures, seizure management, and preoperative risk stratification. It further discusses the intricacies of the management of fever, infection, electrolytes, bleeding disorders, and endocrine problems in the context of central nervous system injury. A particular emphasis is placed on the management of pressure injuries, pain management, and physical and occupational therapy, which are critical areas in the care of the neurosurgical patient. Finally, it reviews the types of contributions that palliative care can make to the care of the neurosurgical patient. The book’s objective is to provide a practical tool, and, where appropriate, its chapters include algorithms and tables to increase the efficiency of medical decision-making when caring for these patients.

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Części książek na temat "Efficiency of Stratification"

Geng, Yiwa, i Xiongbin Liu. "Numerical Simulation of the Transient Flow Characteristics and Thermal Stratification Phenomena in the Passive Residual Heat Removal System of NHR-200-II". W Springer Proceedings in Physics, 1031–45. Singapore: Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-99-1023-6_87.

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AbstractThe NHR-200-II nuclear heating reactor is a multi-purpose small integral pressurized water reactor (iPWR) developed by the Institute of Nuclear and New Energy Technology (INET) of Tsinghua University. The design of NHR-200-II features a reactor core with thermal power of 200MW, in-vessel hydraulically-driven control rods and passive residual heat removal (PRHR) systems, et.al. Passive residual heat removal experiments were conducted in a scaled integral test facility for NHR-200-II. The PRHR experiments in the scaled facility were simulated by a layered RELAP5 system model to study the flow characteristics of the PRHR system in different primary fluid temperatures and different valve states. The phenomenon of reversed flow occurred in some primary heat exchangers in the numerical simulations when the primary fluid temperature was higher than certain level, which was consistent to the experiments. The simulated uneven outlet temperature distribution of the primary heat exchangers was also consistent with the experimental data when the isolation valves for the steam generator was kept open. Thermal stratification effect in the headers of the PRHR system played an important role in the phenomenon of uneven outlet temperature distributions, and the layered RELAP5 model was proven to be an efficient method for preliminary estimation of thermal stratification effect in the headers.

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Iliou, Marie Christine, i Catherine Monpere. "Early assessment and risk stratification". W ESC Handbook of Cardiovascular Rehabilitation, 41–48. Oxford University Press, 2020. http://dx.doi.org/10.1093/med/9780198849308.003.0006.

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A pre-participation medical assessment before cardiac rehabilitation (CR) is mandatory in order to deliver a safe programme tailored to the individual patient. This initial evaluation also aims to increase patient adherence and the efficiency of the programme. The entry assessment includes the following components: history, global patient evaluation including clinical questionnaires, physical examination, laboratory analysis, and non-invasive cardiovascular testing. Following this assessment, a risk stratification should be performed to determine the appropriate CR modalities.

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Excoffier, Jean-Baptiste, Elodie Escriva, Julien Aligon i Matthieu Ortala. "Local Explanation-Based Method for Healthcare Risk Stratification". W Studies in Health Technology and Informatics. IOS Press, 2022. http://dx.doi.org/10.3233/shti220520.

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Decision support tools in healthcare require a strong confidence in the developed Machine Learning (ML) models both in terms of performances and in their ability to provide users a deeper understanding of the underlying situation. This study presents a novel method to construct a risk stratification based on ML and local explanations. An open-source dataset was used to demonstrate the efficiency of this method that well identified the main subgroups of patients. Therefore, this method could help practitioners adjust and build protocols to improve care deliveries that would better reflect patient’s risk level and profile.

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Marchant, Richard, i Catherine M. Yule. "Aquatic Macroinvertebrates". W Freshwater Ecology and Conservation, 240–54. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198766384.003.0011.

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Sampling of aquatic macroinvertebrates requires techniques that are efficient and representative. Stratification of sampling units is a practical way of ensuring representative coverage of the habitat. However, efficiency of sampling devices used in the field and techniques for extraction of specimens from samples has rarely been assessed. Commonly used qualitative and quantitative samplers are described as well as the situations in which a particular device is most likely to be useful. The efficiency of these devices can be estimated using a technique known as removal sampling, whose underlying statistical theory is well understood. The laboratory examination of samples is straightforward but tedious. Flotation of specimens from inorganic material and subsampling are two methods of speeding up laboratory processing. Small cryptic species or small instars are easily obscured by detritus when picking specimens from samples under low magnification. By scanning samples twice the efficiency of extraction of specimens can be estimated.

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Orekhova, Inessa M. "Employed and unoccupied population of the Republic of Tyva: potential and efficiency of use". W Features of social stratification in the Republic of Tyva, 29–45. Institute of Sociology of FCTAS RAS, 2019. http://dx.doi.org/10.19181/inab.2019.3.3.

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Pinheiro, Rómulo, i Bjørn Stensaker. "Balancing Efficiency and Equity in a Welfare State Setting: High Participation Higher Education in Norway". W High Participation Systems of Higher Education, 386–417. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198828877.003.0014.

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This chapter provides a detailed and extensive assessment of Norway’s high participation system (HPS) of higher education. It starts from a historical analysis of higher education enrolment since massification after World War II. Norway attempts to combine equity with relevancy, efficiency, and accountability. In relation to the general process of expansion, driven by family aspirations, and HPS governance and diversity, including the growing importance of larger institutions with comprehensive missions, Norway largely fits HPS propositions, though like other Nordic countries it departs significantly from the propositions in terms of stratification (low) and equity (high). There are signs however of increased research competition and formation of a steeper hierarchy.

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Holbourn, Ann, Wolfgang Kuhnt, Karlos G. D. Kochhann, Kenji M. Matsuzaki i Nils Andersen. "Middle Miocene climate–carbon cycle dynamics: Keys for understanding future trends on a warmer Earth?" W Understanding the Monterey Formation and Similar Biosiliceous Units across Space and Time. Geological Society of America, 2022. http://dx.doi.org/10.1130/2022.2556(05).

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ABSTRACT The late early to middle Miocene period (18–12.7 Ma) was marked by profound environmental change, as Earth entered into the warmest climate phase of the Neogene (Miocene climate optimum) and then transitioned to a much colder mode with development of permanent ice sheets on Antarctica. Integration of high-resolution benthic foraminiferal isotope records in well-preserved sedimentary successions from the Pacific, Southern, and Indian Oceans provides a long-term perspective with which to assess relationships among climate change, ocean circulation, and carbon cycle dynamics during these successive climate reversals. Fundamentally different modes of ocean circulation and carbon cycling prevailed on an almost ice-free Earth during the Miocene climate optimum (ca. 16.9–14.7 Ma). Comparison of δ13C profiles revealed a marked decrease in ocean stratification and in the strength of the meridional overturning circulation during the Miocene climate optimum. We speculate that labile polar ice sheets, weaker Southern Hemisphere westerlies, higher sea level, and more acidic, oxygen-depleted oceans promoted shelf-basin partitioning of carbonate deposition and a weaker meridional overturning circulation, reducing the sequestration efficiency of the biological pump. X-ray fluorescence scanning data additionally revealed that 100 k.y. eccentricity-paced transient hyperthermal events coincided with intense episodes of deep-water acidification and deoxygenation. The in-phase coherence of δ18O and δ13C at the eccentricity band further suggests that orbitally paced processes such as remineralization of organic carbon from the deep-ocean dissolved organic carbon pool and/or weathering-induced carbon and nutrient fluxes from tropical monsoonal regions to the ocean contributed to the high amplitude variability of the marine carbon cycle. Stepwise global cooling and ice-sheet expansion during the middle Miocene climate transition (ca. 14.7–13.8 Ma) were associated with dampening of astronomically driven climate cycles and progressive steepening of the δ13C gradient between intermediate and deep waters, indicating intensification and vertical expansion of ocean meridional overturning circulation following the end of the Miocene climate optimum. Together, these results underline the crucial role of the marine carbon cycle and low-latitude processes in driving climate dynamics on an almost ice-free Earth.

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Heckman, George, i Pálmi V. Jónsson. "Comprehensive geriatric assessment". W Oxford Textbook of Geriatric Medicine, 127–34. Oxford University Press, 2017. http://dx.doi.org/10.1093/med/9780198701590.003.0017.

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In the context of population ageing, the provision of person-specific care to older persons is complicated by the presence, in a single individual, of multiple chronic conditions, and an increasingly complex, non-institutionally-based, service delivery framework. The most complex seniors benefit from a comprehensive geriatric assessment which, in order to promote greater health system integration and coordination, must be standardized across care delivery sectors. InterRAI instruments provide such functionality, which not only supports more efficient and comprehensive care planning, but leads to multiple useful derivative applications for clinicians, health administrators, and policy makers, such as screeners, risk stratification algorithms, outcome scales, quality indicators, and case-mixed indices. Furthermore, clinical information collected through interRAI instruments provide a rich and robust resource for health research.

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Gill, Harman S. "Shortness of Breath". W Acute Care Casebook, redaktor Evie Marcolini, 119–23. Oxford University Press, 2018. http://dx.doi.org/10.1093/med/9780190865412.003.0024.

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Chest pain and dyspnea are complaints frequently associated with a diagnosis of pulmonary embolism but may also be associated with other numerous cardiac and pulmonary disease processes encountered daily in the emergency department. This case presents the classic historical risk factors of malignancy and recent surgery in combination with typical clinical findings of acute onset of chest pain and dyspnea that is worse with deep inspiration. A sequential and methodological assessment through a thorough physical exam, electrocardiogram, chest X-ray, and lab testing such as troponin, pro-brain natriuretic peptide, and D-dimer testing allow the emergency medicine practitioner to be accurate, thorough, and efficient. Once a diagnosis is made, the stratification of massive versus submassive is dictated by hemodynamic stability and the presence or absence of acute right ventricular strain to further guide treatment and disposition.

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Rochecouste, Jean-Francois, John Baker i Bill Crabtree. "Conservation Agriculture in Australian dryland cropping and in New Zealand: the lessons of 70 years". W Burleigh Dodds Series in Agricultural Science, 599–624. Burleigh Dodds Science Publishing, 2022. http://dx.doi.org/10.19103/as.2021.0088.15.

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Australia and New Zealand have seen a rapid adoption rate in Conservation Agriculture in the areas of no-till and stubble retention. The two countries have different stories, and this will be highlighted in this chapter. For Australia crop diversification has not changed substantially, and the balance required between diversification and the variable return of different crops is still a major challenge for farmers, with wheat remaining over half of the national crop. The main changes in tillage practices involved the adoption of narrow tine and disc planters to minimise soil disturbance along with stubble retention, crop rotation and controlled traffic farming have followed suit. Current trends involve an increasing use of GPS technology combined with remote and proximal sensors to more efficiently deliver resources such as fertiliser and chemicals. Precision technology is also being used to reposition the planting row to the inter-row between the standing stubble. Herbicide resistance is becoming an increasing problem. Emerging issues include nutrient stratification, sub-surface acidification and an increase in diseases from stubble retention.

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Streszczenia konferencji na temat "Efficiency of Stratification"

Khan, Fahad, i Brian J. Savilonis. "Thermal Stratification in Spherical Tanks". W ASME 2014 8th International Conference on Energy Sustainability collocated with the ASME 2014 12th International Conference on Fuel Cell Science, Engineering and Technology. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/es2014-6429.

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Spherical tanks have the potential for cost reduction in sensible thermal energy storage (TES) systems, by using less tank building material and insulation. The current CFD study compares the Thermal Efficiency (TE) of a thermocline storage system in a spherical tank to a cylindrical tank of the same volume. A parametric study is then performed on a spherical tank during the discharge process to determine the flow parameters that govern the thermocline formation and entrainment. The following parameters are used: tank diameter to inlet diameter ratio D/d = 10, inlet velocity (0.02–0.1 m/s), and ΔT (10–70° C), leading to an inlet Froude number (0.4–3), inlet Reynolds number (500–7500), and tank Richardson number (2–100). The results show a significant correlation between the inlet Reynolds and inlet Froude numbers, and the tank TE, in addition to a weak correlation between the tank Richardson number, based on the tank diameter, and the tank TE. The parametric study also shows a maximum tank TE at a Froude number equal to 0.5, and a proportional decrease of TE as the Reynolds number increases.

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Kim, Sayop, Joohan Kim, Ashish Shah, Pinaki Pal, Riccardo Scarcelli, Toby Rockstroh, Sibendu Som, Yunchao Wu i Tianfeng Lu. "Numerical Study of Advanced Compression Ignition and Combustion in a Gasoline Direct Injection Engine". W ASME 2019 Internal Combustion Engine Division Fall Technical Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/icef2019-7281.

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Abstract Multi-mode combustion strategies may provide a considerable thermal efficiency improvement targeted at part-load operating conditions for light-duty spark-ignition (SI) engines. The extension from boosted SI mode at high loads to advanced compression ignition (ACI) mode at low loads can be achieved by increasing compression ratio and utilizing intake air heating. In order to enable an accurate control of intake charge condition for ACI control and rapid mode-switches, it is essential to gain fundamental insight into the autoignition process with regard to thermal and fuel-air mixture stratification in the combustion chamber. In this work, a computational fluid dynamics (CFD) study is carried out to reveal some degrees of correlation between the mixture and thermal stratifications induced by the cylinder wall temperature and combustion-phasing across varying engine load conditions. The computational analysis begins with a calibrated simulation setup best matching the engine experiments, and subsequently evaluates the baseline setup for an extended range of engine load conditions for two excess-air ratio cases. The present study emphasizes the dominance of thermal stratifications for autoignition process due to wall temperature effects depending on the engine load conditions of interest. In addition, this study also aims to provide insight into the impact of mixture stratification on cyclic variability, especially at colder wall engine conditions (e.g., cold start). Observations herein provide highlight of the propensity of autoignition in correlation with mixture reactivity space.

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Musu, E., S. Zanforlin i R. Gentili. "Four Stroke Engine Geometry for Stratified Charge Combustion". W ASME 2005 Internal Combustion Engine Division Fall Technical Conference. ASMEDC, 2005. http://dx.doi.org/10.1115/icef2005-1218.

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In four-stroke engines direct injection increases power and fuel economy, which is further improved by charge stratification, due to pumping loss reduction and better combustion efficiency at partial loads. Charge stratification can be obtained by different techniques and injector designs. In every case late injection is necessary for stratification, which however is impaired by fuel dilution and spreading in consequence of burnt gas expansion, leading to incomplete combustion at very light loads. A numerical study has been carried out modifying KIVA code to handle new piston shapes. An innovative combustion chamber that is split in two volumes and allows fuel confinement during combustion has been conceived. CFD comparison has been made between a conventional combustion chamber and the proposed new one in term of combustion efficiency. Combustion is enhanced by the new design and unburnt emissions are reduced.

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Zhang, Shengshuai, Naihua Wang i Xiangyu Chi. "A Numerical Investigation of the Mixing in the VCT During the Dilution Process". W 2022 29th International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/icone29-91885.

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Abstract The Volume Control Tank (VCT) is an indispensable device ofChemical and Volume Control System in the primary loop. The incoming water cannot be quickly mixed with the original boric acid solution in the VCT during the dilution process. The poor mixing would delay the reactive control of the core, which increases the time consumption of nuclear power plant operations and brings adverse impacts on core stability. A numerical investigation of the mixing in the VCT during the dilution process is carried out. The numerical methods were validated by experimental data. It is found that there are two different mixing modes in the tank, and the mixing and flow characteristics under different mixing modes are analyzed. It is found that the concentration stratification increases the flow resistance, which has a negative impact on the mixing. Increasing the inlet velocity can effectively avoid stratification and improve mixing efficiency. Increasing the jet density difference will aggravate the stratification in the tank, and even cause the phenomenon of double stratification. The work in this paper has certain guidance for understanding the internal fields in the VCT during the dilution process and improving the mixing efficiency in the VCT.

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Dev, Shouvik, Tongyang Gao, Xiao Yu, Mark Ives i Ming Zheng. "Fuel Stratification and Partially Premixed Combustion With Neat N-Butanol in a Compression Ignition Engine". W ASME 2017 Internal Combustion Engine Division Fall Technical Conference. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/icef2017-3676.

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Homogeneous Charge Compression Ignition (HCCI) has been considered as an ideal combustion mode for compression ignition engines due to its superb thermal efficiency and low emissions of nitrogen oxides (NOx) and particulate matter (PM). However, a challenge that limits practical applications of HCCI is the lack of control over the combustion rate, which either deteriorates thermal efficiency at low engine load, or produces excessive pressure rise rate and combustion noise at high engine load. Fuel stratification and partially premixed combustion (PPC) have considerably improved the control over the heat release profile with modulations of the ratio between premixed fuel and directly injected fuel, as well as injection timing for ignition initiation. It leverages the advantages of both conventional direct injection compression ignition and HCCI. Compared with those of HCCI, the ignition ability and combustion efficiency of PPC are significantly enhanced at low engine load, and the low emissions of NOx and PM are maintained with lower pressure rise rate. In this study, neat n-butanol is employed to generate the fuel stratification and partially premixed combustion in a single cylinder compression ignition engine. A fuel such as n-butanol can provide additional benefits of even lower emissions, and can potentially lead to a reduced carbon footprint and improved energy security if produced appropriately from biomass sources. Intake port fuel injection (PFI) of neat n-butanol is used for the delivery of the premixed fuel, while the direct injection (DI) of neat n-butanol is applied to generate the fuel stratification. Effects of PFI-DI fuel ratio, DI timing, and intake pressure, on the combustion, are studied in detail. Different conditions are identified at which clean and efficient combustion can be achieved at a baseline load of 6 bar IMEP. An extended load of 14 bar IMEP is demonstrated using stratified combustion with combustion phasing control.

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Wang, Shuping, i Jane H. Davidson. "Performance of Rigid Porous Stratification Manifolds With Interpretation for Off-Design Operation". W ASME 2013 7th International Conference on Energy Sustainability collocated with the ASME 2013 Heat Transfer Summer Conference and the ASME 2013 11th International Conference on Fuel Cell Science, Engineering and Technology. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/es2013-18015.

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Thermal stratification of solar water storage tanks improves collector efficiency and provides higher quality energy to the user. A crucial aspect of maintaining stratification is preventing mixing in the tank, particularly during solar charging and hot water draws. An effective and simple approach to flow control is an internal stratification manifold. In this paper, the performance of the rigid porous manifold, which consists of a series of vertical hydraulic resistance elements placed within a perforated tube, is considered for charging operation. A 1-D model of the governing mass, momentum, and energy conservation equations is used to illustrate the procedure for designing a manifold and to explore its performance over a broad range of operating conditions expected in solar water storage tanks. A manifold performance indicator (MPI) is used to evaluate the effectiveness of the manifold relative to an inlet pipe positioned at the top of the tank. The rigid porous manifold improves the stratification in the tank over a wide range of operating conditions unless the inlet flow rate is significantly reduced from the design point.

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Wolde, Ian, i Alejandro Caroca. "Assessing Stratification Efficiency During Charging and Discharging Processes of Thermal Storage Tank Using Modified Inlet Diffusers". W ISES Solar World Congress 2019/IEA SHC International Conference on Solar Heating and Cooling for Buildings and Industry 2019. Freiburg, Germany: International Solar Energy Society, 2019. http://dx.doi.org/10.18086/swc.2019.24.11.

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Castell, A., C. Sole´, M. Medrano, M. Nogue´s i L. F. Cabeza. "Comparison of Stratification in a Water Tank and a PCM-Water Tank". W ASME 2007 Energy Sustainability Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/es2007-36074.

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Most of the storage systems available on the market use water as storage medium. Enhancing the storage performance is necessary to increase the performance of most systems. The stratification phenomenon is employed to improve the efficiency of storage tanks. Heat at an intermediate temperature, not high enough to heat up the top layer, can still be used to heat the lower, colder layers. There are a lot of parameters to study the stratification in a water tank such as the Mix Number and the Richardson Number among others. The idea studied here was to use these stratification parameters to compare two tanks with the same dimensions during charging and discharging processes. One of them is a traditional water tank and the other is a PCM-water (a water tank with a Phase Change Material). A PCM is good because it has high energy density if there is a small temperature change, since then the latent heat is much larger than the sensible heat. On the other hand, the temperature change in the top layer of a hot water store with stratification is usually small as it is held as close as possible at or above the temperature for usage. In the system studied the Phase Change Material is placed at the top of the tank, therefore the advantages of the stratification still remain. The aim of this work is to demonstrate that the use of PCM in the upper part of a water tank holds or improves the benefit of the stratification phenomenon.

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Lawler, Benjamin, Satyum Joshi, Joshua Lacey, Orgun Guralp, Paul Najt i Zoran Filipi. "Understanding the Effect of Wall Conditions and Engine Geometry on Thermal Stratification and HCCI Combustion". W ASME 2014 Internal Combustion Engine Division Fall Technical Conference. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/icef2014-5687.

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Thermal stratification of the unburned charge in the cylinder has a profound effect on the burn characteristics of a Homogeneous Charge Compression Ignition (HCCI) engine. Experimental data was collected in a single cylinder, gasoline-fueled, HCCI engine in order to determine the effects of combustion chamber geometry and wall conditions on thermal stratification and HCCI combustion. The study includes a wall temperature sweep and variations of piston top surface material, piston top geometry, and compression ratio. The data is processed with a traditional heat release routine, as well as a post-processing tool termed the Thermal Stratification Analysis, which calculates an unburned temperature distribution from heat release. For all of the sweeps, the 50% burned point was kept constant by varying the intake temperature. Keeping the combustion phasing constant ensures the separation of the effects of combustion phasing from the effects of wall conditions alone on HCCI and thermal stratification. The results for the wall temperature sweep show no changes to the burn characteristics once the combustion phasing has been matched with intake temperature. This result suggests that the effects of wall temperature on HCCI are mostly during the gas-exchange portion of the cycle. The ceramic coatings were able to very slightly decrease the thermal width, increase the burn rate, increase the combustion efficiency, and decrease the cumulative heat loss. The combustion efficiency increased with the lower surface area to volume ratio piston and the lower compression ratio. Lastly, the compression ratio comparison showed a noticeable effect on the temperature distribution due to the effect of pressure on ignition delay, and the variation of TDC temperature required to match combustion phasing.

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Karg Bulnes, Fernando, Kyle R. Gluesenkamp i Joseph Rendall. "Comparison of Plug Flow and Multi-Node Stratified Tank Modeling Approaches Regarding Computational Efficiency and Accuracy". W ASME 2020 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/imece2020-23369.

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Abstract Residential water heaters contain water stratified by temperature-driven density differences. This implies that a water tank can reach a state in which the top and bottom sections have different temperatures, unless mixing happens. A high degree of thermal stratification can improve the efficiency of some water heaters, by saving the amount of energy required for the heat-up process. Studies of stratification became popular in the 1970s and it remains an active research topic today. The research has led to the development of different models and techniques to better predict and define a stratified tanks behavior. By comparing these models and techniques used previously to describe thermal stratification, the phenomenon could be better understood, exploited, and used to increase efficiency and thermal energy capacity in modern water tanks. From the existing models, we found the one-dimensional standard plug-flow and a multi node model to be appropriate for analyzing the processes of the heat up and cool-down in a water tank. These two models are based on energy balances. This work involved comparing the accuracy and computational effort needed to implement these models. To assess accuracy, we compared both types of existing models to experimental data (also collected in this work) which included a heat up process using an external heat pump. This external process included a layering process that has an eddy diffusivity at five times the rate of thermal diffusion. For this project, we implemented the models in MATLAB, the multi-paradigm numerical computing environment. We quantified model accuracy using the root mean squared error between modeled data and experimental data for six measured tank temperatures. Comparing the accuracy and the computational time taken to run the simulation provides a method to contrast the performance of each model and a way to rate it. The multi node model was run using from 6 to 96 spatial nodes; the plug flow model was run using 1 to 0.001 °C temperature bin sizes. Additionally, timesteps were varied from 4 to 236 s. The results quantify the tradeoff between accuracy and computational time, providing guidance for simulations to intelligently select the best model type and simulation parameters. This research can be used to validate the pre-existing models and possibly improve the modern water tank.

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Raporty organizacyjne na temat "Efficiency of Stratification"

Bowlin, Elizabeth, i Puneet Agarwal. PR-201-153718-R03 Integrity Assessment of DTI Pipelines Using High Resolution NDE in Select Areas. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), maj 2018. http://dx.doi.org/10.55274/r0011486.

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Hydrostatic test and In-Line Inspection are the prescribed integrity assessment methods cited in various Codes and Regulations and have been proven to enhance pipeline safety. But a significant number of pipelines across the world remain difficult to inspect and impractical to modify for inspection by the prescribed methods due to physical configurations or operating conditions. This research performs a state of the art (SOTA) analysis of NDE technology readiness considering physical and operational barriers and technology deployment from inside, outside or over pipelines, and the possible role of inspection sampling to conclude pipeline integrity and justify intervals for conversion for piggability or hydrotest. The goal of the research is to propose alternatives to ILI for safe prioritization and scheduling for conversion or replacement and not to replace hydrostatic test or ILI as currently prescribed in Codes and Regulations. The scope of the research is limited to technologies and integrity management concerning metal loss threat. This report represents the third and final update of prior reports from the two preceding years presenting a compendium of technologies describing technology readiness for state of the art non-destructive evaluation (NDE) technologies intended for low resolution pipeline condition screening and high resolution NDE for deployment at sample locations with capabilities applicable to difficult to inspect pipeline configurations. Integrated cleaning and inspection pigs, smart balls, external deployed ultrasonic, radiographic and magnetometry are pipe wall screening technologies evaluated in the reports. A structured process is proposed for assessing pipeline integrity based on low resolution screening of the full length of a pipeline segment followed by high resolution NDE samples at locations where screening indicates locations of possible wall loss. The process employs extreme value analysis for prediction of maximum metal loss severity across the screened segment. For instances where no metal loss indications reported by screening or from high resolution samples an alternative "compliance approach" is also addressed. Case studies are presented where PRCI members have deployed some of the technologies referenced in the NDE SOTA phase of the research and implemented the proposed extreme value or the compliance approaches. Validation of fitness for service conclusions based on inspection sampling by comparison with full length high resolution ILI or hydrostatic test are included in some of the case studies. The conclusions of the case studies demonstrate integrity conclusions obtained from the PRCI structured process are conservative and consistent with ILI or hydrostatic test conclusions. Based on the experience from the case studies and the SOTA, a metal loss screening efficiency factor (MLSE) is proposed enabling pipeline operators to understand the general relationship between screening level (sample stratification) and direct examination (inspection sampling) required to provide equivalent understanding of pipe wall condition, limited to metal loss. As mentioned by ASME/API ILI has limitations that need to be considered in its deployment and full discovery of metal loss conditions. Under some conditions (noted by API 1163) ILI predictions can be accepted without any direct examinations or verifications, i.e full length screening (high resolution) and no verification samples. At the other end of the spectrum random sampling can be theoretically deployed as a screening approach but depending on the condition of the pipeline, the high-resolution sample area could be very large to obtain a significant integrity conclusion. This report proposes a comparative scale of effectiveness for SOTA pipe wall screening technologies that offer the operator an expectation of high resolution NDE sample size. There is a related webinar

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