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"Expanders"
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Expanders for oil and gas operations
Filled with effective methods for recovering gas energy using expanders, this practical resource offers in-depth details on different types of expanders, addressing the background, mechanical design features, design and operating requirements, operational processes, and potential problems for each class expander.
Book
Expander design procedures and selection criterion for small rated organic rankine cycle systems
The particular aspect of this work is the new approach to expander design procedure for small rated ORC. In fact, once all the calculation procedures have been defined, they have been implemented in Matlab code. This code, once the design process is complete, provides an indication of the optimal expander configuration to adopting to that specific system. For these reasons, this paper aims to analyze all the preliminary expanders' design procedures, both dynamic and volumetric. The reasons lie in the development of low‐enthalpy heat recovery systems (systems that allow simultaneous production of electrical and thermal energy made available in the form of water at a temperature of 60‐90°C), with the aim of optimizing any energy system. Within these energy systems, the expander is the main component, responsible for power generation. It is, therefore, necessary and useful to analyze in detail every expander configuration, highlighting the different features. For each component will be described the theory on which is based the choice and its design and a possible software implementation is supplied. Finally, a criterion for the choice of the optimal expander is proposed, based on some operational considerations and other construction and structural constraints, such as overall dimensions and weight, lubrication, MTBF, feasibility, reliability, and coupling with the electric generator. The particular aspect of this work is the new approach to expander design procedure for small rated ORC. In fact, once all the calculation procedures have been defined, they have been implemented in a Matlab code. This code, once the design process is complete, provides an indication on the optimal expander configuration to adopting for that specific systems.
Journal Article
Expander Technologies for Automotive Engine Organic Rankine Cycle Applications
The strive towards ever increasing automotive engine efficiencies for both diesel and gasoline engines has in recent years been forced by ever-stringent emissions regulations, as well as the introduction of fuel consumption regulations. The untapped availability of waste heat in the internal combustion engine (ICE) exhaust and coolant systems has become a very attractive focus of research attention by industry and academia alike. Even state of the art diesel engines operating at their optimum lose approximately 50% of their fuel energy in the form of heat. As a result, waste heat recovery (WHR) systems have gained popularity as they can deliver a reduction in fuel consumption and associated CO2 emissions. Of these, the Organic Rankine Cycle (ORC) is a well matured waste heat recovery technology that can be applied in vehicle powertrains, mainly due to the low additional exhaust backpressure on the engine and the potential opportunity to utilize various engine waste heat sources. ORCs have attracted high interest again recently but without commercial exploitation as of today due to the significant on-cost they represent to the engine and vehicle. In ORCs, expansion machines are the interface where useable power production takes place; therefore, selection of the expander technology is directly related to the thermal efficiency of the system. Moreover, the cost of the expander-generator units accounts for the largest proportion of the total cost. Therefore, selection of the most appropriate expander is of great importance at the early stage of any automotive powertrain project. This study aims to review the relevant research studies for expansion machines in ORC-ICE applications, analyzing the effects of specific speed on expander selection, exploring the operational characteristics of each expander to further assist in the selection of the most appropriate expander, and comparing the costs of various expanders based on publically available data and correlations.
Journal Article
Super approximation for \\(\\text{SL}_2\\times \\text{SL}_2\\) and \\(\\text{ASL}_2\\)
Let \\(S\\subset \\text{SL}_2(\\mathbb Z)\\times \\text{SL}_2(\\mathbb Z)\\) or \\(\\text{SL}_2(\\mathbb Z)\\ltimes \\mathbb Z^2\\) be finite symmetric and assume \\(S\\) generates a group \\(G\\) which is a Zariski-dense subgroup \\(\\text{SL}_2(\\mathbb Z)\\times \\text{SL}_2(\\mathbb Z)\\) or \\(\\text{SL}_2(\\mathbb Z)\\ltimes \\mathbb Z^2\\). We prove that the Cayley graphs $$\\{\\mathcal Cay(G(\\text{mod } q), S (\\text{mod } q))\\}_{q\\in \\mathbb Z}$$ form a family of expanders.
Paper
Design and research on the hydrogen liquefaction process coupled with LNG precooling and multistage deep cooling
A novel hydrogen liquefaction process is proposed to address the high energy consumption issue in hydrogen liquefaction processes. Based on the dual mixed-refrigerant hydrogen liquefaction process, a new LNG-precooled hydrogen liquefaction process is introduced. This process integrates an LNG cold energy precooling system with a cascade refrigeration-assisted precooling system. Using Aspen HYSYS software, simulations and optimizations were conducted with the specific energy consumption ( SEC ) as the objective function. The results demonstrate that the proposed process achieves an SEC of 4.49 kWh/kgLH 2 and an exergy efficiency of 64.05%. The exergy losses in the ortho-para hydrogen converters and expanders are the most significant, accounting for 39.91% and 31.64%, respectively.
Journal Article
Expanders and growth of normal subsets in finite simple groups of Lie type
We show that some classical results on expander graphs imply growth results on normal subsets in finite simple groups. As one application, it is shown that given a nontrivial normal subset \\( A \\) of a finite simple group \\( G \\) of Lie type of bounded rank, we either have \\( G \\setminus \\{ 1 \\} \\subseteq A^2 \\) or \\( |A^2| \\geq |A|^{1+\\epsilon} \\), for \\( \\epsilon > 0 \\). This improves a result of Gill, Pyber, Short and Szabó, and partially resolves a question of Pyber from the Kourovka notebook. We also propose a variant of Gowers' trick for two subsets, and give applications to products of large subsets in groups of Lie type, improving some results of Larsen, Shalev and Tiep.
Paper
The super approximation property of \\(\\mathrm{SL}_2(\\mathbb{Z}/q\\mathbb{Z}) \\times \\mathrm{SL}_2(\\mathbb{Z}/q\\mathbb{Z}) \\times \\mathrm{SL}_2(\\mathbb{Z}/q\\mathbb{Z})\\)
Take \\(S \\subset \\mathrm{SL}_2(\\mathbb{Z}) \\times \\mathrm{SL}_2(\\mathbb{Z})\\times \\mathrm{SL}_2(\\mathbb{Z})\\) be finite symmetric and assume \\(S\\) generates a group \\(G\\) which is Zariski-dense in \\(\\mathrm{SL}_2 \\times \\mathrm{SL}_2\\times \\mathrm{SL}_2(\\mathbb{Z})\\). This paper proves that the Cayley graphs $$ \\{\\mathcal{C} a y(G(\\bmod q), S(\\bmod q))\\}_{q \\in \\mathbb{Z}_{+}} $$ form a family of expanders.
Paper
Complete lagrangian self-expanders in \\(\\mathbb C^{2}\\)
In this paper, we obtain a classification theorem of \\(2\\)-dimensional complete Lagrangian self-expanders with constant squared norm of the second fundamental form in \\(\\mathbb C^{2}\\).
Paper
Coboundary expansion and Gromov hyperbolicity
We prove that if a compact \\(n\\)-manifold admits a sequence of residual covers that form a coboundary expander in dimension \\(n-2\\), then the manifold has Gromov-hyperbolic fundamental group. In particular, residual sequences of covers of non-hyperbolic compact connected irreducible 3-manifolds are not 1-coboundary expanders.
Paper
Polymers for Osmotic Self-Inflating Expanders in Oral Surgical Procedures: A Comprehensive Review
Soft-tissue expansion is a critical challenge in regenerative oral surgeries. This scoping review maps the research on polymers used in osmotic self-inflating expanders, assessing their applications, characteristics, and potential in oral surgical procedures. The study analyzed 19 articles from the PubMed, Scopus, Web of Science, and Embase databases, primarily focusing on in vivo research (78.9%) investigating polymeric tissue expanders. The review examined polymer compositions, methodologies, and tissue responses across various animal models. Osmed® hydrogel was the most studied material, with research exploring its expansion capabilities in rabbits, goats, pigs, rats, and beagle dogs. The findings showed diverse tissue expansion ranges and minimal inflammatory responses, indicating the potential for oral surgical applications. Despite promising results, gaps such as inconsistent expansion measurements and the lack of standardized protocols were identified. These findings highlight the need for further research to develop new polymer formulations and optimize device design to enhance safety, efficacy, and clinical predictability. This review provides a foundation for advancing polymeric tissue expander technologies, offering the potential for safer and more effective minimally invasive regenerative oral surgeries.
Journal Article