Βέλτιστος σχεδιασμός ποδός σε ευθείς οδόντες εξειλιγμένης για μέγιστη αντοχή σε κάμψη με χρήση καμπυλών Bezier

In this thesis, a method of using a novel fillet design for spur gear teeth, in order to improve their strength and their loading capacity, is developed and presented. According to this method, the conventional trochoidal fillet profile and the segment of the root circle that corresponds to the half of the space between two successive teeth is replaced by a suitable Bézier curve. The shape of this curve is altered by changing two parameters in order to create a tooth profile with reduced first tensile principal stress at its root fillet. These teeth are first modelled geometrically and then their behaviour in bending is studied by assuming loading at their Highest Point of Single Tooth Contact (HPSTC). The maximum principal stress that appears at the root fillet of each model is calculated using Finite Element Analysis (FEA). After the analysis of all the models, an interpolation method is used, in order to define the combination of the parameters that corresponds to the optimum model. The next step is to investigate if interference between the tip of the mating gear and the resulting tooth geometry, exists. Finally, the results of this thesis are compared with similar efforts that have been made in the past on improving the strength of spur gears

NEXT GENERATION HIGH TEMPERATURE HEAT PUMPS

The presentation is about next generation high temperature heat pumps Reduce CO2- and pollutant emissions from industrial processes and power plants, Research and development for a successful energy transition in industr

An alternative architecture of the Humphrey cycle and the effect of fuel type on its efficiency

Conventional gas turbines are a very mature technology, and performance improvements are becoming increasingly difficult and costly to achieve. Pressure‐gain combustion (PGC) has emerged as a promising technology in this respect, due to the higher thermal efficiency of the respective ideal gas turbine cycles. The current work analyzes two layouts of the Humphrey cycle for gas turbines with pressure‐gain combustion. One layout replicates the classical layout of gas turbine cycles, whereas an alternative one optimizes the use of pressure‐gain combustion by ensuring the operation of the combustor at stoichiometric conditions. In parallel, both cycle layouts are studied with two different fuels—hydrogen and dimethyl ether—to account for differences in combustion specific heat addition and its effect on cycle efficiency. The current work concludes with an attempt to benchmark the maximum losses of a plenum to achieve efficiency parity with the Joule cycle, for a given pressure gain over a PGC combustor. It is found that the cycle layout with stoichiometric combustion results in an increase in thermal efficiency of up to 7 percentage points, compared to the classic cycle architecture. Moreover, the thermal efficiency of the new layout is less sensitive to the turbine inlet temperature, especially at low compressor pressure ratios. The study of the two fuels has shown that the larger mass specific heat addition leads to higher cycle thermal efficiency and should be considered during the fuel choice. Finally, the maximum allowable plenum pressure loss that results to efficiency parity with the Joule cycle has been computed for a given combustor pressure gain. For turbine inlet temperatures above 1500°C, pressure gain above 1.6 would allow for at least 20% relative pressure drop in the plenum. The respective pressure gain becomes considerably higher for lower turbine inlet temperatures.TU Berlin, Open-Access-Mittel – 202

CD20-mediated B cell depletion in acetylcholine receptor autoantibody-positive myasthenia gravis

Myasthenia gravis (MG) is an autoimmune disorder characterized by muscle weakness and fatigue, mediated in the majority of cases by IgG1 autoantibodies targeting the acetylcholine receptor (AChR). As AChR autoantibodies have been shown to be pathogenic, therapies targeting B cells have been applied in patients with AChR MG for more than a decade. Recently, a phase 2 trial of the CD20-targeting agent, rituximab, in AChR MG unfortunately failed to meet its primary endpoint. Converging data however from non-randomized clinical series, some of which with more participants than the phase 2 trial, support efficacy of rituximab in AChR MG, especially early onset disease. In this opinion article, we summarize both clinical data and mechanistic principles on the use of CD20 depletion therapy in AChR MG, which we believe lend support to the argument that CD20 depletion can still be a useful therapeutic strategy for patients with AChR MG

The impact of heat pump load flexibility on its process integration and economics

The conventional methodology of heat pump integration has found application in various industries, including cheese production, spray drying, milk evaporation systems, brewing, and meat processing. While several approaches have been developed for optimizing direct and indirect heat recovery in non-continuous industrial processes, the optimal integration of heat pumps in non-continuous processes remains a challenge. This paper introduces a systematic methodology that leverages extensive datasets of time-resolved industrial process data to determine the optimal heat pump integration and the level of heat pump load flexibility that maximizes the economic benefit. Thus, the work establishes a connection between the domain of Process Integration and heat pump load flexibility. Additionally, the study provides insights on the requirements for load flexibility during the design phase of the heat pump, offering an estimation on the need for research on heat pump flexibility. The findings indicate the presence of a load flexibility threshold in the examined case study, beyond which additional load flexibility yields diminishing returns. Furthermore, the study shows that different heat pump integration parameters are chosen based on the heat pump’s capability for load flexibility. Within the investigated case, a heat pump with a minimum load of 55% increases the net present value by 19.3% compared to a load inflexible heat pump

Heat transfer measurements in a hydrogen-oxyfuel combustor

In the context of emission-free electricity generation, the authors developed a novel hydrogen-oxygen combustor, which is based on swirl-stabilized combustion technology and steam dilution. Following previous burner characterization, the current study investigates the heat transfer conditions in the combustion chamber wall. To this end, a carefully controlled co-flow of air is used to cool the combustion chamber in an annular duct, which surrounds it. Temperature measurements enable the evaluation of the heat flux from the combustor flow to the walls, local wall temperatures, and the Nusselt numbers on the hot and the cold side. The extremely high wall temperatures, caused by the H2/O2 flame, can be reduced by steam dilution down to approximately 900 K. Even better cooling could be reached by using the dilution steam as the coolant before it flows to the plenum. The Nusselt numbers at the inner combustion chamber wall are in the order of 10–50 and increase with the thermal power and the steam dilution ratio

A service-oriented national e-theses information system and repository

Introduction In this article we present an overview of the information technology infrastructure that supports the operation of the Greek National Archive of Doctoral Theses (HEDI). The infrastructure, which has been recently re-developed replacing a legacy system, makes use of repository software, in particular the DSpace platform, as part of a service-oriented information system based on open source components

A service-oriented national e-theses information system and repository

Introduction In this article we present an overview of the information technology infrastructure that supports the operation of the Greek National Archive of Doctoral Theses (HEDI). The infrastructure, which has been recently re-developed replacing a legacy system, makes use of repository software, in particular the DSpace platform, as part of a service-oriented information system based on open source components