Air recovery assessment on high-pressure pneumatic systems

A computational simulation and experimental work of the fluid flow through the pneumatic circuit used in a stretch blow moulding machine is presented in this paper. The computer code is built around a zero-dimensional thermodynamic model for the air blowing and recycling containers together with a non-linear time-variant deterministic model for the pneumatic three stations single acting valve manifold, which, in turn, is linked to a quasi-one-dimensional unsteady flow model for the interconnecting pipes. The flow through the pipes accounts for viscous friction, heat transfer, cross-sectional area variation, and entropy variation. Two different solving methods are applied: the method of characteristics and the Harten-Lax-Van Leer (HLL) Riemann first-order scheme. The numerical model allows prediction of the air blowing process and, more significantly, permits determination of the recycling rate at each operating cycle. A simplified experimental set-up of the industrial process was designed, and the pressure and temperature were adequately monitored. Predictions of the blowing process for various configurations proved to be in good agreement with the measured results. In addition, a novel design of a valve manifold intended for the polyethylene terephthalate (PET) plastic bottle manufacturing industry is also presented.Peer ReviewedPostprint (author's final draft

Taguchi techniques as an effective simulation-based strategy in the design of numerical simulations to assess contact stress in gerotor pumps

The contact problem of a trochoidal gear is a drawback and a well-known performance indicator of a gerotor pump. Although numerical simulations aid in the evaluation of contact stress, the difficult task of determining geometrical parameters, operating conditions, and the number of simulations to run falls to the designer. This paper presents the Taguchi techniques as an effective simulation-based strategy to narrow down the geometrical parameter combinations, reducing the solution space and optimizing the number of simulations. The work is first focused on the validation of the proposed numerical model by means of published contact stress results of recognized researchers in the field, as well as the unification of nomenclature and notation. Then, the Taguchi approach is based on a sequence of four experiments, ranging from the screening case with two levels and seven parameters to multiple levels and four parameters with three software input operating conditions (temperature, torque, and friction coefficient) emulating noise effects. The contact stresses of 128 gear sets, having common volumetric capacity and dimensional constraints to detach mechanical performance from flow rate and casing, were analyzed. Results prove the feasibility of the proposed methodology by identifying the most suitable gear set configuration and predicting the quantifiable performances of a real-working gerotor pumpE.B.-M. is a Serra Húnter fellow. The authors would like to acknowledge the Generalitat de Catalunya for providing the necessary support to the research groups IAFARG (SGR 286, https://iafarg.upc.edu, accessed on 1 September 2022), CATMech (Tecnio, https://catmech.upc.edu/home, accessed on 1 September 2022), and Doctorats Industrials (2020 DI 45). The authors would like to thank Byon Zambrano Risco for participating in the research reported in this paperPostprint (published version

Effectively integrating research argumentation in syllabus learning: A case study of reading journal articles in four fourth-year engineering fluid mechanics courses

In an emerging trend in engineering education students are engaged in the scientific discovery process through reading about research published in articles rather than textbooks. A research-based and curriculum-oriented intervention in an undergraduate course was designed to elucidate whether students can progressively gain reading skills when provided with selected articles explicitly related to fluid mechanics research. The aim was also to monitor student awareness of their own progress. A questionnaire was designed to evaluate how fourth-year fluid technology students perceived their reading skills during the teaching intervention. A progressive strategy was applied, including warm-up readings, in- and out-of-class assignments, and best practice lectures. Two parallel test exams and test readings were associated and quantitatively analyzed. Each cohort was randomly divided into two groups, and each group was assigned a different test reading before the lectures; the readings were then switched for the post-lecture assignment. The results demonstrate that the students acquired selective reading skills and awareness of accomplishment. The analyses indicated that learners gained an understanding of the core concepts and gave positive feedback on the teaching materials and schedule. These findings may serve as a guide for engineering educators to improve the preparation of undergraduate studentsPostprint (author's final draft

Dryout and replenishment of bottom-heated saturated porous media with an overlying plain water layer

The aim of this paper is to elucidate the influence of the physical properties of both phases—solid matrix and saturating liquid—of bottom-heated porous media with an overlying plain water layer. The dryout, the stability of the system’s water layer-vapor region, and the thermal state evolution are studied. The porous media under study are a bronze powder saturated by water, and a solution of surfactant and coarse sand saturated by the same liquids. From the experimental data obtained, a theoretical approach is carried out to describe the dryout and rewetting process. The influence of the nature and physical properties of the solid and liquid phases is also analyzed, with special attention to the addition of surfactant in the saturating liquid.Postprint (published version

A review of gerotor technology in hydraulic machines

Over the years, numerous investigations have established the gerotor fundamentals. This work aims to provide a complete review of the literature from the last decade, focusing on the articles published in the past five years on gerotor technology in hydraulic machines. The report gives a catalogue of guidelines based on the trochoidal-envelope definition, a background analysis, the worldwide distribution of articles in each continent and country and the most frequently used keywords in the field. The paper identifies state-of-the-art research, and reports on current mainstream ideas. From the historical background, this literature review reports the current approaches in gerotor pumps (geometry and performance approaches, modeling and numerical simulations), orbital motors and new concepts. The report will serve as a guide and a directory for novel engineers working with gerotor technology in hydraulic machines. Another intention of this paper is to disseminate the works of the researchers who use this technology around the world, and to provide a scenario for future international collaboration. The paper gives an account of the disparity between academia and engineering applications. There is currently very little published literature on design and production methodologies for gerotor pumps and orbital motors. Hence, the future goal is to collect recommendations that combine academia and industry expertise to make better use of these extensive studies in the fieldPostprint (published version

Flipped learning and threshold concepts in the Turbomachinery section of Fluid Engineering course

This paper outlines a practical intervention aiming to collect the effects of introducing flexible learning in engineering higher education. The work dis- cusses the implementation of the flipped classroom method and the threshold concepts in the Turbomachinery section of Fluid Engineering course in the third year of Mechanical Engineering (Bachelor's degree) at the Universitat Politècnica de Catalunya. Fluid Engineering is traditionally one of the hardest courses involving a complex interaction between understanding concepts and using those concepts in the solution of cases, which also require the devel- opment of a set of skills. This case study is centred on two student cohorts, and the research spans over two consecutive Fall semesters. The study is based on sound pedagogy of educational technologies, in practice, frequent student-to-instructor interaction, academic results, and statistical and survey analyses. A principal conclusion is that overall class performance is much higher than that of the previous courses. The results indicate that learners gained under- standing from semester to semester and no statistical significance was ob- served between group and exam format. Students were satisfied with the level of suitability and the degree of compliance of the new implementation and found it constructive in their learning process, an important educational benefit. This positive experience, in terms of benefit-cost and outcomes, en- courages the intervention without sacrificing any curriculum syllabus, but taking advantage and bringing the benefits of interactivity distance learning technologies and traditional face-to-face lectures. This scholarly research aims to contribute to this area, by abandoning traditional lecturing in favour of active learningPostprint (author's final draft

Numerical simulation of a supersonic ejector for vacuum generation with explicit and implicit solver in openfoam

Supersonic ejectors are used extensively in all kind of applications: compression of refrigerants in cooling systems, pumping of volatile fluids or in vacuum generation. In vacuum generation, also known as zero-secondary flow, the ejector has a transient behaviour. In this paper, a numerical and experimental research of a supersonic compressible air nozzle is performed in order to investigate and to simulate its behaviour. The CFD toolbox OpenFOAM 6 was used, with two density-based solvers: explicit solver rhoCentralFoam, which implements Kurganov Central-upwind schemes, and implicit solver HiSA, which implements the AUSM+up upwind scheme. The behaviour of the transient evacuation ranges between adiabatic polytropic exponent at the beginning of the process and isothermal at the end. A model for the computation of the transient polytropic exponent is proposed. During the evacuation, two regimes are encountered in the second nozzle. In the supercritic regime, the secondary is choked and sonic flow is reached. In the subcritic regime, the secondary flow is subsonic. The final agreement is good with the two different solvers, although simulation tends to slightly overestimate flow rate for large values region.Peer ReviewedPostprint (published version

Flexible rod design for educational wind balance

This is a copy of the author 's preprint version of an article published in the journal Experimental techniques. The final publication is available at Springer via http://dx.doi.org/10.1007/s40799-016-0017-9This article provides a technical description of a flexible hinge for wind tunnel rigs. For academic purposes, the device was integrated into several rod flexures to build a home-made external wind balance system. The cylindrical elastic element incorporates several notches, and the flexure linkage is able to transmit force in the main axial direction without hindering perpendicular movement. The flexural element described here is simple and easily manufactured, and can also be used with other types of wind balance. The flexure described in this article has similar functionality to those mentioned in the reference section, but has a more compact element. The project's effectiveness was demonstrated in a series of experimental comparisons of forces and moments measured on a wing using the N.A.C.A. Clark-Y airfoil profile.Preprin

Graphic method to evaluate power requirements of a hydraulic system using load-holding valves

It is very well known that the use of a load-holding valve (LHV) in a hydraulic system introduces additional energy consumption. This article presented a simplified graphical method for analyzing the power requirements of hydraulic systems equipped with load-holding valves for overrunning load control. The method helps to understand the performance of load-holding valves during actuator movement. In addition, it allows visualization of the influence on the overall system consumption of the main parameters (pilot ratio, set pressure) and others such as flow rate, back pressure, and load force. The method is attractive because, with only the pressures at the three ports and the valve relief function curve, it is sufficient to evaluate the energy consumption and to define the power ratio as an index indicating the percentage of energy that is to be used to open the LHV valve. The method was applied to real cases, in particular to two types of lifting mobile machines. It Citation: Berne, L.J.; Raush, G.; Roquet, P.; Gamez-Montero, P.-J.; Codina, E. Graphic Method to Evaluate Power Requirements of a Hydraulic System Using Load-Holding Valves. Energies 2022, 15, 4558. https://doi.org/ 10.3390/en15134558 Academic Editors: Paolo Casoli and Massimo Rundo Received: 10 May 2022 Accepted: 16 June 2022 Published: 22 June 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). was validated following several outdoor tests on two mobile machines where experimental data were obtained. During tests, both machines were equipped with a set of seven different performance LHV valves. The described method could be beneficial for hydraulic machine manufacturers engaged in designing lifting devices when selecting a suitable valve for energy efficiency applications, especially nowthat the trend towards electrification is a realityPostprint (published version

Promoting lab engagement in experimental compressible flow modelling

The present work depicts the development of an experimental equipment that reveals compressible fluid dynamics, while collecting data from an incompressible flow like water in an open-channel. It consists of an extensive theoretical framework followed by a practical analysis, the aim of which was to trigger the hydraulic jump, both normal and oblique, in order to illustrate its hydro-gasdynamic analogy with a shock wave, occurring in supersonic compressible flows. The assembly, called “water table”, arises from the necessity of economical alternatives to expensive supersonic wind tunnels in the experimental study of compressible flows. Thus, a canal based on a Laval nozzle was constructed where water flow could experiment a hydraulic jump. Through its visual and experimental perception, fellow interested could more easily understand the physics and engineering behind this phenomenon. Multiple design alternatives were evaluated considering environmental, economic, functional and aesthetic factors. A low-cost implementation was critical in the design process. The measurements revealed that the geometry of the nozzle and the wedges designed as obstacles to cause obliquity were the most influential elements in the formation of a hydraulic jump in the set-up. Regarding the experimental variables, the upstream and downstream heights had the highest relevance. Therefore, their manipulation and analysis could lead to further educational investigations. This research is a step forward to support students in the understanding of compressible flow principles by providing an in-house experimental set-up. The equipment is an opportunity of carrying out lab measurements, which certainly guides to a major commitment in the fieldPostprint (published version