Performance Enhancement in Sliding Vane Rotary Compressors through a Sprayed Oil Injection Technology

In Sliding Vane Rotary Compressors, as well as in most of positive displacement machines, the oil is injected to fulfill sealing and lubrication purposes. However, the oil injection could produce an additional effect during the compression phase with a great saving potential from the energetic point of view. Being the air inside the cell at a higher temperature than the oil injected, a cooling effect could be achieved so decreasing the mechanical power required for the compression. At the moment, the oil is introduced inside the compressor vanes through a series of simple holes that are only able to produce solid jets. In this way any effective heat transfer is prevented, as demonstrated by p-V measurements inside the cells during the compression phase. In the current study, a theoretical model of a sprayed oil injection technology was developed and further experimentally validated. The oil was injected along the axial length of the compressor through a number of pressure swirl atomizers which produced a very fine spray. The conservation equations, solved with a Lagrangian approach, allowed to track the droplets evolution from the injection until the impingement onto the metallic surfaces of the vanes. The theoretical approach assessed the cooling effect due to the high surface to volume ratio of the droplets and a reduction of the indicated power was predicted. The model validation was carried out through a test campaign on an mid-size sliding vane compressor equipped with a series of pressure swirl injectors. The reconstruction of the indicator diagram as well as the direct measurements of torque and revolution speed revealed a reduction of the mechanical power absorbed close to 7 % using an injection pressure of 20 bar. The model is in a satisfactory agreement with the tests and it also confirms the experimental trends available in the literature. A parametric analysis on the injection pressure and temperature and on the cone spray angle was eventually carried out in order to identify an optimal set of operating injection parameters

Crossed Kirschner’s wires for the treatment of anterior flail chest: an extracortical rib fixation

Objective: Thoracic trauma may be a life-threatening condition. Flail chest is a severe chest injury with high mortality rates. Surgery is not frequently performed and, in Literature, data are controversial. The authors report their experience in the treatment of flail chest by an extracortical internal-external stabilization technique with Kirshner’s wires (K-wires). Methods: From 2010 to 2015, 137 trauma patients (109 males and 28 females) with an average age of 58.89±19.74 years were observed. Seventeen (12.41%) patients presented a flail chest and of these, 13 (9.49%) with an anterior one. All flail chest patients underwent early chest wall surgical stabilization (within 48 hours from the injury). Results: In the general population, an overall morbidity of 21.9% (n=30 of 137) and a 30-day mortality rate of 5.1% (n=7 of 137) were observed. By clustering the population according to the treatment (medical or interventional vs surgical), significant statistically differences between the two cohorts were found in morbidity (12.65% vs. 34.48%, P=0.002) and mortality rates (1.28% vs. 10.34%, P=0.017). In patients undergoing chest wall surgical stabilization, with an average Injury Severity Score of 28.3±5.2 and Abbreviated Injury Score (AIS) of 8.4±1.7, an overall morbidity rate of 52.9% (n=9) and a mortality rate of 17.6% (n=3) were found. Post-surgical device removal, in local anesthesia or mild sedation, was performed 42.8±2.9 days after chest wall stabilization and no cases of wound infection, dislodgment of the wires or osteosynthesis failure were reported. Moreover, in these patients, an early postoperative improvement in pulmonary ventilation (ΔpaO2 and ΔpCO2 : +9.49 and -5.05, respectively) was reported. Conclusion: Surgical indication for the treatment of flail chest remains controversial and debated both due to an inadequate training and the absence of comparative prospective studies between various strategies. Our technique for the surgical treatment of the anterior flail chest seems to be anachronistic, but the aspects described, both in terms of technical features and of outcome and benefits (health, economic), allow to evaluate the effectiveness of this approach. Keywords: Flail chest, Chest trauma, Kirschner’s wire, Injury Severity Score, Abbreviated Injury Score

CFD Analysis of an ORC Vane Expander using OpenFOAM Solver

Recent studies on the use of 3D Computational Fluid Dynamics (CFD) for the analysis and design of sliding vane machines has proved beneficial for the detailed evaluation and optimisation of the vane expanders for a given working fluid and operating condition. The authors have earlier developed a customised rotor grid generator for integration with commercial CFD solvers and validated it for use in typical small-scale ORC expanders for waste heat recovery. In this paper, this customised grid generation is extended to an open source CFD solver OpenFOAM, by using a connectivity methodology originally developed for roots blower and twin-screw machines. The control of the rotor grid deformation is through a user code integrated within the flow solver. A case study of the reference ORC expander operating with R245fa was used for validation. The available experimental data for three operating conditions are compared with the results calculated with ANSYS CFX and OpenFOAM-v1912 solvers. During the filling and expansion process, the internal pressure traces are accurately captured by both the solvers and the difference is within 0.05 bar with measurements. However, between the outlet port closure and inlet port opening process the pressure and temperature prediction with OpenFOAM solver is considerably different from the ANSYS CFX solver. It was observed that the OpenFOAM solver is resulting into a non-physical low temperature zone upstream to the tangency region of the rotor and the stator that goes below 80℃. Overall, CFD solution obtained with the commercial solver ANSYS CFX is much more stable and robust than the open source OpenFOAM solver. The generic nature of the deforming grid generation used with an open source CFD solver presented in the paper allows broadening of the utilisation of CFD modelling tools for the design of vane machines

Surgical management of cardiac tamponade: Is left anterior minithoracotomy really safe and effective?

Objective: Cardiac tamponade is a life-threatening clinical entity that requires an emergency treatment. Cardiac tamponade can be caused both by benign and malignant diseases. A variety of methods have been described for the treatment of these cases from needle-guided pericardiocentesis, balloon-based techniques to surgical pericardiotomy. The Authors report their experience in surgical management of cardiac tamponade and an exhaustive review of literature. Methods: This study involved 61 patients (37 males and 24 females) with an average age of 61.80 ± 16.32 years. All patients underwent emergency surgery due to the presence of cardiac tamponade. Results: Cardiac tamponade was caused by a benign disease in 57.40% of patients. In cancer patients group, lung cancer, breast cancer and malignant pleural mesothelioma were the most common neoplasms (17-27, 87%). The average preoperative size of pericardial effusion at M-2D echocardiography was 30.15 ± 5.87 mm. Postoperative complications were observed in 11 patients (18%). The reoperation rate was 3.3% (2 patients) due to relapsed cardiac tamponade. 30-day mortality rate was 3.3%. Overall cumulative survival was 29.9 ± 20.1 months. Twenty-nine patients (47.5%) died during the follow up period. By dividing the population into two groups, group B (benign) and group M (malignant), there was a statistically significant difference (P<0.001) in terms of survival. Conclusion: In conclusions, anterior minithoracotomy for surgical treatment of cardiac tamponade has to be held into account in patients both with benign diseases and malignancies. Keywords: Cardiac tamponade, Minithoracotomy, Pericardial malignancies, Overall surviva

Modeling and Experimental Activities on a Small-scale Sliding Vane Pump for ORC-based Waste heat Recovery Applications☆

Abstract Pumping work in energy recovery units based on Organic Rankine Cycles (ORC) can severely affect the net power output recovered. Nevertheless, in recent years scientific andindustrial communities mainly focused on expanders' development. In order to address this lack of know-how and equipment, the current paper presents the development of a positive displacement ORC pump based on the sliding vane rotary technology. The machine was installed in a power unit for low-medium grade thermal energy recoverythat operated with oil at 70-120C as upper thermal source and tap water as lower one. Working fluid was R236fa while cycle pressure ratio ranged from 2.8 to 3.7. The ORC pump was also tested at different revolution speedssuch that mass flow rate varied between 0.05kg/s and 0.12kg/s. These experimental data were further used to validate a comprehensive one-dimensional model that takes into account fluid dynamic filling and emptying processes, closed vane transformation and leakages at blade tip, rotor slots and end walls clearances. Viscous and dry friction phenomena occurring between components in relative motion were additionally considered. A full operating map of the sliding vane pump was eventually retrieved to explore multiple off-design operating conditions. The parametric and modular structure of the model will act as a design platform to outline enhanced ORC sliding vane pump prototypes

Mechanical Energy Recovery from Low Grade Thermal Energy Sources

An ORC based power plant for waste heat recovery in stationary applications has been developed and experimentally characterized. The aim of the study was to investigate the performance of a sliding vane rotary expander as the device to convert the enthalpy of the working fluid, namely R236fa, into mechanical and electric energy. A theoretical model of the expander supported the design and allowed to assess the thermodynamic transformations that take place in it. Furthermore, a deep experimental campaign explored the behavior of the expander and the one of the recovery system also at off design conditions. The experimental activity on the expander included the reconstruction of the indicated diagram using a set of high frequency piezoelectric pressure transducers that provided an accurate prediction of the pressure evolution inside the cell. The overall cycle efficiency achieved was close to 8% and further improvements concerned to the expander design have been addressed. The temperature of the upper thermal source at around 120 °C and the mechanical output power close to 2 kW make the expander and the whole system suitable for plenty of potential recovery applications. © 2013 The Authors

Exploiting Multiple Abstractions in Episodic RL via Reward Shaping

One major limitation to the applicability of Reinforcement Learning (RL) to many practical domains is the large number of samples required to learn an optimal policy. To address this problem and improve learning efficiency, we consider a linear hierarchy of abstraction layers of the Markov Decision Process (MDP) underlying the target domain. Each layer is an MDP representing a coarser model of the one immediately below in the hierarchy. In this work, we propose a novel form of Reward Shaping where the solution obtained at the abstract level is used to offer rewards to the more concrete MDP, in such a way that the abstract solution guides the learning in the more complex domain. In contrast with other works in Hierarchical RL, our technique has few requirements in the design of the abstract models and it is also tolerant to modeling errors, thus making the proposed approach practical. We formally analyze the relationship between the abstract models and the exploration heuristic induced in the lower-level domain. Moreover, we prove that the method guarantees optimal convergence and we demonstrate its effectiveness experimentally.Comment: This is an extended version of the paper presented at AAAI 2023, https://doi.org/10.1609/aaai.v37i6.2588

Numerical CFD simulations on a small-scale ORC expander using a customized grid generation methodology

Positive displacement machines are the most suitable devices for small-scale waste heat to power conversion units based on an Organic Rankine Cycle (ORC) due to their capabilities of handling small mass flow rates and high pressure ratios. Among the technologies, sliding vane machines provide unique features such as low operating revolution speed, geometrical flexibility and uncomplicated manufacturing. Nonetheless, research and product development in this field have been constrained by the lack of interfaces between deforming and moving fluid domains that characterize sliding vane devices and the design tools at the state of the art. This research work tackles this challenge and presents the development of an analytical grid generation for sliding vane machines that is based on user defined nodal displacement. Through this approach, the numerical methodology discretizes the fluid domains enclosed between the cells and ensures conservation of intrinsic quantities by maintaining the cell connectivity and structure. Transient 3D single phase simulations on a small scale ORC expander were further set up in the ANSYS CFX solver and provided insights on the main flow field as well as in the leakage paths between rotor blade tips and casing. The numerical results were eventually validated with reference to an experimental dataset related to a waste heat to power conversion application in compressed air systems where the sliding vane ORC expander worked with R236fa, at a pressure ratio of 2.65 and at 1551 RPM

Grid generation methodology and CFD simulations in sliding vane compressors and expanders

The limiting factor for the employment of advanced 3D CFD tools in the analysis and design of rotary vane machines is the unavailability of methods for generation of computational grids suitable for fast and reliable numerical analysis. The paper addresses this challenge presenting the development of an analytical grid generation for vane machines that is based on the user defined nodal displacement. In particular, mesh boundaries are defined as parametric curves generated using trigonometrical modelling of the axial cross section of the machine while the distribution of computational nodes is performed using algebraic algorithms with transfinite interpolation, post orthogonalisation and smoothing. Algebraic control functions are introduced for distribution of nodes on the rotor and casing boundaries in order to achieve good grid quality in terms of cell size and expansion. In this way, the moving and deforming fluid domain of the sliding vane machine is discretized and the conservation of intrinsic quantities in ensured by maintaining the cell connectivity and structure. For validation of generated grids, a mid-size air compressor and a small-scale expander for Organic Rankine Cycle applications have been investigated in this paper. Remarks on implementation of the mesh motion algorithm, stability and robustness experienced with the ANSYS CFX solver as well as the obtained flow results are presente

Conventional vs. extended D2 lymphadenectomy in gastric cancer patients: less is more?—more or less

n/