We develop a simplified model of choked flow in pipes for CO.sub.2-water solutions as an important step in the modelling of a whole hydraulic system with the intention of eliminating the carbon ...dioxide generated in air-independent submarine propulsion. The model is based on an approximate fitting of the homogeneous isentropic solution upstream of a valve (or any other area restriction), for given fluid conditions at the entrance. The relative maximum choking back-pressure is computed as a function of area restriction ratio. Although the procedure is generic for gas solutions, numeric values for the non-dimensional parameters in the analysis are developed only for choking in the case of carbon dioxide solutions up to the pure-water limit.
Thermodynamic models constitute one of the essential tools to properly design supersonic ejectors. However, by their simplistic nature, most of said models remain unable to properly integrate the ...adequate physics that takes place within the device. Most notably, the Fabri-choking theory constitutes the building block of the large majority of those models. However, it has recently been shown that the so-called compound-choking theory may be better suited to predict the behavior of a double choked ejector. In the present study, a new state-of-the-art thermodynamic model based on the compound-choking theory is presented. First, the algorithm of the on- and off-design model is laid out. Then, the link between Fabri- and compound-choking is clarified by comparing the model with its Fabri-choking counterpart. Characteristic curves are calibrated onto air and R134a experimental data. Finally, an analytical study is performed to show that imposing the compound-choking is actually equivalent to maximizing the mass flow rate within the ejector.
•A new thermodynamic model for ejectors based on the compound-choking is presented.•The model is able to fit well to air and R134a experimental data.•Compound-choking and Fabri-choking criteria are related.•The compound-choking criterion maximizes the mass flow rate within the ejector.
The performance of supersonic ejectors is mainly limited by the choking of the flow. Below a critical pressure, the entrainment capability of the ejector remains indeed constant. As the coefficient ...of performance of ejector-based heat driven refrigeration cycles (HDRC) is directly linked to the ejector entrainment ratio, it constitutes a real limitation towards better overall cycle performance. The compound-choking criterion has recently demonstrated to better explain this limitation compared to the Fabri-choking theory for supersonic ejectors working with air. However, as all ejector-driven HDRCs work with real gas refrigerants, this criterion needs to be extended to real gases. In the present work, the compound-choking criterion is first extended analytically to real gases. Wall-resolved turbulence modelings for supersonic ejectors working with R134a and blends of R134a and HydroFluoroOlefeins (HFO) are then performed. An improved thermodynamic model is finally used to demonstrate the superiority of the compound-choking criterion over the Fabri-choking one for supersonic ejectors. Results show that the β parameter constitutes an unambiguous indicator of the ejector choking condition, much better suited to determine the operating regime than the sonic line criterion. Moreover, the mean error in entrainment ratio predictions is reduced from 17.54% to 5.28% when using the compound-choking theory instead of the Fabri-choking one, with virtually no difference in the complexity or computational cost of the model.
•The compound-choking theory is applied to single-phase supersonic ejectors.•The compound-choke theory leads to more accurate supersonic ejector models.•The condition β<0 is a clear indicator of the supersonic ejector operating regime.•The theory is applicable to different operating conditions and working fluids.
While the limitation of the entrainment ratio in supersonic ejectors is a well-known phenomenon, there is still a need to gain insight on the choking phenomena at play in on-design operation. In ...state-of-the-art simplified models of supersonic ejectors, the secondary stream is assumed to reach sonic velocity in a hypothetical throat (Fabri-choking). However, an alternative explanation of the entrainment limitation known as the compound-choking theory states that a nozzle flow with two streams at different stagnation pressures may be choked with a subsonic stream if the other one is supersonic. In this paper, the compound-choking is highlighted in a supersonic ejector through a thorough analysis of numerical simulations validated against experimental data. In addition, comprehensive experimental data of supersonic ejectors are used to assess the performance of the compound-choking theory to predict the entrainment ratio in the on-design regime in various configurations. Most predictions are in the ±10% range when compared to the experimental data. Compared to state-of-the-art 1D models relying on the Fabri-choking assumption, the compound-choking theory is shown to generally perform better regarding the prediction of the on-design entrainment ratio. This study suggests that the compound-choking theory is well suited to model the choking process in supersonic ejectors.
•CFD calculations show that the flow may be choked with a subsonic secondary stream.•The compound-choking theory is well suited to model the choking process at play.•Most theoretical predictions are in the ±10% range when compared to the experimental data.•The use of this theory could lead to more efficient simplified models of supersonic ejectors.
A cow was presented with profuse salivation, in-appetence, swelling on neck region, dull, depressed and increasing abdominal size since last two days. On clinical examination, salivation, sunken eye, ...hard non-movable mass on neck region and bloat was observed. Based on history and clinical signs, the case was diagnosed as oesophageal obstruction. Taking all aseptic precautions under local infiltration, surgery was performed and onion was removed with uneventful recovery. Keywords: Choke; oesophagus; oesophagotomy; onion; rumenotomy
•A double-choking theory is proposed.•A quantitative analysis of the entrainment choking flow has achieved.•The inherent reason behind the evolution law of ejector performance is illuminated.•The ...fundamental link between entrainment performance and choking flow is revealed.•The evolution laws under various operational and geometry parameters have explained.
There are few systematic studies to investigate the inherent reason behind the evolution law of ejector performance, only some simple qualitative or roundabout analysis. In this paper, a double-choking theory is proposed to provide an in-depth explanation of the evolution laws of ejector performance. The systematic investigation and quantitative analysis focus on the influences of various operational and geometrical parameters on the ejector choking flows. Key results revealed that the flow area of the primary jet flow at the choking cross-section Apy almost linearly increases with higher primary flow pressure pp0, while the entrainment choking area Aey declines instead, and thus the entrainment ratio ε decreases. The mixing pressure py significantly increases with entrainment pressure pe0, and Apy partly reduces. Consequently, Aey becomes larger and ε is accordingly with an over-double increase. Apy undergoes a continuous decrease when the area ratio of primary nozzle λt increases, and thus ε rises consistently although Aey1 eventually experiences a slight decrease. However, the choking state of the entrained flow would discontinue as λt exceeds its critical value λtc. Additionally, Aey increases substantially when the area ratio of the constant-area section λ3 enlarges, while Apy and py always remain unchanged. Accordingly, ε follows the same increasing trajectory as Aey. These impactful results could serve as an essential guide for optimizing the ejector design, and also ensure a clearer perspective to understand the fundamental link between the ejector’s entrainment performance and choking flow.
A review of recent research outcomes in downstream flow choking-driven unstart is presented. Unstart is a flow phenomenon at the inlet that severely reduces the air mass flow rate through the engine, ...causing a loss of thrust and considerable transient mechanical loading. Therefore, unstart in a scramjet engine crucially affects the design and the operation range of hypersonic vehicles. Downstream flow choking is known to be one of the major mechanisms inducing inlet unstart, as confirmed by recent scramjet-powered flight tests. The current paper examines recent research progress in identifying flow choking mechanisms that trigger unstart. Three different flow choking mechanisms are discussed: flow blockage, mass addition, and heat release from combustion reactions. Current research outcomes on the characteristic of unstarting flows, such as transient and quasi-steady motions, are reviewed for each flow choking mechanism. The characteristics of unstarted flows are described including Buzzing phenomena and oscillatory motions of unstarted shockwaves. Then, the state-of-the-art methods to predict, detect, and control unstart are presented. The review suggests that further investigations with high-enthalpy ground facilities will aid understanding of heat release-driven unstart.
To quantify the associations of foreign body airway obstruction (FBAO) basic life support (BLS) interventions with FBAO relief and survival to discharge.
We identified prehospital FBAO patient ...encounters in Alberta, Canada between Jan 1, 2018 and Dec 31,2021 using the provincial emergency medical services’ medical records, deterministically linked to hospital data. Two physicians reviewed encounters to determine cases and extract data. Multivariable logistic regression determined the adjusted odds ratio of FBAO relief (primary outcome) and survival to discharge for the exposure of BLS interventions (abdominal thrusts AT, chest compressions/thrusts CC, or combinations) relative to back blows BB. Intervention-associated injuries were identified using International Classification of Diseases codes, followed by health records review.
We identified 3,677 patient encounters, including 709 FBAOs requiring intervention. Bystanders performed the initial BLS intervention in 488 cases (77.4%). Bystanders and paramedics did not relieve the FBAO in 151 (23.5%) and 11 (16.7%) cases, respectively. FBAOs not relieved before paramedic arrival had a higher proportion of deaths (n = 40.4% versus n = 9242.4%, p < 0.001). AT and CC were associated with decreased odds of FBAO relief relative to BB (adjusted odds ratio aOR 0.49 95%CI 0.30–0.80 and 0.14 95%CI 0.07–0.28, respectively). CC were associated with decreased odds of survival to discharge (aOR 0.04 95%CI 0.01–0.32). AT, CC, and BB were implicated in intervention-associated injuries in four, nine, and zero cases, respectively.
Back blows are associated with improved outcomes compared to abdominal thrusts and chest compressions. These data can inform prospective studies aimed at improving response to choking emergencies.
Transition problems in a smooth open-channel flow consist of a solution of the third- or higher-degree algebraic equations to determine the choke-free or post-choking depths at downstream and ...upstream sections, respectively. Graphical solutions of trapezoidal, circular and exponential channels and analytical solution for rectangular channels have been obtained in the past. However, these solutions are cumbersome and so are difficult for field applications. In the present work, a general transition problem in exponential channels has been formulated in terms of alternate-depth ratio. A governing algebraic equation representing incipient choking condition has been derived for the exponential channel (rectangular, parabolic and triangular). Furthermore, the method of applying the same to calculate the choke free and post-choking depth at downstream and upstream sections has been presented in this paper. Exact solutions for the case of rectangular and parabolic channels have been obtained. After observing, the impossibility of exact solutions for triangular channels and the cumbersome nature of the solutions for rectangular and parabolic channels, empirical solution for the post-choking depth at upstream section has been carried out for the exponential channel. The empirical relation between the shape factor
and upstream Froude number
for the incipient condition has been obtained for all channel types. The result shows that for
, the absolute error in
is less than 1% in all channel types, while for
, this value goes up to 1.1%, 1.6% and 1.8% for rectangular, parabolic and triangular channels, respectively. These empirical solutions are simple for field applications with negligible error. The methodologies presented in this paper have been corroborated using examples from various sources.
Choking is the entry of a foreign object into the throat or respiratory tract. This is a dangerous condition that can happen to anyone. In cases of choking in children, the initial treatment that can ...be done is back blows and chest thrusts. This activity was carried out to provide Health Education to students and teachers at SDN Gisik Cemandi Sidoarjo, as well as to gain skills in helping children and the community in their environment if a child experiences a choking incident. The implementation method is carried out in the form of a lecture using power points, posters with pictures of signs of choking, and how to handle it independently, and the Heimlich Maneuver. The results of the activity were that participants received information and increased their knowledge regarding the signs of choking, and how to handle it independently as well as the Heimlich Maneuver to students and teachers at SDN Gisik Cemandi Sidoarjo on November 11, 2023. The results of the socialization on handling emergency choking carried out at SDN Gisik Cemandi Sidoarjo were considered effective so that students and teachers are able to provide first aid in cases of choking.
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