Experimental Characterization of an Adaptive Supersonic Micro Turbine for Waste Heat Recovery Applications

Micro turbines (<100 kWel) are commercially used as expansion machines in waste heat recovery (WHR) systems such as organic Rankine cycles (ORCs). These highly loaded turbines are generally designed for a specific parameter set, and their isentropic expansion efficiency significantly deteriorates when the mass flow rate of the WHR system deviates from the design point. However, in numerous industry processes that are potentially interesting for the implementation of a WHR process, the temperature, mass flow rate or both can fluctuate significantly, resulting in fluctuations in the WHR system as well. In such circumstances, the inlet pressure of the ORC turbine, and therefore the reversible cycle efficiency must be significantly reduced during these fluctuations. In this context, the authors developed an adaptive supersonic micro turbine for WHR applications. The variable geometry of the turbine nozzles enables an adjustment of the swallowing capacity in respect of the available mass flow rate in order to keep the upper cycle pressure constant. In this paper, an experimental test series of a WHR ORC test rig equipped with the developed adaptive supersonic micro turbine is analysed. The adaptive turbine is characterized concerning its off-design performance and the results are compared to a reference turbine with fixed geometry. To create a fair data basis for this comparison, a digital twin of the plant based on experimental data was built. In addition to the characterization of the turbine itself, the influence of the improved pressure ratio on the energy conversion chain of the entire ORC is analysed.

Steady State Experimental Characterization of a Twin Entry Turbine under Different Admission Conditions

The increasingly restrictive limits on exhaust emissions of automotive internal combustion engines imposed in recent years are pushing OEMs to seek new solutions to improve powertrain efficiency. Despite the increase in electric and hybrid powertrains, the turbocharging technique is still one of the most adopted solution in automotive internal combustion engines to achieve good efficiency with high specific power levels. Nowadays, turbocharged downsized engines are the most common solution to lower CO2 emissions. Pulse turbocharging is the most common boosting layout in automotive applications as the best response in terms of time-to-boost and exhaust energy extraction. In a high-fractionated engine with four or more cylinders, a twin entry turbine can be adopted to maximize pulse turbocharging benefits and avoid interaction in the discharge phase of the cylinders. The disadvantages of the twin entry turbine are mainly due to the complexity of the exhaust piping line and the high amount of information required to build a rigorous and reliable matching model. This paper presents a detailed experimental characterization of a twin entry turbine with particular reference to the turbine efficiency and the swallowing capacity under different admission conditions. The steady flow experimental campaign was performed at the turbocharger test bench of the University of Genoa, in order to analyze the behavior of the twin entry turbine in full, partial and unbalanced admission. These are the conditions in which the turbine must work instantaneously during its normal operation in engine application. The results show a different swallowing capacity of each sector and the interactions between the two entries.

A Numerical Swallowing-Capacity Analysis of a Vacant, Cylindrical, Bi-Directional Tidal Turbine Duct in Aligned & Yawed Flow Conditions

Introducing a duct along the perimeter of a rotor has been acknowledged to augment turbine performance. The outcome causation due to a bi-directional, cylindrical shroud, however, is uncertain. This study analyses the hydrodynamic swallowing capacity of a true-scale, vacant duct for tidal turbine applications in aligned and yawed inlet flow conditions by utilising three-dimensional unsteady computational fluid dynamics. The performance is investigated within free-stream magnitudes of 1 to 7 m.s−1, and a bearing angular range of 0° to 45° with the duct axis. In proportion to the free-stream magnitude, the normalised axial velocity through the duct increases as a result of a diminishment in pressure drag. Within yawed flow, the maximum capacity falls at a bearing of 23.2°, resulting in a performance increase of 4.13% above that at aligned flow conditions. The analysis concludes that the augmentation at yawed flow occurs due to the duct cross-sectional profile lift variation with angle-of-attack. Towards nominal yaw angle, the internal static pressure reduces, permitting a higher mass-flow rate. Beyond the nominal angle-of-attack, flow separation occurs within the duct, increasing pressure drag, thereby reducing the swallowing capacity.

Effects of Olfactory Stimulation on Swallowing Function in Taiwanese Older Adults

This pretest-posttest pilot study was to examine the effects of how olfactory stimulation (OS) influenced swallowing function in older adults. Forty-four community-dwelling older residents (24 OS & 20 control) from southern Taiwan were recruited. Participants in the intervention group administered pre-meal OS using odor and flavor inhalation. The study found that physiological responses for different food textures significantly differed between groups at post-test ( p ≤ .02). Within the experimental group, swallowing function, and individual satisfaction showed significant differences before and after the odor inhalation over time ( p < .01, [Formula: see text] = 0.16–0.33). An individual’s satisfaction to their own swallowing capacity was largely enhanced by the significant interaction between time and group ( F[1, 42] = 11.34, p = .002, [Formula: see text] = 0.21), but not for physiological response to OS and swallowing function. The results suggest OS may be advantageous to improving physiological response to OS, swallowing function and satisfaction with swallowing capacity in older adults.

A New Method for Impeller Inlet Design of Supercritical CO2 Centrifugal Compressors in Brayton Cycles

Supercritical Carbon Dioxide (SCO2) is considered as a potential working fluid in next generation power and energy systems. The SCO2 Brayton cycle is advantaged with higher cycle efficiency, smaller compression work, and more compact layout, as compared with traditional cycles. When the inlet total condition of the compressor approaches the critical point of the working fluid, the cycle efficiency is further enhanced. However, the flow acceleration near the impeller inducer causes the fluid to enter two-phase region, which may lead to additional aerodynamic losses and flow instability. In this study, a new impeller inlet design method is proposed to achieve a better balance among the cycle efficiency, compressor compactness, and inducer condensation. This approach couples a concept of the maximum swallowing capacity of real gas and a new principle for condensation design. Firstly, the mass flow function of real gas centrifugal compressors is analytically expressed by non-dimensional parameters. An optimal inlet flow angle is derived to achieve the maximum swallowing capacity under a certain inlet relative Mach number, which leads to the minimum energy loss and a more compact geometry for the compressor. Secondly, a new condensation design principle is developed by proposing a novel concept of the two-zone inlet total condition for SCO2 compressors. In this new principle, the acceptable acceleration margin (AAM) is derived as a criterion to limit the impeller inlet condensation. The present inlet design method is validated in the design and simulation of a low-flow-coefficient compressor stage based on the real gas model. The mechanisms of flow accelerations in the impeller inducer, which form low-pressure regions and further produce condensation, are analyzed and clarified under different operating conditions. It is found that the proposed method is efficient to limit the condensation in the impeller inducer, keep the compactness of the compressor, and maintain a high cycle efficiency.

Swallowing, Chewing and Speaking: Frequently Impaired in Oculopharyngeal Muscular Dystrophy

Background: Oculopharyngeal muscular dystrophy (OPMD) is a late onset progressive neuromuscular disorder. Although dysphagia is a pivotal sign in OPMD it is still not completely understood. Objective: The aim of this study was to systematically investigate oropharyngeal functioning in a large OPMD population. Methods: Forty-eight genetically confirmed OPMD patients completed questionnaires, performed clinical tests on swallowing, chewing, speaking, tongue strength and bite force, and underwent videofluoroscopy of swallowing. Descriptive statistics was used for all outcomes and logistic regression to investigate predictors of abnormal swallowing. Results: Eighty-two percent reported difficulties with swallowing, 27% with chewing and 67% with speaking. Patients performed significantly worse on all oropharyngeal tests compared to age-matched controls except for bite force. Also asymptomatic carriers performed worse than controls: on chewing time, swallowing speed and articulation rate. During videofluoroscopy, all patients (except one asymptomatic) had abnormal residue and 19% aspirated. Independent predictors of abnormal residue were reduced swallowing capacity for thin liquids (OR 10 mL = 0.93; 20 mL = 0.95) and reduced tongue strength for thick liquids (OR 10 mL = 0.95); 20 mL = 0.90). Aspiration of thin liquids was predicted by disease duration (OR = 1.11) and post-swallow residue with 20 mL (OR = 4.03). Conclusion: Next to pharyngeal dysphagia, chewing and speaking are also frequently affected in OPMD patients, even in asymptomatic carriers. Residue after swallowing is a very early sign, while aspiration is a later sign in OPMD. For clinical follow-up monitoring of subjective complaints, swallowing capacity and tongue strength seems relevant.