Centrifugal compressor is seen as the predominant choice in turbocharging and natural gas transportation. The energy loss measurement in centrifugal compressor is of great essence, especially under ...instability conditions. Based on one-dimensional model and simulations, each energy loss mechanism in diffuser was evaluated by defining the weight coefficient representing the influence of energy loss on compressor performance. The thermodynamics in the diffuser was investigated under design and stall inception conditions. Vortex transportation and synergy angle analysis was realized to identify the correlation between energy losses and stall identification. The results indicate that the skin friction loss accounts for 75.06% of the total energy loss in diffuser, while 16.96% and 7.98% for diffusion and secondary loss near stall condition, respectively. The determination of stall in vanless diffuser may be confirmed according to the combination of secondary vorticity coefficient and synergy angle. Due to small inflow angle and large width ratio of the diffuser, stall inception is the results of secondary flow sweep and momentum loss induced by diffusion. The weight function was originally modelled to quantize the influence of energy loss on flow aerodynamics. The present work may shed lights on stall identification and energy loss reduction in industrial compressor.
The development of space technology brings about an increasing demand for electric thrusters. Iodine has been considered a feasible alternative to resource-critical xenon. Numerical and experimental ...methods are used to study the performance of the iodine-fed Hall thruster. The ionization and acceleration characteristics are investigated in the simulation with a particle-in-cell/Monte Carlo collision model. Different from previous simulations of noble gas, the dissociation equation of molecular iodine is added to the code for propulsive performance evaluation. A dissociation region in the discharge chamber is presented and described in detail. The propulsive performances of the iodine-fed Hall thruster are calculated by the plasma parameters. Meanwhile, the experimental measurements are finished for model verification and performance comparison at nominal conditions. The measured data is slightly lower than the simulated data. The error between them is about 1.65%. The reasons are analyzed and discussed. Then, the performance is predicted and measured using this simulated and experimental method within 20% mass flow rate and 10% anode voltage fluctuations relative to the nominal condition. Further optimizations of the simulation and experiment are in progress.
•A 2D model of an iodine-fed Hall thruster is built to investigate the spatial axial profiles of important plasma parameters. Different from traditional PIC/MCC simulation for noble gas, the iodine molecular dissociation process is added to the codes. Based on the simulated results, the discharge chamber of the thruster can be divided into four regions: the near-anode region, dissociation region, ionization region, and acceleration region.•The experimental platform and equipment are built. The iodine ignition experiment of the thruster is finished. The performance parameter measurement has been conducted to verify the model.•Considering the influence of input parameter changes on thruster performance, thrust and anode-specific impulse with ±20% iodine propellant mass flow rate fluctuation and ±10% anode voltage fluctuation are calculated and measured, respectively. The simulated result is in good agreement with the experimental data.
•The postharvest kiwifruit was modeled as a multiscale body of flesh and skin.•A finite element model was developed to simulate the drop case process.•The stress, force, energy, and bruise behavior ...of kiwifruit were described by FEM.•The compared results showed the low-level errors between simulation and experiment.
Bruising is one of the most common mechanical damages of fruit, but it is difficult to detect quantitatively. In this study, the finite element method (FEM) was utilized to predict the bruise susceptibility of harvested kiwifruit. The elastic-plastic material properties of fruit flesh at different ripening times, including Young’s modulus, bio-yield stress and tangent modulus, were measured using the compression test. Then the fruit were modeled as a multiscale body of flesh and skin, and a finite element model was developed for dropped fruit. The drop scenarios were successfully simulated by FEM, and the results showed simultaneous activities of the simulation and high speed camera recordings. Results of FEM-based simulation showed that the bruise susceptibility increased with ripening time, but that different drop heights resulted in similar levels of bruise susceptibility. In addition, the horizontal orientation would cause higher bruise susceptibility than the vertical orientation. Results of accuracy analysis showed that the hourglass energy in any of the simulation scenarios kept in a very low level (<5%). The maximum errors between simulation and high speed camera recordings were 5.0%, 19.0% and 11.9% for initial velocity, maximum deformed length and contact time, respectively. Compared with experimental measurement, the maximum errors of simulation were 17.1% for bruise volume and 18.3% for bruise susceptibility. The results confirmed the FEM was reliable for prediction of bruise susceptibility of the fruit, and would be an effective approach to further investigate the bruise damage.
The literature cites many factors that influence a nurse's decision when choosing their workplace. However, it is unclear which attributes matter the most to newly graduated nurses. The study aimed ...to identify the relative importance of workplace preference attributes among newly graduated nurses.
A cross-sectional study.
We conducted an online survey and data were collected in June 2022. A total of 1111 newly graduated nurses in South Korea participated. The study employed best-worst scaling to quantify the relative importance of nine workplace preferences and also included questions about participants' willingness to pay for each workplace preferences. The relationships between the relative importance of the workplace attribute and the willingness to pay were determined using a quadrant analysis.
The order according to the relative importance of workplace preferences is as follows: salary, working conditions, organizational climate, welfare program, hospital location, hospital level, hospital reputation, professional development, and the chance of promotion. The most important factor, salary, was 16.67 times more important than the least important factor, the chance of promotion, in terms of choosing workplace. In addition, working conditions and organizational climate were recognized as high economic value indicators.
Newly graduated nurses nominated better salaries, working conditions, and organizational climate as having a more important role in choosing their workplace.
The findings of this study have important implications for institutions and administrators in recruiting and retaining newly graduated nurses.
Accurate measurement of milling forces is essential for monitoring and optimizing the milling process. The table dynamometer is widely used to measure the milling force because it does not change the ...dynamic characteristics of the spindle. However, the measured milling force will be distorted because it is conditioned by the vibration of the surrounding system and the natural frequency of the table dynamometer. Therefore, it is necessary to compensate for these dynamically induced errors in milling force measurement. This work aims to develop and test a novel compensation technique based on the improved Luenberger observer. First, the reason for the distortion of the milling force measured by the dynamometer is analyzed by the impact hammer test. Second, the transfer function fitting accuracy is improved by a band-fitting method. Third, the <inline-formula><tex-math notation="LaTeX">l_{1}</tex-math></inline-formula> performance is introduced to obtain the gain parameter of the improved Luenberger observer, and the assumption that some prior knowledge about the process disturbance is removed. Finally, the effectiveness of the proposed method is verified by numerical simulation and experiment, and the specific application of the proposed method in milling force measurement is presented.
The outwardly propagating spherical flame method was used to measure the laminar burning velocity of a Chinese commercial gasoline and gasoline surrogates. Measurements were conducted at different ...equivalence ratios of 0.8 to 1.5, initial temperatures of 358 K, 403 K, and 448 K and initial pressures of 1 atm, 2 atm and 5 atm in a constant volume bomb. The primary reference fuel (PRF-92, vol. %: 92% iso-octane + 8% n-heptane) and toluene reference fuel (TRF-92, vol. %: 16.69% iso-octane + 22.65% n-heptane + 60.66% toluene) surrogates were proposed to predict the laminar burning velocity of commercial gasoline. It was found that the TRF-92 was able to successfully reproduce the laminar burning velocity of commercial gasoline under various experimental conditions. The chemical kinetic model of Park et al. was validated and used to simulate the laminar burning velocity. The simulated laminar flame speeds showed good agreement with the experimental values.
•A highly accurate and dynamic isothermal calorimeter is developed.•Heat generation rate at different operation conditions is measured.•Total heat generation and energy efficiency are analyzed and ...compared.•A new calorimetric method is developed to characterize heat source terms.
Fundamental understanding of heat generation of lithium-ion batteries during operations is crucial to the cost-effective and efficient design of a thermal management system (TMS) in electric vehicles. Accurate characterization of the heat requires a calorimeter that meets inherent dynamics of the heat with accuracy. Therefore, we have developed an isothermal calorimeter using the thermoelectric assemblies (TEAs) along with the temperature control and Kalman filter, which is used to measure the heat generation rate (HGR) of large format pouch type lithium-ion batteries as an example. The measured HGR is a function of charge and discharge rates, state-of-charge (SOC), and temperatures. Analysis has shown that both the HGR and the ratio of the total heat generation to the total energy stored or released (pheat) of the tested cells increase as the current increases or the temperature decreases. In addition, a new calorimetric method is developed which enables a simultaneous determination of the entropy coefficient and internal resistance in the reversible and irreversible heat source terms in the frequency domain. The method can reduce the testing time about 92% compared with those by the conventional potentiometric method and electrochemical impedance spectroscopy (EIS) analysis, respectively, and the determined parameters are in good accordance with the reference values. Moreover, the calculated reversible and irreversible heat sources terms are compared with the experimental measurement and matched each other.
•Thermophysical properties of different nanofluids were measured.•New correlations were extracted using regression, NN and ANFIS for nanofluids.•Numerical simulation was performed to optimize a ...double-pipe heat exchanger.•Some nanofluids present good results as working fluids in refrigeration systems.
This work is concerned with a comparison of measured and theoretical thermophysical properties of different nanofluids and using the properties to evaluate their suitability as a secondary working fluid in refrigeration systems, aiming at the external thermodynamic losses. Single-Walled Carbon Nanotubes (SWCNT) and silver nanoparticles were dispersed in distilled water to produce the nanofluid samples. After that and by using the regression, a neural network (NN), an adaptive neuro-fuzzy inference system (ANFIS) and through obtained experimental data, new correlations were extracted to determine the thermophysical properties of nanofluids. Then, a numerical simulation was performed taking into account a mathematical model for thermodynamic optimization of a double-pipe heat exchanger. A comparison between the results obtained by the measured data or those which is obtained by soft-computing techniques and those evaluated theoretically by previous available models were carried out, showing a notable difference among the results. The results obtained with the experimental or soft-computing data show that in the case that the heat exchanger is optimized to minimize the external entropy generation, silver nanofluids (at any volumetric concentration) and the SWCNT nanofluids (at lower concentrations) presented positive results, whereas using the former existing theoretical data indicated that silver nanofluids showed negative results and SWCNT nanofluids presented positive results in all volumetric concentrations.
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•The 3D numerical model of the floor heating was developed using Comsol Multiphysical software.•The mean error deviation between experimental and numerical simulation measurements is ...less than 3%.•The design and construction parameters have an influence on the heating floor thermal response.•The optimized heating floor model allows us to offer a temperature in the thermal comfort range.
In recent years, the installation of underfloor heating systems has increased considerably in many countries, due to their ability to be connected to a solar thermal collector in order to benefit from clean and renewable energy. This promising technology allows for reduced energy consumption, achieves a higher level of comfort, and ensures a more homogeneous temperature distribution than conventional heating systems. A huge loophole is detected in research works concerning the three-dimensional numerical modelling of the thermal behavior of underfloor heating by COMSOL Multiphysics software. The present study aims to reduce these knowledge gaps and to analyze the thermal behavior of the direct solar floor numerically and experimentally under the specific climatic conditions of Casablanca, Morocco. Visualize the thermal behavior of the underfloor heating system and the heating circuit as a 3D model using COMSOL Multiphysics software, based on the finite element method by investigating the influence of various design and operational parameters to select the best parameters that guarantee thermal comfort in the case of installing this heating system in traditional bathrooms.
The results obtained by numerical simulation are then compared with those of the experimental measurements in order to verify the validity of the numerical model. The average deviation between the simulated and measured surface temperatures is approximately 1.04%, while the deviation in pipe temperature is around 3.13%, which shows a very good agreement between the numerical and experimental results. In addition, the results of the parametric study indicate that the key elements for enhancing the floor heating system are primarily a floor covered by tile with a minimum thickness of 5 mm, a pipe spacing of approximately 15 cm, a PER pipe diameter of 16/20 mm, and a thermal insulation layer with a thickness of 50 mm made of XPS or polystyrene. The incorporation of these improvements in the standard model ensures a surface temperature within the thermal comfort range of a less warm bathroom, approximately 34.13 °C, and a high heat flux emitted at the surface around 502.07 W compared to the standard model. In the literature, it was found that the comparison of architectural characteristics of direct solar floors receives minimal attention, with most studies only comparing systems in terms of thermal comfort or energy efficiency. In this study, the analysis and interpretation of the results obtained can be used to help engineers and designers select the type and dimensions of the best materials for heating floors installed in traditional bathrooms in Morocco.
Abstract Due to the importance of supercritical fluid technology (SFT) in different industries, it has been the subject of intense research in recent decades. Solubility is a key concept in SFT. In ...fact, obtaining knowledge about the theoretical concepts of solubility and related experimental measurement methods can be useful in developing and improving the quality of research in this field. This study reviews the fundamental knowledge of solubility in supercritical fluids and investigates the significant topics in this field, including high-pressure phase behavior, experimental measurement methods, modeling, and molecular simulation of solubility.
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