Outlet Conditions Research Articles

Performance of a shallow solar pond coupled with a heat pump cycle for thermal energy in net zero-energy buildings

Refrigerant evaporation, in heat pumping systems, is a particularly complex process. Since the evaporator is subjected to environmental conditions, several factors weigh in on overall system performance, mainly, the additional energy input from the surroundings. This renders the evaporation process especially susceptible to gaps and fluctuations of said energy availability, particularly in solar-assisted setups. Despite the, comparatively, high heat flux associated to this source, these occurrences make them suitable mostly for low-to-medium thermal requirements, especially in regions with more extreme climates. The present work introduces a novel evaporator design, based on solar ponds. The proposed evaporation device incorporates a short-term, passive, thermal storage solution to compensate for gaps in energy availability. A mathematical-thermal model is developed and a performance assessment is conducted based on real seasonal atmospheric and operation conditions. For this study R134a, R152a, R1234yf and R1234ze(E) were used as working fluids. The proposed heat pump configuration is evaluated for hot water production at 55 °C, indoor air heating at 18–22 °C and a combined simultaneous scheme. The results show that this configuration performs well under moderate climate conditions. For hot water production during spring, highest outlet temperature of 68.54 °C for the R1234yf working fluid, were reached and maintained after the first 13 h. Internal thermal capacitor reached an average temperature of 61.88 °C for R1234yf. During winter, these temperatures decrease almost by a third, with 40.6 °C for R1234yf working fluid. However, daily average outlet temperature of 64.8°Care reached within the first 15 h of operation. Despite a lower thermal storage, with average capacitor, the system yielded consistent average outlet temperature of 20.7 °C. For a simultaneous operation scheme, desired outlet water temperature, is reached within the first 16 h of operation, whilst the indoor air temperature reaches comfort levels within the first 12 h. Despite employing part of the energy absorbed to maintain a stable comfort condition within the dwelling, instead of compensating the heat loss of the hot water tank, both goals are achieved. The inclusion of an inner thermal capacitor that collects and stores energy at a much higher rate provides the refrigerant with an additional heat source. This results in a more effective overall energy absorption of the evaporator, which exceeds the rate at which heat is dissipated from the tank/dwelling to the environment. This heat loss buffer lessens, considerably, the thermal demand during periods with lower energy availability, resulting in achievable outlet conditions.

Experimental and numerical analysis of a three-fluid membrane-based ionic liquid desiccant absorber

Membrane-based liquid desiccant system is a promising technology for efficient humidity control. Also, in comparison to systems using conventional desiccants, ionic liquid (IL) desiccants enable increased system operational envelope and efficiency. In this study, a finite difference numerical model is developed for an IL-based counter and cross flow internally cooled polymer heat and mass exchanger (i.e. absorber). A super-hydrophobic membrane separates the IL desiccant and air flows while allowing moisture transfer from air to IL. The numerical model determines the outlet conditions of all three absorber fluids (water, desiccant, and air), establishing the absorber heat and mass transfer performance. The model was compared with the experimental data obtained from an IL desiccant absorber under a wide variety of water, desiccant, and air inlet conditions. The maximum discrepancy between the model predictions and experimental data for the air exit temperature, air exit relative humidity, cooling water exit temperature, and solution exit temperature are 4%, 9%, 5%, and 2%, respectively. A comprehensive parametric study is then conducted to evaluate the sensitivity of the absorber performance to different input conditions. This highly accurate model and parametric study of a membrane-based absorber can be utilized in design and performance analysis of emerging liquid desiccant dehumidification and separate sensible and latent cooling (SSLC) systems.

Influence of Surface Roughness on a Highly Loaded Axial Compressor Stage Performance at Low Reynolds Number

In the present study, a numerical simulation was conducted to investigate the influence of surface roughness on the aerodynamic performance of a 1.5-stage highly loaded axial compressor at low Reynolds number. It was especially considered how the roughness Reynolds number ( k + ) affected the change of the inlet and outlet conditions, the growth of the separation bubble (LSB), the status of the limiting streamline, and the patterns of the wake. Regarding the roughness settings, five roughness magnitudes and four roughness locations were mainly studied. The results showed that at low Re, surface roughness mainly improved the stage performance by reducing the length and width of the LSB as well as the rotor tip vorticity, delaying the occurrence of three-dimensional flow separation and increasing the turbulence level near the wall. However, it also aggravated the incoordination between the subsequent stages to a certain extent, which limited further improvement of the overall aerodynamic performance. Generally, with k + increasing, the compressor aerodynamic performance improved and achieved the best at k + = 137.8 . The maximum increases in the total pressure ratio, peak efficiency, and chocked mass flow were approximately 4.01%, 5.34%, and 2.24%, respectively. In addition, for all the four roughness locations, the roughness covering from the leading edge to 50% of the axial chord length on the suction surface had a relatively evident advantage in improving the compressor peak efficiency because of the better control of the LSB and wall shear stress.

Application of projection methods to simulating mass transport in reverse osmosis systems

Reverse Osmosis has important applications to seawater desalination and advanced water treatment. Its efficiency depends, however, on unsteady fluid flow and solute transport that are challenging to simulate. The challenges arise due to interactions between solute boundary layers and unsteady vortical flow structures generated by complicated geometries. These flow structures also interact with semi-permeable membranes through which the permeate flow depends on the local pressure. We show that this additional pressure coupling causes the temporal accuracy of traditional projection methods to drop to first-order. We track the source of this accuracy drop to the treatment of viscous terms in the derivation of the Poisson equation used to update the velocity and pressure fields. This allows us to propose a modified projection method that recovers second-order temporal accuracy. Finally, we show that the modified projection method can be coupled to convective outlet conditions and immersed boundary conditions to simulate reverse osmosis in steady and unsteady flow regimes.

Aerodynamic design and multi-dimensional performance optimization of supercritical CO2 centrifugal compressor

This paper dedicates to develop a systematic approach of design and multi-dimensional performance optimization of the Supercritical carbon dioxide (SCO2) compressor. A 5 MW SCO2 simple regenerative cycle used in small scale lead-cooled fast reactor (SLFR) was firstly proposed and simulated to define the operation condition of SCO2 compressor. Under the inlet and outlet condition of 305.15 K/7.56 MPa and 22 MPa, isentropic efficiency and mass flow rate of 80% and 69.88 kg·s−1 respectively was obtained. Secondly, a single stage centrifugal compressor was applied as the SCO2 compressor and one-dimensional (1D) design based on self-developed code was conducted to determine the basic geometry of the compressor, the code was verified with experiments and shows satisfactory accuracy. Additionally, CFD analysis was carried out to validate the results of 1D design and also shows good agreement. Then, three one-dimensional optimizations, two single objective optimizations using Particle Swarm Optimization (PSO) and one multi-objective optimization using Genetic Algorithm (GA), on aerodynamic efficiency of the SCO2 centrifugal compressor were performed based on 1D design code, five crucial parameters with ± 5% variation range were optimized. The 1D optimization results show that the isentropic efficiency received an improvement of about 5 percentage points compared to that of 1D design. Lastly, three-dimensional optimization concentrated on the blade profile of impeller were conducted on a fully automatic optimization platform to further improve the isentropic efficiency of SCO2 centrifugal compressor. Wrap angle and the leading and trailing edge of the main blade were optimized. Two optimal impellers with wrap angle in the range of + 5% and −5% were obtained respectively, the former impeller got the highest pressure ratio, while the latter one gained a higher isentropic efficiency but the lowest pressure ratio over the whole operation range.

A Novel Design and Performance Evaluation Technique for a Spool-Actuated Pressure-Reducing Valve

Solenoid-actuated pressure-reducing valves are commonly used in hydraulic machinery. Most studies on solenoid-actuated pressure control devices are focused on the electrical input signals or on the control techniques for the solenoid valves, but no study has been done that determines the influence of the design parameters on the valve’s output. Before designing a controller, it is imperative to know the valve’s performance by determining the significance of each valve parameter. In this study, established physical laws from fluid dynamics and mechanics are used to build a model that is solved using the ODE 45 solver of Simulink in the time domain. The actuating force, up to 15 N, exerted on the spool and the inlet pressure, ranging from 50 to 80 bar, are obtained through experimentation. It is found that the output pressure fluctuates significantly if the outlet is blocked, while at the fully opened outlet condition, a flow rate of 12 (L/min) was obtained. A pin diameter of 2.15 mm enables us to vary the output pressure between 0 and 41 bar. We found that higher inlet pressure leads to lower output pressure as the outlet is opened. No linearization of the actual mathematical model is performed, which makes the study unique.

Optimal Designed Experiments for Reliable Model Calibration of a fixed-speed Scroll Compressor with R410A and R32

Mainly to provide heat, the building sector accounts for about 18 % of overall global CO2 emissions. By exchanging conventional technologies in the near future, heat pumps are a key technology to systematically decarbonise the heat supply chain. The efficiency of a heat pump strongly depends on its compressor’s efficiency. Thus, the compressor is the subject of current research. The compressor performance depends on the fluid with its inlet and outlet conditions, an appropriate oil, and the mechanic compression principle. Based on that, the performance is expressed by the isentropic and volumetric efficiency. To describe a compressor in detail and fluid independent is challenging. Therefore, many theoretical studies have been conducted, while in comparison experimental studies are rare. To overcome this imbalance, this study focuses a detailed experimental investigation of a 4 kW Copeland scroll compressor with R410A and R32 on a fully automated compressor test stand. Within this paper, we present a method for in-depth uncertainty analysis, which ensures the usability and comparability of our experimental results to other experiments. We store our results in optimal calibrated simulation models based on optimal experimental design. This allows us to reduce experimental effort up to 70 % compared to full factorial experimental designs. To prove the method in a compressor and two fluids, we apply it to a fixed-speed scroll compressor with R410A and R32. The test stand is able to conduct all experiments automatically and part load behaviour of both refrigerants can be summarized in a model according to recent Literature with an overall uncertainty below 8 % for R410A. For R32, the method fails. Utilizing this method, we aim at open-source experiments in order to accelerate the solution of complex research questions.

Assessment of an energy efficient closed loop heat pump dryer for high moisture contents materials: An experimental investigation and AI based modelling

The aim of this study is to discuss the experimental performance analysis and deep learning based modelling of moist sodium polyacrylate material (also known as Orbeez) in a closed-loop heat pump dryer using R-134a as a secondary fluid. The experiments are performed on different weights of Orbeez at a constant air flow rate to calculate different performance parameters like coefficient of performance of the heat pump, drying rate, heat transfer rate by condenser, moisture extraction rate, and specific moisture extraction rate. The higher test loads such as 6, 7, and 8 kg are found better in terms of maximum coefficient of performance (5.2–5.8) and heat transfer rate (0.56–0.64 kW). Similarly, the higher test loads such as 6, 7, and 8 kg yield the highest moisture extraction rate (∼0.66–0.75 kg/h), specific moisture extraction rate (∼2.15–2.27 kg/kWh), and weight reduction (∼91%). The water removal rate depends on the moisture diffusivity, and it increases with an increase in the drying air temperature and drying air velocity. In addition, a deep learning model considering the most influential dryer inlet conditions (air temperature, air relative humidity, and airflow rate), time, and weight as the input features to estimate the dryer outlet conditions and weight reduction for assessment of drying kinetics of the considered material. A high accuracy (coefficient of determination = 0.997) makes it a simple, cost effective, and reliable method to predict the drying performance of various materials with a closed loop heat pump dryer.

English

BACKGROUND Indoor air pollution is responsible for more than 1.5 million deaths and 2.7 % of the global burden of disease as per WHO report. Globally, more than three billion people depend on solid fuels including biomass and coal. Nearly 4 million people die prematurely from illnesses attributed to household air pollution from inefficient cooking practices using polluting stoves paired with solid fuels and kerosene. As a customary involvement in cooking; women are obliged to breathe the air polluted with biomass fuels and tend to experience the largest exposures and health burdens. Hence this study was done to assess the determinants of indoor air pollution (IAP) and its health impact among women residing in rural areas of Bengaluru. METHODS A community based cross sectional study was conducted among household women residing in rural population of Bengaluru over a period of 4 months. Based on prevalence rate of sources for indoor air pollution being 49 % from the earlier studies the estimated sample was 500. Household women were interviewed by simple random sampling technique. RESULTS The mean age of the participants was 46.9 + 15yrs. where 42.4 % belonged to 40 - 59 yrs. of age group. In majority of households, 84.4 % used LPG as a cooking fuel. Type of fuel, second-hand smoking, smoke from the neighbourhood and use of mosquito repellents were found to be sources while poor housekeeping, inadequate ventilation, and lack of smoke outlet in kitchen were contributing factors for IAP. Irritation in eyes, cough, difficulty in breathing, running nose and chronic respiratory diseases were the perceived symptoms due to IAP. CONCLUSIONS Majority of households in the current study were exposed to IAP due to passive smoking, smoke from the neighbourhood and use of mosquito repellents while improper ventilation, absence of smoke outlet and humid conditions accentuated it. Community awareness program and cost effective interventions is the need of the hour. KEY WORDS Indoor Air Pollution, Rural Population, Women's Health

TEM Characterization of Long Term Aged Interconnect Oxide Layers from Real Stack

Steel interconnect robustness under SOFC conditions for extended operation remains a challenge. The observation and analysis of the interconnect microstructure aged in real conditions for long periods provides analysis data to help to understand degradation and potentially to design accelerated testing.In this study, TEM observations of the cross section of interconnects aged in real conditions (9000h and 20000h stacks) are presented. The interconnects are Crofer22APU with the air side coated with manganese cobalt oxide (MCO) to prevent chromium evaporation and increase oxidation resistance. FIB-prepared lamella from the inlet and outlet air side are analysed by TEM imaging and EDX. A major difference between inlet and outlet is the position of Mn-rich grains in the chromia scale: at the inlet, Mn-rich grains are located at the metal/chromia interface (figure 1(a)) while at the outlet, Mn-rich crystals are located close but not directly adjacent to the metallic bulk (figure 1(b)). The inlet microstructure has been observed in the literature in an oxidation study of MCO coated steel [1]. However, the outlet case which was observed for both the 9000h and 20000h aged stack samples was not yet reported in the literature, to the best of our knowledge. The difference between the inlet and outlet position was observed as well on a 15000h aged sample by SEM, and may be explained by differences between the inlet and outlet conditions: higher temperature at the outlet, as well as lower oxygen content. In addition to this particular Mn position, Fe particles are also observed in the chromia scale, confirming results previously described in the literature[2]. The analysis of the MCO coating also shows an inner denser layer, as expected after ageing at high temperature[3]. Analysis of the segregation of cobalt oxide at the MCO grain boundaries is also presented.More investigations are necessary to explain the complete oxidation mechanisms of the MCO-coated Crofer interconnect. However, the important role of the coating in interconnect oxidation is shown. The understanding of all reactions and the analysis of interconnects aged in real conditions, on different locations, should help designing more reliable combinations, better predictive models and possibly accelerated tests.[1] S. Molin et al., « Microstructural and electrical characterization of Mn-Co spinel protective coatings for solid oxide cell interconnects », J. Eur. Ceram. Soc., vol. 37, no 15, p. 4781-4791, déc. 2017, doi: 10.1016/j.jeurceramsoc.2017.07.011.[2] L. V. Gambino, N. J. Magdefrau, et M. Aindow, « Microstructural effects of the reduction step in reactive consolidation of manganese cobaltite coatings on Crofer 22 APU », Mater. High Temp., vol. 32, no 1-2, p. 142-147, janv. 2015, doi: 10.1179/0960340914Z.00000000090.[3] B. Talic, V. Venkatachalam, P. V. Hendriksen, et R. Kiebach, « Comparison of MnCo2O4 coated Crofer 22 H, 441, 430 as interconnects for intermediate-temperature solid oxide fuel cell stacks », J. Alloys Compd., vol. 821, p. 153229, avr. 2020, doi: 10.1016/j.jallcom.2019.153229. Figure 1

Energy performance analysis of a membrane dehumidification system

In warm and humid climates, a primary source of building energy consumption is dehumidification of conditioned air supplied to the building spaces. The system analyzed utilizes a selective membrane to remove water vapor from ambient air instead of a vapor compression cycle or a desiccant. This work analyzed a membrane dehumidification system with a focus on the system energy performance. A system performance goal was set by the project sponsor for an inlet air condition of 32.2 °C and 90% relative humidity, an outlet condition of 12.8 °C and 50% relative humidity and a total cooling load of 3.52 kW resulting in a target COP latent for the system of 3.34. Models of the basic system components were used to develop the system, analyze operating parameters and predict performance. The results indicate that the system requires two optimizations to meet the target performance: condenser pressure optimization and the use of multiple membrane segments operating at different pressures. Subsequently, a model was developed to analyze the performance of the final system configuration under a variety of operating conditions and yielded a maximum COP latent of 4.37 for membrane properties comparable to those of the earliest membrane module tested. This may be compared with a COP of about 3.5 for current refrigeration technology at these conditions. The best small membrane sample produced to date would increase the COP latent of the membrane system to well above 8, suggesting that the membrane system has high promise. Uncertainty analysis was also performed to assess the simulation results.

One-Dimensional Analysis of Double Annular Combustor for Reducing Harmful Emissions

The number of aircraft flights worldwide has increased steadily since the introduction of air transportation to the public. Accordingly, environmental issues caused by the exhaust gases of aircraft engines have emerged. In particular, international organizations have crafted emission regulations since gases exhausted during takeoff and landing have been identified as the direct cause of air pollution near airports. Nitrogen oxides (NOx) produced at high combustion temperatures and carbon monoxide (CO) due to incomplete combustion affect the performance of the combustion chamber. Therefore, annular combustors comprising two annular zones have been developed to reduce the emissions of these two substances, which occur under different conditions. Parameters that should be considered when modifying a conventional single annular (SAC) to a double annular combustor (DAC) are discussed herein. In this paper, an optimization algorithm for obtaining the main design parameters of the DAC is presented to minimize NOx and CO emissions and an operation solution for reducing carbon monoxide emission is identified. A thermodynamic model of a high-bypass turbofan engine (PS-90A) is used to establish the inlet and outlet conditions of the combustor. Analysis results show that NOx emissions can be effectively reduced by adjusting the design parameters and CO emissions can be significantly decreased by partially turning off the fuel supply based on the engine cycle.

Numerical analysis of the flow pattern in convergent vortex tubes for cyclone cooling applications

The use of swirling flows in cyclone cooling systems is a promising method for internal cooling applications for instance in the leading edge of gas turbine blades. However, vortex breakdown can occur in such flows, which is associated with an axial flow reversal.Within the scope of this investigation a numerical parameter study was conducted in order to explore the impact of convergent tube geometries on the flow pattern. For this purpose, Delayed Detached Eddy Simulations (DDES) were conducted for a Reynolds number of 10,000 and a swirl number of 5.3. First of all, the numerically obtained velocity field was compared to experimental data for a reference tube with a constant cross-section. This validation showed overall good agreement. Subsequently, the same reference tube was compared to four convergent tubes. The latter ones comprised three geometries with linearly decreasing diameters reaching convergence angles of 0.42deg., 0.61deg. and 0.72deg., respectively. Furthermore, an additional tube featuring a hyperbolic diameter decrease was considered.The current investigation demonstrates that convergent vortex tubes impose a flow acceleration that suppresses the vortex breakdown phenomenon. Moreover, the axial velocity can be associated to different flow regimes with supercritical and subcritical character. These regimes indicate that the flow field within convergent tubes is less affected by the outlet conditions. Moreover, a physical reason is given that explains the formation of different flow regimes and their associated backflow as pressure-driven phenomenon. Furthermore, a modified Q-criterion illustrates two double helix vortex systems that can both be stabilized by choosing an appropriate geometry.

Modeling approaches for temperature-programmed gas chromatographic retention times under vacuum outlet conditions

This contribution evaluates the performance of two predictive approaches in calculating temperature-programmed gas chromatographic retention times under vacuum outlet conditions. In the first approach, the predictions are performed according to a thermodynamic-based model, while in the second approach the predictions are conducted by using the temperature-programmed retention time equation. These modeling approaches were evaluated on 47 test compounds belonging to different chemical classes, under different experimental conditions, namely, two modes of gas flow regulation (i.e., constant inlet pressure and constant flow rate), and different temperature programs (i.e., 7 °C/min, 5 °C/min, and 3 °C/min). Both modeling approaches gave satisfactory results and were able to accurately predict the elution profiles of the studied test compounds. The thermodynamic-based model provided more satisfying results under constant flow rate mode, with average modeling errors of 0.43%, 0.33%, and 0.15% across all the studied temperature programs. Nevertheless, under constant inlet pressure mode, lower modeling errors were achieved when using the temperature-programmed retention time equation, with average modeling errors of 0.18%, 0.18%, and 0.31% across the used temperature programs.

Experimental and Numerical Study of Laminar-Turbulent Transition on a Low-Pressure Turbine Outlet Guide Vane

AbstractThis work presents an experimental and numerical investigation of the laminar-turbulent transition and secondary flow structures in a turbine rear structure (TRS). The study was executed at engine representative Reynolds number and inlet conditions at three different turbine load cases. Experiments were performed in an annular rotating rig with a shrouded low-pressure turbine upstream of the TRS test section. The numerical results were obtained using the shear stress transport k − ω turbulence model and the Langtry–Menter γ − θ transition model. The boundary layer transition location at the entire vane suction side is investigated. The location of the onset and the transition length are measured using IR-thermography along the entire vane span. The IR-thermography approach was validated using hot-wire boundary layer measurements. Both experiments and computational fluid dynamics (CFD) show large variations of transition location along the vane span with strong influences from endwalls and turbine outlet conditions. Both agree well with traditional transition onset correlations near midspan and show that the transition onset Reynolds number is independent of the acceleration parameter. However, CFD tends to predict an early transition onset in the midspan vane region and a late transition is present in the hub region. Furthermore, in the hub region, CFD is shown to overpredict the transverse flow and related losses.

A study on steam cycle optimization for integrating energy storage system to nuclear power plant

As the share of renewable energy will be increasing, there is a growing interest in flexible power sources and energy storage systems due to the intermittent nature of renewable energy. We propose the Energy Storage System (ESS) integrated Nuclear Power Plant (NPP) as a solution. The system operates on load-following by branching the mass flow from the steam cycle to the ESS without changing the reactor thermal output. However, the merging point can be different for heat storing ESS and work storing ESS because the outlet conditions of the ESS vary depending on the type of ESS. In this study, the merging points are categorized into two types, feedwater heater and condenser. At each merging point, cycle optimization is performed while increasing the branch flow into ESS. The optimization goal is to maintain the feedwater temperature at the inlet of a steam generator. The power output and energy delivered to the ESS according to the merging point are estimated. From this study, it was found that when 25% of the inlet mass flow rate to the low-pressure turbine is diverted to ESS, the overall output of the steam cycle is decreased by 44.17% for the heat conversion ESS and 49.95% for the work conversion ESS.

Computational Analysis Of 2d Aerospike Nozzle With Base Bleed At Different Altitudes

In the present-day scenario, several nozzles are being developed to achieve better efficiency. Among them, the aerospike is one such nozzle. The aerospike nozzles are yet to be utilized in the aerospace sector but are believed to exhibit better performance than the conventional bell-shaped nozzles that are currently in service. The geometry of the aerospike nozzle enables it to adjust to its environment by modifying its outer jet boundary thus, making it more efficient than the other types of nozzles.
 Simple approximation method is used to get the coordinates of the nozzle contour using MATLAB. To compare the performance characteristics, both full and truncated spike nozzles were designed using SOLIDWORKS. In order to improve the performance of the truncated aerospike nozzles, they are provided with base bleeds. The flow behaviour was analysed using Computational Fluid Dynamics (CFD) software – ANSYS. These designs were simulated for different pressure outlet conditions, to compare the performance of full length, truncated spike with and without base bleed, at different altitudes.

Study of flow over piano key weir of different plan shapes with free and partially submerged outlet conditions

Abstract Piano key weirs are being increasingly used for better flood passage downstream, both as a new structure or on top of hydraulic structures like a dam, to increase their discharging capacity as well as reservoir storage. Much research has been done on rectangular plan-form, while other plan-forms warrant attention. The present study focuses on two different plan geometries of PKW, i.e., rectangular (RPKW) and trapezoidal with angle α equal to 9 degrees (TPKW9) for their head-discharge relation in a wide channel of 0.984 m width under free-flow condition. Since the role of CFD is increasingly becoming prominent in present times, a numerical study using ANSYS-FLUENT was also carried out to ascertain its relevance in predicting flows around complex structures like PKW. Further, the tailgate was closed to render the PKW's outlet from partial to fully submerged conditions. The effect of these submerged outlets was studied for any changes in the discharging capacity of the PKW. The study shows RPKW to be more hydraulically efficient than TPKW9 for the model geometry. Further, the study finds that under partial to full submergence of PKW outlets, both PKW units' discharging capability remains unchanged.

Three-Dimensional Performance Analysis of a Radial-Inflow Turbine for Ocean Thermal Energy Conversion System

Turbine is one of the key components of the ocean thermal energy conversion system (OTEC), and its aerodynamic performance and geometric dimension affect the performance of the system directly. This paper proposes a design method for the radial inflow turbine suitable for the ocean thermal energy conversion based on the parameter optimization of the ocean thermal energy conversion system. Aiming at the application characteristics of marine thermal energy conversion in a small temperature difference environment and the special thermophysical properties of the organic working fluid in this environment, one-dimensional design and three-dimensional CFD analysis of the turbine is separately done, of which the results were compared. At the same time, the performance of the turbine was verified by changing the inlet and outlet conditions of the radial turbine under the design conditions. The conclusion is that the three-dimensional CFD results of the turbine are in good agreement with the one-dimensional design, and the internal flow field of the turbine is stable, without obvious backflow and eddy current, which meets the application requirements of the ocean thermal energy conversion.

Abstract P344: Validation of Computational Fluid Dynamics Against PC-MRI Measurements of Blood Flow in Healthy Intracranial Arteries: On the Threshold to Clinical Utility for Stroke Prediction

Aim: Computational Fluid Dynamics (CFD) modeling of blood flow is a promising technique to obtain hemodynamic biomarkers and predict recurrent strokes. Few studies, however, have validated CFD against other methods for measuring hemodynamics, e.g. phase contrast MRI (PC-MRI). To resolve the uncertainties about the accuracy of CFD, this study validates the results of an automated software that combines deep learning and CFD for simulating blood flow given an MR angiogram against PC-MRI. Methods: Intracranial arteries in 10 healthy volunteers (60% male, mean age 38 ± 16 years) were automatically segmented from TOF MRA obtained at 3T using deep learning. Subject-specific CFD modelling was undertaken. PC-MRI flow rate for each subject was used at the inlet boundary condition, but not at the outlets. Outlet boundary condition was set to lumped parameter Windkessel model, with the resistance programmatically determined using allometric scaling laws based on the dimension and branching of vasculature. For comparison, two commonly used outlet conditions (exponent 2 & 3 in Murray’s Law) were also considered. CFD results for flow rate and wall shear stress were compared against PC-MRI using Pearson’s correlation coefficient. Results: The flow rate across major intracranial arteries from CFD was in excellent agreement with the PC-MRI (MCA: r = 0.83, ACA: r = 0.81 & PCA: r = 0.82). In addition, there was good correlation for both wall shear stress (WSS) and WSS Ratio (WSSR, i.e. the ratio of WSS between a branch and its parent vessel) (MCA (WSS/WSSR): r = 0.6/0.77, ACA (WSS/WSSR): r = 0.86/0.93 & PCA (WSS/WSSR): r = 0.72/0.85). The inter-subject variability of the flow rate (i.e. standard deviation) obtained from CFD matched closely the variation range observed from PC-MRI and the literature. The two alternative outlet models behaved similarly but suffered from vessel truncation and high errors in some cases. Conclusion: CFD modelling of blood flow in intracranial arteries from static images has good agreement with PC-MRI measurements when allometric scaling laws are applied for setting Windkessel outflow conditions. This lays the foundation for using CFD to predict recurrent strokes as the technique uses standard MRA images already commonly acquired for stroke evaluation.