Enhanced Design of Flat Box Collector for Photovoltaic Thermal System Based on Numerical Computational Fluid Dynamics Simulation and Experimental Evaluation

The paper presents an extensive investigation of a small-scale sliding vane rotary expander operating with R245fa. The key novelty is in an innovative operating layout, which considers a secondary inlet downstream of the conventional inlet port. The additional intake supercharges the expander by increasing the mass of the working fluid in the working chamber during the expansion process; this makes it possible to harvest a greater power output within the same machine. The concept of supercharging is assessed in this paper through numerical computational fluid dynamics (CFD) simulations which are validated against experimental data, including the mass flow rate and indicated pressure measurements. When operating at 1516 rpm and between pressures of 5.4 bar at the inlet and 3.2 bar at the outlet, the supercharged expander provided a power output of 325 W. The specific power output was equal to 3.25 kW/(kg/s) with a mechanical efficiency of 63.1%. The comparison between internal pressure traces obtained by simulation and experimentally is very good. However, the numerical model is not able to account fully for the overfilling of the machine. A comparison between a standard and a supercharged configuration obtained by CFD simulation shows that the specific indicated power increases from 3.41 kW/(kg/s) to 8.30 kW/(kg/s). This large power difference is the result of preventing overexpansion by supercharging. Hence, despite the greater pumping power required for the increased flow through the secondary inlet, a supercharged expander would be the preferred option for applications where the weight of the components is the key issue, for example, in transport applications.

Propeller performance greatly influences the overall efficiency of the turboprop engines. The aim of this study is to perform a propeller blade shape optimization for maximum aerodynamic efficiency with a minimal number of high-fidelity model evaluations. A physics-based surrogate approach exploiting space mapping is employed for the design process. A space mapping algorithm is utilized, for the first time in the field of propeller design, to link two of the most common propeller analysis models: the classical blade-element momentum theory to be the coarse model; and the high-fidelity computational fluid dynamics tool as the fine model. The numerical computational fluid dynamics simulations are performed using the finite-volume discretization of the Reynolds-averaged Navier–Stokes equations on an adaptive unstructured grid. The optimum design is obtained after few iterations with only 56 computationally expensive computational fluid dynamics simulations. Furthermore, an optimization method based on design of experiments and kriging response surface is used to validate the results and compare the computational efficiency of the two techniques. The results show that space mapping is more computationally efficient.

In this paper the micro-channel methanol steam reforming reactor was studied, which one was designed to generate hydrogen, and the generated hydrogen was used in the vehicle fuel cells, especially in the high temperature proton exchange membrane (HT-PEM) fuel cells. Computational fluid dynamic simulations and experiments were carried out to investigate the performance of the micro-channel reactor under different design parameters. Through the combination of the numerical computational fluid dynamics simulations and the experiments, the performance of the micro-channel reactor was studied from the fluid flow characteristics (the fluid flow uniformity and the pressure drop) and the hydrogen production performance (the kinetics of the steam reforming reaction). The results indicated that the velocity uniformity coefficients in the inlet zones of the oxidizing side and the reforming side are high, the fluids inside the micro-channel reactor are uniformly distributed. The reaction to produce hydrogen from the methanol aqueous solution in the micro-channel reactor was simulated and tested, it indicated that the content of the reformed gas can meet the requirements. In addition, the temperature uniformity inside the micro-channel reactor was improved by adjusting the inlet temperature of the reforming side and the air volume of the oxidizing side. KeywordsMicro-channel reactorMethanol steam reformingHydrogenFuel cell

Numerical computational fluid dynamics simulations have been performed on 2D sandwich models to compare the performance of low‐temperature cofired ceramics (LTCC)/LTCC and Si/Si sandwiches used in reactive bonding. In the sandwich model layers of solder, silver and a reactive multilayer used to bond the substrates are modeled. Additional to this, the surrounding air environment is also modeled. For simulating the heat released by the multilayer system, a user‐defined function in the form of a square wave is written for the heat source with a defined width, corresponding to the reaction width, and this propagates at a fixed speed. Two sandwiches, one with LTCC/LTCC, and the other with Si/Si, are simulated and their response analyzed in terms of the solidification/melting of the solder and their respective time–temperature histories.

Due to its non-intrusive nature and ease of implementation, the Non-Intrusive Reduced Basis (NIRB) two-grid method has gained significant popularity in numerical computational fluid dynamics simulations. The efficiency of the NIRB method hinges on separating the procedure into offline and online stages. In the offline stage, a set of high-fidelity computations is performed to construct the reduced basis functions, which is time-consuming but is only executed once. In contrast, the online stage adapts a coarse-grid model to retrieve the expansion coefficients of the reduced basis functions. Thus it is much less costly than directly solving a high-fidelity model. However, coarse grids in heterogeneous porous media of flow models are often accompanied by upscaled hydraulic parameters (e.g. hydraulic conductivity), thus introducing upscaling errors. In this work, we introduce the two-scale idea to the existing NIRB two-grid method: when dealing with coarse-grid models, we also employ upscaled model parameters. Both the discretization and upscaling errors are compensated by the rectification post-processing. The numerical examples involve flow and heat transport problems in heterogeneous hydraulic conductivity fields, which are generated by self-affine random fields. Our research findings indicate that the modified NIRB method can effectively capture the large-scale features of numerical solutions, including pressure, velocity, and temperature. However, accurately retrieving velocity fields with small-scale features remains highly challenging.

Improving the efficiency of jet engines is essential to reduce aircraft emissions. This requires increases in High-Pressure Turbine (HPT) entry temperatures, resulting in a rise in thermal loading which is particularly problematic for the HPT blade tip. Hot gas leaks through the clearance gap between the blade and the casing causing high heat fluxes, most notably on the thin squealers which are challenging to adequately cool, expediting degradation and reducing efficiency. This work examines how tip temperatures can be reduced by using fanned holes to cool the blade tip instead of conventional cylindrical holes. Representative linear cascade experiments demonstrate a local 15–45% improvement in cooling film effectiveness across mass flow rates and tip clearances on the critical pressure side rim, and a 10% decrease in heat transfer coefficient across the tip. Numerical computational fluid dynamics simulations complement the experimental work and show that the diffusion of flow by the fanned cooling holes increases the attachment of the coolant to the blade, delays mixing with the mainstream gas and distributes the coolant over a larger surface area. As coolant mass flow increases, the improvement margin diminishes due to greater coolant separation from the blade surface at higher blowing ratios for both fanned and cylindrical cooling holes. Increasing tip clearance results in heightened coolant dilution caused by larger over-tip leakage mass flow rates.

The significance of long-span bridges being susceptible to wind-induced vibrations and the need for evaluating their aerodynamic performance is the focus of this study. The main emphasis is on experimental methods for assessing the bridges’ aerodynamic stability, using sectional model tests with the free vibration technique. The dynamic properties of the model are determined from the measured response, using various system identification methods, including the modified Ibrahim time domain (MITD) and iterative least squares (ILS) for two-degree-of-freedom systems and the logarithmic decrement method (LDM) and the Hilbert transform method (HTM) for single-degree-of-freedom (SDOF) systems. A new dynamic testing setup was designed to facilitate single-degree-of-freedom (heave and pitch) and coupled two-degree-of-freedom (2DOF) motion in a wind tunnel section model. The vertical and torsional stiffnesses of the model were adjusted with elastic springs. A Great Belt Bridge section model was selected for testing due to its streamlined aerodynamic shape. The direct and crossflow derivatives were extracted from the measured response using the system identification methods mentioned. Additionally, analytical studies and numerical computational fluid dynamics simulations were conducted to validate the experimental results. The study found that HTM is most effective in SDOF due to its ability to extract both damping and frequency from the nonlinear response, whereas the MITD method is faster in converging system parameters in 2DOF system tests. The experimental and numerical results are comparable to the flat plate, which confirms the streamlined behavior of the Great Belt section from an aerodynamic perspective.

Brain aneurysms occur when the wall of a blood vessel weakens and expands. The rupture of a brain aneurysm has devastating effects. However, the precise causes of this disease are still unknown, although it is believed that blood flow plays a key role. The flow within aneurysms is complex, difficult to measure and interpret, with more studies needed. The purpose of the present study is therefore to evaluate the decomposition of blood flow within aneurysms, to improve our understanding and potentially help separate pathological from physiological flow patterns. Direct numerical computational fluid dynamics simulations, using OpenFOAM, are evaluated using spectral proper orthogonal decomposition (SPOD) and triple decomposition, or phase-averaging, techniques. The velocity and the wall shear stress fields are decomposed. Phase-averaging is used to separate the base pulsatile and physiological laminar flow from the turbulent fluctuations, while the SPOD is used to identify the most energetic space–time coherent structures in the flow. The results obtained from the decomposition techniques are promising, in particular with the SPOD identifying a significant frequency peak around 25 Hz in the realistic aneurysm geometry studied here. In addition, two main vortical structures are identified in the mean flow. Decomposition assessments such as the ones performed in this study can have important consequences in the evaluation of aneurysm pathophysiology, considering that vascular walls may be affected differently depending on the flow structure and characteristic frequencies.

This paper studies the mixing manifold, a specific component of aeronautical low-pressure air conditioning systems, in an effort to optimize cabin thermal regulation. This component homogenizes hot and cold air fluxes using turbulent, incompressible swirl flows. We identify several flow regimes in the manifold, depending on boundary conditions and the absence or presence of flow control devices in the manifold. A scaled-down model (0.445) is first validated in terms of kinetic and thermal similarity, and is then used for the experimental part of the study. We then identify physical phenomena by acoustic analyses and numerical computational fluid dynamics simulations. We found a precessing vortex breakdown to be present in several of the configurations studied, creating high acoustic noise and vibratory fatigue problems. Solutions are then proposed to avoid these sources of passenger discomfort. The mixing manifold spatial dimensions are also reduced, striking a good compromise between flow-mixing quality, pressure loss, and acoustic noise, to meet aeronautical weight reduction specifications for composite structures.

ABSTRACTThe present study deals with the numerical analysis of the water droplet evaporation in the carrier gas inside an ultrasonic spray pyrolysis (USP) device. Droplet evaporation is studied through numerical computational fluid dynamics simulation using Ansys Fluent version 16.1 software. The governing equations for mass, momentum, and energy contain source terms for the effects of droplet evaporation. The results are provided as time dependent evaporation rate, temperature and diameter of droplet. Additional experimental evaporation of HAuCl4 solution droplets with temperatures of 80, 100 and 120°C was performed on a USP device. The obtained dried particles of gold chloride were characterized with TEM and analysed for their size and shapes to determine the effect of evaporation rate on the dried particle morphology. This provides insight into selecting optimal parameters for gold nanoparticle synthesis with HAuCl4 in USP, for targeted sizes and shapes of the nanoparticles.

This paper combines lumped parameter thermal network and flow network techniques to perform thermal analysis of electric machine. The method is applied to investigate the efficiency of a novel cooling design for a high-power-density motor based on airflow. A lumped thermal circuit is used to develop a theoretical model for the heat transfer problem of the machine. The 11 nodes and 19 thermal resistance thermal network circuit is used to discretize the heat equation while the 2 node flow network circuit is used to model convection which is fed back in the thermal circuit. The model is compared with numerical computational fluid dynamics simulation, performed on the CAD model of the machine. The machine is rated at 2kW, 40Arms, 15000 min^−1 with 2 pole-pairs surface permanent magnet.

Influence of fuel distribution on co-combustion of sludge and coal in a 660 MW tangentially fired boiler

An improved air amplifier design that takes advantage of the combined effects of aerodynamic and electrodynamic focusing was developed to couple a nanoelectrospray ionisation (nano-ESI) source and the heated mass spectrometer inlet to improve the sensitivity of a mass spectrometer. The new design comprises an electrodynamic ion funnel integrated into the main air pathway of the air amplifier to more effectively focus and transmit gas-phase ions from the nano-ESI source into the heated mass spectrometer inlet. Numerical computational fluid dynamics simulations were carried out using a commercial software package, ANSYS FLUENT, to provide more detailed information about the device's performance. The gas flow field as well as the electric field patterns and the Lagrangian ion motion were conveniently simulated using this single package and custom-written, user-defined functions. Experimental results show a nearly five-fold improvement in reserpine ion intensity with the air amplifier operated at a nitrogen gauge pressure of 40 kPa and no direct current (DC) or radiofrequency (RF) potentials applied to the ion funnel when the distance between the electrospray emitter and sampling inlet tube was 24 mm, as compared to direct sample infusion from the same distance without the air amplifier. More importantly, a nearly three-fold additional gain in ion intensity was measured when both DC and RF potentials were co-applied, resulting in more than a 13-fold overall ion intensity gain which could be attributed to the combined air amplifier aerodynamic and ion funnel electrodynamic focusing effect.

Extrusion-based bioprinting is a powerful tool for fabricating complex cell-laden constructs. Embedded ink writing (EIW) is an extrusion-based printing technique wherein a nozzle embedded into a support bath writes continuous filaments. Because it allows for low-viscosity inks, EIW is particularly useful for bioprinting. One of the largest challenges in extrusion-based bioprinting is limiting the damage that cells experience inside the nozzle. Longer shear stress durations and higher shear stress magnitudes lead to more damage. Shape fidelity is also critical for bioprinting. Filaments in EIW can exhibit defects such as sharp edges and large aspect ratios, which can lead to porosity, surface roughness, and poor mechanical properties in the final part. We use numerical computational fluid dynamics simulations in OpenFOAM to evaluate whether common shear stress mitigation techniques improve cell viability without causing shape defects. Critically, we find that using a conical nozzle, increasing the nozzle diameter, decreasing the print speed, and decreasing the ink viscosity can improve the viability of stress magnitude-sensitive cells, but using a conical nozzle, increasing the nozzle length, and decreasing the print speed can increase damage in stress duration-sensitive cells. Additionally, using a conical nozzle or a larger nozzle can lead to larger shape defects in printed filaments. Material selection and printing parameter selection in embedded bioprinting should take into account allowable shape defects, allowable cell damage, and cell type.

Following the development of the muffler with the optimal guide fins (MOGF) in the companion paper (Part 1), this study optimizes the muffler outlet in terms of structure and geometry to further improve the thermal uniformity of the hot‐side heat exchanger (HHE). Two outlet structures and two outlet geometry parameters (i.e., outlet angle φ and outlet position y) are proposed. The exhaust flow uniformity of HHE serves as an assessment criterion in numerous computational fluid dynamics simulations to determine the optimal outlet structure and optimal values of φ and y. The outlet of the MOGF is then modified based on the simulation results to create the muffler with the optimal guide fins and outlet (MOGFO). Various experiments on the MOGFO are conducted to verify the simulation results and evaluate the improvement of the HHE's thermal uniformity. The simulation results prove that the optimal outlet improves the exhaust flow uniformity by 1.78% on average compared with the original outlet. In experiments, the combination of optimal muffler's outlet and optimal muffler's guide fins on the MOGFO raises the thermal uniformity of HHE by an average of 22.71% and 50% compared with the MOGF and the muffler model with nonoptimal guide fins and outlet in Part 1, respectively. The remarkable outcomes of this paper, together with Part 1, are expected to enhance the efficiency and lifespan of the thermoelectric generator unit.