Dynamic Inlet Research Articles

Dynamic thermal performance analysis and experimental study of cascaded packed-bed latent thermal energy storage integrated solar trough collectors

The instability of the renewable energy significantly impacts the thermal performance of solar thermoelectric systems. In this paper, a coupling system consisting of solar trough collector and double-layer cascaded packed-bed latent heat storage system (PLTES) is constructed to investigate thermal performance and operating parameters under dynamic conditions. Additionally, the experimental platform was upgraded to evaluate the dynamic charging/discharging process of the cascaded PLTES. The results show that under dynamic inlet heat flow, the PLTES exhibits only one peak temperature difference, and the average temperature is lower than that in the steady-state. The cascade-packed structure promotes a more uniform temperature and liquid phase distribution, resulting in a longer heat flow output. Higher mass flow rates of the heat flow increase convective heat transfer and reduce the temperature difference, though they have little effect on the energy efficiency. Conversely, an increase in capsule diameter significantly reduces the energy efficiency. Experimental results indicate that under dynamic conditions, the total charge-discharge capacity of the cascade system decreases by 0.5 MJ and 0.9 MJ, and the energy efficiency decreases by 0.15. Nevertheless, the energy efficiency of the cascaded PLTES (0.57) is higher than that of the single layer (0.5).

Operational strategy optimization of an existing ground source heat pump (GSHP) system using an XGBoost surrogate model

Ground source heat pumps (GSHPs) are experiencing a surge in popularity due to their efficient use of geothermal energy for building heating and cooling. Optimizing GSHP systems is crucial for maximizing heat extraction efficiency. However, existing research primarily focuses on design-stage optimization, neglecting the potential of improving operational strategies in already deployed systems. This study proposes a novel method for optimizing the operational strategy of existing GSHPs with machine-learning-based surrogate models. Our approach considers both demanded heat extraction and the variability of GSHP operation, including running and idle times. First, a numerical model is established with a closed-loop procedure replicating real-world GSHP operation, capturing dynamic inlet temperature changes. The Latin hypercube sampling is subsequently employed to generate sufficient data for XGBoost model development, where a designed disassembly method is proposed to shed light on the problem of a fixed number of input parameters. The operational strategy of the GSHP system is then implemented to offer solutions for both regular and irregular modes. The effectiveness of the method is validated using 40 days of real-case monitoring data. The results demonstrate that the surrogate model achieves high accuracy, with an absolute temperature difference error below 0.1 K and a heat extraction absolute percentage error (APE) less than 2.0 %. Additionally, the optimized operational strategy reduces total operation time by 2–9 % solely through scheduling adjustments, showcasing its significant practical potential. This study presents an efficient method for optimizing the operational strategies of existing GSHPs while highlighting the value of process-accelerated optimization using numerical simulation-based surrogate models.

Experimental investigation of wind turbine stress and power characteristics under dynamic changes in wind direction

ABSTRACT The dynamic inlet conditions of variable wind direction had an obvious influence on the response of wind turbine stress and power, and accurately analyzing their changing characteristics is of great significance to enhancing wind turbines’ stability and efficient operation. Experiments were performed in a wind tunnel, where the wind turbine was mounted on a rotating platform to simulate dynamic changes in wind direction at prescribed speeds and angles. The wind turbine’s stress and power were measured. Results show that the stress was minimally reduced by 4.4% (tower) and 1.7% (blade) when the wind direction change angle was small. Maximum stress reduction of 92% (tower) and 93% (blade) with increasing wind direction change angle. As the wind direction change speed increased, the magnitude of the drop in blade stress decreased by 6% ~32%. The decrease in power coefficient and rotational speed at small wind direction change angles and large wind direction change speeds were not significant, and the fluctuations were more obvious. The coupling of aerodynamic deterioration and inertial effects during dynamic changes in wind direction was one of the main reasons for the variations in the wind turbine power and stress response.

Numerical model of PCM heat exchange based on dynamic boundary

Using phase change material (PCM) to store solar energy can effectively alleviate energy and environmental problems. The accurate numerical models are the guarantee to promote the practical application of hydrated salt PCM. However, the phenomenon of supercooling and phase change hysteresis makes the PCM present various operating states under the actual dynamic inlet boundary conditions, which makes it difficult to solve the temperature field. In this study, a numerical model is established, which can independently determine whether each computing node is in the heating mode, the cooling mode, the heating after partial solidification mode, or the cooling after partial melting mode at each moment. The calculation codes for the first two modes in the model have been verified experimentally, and the latter two modes are modeled using the curve scale method proven to be the most accurate. To test the running process of the numerical model, a dynamic inlet boundary condition was constructed and input. The operation results show that the numerical model can smoothly switch the mode of each node and then solve it.

Feasibility Assessment of a Dual Intake-Port Scroll Expander Operating in an ORC-Based Power Unit

The main driver of research in the road transportation sector is almost certainly the development of technologies which allow for the reduction of CO2 emissions from internal combustion engines (ICEs). Wasted heat recovery (WHR) from the exhaust gases of ICEs based on organic rankine cycle (ORC) power units is one of the most promising technological solutions. However, several issues are raised when the recovery unit is scaled down to small applications, not to mention the fact that thermal sources are characterized by their intrinsically transient nature, as is the case with ICEs. In fact, this leads the ORC unit having to work frequently in off-design conditions. To successfully overcome this issue, the proper design and selection of the expanders are crucial. They are generally chosen from volumetric-type machines, thanks to their capacity to deal with time-varying thermo-fluid dynamic inlet properties. Among them, scroll machines represent one of the best solutions, despite them not yet being optimized as expanders, with them having been studied more as compressors. Dual-intake-port (DIP) technology is a novel solution used to enhance the performance of scroll machines. The effectiveness of this technology was assessed thanks to a comprehensive, experimentally-validated theoretical model of the scroll. It demonstrated that DIP technology can produce a 25% increase in mechanical power with respect to the baseline machine, without modifying the in–out pressure ratio. Maintaining a constant pressure difference across the expander at 5.6 bar, the power grew from 1131 W to 1410 W with the adoption of DIP technology. This power boost is lower than that achieved with a comparable DIP sliding rotary vane expander (SVRE) already studied by the authors, but the DIP Scroll achieved a higher efficiency (50–60%) when compared to the DIP SVRE case (40%).

Fast, Miniaturized, Real-Time Unit for Sampling, Modulation, and Separation in Detection of Hazardous Chemicals.

A sampling, modulation, and separation (SMS) unit was tested for detection of hazardous chemicals. The SMS unit, designed and developed for on-site sampling and analysis, consists of a dynamic inlet system coupled with a fast, miniaturized gas chromatograph (GC). Feasibility of the SMS unit was evaluated together with a hazardous chemical vapor generator. The performance of the SMS unit was tested with automated thermal desorption after SMS to collect samples for GC-mass spectrometry (GC-MS) measurements. Detection of sarin nerve agent was verified. Additionally, the vapor generator was connected to the SMS unit, which was hyphenated with a photoionization detector (PID), thus creating a fast GC-PID system. This system gave a positive response for degradation products of sulfur mustard, thereby indicating suitability of the SMS-PID unit for field drone applications.

Physics-Based Simulations of Flow and Fire Development Downstream of a Canopy

The behavior of a grassland fire propagating downstream of a forest canopy has been simulated numerically using the fully physics-based wildfire model FIRESTAR3D. This configuration reproduces quite accurately the situation encountered when a wildfire spreads from a forest to an open grassland, as can be the case in a fuel break or a clearing, or during a prescribed burning operation. One of the objectives of this study was to evaluate the impact of the presence of a canopy upstream of a grassfire, especially the modifications of the local wind conditions before and inside a clearing or a fuel break. The knowledge of this kind of information constitutes a major element in improving the safety conditions of forest managers and firefighters in charge of firefighting or prescribed burning operations in such configurations. Another objective was to study the behavior of the fire under realistic turbulent flow conditions, i.e., flow resulting from the interaction between an atmospheric boundary layer (ABL) with a surrounding canopy. Therefore, the study was divided into two phases. The first phase consisted of generating an ABL/canopy turbulent flow above a pine forest (10 m high, 200 m long) using periodic boundary conditions along the streamwise direction. Large Eddy Simulations (LES) were carried out for a sufficiently long time to achieve a quasi-fully developed turbulence. The second phase consisted of simulating the propagation of a surface fire through a grassland, bordered upstream by a forest section (having the same characteristics used for the first step), while imposing the turbulent flow obtained from the first step as a dynamic inlet condition to the domain. The simulations were carried out for a wind speed that ranged between 1 and 12 m/s; these values have allowed the simulations to cover the two regimes of propagation of surfaces fires, namely plume-dominated and wind-driven fires.

Numerical Study of Nacelle Wind Speed Characteristics of a Horizontal Axis Wind Turbine under Time-Varying Flow

Nacelle wind speed transfer function (NTF) is usually used for power prediction and operational control of a horizontal axis wind turbine. Nacelle wind speed exhibits high instability as it is influenced by both incoming flow and near wake of a wind turbine rotor. Enhanced understanding of the nacelle wind speed characteristics is critical for improving the accuracy of NTF. This paper presents Reynolds-averaged Navier–Stokes (RANS) simulation results obtained for a multi-megawatt wind turbine under both stable and dynamic incoming flows. The dynamic inlet wind speed varies in the form of simplified sinusoidal and superposed sinusoidal functions. The simulation results are analyzed in time and frequency domains. For a stable inlet flow, the variation of nacelle wind speed is mainly influenced by the blade rotation. The influence of wake flow shows high frequency characteristics. The results with stable inlet flow show that the reduction of the nacelle wind speed with respect to the inlet wind speed is overestimated for low wind speed condition, and underestimated for high wind speed condition. Under time-varing inflow conditions, for the time scale and fluctuation amplitude subject to the International Electrotechnical Commission (IEC) standard, the nacelle wind speed is mainly influenced by the dynamic inflow. The variation of inflow can be recovered by choosing a suitable low pass filter. The work in this paper demonstrates the potential for building accurate NTF based on Computational Fluid Dynamics (CFD) simulations and signal analysis.

Numerical Simulations of a Gas–Solid Two-Phase Impinging Stream Reactor with Dynamic Inlet Flow

Fluid flow characteristics and particle motion behavior of an impinging stream reactor with dynamic inlet flow (both inlet velocity patterns exhibit step variation) are investigated and discussed with the computational fluid dynamics–discrete element method (CFD–DEM). The effect of T (variation period of the dynamic inlet flow) and ∆u (inlet velocity difference) on the motion characteristics of single and multiple particles, as well as the mean particle residence time, are studied and discussed. The research results indicate that, compared with the traditional impinging stream reactor (both inlet velocities are equal and constant) with equal mean inlet velocity (um) within one period, the impinging surface is instantaneously moving and the flow regime is varied with time in the impinging stream reactor with dynamic inlet flow. The impinging stream reactor with dynamic inlet flow provides higher cost performance over the traditional impinging stream reactor, under equal um, in terms of single-particle residence time. Moreover, three new particle motion modes exist in multi-particle motions of the impinging stream reactor with dynamic inlet flow; particles are accelerated by the original or reverse fluid and perform oscillatory motion at least once after an interparticle collision. Whether it is a single particle or multi-particles, the mean particle residence time reaches a maximum value when T/2 is approximately equal to the first particle acceleration time, since the maximum axial kinetic energy increases in every oscillatory motion compared with traditional impinging stream, and the number of oscillatory motions is increasing. The mean residence time of a particle in the impinging stream reactor with a dynamic inlet flow increases with increasing ∆u, since the dynamic inlet conditions and increasing ∆u can continuously supply more energy to particles and thus cause more particles to enter one of the three new modes of particle motion.

Field and numerical investigations of the morpho-hydrodynamic processes of the tidal inlet at Shippagan Gully, New Brunswick, Canada

ABSTRACT This paper presents the result of a multiyear study consisting of field measurements and numerical modeling of a highly dynamic tidal inlet located on the west side of the Gulf of Saint Lawrence near Le Goulet, New Brunswick, Canada. Due to a lack of human intervention in the past few decades, natural processes have taken hold of this tidal inlet and large volumes of sediment have been deposited within the inlet. The Shippagan Gully inlet transects the Acadian Peninsula and is therefore subject to tidal forcing from both ends. An appreciable phase lag present in the two open ocean boundaries results in ebb flows through Shippagan Gully, which regularly exceed 2 m/s, to be twice as strong as the flood flows. This flow imbalance along with a long history of human intervention has created a complex and highly dynamic tidal inlet. The purpose of the study was to develop a numerical model of the hydrodynamic and morphological processes that occur at Shippagan Gully and to use the model to assess alternative engineering measures that could be implemented to promote a safe and navigable channel through the inlet.

Experimental and Numerical Studies on Flow and Turbulence Characteristics of Impinging Stream Reactors with Dynamic Inlet Velocity Variation

Impinging stream technique has been widely used in engineering industries. Insufficient data are available on the effects of dynamic inflow conditions on the flow and turbulence characteristics of an impinging stream reactor. In this study, we investigate and discuss the flow and turbulence characteristics of an impinging stream reactor with dynamic inlet velocity variation, e.g., sinusoidal, parabolic, step or triangular variation. The effects of period, amplitude, phase difference, mean inlet velocity and type of dynamic inlet velocity variation on the motional behaviors of the impinging surface and the mean turbulence kinetic energy (k) of the impingement region are investigated and discussed using particle image velocimetry (PIV) and computational fluid dynamics (CFD) at various values of L/D (the ratio of impinging spacing to nozzle diameter). The results show that the impinging surface makes back-and-forth motions in impinging stream reactors with dynamic inlet velocity variation. The mean k of the impingement region during one period is dominated by both the inlet velocity conditions and the geometric configuration. Dynamic inflow conditions bring more turbulence energy and pulsating characteristics to impinging zones over constant inlet velocity for an instantaneously moving impinging surface. Impinging stream reactors with dynamic inlet velocity variation provides more intense turbulence properties over conventional impinging stream reactors at the same mean inlet velocity. This work shows that the impinging streams with dynamic inlet velocity variation has strong potential for future relevant reactors and processes for engineering applications.

Numerical Investigation of Icing Effects on Dynamic Inlet Distortion

The effect of the simulated ice accretion on the dynamic distortion of a diffusing S-duct inlet is numerically investigated. The LES turbulence model is used to simulate the unsteady flow separation and vortex shedding from the duct curvatures and ice accretion. The numerical methods for unsteady-flow solutions are validated with the wind-tunnel test data for dynamic inlet distortion. The results show that the protruding glaze ice horns create the strong vortex shedding structures that produce additional flow unsteadiness at the inlet engine face. In particular, the symmetrical glaze ice that uniformly covers the entire inlet lip increases the total pressure loss and fluctuation level more than the asymmetrical glaze ice with a less blockage to inlet flow. Furthermore, the symmetrical glaze iced inlet induces 17 times more severe instantaneous peak distortion than clean inlet at the free stream Mach number of 0.34.

Tidal exchange in a choked coastal lagoon: A study of Mundaú Lagoon in northeastern Brazil

Changes in the inlet morphology of choked coastal lagoons often restrict the water exchange with the sea, making them vulnerable to pollution events and eutrophication processes. In this study, the importance of tides for the water exchange was investigated in Mundaú Lagoon, which is a choked lagoon located in northeastern Brazil that has a very dynamic inlet and channel system. The analysis was carried out for critical scenarios during the dry season when the river flow to the lagoon decreases markedly. The concepts of integrated flushing time and spatially distributed residence time scales were applied using a Lagrangian particle tracking approach coupled with a hydrodynamic model. The flushing time of Mundaú Lagoon was estimated to be 12.6 days during neap tide and 5.7 days during spring tide, including a return flow factor. Employing an e-folding form, the corresponding value was calculated to be 64 and 54 days for particles allowed and not allowed to return to the lagoon, respectively. The spring tides were responsible for the most pronounced water exchange in the Mundaú Lagoon. Different particles release times displayed the effect of the initial tidal conditions on the flushing time; lower exchange times were estimated for releases during ebb tides and spring tides. The integrated estimation of the water exchange when imposing a scenario of most frequent wind conditions indicated a considerable delay caused by this forcing, increasing the flushing time up to 23 days. Another observed effect of the wind was a spatial redistribution of the tidal exchange in the lagoon into different zones with similar residence time.

Asymptotic analysis for the inlet relative humidity effects on the performance of proton exchange membrane fuel cell

In order to study the inlet relative humidity (RH) effects on the performance of proton exchange membrane fuel cell (PEMFC), the inlet humidification efficiency (IHE) model is proposed. The total water content of PEMFC is consisted of two parts including the internal electro-migration water content and the external water content of the humidified gas. The dynamic inlet humidification efficiency is derived. The current density of PEMFC is calculated by the incorporating parameters including inlet humidification efficiency and water content of the humidified gas in the IHE model. Firstly, the schedule diagram of calculation is given and the geometric model is established according to actual size of PEMFC. The computational meshes are partitioned by using the software (Gambit). The IHE model is imported into the computational fluid dynamics software (Fluent). Secondly, the experimental system is established and experiments have been done at the operating temperature of 70 °C and at 40% RH, 55% RH, 70% RH, 85% RH and 100% RH, respectively. Finally, the contours of H2O molar concentrations (both in anode channels and cathode channels), membrane water content (MWC) and polarization curves of the IHE model, the Fluent model and experimental are compared and analyzed at above experimental conditions. The results show that the species distribution uniformities of the IHE model such as H2O molar concentrations (both in anode channels and cathode channels) and MWC are the best when the PEMFC at 100% RH. When the operating temperature is 70 °C (40% RH and 350mA/cm2), the accuracy of the IHE model is improved by 79% compared with the Fluent model. When the operating temperature is 70 °C (40% RH and 350mA/cm2), the inlet humidification efficiency reaches 57%.

Preparation of Helium Isotope‐certified Reference Materials by Gravimetry

An advanced gravimetric system was used to produce certified reference materials of mixtures of helium isotopes, traceable to the Système International d'Unitès (SI unit) of moles. Critical factors in developing isotope reference mixtures include the purity assessment of the source gases before preparation, the weighing system used for gravimetric mixing, a well‐developed gas filling system, and internal consistency among the mixtures. Three artificial helium isotope reference mixtures were prepared with absolute isotope ratios, R( 4He/ 3He), of 18.905 ± 0.036, 98.78 ± 0.21, and 209.82 ± 0.44 (k = 1), respectively. The internal consistency between the mixtures was verified using a precision single‐focusing magnetic sector‐type mass spectrometer with a dynamic inlet system. The results showed that the proportions of the three reference isotope mixtures were well within the measurement uncertainty. The isotope reference mixtures were produced with the highest metrological uncertainty level.

HYDRODYNAMIC AND MORPHOLOGIC MODELING OF ALTERNATIVE DESIGN SCENARIOS FOR SHIPPAGAN GULLY, NEW BRUNSWICK CANADA

This paper describes a comprehensive study comprising field measurements and numerical modeling of hydrodynamic and sedimentary processes undertaken to help assess alternative engineering measures for promoting and maintaining a stable and safe navigation channel through a dynamic tidal inlet. Shippagan Gully is a dynamic tidal inlet located on the Gulf of St-Lawrence near Le Goulet, New Brunswick, Canada. The tidal lagoon transects the Acadian Peninsula, hence the flows through the inlet are controlled by the tidal phase lag between the two open boundaries. Due to the nature of this phase lag, the ebb flows through Shippagan Gully, which regularly exceed 2 m/s, are typically twice as strong as the flood flows. As a consequence of this imbalance, the hydrodynamic and sedimentary processes at the inlet, and the morphologic features produced by these processes, are strongly dominated by the ebb flows. Over the past decades, shipping activities through Shippagan Gully have been threatened due to sediment deposition along the east side of the inlet which has caused the channel to narrow and shift westward. The objective of the present study was to develop an improved numerical model of the hydrodynamic and sedimentary processes at Shippahan Gully, and then apply the model to assess different engineering interventions for stabilizing the inlet and improving navigation safety.

Influence of Working Parameters on Dynamic Pressure Effect of Heavy Constant Flow Hydrostatic Center Rest

In order to increase the working performance of a heavy constant flow hydrostatic center rest, a theoretical study concerning the lubricating oil film dynamic pressure effect of the heavy constant flow hydrostatic center rest is described. The Computational Fluid Dynamics and the Finite Volume Method have been used to compute numerically the static pressure field and the total pressure field of the lubricating oil film. The influences of spindle rotating rate, lubricating oil dynamic viscosity and inlet flow rate on the lubricating oil film dynamic pressure effect of the heavy constant flow hydrostatic center rest were analyzed based on the computational fluid dynamics and lubrication theory, and the influencing laws were revealed. By means of this method, the reasonable data can be provided for reasonably controlling dynamic pressure and structure optimal design of the heavy constant flow hydrostatic center rest.

MORPHOLOGICAL MODELING OF A HIGHLY DYNAMIC TIDAL INLET AT SHIPPAGAN GULLY, CANADA

This paper is presenting the results of an extensive field and numerical modeling investigation of a morphologically dynamic tidal inlet. Shippagan Gully is a tidal inlet located near Shippagan, New-Brunswick, Canada, on the Gulf of Saint Lawrence. It is a particularly complex tidal inlet due to the fact that its tidal lagoon transects the Acadian peninsula and is open to the Bay des Chaleurs at its opposite end. As such, two open boundaries with phase lagged tidal cycles drive flow through the inlet, alternating direction with each tide and reaching velocities in excess of 2 m/s. Hydrodynamic and morphological processes at the site are further complicated by the presence of a highly variable wave climate. Presently, shipping practices through the inlet are limited due to continual sedimentation within and immediately offshore from Shippagan Gully. As such, an extensive field study, desktop analysis and numerical and morphological modeling of Shippagan Gully have been conducted in order to provide guidance for future works. Modeling was conducted using the CMS-Wave and CMS-Flow numerical modeling system. Sedimentation inside the inlet was shown to be ebb tide-induced deposition; while wave induced deposition was demonstrated elsewhere. The methodology and selected results of this study are presented herein.

A model and simulation of cathode flooding and drying on unsteady proton exchange membrane fuel cell

A water balance has a significant impact on the overall system performance in proton exchange membrane fuel cell. An actual fuel cell application has a dynamic electrical load which means also dynamic electrical current. Therefore, since this electrical current is known, the water production from the fuel cell reaction is also able to be predicted. As long as the fuel cell water transportation model is provided, the present liquid water inside the porous medium is also able to be modeled. A model of the liquid water saturation level in a fuel cell in unsteady load condition was proposed. This model is a series of the water transportation model of water saturation level for the final output of proton exchange membrane (PEM) fuel cell to predict the flooding or drying of PEM fuel cell. The simulation of vehicle fuel cell in different dynamic load profiles and different inlet air conditions was done using this model. The simulation result shows that PEM fuel cell with different dynamic load profiles has different liquid water saturation level profiles. This means that a dynamic load fuel cell requires also a dynamic input air humidification.

압력에 따른 평행박막 밸브의 자율 변형을 이용한 수동형 유량 제어기의 동적특성 평가

본 연구에서는, 미소유체시스템 상에서 정밀한 유체 제어를 위해 입력압력이 변하여도 일정한 유량을 유지할 수 있는 수동형 유량제어기를 개발함에 있어, 주기적으로 변화하는 압력에 대한 유량제어기의 동적특성을 평가하였다. 압력 변화의 주기보다 짧은 시간 내에 유량을 측정하기 위하여 입자영상속도계(Particle Image Velocimetry, PIV) 방법을 이용하였다. 지름이 0.7μm 인 형광입자가 담긴 탈이온수를 유량제어기에 공급하고, 펄스레이저와 형광현미경을 이용하여 10μs 간격의 연속된 사진을 얻고 이를 분석하여 유량제어기를 통과한 후의 유체의 속도를 측정하였다. 개발된 유량제어기는 20kPa과 50kPa사이를 주기적으로 변화하는 60Hz 의 압력 하에서 0.194±0.014m/s 의 일정한 유속을 유지함을 실험적으로 확인하였다. 압력의 주파수를 1~60Hz까지 변화시켜가며 수행한 실험에서도 유량제어기는 압력의 주파수에 상관없이 5.82±0.29μl/s 의 일정한 유량 공급이 가능함을 확인하였다.