Large Pressure Research Articles

Stability Analysis of Cofferdam with Double-Wall Steel Sheet Piles under Wave Action from Storm Surges

Double-wall steel sheet piles (DSSPs) are widely used in large-span cofferdams for docks due to their good performance against wave action during storm surges. This paper describes a study of the dynamic behavior of a DSSP cofferdam under wave action through flume tests and a numerical simulation that combined computational fluid dynamics (CFD) and the finite element method. The influences of the water level and wave height on the DSSP cofferdam were investigated experimentally and numerically. Tall waves in shallow water broke upon and impacted the seaside pile with large dynamic wave pressure, dramatically increasing the stress and displacement of the seaside pile. The overlap of the traveling and reflected waves increased the excess pore water pressure near the seaside pile due to taller overlapped waves and higher wave frequency. The DSSP cofferdam failed under the combined actions of the dynamic wave pressure and erosion of the landside seabed. The leakage and overflow of the breaking waves resulted in significant erosion of the landside seabed and greatly weakened the support of the seabed. The dynamic wave pressure then pushed the DSSP cofferdam until it failed. The simulation with the combined methods of CFD and FEM resulted in trends that were similar to those of the test measurements. Compared to the quasi-static method and pseudo-dynamic method, the results of the simulation via the present method were much closer to the test results because the simulation included the effects of breaking waves. The reinforced measure worked well to prevent the DSSP cofferdam in a sandy seabed foundation from continuous failures of deformation–leakage–erosion–tilting. However, it failed in a clay interlayer seabed foundation due to the large settlement.

Analysis of unsteady flow and pressure pulsation of multistage centrifugal pump based on actual size

In this paper, the unsteady flow and pressure pulsation in 11-stage centrifugal pump were analyzed based on large eddy simulation. The performances from the numerical simulation agreed with the ones from the experiment. The numerical results show that large pressure gradient area appears on trailing edge of blade pressure surface, and large vorticity intensity area appears on blade suction surface and trailing edge. The vortexes in the impeller passage decrease obviously with the increase of flow rate from 0.4 Q to 1.2 Q. As the stage increase, there is a local high pressure area at the tongue and it affects the fluid backflow. The main frequency of the pulsation at the impeller inlet is the blade passing frequency ( fBPF), and the main frequency at the impeller outlet and the interface is 2 fBPF. Due to interstage interference, the main frequency of the second impeller includes blade passing frequency of the first stage impeller (5 fn) and its own blade passing frequency (7 fn). With the increase of the stages, the rule of pulsation gradually tends to be consistent.

Analytical prediction for time-dependent interaction of a circular tunnel excavated in strain-softening rock mass

Viscoelastic plastic solutions for tunnel excavation in strain-softening rock mass and tunnel-rock interaction are proposed based on the Mohr-Coulomb and the Generalized Zhang-Zhu (GZZ) strength criterion considering stress path. The solutions are verified by numerical simulations, results show that the theoretical solutions are close to the simulated data. The evolutions of rock stresses, strains, displacements and support pressure were investigated and the influences of residual strength parameter, support stiffness, support timing, initial support pressure and viscosity coefficient on the rock deformation and the support pressure are discussed by proposed solution. It is found that strain-softening results in large deformation and high support pressure, with stiffer support and a larger viscosity coefficient contributing to even greater support pressure. Ductile support is recommended at the first stage to release the energy and reduce the support pressure by allowing a relatively large deformation. The support pressure, especially the additional support pressure at the second stage will be much smaller if a higher initial support pressure is applied at the first stage. This can not only control the displacement rate of surrounding rock and improve the tunnel stability at the first stage by exerting sufficient support pressure immediately after tunnel excavation, but also greatly reduce the pressure acted on permanent support and improve the structure stability at the second stage. Therefore, to avoid the instability of support structure, ductile support, which could not only deform continuously but also provide sufficient high support pressure, is recommended at the first stage.

An integrated EOS, pore‐crush, strength and damage model framework for near‐field ground‐shock

AbstractAn integrated Equation of State (EOS) and strength/pore‐crush/damage model framework is provided for modeling near to source (near‐field) ground‐shock response, where large deformations and pressures necessitate coupling EOS with pressure‐dependent plastic yield and damage. Nonlinear pressure‐dependence of strength up to high‐pressures is combined with a Modified Cam‐Clay‐like cap‐plasticity model in a way to allow degradation of strength from pore‐crush damage, what we call the “Yp‐Cap” model. Nonlinear hardening under compaction allows modeling the crush‐out of pores in combination with a fully saturated EOS, that is, for modeling partially saturated ground‐shock response, where air‐filled voids crush. Attention is given to algorithmic clarity and efficiency of the provided model, and the model is employed in example numerical simulations, including finite element simulations of underground explosions to exemplify its robustness and utility.

Optimization and performance improvement of ultra-low temperature cascade refrigeration system based on the isentropic efficiency curve of single-screw compressor

In this paper, a cascade refrigeration system equipped with a single-screw compressor (SSC-CRS) is proposed and built in order to achieve the goal of high load cooling capacity under ultra-low temperature conditions. Firstly, the isentropic efficiency curve of the single-screw compressor (SSC) is fitted through experimental method in response to the characteristics of low suction temperature and large pressure ratio of the compressor. In addition, the analysis of SSC-CRS with 28 refrigerant pairs are made to compare the coefficient of refrigeration (COP) and power consumption. On the basis of the cascade system, the paper compares the improvement of performance between two circuits with SSC: vapor injection cascade refrigeration system (SSC-ICRS) and ejector vapor injection cascade refrigeration system (SSC-EICRS). The results indicate the COP improvement rate of SSC-ICRS system is 17.39 %–41.98 % and the COP improvement rate of SSC-EICRS system is 49.46 %–68.37 % compared with SSC-CRS.

2D unified atmosphere and wind simulations of O-type stars

Context. Massive and luminous O-type star (O star) atmospheres with winds have been studied primarily using one-dimensional (1D), spherically symmetric, and stationary models. However, observations and theory have suggested that O star atmospheres are highly structured, turbulent, and time-dependent. As such, when making comparisons to observations, present-day 1D modeling tools require the introduction of ad hoc quantities such as photospheric macro- and microturbulence, wind clumping, and other relevant properties. Aims. We present a series of multi-dimensional, time-dependent, radiation-hydrodynamical (RHD) simulations for O stars that encapsulate the deeper sub-surface envelope (down to T ~ 450 kK), as well as the supersonic line-driven wind outflow in one unified approach. Our overarching aim is to develop a framework that is free from the ad-hoc prescriptions that plague present-day 1D models. Here, we start with an analysis of a small set of such multi-dimensional simulations and then compare them to atmospheric structures predicted by their 1D counterparts. Methods. We performed time-dependent, two-dimensional (2D) simulations of O star atmospheres with winds using a flux-limiting RHD finite volume modelling technique. Opacities are computed using a hybrid approach combining tabulated Rosseland means with calculations (based on the Sobolev approximation) of the enhanced line opacities expected for supersonic flows. The initial conditions and comparison models were derived using similar procedures as those applied in standard 1D stationary model atmosphere with wind codes. Results. Structure starts appearing in our simulations just below the iron-opacity peak at ~200 kK. Local pockets of gas with radiative accelerations that exceed gravity then shoot up from these deep layers into the upper atmosphere, where they interact with the line-driven wind outflow initiated around or beyond the variable photosphere. This complex interplay creates large turbulent velocities in the photospheric layers of our simulations, on the order of ~30–100km s−1, with higher values for models with higher luminosity-to-mass ratios. This offers a generally good agreement with observations of large photospheric ‘macroturbulence’ in O stars. When compared to 1D models, the average structures in the 2D simulations display less envelope expansion and no sharp density-inversions, along with density and temperature profiles that are significantly less steep around the photosphere, and a strong anti-correlation between velocity and density in the supersonic wind. Although the wind initiation region is complex and highly variable in our simulations, our average mass-loss rates agree well with stationary wind models computed by means of full co-moving frame radiative transfer solutions. Conclusions. The different atmospheric structures found in 2D and 1D simulations are likely to affect the spectroscopic determination of fundamental stellar and wind parameters for O stars as well as the empirical derivation of their chemical abundance patterns. To qualitatively match the different density and temperature profiles seen in our multi-dimensional and 1D models, we need to add a modest amount of convective energy transport in the deep sub-surface layers and a large turbulent pressure around the photosphere to the 1D models.

Modelling of flue gas injection and collaborative optimization of multi-injection parameters for efficient coal-based carbon sequestration combined with BP neural network parallel genetic algorithms

Cooperative equalization among the injection parameters can control the economic objective function to ensure the efficiency of gas-mixture-enhanced coalbed methane recovery (GM-ECBM). This study first proposed and validated a refined thermal-hydro-mechanical-chemical (THMC) coupling model with a convenient permeability model. Based on GM-ECBM numerical calculation results under different combinations of injection parameters, different types of cost-income objective functions, including different costs and incomes, were optimized by parallelly applying a genetic algorithm and backpropagation neural network (GA-BP). Using the recovery rate as the index, a small inter-well distance and a large injection pressure can increase the optimal CO2 proportion. The effectiveness of enhancing the injection temperature was significantly correlated with both inter-well distance and the injection pressure. Cooperative equalization among the injection parameters can explain different viewpoints of different scholars on the temperature effect. Large Henry’s law constants resulted in low carbon sequestration and coalbed methane (CH4) production but did not affect the optimal CO2 proportion. High carbon sequestration and CH4 prices corresponded to small inter-well distances and large injection pressure. Based on the objective function, the optimal inter-well distance and the injection temperature were 175–220 m and 305.5–311.5 K, respectively. The volumetric adsorption-induced expansion coefficient (VAEC) of CO2 determined the optimal CO2 proportion, the optimization feasibility of the injection scheme, and the applicability of GM-ECBM.

Can Black Holes or Other Relativistic Space Objects Be a Source of Dark Energy?

We consider the hypothesis that the sources of dark energy (DE) could be black holes (BHs) or more exotic objects, such as naked singularities or gravastars. We propose a definition of the presence of DE in the Universe and a criterion for what can be considered the source of this dark energy. It is based on the idea of the accelerated expansion of the Universe, which requires antigravity caused by large negative pressure. A recently proposed hypothesis, that the mass of BHs increases with time according to the same law as the volume of the part of the Universe containing it and the population of BHs can mimic DE, is examined. We demonstrate the reasons why it cannot be accepted, even if all the assumptions on which this hypothesis is based are considered true.

Numerical Analysis of the Effects of Fuel Injection Duration and Spray Angle on the Combustion Process in a Compression Ignition Engine

The changes in injection strategies for diesel engines have a major impact on the performance and pollutant emission characteristics of diesel engines. If injection strategies like injection duration, injection timing, injection pressure and spray angle are properly adjusted, combustion can be improved. The engine performance will increase and emissions will decrease with the combustion improvement. In this work, the influences of injection duration and spray angle on the combustion characteristics of single cylinder, natural aspirated, electronically controlled injection, compression ignition engine were investigated. In the first stage of the work, experiments were executed on a single cylinder CI engine using a Cussons P8160 DC dynamometer. After the experiments, the piston bowl geometry of the engine was modeled and numerical simulation studies were achieved at 7 different injection durations and 7 different spray angles using Converge CFD software. As a result of this study, it was observed that there is a good match between experimental and simulation data of heat release rate (HRR) and in-cylinder pressure. In-cylinder pressure decreased with longer injection duration. The highest max. in-cylinder pressure was roughly 101.0 bar at 4°CA injection duration and the lowest max. in-cylinder pressure was roughly 82.0 bar at 10°CA injection duration. When the HRR data were analyzed, it was seen that as the injection duration increased, the amount of heat released by combustion decreased. When examining the results of the spray angle analysis, it was concluded that there were not very large differences in-cylinder pressure and HRR data, and there was a difference of 1.4 bar between the highest and lowest max. in-cylinder pressure values. In addition, the highest in-cylinder pressure of approximately 86.7 bar was obtained at a spray angle of 77°. It was observed that the CA50 value was obtained at angles closer to the top dead center by increasing the spray angle and decreasing the injection duration. Moreover, the longest combustion durations were realized at 60° spray angle and 10°CA injection duration.

The Impact of Nozzle Opening Thickness on Flow Characteristics and Primary Electron Beam Scattering in an Environmental Scanning Electron Microscope.

This paper describes the methodology of combining experimental measurements with mathematical-physics analyses in the investigation of flow in the aperture and nozzle. The aperture and nozzle separate the differentially pumped chamber from the specimen chamber in an environmental scanning electron microscope (ESEM). Experimental measurements are provided by temperature and pressure sensors that meet the demanding conditions of cryogenic temperature zones and low pressures. This aperture maintains the required pressure difference between the chambers. Since it separates the large pressure gradient, critical flow occurs on it and supersonic gas flow with the characteristic properties of critical flow in the state variables occurs behind it. As a primary electron beam passes through the differential pumped chamber and the given aperture, the aperture is equipped with a nozzle. The shape of the nozzle strongly influences the character of the supersonic flow. The course of state variables is also strongly influenced by this shape; thus, it affects the number of collisions the primary beam's electrons have with gas molecules, and so the resulting image. This paper describes experimental measurements made using sensors under laboratory conditions in a specially created experimental chamber. Then, validation using mathematical-physical analysis in the Ansys Fluent system is described.

Characteristics of micron-scale pore-fracture modification in marine shale reservoirs with different combustion explosion energy

The combustion explosion fracturing of shale with in-situ methane is a revolutionary fracturing technique, but the modification characteristics of reservoir pores and fractures by combustion explosion energy level are still unclear. In order to study the transformation characteristics of micron-scale pore-fracture systems of marine shale reservoirs with different combustion explosion energies, this study selected a section of shale samples from the Longmaxi Formation in the Luzhou block in the southern Sichuan Basin to carry out different energy gradient combustion explosion test, named W1∼W5 (25–91 MPa). Based on micron CT scanning technology, the three-dimensional reconstruction of shale samples before and after combustion explosion was carried out to analyze the effect of combustion explosion energy on the transformation of the pore-fracture system characteristics. The results show that at the energy between 25 MPa and 45 MPa, the variation characteristics of cracks before and after explosion are not obvious. When the energy of the explosion is in the range of 61 MPa–91 MPa, the cracks gradually extend and become longer, and the distribution density of cracks becomes higher and more interconnected. After the explosion at 91 MPa, it can be seen that a number of annular cracks are generated at the edge of the sample, which are interconnected with radial cracks. Total porosity, connected porosity, pore number, and total pore volume of the shale increased after combustion explosion, where the total porosity at the combustion explosion energy of 91 MPa have the largest increment, while the connected porosity, pore number, and total pore volume in the combustion explosion energy of 71 MPa have the largest relative increments, indicating that there is a fracturing pressure value that strongly breaks through the bottleneck when the explosion pressure is between 61 MPa and 71 MPa. A comparison of different pore size sections before and after the combustion explosion pore volume share found that the explosion pressures of 25 MPa, 45 MPa and 91 MPa tend to expand from 100 to 200 μm pore size to form a larger volume share of >200 μm cracks, while at the explosion pressure of 71 MPa, more inclined to transform the 0–100 μm pores, so that the pores gradually transition to the 100–200 μm. Analysis shows that the gas explosion generates a large pressure, release a large amount of heat. Due to the high temperature and high pressure coupling effect, the pore-fracture in the shale changes significantly. Strong stress waves lead to stress concentration at the tip of shale and crack expansion and extension. At the same time, the local expansion force causes “pore expansion effect”. Various mineral particles in the shale undergo differential expansion, along the crystal rupture or through the crystal rupture. New pore fractures are also generated when the original pores keep expanding, which improves the shale pore connectivity. This understanding can provide a theoretical basis for the selection of the energy level of the in-situ methane combustion explosion in shale.

A behavioral nonlinear modeling implementation for MEMS capacitive microphones

We are highlighting the behavioral nonlinear system-level modeling approach for MEMS capacitive microphones. The combination of finite element modeling and large signal nonlinear circuit modeling provides a strong capability to predict electroacoustical performance for capacitive transductions. Circuit simulation tools such as Cadence Virtuoso have emerged as powerful aids in designing behavioral models in both linear and nonlinear regimes. Typical small signal lumped element models fail to capture the MEMS behavior which changes over pressure and electrical bias conditions. The models described herein capture diaphragm displacement and capacitance change over large pressure ranges for a simply supported circular plate. This can be coupled with the electrostatic force, due to the applied bias voltage, and converted back to pressure, thereby realizing a feedback loop in the circuit model. The nonlinear model capability is extended to predict capacitance-bias behavior and estimate pull-in of the MEMS device. The microphone sensitivity, signal-to-noise ratio, and harmonic distortions are accurately predicted using the nonlinear large signal model when compared to measured microphone data.

Development of multilevel mesh adaptivity for global variance reduction in Monte Carlo code cosRMC

The mesh-based weight window method is a widely used global variance reduction technique for Monte Carlo particle transport calculation. In order to meet the fine voxel division required for high-quality weight window distribution, the uniform structured mesh division will lead to large memory footprint pressure. This work focused on the research of the multilevel adaptive mesh algorithm, using a recursive algorithm to adjust the voxel resolution adaptively according to the material of geometry. Then the adaptive mesh algorithm was applied to the weight window generator based on the response matrix method by establishing the neighbor relationship of adaptive mesh. And an optimization method for memory allocation of the response matrix solver was proposed, effectively reducing the memory footprint of the response matrix solver in parallel computing. In the calculation of the CFETR model, the calculation efficiency under the weight window based on adaptive mesh was increased by 53.3 % compared with the weight window based on uniform mesh, and the proportion of voxels with a statistical error less than 10 % reached 93.33 %, which verified the effectiveness of the multilevel adaptive mesh algorithm.

Spectral profile of ro-vibrational transitions of HCl broadened by He, Ar and SF6: Testing the β-correction to the Hartmann-Tran profile and the speed dependent (complex) hard collision model

The β-correction to the Hartmann-Tran (HT) profile, recently introduced to model the spectral shape of a molecular transition strongly affected by the Dicke narrowing effect (Konefal et al., JQSRT 242 (2020) 106,784), the HT profile (Ngo et al., JQSRT 129 (2013) 89), and the speed dependent (complex) hard collision model (SDcHC, in which the velocity changing collision rate is characterized by a complex number) are tested using spectra of two rovibrational lines of HCl. The R(5) and R(9) lines of the fundamental band of HCl broadened by He, Ar and SF6 have been recorded with a difference-frequency laser spectrometer for total pressures ranging from 12 to 930 mbar. These lines, measured in large pressure ranges with different collision-partners provide a meaningful test of the above-mentioned line-shape models. The results confirm that non-Voigt effects are significant for HCl broadened by Ar and SF6 and mainly due to the large influence of the Dicke narrowing effect. For HCl-SF6 and HCl-Ar, especially for the R(9) line, using the β-correction together with the HT profile (and with the speed-dependent hard collision model, SDHC) significantly improves the fit residuals while it has no effect on (or tends to deteriorate) the quality of the fit for HCl-He and for the R(5) line of HCl-SF6, for which the influence of velocity changing collisions is smaller. Except for HCl-He, the SDcHC model leads to better quality of fit compared to the HT profile. The results also show that numerical correlations between refined line-shape parameters of the HT profile are important and can lead to ill-determined parameters while they are more properly determined with the SDcHC model.

Fractional Trading

Abstract Fractional trading (FT)—the ability to trade less than a whole share—removes barriers to high-priced stocks and facilitates entry by capital-constrained retail investors. We observe a surge of tiny trades, measured using off-exchange one-share trades, among high-priced stocks compared to low-priced stocks after FT is introduced to the U.S. equity markets. These tiny trades, when coordinated during attention-grabbing events, are forceful enough to exert large price pressure on high-priced stocks. Further evidence suggests that FT can even fuel meme-stock-like trading frenzies and bubbles in high-priced stocks, for which the feedback effect likely plays a role. (JEL G10, G12, G14, G18, G32, G41)

Numerical Study of Rarefied Gas Flow in Diverging Channels of Finite Length at Various Pressure Ratios

In the present work, the gas flows through diverging channels driven by small, moderate, and large pressure drops are studied, considering a wide range of the gas rarefaction from free molecular limit through transition flow regime up to early slip regime. The analysis is performed using the Shakhov kinetic model, and applying the deterministic DVM method. The complete 4D flow problem is considered by including the upstream and downstream reservoirs. A strong effect of the channel geometry on the flow pattern is shown, with the distributions of the macroscopic quantities differing qualitatively and quantitatively from the straight channel flows. The mass flow rate data set from the complete solution is compared with the corresponding set obtained from the approximate kinetic methodology, which is based on the fully developed mass flow rate data available in the literature. In addition, the use of the end-effect approach significantly improves the applicability range of the approximate kinetic methodology. The influence of the wall temperature on the flow characteristics is also studied and is found to be strong in less-rarefied cases, with the mass flow rate in these cases being a decreasing function of the temperature wall. Overall, the present analysis is expected to be useful in the development and optimization of technological devices in vacuum and aerospace technologies.

Numerical investigation into the thermo-hydro-mechanical behavior in unsaturated soils considering hypergravity effect

Unsaturated soils are commonly found in coastal regions and marine sediments, where understanding the thermo-hydro-mechanical (THM) behavior, especially regarding phase transition, is crucial for related practical engineering applications. Centrifugal model offers an effective means to reflect the prototype with smaller scale and shorter duration under hypergravity conditions. Present studies on similarity based on governing equation analysis of the THM coupled responses are mainly focused on saturated rather than unsaturated soils, nor involved with different boundary conditions. This paper theoretically derives the similarity of THM behavior of unsaturated soils between the centrifugal model and prototype, and numerically assesses the similarity considering Dirichlet / Neumann condition based on the open-source FEM code OpenGeoSys. In addition, numerical results shows that phase transition between liquid water and water vapor will occur under temperature variation, and pore pressure difference rather than initial pore pressure causes the difference of THM coupled responses. Significant pore pressure variation will be amplified with increase of gas diffusion coefficient, and large air entry pressure corresponds to high liquid saturation and obvious phase transition.

Experimental and Computational Investigation of Flow Boiling in a 52 μm Hydraulic Diameter Microchannel Evaporator With Inlet Restrictions and Heat Spreading

Abstract Microchannel flow boiling presents an effective thermal management strategy for high heat flux (>1 kW/cm2) devices. Fundamental mechanisms of microchannel flow boiling behaviors are difficult to determine due to macroscopic limitations of experimental hardware. In addition, flow stabilizing features of microchannel evaporators such as inlet restrictions and heat spreading further complicate fluid flow and heat transfer dynamics. Computational models, when utilized with experiments, can provide a more detailed understanding of behaviors which cannot be determined experimentally. The present study developed a computational model for flow boiling heat transfer in a 52 μm silicon microchannel evaporator designed to cool a laser diode bar, with inlet restrictions and a nonuniform heating profile at the channel level. A conjugate heat transfer model along with a coupled level set and volume of fluid (CLSVOF) model was created in ansysfluent and compared with experimental flow boiling data to gain further insights into the performance of a realistic microdevice. Heat spreading in the channel outside of the heater footprint was observed due to the high thermal conductivity of the silicon substrate. The inlet orifices impacted local flow patterns by creating a large pressure drop and forming a recirculation zone immediately downstream. This behavior resulted in pressure recovery zones and regions of separated flow boiling behavior. Bubbly, slug, and churn flows were seen to be dominant flow regimes. The heat transfer coefficient was found to be dependent on heat flux and flow regime, and more weakly on mass flux and outlet vapor quality.

Multiphysics and multi-scale design and analysis of nuclear thermal propulsion pellet bed reactor based on spherical cermet fuel element

Due to the advantages of high thrust and high specific impulse, nuclear thermal propulsion (NTP) is a preferred near-term rocket engine technology for future Mars missions. This article introduces the reactor design based on spherical cermet fuel element, with the aim of studying the feasibility of applying this new fuel in NTP system. First, design requirements are determined based on the unique features of NTP. In terms of neutronics, the effect of rocket launch accidents and fuel loss caused by high-temperature hydrogen are considered. Thermal hydraulics refer to the requirements of NASA's Mars Design Reference Architecture 5.0 (DRA 5.0) for impulse, thrust, and thrust to weight ratio. Second, based on the requirements above, the optimal reactor configuration parameters are obtained with the goal of maximizing the thrust to weight ratio: reactor radius 51.1 cm, height 106 cm, aspect ratio 1.04, reflector 13 cm, and reactor mass 3940 kg. Finally, the performances of the optimal reactor design are analyzed. The neutron spectrum shows a characteristic of fast neutron spectrum, and fuel loss analysis shows that the core can withstand a fuel mass loss of about 4 wt%. In addition, the core axial and radial power distribution are calculated, with an overall power peak factor of 1.26. The thermal hydraulic calculation provides a range of core operating conditions that satisfy the design requirements of DRA 5.0 and temperature, with power of 620 ∼ 950 MW and flow rate of 16 ∼ 24 kg/s. Compared with the ANL200/2000 reactor using prismatic cermet, it has the advantage of higher specific impulse. The main disadvantage is the large pressure drop, which prevents it from being applied to the scenarios of high power and high thrust. Therefore, for NTP reactor using spherical cermet elements, it should be applied to low to medium power scenarios.

Numerical Study of Thermal Performance on Fin and Tube Heat Exchanger with Flat Rectangular and Sinusoidal Winglet Vortex Generators

Generation of vortices in the fin and tube heat exchanger is one of the common methods to reduce the air-side thermal resistance. This study deals with the enhancement of heat transfer in the air side using conventional rectangular and sinusoidal sine wave vortex generators. The vortex generators are placed in the downstream location of the tube in the common flow-down configurations and the range of Reynolds number is maintained about 400 to 1100. The results of the above vortex generators are compared with baseline configuration based on thermos-hydraulic criterion parameters like variation in the flow structure, variation in the temperature distribution, variation in the pressure distribution, variation in the friction factor, and overall thermal enhancement factor. Based on the comparative numerical analysis, sinusoidal and conventional rectangular winglet shows good heat transfer enhancement in that they have a large pressure loss penalty.