Thermal Jet Research Articles

The absence of a dense potential core in supercritical injection: A thermal break-up mechanism

Certain experiments in quasi-isobaric supercritical injection remain unexplained by the current state of theory: Without developing a constant value potential core as expected from the mechanical view of break-up, density is observed to drop immediately upon entering the chamber. Furthermore, this phenomenon has never been captured in computational fluid dynamics (CFD) despite having become a de facto standard case for real fluid CFD validation. In this paper, we present strong evidence for a thermal jet disintegration mechanism (in addition to classical mechanical break-up) which resolves both the theoretical and the computational discrepancies. A new interpretation of supercritical jet disintegration is introduced, based on pseudo-boiling, a nonlinear supercritical transition from gas-like to liquid-like states. We show that thermal disintegration may dominate classical mechanical break-up when heat transfer takes place in the injector and when the fluid state is sufficiently close to the pseudo-boiling point. A procedure which allows to capture subsided cores with standard CFD is provided and demonstrated.

Research on the Effect of ETCI Based HCCI Technology in the Best Fuel Area

Exhaust check point injection compression ignition (ETC� ), the trapped promote internal thermal residues high temperature high pressure jet fuel mixture is one of the most effective methods to achieve homogeneous charge compression ignition (HCCI). This paper is based on the ETCcombustion mode to study the effect of timing heating of the exhaust valve and the cooling effect of the pressure on the combustion process.. Results show that the best fuel economy can start injection of Ca BTDC at 1500r/min, the exhaust valve timing on combustion properties are strongly influenced by the 370, Shan'xi. Using the residual gas coefficient of the exhaust valve timing control, the combustion stage can be controlled indirectly by the intake temperature of the cylinder. In addition, constant pressure, inlet pressure increasing can increase the excess air coefficient decrease the mixture of average air temperature, which can also be control as the key parameters of the combustion phase in some areas. Therefore, the reasonable cooperation between the exhaust valve timing and the pressure pressure can effectively control the combustion process and emission minimization. At 1500r / min, 30 (calcium negative valve overlap (NVO) and 0.18 MPa pressure, the limit of low load and high load limit of HCCI combustion can be reached 0.27 MPa and 0.723 MPa, respectively.

Research on the Law of Thermal Effect of Floating Nuclear Power Plants Thermal Discharge

The waste heat emissions of thermal discharge from floating nuclear power plants may have a negative thermal effect on the environment. Study on the dilution and diffusion of cooling water plays an important role in thermal pollution prevention. The cooling water discharge process can be condensed into the thermal jet in cross flow. According to the theory of computational fluid dynamics, the mathematical model of round horizontal thermal jets in cross flow is established. The 3D numerical simulation of thermal jets based on finite volume method is achieved by using the Realizable k-ε turbulence model and the Semi-implicit method for pressure linked equations, and the three-dimensional trajectory of thermal jet are obtained. The rationality of analysis method is approved by comparing calculation value with experimental value. The temperature distributions in thermal jets are studied through the numerical experiments conducted under different cross-flow velocity and different emission angle. As a result, the impacts of these conditions on thermal pollution area are found, and the theoretic bases are provided for the design of the cooling water discharge pipe.

다중써멀버블 잉크젯방식의 3D 프린팅 시스템 개발 및 성능평가

Recently, 3D printing technology is a hot issue in various industrial fields. According to the user’s application, it allows for the free form fabrication method to be utilized in a wide range. The powder based fusion technique is one of the 3D printing methods. When using this method it is possible to apply the various binder jetting techniques such as piezo, thermal bubble jet, dispenser and so on. In this paper, a multi thermal bubble ink jet was integrated for jetting of powder binding material and developing a power fused 3D printing system. For high quality 3D printing parts, it needs an analysis and evaluation of the behavior of the thermal bubble ink jet head. In the experiment, a correlation between jetting binder quantity and layer thickness of powder was investigated, and a 3D part model was fabricated, which was used by measuring the scale factor.

RADIO OBSERVATIONS OF THE STAR FORMATION ACTIVITIES IN THE NGC 2024 FIR 4 REGION

Star formation activities in the NGC 2024 FIR 4 region were studied by imaging centimeter continuum sources and water maser sources using several archival data sets from the Very Large Array. The continuum source VLA 9 is elongated in the northwest-southeast direction, consistent with the FIR 4 bipolar outflow axis, and has a flat spectrum in the 6.2-3.6 cm interval. The three water maser spots associated with FIR 4 are also distributed along the outflow axis. One of the spots is located close to VLA 9, and another one is close to an X-ray source. Examinations of the positions of compact objects in this region suggest that the FIR 4 cloud core contains a single low-mass protostar. VLA 9 is the best indicator of the protostellar position. VLA 9 may be a radio thermal jet driven by this protostar, and it is unlikely that FIR 4 contains a high-mass young stellar object (YSO). A methanol 6.7 GHz maser source is located close to VLA 9, at a distance of about 100 AU. The FIR 4 protostar must be responsible for the methanol maser action, which suggests that methanol class II masers are not necessarily excited by high-mass YSOs. Also discussed are properties of other centimeter continuum sources in the field of view and the water masers associated with FIR 6n. Some of the continuum sources are radio thermal jets, and some are magnetically active young stars.

FIRST DETECTION OF THERMAL RADIOJETS IN A SAMPLE OF PROTO-BROWN DWARF CANDIDATES

We observed with the Jansky Very Large Array at 3.6 and 1.3 cm a sample of 11 proto-brown dwarf (BD) candidates in Taurus in a search for thermal radio jets driven by the most embedded BDs. We detected for the first time four thermal radio jets in proto-BD candidates. We compiled data from UKIDSS, 2MASS, Spitzer, WISE, and Herschel to build the spectral energy distribution (SED) of the objects in our sample, which are similar to typical Class I SEDs of young stellar objects (YSOs). The four proto-BD candidates driving thermal radio jets also roughly follow the well-known trend of centimeter luminosity against bolometric luminosity determined for YSOs, assuming they belong to Taurus, although they present some of radio emission compared to the known relation for YSOs. Nonetheless, we are able to reproduce the flux densities of the radio jets modeling the centimeter emission of the thermal radio jets using the same type of models applied to YSOs, but with corresponding smaller stellar wind velocities and mass-loss rates, and exploring different possible geometries of the wind or outflow from the star. Moreover, we also find that the modeled mass outflow rates for the bolometric luminosities of our objects agree reasonably well with the trends found between the mass outflow rates and bolometric luminosities of YSOs, which indicates that, despite the excess centimeter emission, the intrinsic properties of proto-BDs are consistent with a continuation of those of very low-mass stars to a lower mass range. Overall, our study favors the formation of BDs as a scaled-down version of low-mass stars.

ALMA reveals a candidate hot and compact disc around the O-type protostar IRAS 16547−4247

We present high angular resolution ($\sim$ 0.3$"$) submillimeter continuum (0.85 mm) and line observations of the O-type protostar IRAS 16547$-$4247 carried out with the Atacama Large Millimeter/Submillimeter Array (ALMA). In the 0.85 mm continuum band, the observations revealed two compact sources (with a separation of 2$"$), one of them associated with IRAS 16547$-$4247, and the other one to the west. Both sources are well resolved angularly, revealing a clumpy structure. On the other hand, the line observations revealed a rich variety of molecular species related to both continuum sources. In particular, we found a large number of S-bearing molecules, such as the rare molecule methyl mercaptan (CH$_3$SH). At scales larger than 10,000 AU, molecules (e.g., SO$_2$ or OCS) mostly with low excitation temperatures in the upper states (E$_k$ $\lesssim$ 300 K) are present in both millimeter continuum sources, and show a southeast-northwest velocity gradient of 7 km s$^{-1}$ over 3$"$ (165 km s$^{-1}$ pc$^{-1}$). We suggest that this gradient probably is produced by the thermal (free-free) jet emerging from this object with a similar orientation at the base. At much smaller scales (about 1000 AU), molecules with high excitation temperatures (E$_k$ $\gtrsim$ 500 K) are tracing a rotating structure elongated perpendicular to the orientation of the thermal jet, which we interpret as a candidate disk surrounding IRAS 16547$-$4247. The dynamical mass corresponding to the velocity gradient of the candidate to disk is about 20 M$_\odot$, which is consistent with the bolometric luminosity of IRAS 16547$-$4247.

MIXED CONVECTION JET IMPINGEMENT COOLING OF A RECTANGULAR SOLID HEAT SOURCE IMMERSED IN A POROUS LAYER

The jet impingement cooling of a solid rectangular block heated from below and immersed in a fluid-saturated porous medium is considered for investigation numerically. The jet direction is considered to be perpendicular from the top to the solid rectangular block. Therefore the jet flow and the buoyancy-driven flow are in opposite directions. For a fixed block length, the governing parameters in the present Darcy flow problem are: Rayleigh number (Ra), Peclet number (Pe), solid-to-porous thermal conductivity ratio (Kr), the dimensionless thickness (or height) of the solid wall (H), in addition to the dimensionless jet width (D). The results are presented in the mixed convection regime with wide ranges of the governing parameters. At low values of Pe (natural convection cases), it is found that the effect of Pe and the jet width are negligible and the average Nusselt number (Nu) is increasing with the increase of either Rayleigh number or the thermal conductivity ratio, or decreasing the thickness of the solid wall. At high values of Pe (forced convection cases), it is found that the effect of Ra is negligible and Nu increases with either increasing Pe values, the thermal conductivity ratio or jet width, or decreasing the thickness of the solid wall. At moderate values of Pe (opposing mixed convection cases), it is observed that the values of average Nusselt number show minimum values. The value of Pe at which minimum Nu occurs depends on Ra, thermal conductivity ratio, jet width, and the thickness of the solid wall. At low values of either Ra or thermal conductivity ratio, this case where Nu shows a minimum value is not obvious. It is found that the thinner solid walls have higher values of the average Nusselt number with other parameters fixed. Therefore, for cooling applications, the numerical results indicate that the solid wall should be as thin as possible, with high thermal conductivity. The present results show that the cooling rate with the opposing missed convection mode is lower than that with the natural convention mode. The results show that the effect of the jet width D can be incorporated by plotting the average Nusselt number against Pe × D, where the results form a single curve for different values of the jet width.

A study on reduction of processing time and improvement of strength by using photopolymer resin in the 3DP process with powder base

The 3DP technology is one of the additive manufacturing technologies that have recently come into the spotlight and are being applied to various fields. This technology has the advantage of enabling high speed printing which, is done on the basis of the ink-jet technology and the system to be constructed at a low cost. However, it has also the negative side that requires extra time for curing after 3D shape fabrication. On the other hand a postprocessing period is meant to increase the mechanical strength of the product. Therefore, in this study, an innovative 3DP process is recommended to improve the strength of product without any postprocessing. To verify the feasibility of the proposed process, a 3DP system was developed to test the mechanical strength experiment of the fabricated specimens. As a result, it was confirmed that the specimens fabricated by the proposed process had three times higher compression and yield strength than post-processed systems for improving the strength through the conventional thermal bubble jet process. To this effect, a proposed 3DP process would remarkably reduce the total fabrication time because there is no dry time and post-processing time after fabrication in the proposed process.

On the van der Waals gas flow in a thermal jet

Stationary subsonic and supersonic van der Waals gas flows in a thermal jet are considered. It is shown that in the case of ideal gas in length of both cooled and heated jets, temperature extremums can be observed, which is associated with the existence of bifurcation values of the Speed number, M = 1 and \(M = 1/\sqrt \gamma \). Concerning the van der Waals gas flow in the range of density values close to the critical one, there appear two more bifurcations of Mach numbers M ≪ 1, one of them in a cooled jet is anomalous, causes appearance of two temperature extremums in jet length, and is associated with anomalous behavior of sound speed. These regions of anomalous flows can actually be observed only for heavy gases like xenon.

Gas flow transition over sound speed in a thermal jet

Monograph [1] represents the generalities of choosing such parameters and conditions of a one-dimensional gas flow in a channel, which make it possible, without compression shock, to transfer gas from the subsonic regime to the supersonic regime; the known relation of actions inversion from which, in particular, follows the possibility of flow transition over the sound speed in a cylindrical jet via changing the sign of the heat flux through the channel wall. However, creation of such a thermal jet (Vulis jet) is hampered by the influence of friction forces on the flow, which leads to acceleration of the subsonic flow and deceleration of the supersonic flow. Here we analyzed the possibility of transition of a stationary flow to supersonic regime in the case of combined action of friction forces and heat flux, found the condition of the change of sign of the latter, and also proposed and numerically analyzed several schemes of transition to a supersonic flow.

Effects of Different Vents Location on Flow Characteristics of Air Conditioning

When using numerical simulation method for solving fluid flow and heat transfer problems, need to follow the basic equations. Each control equations generally use common form of expression, build a wall collision effects on indoor thermal environment situation jet and jet corner collision of two jets in the form of physical models under its numerical simulation were studied in the form of three jets collide.

Rapidly increasing collimation and magnetic field changes of a protostellar H2O maser outflow

W75N(B) is a massive star-forming region that contains three radio continuum sources (VLA 1, VLA 2, and VLA 3), which are thought to be three massive young stellar objects at three different evolutionary stages. VLA 1 is the most evolved and VLA 2 the least evolved source. The 22 GHz H2O masers associated with VLA 1 and VLA 2 have been mapped at several epochs over eight years. While the H2O masers in VLA 1 show a persistent linear distribution along a radio jet, those in VLA 2 are distributed around an expanding shell. Furthermore, H2O maser polarimetric measurements revealed magnetic fields aligned with the two structures. Using new polarimetric observations of H2O masers, we aim to confirm the elliptical expansion of the shell-like structure around VLA 2 and, at the same time, to determine if the magnetic fields around the two sources have changed. The NRAO Very Long Baseline Array was used to measure the linear polarization and the Zeeman-splitting of the 22 GHz H2O masers towards the massive star-forming region W75N(B). The H2O maser distribution around VLA 1 is unchanged from that previously observed. We made an elliptical fit of the H2O masers around VLA 2. We find that the shell-like structure is still expanding along the direction parallel to the thermal radio jet of VLA 1. While the magnetic field around VLA 1 has not changed in the past 7 years, the magnetic field around VLA 2 has changed its orientation according to the new direction of the major-axis of the shell-like structure and it is now aligned with the magnetic field in VLA 1.

Numerical Modeling of Turbulent Buoyant Wall Jets in Stationary Ambient Water

AbstractThe main focus of this study is on the near-field flow and mixing characteristics of the thermal and saline wall jets. A numerical study of the buoyant wall jets discharged from submerged outfalls (e.g., from desalination plants) has been conducted. The performance of different Reynolds-averaged Navier-Stokes (RANS) turbulence models has been investigated and various k-e, k-ω, and other turbulence models have been studied. The results of cling length, plume trajectory, temperature dilutions, and temperature and velocity profiles are compared to both available experimental and numerical data. It was found that two models perform best among the seven models chosen in this paper. According to the results from different simulations, the paper proposes corresponding relationships and comparative graphs that are helpful for a better understanding of buoyant wall jets.

DYNAMIC ENERGY MODELING OF AN EXPERIMENTAL BUILDING EQUIPPED WITH AN UNDERFLOOR AIR DISTRIBUTION (UFAD) SYSTEM

In this study, experimental and simulation studies were performed in a building equipped with an UFAD system in order to investigate the applicability of a new approach designed for prediction of the energy consumption of a residential building with an UFAD system. In this approach, a zonal model, Pressurized zOnal Model with the Air diffuser (POMA), was coupled with a thermal jet model and integrated into a traditional multizone thermal model. The coupled model was verified experimentally. This integrated model has the ability to take into account the characteristics of an UFAD system and thus accurately simulate its energy consumption. A case study was carried out using both approaches: Multi-zone approach and the new developed integrated zonal/jet/multizone model. A quantitative comparison, in terms of energy demand of a building with an UFAD system, shows that the difference can reach 14% and thus indicates that the traditional multizone modeling approach is not appropriate to use for UFAD system in the building energy prediction.

Acetylene Ignition Process in Combustion Thermal Spray

The acetylene ignition process in combustion thermal spray is typical of a laminar diffusion jet. It has all the features of a free jet. The aim of this research is to obtain the detail sparking ignition evolution process and the chemical reaction time scale and calculate the critical radius and minimum energy input required to produce a self-propagating flame in an acetylene fuel jet. Experiments are carried out by using a unique high-speed continuous CCD camera. The results show that the full sparking ignition time needs about 8 ms and this time scale can be used in the calculation of the flame flow fields in the combustion thermal spray jet.

R&D of a New De-Icing Device Based on Synthetically De-Icing Techniques

The thermal water-jet technology and mechanical milling method are comprehensively applied in the design of the new de-icing device. These two kinds of de-icing methods are combined as a set of multi-functional system, in which the thermal water jet cuts the ice layer into separated sections, and then the mechanical milling unit can easily remove the remaining sections. To obtain the affecting factors in the new de-icing device, repeated indoor experiments were conducted and the data was analyzed, which would provide some theoretical references to further optimize the design.

Numerical study of fractal characteristics of heat transfer interface in two-dimensional thermal planer jets

A numerical study of fractal characteristics of heat transfer interface in incompressible two-dimensional thermal planar jets is conducted. The fractal characteristics of heat transfer interface are investigated under three typical Prandtl numbers and two-types of inflow velocity profiles. The results show that heat transfer interface is fractal, and the fractal dimension decreases as the Prandtl number increases. It is caused mainly by the non-negligible effect of rapider development of thermal diffusion than momentum diffusion, which could produce finer structures in lower Pr flows. Moreover, this trend is enhanced by the increased inflow momentum thickness of the jets, as a thicker inflow boundary layer could initiate more space for heat transfer development.

HELIOS: A helium line-ratio spectral-monitoring diagnostic used to generate high resolution profiles near the ion cyclotron resonant heating antenna on TEXTOR

Radial profiles of electron temperature and density are measured at high spatial (∼1 mm) and temporal (≥10 μs) resolution using a thermal supersonic helium jet. A highly accurate detection system is applied to well-developed collisional-radiative model codes to produce the profiles. Agreement between this measurement and an edge Thomson scattering measurement is found to be within the error bars (≲20%). The diagnostic is being used to give profiles near the ion cyclotron resonant heating antenna on TEXTOR to better understand RF coupling to the core.

DYNAMICS INSIDE THE RADIO AND X-RAY CLUSTER CAVITIES OF CYGNUS A AND SIMILAR FRII SOURCES

We describe approximate axisymmetric computations of the dynamical evolution of material inside radio lobes and X-ray cluster gas cavities in Fanaroff-Riley II (FRII) sources such as Cygnus A. All energy is delivered by a jet to the lobe/cavity via a moving hotspot where jet energy dissipates in a reverse shock. Our calculations describe the evolution of hot plasma, cosmic rays (CRs), and toroidal magnetic fields flowing from the hotspot into the cavity. Many important observational features are explained. Gas, CRs, and field flow back along the cavity surface in a "boundary backflow" consistent with detailed FRII observations. Computed ages of backflowing CRs are consistent with observed radio-synchrotron age variations only if shear instabilities in the boundary backflow are damped and we assume this is done with viscosity of unknown origin. We compute a faint thermal jet along the symmetry axis and suggest that it is responsible for redirecting the Cygnus A nonthermal jet. Magnetic fields estimated from synchrotron self-Compton (SSC) X-radiation observed near the hotspot evolve into radio lobe fields. Computed profiles of radio-synchrotron lobe emission perpendicular to the jet reveal dramatically limb-brightened emission in excellent agreement with FRII observation, although computed lobe fields exceed those observed. Strong winds flowing from hotspots naturally create kiloparsec-sized spatial offsets between hotspot nonthermal X-ray inverse Compton (IC-CMB) emission and radio-synchrotron emission that peaks 1–2 kpc ahead where the field increases due to wind compression. In our computed version of Cygnus A, nonthermal X-ray emission increases from the hotspot (some IC-CMB, mostly SSC) toward the offset radio-synchrotron peak (mostly SSC).