Thermal Jet Research Articles

Microstructured SiOx thin films deposited from hexamethyldisilazane and hexamethyldisiloxane using atmospheric pressure thermal microplasma jet

Mictrostructured silicon oxide (SiOx) thin films were deposited on glass and metal substrates from 1,1,1,3,3,3-hexamethyldisilazane (HMDSN) and hexamethyldisiloxane (HMDSO) by using atmospheric-pressure thermal microplasma jet. Two kinds of string-like products, randomly bent string-like products and linear string-like products, were deposited and they formed microstructured films. The bent string-like products formed labyrinth-like structures and the linear string-like products lay in parallel to form a large aligned structure. The width of both the bent and linear string-like products was from 1 to 3 μm, regardless of the kind of the precursor but depending on the plasma irradiation conditions. The influence of various surface microstructure of substrates on the formation of the SiOx microstructure was investigated to make clear the mechanism for the formation of the microstructures.

Highly Reliable Superhydrophobic Surface with Carbon Nanotubes Immobilized on a PDMS/Adhesive Multilayer.

We propose a new superhydrophobic surface that contains a carbon nanotube (CNT)-implanted poly(dimethylsiloxane) (PDMS)/adhesive multilayer. The adhesive provides very strong adhesion between the CNT-implanted PDMS layer and the substrate, and the CNTs on the surface exhibit superhydrophobicity. Therefore, the CNT-implanted PDMS/adhesive (CIPA) layer provides a highly reliable surface for superhydrophobicity. The fabricated CIPA surface performs far better than previously reported surfaces in terms of stability tests, such as contamination and solvent tests, and physical contact, including thermal pressure, bending, adhesion, and water jet tests. If a portion of the CIPA surface is destroyed, the surface is immediately restored because the material can regenerate the surface to its initial state. The surface can therefore maintain its superhydrophobicity even when damaged in rough environments, without self-healing or additional repair. Furthermore, because the adhesive is sprayed and coated on the surface of the substrate, a CIPA surface can be formed on three-dimensional shapes, including curved surfaces, and on various substrates.

Numerical simulation on the characteristics of thermal buoyant jets with the different flow profiles in crossflow

In this paper, the numerical simulation on the characteristics of thermal buoyant jets of the cross-flow equal area of the round hole and square hole thermal jets is carried out, which based on the SIMPLE algorithm and Fluent’s RSM model. According to the calculation results, the variation characteristics of velocity and temperature of single-hole jets with the different flow profiles in crossflow are analyzed, and the decay laws of velocity and temperature in heat jet are obtained. The results show that the closer to the jet exit, the more rapidly the speed change, and there is a clear jet mainstream area, but the speed fluctuations gradually weaken with the flow to the downstream. The dimensionless temperature difference of the trajectory of thermal buoyant jets decreases gradually along the direction of incoming flow, and the trajectory centre of the thermal buoyant jets moves away from the outlet. Compared with the square hole, the round hole jet impactes on the incoming flow strongly, causes more intense mixing with the surrounding fluid, and increases velocity and temperature attenuate at faster rate.

Model evaluation and experimental validation of thermal jet drilling for geothermal energy

Thermal jet drilling is a technology, which has the potential to be suitable for the exploitation of geothermal energy in relatively deep formations with low costs. Several investigations on this drilling method have been carried out for the depths of less than 1 km or deeper than 2 km. To the best of our knowledge, there is almost no specific study on simulation for thermal jet drilling at the depths between 1 km and 2 km. This paper focuses on investigating applications of different reaction (i.e., laminar, non-premixed, eddy dissipation concept, eddy dissipation model and finite rate), turbulence (i.e., standard k-epsilon, realizable k-epsilon, renormalization group k-epsilon and scale-adaptive simulation) and radiation (i.e., P1, discrete ordinate, discrete transfer radiation model and surface-to-surface) models to downhole reaction of thermal jet drilling. The objective is to identify the pros and cons of each model and determine a set of models that are the most appropriate for the reaction. Experiments are also carried out and data are collected as the benchmark for comparison. Relative errors and iteration for convergence are analyzed for each simulation model. Results show that the modified simulation temperature by considering the environmental temperature becomes more accurate compared with the experimental data. The laminar model over-predicts the temperature and yields unreasonable results. Finite rate and eddy dissipation model are the candidates with highest accuracy and acceptable computational time within selected model settings and boundary conditions. In addition, compared with renormalization group, realizable and scale-adaptive simulation turbulence models, the standard k-epsilon model is the most appropriate model under the conditions selected for this investigation. The discrete ordinate model can be applicable for the simulation if the error tolerance is 10%. The P1 model is the most suitable radiation model. Results in this paper can provide implications for the reaction simulation of thermal jet drilling.

Evaluation of the Role of Balneotherapy in Rehabilitation Medicine.

Balneotherapy is a treatment with healing waters, which includes bathing and physiotherapy in thermal water, therapeutic drinks, medical massage, and water jet massage. It is based on the buoyancy, physical properties, temperature, and chemical effects of mineral water. Throughout European and Japanese medical institutions, balneology and hot spring therapy is very much a part of routine medical treatment. The mechanism of balneotherapy is not yet completely understood. Balneotherapeutic procedures are mainly performed for the prevention, treatment, and rehabilitation of musculoskeletal diseases, but they have also proven useful for various other indications such as for the treatment or rehabilitation of dermatological diseases, immuno-inflammatory diseases, chronic pain syndromes, chronic cardiac diseases, and metabolic syndromes or neurological diseases as well as in the rehabilitation of patients with psychiatric conditions. Balneotherapy works well in the case of muscle tension, as it is relieving and relaxing, and it may be associated with improvement of various diseases. However, further investigations are necessary to determine the effectiveness, safety, standard procedures, and potential side effects of balneotherapy.

Experiments and numerical simulation for a thermal vertical jet into a rectangular water tank

Abstract In this paper, experimental measurements and numerical CFD calculations are carried out for the problem of a vertical thermal water jet into a rectangular water tank. We consider two cases; the first case is to inject a hot-water jet with a uniform inlet temperature (UIT) into a cold-water tank. The second case is to inject a cold-water jet with non-uniform inlet temperature (NUIT) into a hot-water tank. In the UIT case, we examine the effects of the temperature-difference. In the case of NUIT, we studied the effects initial temperatures with constant flow rate; and different flow rates at constant initial temperature. Both turbulence intensity and Reynolds number are formulated to be a function of the inlet temperature for the NUIT case. The numerical simulations are carried out under the same conditions of the experiments. We use the realizable k - e model to describe the turbulent flow with the energy equation. The symmetrical 3D half of the tank has been considered to reduce the computational cost. The water density is treated as a piecewise-linear of temperature. The turbulence at the inlet is characterized by the hydraulic diameter and the turbulence intensity. Several quantities are obtained and analyzed such as pressure, velocity, temperature, and turbulence. A good agreement between simulation and experimental results at low temperatures, while at high temperatures there is acceptable agreement with some quantitative differences. In spite of there are some differences between the measurements and the simulation in a certain case, nevertheless, the qualitative comparison is quite well. The thermal stratification occurs clearly with high temperature-difference, however, after a certain time, the thermal stratification is mixing. Moreover, when a cold-water jet enters a mixed hot water tank, stratification comes early and after a certain time, it mixes. For the UIT cases, the tank is totally mixing, while, for the NUIT cases the stratification clearly occurs.

Flow patterns of vertical plane thermal buoyant jet in shallow water

A heated plane water jet impinging vertically onto free water surface has been numerically studied based on large eddy simulation method coupled with the volume of fluid approach. The Boussinesq approximation is adopted to simulate the effect of buoyancy. Results showed that there exist two flow patterns for the plane thermal buoyant jet, which are the stable impinging flow pattern and the flapping impinging flow pattern. Distinct temperature stratification can be found in the stable impinging flow pattern, while it disappears in the flapping impinging flow pattern.

Radio outburst from a massive (proto)star

Context. Recent observations of the massive young stellar object S255 NIRS 3 have revealed a large increase in both methanol maser flux density and IR emission, which have been interpreted as the result of an accretion outburst, possibly due to instabilities in a circumstellar disk. This indicates that this type of accretion event could be common in young/forming early-type stars and in their lower mass siblings, and supports the idea that accretion onto the star may occur in a non-continuous way. Aims. As accretion and ejection are believed to be tightly associated phenomena, we wanted to confirm the accretion interpretation of the outburst in S255 NIRS 3 by detecting the corresponding burst of the associated thermal jet. Methods. We monitored the radio continuum emission from S255 NIRS 3 at four bands using the Karl G. Jansky Very Large Array. The millimetre continuum emission was also observed with both the Northern Extended Millimeter Array of IRAM and the Atacama Large Millimeter/Submillimeter Array. Results. We have detected an exponential increase in the radio flux density from 6 to 45 GHz starting right after July 10, 2016, namely ~13 months after the estimated onset of the IR outburst. This is the first ever detection of a radio burst associated with an IR accretion outburst from a young stellar object. The flux density at all observed centimetre bands can be reproduced with a simple expanding jet model. At millimetre wavelengths we infer a marginal flux increase with respect to the literature values and we show this is due to free–free emission from the radio jet. Conclusions. Our model fits indicate a significant increase in the jet opening angle and ionized mass loss rate with time. For the first time, we can estimate the ionization fraction in the jet and conclude that this must be low (<14%), lending strong support to the idea that the neutral component is dominant in thermal jets. Our findings strongly suggest that recurrent accretion + ejection episodes may be the main route to the formation of massive stars.

Flame extension area of unconfined thermal ceiling jets induced by rectangular-source jet fire impingement

Flame extension area is a significant parameter of thermal ceiling jet, which directly determines the strong heat transfer area between the thermal plume and the building ceiling. Experiment was conducted to investigate the flame extension area induced by rectangular source fires in this work. Results show that the flame extension area data sets can not be precisely predicted by former correlations. The aspect ratio of rectangular fire source has an influence on flame extension area; the fire source with smaller aspect ratio leads to a larger flame extension area. Finally, a global non-dimensional correlation combined the effects of source-ceiling height, heat release rate, source aspect rations are proposed to predict the flame extension area of flat unconfined ceiling jets. The new proposed correlation can also provide reference for the flame extension area beneath the confined tunnel ceiling during a tunnel fire. This work can supply added results to complement the existing knowledge of flame extension beneath the building roof and it can also provide directions for the fire risk assessment and fire protection design of buildings.

The energy distribution of electrons in radio jets

Black-hole and neutron-star X-ray binaries exhibit compact radio jets, when they are in the so called quiescent, hard, or hard intermediate states. The radio spectrum in these states is flat to slightly inverted. It is widely accepted that the energy distribution of the electrons, in the rest frame of the jet, is a power law with index p. A power-law energy distribution of the electrons in the jet is sufficient to explain the flat to slightly inverted spectrum emitted by the jet from radio to near infrared wavelengths, but is it necessary? Contrary to what our thinking was decades ago, now we know that the jets originate in the hot inner flow around black holes and neutron stars. Thus, we have investigated the spectrum that is emitted by a thermal jet with kT in the range 100-250 keV. We have computed the emitted spectrum from radio to near infrared using either a thermal distribution of electrons or a power-law one. We have found that parabolic jets with a thermal distribution of electrons give inverted spectra with alpha in the range 0-0.4, while jets with a power-law distribution of electrons give inverted spectra with alpha in the range 0-0.2. The rest of the parameters are kept the same in the two cases. The break frequency, which marks the transition from optically thick to optically thin synchrotron emission, is comparable for the two electron energy distributions. Our conclusion is that, contrary to common belief, it is not necessary to invoke a power-law energy distribution of the electrons in a jet to explain its flat to slightly inverted radio spectrum. A relativistic Maxwellian produces similar spectra. Thus, the widely invoked corona around black holes in X-ray binaries may actually be the jet.

A concordant scenario to explain FU Orionis from deep centimeter and millimeter interferometric observations

We resolved FU Ori at 29-37 GHz using the JVLA with $\sim$0$''$.07 resolution, and performed the complementary JVLA 8-10 GHz observations, the SMA 224 GHz and 272 GHz observations, and compared with archival ALMA 346 GHz observations to obtain the SEDs. Our 8-10 GHz observations do not find evidence for the presence of thermal radio jets, and constrain the radio jet/wind flux to at least 90 times lower than the expected value from the previously reported bolometric luminosity-radio luminosity correlation. The emission at $>$29 GHz may be dominated by the two spatially unresolved sources, which are located immediately around FU Ori and its companion FU Ori S, respectively. Their deconvolved radii at 33 GHz are only a few au. The 8-346 GHz SEDs of FU Ori and FU Ori S cannot be fit by constant spectral indices (over frequency). The more sophisticated models for SEDs suggest that the $>$29 GHz emission is contributed by a combination of free-free emission from ionized gas, and thermal emission from optically thick and optically thin dust components. We hypothesize that dust in the innermost parts of the disks ($\lesssim$0.1 au) has been sublimated, and thus the disks are no more well shielded against the ionizing photons. The estimated overall gas and dust mass based on SED modeling, can be as high as a fraction of a solar mass, which is adequate for developing disk gravitational instability. Our present explanation for the observational data is that the massive inflow of gas and dust due to disk gravitational instability or interaction with a companion/intruder, was piled up at the few au scale due to the development of a deadzone with negligible ionization. The piled up material subsequently triggered the thermal and the MRI instabilities when the ionization fraction in the inner sub-au scale region exceeded a threshold value, leading to the high protostellar accretion rate.

Deep into the Water Fountains

(Abridged) The formation of large-scale (hundreds to few thousands of AU) bipolar structures in the circumstellar envelopes (CSEs) of post-Asymptotic Giant Branch (post-AGB) stars is poorly understood. The shape of these structures, traced by emission from fast molecular outflows, suggests that the dynamics at the innermost regions of these CSEs does not depend only on the energy of the radiation field of the central star. Deep into the Water Fountains is an observational project based on the results of programs carried out with three telescope facilities: The Karl G. Jansky Very Large Array (JVLA), The Australia Telescope Compact Array (ATCA), and the Very Large Telescope (SINFONI-VLT). Here we report the results of the observations towards the WF nebula IRAS 18043$-$2116: Detection of radio continuum emission in the frequency range 1.5GHz - 8.0GHz; H$_{2}$O maser spectral features and radio continuum emission detected at 22GHz, and H$_{2}$ ro-vibrational emission lines detected at the near infrared. The high-velocity H$_{2}$O maser spectral features, and the shock-excited H$_{2}$ emission detected could be produced in molecular layers which are swept up as a consequence of the propagation of a jet-driven wind. Using the derived H$_{2}$ column density, we estimated a molecular mass-loss rate of the order of $10^{-9}$M$_{\odot}$yr$^{-1}$. On the other hand, if the radio continuum flux detected is generated as a consequence of the propagation of a thermal radio jet, the mass-loss rate associated to the outflowing ionized material is of the order of 10$^{-5}$M$_{\odot}$yr$^{-1}$. The presence of a rotating disk could be a plausible explanation for the mass-loss rates estimated.

JVLA Observations of Young Brown Dwarfs

Abstract We present sensitive 3.0 cm JVLA radio continuum observations of six regions of low-mass star formation that include twelve young brown dwarfs (BDs) and four young BD candidates. We detect a total of 49 compact radio sources in the fields observed, of which 24 have no reported counterparts and are considered new detections. Twelve of the radio sources show variability in timescales of weeks to months, suggesting gyrosynchrotron emission produced in active magnetospheres. Only one of the target BDs, FU Tau A, was detected. However, we detected radio emission associated with two of the BD candidates, WL 20S and CHLT 2. The radio flux densities of the sources associated with these BD candidates are more than an order of magnitude larger than expected for a BD and suggest a revision of their classification. In contrast, FU Tau A falls on the well-known correlation between radio luminosity and bolometric luminosity, suggesting that the emission comes from a thermal jet and that this BD seems to be forming as a scaled-down version of low-mass stars.

Large-volume excitation of air, argon, nitrogen and combustible mixtures by thermal jets produced by nanosecond spark discharges

This work presents experimental observations of strong expanding thermal jets following the application of nanosecond spark discharges. These jets propagate in a toroidal shape perpendicular to the interelectrode axis, with high velocities of up to 30 m s−1 and over distances of the order of a cm. Their propagation length is much larger than the thermal expansion region produced by the conventional millisecond sparks used in car engine ignition, thus greatly improving the volumetric excitation of gas mixtures. The shape and velocity of the jets is found to be fairly insensitive to the shape of the electrodes. In addition, their spatial extent is found to increase with the number of nanosecond sparks and with the discharge voltage, and to decrease slightly with the pressure between 1 and 7 atm at constant applied voltage. Finally, this thermal jet phenomenon is observed in experiments conducted with many types of gas mixtures, including air, nitrogen, argon, and combustible CH4/air mixtures. This makes nanosecond repetitively pulsed discharges particularly attractive for aerodynamic flow control or plasma-assisted combustion because of their ability to excite large volumes of gas, typically about 100 times the volume of the discharge.

Micro vapor bubble jet flow for safe and high-rate fluorescence-activated cell sorting.

Safe, high-rate and cost-effective cell sorting is important for clinical cell isolation. However, commercial fluorescence-activated cell sorters (FACS) are expensive and prone to aerosol-induced sample contamination. Here we report a microfluidic cell sorter allowing high rate and fully enclosed cell sorting. The sorter chip consists of an array of micro heating hotspots. Pulsed resistive heating in the hotspots produces numerous micro vapor bubbles with short duration, which gives rise to a rapid jet flow for cell sorting. With this method, we demonstrated high sorting rate comparable to commercial FACS and the significant enrichment of rare cancer cells. This vapor bubble based cell sorting method can be a powerful tool for contamination-free and affordable clinical cell sorting such as circulating tumor cell isolation and cancer cell therapy.

Interstellar Medium and Star Formation Studies with the Square Kilometre Array

Stars and planetary systems are formed out of molecular clouds in the interstellar medium. Although the sequence of steps involved in star formation are generally known, a comprehensive theory which describes the details of the processes that drive formation of stars is still missing. The Square Kilometre Array (SKA), with its unprecedented sensitivity and angular resolution, will play a major role in filling these gaps in our understanding. In this article, we present a few science cases that the Indian star formation community is interested in pursuing with SKA, which include investigation of AU-sized structures in the neutral ISM, the origin of thermal and non-thermal radio jets from protostars and the accretion history of protostars, and formation of massive stars and their effect on the surrounding medium.

THE RADIO JET ASSOCIATED WITH THE MULTIPLE V380 ORI SYSTEM

ABSTRACT The giant Herbig–Haro object 222 extends over ∼6′ in the plane of the sky, with a bow shock morphology. The identification of its exciting source has remained uncertain over the years. A non-thermal radio source located at the core of the shock structure was proposed to be the exciting source. However, Very Large Array studies showed that the radio source has a clear morphology of radio galaxy and a lack of flux variations or proper motions, favoring an extragalactic origin. Recently, an optical–IR study proposed that this giant HH object is driven by the multiple stellar system V380 Ori, located about 23′ to the SE of HH 222. The exciting sources of HH systems are usually detected as weak free–free emitters at centimeter wavelengths. Here, we report the detection of an elongated radio source associated with the Herbig Be star or with its close infrared companion in the multiple V380 Ori system. This radio source has the characteristics of a thermal radio jet and is aligned with the direction of the giant outflow defined by HH 222 and its suggested counterpart to the SE, HH 1041. We propose that this radio jet traces the origin of the large scale HH outflow. Assuming that the jet arises from the Herbig Be star, the radio luminosity is a few times smaller than the value expected from the radio–bolometric correlation for radio jets, confirming that this is a more evolved object than those used to establish the correlation.

Thermal durability and fracture behavior of layered Yb-Gd-Y-based thermal barrier coatings in thermal cyclic exposure

The effects of structural design on the thermal durability and fracture behavior of Yb-Gd-Y-based thermal barrier coatings (TBCs) were investigated through thermal cyclic exposure tests, such as furnace cyclic thermal fatigue (FCTF) and jet engine thermal shock (JETS) tests. The effects of composition in the bond coat and feedstock purity for the buffer layer on its lifetime performance were also examined. To overcome the drawbacks of Yb-Gd-Y-based material with inferior thermal durability due to poor mechanical properties and low coefficient of thermal expansion, a buffer layer was introduced in the Yb-Gd-Y-based TBC systems. In FCTF tests, the TBCs with the buffer layer showed a longer lifetime performance than those without the buffer layer, showing the longest thermal durability in the TBC with the Co-Ni-based bond coat and the buffer layer of regular purity. In JETS tests, the TBC with the Ni-based bond coat and the buffer layer of high purity showed a sound condition after 2000cycles, showing better thermal durability for TBC with the Co-Ni-based bond coat rather than that with the Ni-based bond coat in the single layer coating without the buffer layer. The buffer layer effectively enhanced the thermal durability in slow temperature change (in the FCTF test), while the bond-coat composition and the feedstock purity for the buffer layer were found to be important factor to improve the thermal durability of the TBC in fast temperature change (in the JEET test). Finally, these research findings allow us to control the structure, composition, and feedstock purity in TBC system for improving the thermal durability in cyclic thermal environments.

Development of a low thermal resistance water jet cooled heat sink for thermoelectric refrigerators

In order to increase the performance of thermoelectric coolers, the thermal resistances of the heat sinks must be minimized. We demonstrate a low thermal resistance water cooled heat sink design for the hot side of a commercial low-cost thermoelectric refrigerator. An inline confined-jet array heat sink has been designed wherein the coolant directly impinges on the thermoelectric module, thereby eliminating the interfacial thermal resistance. The design was tested using CFD simulations and experimentally using a 3D printed prototype. A low thermal resistance 0.025K/W was achieved with a small pressure drop of 25kPa. The thermal resistance predicted using CFD matched well with the experiments. The study demonstrated the capacity for impinging jet heat sinks to eliminate interfacial contact resistance and the exciting potential for 3D printed heat sinks to provide advanced integrated cooling solutions.

Research on heat transfer characteristic for hot oil spraying heating process in crude oil tank

The finite volume method and standard k−ε turbulence model are used to numerically investigate the heat transfer features of crude oil inside the floating roof tank under the hot oil spraying heating mode. The results indicate that this heat transfer process has the essential features of the thermal buoyancy jet flow. The jet flow is divided into the strong buoyancy, weak buoyancy and common buoyancy process according to Froude number of the jet flow. Bigger Froude number of the jet flow indicates stronger heat exchange strength and more uniform distribution of oil temperature. Smaller Froude number indicates stronger buoyancy, weaker heat exchange strength and more obvious hierarchical distribution feature of the oil temperature inside the tank. Two indices (efficiency and uniformity) are introduced and examined which could be of practical usage. According to the simulated result, higher nozzle speed and proper spraying temperature which results in a lager Froude number can achieve better heating effect by taking two previous indices as evaluation criterion. For the practical engineering usage, the spraying temperature and nozzle speed should be adjusted synchronously based on Froude number.