Ablative Heat Research Articles

Ablation laser and heating laser combined to cold spraying

Cold spraying is particularly suitable for the elaboration of coatings sensitive to heat and oxidation. As spraying particles are not subjected to melting, the adhesion and formation of the coating is due to the kinetic energy transmitted to the particles by accelerating gas. Bonding mechanisms are not only strongly dependent on the particle velocity but also on the state of the substrate surface. The presence of surface pollutants inhibits the coating elaboration. Surface modifications are necessary to reach a high adhesion between the coating and the substrate. A laser ablation and a laser heat treatment are proposed to prepare the substrate prior to cold spraying. Ablation laser is used to eliminate adsorbed pollutant molecules and heating laser is employed to improve the contact between substrate and particles and coating substrate adherence. The bonding of aluminium coating on aluminium 2017 alloy was evaluated by tensile adhesion tests and demonstrated the strong influence of the laser treatments in comparison with conventional processes (grit blasting and degreasing).

Ablative heat transfer in a shrinking packed‐bed of ZnO undergoing solar thermal dissociation

AbstractA transient heat transfer model is formulated for a shrinking packed‐bed of reacting ZnO particles exposed to concentrated solar irradiation. The model combines conduction, convection, and radiation heat transfer with simultaneous sintering and reaction kinetics. Validation is accomplished in terms of temperatures and dissociation rates experimentally measured using a solar‐driven thermogravimeter with ZnO packed‐bed samples subjected to solar flux concentration ratios in the range 1225–2133 suns and surface temperatures in the range 1834–2109 K. Operating conditions are typical of an ablation regime controlled by the rate of radiative heat transfer to the first layers of ZnO undergoing endothermic dissociation. © 2009 American Institute of Chemical Engineers AIChE J, 2009

On an analytical model of the aerothermodynamics of fluid–structure interaction

An analytical model of the aerothermodynamics of fluid–structure interaction through an ablative wall is developed, involving: (i) the solution to the Navier–Stokes equations in the fluid; (ii) the solution to the equations of thermoelasticity in the solid wall; (iii) the matching of the two solutions across the fluid–wall interface by continuity of normal and tangential stresses and jump of the heat flux equal to the heat of ablation. These three matching conditions determine the three constants of integration, besides the boundary conditions: (i) in the free stream far above the wall, the fluid velocity and temperature are given; (ii) in the backing material below the wall the temperature is given and displacement is assumed to be zero. In order to arrive at a simple analytical solution the simplest geometry is chosen: two-dimensional, with a flat fluid–wall interface, and all quantities in the fluid and structure depending only on distance from the wall. Extensions to unsteady and three-dimensional cases would be more complex. The present theory specifies: (i) the velocity, pressure and density in the fluid; (ii) the displacement vector, and strain and stress tensors in the structure; (iii) the temperature and heat flux in the fluid and structure, including discontinuities across the fluid–wall interface. The model is applied to examples of (a) hypersonic flight and (b) atmospheric re-entry.

Ablation mechanism of polymer layered silicate nanocomposite heat shield

Recent advances in polymer layered silicate nanocomposites especially improve flammability resistance; encourage the examination of this unique class of evolving materials as potential ablatives. Polymer layered silicate nanocomposites show excellent potential as ablative heat shields. Determining the thermal diffusivity together with the mass and energy transfer is an important problem encountered in design of heat shield system which pyrolyses and ablates at high temperature. The aim of this work is to give information on the influence of the experimental conditions to the estimated effective thermal diffusivity of ablative nanocomposite and composite materials. Here, we present the inverse solution to estimate the parameter used to identify the effective thermal diffusivity of resol type phenolic resin-asbestos cloth montmorillonite layered silicate nanocomposite and its composite counterpart. The experimental setup consists of a standard oxyacetylene flame test. The transient temperature measurements, taken from the top surface and through the thickness of the samples, are used in the inverse analysis to estimate the change of the effective thermal diffusivity. The results of this work clarify the mechanism of the ablation and thermal diffusivity of the layered silicate nanocomposite heat shields due to the high temperature degradation in comparison with its composite counterpart.

Erratum on "Erratum on 'Performance of a Low Density Ablative Heat Shield Material'"

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Improved modelling of electrothermal plasma source with radiation transport

An improved one-dimensional, time-dependent model with radiation transport is developed and used to simulate the evolution and flow of Ohmically heated nonideal plasma in the capillary of an electrothermal (ET) plasma source operated in the ablation stabilized arc regime. The model uses the Ohmic input power, recovered from the experimentally measured impedance, as the sole driving force of the computations to circumvent depending on arguable theoretical models of the resistivity of nonideal plasma. A consistent model of the equation of state and thermodynamic functions of weakly nonideal multi-component plasma mixtures is implemented and used to calculate the thermodynamic properties of the ET plasma generated from the ablation of the capillary wall. The flow velocity at the bore exit is not allowed to exceed the local sound speed and no prior assumptions of choked-flow are made at the bore exit. The frequency-dependent and frequency-averaged opacities of the plasma have been calculated considering the basic atomic processes of photoionization, inverse bremsstrahlung, resonant photoabsorption as well as electron scattering. Radiation transport has been implemented by modelling the plasma column as a grey gas the emissivity of which is calculated using an effective beam length Leb. The radiative heat flux escaping the surface of the grey plasma column is used to calculate the rate of the ablated mass improving the temporal behaviour of the calculated plasma parameters. Particular attention is devoted to investigating the ablation process and the evaluation of the so-called heat of ablation. Computational results are presented and discussed.

Correlation of Hybrid Rocket Propellant Regression Measurements with Enthalpy-Balance Model Predictions

An enthalpy-balance fuel-grain regression model is presented. The regression model, based on the longitudinally averaged fuel recession rates, is shown to accurately predict the chamber pressure, thrust and specific impulse performance of small and medium scale hybrid rocket motors. The key to the model predictions is the longitudinal enthalpy balance between the fuel grain heat of ablation and the convective heat transfer from the flame zone to the model surface. Convective heat transfer is related to the surface skin friction using the Reynolds analogy for turbulent flow. Simple flat plate models are used to predict the longitudinally averaged skin friction coefficient. Chemical properties of the combustion products were evaluated using the NASA Computer Equilibrium with Applications (CEA) Combustion code. Model predictions for a nitrous oxide (N 2 O) and hydroxylterminated poly butadiene (HTPB) motor are compared to data from a small-scale test firing with a 10.2-cm diameter motor. Suggestions for model improvements are offered.

Erratum on "Performance of a Low Density Ablative Heat Shield Material"

Erratum on "Performance of a Low Density Ablative Heat Shield Material"

A theoretical appraisal of the effectiveness of idealised ablative coatings for steel protection

The use of sacrificial ablative heat shields has proved effective in protecting spacecraft on earth re-entry. However, the use of ablative coatings in the protection of structural steel appears to be limited. This paper uses a mathematical model to assess the likely effectiveness of using such a coating on steel beam sections in furnace tests. In particular, the important coating properties are identified and quantified in order to maximise the failure time (defined as the time taken for the average steel temperature to reach a preset value such as 823 K). The model produces interesting results and demonstrates that it should be possible to use coatings of moderate thickness (∼10 mm) to attain failure times of the order of 1 h, provided that other critical coating properties such as the coating Biot number, Stefan number and diffusive timescale fall within specific ranges.

Performance of a Low Density Ablative Heat Shield Material

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Nanofilled silicone dielectrics prepared with surfactant for outdoor insulation applications

This paper reports on the heat erosion resistance of various silicone rubber compositions under infrared laser heating that simulates the dry band arcing phenomenon on outdoor insulation. The composites are made using a two-part addition cure silicone rubber, with various amounts of alumina, natural silica, or fumed silica, nano-or micron size, and different amounts of Tritontrade X-100 surfactant. It is shown that the surfactant greatly improves the dispersion of nanosized particles, yielding composites that are more homogeneous, with improved resistance to heat ablation. Significantly improved dispersion in the presence of surfactant is confirmed by SEM analysis for some nanofillers, while very little effect is observed for others. The surfactant is beneficial up to the point where the filler surface is saturated with the additive. Fumed silica is shown to impart greater heat ablation resistance than natural silica and alumina. Furthermore, a distinct protection mechanism appears to be operative for fumed silica and natural silica as opposed to alumina.

Clinical improvement and shrinkage of uterine fibroids after thermal ablation by magnetic resonance‐guided focused ultrasound surgery

Hysterectomy or myomectomy are the accepted treatments for symptomatic uterine fibroids. Heat ablation of uterine fibroids has been shown to be an effective alternative treatment. The aim of this study was to determine the clinical efficacy of non-invasive thermal ablation by transcutaneous magnetic resonance-guided high-intensity focused ultrasound (MRgFUS) for the treatment of symptomatic uterine fibroids. In this prospective study, MRgFUS ablation of uterine fibroids was performed in 35 symptomatic women scheduled for hysterectomy. Clinical symptoms, patient satisfaction and uterine size were determined at 1 month and 6 months after the procedure. This outpatient procedure was very well tolerated by all women. Sixty-nine percent (24/35) of the treated patients reported either significant or partial improvement in symptoms. Treated fibroids decreased in volume by 12% and 15% at 1 and 6 months, respectively. Minor transient side-effects were observed in two women. Six women underwent hysterectomy during the follow-up period. This study demonstrates the clinical efficacy of MRgFUS ablation of uterine fibroids. This novel, non-invasive surgical approach may offer an alternative therapy for women with uterine fibroids.

New Modality for Maximizing Cryosurgical Killing Scope While Minimizing Mechanical Incision Trauma Using Combined Freezing-Heating System

Cryosurgery is a minimally invasive surgical technique using extremely low temperature to destroy undesired tissues. A surgical freezing margin of at least 1 cm is often recommended to avoid local tumor recurrence after surgery. For treating slender or elongated solid tumors in a conventional cryosurgery, simultaneous insertion of multiple cryoprobes is a necessity to guarantee an adequate killing scope. However, the risk of mechanical incision trauma may outweigh the benefits of such therapy. To resolve this difficulty, we proposed a new cryosurgical treatment modality, which can significantly maximize the killing scope while minimize the incision trauma, using the recently developed combined cryosurgical-hyperthermia treatment system (CCHTS). The method, named as one time’s percutaneous insertion while multiple times’ freezing∕heating ablation, is rather flexible in administrating a complex cryosurgical process and avoids certain shortcomings of conventional freezing strategies. Owing to the powerful heating function, the present probe can be easily moved back along its original incision tract to the desired positions immediately after initiating the heating. Then, a new iceball can be formed there while the iceballs generated before still remain unmelted in the following cycles. Consequently, a slender iceball could be generated to embrace the whole elongated tumor. This is, however, rather hard to achieve for a conventional cryosurgery with only one single freezing function or using only one probe. To visually demonstrate the feasibility and potential advantage of the present method, proof of concept in vitro gel experiments were performed. In addition, tests and corresponding theoretical simulations were performed on pork tissues. All the results indicate that the elongated iceball could be easily generated by using only one CCHTS probe owing to its strong freezing∕heating capability. In this way, a large number of incisions with multiple probes, commonly adopted in a conventional cryosurgery, can be avoided and the serious mechanical trauma including potential dangers can thus be significantly reduced. Meanwhile, the cost for the operation and postmedical care will be lowered. The present strategies are expected to be valuable in administrating a highly efficient and minimally invasive cryosurgery in the near future.

Numerical Simulation of Thermal Stress Field of Arc-Shaped Thermal-Protection Component

For the purpose of studying material cluster design and shape design of a certain arc-shaped thermal-protection component rationally, the ablation behavior and thermal stress distribution are studied by using the method of finite element numerical simulation. The study includes ablation tests, numerical simulation of temperature field, calculation of ablation thickness and numerical simulation of unsteady thermal stress field of the component. The simulation results are consistent with the results of ablation tests, which shows that the shape design of the arc-shaped thermal-protection component is rational and the dangerous periods of the component ablation are the time of initial heating and initial ablation boundary retreat.

Determination of Thermophysical Properties for Polymer Films using Conduction Analysis of Laser Heating

Determination of the thermophysical properties of thin film materials is important for modeling and optimizing laser microvia drilling of organic substrates in microelectronics applications. Techniques to measure the density, thermal conductivity, thermal diffusivity, thermal decomposition point, and specific ablation heat of thin polymer films are described. An experimental apparatus was set up for laser heating of the sample. To measure the thermal diffusivity, an analytic heat transfer model is developed. One-dimensional heat conduction is assumed due to the small thickness of the film compared to the radius of the laser beam. The value of thermal diffusivity is obtained by fitting the experimental data to the theory. The specific ablation heat is obtained by measuring the mass loss during laser ablation. The experimental apparatus and the property determination methodology can also be applied to thin samples of other materials.

Finite Element Method for Thermal Analysis and Ablative Calculation of Heat Protection Materials

Finite element method (FEM) was used for planar ablation problem of heat protection materials based on thermal analysis. ANSYS, a commercial FEM code, was employed for modeling and calculating, and material deleting and boundary moving problems were solved with its advanced techniques. Various heat flux (HF) densities ranging from 1 to 10 MW/m2 as thermal loads were investigated to the effects of heat conduction and ablation, respectively. The results showed that a sudden thermal load can cause great temperature rise and high thermal gradient near the surface of the material. The ablative quantity and ablation rate were also calculated, and mathematical models have been deduced for them.

Retrospective Evaluation of Three Treatment Methods for Primary Hyperparathyroidism in Dogs

The medical records of 110 dogs treated for primary hyperparathyroidism were reviewed. Dogs were treated via parathyroidectomy (n=47), percutaneous ultrasound-guided ethanol ablation (n=15), or percutaneous ultrasound-guided heat ablation (n=48). Forty-five of 48 (94%) parathyroidectomies resulted in control of hypercalcemia for a median of 561 days. Thirteen of 18 (72%) ethanol ablation procedures resulted in control of hypercalcemia for a median of 540 days. Forty-four of 49 (90%) heat-ablation treatments resulted in control of hypercalcemia for a median of 581 days.

A study of tool design for minimization of heat-affected zone in rapid heat ablation process

Rapid prototyping and manufacturing (RPM) technologies have been widely adopted by the industry because of the potential of these technologies to rapidly fabricate three-dimensional parts with geometrical complexity from a CAD model in a CAD/CAM environment. Machining processes as RPM technologies have shown the fundamental disadvantages of unsatisfactory cutting mechanisms, such as excessive cutting time and leftover material caused by the cutting mechanism. Therefore, a new rapid manufacturing process using the heated tool, rapid heat ablation (RHA) process, has been developed with a new material removal method in order to solve the problems. In this paper, the tool for the RHA process is devised to minimize the heat-affected zone and also investigated for verification. TRIZ well known as creative problem solving method is applied to resolve the contradictive requirements of the tool. The devised tool has tangential grooves on the side of the tool separated into two regions for minimization of the heat-affected zone. For the detailed design of the tool, numerical model is established with several assumptions. Numerical and experimental results show that the devised tool fulfils its requirements. It demonstrates the practicality of the tool that three-dimensional shapes are ablated using the heated tool with tangential grooves.

Morphology changes of CuCl thin films induced by photo‐irradiation

AbstractWe have irradiated CuCl films, which are prepared by a vacuum vapor deposition method, with pico‐second light pulses of 82 MHz repetition rate at the photon energy of 3.290 eV. After a long time of photo‐irradiation, the photo‐irradiated region is recognized by eye for thin films. We observe the surface morphology by atomic force microscopy at room temperature. For a 50 nm thick film, surface structure changes such as surface smoothing, nanometer‐scale and micrometer‐scale structures formation are observed, which depend on the position in the photo‐irradiated region, while such changes are not detected for a 200 nm thick film. The effects of ablation and local heating by the photo‐irradiation are excluded for the mechanism of the observed morphology change. The abundance change of Cu and Cl in the film is also detected by the Auger microprobe measurement. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Preliminary studies on the planetary entry to Jupiter by aerocapture technique

Preliminary studies on the planetary entry to Jupiter by aerocapture technique are studied in order to complete technological challenges to deliver scientific probe with low cost and smaller mass of the spacecraft to Jupiter. Jupiter aerocapture corridor determination based on maximum deceleration limit of 5 g (lower corridor) and aerocapture capability (upper corridor) at Jupiter are carefully considered and calculated. The results show about 1700 m/s of saving velocity due to aerocapture could be possible in some cases for the spacecraft to be captured by Jovian gravitational field. However, the results also show that Jovian aerocapture is not available in some cases. Hence, careful selection is needed to realize Jovian aerocapture. Also the numerical simulation of aerodynamic heating to the spacecraft has been conducted. DSMC method is used for the simulation of flow fields around the spacecraft. The transient changes of drag due to Jovian atmosphere and total heat loads to the spacecraft are obtained. The results show that the estimated heat loads could be within allowable amount heat load when some ablation heat shield technique is applied.