Thermal Penetration Depth Research Articles

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The second generation thermal ablation devices have been widely accepted as alternative therapies for the treatment of menorrhagia. What may be less understood by the treating gynecologist are the mechanism of thermal penetration for these devices and more importantly the depth of thermal penetration of each device into the uterine tissue. Evidence of serosal heating in the absence of uterine perforation exists for second generation devices, as evident by a review of reports to the FDA MAUDE data base and journal publications. In this evaluation, transvaginal ultrasound was employed to measure the myometrium as a pre-operative assessment for patients prior to endometrial ablation. A minimum myometrium measurement was used to determine patient candidacy for thermal endometrial ablation. Urban gynecology group practice. Pre-menopausal women presenting for evaluation and consultation for treatment options for excessive menstrual bleeding. Transvaginal ultrasound prior to endometrial ablation. Depths of thermal penetration based on documentation within SSEDs and publications for the devices will be presented to support the understanding and importance on the use of ultrasound to successfully identify patients with thinned myometrial areas, and thus exclude them from treatment with a thermal endometrial ablation device. Ultrasound examples will be presented to demonstrate myometrial evaluation, complex scenarios for assessment, and regions of identified thin areas. Transvaginal ultrasound is a valuable tool for assessment of the myometrium prior to thermal endometrial ablation. Particular attention should be paid to patients with LTCS scars or other uterine surgery in order to reduce the risk of injury in the presence of a thinned myometrium.

Effect of excimer laser annealing on the structural properties of silicon germanium films

We investigated the use of a pulsed excimer laser having a wavelength of 248 nm, a pulse duration of 38 ns, and an average fluence between 120 and 780 mJ/cm2 to locally tailor the physical properties of Si1−xGex (18% < x < 90%) films deposited by low-pressure chemical vapor deposition at temperatures between 400 and 450 °C. Amorphous as-deposited films showed, after laser annealing, strong {111} texture, a columnar grain microstructure, and an average resistivity of 0.7 mΩ cm. Atomic force microscopy indicated that the first few laser pulses resulted in a noticeable reduction in surface roughness, proportional to the pulse energy. However, a large number of successive pulses dramatically increased the surface roughness. The maximum thermal penetration depth of the laser pulse is demonstrated to depend on the fluence and the film structure being either polycrystalline or amorphous. Finally, a comparison between excimer laser annealing and metal-induced crystallization and rapid thermal annealing is presented.

Comments on “Thermophysical-property-based selection of tool protective coatings for dry machining of steels” by Wit Grezesik et al., Journal of Manufacturing Science and Engineering., Nov. 2003, Vol. 125, pp. 689–695

Contributed by the Manufacturing Engineering Division for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received January 26, 2004; revised July 20, 2004. Associate Editor: M. A. Davies.Thermal matching of coating-tool materials to optimize dry machining of steels is an interesting idea. Grezesik et al. find that the thermal properties of the materials involved, namely, the thermal diffusivity and the thermal conductivity, control the thermal and tribological behavior outputs of the machining process. Such a finding has been detailed in the discussor’s own work when studying dry sliding of metallic contacts 12, however, the physical interpretation of the contact parameter b in the manuscript is not apparent. The parameter b is originally given by: b=KρC1/2 where K is the thermal conductivity, ρ is the mass density, and C is the specific heat. In this form, the contact coefficient b represents the interaction between the injection of frictional heat normal to the surface of contact and the thermal storage of the bulk material. Now recasting the contact coefficient to the form b=KD−1/2 is perhaps more revealing of its physical significance. Note that in this form, b represents the interaction between the speed of heat injection through the surface and the speed by which the heat spreads through a given area. Now, the diffusivity will attempt to homogenize the distribution of heat throughout a given area of the material, thus attempting a uniform distribution of temperature. The conductivity, on the other hand, will attempt to inject heat normal to the contact surface. Thus, the parameter b represents a balance between heat injection and heat distribution, that is, b is a measure of heat intensity at the contact spot. Perhaps more indicative of the physical role of the parameter b is the term “coefficient of heat penetration” 3 or thermal effusivity, which indicates another physical attribute of transient thermal transport between sliding contacts. The effusivity plays a detrimental role in the evolution of heat transfer in sliding as it represents the effects of thermal inertia on a medium. In two contacting materials, the material with higher effusivity will resist the penetration of the thermal flux. Whereas the material with lower effusivity will allow deeper penetration. As such, the ratio of the effusivity of two conducting materials (such as the coating and the substrate) will influence the thickness of the thermal layer and, thereby, the dissipation of the heat flux generated in machining. Moreover, the rate of change in the effusivity will affect the rate of change in the depth of thermal penetration and, thereby, the growth of the temperature gradient. The ultimate effect will be the creation of a thermally supersaturated layer 4 that controls the quality of the machined surface and tool wear. While the generation of heat flux in machining is not directly linked to the variation in the thermal conductivity, conduction of heat away from the surface is linked to that variation. The variation of the thermal conductivity, along with the evolution of the temperature gradient, will affect the partition of the generated heat among the tool-coating assembly, the work piece, and the chip. That is, the thermal loads on each of the previous components will follow the change in the conductivity. An increase in the conductivity will lead to a corresponding increase in the heat conducted to either the work piece or the tool. If such an increase is associated with a decrease in thermal diffusion, the intensity of heat will increase locally. This will reduce the material flow stress and, therefore, frictional stress. The notion that the contact length can be effectively used for the control of heat flux and temperature at the interface was based on the temperature dependence of the thermal number Pec. It seems that the authors have avoided the physical interpretation of that number. Figure 5 of Grezesik’s paper shows a delay in reaching the maximum temperature at higher thermal numbers. This is due to the dominance of convection, which helps cooling the interface. Thus Fig. 5 suggests that the rate of temperature rise and not the temperature (and thereby thermal property variation) may be controlled by controlling the thermal number. However, this may prove difficult to achieve, as the thermal number is not a process parameter.

Characterization of regenerator materials for thermoacoustic refrigeration

A bellows bounce test apparatus using a mechanically resonant gas-filled metal bellows, coupled to moving-magnet linear motor, contained within a pressure vessel, has been developed for the testing of porous regenerator materials that might be useful for thermoacoustic refrigeration. The apparatus provides a combination of operating pressures, gases, amplitudes, and frequencies that can cover a large range of Reynolds numbers and Lautrec numbers (ratio of the hydraulic radius to the thermal penetration depth). We will report initial results obtained with this apparatus using two ceramic Celcor samples (400 and 600 cells/in*in) over four orders-of-magnitude in Reynolds number. The experimental results were in good agreement with the linear acoustic approximation at low Reynolds numbers, but deviate at higher Reynolds numbers for the viscous component of the pressure drop. For low Lautrec numbers, the dimensionless pressure drop depends on both Lautrec and Reynolds numbers. For Lautrec numbers greater than one (Poiseuille flow regime), there is no frequency (Lautrec) dependence. Similitude analysis collapses all data on both viscous (in-phase) and inertial (quadrature) pressure drops suggesting that introduction of the Lautrec number (or some dimensionless variable related to penetration depth) was required and measurements on samples of more complicated geometries should provide reliable results.

The onset of transient convection in fluid-saturated porous layer heated uniformly from below

A theoretical analysis of convective instability is conducted in an initially quiescent, fluid-saturated, horizontal porous layer heated from below with constant heat flux. Darcy's law is used to model the fluid motion and linear stability theory is employed to predict the onset of buoyancy-driven convective motion. Under the principle of exchange of stabilities, the stability analysis is performed on the basis of the propagation theory which adopts the thermal penetration depth as a characteristic length scaling factor. The result predicts the critical condition of onset of buoyancy-driven convection which is governed by the Darcy-Rayleigh number

Modeling of hot gas flow through a feed stream within a horizontal pipe

AbstractHigh heat penetration into a feed stream within a horizontal pipe is described mathematically with a gas flow and heat transfer model. Influences of varied factors on the gas flow and heat transfer in porous media are examined for different conditions. The temperature of the packed‐bed particles and the gas velocity distribution curves are obtained for the feeding service at interruption and at regular charge operating conditions. The numerical results show that the thermal effect to the packed‐bed particles by the seepage flow fluid is high only in the position near the gas entrance. The thermal penetration depth tends to increase with the seepage flow velocity and decrease with the feed rate. The operating conditions and the porosity of solid bed have importance effects on the gas velocity and temperature field in the thermal penetration zone. The model results are found to compare favorably with the experimental data available in the literature. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(6): 553–565, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10109

Heat Transfer and Gas Flow through Feed Stream within Horizontal Pipe

In the feeding process, the feed stream forms a moving packed bed of particle from the feedstock in the feed channel. When the feeding is at emergency interruption especially in the case of flooding and uncontrollable discharge, the hot gases from reactor would infiltrate into the feed stream. The high heat penetration into feed stream would affect the feeder performance. In this paper, transient thermal response of feed stream within horizontal pipe is described mathematically with a gas flow and heat transfer model. Influences of varied factors on the thermal penetration into feed stream are examined for different conditions. The temperature of the packed-bed particles and the gas velocity distribution curves are obtained for the feeding service at interruption and at normal operating conditions. The numerical results show that the thermal penetration to the packed-bed particles by the seepage flow fluid is high only in the position near the gas entrance. The thermal penetration depth tends to increase with the seepage flow velocity and decrease with feeding rate. There is no appreciable thermal penetration in the feed stream when the feeding service is at normal running. The operating conditions and the porosity of solid bed have importance effects on the gas velocity and temperature field in the thermal penetration zone. A test system is set up to determine the transient thermal response experimentally for the packed bed of particles within a horizontal pipe. The model results are found to compare favorably with the experimental data.

Time-resolved plasma spectroscopy of thin foils heated by a relativistic-intensity short-pulse laser.

Time-resolved K-shell x-ray spectra are recorded from sub-100 nm aluminum foils irradiated by 150-fs laser pulses at relativistic intensities of Ilambda(2)=2 x 10(18) W microm(2)/cm(2). The thermal penetration depth is greater than the foil thickness in these targets so that uniform heating takes place at constant density before hydrodynamic motion occurs. The high-contrast, high-intensity laser pulse, broad spectral band, and short time resolution utilized in this experiment permit a simplified interpretation of the dynamical evolution of the radiating matter. The observed spectrum displays two distinct phases. At early time, < or =500 fs after detecting target emission, a broad quasicontinuous spectral feature with strong satellite emission from multiply excited levels is seen. At a later time, the He-like resonance line emission is dominant. The time-integrated data is in accord with previous studies with time resolution greater than 1 ps. The early time satellite emission is shown to be a signature of an initial large area, high density, low-temperature plasma created in the foil by fast electrons accelerated by the intense radiation field in the laser spot. We conclude that, because of this early time phenomenon and contrary to previous predictions, a short, high-intensity laser pulse incident on a thin foil does not create a uniform hot and dense plasma. The heating mechanism has been studied as a function of foil thickness, laser pulse length, and intensity. In addition, the spectra are found to be in broad agreement with a hydrodynamic expansion code postprocessed by a collisional-radiative model based on superconfiguration average rates and on the unresolved transition array formalism.

Thermal Diffusion and Associated Stress Field due to High Speed Source

This paper presents a simple model of the thermal transport caused by a source moving at high speeds along an infinite half-space. The steady-state solution is obtained and examined to determine the effects of source velocity on the effective thermal penetration depth. The temperature field produced for a particular set of boundary conditions is then expanded to indicate how an abrupt temperature application can create a stress wave response incorporating the relationships included in a well-known hydrocode.

Femtosecond laser induced ablation of crystalline silicon upon double beam irradiation

Ultra-short pulsed laser radiation has been shown to be effective for precision materials processing. Advantages include the non-thermal nature of ablation process and short thermal penetration depth. These are ideal characteristics for precision microstructuring and controlled ablation. A crystalline silicon sample is subjected to two optically separated ultra-fast laser pulses of full width half maximum (FWHM) duration of about 80 fs. These pulses are delivered at wavelength λ=800 nm by a solid-state laser pumped Ti:Al 2O 3 femtosecond oscillator seeding a regenerative amplifier. Femtosecond-resolved imaging pump-and-probe experiments in reflective and Schlieren configurations have been performed to investigate plasma dynamics and shock wave propagation during the sample ablation process.

Detailed Numerical and Experimental Investigation of Non-Isothermal Sintering of Amorphous Polymer Material

Abstract Simulations and experiments are performed to investigate the coupled thermal and morphological response of polymer material during non-isothermal sintering. The experimental results are utilized to validate a numerical model that describes the response of the system. Predictions of the material expansion, its subsequent contraction due to sintering, and the temperature evolution are obtained and favorably compared with experimental results. Parametric simulations are performed to acquire additional insight into the dynamics of non-isothermal sintering while a relationship is established to describe the ratio of the sintering penetration depth to the thermal penetration depth and its dependence upon the boundary and initial temperatures.

Thermal Disturbances in Near Critical Fluids

Previous research into the piston effect used only the van der Waals equation of state for numerical simulation of the piston effect at conditions very close to the critical point. The real gas equation of state is used to compare the pressure and temperature response of oxygen and hydrogen at the critical pressure contained between two infinite parallel plates due to a thermal disturbance at one boundary. The plates were fixed with a separation distance of 2.5 mm. The bulk fluid was initialized to various temperatures ranging from 0.50 to 0.95 times the critical temperature, and then one plate would undergo a step change to 1 K above the critical temperature. The pressure rise in hydrogen after five acoustic time periods was only 17% of the pressure rise in oxygen. The temperature increase in hydrogen was only 30% of the temperature rise in oxygen. On the diffusion timescale, the pressure rise in the oxygen is an order of magnitude larger than the pressure rise in hydrogen for the same thermal penetration depth. The temperature rise in oxygen is four times greater than the temperature rise in hydrogen

Numerical investigations of flow and energy fields near a thermoacoustic couple.

The flow field and the energy transport near thermoacoustic couples are simulated using a 2D full Navier-Stokes solver. The thermoacoustic couple plate is maintained at a constant temperature; plate lengths, which are "short" and "long" compared with the particle displacement lengths of the acoustic standing waves, are tested. Also investigated are the effects of plate spacing and the amplitude of the standing wave. Results are examined in the form of energy vectors, particle paths, and overall entropy generation rates. These show that a net heat-pumping effect appears only near the edges of thermoacoustic couple plates, within about a particle displacement distance from the ends. A heat-pumping effect can be seen even on the shortest plates tested when the plate spacing exceeds the thermal penetration depth. It is observed that energy dissipation near the plate increases quadratically as the plate spacing is reduced. The results also indicate that there may be a larger scale vortical motion outside the plates which disappears as the plate spacing is reduced.

The use of parallel-plate regenerators in thermoacoustic-Stirling engines

The regenerator is a key element in a thermoacoustic-Stirling engine. Typically, it is made by stacking up many layers of fine-mesh stainless-steel screen. With a high heat capacity and a typical pore size much smaller than the thermal penetration depth, it provides a nearly isothermal environment at the acoustic frequency. By almost eliminating the temperature oscillations of the gas in it, the regenerator minimizes the unwanted enthalpy flux from the hot heat exchanger to ambient heat exchanger and keeps the engine’s efficiency high. However, the small pore size also causes a significant amount of viscous dissipation, which lowers the efficiency. A regenerator made of parallel plates can be designed to provide the same heat transfer properties as a screen regenerator with much lower viscous dissipation. By replacing a screen based regenerator with a carefully constructed parallel-plate regenerator, the acoustic power output of a thermoacoustic-Stirling engine is nearly doubled, with significant increases in efficiency at high amplitudes. [Work funded by the Office of Basic Energy Sciences within the U.S. DOE.]

Dynamic measurements of the thermal dissipation function of reticulated vitreous carbon

A volume modulation technique is employed to measure the complex compressibility of a gas in reticulated vitreous carbon (RVC). The complex compressibility depends on the geometry-dependent thermal coupling between the gas and the solid walls, and is related to the thermoacoustic function fκ, or equivalently F(λT). By measuring samples of different cross section and length, all external boundary effects are eliminated, so that F(λT) corresponding to bulk RVC is determined. Working down to very low frequencies achieves a wide range of values for the ratio of the thermal penetration depth to the mean pore size. As a test of the concept of “capillary-based porous media,” the results are compared to analytical solutions for F(λT) in circular, parallel plate and pin-array geometries. Measurements made at peak-to-peak gas displacement amplitudes exceeding the pore size in at least half of the sample showed no observable deviation from the small-amplitude results.

Multiquadrant digital analysis of shoulder capsular thickness

Purpose: Nonablative thermal capsular shrinkage has been developed in an attempt to address the plastic capsule deformation thought to cause increased rates of recurrent instability following arthroscopic stabilization procedures. Although the temperature required to optimize collagen shrinkage is known, a safe depth of thermal penetration, in various locations about the shoulder capsule, has not been defined. The purpose of this study was to measure shoulder capsule thickness by quadrant and circumferentially from the glenoid to the humerus so that thermal energy in shoulder procedures can be more precisely applied to limit possible injury to pericapsular structures. Type of Study: This is an anatomic study using a cadaveric shoulder specimens. Materials and Methods: Soft tissue was dissected from 8 fresh cadaveric shoulders to isolate intact glenohumeral joint capsules. The humeral insertion was released and the capsule was cut into 6 longitudinal quadrants around the glenoid. The capsule specimens were then flash frozen and stored at −80°C. Quadrant tissue was cut into longitudinal sections 14 to 16 μm wide and stained with hematoxylin and eosin. The specimens were then digitized under a dissecting microscope and measured using computer imaging software at approximately 4-mm intervals. Two-way analysis of variance (ANOVA) was performed on the measurements of the intact capsule specimens 2.5 cm off the glenoid. Humeral insertion data were recorded separately. Results: A total of 248 separate measurements were made throughout the capsule in 8 specimens. Capsular thickness increased from an average of 2.42 mm anteriorly to 2.80 mm in the inferior capsular pouch and again thinned to 2.22 mm posteriorly. Global shoulder capsule thickness ranged from 1.32 to 4.47 mm. When analyzed by position, from glenoid to humerus, a general thinning was noted with a mean thickness of 3.03 mm at the glenoid to 2.17 mm at the humeral insertion. Two-way ANOVA showed a significant thickness variation along the specimen (P <.05), a nearly significant thickness variation with regard to quadrant (P <.03), and no significant interaction (P >.07) when applied to specimen measurements approximately 2.5 cm off the glenoid. Conclusions: The thickness of the shoulder capsule ranges from 1.32 to 4.47 mm, with a significant thinning laterally from the glenoid to the humerus. Further, capsule thickness ranges from 2.76 to 3.18 mm in the regions in closest proximity to the axillary nerve. These data may help determine the proper amount of thermal penetration necessary when performing shrinkage procedures and provide safety guidelines to limit the depth of thermal penetration to avoid possible injury to pericapsular structures.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 16, No 5 (July), 2000: pp 457–461

Traveling-wave heat pumping in stack-spaced pores

Both standing and traveling waves cause heat flow near surfaces. Thermoacoustic refrigerators are based on two well-studied types of acoustically induced heat flow: (1) heat pumping concentrated about a thermal penetration depth from a surface due to a standing wave, and (2) heat pumping much closer to the surface due to a traveling wave. This talk examines another thermoacoustic pumping mechanism, induced by a traveling wave but occurring mostly a thermal penetration depth from the surface. This sort of heat pumping, therefore, is greatest for pore sizes typical of stacks rather than regenerators. Unlike ‘‘Stirling pumping’’ (traveling-wave heat pumping that occurs very close to a surface), which is independent of surface temperature gradient, this mechanism is proportional to temperature gradient. It pumps heat down the temperature gradient, and is thus a sort of ‘‘thermoacoustic short circuit,’’ detrimental to all types of working thermoacoustic devices. It appears to set an upper limit on the pore size of the regenerator in a thermoacoustic Stirling-type refrigerator that depends on temperature gradient. Analytical and graphical results will be presented, along with a Lagrangian ‘‘moving-parcel picture’’ that explains the results on physical grounds. [Work supported by ONR and NSF.]

The Principles of Micro-Thermal Analysis and its Application to the Study of Macromolecules

A newly developed Micro-Thermal Analyzer affords images based on thermal properties such as thermal conductivity, thermal diffusivity, and permits localized thermal analyses on samples of a square micrometer area by combining the imaging ability of the atomic force microscope and the thermal characterization ability of temperature-modulated differential scanning calorimetry. Since thermal penetration depth depends on frequency, one can obtain depth profiles of thermal conductivity and thermal diffusivity by varying the modulation frequency. Also, the analyzer can be used to characterize phase-transition temperatures, such as glass and melting transitions, of small sample regions with a precision of about ±3 K. Heating rates can be varied between 1 and 1500 K min−1. Modulation frequencies can be applied in the range from 2 to 100 kHz. We applied this new type of instrument to characterize microscopic thermal and structural properties of various polymer systems. The operation principles of the instrument are described, application examples are presented, and the future of the technique is discussed.

A parametric study on the cooling characteristics of an infrared detector cryochamber

This work investigates the steady and transient cooling characteristics of an infrared (IR) detector cryochamber, which has a critical effect on the cooling load that a refrigeration system should carry away. The current thermal modeling considers the conduction heat transfer through a cold well, the gaseous conduction due to outgassing, and the radiation heat transfer. The steady cooling load is obtained by using a fin equation. The transient cooling performance, i.e., the cool-down time, is determined using a finite difference method. It is shown that the gaseous conduction plays an important role in determining the steady cooling load, whereas it has a negligible effect on the cool-down time due to a short thermal penetration depth. The steady cooling load increases linearly with the bore conductivity when it is high. However, when the bore conductivity is low and the gas pressure is high, the cooling load becomes more sensitive to the bore conductivity. The steady cooling load increases linearly with the difference between the ambient temperature and the detector operation temperature, but rather the cool-down time is proportional to the square of the temperature difference. The results of this work can be used to determine the thermally optimal design and operation conditions of the cryochamber.

Depth of Thermal Penetration: Effect of Relaxation and Thermalization

Depth of Thermal Penetration: Effect of Relaxation and Thermalization