An Analytical Evaluation of the Optimal Thermal Dose Delivery Parameters for Thermal Therapies

This study derives the first analytic solution for evaluating the optimal treatment parameters needed for delivering a desired thermal dose during thermal therapies consisting of a single heating pulse. Each treatment is divided into four time periods (two power-on and two power-off), and the thermal dose delivered during each of those periods is evaluated using the non-linear Sapareto and Dewey equation relating thermal dose to temperature and time. The results reveal that the thermal dose delivered during the second power-on period when T>43C (TD2) and the initial power-off period when T>43C (TD3) contribute the major portions of the total thermal dose needed for a successful treatment (taken as 240 CEM43°C), and that TD3 dominates for treatments with higher peak temperatures. For a fixed perfusion value, the analytical results show that once the maximum treatment temperature and the total thermal dose (e.g., 240 CEM43°C) are specified, then the required heating time and the applied power magnitude are uniquely determined. These are the optimal heating parameters since lower/higher values result in under-dosing/over-dosing of the treated region. It is also shown that higher maximum treatment temperatures result in shorter treatment times, and for each patient blood flow there is a maximum allowable temperature that can be used to reach the desired thermal dose. In addition, since TD2 and TD3 contribute most of the total thermal dose, and they are both significantly affected by the blood flow present for high treatment temperatures, these results show that perfusion effects must be considered when attempting to optimize high temperature thermal therapy treatments (no excess thermal dose delivered, minimum power applied and shortest treatment time attained).

Time and Space Series Analysis of Spectral Radiation Intensities for a Partially Premixed Turbulent Flame

A recently developed technique called time and space series analysis was used to calculate the mean and fluctuating spectral radiation intensities leaving diametric and chord-like paths in turbulent partially premixed flames. A standard flame (Flame D) from Sandia Workshop on Turbulent Non-premixed Flames was selected to allow an evaluation of the radiation calculations at least at the single point statistics level. Measurements of spectral radiation intensities using a fast infrared array spectrometer provide an evaluation of the computations and also allow estimation of the length and time scales of scalar fluctuations, which appear as model parameters in the time and space series analysis modeling.

Simulation of Vorticity-Buoyancy Interactions in Fire-Whirl-Like Phenomena

In this study the commercial flow code STAR-CD has been used to simulate a laboratory experiment involving a so-called fire whirl. Such phenomena are typically characterized as exhibiting significantly enhanced mixing and consequently higher combustion rates due to an interaction of buoyancy and vorticity, but the details of this are only beginning to be understood. The present study focuses attention on this interaction in the absence of combustion, thus removing significant complications and allowing a clearer view of the vorticity-buoyancy interaction itself.

Numerical Simulation and Experimental Validation of the Dynamics of a Single Bubble During Pool Boiling Under Constant and Time-Varying Reduced Gravity Conditions

The numerical simulation and experimental validations of the growth and departure of a single bubble on a horizontal heated surface during pool boiling under reduced gravity conditions have been performed here. A finite difference scheme is used to solve the equations governing mass, momentum and energy in the vapor liquid phases. The vapor-liquid interface is captured by level set method, which is modified to include the influence of phase change at the liquid-vapor interface. The effects of reduced gravity conditions, wall superheat and liquid subcooling and system pressure on the bubble diameter and growth period have been studied. The simulations are also carried out under both constant and time-varying gravity conditions to benchmark the solution with the actual experimental conditions that existed during the parabolic flights of KC-135 aircraft. In the experiments, a single vapor bubble was produced on an artificial cavity, 10 μm in diameter microfabricated on the polished silicon wafer, the wafer was heated electrically from the back with miniature strain gage type heating elements in order to control the nucleation superheat. The bubble growth period and the bubble diameter predicted from the numerical simulations have been found to compare well with the data from experiments.

Characterization of Pore Diameters in Highly Porous Media

In this paper, a method for the experimental characterization of the equivalent pore diameter of highly porous open structures is presented. The commonly used characterization of such structures through geometrical properties like ppi number (porous per inch) and porosity proves to be not sufficient for the characterization of length scales related to heat and mass transfer. The procedure used here utilizes the quenching limits for flame propagation as characterization criterion. The determined equivalent pore diameter corresponds to the quenching diameter for a tube-geometry filled with the same combustible mixture. The quenching limit was determined by adjusting critical conditions, which are defined by a constant critical Pe´clet number comprising the laminar flame velocity instead of the flow velocity. Variations of oxygen content and air ratio were used in order to change the laminar flame speed and find the quenching limit for a given porous medium. The equivalent pore diameter determined with this method is a characteristic length scale of the porous medium geometry and is related to the heat transfer between the gas phase and the solid porous structure. The validation of the method was performed on sphere packings with well-documented properties. Several practically relevant highly porous media like foams and fabric lamellae structures were characterized and the results are discussed. Based on the effective heat conductivity (EHC) models of Zehner, Bauer and Schlu¨nder [1–3] for packed beds, an adapted model for foam structures was developed. The adapted model utilizes the equivalent pore diameters determined in the paper and predictions are presented.

Deposition of Small Particles From Turbulent Flows

This paper deals with particle deposition onto solid walls from turbulent flows. The aim of the study is to model particle deposition in industrial flows, such as the one in gas turbines. The numerical study has been carried out with a two fluid approach. The possible contribution to the deposition from Brownian diffusion, turbulent diffusion and shear-induced lift force are considered in the study. Three types of turbulent two-phase flows have been studied: turbulent channel flow, turbulent flow in a bent duct and turbulent flow in a turbine blade cascade. In the turbulent channel flow case, the numerical results from a two-dimensional code show good agreement with numerical and experimental results from other resources. Deposition problem in a bent duct flow is introduced to study the effect of curvature. Finally, the deposition of small particles on a cascade of turbine blades is simulated. The results show that the current two fluid models are capable of predicting particle deposition rates in complex industrial flows.

Microscopic Activation Phenomena in Heterogeneous Nucleation

The energy property in liquid near the wall was theoretically investigated to understand the effects of wall surface on inception process of nucleation or embryo bubble formation in boiling systems. Analyses indicate that the liquid near heating wall has higher pressure than in bulk region owing to existence of strong attractive forces, and this pressure could maintain a stable liquid microlayer and cause a steady energy peak near the wall. So a vapor embryo is likely to occur beyond the stable microlayer instead of exactly at the solid surface. The stable liquid layer may also be the inception structure of the ultrathin film before nucleation occurs. Fluctuations enhance the phenomenon of energy peak until the nucleation occurs, while energy peak promotes nucleation. Employing the concept of energy peak, the inception phenomena of the microlayer and the formation of embryo bubbles near solid surface were described.

Three Boiling Instability Modes in Silicon Microchannels

Depending on the heat flux, mass flux, and subcooling of inlet water, three boiling instability modes in silicon microchannels are possible. These are: the LTAF (Liquid/Two-phase Alternating Flow) mode, the CTF (Continuous Two-phase Flow) mode, and the LTVAF (Liquid/Two-phase/Vapor Alternating Flow) mode. It is found that the LTAF mode occurs at low heat flux and high mass flux, and has medium-amplitude temperature and pressure oscillations. The CTF mode appears at the medium heat flux and medium mass flux, and has small-amplitude temperature and pressure oscillations. The LTVAF mode appears at high heat flux and low mass flux, and has large-amplitude temperature and pressure oscillations. During the two-phase period of the LTAF mode, bubbly flow is found to be the dominant flow pattern. Some peculiar flow patterns are observed during the two-phase period of CTF and LTVAF modes under the experimental conditions.

Diode-Laser-Based Sensor Measurements of Nitric Oxide and Carbon Monoxide in Combustion Exhaust Streams

All-solid-state continuous-wave (cw) laser systems for ultraviolet (UV) absorption measurements of the nitric oxide (NO) molecule and mid-infrared (IR) absorption measurements of carbon monoxide (CO) were developed and demonstrated. For the NO sensor, 250 nW of tunable cw UV radiation at 226.8 nm is produced by sum-frequency-mixing in a beta-barium borate crystal. For the CO sensor, 2μW of tunable cw IR radiation at 4.5 μm is produced by difference-frequency mixing in a periodically-poled lithium niobate crystal. A tunable external-cavity diode laser (ECDL) provides one of the fundamental beams for both processes so that the wavelength of the generated UV/IR can be tuned over NO/CO absorption lines to produce a fully resolved absorption spectrum. The sensors were used for measurements in the exhaust stream of an operating auxiliary power unit (APU) gas turbine engine and a well-stirred reactor (WSR). During these tests, NO was measured in the exhaust at levels below 10 ppm. For measurements at levels above 20 ppm, the NO emission levels obtained using the new sensor agreed with the results of probe sampling chemiluminescent analyzer results to within 10%. A detection limit of 0.8 ppm of per meter path length at 1000 K is estimated for the NO sensor. Measurements with the CO sensor demonstrated an agreement with extractive probe sampling to within 15%. The estimated detection limit of the CO sensor is a few ppm per meter path length at 1000 K.

Theoretical Analysis of Flame Propagation in Meso and Microscale Channels

Extinction and flame propagation in a meso and microscale channels are investigated analytically. Emphasis was paid to the coupling of wall heat loss, wall preheating, external heat loss and chemical reaction. The results showed that, wall thermal properties, channel width and flow velocity have dramatic effects on the flame propagation and lead to multiple flame regimes and extinction limits. With the decrease of channel width, flame reaches its first quenching limit, the so called critical quenching distance. However, with a further decrease of channel width, the results show that there exists a slow burning flame. With the increase of wall heat loss the speed of the slow burning flame slightly decreases and eventually reaches its second burning limit. With the change of the flow velocity, the results show that sub-limit flame can only exist at flow velocity larger than a critical value. At moderate flow velocity, flame speed increases with the increase of flow speed. At very large flow velocity, flame will be blown off. The above results are confirmed from the recent experimental data.