The identification and quantification of volatile species formed in the thermal degradation of tobacco substrates was investigated by TG-FTIR analysis. A specific experimental methodology was developed to obtain quantitative data on key components of interest present in evolved gases during TG-FTIR runs in air and nitrogen at low heating rates. Multivariate deconvolution techniques were used to identify the contributions of the key components of interest to the overall FTIR spectra. Validation runs were carried out to test the limits of the TG-FTIR technique. Significant data were obtained for the quantitative characterization and the emission profiles of some key components of evolved gases, such as acetaldehyde, carbon dioxide, carbon monoxide, nicotine, and water. A different experimental strategy based on the use of a fixed bed reactor was applied to the characterization of glycerol evolved from the tobacco substrate, thus obtaining a complete figure of the main components of the evolved gases formed during the slow thermal decomposition of tobacco substrates in nitrogen and air.
The scattering and absorption of laser radiation by previously ablated plumes in laser ablation (known as the shielding effect) dramatically affect the efficiency of laser ablation process. The ablated plumes consisting of water vapor, droplets, and particles are modeled as a gas-particle equilibrium mixture by solution of the Euler equations combined with the transport equation for the ratio of heat capacities. Shielding effect on the overall ablated mass by multiple plumes is studied for a wide range of concentration of particles in vaporized plumes, various laser repetition rates, scattering, and absorption of laser energy. The shielding phenomenon is studied for short sequences of discrete plumes to focus on the shielding effect of individual plumes. The results of numerical modeling were compared to experimental results of laser-induced water explosive vaporization. Ablation rate was calculated for a single ablated plume and for the sequence of six laser pulses at the repetition rates of 0.33 and 1MHz at which gas dynamics interactions between plumes are strong but plumes have not yet form a continuous jet. A single ablated plume has an initial semispherical shape which transforms into mushroomlike cloud with a thin stem and a ring vortex as it was observed in experiments with water and cornea ablation. For the plume with a given ablated mass, the longer ejection of plume with smaller density produces the plume with smaller shielding capacity. For multiple laser pulses, the velocity of ejected mixture increases from the center of the target to its periphery because of the shielding effect. The ablated mass of the current plume depends on the attenuation of the incident laser beam energy caused by the propagation of laser beam through previously ablated plumes. In the case of laser energy absorption, the ablation rate per pulse exceeds 2–2.5 times the rate obtained for the laser energy scattering.
New generation supercomputers with three dimensional stacked chip architectures pose a major challenge with respect to removal of dissipated heat which can reach currently as high as 250 W/cm2 in multilayer chip stacks of less than 0.3 cm3 volume. Interlayer integrated water cooling [1] is a very promising approach for such high heat flux removal due to much larger thermal capacity and conductivity of water compared to air, the traditional cooling fluid. In the current work, a multiscale conjugate heat transfer model is developed for integrated water cooling of chip layers and validated with experimental measurements on a specially designed thermal test vehicle that simulates a four tier chip stack with a footprint of 1 cm2. The cooling heat transfer structure, which consists of microchannels with cylindrical pin fins, is conceived in such a way that it can be directly integrated with the device layout in multilayer chips. Every composite layer is cooled by water flow in microchannels (height: 100 μm), which are arranged in 2 port water inlet-outlet configuration. The total power removed in the stack is 390 W at a temperature gradient budget of 60 K from liquid inlet to maximal junction temperature, corresponding to about 1.3 kW/cm3 volumetric heat flow. The computational cost and complexity of detailed CFD modeling of heat transfer in stacked chips with integrated cooling can be prohibitive. Therefore, the heat transfer structure is modeled using a porous medium approach, where the model parameters of heat transfer and hydrodynamic resistance are derived from averaging the results of the detailed 3D-CFD simulations of a single stream-wise row of fins. The modeling results indicate that an isotropic porous medium model does not accurately predict the measured temperature fields. The variation of material properties due to temperature gradients are found to be large, therefore variable properties are used in the model. It is also shown that the modeling of the heat transfer in the cooling sublayers requires the implementation of a porous medium approach with a local thermal non-equilibrium as well as orthotropic heat conduction and hydrodynamic resistance. The improved model reproduces the temperatures measured in the stack within 10%. The model is used to predict the behavior of multilayer stacks mimicking the change of heat fluxes resulting from variations in the computational load of the chips during their operation.
New generation supercomputers with three dimensional stacked chip architectures pose a major challenge with respect to the removal of dissipated heat, which can reach currently as high as 250 W/cm2 in multilayer chip stacks of less than 0.3 cm3 volume. Interlayer integrated water cooling is a very promising approach for such high heat flux removal due to much larger thermal capacity and conductivity of water compared with air, the traditional cooling fluid. In the current work, a multiscale conjugate heat transfer model is developed for integrated water cooling of chip layers and validated with experimental measurements on an especially designed thermal test vehicle that simulates a four tier chip stack with a footprint of 1 cm2. The cooling heat transfer structure, which consists of microchannels with cylindrical pin-fins, is conceived in such a way that it can be directly integrated with the device layout in multilayer chips. Every composite layer is cooled by water flow in microchannels (height of 100 μm), which are arranged in two port water inlet-outlet configuration. The total power removed in the stack is 390 W at a temperature gradient budget of 60 K from liquid inlet to maximal junction temperature, corresponding to about 1.3 kW/cm3 volumetric heat flow. The computational cost and complexity of detailed computational fluid dynamics (CFD) modeling of heat transfer in stacked chips with integrated cooling can be prohibitive. Therefore, the heat transfer structure is modeled using a porous medium approach, where the model parameters of heat transfer and hydrodynamic resistance are derived from averaging the results of the detailed 3D-CFD simulations of a single streamwise row of fins. The modeling results indicate that an isotropic porous medium model does not accurately predict the measured temperature fields. The variation of material properties due to temperature gradients is found to be large; therefore, variable properties are used in the model. It is also shown that the modeling of the heat transfer in the cooling sublayers requires the implementation of a porous medium approach with a local thermal nonequilibrium, as well as orthotropic heat conduction and hydrodynamic resistance. The improved model reproduces the temperatures measured in the stack within 10%. The model is used to predict the behavior of multilayer stacks mimicking the change of heat fluxes resulting from variations in the computational load of the chips during their operation.
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