Orlando Ruiz

Evaporation of Water Droplets Placed on a Heated Horizontal Surface

A numerical analysis of the evaporation process of small water droplets with diameters of I mm or less that are gently deposited on a hot isothermal solid surface has been performed. This study considers the internal fluid motion that occurs as a result of the thermocapillary convection in the droplet and it determines the effect of fluid motion on the heat transfer between the drop and the solid surface. This study is particularly relevant because the internal fluid motion has not been considered in previous numerical and analytical models presented in the literature. To assess the effects of internal fluid motion, the model results are compared to numerical results provided by a heat conduction model that neglects the fluid motion. The Navier-Stokes and Thermal Energy equations are solved using the Artificial Compressibility Method with Dual Time Stepping. Boundary-fitted grids are used to track the changes in the droplet surface shape during the evaporation process

Characterization of thermal inkjet technology TNT deposits by fiber optic-grazing angle probe FTIR spectroscopy

Fiber Optic Coupled/Grazing Angle Probe Fourier Transform Infrared Spectroscopy has made possible to develop new methods for detection of traces of chemical compounds on surfaces. Thermal Inkjet Technology is able to deposit very small amounts of chemical compounds, including energetic materials, in a specific location on a surface. Aliquots of TNT solutions were deposited on stainless steel film. A thin coating of TNT can be produced by controlling the concentration of TNT, the number of drops dispensed and the distribution of drops over the surface. A Vector 22, a Bruker Optics FTIR fiber coupled to a Remspec Corp. grazing angle head was used for the experiments. The spectra were recorded at 4 cm-1 resolution and 50 scans. The results of the experiments gave intense absorption bands in the fingerprint region of the infrared spectra that were used for quantification. Chemometrics routines were applied in the enhancement of the quantitative analysis.

Review of the various analytical techniques and algorithms for detection and quantification of TATP

The objective of this research is to design and develop a multi-sensor capable of fast detection and of recognition optimization of the techniques for used for quantification of TATP by Pattern Recognition. In particular, the long range goal of the research is to use sensor fusion and sensor “talking” modalities to couple Stand Off detectors with Chemical Point detectors for detection of airborne chemical agents and detection of Improvised Explosive Devices (IEDs). Vibrational spectroscopy techniques are very fast and can be used for real time detection. Good results have been obtained with various target molecular (chemical) systems such as TATP, TNT and DNT. Samples of TATP were detected and quantified in air, in solution and in solid phase on surfaces by different techniques. FTIR Spectroscopy and GS-MS were used to generate new analytical procedures for detection and analysis of the organic peroxide. These procedures were compared and taken to their limits by optimization with Chemometrics, Partial Least Squares (PLS), and Discriminant Analysis (DA).

Standoff infrared detection of explosives at laboratory scale

An actively operated standoff infrared detection system was designed from commercial infrared equipment: VECTOR 22 FTIR (Bruker Optics), an external mirror and an external MCT detector. One type of experiment was done for IR detection of high explosives RDX and TNT on reflective surfaces. In the detection on surface, the samples were move to different distances and a beam of infrared light was reflect on surface in angle of ~ 0° (backward collection from surface normal). First the samples: 2 to 30 μg/cm2 of high explosives TNT and RDX were characterized after depositing on stainless steel reflective surfaces using Reflection-Absorption Infrared Spectroscopy (RAIS). Then targets were moved to increasing distances: 3 to 12 feet and remote-sensed spectra were collected in active reflectance mode. The limits of detection were determined for all distances measured in both nitroexplosives. Limit of detection of 18 and 20 μg/cm2 for TNT and RDX respectively in the longest distances measured.

Characterization of layers of Tetryl, TNB, and HMX on metal surfaces using fiber optics coupled grazing angle-FTIR

Fiber optics coupled-grazing angle probe Fourier transform infrared (FTIR) spectroscopy and infrared microspectroscopy have been used for characterization of the distribution and form of layers of some explosives deposited on stainless steel sheets. Among the explosives tested were trinitrobenzene, HMX and Tetryl. Various solvents were used to deposit the films on stainless steel slides. Isopropyl alcohol was the preferred solvent because it produced more homogeneous mass distributions of target explosives on the substrates. The film thickness, analyte distribution and the relation of thickness to infrared absorption/reflection response of these explosives were compared with those previously reported for TNT, 2,4-DNT and RDX. This comparison was used for described the general optical behavior of the explosives studied.

VIBRATIONAL SPECTROSCOPY OF CHEMICAL AGENTS SIMULANTS, DEGRADATION PRODUCTS OF CHEMICAL AGENTS AND TOXIC INDUSTRIAL COMPOUNDS

This paper focuses on the measurement of spectroscopic signatures of Chemical Warfare Agent Simulants (CWAS), degradation products of chemical agents and Toxic Industrial Compounds (TIC) using vibrational spectroscopy. Raman Microscopy, Fourier Transform Infrared Spectroscopy in liquid and gas phase and Fiber Optics Coupled-Grazing Angle Probe-FTIR were used to characterize the spectroscopic information of target threat agents. Ab initio chemical calculations of energy minimization and FTIR spectra of Chemical Warfare Agents were accompanied by Cluster Analysis to correlate spectral information of real agents and simulants.

A Conservative Iterative-Based Zonal Decomposition Scheme for Conduction Heat Transfer Problems

A new conservative iterative-based zonal decomposition technique for the solution of complex heat conduction problems is proposed. This numerical technique is based on dividing the domain into subdomains and ensuring that the heat flux and temperature are continuous at the boundary between subdomains. An example problem is used to illustrate the zonal decomposition technique for both steady and transient problems. This numerical technique results in accuracy which equals or exceeds traditional finite difference solutions and solution times which are significantly less than traditional finite difference solutions. A numerical relaxation parameter is introduced and its value is optimized to provide the most rapid convergence to an accurate solution

Near Critical Heat Flux From Small Substrates Under Controlled Spray Cooling

The increasing power density on electronic components has resulted in temperature problems related to the generation of hot spots and the need to remove high heat flux in small areas. This work is aimed at the cooling of small surfaces (1 mm × 1.2 mm) by using a monodisperse spray from thermal ink jet (TIJ) atomizers. Heat fluxes near the critical heat flux (CHF) are obtained for different conditions of cooling mass flow rate, droplet deposition, and number of active droplet jets. Experimental results at quasiequilibrium show the heat flux scales to the cooling mass flow rate. It is observed that two simultaneously activated jets result in slightly smaller heat flux compared to a single jet of droplets for the same mass flow rate. Droplet momentum and spreading or splashing, as determined by a combination of Weber number and Reynolds number effect via K = We1/2 Re1/4 , may impact the efficiency of the delivery of the cooling mass flow. Current experimental results at K = 24.5 and K = 52.2 for the copper surface temperatures ranging 110 – 120 °C indicate there is little influence of the splashing on the heat dissipation. System heat losses are measured experimentally and compared to a numerical and analytical solution to estimate the actual heat dissipated by the droplet change of phase.Copyright

Detection of hazardous liquids concealed in glass, plastic, and aluminum containers

The use of liquid explosives by terrorists has raised the attention to the use of hazardous liquids as threats to people, buildings and transportation systems. Hazardous liquids such as explosive mixtures, flammables or even chemical warfare agents (CWA) can be concealed in common containers and pass security checks undetected. This work presents three non invasive, non destructive detection approaches that can be used to characterize the content of common liquid containers and detect if the liquid is the intended or a concealed hazardous liquid. Fiber optic coupled Raman spectroscopy and Stand off Raman spectroscopy were used to inspect the content of glass and plastic bottles and thermal conductivity was used to asses the liquid inside aluminum cans. Raman spectroscopy experiments were performed at 532 nm, 488 nm and 785 nm excitation wavelengths. The hazardous liquids under consideration included CWA simulant DMMP, hydrogen peroxide, acetone, cyclohexane, ethanol and nitric acid. These techniques have potential use as a detector for hazardous liquids at a check point or to inspect suspicious bottles from a distance.

CFD Model of the Thermal Inkjet Droplet Ejection Process

Numerical simulations of the thermal inkjet (TIJ) droplet ejection process are performed. The computational approach is based on a volume of fluid (VOF) formulation. This method allows determining the coupled flow and thermal fields in the firing chamber in addition to the phase change processes that take place during the drive bubble formation, expansion, and collapse. The drive bubble pressure is a result of the phase change heat transfer during the heating pulse and is not imposed by a pressure heuristic approach. A commercially available TIJ architecture was chosen as a baseline to assess the computational model predictions of ejected droplet volume and droplet velocity during a firing cycle. These computational model predictions were compared to experimental results demonstrating an excellent agreement. The transient histories of pressure in the vapor bubble, temperature, and heat transfer rate to the fluid are analyzed to explain some of the relevant physical processes observed.Copyright