Three dimensional transient analysis of bubble dynamics in centrifugal bubble singlet oxygen generator for scalable COIL

The generator of singlet oxygen (SOG) remains still a challenge for a chemical oxygen-iodine laser (COIL). Hitherto, only chemical generators based on the gas-liquid reaction system (chlorine-basic hydrogen peroxide) can supply singlet oxygen, O₂(¹Δ), in enough high yields and at pressures to maintain operation of the high power supersonic COIL facilities. Employing conventional generators of jet-type or rotating disc-type makes often problems resulting mainly from liquid droplets entrained by an O₂ (¹Δ) stream into the laser cavity, and a limited scalability of these generators. Advanced generator concepts investigated currently are based on two different approaches: (i)O₂(¹Δ) generation by the electrical discharge in various configurations, eliminating thus a liquid chemistry, and (ii) O₂(¹Δ) generation by the conventional chemistry in novel configurations offering the SOG efficiency increase and eliminating drawbacks of existing devices. One of the advanced concepts of chemical generator - a spray SOG with centrifugal separation of gasliquid phases - has been proposed and investigated in our laboratory. In this paper we present a description of the generator principle, some essential results of theoretical estimations, and interim experimental results obtained with the spray SOG.

The paper describes a study of pulse-periodic operation of a chemical oxygen-iodine laser. The generator in use was of the jet type with high chlorine utilization degree (• 97%). Atomic iodine was released by dissociating methyl-iodide ( KG 3 I) in volumetric electric discharge. Steady lasing was achieved at a repetition rate up to 30 Hz. The emission energy attained per individual pulse in a train was 1.1 J at a pulse energy repeatability of (3÷ 5) % and a specific energy extraction from the active medium of 1.7 J/L. The lasing pulse duration depended on the concentra-tion of methyl-iodide and the energy deposited into discharge. The minimal half-height duration of pulses was achieved as 10 µ m at a concentration of atomic iodine in the laser cavity ~1*10 15 cm -3 . Key words: chemical oxygen-iodine laser, pulse-periodic, methyl-iodide, volumetric electric discharge The pulse-periodic chemical oxygen-iodine laser (COIL) is considered by us as a likely applicant to technologies requiring the conditions that are unattainable so far with the aid of solid-state pulse-periodic lasers. It means the range of average lasing power from 1 to 10 kW at a per-pulse lasing energy up to 10 J. There are at least two approaches possible to get COIL in pulse-periodic mode of operation. The first consists of Q-switching in the laser cavity or gain modulation in the active medium. Along with this, the active medium is produced by mixing singlet oxygen with molecular iodine just as it takes place in cw lasing case. Application of this method to formation of large-volume active media has well-known restrictions applied to relaxation processes occurred during the interaction between singlet oxygen and iodine and we’d not describe it here. Another method proposed by scientists of the Lebedev Institution and confirmed by specialists in China assumes using an initially stable mix of singlet oxygen and iodine dissociating by one or another method upon filling the laser cavity by appropriate gases [1, 2, 3].

A chemical method of atomic iodine generation for the chemical oxygen-iodine laser (COIL) was studied. This method is based on fast reaction of gaseous hydrogen iodide with chemically produced fluorine atoms formed by a preceding reaction of molecular fluorine with nitrogen oxide. Iodine at oms were generated in special reactors and injected into the supersonic flow of nitrogen in the COIL cavity. Concentration profiles of atomic iodine both along and perpendicular to the primary gas flow were measured in dependence on flow rates of the reaction gases. Very high concentration of atomic iodine (up to 3.2x10 15 cm -3 ) was measured in the laser cavity with a good yield related to both F 2 (up to nearly 100 %) and HI (up to 60%). An important advantage of this method is using of commercially available reactive gases. Some drawback of this method for its application in the COIL is a rather high gas temperature (250 – 400 K). Keywords: atomic iodine, atomic fluorine, Chemical Oxygen-Iodine Laser, COIL

A gas-sampling diagnostic has been developed to determine the molecular composition in real time of the gaseous flow emanating from a 1(Delta) g oxygen generator. This excited state oxygen is the energy source for a chemical oxygen-iodine laser (COIL). The major constituents in the flow, helium, oxygen, chlorine and water are drawn from the generator and transported to a quadrupole mass spectrometer for analysis. Information derived from this instrument such as chlorine utilization, water vapor content and flow impurities will advance our understanding of the oxygen generator performance. Precise measurements of water content are particularly important because of its energy quenching effect on I*, the lasing species in a COIL. This diagnostic may also be used to measure the mixing distribution of molecular iodine in the supersonic excited oxygen flow downstream of the nozzles. This paper discusses the criteria for the design of the gas-sampling diagnostic.

The singlet oxygen generator (SOG) generates singlet oxygen for a chemical oxygen iodine laser (COIL), using the gas-liquid reaction between basic hydrogen peroxide (BHP) and Cl2 gas. The Jet-SOG has been widely used, wherein jet BHP from small orifices reacts with Cl2 gas, and the BHP utilization is less than 1% in a single pass through the reaction zone. To improve BHP utilization, the reaction surface with Cl2 gas should be increased, and the droplet diameter of BHP should be decreased. In this study, two types of mist generators were tested for the SOG, with which 65-µm- and 15-µm-diameter droplets were generated. In the 65 µm mist generator, BHP utilization was 22.5% at the Cl2 flow rate of 8.3 mmol/s, and in the 15 µm mist generator, BHP utilization was 41.5% at the Cl2 flow rate of 9.0 mmol/s, that is, BHP utilization of the new SOG, Mist-SOG, markedly exceeded that of the conventional Jet-SOG.

Process designs were evaluated for the continuous, large-scale generation of singlet delta oxygen for use in a chemical oxygen-iodine laser. The excited singlet oxygen is generated from the chemical reaction of chlorine gas with basic hydrogen peroxide. The chemical reaction also produces a large waste brine stream that can be controlled by recycling through a chlor-alkali cell, which regenerates the reactants Cl2 and NaOH. To prevent deactivation of this excited oxygen, a large excess of hydrogen peroxide is typically used to change the reaction mechanism. This use of excess hydrogen peroxide or nonstoichiometric generation leads to substantial increases in capital and operating costs when compared with theoretical stoichiometric (no excess) generation. For the generation of singlet oxygen at a 500-kW level of equivalent lasing power, a theoretical stoichiometric plant producing all reactants has an estimated capital cost of $38 million. The capital cost for a nonstoichiometric plant is $98 million. Operating costs are $0.68 and $2.12/lb of singlet oxygen, respectively. The energy efficiency of generation is ∼6.3% for the theoretical stoichiometric flow sheet and 3.3% for the nonstoichiometric flow sheet. At this nonstoichiometric efficiency, the use of a chemical oxygen iodine laser for photoneutralization of negative ion beams is probably not competitive with other technologies below a 750-keV neutral beam level.

Functional singlet oxygen generators based on phthalocyanines

The generation of gaseous singlet oxygen by gas‐liquid reaction of chlorine with alkaline solution of hydrogen peroxide in spray form was studied experimentally on the originally designed device with a fast separation of reacted liquid from gas. The singlet oxygen yield, residual chlorine, and water vapor content in gas were measured under different experimental conditions of the centrifugal spray singlet oxygen generator (CSSOG) using nitrogen as a dilution gas. A characteristic feature of the CSSOG is a high utilization of the chemicals and production of singlet oxygen at a very high total pressure even near the atmospheric pressure. This generator developed originally for driving a chemical oxygen‐iodine laser (COIL) could be employed also as an efficient singlet oxygen source in material science, chemical synthesis, and others.

As the heart of chemical oxygen iodine laser (COIL), the singlet oxygen generator (SOG) has been focus of research for many years. A novel eject singlet oxygen generator was designed based on research of industrial ejectors and cyclone separators. Simulations and experiments were performed on the chemical reaction of O2(1). This eject SOG can make larger gas-liquid surface area through nozzle compared with traditional SOGs, and therefore it has a high chemical efficiency. Gas and liquid were separated by a cyclone separator which was designed to fit for the high separation efficiency and low residence time. This SOG has a chlorine utilization of 97%-99% and O2(1) yield of 40%-50%.

A pulsed chemical oxygen-iodine laser (COIL) using atomic iodine generated by volumetric discharge of CH3I is developed and tested. COIL with a gain length of 60 cm is energized by a square pipe-array jet singlet oxygen generator with basic hydrogen peroxide pumping circulations and operated at subsonic gas flow. Maximum output energy of 4.3 J, pulse duration of 50 μs, specific energy extraction from the active medium of 2.0 J/L, and the maximum chemical efficiency of 12.5% are achieved at a chlorine flow rate of 55 mmole/s.

Results of experimental investigation of the chemical generation of atomic iodine for a Chemical Oxygen-Iodine Laser (COIL) are presented. The work was focused on the reaction system with atomic fluorine as an intermediate species produced by the chemical way from gaseous reactants. At the first step, atomic fluorine is produced in reaction of molecular fluorine with nitrogen oxide. Then F atoms react with gaseous hydrogen iodide producing atomic iodine. The efficiency of this two-step process was studied thoroughly in dependence on mixing conditions, flow rate of reacting gases and pressure in the reactor. The results obtained on the small-scale device under experimental conditions simulating pressure and flow conditions in a COIL show that atomic iodine is generated by this alternative, advantageous method with rather high concentrations sufficient for operation of the supersonic COIL.

The recent demonstration of gain and continuous wave power extraction on the electronic P1/2 to P3/2 transition of the I atom using NCl(a1∆) as the pumping species proving the viability of the all gas-phase iodine laser (AGIL), has brought with it the need for an increased theoretical understanding of this complex system. Multiple gas phase chemical processes occur in this system: the generation of Cl atoms with F atoms, the generation of I atoms with Cl atoms, the production of NCl(a1∆) with Cl atoms and HN3, and the pumping of I to the I(P1/2) state with NCl(a1∆). Each of these processes may be composed of multiple individual chemical reactions describing production and loss processes. And finally, this set of processes occurs within a flowing gas, with the exoand endothermicity of the reactions complicating the coupling of the chemical reactions to the fluid dynamics and vice-versa. The goal of this paper is to provide an overview of the current theoretical understanding of this complex system with respect to the numerous measured finite-rate chemical processes and the coupled fluid dynamic-diffusional mixing processes. 1-D explorations of the AGIL finite-rate chemistry mechanism including sensitivity studies are shown. 3-D NavierStokes simulation studies of reactant mixing are examined, and predictions made for conditions to improve mixing and reaction in AGIL device hardware. Confirmation of these predictions in results from recent AGIL power extraction experiments is shown. * Member AIAA. Introduction The development of chemical lasers begins with the demonstration of the first iodine laser by Casper and Pimentel who in 1964 demonstrated lasing on the electronic P1/2 to P3/2 transition of atomic iodine at 1.315μm by photodissociating alkyl iodide compounds. The high energy and high atmospheric transmission of this wavelength developed considerable interest in the chemical generation of the I(P1/2) state. With no known chemical reactions directly producing high concentrations of I(P1/2), interest shifted to the use of energy transfer reactions to generate this state. Derwent, Kearns, and Thrush postulated the use of the first electronic excited state of oxygen, O2(a 1∆), as the transfer agent. O2(a∆) being both metastable and near-resonant with I(P1/2) would provide a logical energy transfer species. McDermott et al provided proof of concept for this hypothesis, demonstrating a laser based on the O2(a 1∆) to I(P3/2) energy transfer and producing the first chemical oxygen-iodine laser (COIL). With the advent of COIL also came the realization of one of its’ primary drawbacks, namely the 2 phase chemistry required to produce O2(a 1∆). The basic hydrogen peroxide solution used during O2(a 1∆) generation constitutes a large fraction of the overall weight of the system and adds water vapor, a relatively strong deactivator of I(P1/2). In order to circumvent the deleterious effects of the 2 phase COIL chemistry, energy donors for I were sought that could be generated in the gas phase at high number densities. The nitrene metastables were recognized as possible replacements for O2(a 1∆) as energy donors, primarily due to their visibility from investigations into their use as agents for generating short wavelength chemical lasers. The isovalent electronic structures of NCl(a1∆) and NF(a1∆) with respect to O2(a 1∆), long lifetimes, and the ability to generate large number densities in the gas phase made NCl(a1∆) and NF(a1∆) likely candidates for iodine energy donors. Yang et al were the first to investigate NCl(a1∆) as an iodine energy donor, measuring the transfer rate and key deactivation rates subsequently followed by a measurement of gain on the I(P1/2) to I( P3/2) transition. Similarly, Ray and Coombe measured the transfer rate followed by a pulsed laser demonstration via pulsed photolysis of ClN3 and CH2I2. With the early work of Yang et al, and Ray and Coombe establishing the viability of an NCl(a1∆) based transfer laser, significant effort was spent on measurement of the key rates constituting the complex chemistry of supporting these experiments. Henshaw measured the temperature dependence of NCl(a1∆) quenching by I(P3/2), as well as rates for chemical generation of NCl(a1∆).20 Setser with co-workers 34th AIAA Plasmadynamics and Lasers Conference 23-26 June 2003, Orlando, Florida AIAA 2003-4310 This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States.

Singlet oxygen generator is the key of chemical oxygen-iodine laser (COIL) which supplies energy for the system. However, the traditional generators have some drawbacks just as the bigger volume and the lower chemical efficiency. Specific surface area is the important factor restricting the development of singlet oxygen generator. Many researches on increasing specific surface area have been done to improve the performance of singlet oxygen generator. A new type eject singlet oxygen generator was introduced in this paper. Ejector was used in gas-liquid reaction. Liquid ejected through the nozzle with high velocity droved by high pressure, and gas ejected into mixing chamber along the tangent of nozzle. Gas and liquid were broken into many small droplets. Gas and liquid reacted in reaction chamber, then the mixture ejected into separator with very high speed. These droplets can produce mount of gas-liquid interface and increase the chemical efficiency of generator. Many numerical simulations have been done on the new type generator According to the simulations, eject singlet oxygen generator is feasible and has prospect. Therefore ejector may be a better type of singlet oxygen generator.

VNIIEF have been conducting chemical oxygen-iodine laser (COIL) research since 1982. With successive set-up optimizations, this laser had its power increased by 1986 from 10 mW to lkW and was used as a basis to design a new research set-up of about 4 kW power and about I min continuous operation [2]. COIL is traditionally designed to incoiporate a singlet oxygen generator (SOG), a heat exchanger, a laser volume and a pump out system. The schematic diagram of this laser is shown in fig. I. One of the most important parameters of COIL active medium is its temperature. One may use temperature measurements at various gas flow sections as indications of the gas flow and gas mixing homogeneity, processes kinetics, etc. During operation, alkali-solved hydrogen peroxide cooled down to T=255 is put into SOG. As chlorine gas is bubbled therethrough, singlet oxygen is generated. The oxygen together with water vapor enters the heat exchanger having temperature T= 193 K. While passing through the heat exchanger, the oxygen cools and becomes free of water vapor. The laser volume will have iodine - argon or iodine -nitrogen gas mixtme at T=393 K injected to the singlet oxygen flow. To protect the resonator mirrors, there will be also argon or nitrogen screen made in the laser volume, this being at room temperature. The gas flow has velocity up to I 00 mis in laser volume.

The pulsed chemical oxygen–iodine laser (COIL) development is aimed at many new applications. Pulsed electric discharge is most effective in turning COIL operation into the pulse mode by instant production of iodine atoms. A numerical model is developed for simulations of the pulsed COIL initiated by an electric discharge. The model comprises a system of kinetic equations for neutral and charged species, electric circuit equation, gas thermal balance equation and the photon balance equation. Reaction rate coefficients for processes involving electrons are found by solving the electron Boltzmann equation, which is re-calculated in a course of computations when plasma parameters changed. The processes accounted for in the Boltzmann equation include excitation and ionization of atoms and molecules, dissociation of molecules, electron attachment processes, electron–ion recombination, electron–electron collisions, second-kind collisions and stepwise excitation of molecules. The last processes are particularly important because of a high singlet oxygen concentration in gas flow from the singlet oxygen chemical generator. Results of numerical simulations are compared with experimental laser pulse waveforms. It is concluded that there is satisfactory agreement between theory and the experiment. The prevailing mechanism of iodine atom formation from the CF3I donor in a very complex kinetic system of the COIL medium under pulse discharge conditions, based on their detailed numerical modelling and by comparing these results both with experimental results of other authors and their own experiments, is established. The dominant iodine atom production mechanism for conditions under study is the electron-impact dissociation of CF3I molecules. It was proved that in the conditions of the experiment the secondary chemical reactions with O atoms play an insignificant role.