Chemical Oxygen-iodine Laser System Research Articles

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

Chemical Oxygen Iodine Laser (COIL) is the shortest wavelength (1.315 μm) chemical laser employing singlet oxygen molecules as the pumping species and iodine atoms as lasing species. Singlet Oxygen Generator (SOG) is essentially the heart of this laser device which is basically a gas–liquid phase chemical reactor. SOG facilitates the reaction between a basic hydrogen peroxide solution (BHP, H2O2 + KOH) and chlorine gas to produce singlet oxygen molecules. Centrifugal Bubble Single Oxygen Generator (CBSOG) is a potential candidate for an alternative SOG with better operating conditions for high throughput and high power COIL systems. In CBSOG Chlorine gas is bubbled through a layer of BHP solution and the required reaction takes place at the gas–liquid interface of the formed bubbles under high speed rotation of the chamber for gravity independent operation. The performance of this device largely depends on the bubble formation characteristics and their traverse inside the BHP layer. The aim of this paper is to present the numerical analysis of the mechanics of bubble formation, detachment and movement in the BHP layer for different operating parameters as applicable to COIL. The determination of conditions for the transition from bubbling to the jetting regime at different centrifugal accelerations of high magnitude (G ∼ 204 g, 306 g & 387 g) with low liquid column thickness (∼6–8 mm) operating under low pressure (∼100 torr) is another point of focus. The Volume of Fluid (VOF) method has been used for the 3-D transient interface tracking between the phases. This paper also compares the simulation results for various gas flow rates and centrifugal accelerations with select experimental results reported elsewhere showing reasonably good agreement.

Optimal design for the support structure of a cavity mirror in a chemical oxygen iodine laser resonator.

The dynamic characteristics of the cavity mirror support structure strongly influence the quality of the output beam. However, the contradiction between excellent dynamic performance and light weight make the design process challenging. To cope with the problems encountered in the original design of a chemical oxygen iodine laser system, this paper presents a two-dimensional adjustable support structure based on spherical constraints with large specific stiffness in the initial design phase. Subsequently, a two-level optimization strategy containing a macro design and a detailed design is adopted to optimize the initial structure. At the macro design stage, a two-step topology optimization procedure is introduced, in which the scale of the optimization model is dramatically reduced using the independent continuous mapping algorithm to improve the calculation speed in the first step, and the gray elements are eliminated using the bi-directional evolutionary structural optimization method to clearly obtain the optimal topology in the second step. This method is verified to overcome the defect of low efficiency, while still eliminating gray elements. At the detailed design stage, an adaptive surrogate model and the multi-objective design optimization method are employed to seek the best compromise between the lower weight and higher dynamic performance. The results from the application to the example of the cavity mirror support structure show that the mass is reduced by 41.8%, and the dynamic performance requirement is fulfilled.

A Chemosorption Vacuum Pump for a Chemical Oxygen Iodine Laser with CO2 Buffer Gases

We present the design and investigation of a novel chemosorption vacuum pump (CSVP) for discharging the exhaust gases of a chemical oxygen-iodine laser system diluted with carbon dioxide (CO2-COIL). The CSVP comprises two fixed-bed reactors separately filled with CO2/H2O and O2/I2/Cl2 adsorbents, which can efficiently chemically absorb the CO2-COIL exhaust gases at room or higher temperature. We consider the effects of the adsorbents in different specifications and fixed beds of various constructions on the adsorption performance of the CSVP. We develop and study the sealed CO2-COIL system with the CSVP. We achieve a stable operation with a cumulative duration time of 40 s for four runs and an average output power up to 2.0 kW at a Cl2 flow rate of ∼158 mmol/s and a CO2 flow rate of 132 mmol/s. The experimental results indicate that the COIL system with the CSVP performs similarly to a conventional COIL with a vacuum tank. Taking into account that the CSVP is free of vibration and noise, avoids air pollution, is easily operated, and has a short preparation time, we believe that the chemosorption vacuum pump is an excellent alternative pump system for a transportable COIL system.

An experimental research on the mixing process of supersonic oxygen–iodine parallel streams

The O 2 ( 1 Δ)/I 2 mixing process is one of the most important steps in chemical oxygen–iodine laser (COIL). Based on the chemical fluorescence method (CFM), a diagnostic system was set up to image electronically excited fluorescent I 2 (B 3 П 0 ) by means of a high speed camera. An optimized data analysis approach was proposed to analyze the mixing process of supersonic oxygen–iodine parallel streams, employing a set of qualitative and quantitative parameters and a proper percentage boundary threshold of the fluorescence zone. A slit nozzle bank with supersonic parallel streams and a trip tab set for enhancing the mixing process were designed and fabricated. With the diagnostic system and the data analysis approach, the performance of the trip tab set was examined and is demonstrated in this work. With the mixing enhancement, the fluorescence zone area was enlarged 3.75 times. We have studied the mixing process under different flow conditions and demonstrated the mixing properties with different iodine buffer gases, including N 2 , Ar, He and CO 2 . It was found that, among the four tested gases, Ar had the best penetration ability, whilst He showed the best free diffusion ability, and both of them could be well used as the buffer gas in our experiments. These experimental results can be useful for designing and optimizing COIL systems. • An analysis method of O 2 ( 1 Δ)/I 2 mixing process using CFM was proposed. • A trip tab set was demonstrated to enhance O 2 ( 1 Δ)/I 2 mixing efficiently. • The optimal flow conditions for mixing with different buffer gases were given. • A comparison between different gases used as iodine buffer gas was conducted.

A MEMS Singlet Oxygen Generator—Part II: Experimental Exploration of the Performance Space

This paper reports the quantitative experimental exploration of the performance space of a microfabricated singlet oxygen generator (muSOG). SOGs are multiphase reactors that mix H2O2, KOH, and Cl2 to produce singlet delta oxygen, or O2 (a). A scaled-down SOG is being developed as the pump source for a microfabricated chemical oxygen-iodine laser system because scaling down a SOG yields improved performance compared to the macroscaled versions. The performance of the muSOG was characterized using O2 (a) yield, chlorine utilization, power in the flow, molar flow rate per unit of reactor volume, and steady-state operation as metrics. The performance of the muSOG is measured through a series of optical diagnostics and mass spectrometry. The test rig, which enables the monitoring of temperatures, pressures, and the molar flow rate of O2 (a), is described in detail. Infrared spectra and mass spectrometry confirm the steady-state operation of the device. Experimental results reveal O2 (a) concentrations in excess of 1017 cm-3, O2 (a) yield at the chip outlet approaching 80%, and molar flow rates of 02(a) per unit of reactor volume exceeding 600 times 10-4 mol/L/s.

Application of profiled ejector in chemical lasers

Recently, the use of profiled ejectors based on constant rate of momentum change [I.W. Eames, Applied Thermal Engineering 22 (2002) 121] along the mixing chamber has been proposed for enhancing the recovery ratio across an ejector stage by minimizing shock losses for application in ejector based refrigeration system. Such ejectors can achieve pressure recovery ratio in excess of 150, thus making the system a compact one. Chemical lasers in general and chemical oxygen-iodine laser (COIL) in particular fall in the high power lasers category and find numerous applications in defense and industry. However, these lasers have not been exploited fully because these require pressure recovery systems for their operation and as such the practical systems are extremely voluminous and bulky. The profiled ejectors find direct applications in these lasers and thus can make the system extremely compact. The conventional supersonic COIL systems operate at a typical stagnation pressure of nearly 20 torr and a cavity static pressure of approximately 3 torr, which are amongst the lowest in the class of chemical lasers. Thus, a low-pressure operation of the laser system demands a high capacity vacuum system. Alternatively, efficient ejector based pressure recovery system has been utilized for achieving direct atmospheric exhaust of the lasing medium. However, a minimum of two-stage conventional supersonic ejectors need to be employed for the operation of the laser system. Multiple stages of the ejector are essential on account of the stagnation pressure loss occurring across a normal shock at the exit of the mixing chamber in each ejector stage. The present study presents a general treatment on the design of a profiled ejector for the case of dissimilar motive and suction fluids that are typical of these lasers. Also, determinations for the increase in recovery ratio for various conditions of entrainment ratio over the conventional ejectors have also been presented. Finally, a computational study using McCormack’s method for Euler system of equations has been carried out to numerically validate the analytical studies for a peripheral air ejector system suitable for a 500 W class COIL employing a flow rate of ∼3 gm/s with an entrainment ratio of 0.025. It has been concluded that a single-stage profiled ejector is sufficient to achieve atmospheric pressure recovery even in the low-pressure systems.

Computation of streamwise vorticity in a compressible flow of a winglet nozzle-based COIL device

Chemical oxygen iodine laser (COIL) is a high-power laser with potential applications in both military as well as in the industry. COIL is the only chemical laser based on electronic transition with a wavelength of 1.315 μm, which falls in the near-infrared (IR) range. Thus, COIL beam can also be transported via optical fibers for remote applications such as dismantling of nuclear reactors. The efficiency of a supersonic COIL is essentially a function of mixing specially in systems employing cross-stream injection of the secondary lasing ( I 2) flow in supersonic regime into the primary pumping (O 2 1Δ g) flow. Streamwise vorticity has been proven to be among the most effective manner of enhancing mixing and has been utilized in jet engines for thrust augmentation, noise reduction, supersonic combustion, etc. Therefore, a computational study of the generation of streamwise vorticity in the supersonic flow field of a COIL device employing a winglet nozzle with various delta wing angles of 5°, 10°, and 22.5° has been carried out. The study predicts a typical Mach number of approximately 1.75 for all the winglet geometries. The analysis also confirms that the winglet geometry doubles up both as a nozzle and as a vortex generator. The region of maximum turbulence and fully developed streamwise vortices is observed to occur close to the exit, at x/ λ of 0.5, of the winglets making it the most suitable region for secondary flow injection for achieving efficient mixing. The predicted length scale of the scalloped mixer formed by the winglet nozzle is 4 λ. Also, the winglet nozzle with 10° lobe angle is most suitable from the point of view of mixing developing cross-stream velocity of 120 m/s with acceptable pressure drop of 0.7 Torr. The winglet geometry with 5° lobe angle is associated with a low cross-stream velocity of 60 m/s, whereas the one with 22.5° lobe angle is associated with a large static and total pressure drop of 1.87 and 9.37 Torr, respectively, making both the geometries unsuitable for COIL systems. The experimental validation shows a close agreement with the computationally predicted values. The studies for the most suitable 10° lobe angle geometry show an observed Mach number of 1.72 with an improved mixing efficiency of 74% due to the occurrence of predicted streamwise vortices in the flow.

Two-stage ejector based pressure recovery system for small scale SCOIL

The chemical oxygen–iodine laser (COIL) is the only chemical laser based on electronic transitions. It is essentially a low pressure, high flow rate system requiring high capacity vacuum pumps for its operation in its standard form. Since, the output power of COIL systems is a direct function of the input fuel rate, power scale up of these systems is a definite possibility which can be utilized in numerous civil and defense applications. However, scaling up and field applications necessitates exploration of possible means of reduction in size of vacuum systems for which an efficient ejector based pressure recovery system qualifies to be the prime candidate. In this paper, the gas dynamic aspects of a two-stage peripheral air ejector system suitable for a 500 W class COIL employing a flow rate of ∼3 gm/s have been presented. The experimental results with this developed ejector system for the simulated flow conditions of the laser under vacuum have indicated a start up pressure in excess of ∼50 Torr in the first stage and more than ∼600 Torr in the second stage. The experimentally observed flow parameters at various locations in the flow field have been validated with the computational results obtained employing Fluent 6.1 software using 2-D axi-symmetric formulation.

Optical spectroscopic based in-line iodine flow measurement system – an application to COIL

Precision measurement of iodine concentration is an essential diagnostic tool in the development and optimization of chemical oxygen-iodine laser (COIL) system. A simple technique based on absorption spectroscopy has been developed and the absorption cell assembly was interfaced with the data acquisition and control system (DACS) for monitoring the iodine flow rate in real time. The assembly is being used in our 500 W COIL system and more than 600 power runs have been given.

Parametric studies of a supersonic COIL with angular jet singlet oxygen generator

Chemical oxygen-iodine laser (COIL) having a wavelength of 1.315 μm has been developed using a singlet oxygen generator (SOG) with a novel approach. Generated singlet oxygen is taken out of the SOG at an angle of 40° to avoid the problem of carry over of droplets, which is one of the major drawbacks of horizontal systems. The system has been operated using uncooled nitrogen as a buffer gas. The paper reports the results on the studies carried out on this COIL system. Under optimum conditions, we have been able to achieve stable and reproducible output power of 350 W for a chlorine flow rate of 22 mmol/s thus yielding a chemical efficiency of 17.5%.

Study on Material Processing of Chemical Oxygen Iodine Laser.

This work describes a chemical oxygen iodine laser (COIL) equipment and its application for material processing of cutting and welding. The COIL is capable of delivering high-power output. The shortwavelength (1315 nm) is suitable for the transmission using optical fibers with excellent beam quality. These characteristics make COIL a candidate for a variety of industrial applications in cutting and welding. A cutting application in decommissioning of nuclear reactors is one purpose of high power COIL system and a welding application in heavy industries of thick material is another purpose. The most important key requirement for an industrial laser is low operating cost. At this point of view there are many kinds of problemsto be solved for industrial application of COIL.

Heuristic method for evaluating COIL performance

A heuristic methodology is described that was developed to evaluate the chemical efficiency of high-power chemical oxygen iodine laser (COIL) devices and its application to the specific evaluation of the U.S. Air Force Phillips Laboratory's RotoCOIL laser. A heuristic equation that forms the basis of this methodology and describes the COIL energy flow, energy losses, and power extraction using measured data, code results, and empirical relations is presented. Using this equation and bounding values for some of its terms, it is shown that for the RotoCOIL performance data the experimentally measured average O 2 ( 1 Δ) yield of 0.40 is nearly 38% below that which would be consistent with the measured extraction power. By relating terms of the heuristic equation to performance of individual components of the COIL system, it is concluded that nearly 50% of the efficiency loss for the RotoCOIL laser derives from oxygen generator and delivery losses, whereas 15% is from nozzle inefficiencies and 11% from resonator losses.

High-power stable chemical oxygen iodine laser

A high-power chemical oxygen iodine laser system has been developed with industrial applications in mind. The present system shows fairly high efficiency, good stability, and reasonably good beam quality applicable to practical applications. Highly efficient power transmission through optical fibers has been demonstrated.

Nature of the red emission in the chemical oxygen iodine laser system

Intense red emission peaking at 703 nm is observed when a heated metal wire is placed downstream of an O 2( 1Δ g) generator used in the chemical oxygen iodine laser (COIL) system. The O 2( 1Δ g) is produced by bubbling Cl 2 through an alkaline solution of H 2O 2. Evidence is presented that strong red emission requires the presence of both O 2( 1Δ g) and Cl 2 in contact with a heated metal surface. Several metals have been used. The red emission spectrum is independent of the metal and the intensity is strongest for copper.

Development of high-power chemical oxygen-iodine laser for industrial application

A scaling up of kW-class chemical oxygen-iodine laser (COIL) is achieved. The key issues for the system design of COIL for industrial application is discussed. The scaled up COIL system of 1-kW output power is now under trial operations. In these operations, a maximum output power of 1100 W, and a continuous operation time of more than 2 h with a power of over 500 W is recorded.

New singlet oxygen generator for chemical oxygen-iodine lasers

Experiments have been carried out to investigate a new method for generating O2(1Δ) with long-time operation of an efficient chemical oxygen-iodine laser system in mind. An impinging-jet nozzle was utilized to atomize a H2O2-KOH solution so that the alkaline H2O2/Cl2 reaction might occur in droplet-gas phase with high excitation efficiency. Experimental results indicate that the present generator can yield as high as 80% of O2(1Δ) with reasonable O2 flow rate.

Efficiency of chemical oxygen-iodine lasers: Theoretical simulation and experiment

A theoretical study on the efficiency of chemical oxygen-iodine laser (COIL) oscillators is described together with experimental data obtained using an efficient COIL system. In order to evaluate chemical oxygen-iodine laser performance, three types of efficiencies (power conversion efficiency, extractable efficiency, and chemical efficiency) were introduced in this investigation. The dependencies of these efficiencies on initial gas components are investigated by theoretical simulation in which the theoretically attainable values of the efficiencies are also given. The validity of this simulation is confirmed by comparing the results with our experimental data. The experiments yielded a high-extractable power efficiency of 75%, which is comparable to the theoretically determined attainable value of 88%.