W. F. Kolbe

Microwave absorption coefficients of atmospheric pollutants and constituents

Abstract Calculations of the transition frequencies and absorption coefficients of microwave rotational transitions are given for a number of atmospheric pollutants and constituents. New measurements of the absorption coefficients are made in the vicinity of 70 GHz. The apparatus used in these measurements is briefly described. The calculated absorption coefficients are compared with these measurements and with existing measurements at other frequencies where available. Transitions with frequencies up to about 200 GHz are considered for the molecules and radicals SO 2 , O 3 , H 2 O, NO 2 , H 2 S, H 2 CO, NH 3 , CO, OCS, N 2 O, NO, OH, O 2 , SO. Also discussed are criteria for the selection of appropriate transitions for the development of high sensitivity monitors to be used in air pollution and combustion research.

140 GHz pulsed fourier transform microwave spectrometer

A high frequency energy pulsing system suitable for use in a pulsed microwave spectrometer (10), including means (11, 19) for generating a high frequency carrier signal, and means (12) for generating a low frequency modulating signal. The carrier signal is continuously fed to a modulator (20) and the modulating signal is fed through a pulse switch (23) to the modulator. When the pulse switch (23) is on, the modulator (20) will produce sideband signals above and below the carrier signal frequency. A frequency-responsive device (31) is tuned to one of the sideband signals and away from the carrier frequency so that the high frequency energization of the frequency-responsive device (31) is controlled by the pulse switch (23).

Absorption coefficients of sulfur dioxide microwave rotational lines

Abstract New calculations of the absorption coefficients of the rotational transitions of 32S16O2 are given for all energy levels up to J = 50 and frequencies less than 200 GHz. A spectrometer incorporating a semiconfocal Fabry-Perot resonant cavity and operating in the vicinity of 70 GHz is described. The calculated absorption coefficients are compared to measured values obtained with this spectrometer and to existing measurements over the frequency range 26–40 GHz. The results obtained are in general agreement to within 5–10%. A detailed knowledge of the absorption coefficient behavior as a function of frequency is of particular interest in the development of high-sensitivity SO2 monitors, and in investigations of the kinetics of fast chemical reactions.

Millimeter‐wave detection of free radicals using pulsed laser photolysis

The application of millimeter‐wave microwave spectroscopy to the detection of free radicals and other species generated by pulsed excimer laser photolysis is described. To detect the radical species, a newly developed 140‐GHz microwave spectrometer employing a high‐Q Fabry–Perot cavity was used. The technique is illustrated by the observation of SO and CS radicals produced by photodissociation at 193 nm of SO2 and CS2, respectively. SO absorption signals from the ground vibrational state transition at 138.17 GHz and the first and second excited vibrational state transitions at 137.28 and 136.45 GHz were measured. CS was detected in several excited vibrational states up to ν=4. Finally, as an example of the application of the technique to chemical kinetic studies, the reaction rate of SO with NO2 was determined. The measured rate coefficient at 298 K of (1.46±0.12)×10−11 cm3 molecule−1 s−1 is in excellent agreement with values reported in other studies. Millimeter‐wave spectroscopy is shown to be a sensiti...

Development of Electro-Optical Instrumentation for Reactor Safety Studies

The development of new electro-optical instrumentation for reactor safety studies is described. The system measures the thickness of the water film and droplet size and velocity distributions which would be encountered in the annular two-phase flow in a reactor cooling system. The water film thickness is measured by a specially designed capacitance system with a short time constant. Water droplet size and velocity are measured by a subsystem consisting of a continuously pulsed laser light source, a vidicon camera, a video recorder, and an automatic image analyzer. An endoscope system attached to the video camera is used to image the droplets. Each frame is strobed with two accurately spaced UV light pulses, from two sequentially fired nitrogen lasers. The images are stored in the video disk recorder. The modified automatic image analyzer is programmed to digitize the droplet size and velocity distributions. Many special optical, mechanical and electronic system components were designed and fabricated. They are described in detail, together with calibration charts and experimental results.

Sensitivity and response time improvements in a millimeter‐wave spectrometer

An improved microwave spectrometer for the detection of gaseous pollutants and other atmospheric constituents is described. The spectrometer, which operates in the vicinity of 70 GHz, employs a Fabry–Perot resonator as a sample cell and uses superheterodyne detection for high sensitivity. The instrument has been modified to incorporate a frequency doubler modulated at 30 MHz to permit operation with a single Gunn oscillator source. As a result, faster response time and somewhat greater sensitivity are obtained. The spectrometer is capable of detecting a minimum concentration of 1 ppm of SO2 diluted in air with a 1‐s time constant. For OCS diluted in air, the minimum detectable concentration is 800 ppb and with a 10‐s time constant 300 ppb.

Measurement of Thickness of Thin Water Film in Two-Phase Flow by Capacitance Method

A technique has been developed for measuring water film thickness in a two-phase annular flow system by the capacitance method. An experimental model of the flow system with two types of electrodes mounted on the inner wall of a cylindrical tube has been constructed and evaluated. The apparatus and its ability to observe fluctuations and wave motions of the water film passing over the electrodes is described in some detail.

Fast Ultrasonic Imaging in a Liquid Filled Pipe

A new method is described for the imaging of the interior of a liquid filled metallic pipe using acoustical techniques. The experimental system incorporates an array of 20 acoustical transducers and is capable of capturing the images of moving bubbles at a frame rate in excess of 300/s. The transducers are mounted circumferentially around the pipe. Each transducer is pulsed in sequence, and the echoes reflected from vapor bubbles in the interior are detected, digitized and processed by a computer to generate an image. The high rate of speed was achieved by the use of newly developed software and electronic circuitry. This approach has eliminated most of the spurious echo signals which degraded the performance of previous imaging systems. The capability of the method is illustrated by imaging actual vapor bubbles in rapid sequence in the pipe.

Acoustic Imaging of Vapor Bubbles through Optically Non-Transparent Media

A preliminary investigation of the feasibility of acoustic imaging of vapor bubbles through optically non-transparent media is described. Measurements are reported showing the echo signals produced by air filled glass spheres of various sizes positioned in an aqueous medium as well as signals produced by actual vapor bubbles within a water filled steel pipe. In addition, the influence of the metallic wall thickness and material on the amplitude of the echo signals is investigated. Finally several examples are given of the imaging of spherical bubbles within metallic pipes using a simulated array of acoustic transducers mounted circumferentially around the pipe. The measurement procedures and a description of the measuring system are also given.

Noise Considerations in Millimeter-Wave Spectrometers

An improved version of a microwave spectrometer operating in the vicinity of 70 GHz is described. The spectrometer, which incorporates a Fabry-Perot resonator and superhet-erodyne detection for high sensitivity is designed for the detection of gaseous pollutants and other atmospheric constituents. The instrument is capable of detecting polar molecules with absorption coefficients as small as 2 x 10-9cm-1. For sulphur dioxide diluted in air, this sensitivity corresponds to a detection limit of 1.2 ppm without preconcentration and with a time constant of 1 second. Measurements and analysis of the noise contributions limiting the sensitivity are presented.