The optic-fiber sensor for measuring steam quality has been made out based on the principle of refractivity modulation. It is made up of optic head, conduct optic fiber, light source, detector and electric circuits. Reflectivity on the boundary between optic head and two-phase steam flow can be determined by refractivity of both sides of the boundary. Intensity of reflected light on the boundary is related to the ratio of water and steam. Provided we know the value of temperature or pressure of the two-phase flow, densities of water and vapor can be known and steam quality can be converted from the volume ratio of water and steam. The measuring range of steam quality is 0-100%, and the accuracy is decided by the level of steam quality measured and by resolution power of the sensor. The resolution and sensitivity of the sensor can be tested with two sorts of liquid of known refractive index. Meanwhile, the stability of output of the sensor is also approved. The sensor has been successfully used in measurement of steam quality in a steam-injection oil well with temperature of 270°C and pressure of 8MPa. The measuring result of steam quality tallies with the actual situation.
Variable temperature standard blackbody (VTSBB) is used as the standard radiation source in laboratory to calibrate working blackbodies. Calibration of VTSBB is difficult for higher requirement in emissivity and temperature. Null Balance Radiation Comparator for comparison of two IR-sources is a sensitive system, but the temperature of the source under test must be got first by other methods for emissivity calculation. The extra procedure of temperature test does not satisfy the requirement of calibration accuracy of VTSBB. By using spectral method, the emissivity and the temperature of a VTSBB will be deduced simultaneously from a series of ratios of radiance measurement. Experiment apparatus consists of five parts: IR-spectroradiometer, IR-collimator, slide stage, freezing point blackbodies (FPBB), and VTSBB. FPBB and VTSBB are laid parallel on slide stage to insure the same distances between their apertures to the IR-spectroradiometer. Radiance of two blackbodies is obtained respectively at points of selected wavelength. According to the principle of least square, emissivity and temperature of VTSBB are solutions of two radiation equations. Wavelength ranges of test are 3μm to 5μm and 8μm to 14μm. The experiment standard deviations are 0.0013 for emissivity and 0.3K for temperature.
A new method of fibre-optic sensor for measuring the steam quality is presented in this paper. A sensor based on refractive index modulation is employed. The sensor is made up of a sapphire probe and fiber, the fiber transmits the optical signal and the sapphire probe detects reflectivity of steam. The surface of sapphire probe can be considered as an assemblage of infinitesimal square-meshes, and each mesh can distinguish between water and vapor, because water and vapor has different refractive index. After measuring temperature and reflectivity as well as analyzing the relation between them and steam quality, we can obtain the steam quality. The result obtained in this paper is also important to optimize the system of fibre-optic sensor.