A new method for measuring wetness of flowing steam based on surface plasmon resonance
 Xinjiang Li^{1, 2},
 Xiaofeng Li^{1} and
 Chinhua Wang^{1}Email author
DOI: 10.1186/1556276X918
© Li et al.; licensee Springer. 2014
Received: 8 December 2013
Accepted: 5 January 2014
Published: 13 January 2014
Abstract
A novel method for realtime and inline wetness measurement based on surface plasmon resonance (SPR) is presented in this paper. The Kretschmann geometry is adopted to excite surface plasmon waves in our measurement system. In order to prevent water coating, an ultrathin layer of hydrophobic coating is formed on the surface of Au layer. The experimental results show that the level of steam wetness can be obtained via the area ratio of water and air on the prism, which is determined by analyzing the SPR spectrum of wet steam based on a Gaussian model. In addition, during the online measurement of flowing wet steam wetness, significant shifts in the resonant position of the SPR spectrum occurred, which can be attributed to the strong interaction of the adjacent water droplets.
Keywords
Stream wetness Surface plasmon resonance Kretschmann configurationBackground
Interest in wet steam research was sparked by the need for efficient steam turbines used in power generation. The subject has become increasingly important in the current decade with the steep increase in fuel cost. Since the 1970s, wetness measurement technology has made a great progress. Although with a simple principle, thermodynamic method has its disadvantages, such as a long measuring period and large error[1, 2]. Optical method, primarily based on light scattering techniques and microwave resonant cavities, has a high measuring precision, however, with the estimation of steam quality strongly depending on the droplet size classification[3–5]. Electrostatic charge and capacitance methods are new with rare studies on electrostatic charge of droplets in wet steam flow in lowpressure steam turbines[6–8]. For its high precision, tracer determination method is popular in nuclear power plants, but there are several adverse aspects such as complicated operating process, intricate data processing, and costly instruments[9, 10]. Therefore, up to now, online measurement of wetness in steam turbines as accessibility is still a major challenge.
Methods
where S_{w} and S_{g} are the area ratio of water and air on SPR surface, respectively. Here, S_{w} and S_{g} can be measured by SPR.
 1.
The transmitter unit is configured to convert the light source into a parallel light beam with transverse magnetic polarization (i.e., the magnetic field direction parallel to the metal/prism surface in Kretschmann configuration). It comprises the DH2000 Deuterium Tungsten Halogen Light Source (Ocean Optics, Dunedin, FL, USA), optical fiber, lens, and polarizer.
 2.
The core component of measuring space is the Kretschmann configuration, also referred to as attenuated total reflection, in which a 45nm Au layer is evaporated on top of a SF2 prism. In order to prevent water coating, a 2 to 3nm ultrathin layer of hydrophobic thiol coating is formed on the surface of the Au layer. In our experiments, the special container on top of the Kretschmann configuration is designed to hold water.
 3.
The receiver, which is composed of lens, optical fiber, and spectrometer, accepts the reflected light and couples it to our spectrometers.
The sensing application of the SPR system can be realized by modulating either the wavelength or incident angle[11]. The controlling of light injection angle requires a fine adjustment of the physical configuration precisely; therefore, we choose to implement such a wetness sensing through controlling and analyzing the reflection spectrum under SPR, i.e., wavelength modulation surface plasmon resonance. Since under different incident angles, SPRs occur in different wavelengths, we fix the incident angle to be 69.3° which simplifies the system as well as provides high enough sensitivity.
Results and discussion
According to the dispersion relation of SPR, the effective permittivity of air droplet (two phases) composition can be obtained without a doubt. There exist several theories which can calculate the effective permittivity of such mixtures. One of the most widely used formulations is the Maxwell Garnett (MG) theory[12]. Unfortunately, MG theory and other dielectric mixture theories[13] are useful only for the case when the gap size between the droplets is far less than the effective wavelength. Notice here that the ratio of gap size of the adjacent droplets to effective wavelength of SP is between 10^{1} and 10^{2}; therefore, the steam wetness cannot be simply derived from the summation of the twophase behavior.
Conclusions
We demonstrate a novel method for wetness measurement based on surface plasmon resonance. The obtained SPR spectrum of wet steam is analyzed by a Gaussian model. From this analysis, the area ratio of water and air via the reflectivity of SPR spectrum of wet steam is determined, and the wetness of wet steam can be obtained. Moreover, a clear shift in the resonant position of SPR with continuously spraying wet steam is observed and has been tentatively ascribed to interaction between adjacent droplets.
Abbreviations
 MG:

Maxwell Garnett
 SP:

Surface plasmon
 SPR:

Surface plasmon resonance.
Declarations
Acknowledgements
The work is supported in part by the National Natural Science Foundation of China (61378057, 91233119, and 61204066), the National 863 HighTech Project of China (2013AA031901), the National Research Foundation for the Doctoral Program of Higher Education of China (20103201110015), and the project of the Priority Academic Program Development (PAPD) of Jiangsu Higher Education Institutions.
Authors’ Affiliations
References
 Li YF, Wang XJ: Experiment technology of heating method for measuring wetness of flowing wet steam. J Eng Therm Energy Power 2001, 16(2):153–156.Google Scholar
 Wang SL, Yang SR, Wang JG: Study on a method of wetness measurement on line and industrial test for steam turbine exhaust. Proc CSEE 2005, 25(17):83–87.Google Scholar
 Kleiz A, Laali AR, Courant JJ: Fog droplet size measurement and calculation in wet steam turbines. In Proceedings of International Conference about Technology of Turbine Plant Operating with Wet Steam, BNES, IMechE, London. New York: Sage; 11–13 October 1988:177–182.Google Scholar
 Mitra C, Maity S, Banerjee A, Pandey A, Behera A, Jammu V: Development of steam quality measurement and monitoring technique using absorption spectroscopy with diode lasers. IEEE Sensors J 2011, 11(5):1214–1219.View ArticleGoogle Scholar
 Han Z, Qian J: Study on a method of steam wetness measurement based on microwave resonant cavity. In 9th International Conference on Electronic Measurement & Instruments, 2009 (ICEMI '09), Beijing, 16–19 August 2009. Piscataway: IEEE; 2009:1–604–1607.Google Scholar
 Rieger NF, Dooley RB: The influence of electrostatic charge in the phase transition zone of a steam turbine. Power Plant Chem 2001, 3(5):255–261.Google Scholar
 Luijtena CCM, van Dongena MEH, Stormbomb LE: Pressure influence in capacitive humidity measurement. Sens Actuators B 1998, 49(7):279–282.View ArticleGoogle Scholar
 Tian R, Du L, Zhang P, Ning D: Experimental research on steam wetness measurement by capacitance sensor. In 2011 AsiaPacific Power and Energy Engineering Conference (APPEEC), Wuhan, 25–28 March 2011. Piscataway: IEEE; 2011:1–5.Google Scholar
 Liu ZL, Geng GS, Gou ZC: Application of nonradioactive tracer determination in determination of primary steam humidity. Heilongjiang Electric Power 2003, 25(3):168–171.Google Scholar
 Dibelius G, Dörr A, Ederhof A, Koziorowski K, Meier F, Ossendorf E, Schermann : Erfahrungen mit der bestimmung der dampffeuchte bei den abnahmeversuchen im kernkraftwerk Biblis. VGB Kraftwerkstechnik 1977, 57(9):610–619.Google Scholar
 Li XF, Yu SF: Extremely high sensitive plasmonic refractive index sensors based on metallic grating. Plasmonics 2010, 5(4):389–394. 10.1007/s1146801091556View ArticleGoogle Scholar
 Maxwell Garnett JC: Colours in metal glasses and in metallic films. Phil Trans of the Royal Society, London, UK 1904, 203: 385–420. 10.1098/rsta.1904.0024View ArticleGoogle Scholar
 Sihvola A: Electromagnetic Mixing Formulas and Applications. London: IEEE Publishing; 1999.View ArticleGoogle Scholar
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