N AN O E X P R E S S Open Access
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*
Abstract
A novel method for real-time 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 shift s 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 configuration
Background
Interest in wet steam research was sparked by the need
for efficient steam turbines used in power generation.
The subject has become increasingly imp ortant 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, thermo-
dynamic method has its disadvantages, such as a long
measuring period and large error [1,2]. Optical method,
primarily based on light scattering techniques and micro-
wave resonant cavities, has a high measuring precision,
however, with the estimation of steam quality strongly
depending on the droplet size classification [3-5]. Electro-
static charge and capacitance methods are new with rare
studies on electrostatic charge of droplets in wet steam
flow in low-pressure steam turbines [6-8]. For its high pre-
cision, 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
In this paper, we consider the use of surface plasmon
resonance (SPR) for measuring steam wetness. Surface
plasmon (SP) waves have been studied since the 1960s.
They can be described as a collective oscillation in electron
density at the interface of metal and dielectric. Resonance
occurs when the wave vector of surface plasmon wave
equals to the tangential component of evanescent wave
vector (i.e., the phase-matching condition) under appropri-
ate incident conditions (e.g., incident angle and wave-
length). Under SPR, the incident light will be strongly
absorbed, showing a deep reflection dip. Since a string-
ent phase-matching condition is needed, SPR is very
sensitive to the system configuration and surrounding
environment, which allows using this unique property
for m easuring steam wetness. According to the dielec-
tric theory, at room temperature, the relative dielectric
constant of saturated water vapor is close to that of air.
Therefore, the wet steam is modeled by spraying atom-
ized water on the hydrophobic coating layer of the
Kretschmann configuration with the d esigned two-
phase nozzle in the experiments. The steam wetness
is regulated through the spra ying quantity, and the
absolute wetness X is given b y [1,2,8]
X ¼
ρ
w
∅
w
ρ
w
∅
w
þ ρ
g
∅
g
100% ð1Þ
* Correspondence: chinhua.wang@suda.edu.cn
1
Institute of Modern Optical Technologies & Collaborative Innovation Center
of Suzhou Nano Science and Technology, Jiangsu Key Lab of Advanced
Optical Manufacturing Technologies & MOE Key Lab of Modern Optical
Technologies, Soochow University, Suzhou 215006, China
Full list of author information is available at the end of the article
© 2014 Li et al.; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons
Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction
in any medium, provided the original work is properly cited.
Li et al. Nanoscale Research Letters 2014, 9:18
http://www.nanoscalereslett.com/content/9/1/18