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ber in the simulation, which was less than 350. Farmer, Pike, and
Cheng (2005) outlined the numerical models available for analyz-
ing complex processes having flow instabilities and complicated
geometries such as spray combustion, acousticwaves and transient
start-up. Breach and Ansari (2007) derived a numerical method
to model dynamically varying vapor–liquid phase equilibrium for
non-ideal binary systems by augmenting the existing constitu-
tive equations of the CFD. Mass transfer during condensation and
vaporizationwasmodeled via equivalently varying source and sink
terms. The mass transfer was governed by chemical potential at
the liquid–vapor interface. Equilibrium was assumed at the phase
boundary during transient mass transfer prior to steady state con-
ditions.Based on this survey, a reasonable number of CFD modeling
studies have been undertaken to model the hydrodynamics and
flow pattern in packed and sieve tray columns. However, a limited
CFD modeling was done to model fluid hydrodynamics over valve
trays. This is probably due to the complex gas–liquid contact upon
the tray caused by this type of valve.
2. Experimental aspects
The experimental rig comprised a 30 cmdiameter, 120 cmheight
transparent column equipped with a single valve tray, an 8 cm
height weir and two downcomers as shown in Fig. 1. A novel
method was employed to investigate the quality of gas–liquid con-
tact. A very light fluctuating plate which was able to move in
upward/downwarddirections,was installedat aheight of 8 cmfrom
the tray. This plate was fabricated from polystyrene foam with a
density of 10 kg/m3 with a total weight of 6.5 g. The air bubbles
trapped by the liquid caused the fluid to hit the fluctuating plate and
move it upward. The fluctuation frequency of this platewas used as
a criterionfor identifying the gas–liquid contactperformance onthe
tray. Three pairs of laser emitter/receiverswere placed at heights of
8.5, 9.5 and 10.5 cmfromthe tray. Thefluctuating plate aswell as the
laser emitter/receivers are also shown in Fig. 1. The red laser inter-
cepted by the receiver is sent to a digital counter that records the
number of disconnections between emitter and receivers caused by
thefluctuating plate. Three valves all of the same shape but different
weights of 10, 13.5 and 20 g were examined.
In order to provide more quantitative results, a set of pho-
tographs using a digital camera were taken from gas bubble
distribution inside the liquid phase. Experimental photographs
have been analyzed using “OlysiaM3” computer software (available
with “Olympus GX71” microscope and “Olympus DP12” camera)
to measure the bubble size distribution in the liquid for the three
examined valves.
2.1. Experimental design method
Analysis of variance (ANOVA) is a reliable tool to analyze and
determine the degree of certainty of experimental data. Nested or
hierarchical design which is an arrangement of ANOVA method, is
applied when the levels of one factor (e.g., factor B) are similar but
not identical for different levels of another factor (e.g., A). In this
design, the levels of factor B nested under the levels of factor A
(Montgomery, 2001). In the present study, the repeatability of the
measured values and the effect of valve weight on its performance
were investigated using two-stage nested designs.2.2. Experimental results
Three valves having the same shapewith differentweightswere
used. The differences in their performances were analyzed pair to
pair using two sets of two-stage nested designs. Each valve was
examined at four different airflow rates and a constant liquid flow