Optimum Values of Pressure-increasing for Self-sustained Oscillationin the grooved channel
Yongning BIAN1, Hirofumi ARIMA2, Yasuyuki IKEGAMI2, Faming SUN1
1State Key Laboratory of Structural Analysis for Industrial Equipment
Dalian University of Technology, 116024, China
2
Institute of Ocean Energy, Saga University, 840-8502, Japan
Abstract
The optimum values of pressure-increasing for self-sustained oscillations in the grooved channels areinvestigated experimentally. Time-various local pressures are measured under different pressure-increasing
conditions with the pressure sensor. The local pressure signal shows that there exists an effective range forincreasing pressure, and with the increment of the inner pressure in the grooved channel, the self-sustainedoscillation will appear in the higher flow rate, contrast to the case of no pressure-increasing. It is foundthat the optimum values of pressure-increasing are different each other for the oscillatory flow withdifferent flow rate. This behavior is very significant for the operation of the efficient heat exchanger inpractical engineering.
Key Words: Optimum value; Increasing or decreasing pressure; Self-sustained oscillation; Grooved channel
1. INTRODUCTION

2. EXPERIMENTAL SETUP

It is an eternal topic to develop and utilize the newclean energy. As an important approach to realize thispurpose, more and more efforts are worth to devote to
the study of the ocean thermal energy conversion(OTEC) system. As a fundamental element of the plate
heat exchanger, the performance of fluid flow and heattransfer in the two-dimensional channels should befurther clarified.
Many studies were carried out in the twodimensional channels, including the plane channel[1],the grooved channel[2~4], the wavy channel[5] and so on.
Based on the previous results, the strengthcharacteristics of self-sustained oscillations in thegrooved channel are carried out[6], and the effect of thepressure-increasing operation on the amplitude of theself-sustained oscillation is found. It seems that there
must have an optimum value of pressure-increasing, at
which, the maximum strength of self-sustained
oscillation and the optimum heat transfer rate would beobtained. This prediction will be very significant forthe practical enhancement operation of the plate heatexchanger.
In this study, the optimum value will be detected
experimentally and more nature behavior will becleared.

The experiments are carried out with the same
apparatus as before[6], as showed in Fig.1. The flow isprovided by a centrifugal pump and the city water isused as the working fluid. The flow rate is adjusted by
the control valve and measured with an electromagnetic flowmeter; Q re- presents the flow rate. Fivepressure sensors are used to measure the local
time-various pressure. The valve-1 and valve-2, locatedat the outlet of the test section and the downstream ofthe flowmeter respectively, are used to obtain thedecreasing or increasing pressure operating condition.

Fig. 1 Schematic diagram of the experimental
systemsensor. Obviously, it is easy to detect the oscillation inthis way. With a mathematical process, the amplitudesof self-sustained oscillation in whole flow regime areobtained, as showed in Fig. 4. It is sure that theself-sustained oscillation mainly appears in the regime
Q=280~360ml/s with no pressure-increasing.
Fig. 2 Dimensions of the test section

3. RESULTS AND DISCUSSION

3.2 Effective range of pressure-increasing
Based on a large number of experiments it is foundthat the pressure-increasing operation is not valid in allrange. The most effective flow range is when
Q=330~360ml/s, i.e. at the late period of the selfsustained oscillation, Fig.5 shows this phenomenon
clearly. Moreover, the amplitudes sensitive to thepressure-increasing operation is found to exist in therange of pressure-increasing flow rate +Q=10~60ml/s.
Then the optimum value of pressure-increasing will beexplored under this range of pressure-increasing flowrate.

3.1 Self-sustained oscillation
To decide the operation condition of the pressureincreasing, the flow regime of self-sustained oscillation
appearance is first examined. Fig.3 shows therepresentative pattern of self-sustained oscillation
when Q=340ml/s, which is recorded by the pressure

3.3 Effective of pressure-increasing operation on theself-sustained oscillation
With the pressure-increasing operation (+Q=10~60ml/s), the relationships between the amplitude and theflow rate are drawn in Fig.6. It is seen that theamplitudes become higher than no pressure-increasing.

The dimensions of the test section are shown in Fig.2.
Only one kind of grooved channel, with the period
length L=20mm, W=200mm, h=2.5mm and thegrooved lengths l=10mm, is used in this study. To
process the data conveniently, the pressure-increasing
value is represented by the change of the flow rate.
Considering the effects of the entrance length, all ofexperimental data are captured from the downstream of
the grooved channel.

6
Q=330ml/s
Q=340ml/s
Q=350ml/s
Q=360ml/s

535

P [kPa]Local pressure [kPa]

3634

432
1

33

0

0.1

0.20.30.4

0.5

0.6

0.7

0.8

0.9

Effective range of pressure-increasing

0-50 -40 -30 -20 -10104050 60

70 80

90 1004Amplitude [kPa]

2Amplitude [kPa]

20 30

Fig. 5 Sensitive range to pressure-increasing

Fig. 3 Self-sustained oscillation at Q=340ml/s

10200

10+Q [ml/s]

Time [s]220240260280300

320

340

360

380

400

+Q=10ml/s+Q=20ml/s+Q=30ml/s+Q=40ml/s+Q=50ml/s+Q=60ml/s

3210240260

280300320340360380400Q [ml/s]

Q [ml/s]Fig. 4 Amplitude of self-sustained oscillation
for whole flow retime

Fig. 6 Relationship between the amplitude
and the flow rate420

3.4 Optimum value of pressure-increasing
To get the optimum value of pressure-increasing, thepeak amplitudes under different pressure-increasing
conditions are checked. Corresponds to the flow rate,
the relationships between the amplitude and thepressure-increasing value are showed in Fig.7~12. It
could be seen clearly that there is an optimum value ofpressure-increasing for different operating condition.
Table 1 lists the optimum value of pressure-increasing
vs. different flow rate. According to the data in thistable, the relationship between the optimum value ofpressure-increasing and the flow rate is displayed inFig.13, that is, approximately, the optimum +Q
increases linearly with the flow rate of the selfsustained oscillation. This result will become an
important reference to the practical operation for theheat exchanger.

4Amplitude [kPa]

Q=325 ml/s
321001050

6070

Q=340 ml/s

2100102030

4050

6070+Q [ml/s]

Fig.10 Amplitude vs. +Q at Q=340ml/s
4Q=355 ml/s

Amplitude [kPa]

Amplitude [kPa]403

Q=310 ml/s
3210102030405060

32107001020+Q [ml/s]

3040506070+Q [ml/s]

Fig. 7 Amplitude vs. +Q at Q=310ml/s

Fig.11 Amplitude vs. +Q at Q=355ml/s

44

Q=360 ml/s

Amplitude [kPa]

Q=320 ml/s

Amplitude [kPa]3044020+Q [ml/s]
Fig.9 Amplitude vs. +Q at Q=325ml/s

Amplitude [kPa]

Furthermore, the emergence of flow rate for theself-sustained oscillation is delay with the increment ofpressure-increasing. On the other hand, the maximum
amplitude corresponding to every flow rate is different
under different pressure-increasing condition; it meansthat there is not a fixed optimum value for differentpressure-increasing operation.

32

10

32

10010203040506070+Q [ml/s]
Fig. 8 Amplitude vs. +Q at Q=320ml/s

010203040

506070+Q [ml/s]

Fig.12 Amplitude vs. +Q at Q=360ml/s

Table 1 Optimum value of pressure-increasing andflow rate of self-sustained oscillation
Q(ml/s)+Q(ml/s)

32020310
1032530340
40355
50360
6070

Acknowledgments This study was supported by theCooperative Research Program of IOES (No. 10013A)
and the Open Foundation of the State Key Laboratoryof Structural Analysis for Industrial Equipment (No.
S09203).
REFERENCES+Q [ml/s]

60
50403020+Q=0.925Q-274.9

100300

310

320

330

340

350

360

370

Q [ml/s]Fig. 13 +Q vs. Q
4. CONCLUSIONSIn the present study, the optimum value of pressureincreasing to the self-sustained oscillation in thegrooved channels is explored experimentally. The mostimportant results are concluded as follows:(1) The self-sustained oscillation, appearing in the lateperiod, is sensitive to the pressure-increasing
operation. There is an effective range when
+Q=10~60ml/s.
(2) The optimum value of pressure-increasing varies
with the flow rate of self-sustained oscillation. The
relationship between them approximately displays
a linear form.

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