Characteristics of Pressure-increasing for Self-sustained Oscillationin Grooved Channels
Yongning BIAN1, Hirofumi ARIMA2, Jingbin ZHU1, Yasuyuki IKEGAMI2
1

State Key Laboratory of Structural Analysis for Industrial Equipment
Dalian University of Technology, 116024, China
2
Institute of Ocean Energy, Saga University, 840-8502, JapanThe characteristics of pressure-increasing for self-sustained oscillations in grooved channels were investigatedexperimentally. Time-varying local pressures were measured under different pressure-increasing conditions with thepressure sensor, and the effects of different pressure-increasing operation on the local pressure were also discussed. The
local pressure signal showed that there exists an effective range for increasing pressure, and with the increment of theinternal pressure in the grooved channel, the self-sustained oscillation will appear in the higher flow rate, contrast tothat of no pressure-increasing. It is seen that the optimum values of pressure-increasing are different each other for theself-sustained oscillatory flow. Moreover, it is also found that the efficient influence of pressure-increasing on theinternal pressure exists in the lower flow rate. The above results are very significant to decide the operating conditionsof the efficient heat exchanger in practical engineering.

Key Words: Optimum Value, Pressure-increasing, Self-sustained Oscillation, Grooved Channe1

1. Introduction
It must be an eternal topic to develop and utilize the new clean energy. As an important approach to realize
this purpose, 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 be further clarified.
Recently, many studies were carried out in the two- dimensional channels, including the plane channel[1], thegrooved channel[2~4], the wavy channel[5] and so on. The previous study results brought out the strengthcharacteristics of the self-sustained oscillations in the grooved channel[6] clearly, and then the effects of thepressure-increasing operation on the amplitude of the self-sustained oscillation had been fully described. 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 will be obtained. This prediction will be very significant for thepractical enhancement operation of the plate heat exchanger.
In this study, the characteristics of pressure-increasing for the self-sustained oscillations will be detected
experimentally, and more features, including the optimum value and the influence of pressure-increasing on theinternal pressure, will be clarified.
Received: 2012.6.14
E-mail: ybian@jdlut.edu.cn

2. Experimental setup
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 is used as the working fluid. The flow rate is adjusted by thecontrol valve and is measured with an electro-magnetic flowmeter; Q represents the flow rate. Five pressure
sensors are used to measure the local time-varying pressure. The valve-1 and valve-2, which are located at theoutlet of the test section and the downstream of the flowmeter respectively, are used to obtain the decreasing or
increasing pressure operating condition.
The dimensions of the test section are shown in Fig.2. Total six kinds of grooved channels, with the period
length L=20mm, W=200mm, h=2.5mm and the grooved lengths l=4,6,8,10,12,14mm, are 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 of experimental data are captured from the downstream of
the grooved channel. Moreover, the flow characteristics in all grooved channels have the similar tendencies, thus
the representative experimental results in the channel l=10mm are mainly discussed here.

Fig. 1 Schematic diagram of the experimental system

Fig. 2 Dimensions of the test section

3. Results and discussion
3.1 Self-sustained oscillation
To decide the operation condition of the pressure-increasing, the flow regime, in which the self-sustainedoscillation appears, is first examined. Fig.3 shows the representative pattern of self-sustained oscillation when
Q=340ml/s, which is recorded by the pressure sensor. Obviously, it is easy to detect the oscillation in this way.
With a mathematical filter processing, the amplitudes of the self-sustained oscillation in whole flow regime are
obtained, as showed in Fig. 4. It is sure that the self-sustained oscillation mainly appears in the regime Q=280~
360ml/s under no pressure-increasing operating condition.
3.2 Effective range of pressure-increasing
Based on a large number of experiments it is found that the pressure-increasing operation is not valid in allrange. The most effective flow range is when Q=330~360ml/s, i.e. at the later period of the self-sustained
oscillation, Fig.5 shows this phenomenon clearly. Moreover, the amplitudes sensitive to the pressure-increasing

Local pressure [kPa]

3635

34

33

00.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1380

400

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

Amplitude [kPa]

2

1

0200

220

240

260

280300

320

340

360

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

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

P [kPa]543
2
1

Effective range of pressure-increasing

0-50 -40 -30 -20 -1001020 304050 60

70 80

90 100+Q [ml/s]

Fig. 5 Sensitive range to pressure-increasing

Amplitude [kPa]

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

32

10240

260

280300320340360

380400420Q [ml/s]Fig. 6 Relationship between the amplitude and the flow rate
operation is found to exist in the range of pressure-increasing flow rate +Q=10~60ml/s. Then the optimum valueof pressure-increasing will be explored under this range of pressure-increasing flow rate.
3.3 Effective of pressure-increasing operation on the self-sustained oscillation
With the pressure-increasing operation (+Q=10~60 ml/s), the relationships between the amplitude and theflow rate are drawn in Fig.6. It is seen that the amplitudes become higher than no pressure-increasing.
Furthermore, the emergence of flow rate for the self-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 means that there is not a fixed optimum value for differentpressure-increasing operation.
3.4 Optimum value of pressure-increasing
To get the optimum value of pressure-increasing, the peak amplitudes under different pressure-increasing
conditions are checked. Corresponding to the flow rate, the relationships between the amplitude and thepressure-increasing value are showed in Fig.7. It could be seen clearly that there exits an optimum value ofpressure-increasing for different operating condition. Table 1 lists the optimum value of pressure-increasing vs.

44

Q=320 ml/s

Amplitude [kPa]

Amplitude [kPa]

Q=310 ml/s
32100102030405060

32107001020+Q [ml/s]

60705060705060

70

Q=340 ml/s

Amplitude [kPa]

Amplitude [kPa]50

4Q=325 ml/s
32132

100102030405060

700102040

44Q=360 ml/s

Amplitude [kPa]

Q=355 ml/s
321030+Q [ml/s]+Q [ml/s]

Amplitude [kPa]

40+Q [ml/s]

4030

321001020304050

60

7001020+Q [ml/s]

3040+Q [ml/s]

Fig. 7 Amplitude vs. +Q at Q=310~360ml/sdifferent flow rate. According to the data in this table, the relationship between the optimum value ofpressure-increasing and the flow rate is displayed in Fig.8, that is, approximately, the optimum +Q increases
linearly with the flow rate of the self- sustained oscillation. This result will become an important reference to thepractical operation for the heat exchanger.
3.5 Sensitivity of pressure-increasing operation
With the increment of Reynolds numbers, the effects under different pressure-increasing conditions areshowed in Fig. 9. For the no pressure-increasing condition P0, the internal pressure of the channel increases
gradually, approximately in linear. But for the pressure-increasing conditions from P+10 to P+70, the internal

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

310

320

325

340

355

360

+Q(ml/s)

1020

30

40

50

60

70

+Q [ml/s]

60
50
40
30
20+Q=0.925Q-274.9

100300

310

320

330

340

350

360

370

Q [ml/s]Fig. 8 +Q vs. Q
pressure of the channel increases with the increment of the value of the pressure-increasing. Furthermore, it isclearly seen that compared with the pressure at the higher Reynolds number, the good effects of pressureincreasing could be obtained at the lower Reynolds number. To easily confirm the above phenomena, thedifference values between each pressure-increasing value and that with no pressure-increasing are calculated andthe relationship between these difference value and the Reynolds number are showed in Fig. 10. Obviously, theeffects of pressure-increasing decline rapidly, the good effects could be found only before Re<1000.

100P0
P+10
P+30
P+50
P+70P(kPa)

80604020001000

2000

3000

Re[-]
Fig. 9 Effects of pressure-increasing operation at different Reynolds numbers

100
P+10ΔP(kPa)

80

P+30
P+50

60

P+70

40
200

1000

2000

3000

Re[-]

Fig. 15 Relationships between the differences value of pressure-increasing and the Reynolds number

4. Conclusions
In the present study, the optimum value of pressure-increasing to the self-sustained oscillation in the grooved
channels is explored experimentally. The most important results are concluded as follows:(1) The self-sustained oscillation, appearing in the later period, 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.
(3) There exists a close relationship between the effect of pressure-increasing and the Reynolds number. The
efficient influence of pressure-increasing on the internal pressure exists in the lower flow rate, i.e., Re<1000.
Acknowledgments This study was supported by the Cooperative Research Program of IOES (No. 11001A) andthe Natural Science Foundation of China (No. 11172059).

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