heat loss comparision between leading edge groove and conventional pad bearing

7/30/2019 Heat Loss Comparision Between Leading Edge Groove and Conventional Pad Bearing.

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Comparison of power loss and pad temperature for leading edge groove

tilting pad journal bearings and conventional tilting pad journal bearings

Kyung-Bo Bang a,, Jeong-Hun Kim a, Yong-Joo Cho b

a Doosan Heavy Industries & Construction, 555 Gwigok-Dong, Changwon, Gyeongnam, Republic of Koreab Department of Mechanical Engineering, Pusan National University, 30 Jangjeon-Dong, Pusan, Republic of Korea

a r t i c l e i n f o

Article history:

Received 2 September 2008Received in revised form

24 October 2009

Accepted 4 December 2009Available online 23 December 2009

Keywords:

LEG tilting pad journal bearing

Pad temperature

Power loss

Seal tooth

a b s t r a c t

A study was undertaken to compare power loss and pad temperature characteristics between LEG

(leading edge groove) tilting pad journal bearings and conventional tilting pad journal bearings withand without a seal tooth. All test bearings were double tilting type with six-pad LOP (Load On Pad),

300.6 mm inner diameter, and 120.0 mm effective length. Pad temperatures and power losses were

compared and evaluated versus rotor rotational speed, oil flow rate, and static load. Four kinds of tilting

pad journal bearings were evaluated, conventional tilting pad journal bearings with and without a seal

tooth and LEG tilting pad journal bearings with and without a seal tooth.

Test results indicate that tilting pad journal bearings without a seal tooth have lower power loss and

pad temperature than tilting pad journal bearings with a seal tooth. Especially, conventional tilting pad

journal bearing without a seal tooth has the lowest power loss and pad temperature among the test

bearings.

& 2009 Elsevier Ltd. All rights reserved.

1. Introduction

Recent trends of steam turbine development require improved

efficiencies, increased stability, and higher ratings (4). In order to

meet these requirements, it is very important to select and design

optimal bearings. Steam turbines designed for fossil fuel power

plants operate under high steam temperatures and pressures for

60 Hz operation with a rotating speed of 3600 rpm. So, they are

easily apt to become unstable due to steam conditions. Conse-

quently, tilting pad journal bearings have been more widely used

to ensure better stability.

As turbine capacity increases, the bearing size must also

increase to support the increased rotor weight. As a result, power

loss and bearing pad temperatures also increase. Especially the tin

based babbitt metals on the pads are more prone to damaged [1].

Leopard [2] and Zeidan [3] showed that the higher temperature

due to the high speed will reduce the babbitt strength, further

limiting the load capacity of the bearing. So, power plantoperators should monitor maximum pad temperatures to ensure

bearing reliability. Recent study to decrease power loss and pad

temperature is as followings. Bang and Kim [4] proposed that pad

temperatures could be reduced by using a partial tilting pad.

Herbage [5] showed that pad temperature could be reduced by

use of copper back instead of steel back. Nicolas [6,7] designed

spray bar blocker to reduce pad temperature. Tanaka [8] and

Zeidan [3] reduced pad temperature by placing nozzles in the

spaces between adjacent pads. Nicolas [9] shows that pad

temperature could be reduced by use of pivot offset and open

end seals. Zeidan [3,10] proposed scraper to reduce inhibit flow of

hot oil. Keith Brockwell, Waldemar Dmochowski, and Scan

Decamillo [11] proposed that LEG bearings with direct lubrication

decreases power loss and pad temperatures dramatically com-

pared to conventional bearings with flooded lubrication. Scan

DeCamillo [12] and Edney SL [13] proposed that LEG bearings

without a seal tooth reduces power loss and pad temperatures

compared to LEG bearings and conventional bearings with a seal

tooth. However, they did not consider conventional bearings

without seal tooth.

Hence, the experimental testing presented in this paper was

conducted to evaluate performance of LEG journal bearings and

conventional journal bearings for steam turbines with and

without a seal tooth. The bearings were six-pad LOP (load on

pad) normally used for high pressure steam turbine applications.

Pad temperature and power losses were measured to compare thestatic performance of LEG journal bearings with conventional

journal bearings. Tests were conducted at various rotating speeds,

bearing loads, and oil flow rates.

2. Experimental set-up

2.1. Test equipment

The test bearing is mounted in the center of the test rig and

support a rotor with a 300mm diameter journal. This rotor is

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Contents lists available at ScienceDirect

journal homepage: www.elsevier.com/locate/triboint

Tribology International

0301-679X/$ - see front matter & 2009 Elsevier Ltd. All rights reserved.

doi:10.1016/j.triboint.2009.12.002

Corresponding author. Tel.: + 8255 2783721; fax: +82 55278 8593.

E-mail address: [email protected] (K.-B. Bang).

Tribology International 43 (2010) 12871293
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1.5 m long and supported by two ball bearings at each end of the

shaft. An air bellows located under the bearing casing to apply the

load to the bearing. Bearing load is adjusted and monitored with a

load cell under the bearing casing. A 225 kW DC motor was

connected to the driving shaft via a belt and pulley. Fig. 1 shows a

schematic of test equipment. A lubrication system supplied ISO

VG32 grade oil to the bearing, which is controlled at a constant

40 1C by a heater and a cooler. A torque meter is installed between

the driving shaft and driven shaft to measure bearing power loss.The test equipment in this study is shown in Fig. 2. Power loss was

measured by multiplying torque and shaft speed. Torquemeter

was installed between driving shaft and driven shaft. And

tachometer was used in order to measure shaft speed. Table 1

shows details of the test equipment capacities.

2.2. Test bearings

Table 2 gives test bearing dimensions. Four bearings were

tested: LEG journal bearings with and without a seal tooth and

conventional journal bearings with a seal tooth and without a seal

tooth. All test bearings are double tilting pad journal bearings

with integral ball type pivot which can tilt axial and tangential

direction.

Fig. 3 shows the seal tooth configuration. Bearings with a seal

tooth have 0.5 mm seal tooth clearance and bearings without a

seal tooth have clearance of 4.0 mm as shown in Table 3.

Fig. 4 shows photos of these test bearings. Rotational direction

was counter-clockwise. Five K-type thermocouples with 1 mm

diameter were installed on each pad at the bearing centerline

position at 5%, 60%, 70%, 80%, 95% of each pad arc length as shown

in Fig. 5. Thermocouples were installed 22.5mm below bearing

surface and the tip of thermocouple is located in the babbitt layer.

2.3. Test conditions

Test conditions are shown in Table 4

Usual bearing load which is 10 kN was selected considering

eccentricity and usual flow rate which is 60 L/min was decided to

make temperature difference 15 1C between oil supply tempera-

ture and oil drain temperature.

2.4. Test procedure

Test was conducted as followings. After installing test bearing,

oil flowed into test bearing in order to flush. Flushing continued to

become oil temperature 401

C. After flushing, bearing load was

Fig. 1. Schematic of test equipment.

Fig. 2. Photos of test equipment.

Table 1

Test equipment capacity.

Equipment Capacity Accuracy

Torquemeter 500 Nm 70.1%

Oil flow rate 200 L/min 71L/min

Load cell 20 Ton 710kg

Table 2

Test bearing dimensions.

Parameter Value

Journal diameter (mm) 300.00

Bearing inner diameter (mm) 300.62

Bearing length (mm) 120.00

Preload 0.0

Effective pad angle (deg) 45.0

Pivot type Integral ball

Pivot offset 0.5

Number of pads 6

Load type LOP

Fig. 3. Configuration of seal tooth: (a) with seal tooth and (b) without seal tooth.

Table 3

Type of test bearings.

Configuration Seal tooth clearance (mm)

Bearing with seal tooth 0.5

Bearing without seal tooth 4.0

K.-B. Bang et al. / Tribology International 43 (2010) 128712931288


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adjusted to zero with air bellows. Before rotor rotates, torque-

meter was adjusted to zero.

When rotor rotates, rotational speed was monitored with

tachometer. As rotor rotates, pad temperature rise due to viscous

friction between rotor and bearing. After pad temperature was

saturated, pad temperature and power loss was measured.

Power loss of bearings was measured by torque and shaft speed.

In order to measure power loss of only tilting pad journal bearings,

power loss of ball bearings to support rotor was measured.In order to secure reliability of test equipment, preliminary

test was conducted. From the preliminary test, difference of pad

temperature is nearly 71.5 1C, and load is 1.0%. Uncertainty

associated with power loss of bearings was nearly 0.4% at

maximum power loss of bearings. Uncertainty of power loss

was regarded small as compared with bearing power loss.

3. Results and discussion

3.1. Power loss vs. bearing load

Fig. 6 shows power loss as a function of rotational speed at a

load of 10 kN and an oil flow of 60 L/min. Journal bearings withouta seal tooth have a lower power loss than journal bearings with a

seal tooth. And as rotational speed increases, power loss of journal

bearings without a seal tooth increase more slowly than those of

journal bearings with a seal tooth.

The conventional journal bearing without a seal tooth has the

lowest power loss of all bearings tested. At 4200 rpm, power loss

of the conventional bearing without a seal tooth was 39.2% lower

than that of the conventional bearing with a seal tooth and 11.3%

lower than the LEG journal bearing without a seal tooth.

Fig. 7 shows power loss versus rotational speed with 60 L/min

oil flow by bearing load. As the bearing load increased from 5 to

20 kN, the power loss of bearing without a seal tooth increased

only 5% at 4200rpm. Other bearings have a similar trend.

Fig. 8 shows power loss versus bearing load with 60 L/min at4200rpm. Power loss of the conventional bearing without a seal

tooth has the lowest power loss of all bearings tested. From these

results, conventional journal bearing without seal tooth has effect

to decrease power loss. And it is evident that the effect of bearing

load on power loss diminishes as rotational speed increases.

Fig. 4. Photos of test bearings: (a) LEG with seal tooth and (b) conv. w/o seal tooth.

Fig. 5. Position of thermocouples: (a) LEG bearing and (b) conventional bearing.

Table 4

Test conditions.

Rotational speed (rpm) Bearing load (kN) Flow rate (L/min)

600

1200

1800 5 30

2400 10 60

3000 15 90

3600 20 120

4200

Fig. 6. Power loss vs. rotational speed with 10 kN, 60 L/min.

K.-B. Bang et al. / Tribology International 43 (2010) 12871293 1289


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3.2. Power loss vs. flow rate

Fig. 9 shows power loss vs. rotational speed by flow rate.

As rotational speed increases, power loss of bearing with a seal

tooth increases sharply. And bearings without a seal tooth havelower power loss than bearings with as seal tooth.

Fig. 10 shows power loss versus flow rate at 4200 rpm with

10 kN. As flow rate decreases, power loss of the bearing without a

seal tooth has lower power loss than conventional bearing with a

seal tooth and LEG bearings.

These results indicate that low flow rate is a very important

factor for decreasing power loss at high speed.

3.3. Pad temperature vs. bearing load

Fig. 11 shows pad temperature profile versus rotational speed.

At 600rpm, maximum pad temperature of the conventional bearing

without a seal tooth is lower than LEG bearing with a seal tooth. But

the difference of pad temperatures between bearings with a seal

tooth and bearings without a seal tooth is relatively small.

On the other hands, maximum pad temperature of conven-

tional bearing without a seal tooth is lower nearly 10.1% for the

LEG bearing without a seal tooth and 16.6% for the LEG bearing

with a seal tooth.From test results, LEG bearing with seal tooth has no good

effect to decrease pad temperature.

Fig. 12 shows pad temperature profile versus position by

varying bearing load at 4200 rpm. As bearing load increases,

maximum pad temperature increased. Under same test

conditions, conventional bearing without a seal tooth has lower

maximum pad temperature than other bearings. At bearing load

increased to 20 kN, LEG bearings have higher pad temperature

than conventional bearings. Particularly, LEG bearing with seal

tooth has highest maximum pad temperature than other bearings.

Fig. 13 shows maximum pad temperature versus bearing load

with 60L/min at 4200rpm.

At low load, journal bearing without a seal tooth has lower pad

temperature. But as bearing load increases, pad temperature of

Fig. 7. Power loss vs. rotational speed with 60 L/min.

Fig. 8. Power loss vs. bearing load with 60 L/min at 4200rpm.

Fig. 9. Power loss vs. rotational speed at 10 kN.

Fig. 10. Power loss vs. flow rate at 10kN, 4200rpm.



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LEG bearings without seal tooth increases more sharply than

other bearings.

That means LEG bearings without seal tooth has lower pad

temperature but increasing rate of pad temperature is higher than

that of conventional bearing without seal tooth.

Fig. 14 shows inlet temperature of loaded pad versus bearingload with 60 L/min at 4200 rpm. Journal bearings without a seal

tooth have lower inlet pad temperature than journal bearings

with a seal tooth. This means that quantity of drained oil from

previous pad at bearings without seal tooth is small. Because

journal bearing without seal tooth increases side leakage due to

large clearance. So pad inlet temperature is low. But because total

supply oil at pad inlet is small, increasing rate of pad temperature

is high comparatively.

3.4. Pad temperature vs. flow rate

Fig. 15 shows pad temperature profile versus position by

varying flow rate at 4200 rpm. At loaded pad, maximum pad

Fig. 11. Pad temperature at 10 kN, 60 L/min: (a) 600 rpm and (b) 4200 rpm.

Fig. 12. Pad temperature vs. position at 4200 rpm, 60 L/min.

Fig. 13. Maximum pad temperature vs. bearing load at 4200rpm, 60 L/min.

Fig. 14. Inlet temperature of loaded pad vs. bearing load at 4200 rpm, 60 L/min.



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temperature of conventional bearing without a seal tooth is lower

than that of bearings with a seal tooth.

As flow rate decreases, pad temperature increases.

Fig. 16 shows maximum pad temperature versus flow rate

with 10k N at 4200 rpm.

At low flow rate with 30 L/min, Bearings without a seal tooth

have lower pad temperature than bearings with a seal tooth. But

as flow rate increases, LEG bearings without seal tooth has higher

pad temperature than LEG bearing with seal tooth and conven-tional bearing with seal. That means LEG bearing without seal

tooth has cooling effect under low flow rate.

On the other hand, conventional bearing without has good

cooling effect any flow rate. But As flow rate increase, cooling

effect of bearing without a seal tooth decreases gradually. This

means cooling effect of journal bearing without a seal tooth

increases as flow rate decreases.

Fig. 17 shows inlet pad temperature of loaded pad versus

bearing load with 60 L/min at 4200 rpm.

Journal bearings without seal tooth have lower inlet pad

temperature than journal bearings with seal tooth. As flow rate

increased from 30 to 120 L/min, inlet pad temperature of

conventional bearing without a seal tooth decreased 5.4 1C but

inlet pad temperature of conventional bearing with a seal tooth

decreased 23.2 1C.

In conclusion, inlet pad temperature of bearings with a seal

tooth remarkably decreases as flow rate increases. On the

contrary, cooling effect of journal bearings with a seal tooth

remarkably decreases as flow rate decreases.

From the test results, journal bearing without a seal tooth have

good cooling effect due to large clearance. Because hot carryover

oil drained side leakage, pad inlet temperature is low at journal

bearings without seal tooth with large clearance. But increasing

rate of pad temperature is high because total supply oil is small.

4. Conclusions

An experimental study was conducted to compare LEG journal

bearings with conventional journal bearings under a variety of

operating conditions. The following conclusions are based on the

results.

1. Journal bearings without seal tooth have lower power loss and

lower pad temperature than those of journal bearings with

seal tooth.

2. Conventional journal bearing without a seal tooth is moreeffective than that of LEG journal bearing without a seal tooth

to decrease power loss and pad temperature.

3. LEG journal bearing with a seal tooth has higher pad

temperature than that of conventional journal bearing with a

seal tooth.

4. As rotational speed increases, power loss of journal bearings

without a seal tooth increase more slowly than those of journal

bearings with a seal tooth.

5. As bearing load increases, effect of bearing load for power loss

decreased.

6. As flow rate decreases, the decreasing rate of power loss of

journal bearings without a seal tooth is higher than that

of bearings with a seal tooth and pad inlet temperature of

bearings with seal tooth rapidly increased.

Fig. 15. Pad temperature profile at 4200rpm with 10 kN.

Fig. 16. Maximum pad temperature vs. flow rate at 4200 rpm with 10 kN.

Fig. 17. Inlet temperature of loaded pad vs. bearing load at 4200 rpm, 10 kN.



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[2] Leopard AJ. Tilting pad bearingslimits of operation. In: ASLE 30th annualmeeting in Atlanta, Georgia, 58 May 1975. pp.111.

[3] Zeidan FY. Paquette DJ. Application of high speed and high performance fluidfilm bearing in rotating machinery. In: Proceeding of the 23th turbomachin-ery symposium, 1994. pp. 20933.

[4] Bang K-B, Kim J-H, Kim C-H. Cooling effect of lubricants and dynamic

characteristics of oil film of partial tilting pad bearing. In: Proceeding ofASME/STLE international joint tribology conference, IJTC2007-44023, 2007.

[5] Herbage BS. High speed journal and thrust bearing design. In: Proceeding ofthe first turbomachinery symposium, 1972. pp. 5661.

[6] Nicholas JC. Pad bearing assembly with fluid spray and blocker bar, US Patentno. 5738447, rotating machinery technology, Inc., Wellsville, New York, 1998.

[7] Nicholas JC. Tilting pad bearing design. In: Proceeding of the 23thturbomachinery symposium, 1994. 17994.

[8] Tanaka M. Thermohydrodynamic performance of a tilting pad journalbearing with spot lubrication. ASME Journal of Tribology 1991;113(3):6159.

[9] Nicholas JC. Tilting pad bearing with spray-bar blockers and by-pass coolingfor high speed, high load applications. In: Proceeding of the 32thturbomachinery symposium, 2003. pp. 2737.

[10] Zeidan FY. Warwick RI. Method and bearing construction for control ofhot oil carryover and loss of lubricant, US Patent no. 5547287, KMC, Inc.,1996.

[11] Brockwell K, Dmochowski W, DeCamillo S. Analysis and testing of the legtilting pad journal bearing-A new design for increasing load capacity,

reducing operating temperatures and conserving energy. In: Proceeding ofthe 23th turbomachinery symposium, 1994. pp. 4356.

[12] DeCamillo S, Brockwell K. A Study of parameters that affect pivoted shoejournal bearing performance in high-speed turbomachinery. In: Proceedingof the 30th turbomachinery symposium, 2001. pp. 922.

[13] Edney SL, Waite JK, DeCamillo SM. Profiled leading edge groove tilting padjournal bearing for light load operation. In: Proceeding of the 25thturbomachinery symposium, 2006. pp. 116.


heat loss comparision between leading edge groove and conventional pad bearing

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