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Research Papers: Hydrodynamic Lubrication

Improved Estimation of Bearing Pads' Inlet Temperature: A Model for Lubricant Mixing at Oil Feed Ports and Validation against Test Data

[+] Author and Article Information
Behzad Abdollahi

Mechanical Engineering Department,
Texas A&M University,
College Station, TX 77845
e-mail: Behzad.Abdollahi90@gmail.com

Luis San Andrés

Mechanical Engineering Department,
Texas A&M University,
College Station, TX 77845
e-mail: Lsanandres@tamu.edu

1Present address: Rotating Machinery Services, Inc., Bethlehem, PA 18020.

2Modern high performance TPJBs employ direct lubrication methods such as spray bars (with blockers) and leading edge grooves.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received July 15, 2018; final manuscript received October 6, 2018; published online November 21, 2018. Assoc. Editor: Stephen Boedo.

J. Tribol 141(3), 031703 (Nov 21, 2018) (12 pages) Paper No: TRIB-18-1268; doi: 10.1115/1.4041720 History: Received July 15, 2018; Revised October 06, 2018

Energy efficient operation of fluid film bearings demands savings in delivery flow while also managing to reduce the temperature in the fluid film and bearing pads. To achieve this goal, tilting pad journal bearings (TPJBs) implement a variety of oil feed arrangements, use pads with highly conductive material and engineered back surface, and also end seals to keep (churning) lubricant within the bearing housing. This paper introduces a novel model for the mixing of flow and thermal energy transport at a lubricant feed port and which sets the temperature of the lubricant entering a pad leading edge. Precise estimation of this temperature (and inlet oil viscosity) largely determine the temperature, and the current model aids to deliver improved temperature predictions in conditions that limit a conventional model, including the ability to impose an actual lubricant supplied flow, specifically when the bearing is operating in either an over-flooded or a reduced flow conditions. An empirical groove efficiency parameter regulates the temperature of the above-mentioned flows to represent conventional and direct lubricant feeding arrangements as well as end-sealed (flooded) or evacuated bearing configurations. Predicted temperatures are compared against published test data for two bearings while revealing the advantages of the novel model, in particular for operation under lubricant starvation. This paper delivers recommendations for the feed port efficiency parameter for various types of oil supply configurations. This parameter, not being a function of bearing operating conditions, allows for proper sizing of pumps, oil reservoirs, and heat exchangers in lube oil delivery systems for a packaged-unit machine.

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References

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San Andrés, L. , and Tao, Y. , 2013, “ The Role of Pivot Stiffness on the Dynamic Force Coefficients of Tilting Pad Journal Bearings,” ASME J. Eng. Gas Turbines Power, 135(11), p. 112505. [CrossRef]
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Abdollahi, B. , 2017, “ A Computational Model for Tilting Pad Journal Bearings: Accounting for Thermally Induced Pad Deformations and Improving a Feeding Groove Thermal Mixing Model,” Master's thesis, Texas A&M University, College Station, TX. http://hdl.handle.net/1969.1/169580
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San Andrés, L. , and Abdollahi, B. , 2018, “ On the Performance of Tilting Pad Bearings: A Novel Model for Lubricant Mixing at Oil Feed Ports With Improved Estimation of Pads' Inlet Temperature and Its Validation against Experimental Data,” Second Asia Turbomachinery and Pump Symposium, Singapore, Mar. 13–15. https://oaktrust.library.tamu.edu/handle/1969.1/172520
San Andrés, L. , and Abdollahi, B. , 2018, “ Advanced Model Prediction vs. Test Data in Tilting Pad Bearings for Compressors,” Chin. J. Turbomach., 60(3), pp. 32–44.

Figures

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Fig. 1

(a) A lubricant feed groove region bounded by adjacent pads in a TPJB with a single orifice and (b) heat fluxes and lubricant flows across the boundaries of a feed groove region

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Fig. 2

A heavily loaded TPJB operating with a large shaft eccentricity (small minimum film thickness)

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Fig. 3

Left: schematic view of a heavily loaded TPJB operating at a large journal eccentricity. Right: a hydraulic network that allocates the supply flow for each feed groove.

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Fig. 4

Illustrations of the film velocity profile entering a pad through its leading edge (a) and (b) and leaving a pad through its trailing edge (c)

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Fig. 5

Predicted fractions of total supply flow (αi) allocated to each groove in a four-pad TPJB taken from Ref. [18]. (Dashed line specifies an even flow distribution at zero load).

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Fig. 6

Predicted fractions of total supply flow (αi) allocated to each groove in a five-pad TPJB taken from Ref. [8]. (Dashed line specifies an even flow distribution at zero load).

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Fig. 7

Mixing in a feed groove region of hot oil leaving an upstream pad (QTEi−1) with a cold supply flow (Qsupi). Including side leakage flow (QSLi) and groove recirculating flow (Qgri) as well as heat transfer with the bounding pads.

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Fig. 8

Groove control volume including fluid streams (solid arrows) and heat flows (hollow arrows). Left: heat flows from a hot upstream oil (ΦTE,SL) and the cold supplied oil (Φsup,SL) into a stream that evacuates from the groove. Right: hot ΦTE, gr and cold Φsup,gr flows into an oil stream that recirculates within the groove.

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Fig. 9

Pads surface temperature rise versus circumferential location. Predictions from current and conventional oil thermal mixing models compared against test data in Ref. [8] (spray-bar, flooded TPJB, Tsup= 50 °C, N = 3 krpm, W/(LD) = 2.5 MPa, and Cgr =0.2).

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Fig. 10

Pads' surface temperature rise versus circumferential location for two supply flow rates (210 L/min and 420 L/min). Predictions compared against test data in Ref. [8] (spray-bar, flooded, Tsup = 50 °C, N = 3 krpm, W/(LD) = 1 MPa, Cgr = 0.2).

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Fig. 11

Pads' surface temperature rise versus angle for operation at three shaft speeds while the supply flow rate is held constant at 420 LPM (spray-bar, flooded, Tsup = 50 °C, N = 1.5, 3 and 4.5 krpm, W/(LD) = 2.5 MPa, Cgr = 0.2, and λ = 0.8)

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Fig. 12

Schematic of lubrication delivery methods. Reproduced with permission from Ref. [19].

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Fig. 13

Pads' surface temperature rise versus circumferential location. Predictions compared against test data in Ref. [20] (spray-bar, evacuated, Tsup= 49 °C, N = 7 krpm, W/(LD)= 0.7, 2.1, 2.9, MPa, and Cgr=0.6).

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Fig. 14

Pads' surface temperature rise versus circumferential location. Predictions compared against test data in Ref. [19] (spray-bar, evacuated, Tsup = 49 °C, N = 16 krpm, W/(LD)= 0.7, 2.1, 2.9, MPa, and Cgr = 0.6).

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Fig. 15

Maximum inner surface temperature on pad #2 versus shaft speed and for specific load, W/(LD) = 0.7, 2.1, and 2.9 MPa. Current predictions and test data in Ref. [20].

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Fig. 16

Predicted flow rate versus shaft speed and specific load W/(LD) = 0.7, 2.1, 2.9 MPa. Conventional thermal mixing model (λ = 0.8). Constant flow rate in tests [19] for spray-bar with evacuated housing.

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Fig. 17

Pads' surface temperature rise versus circumferential location for three lubricant delivery methods. Predictions compared against test data in Ref. [20]. (SBB, spray-bar blocker; LEG, leading edge groove; SO, single orifice; Tsup= 49 °C, N = 16 krpm, W/(LD) = 2.9 MPa).

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