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“Performance and Reliability Improvement

in the Design and Manufacture of Water

Cooled Submersible Pump and Motor bySolid Modeling and CFD”

Prof.P.B. Kadam*

Assistant Professor,

Mechanical Engg. Dept,

T.K.I.E.T. Warananagar,

Dist.-Kolhapur-416113.

[email protected]

Prof. J.S. Bagi Associate Professor,

Production Engg. Dept,

K.I.T’s College of Engineering ,

Dist.- Kolhapur, India.

[email protected]

Abstract

Submersible Pumps have lots of problems regarding durability of bearing bush getting worn out very

fast after its commissioning, winding getting damaged burnt out quickly, the stacked laminations in the motorwere getting twisted or entangle so badly that the motor had to be scraped i.e. no repair possible at all. Total

product failure in just 3 to 4 months.

This paper describes the method to determine the optimum dimensions of the bearing bush made of

specified material and withstand a bearing pressure of bearing bush. The results obtained are verified by using

CFD analysis which is improved in order to meet and anticipate customers increasing demand for performance

and reliability.

Keywords- Reliability; Durability; CFD; Submersible Pumpset; Journal Bearing.

1. Introduction

In India Pumps and Motors are manufactured in mass production. The pump manufacturing companiesinvest around 15 to 20 % of its annual profit into its new design developments. Much of their development

programs are based on pen and paper which are rigorous, exhaustive and time consuming. These organizations

could offer such activities. Due to the fact that its customers have ongoing demand for new products as well as

improvements in existing once.

In early days it is not possible to solve problem by manual calculations in CFD but now a days with

high speed computers and super computers it is possible to solve CFD calculations very easily. Due to high

speed computers all the small scale industries are entering into CFD calculations. The potential quality

improvement through upgrading an existing plant can be judged quickly and efficiently by the use of CFD.Problems and limitations of the old design are clarified by a CFD diagnosis. The CFD analysis of new design

solutions indicates the performance and reliability improvements in V4 submersible pump series of Vira Pumps.

Prof.P.B. Kadam et al. / International Journal of Engineering Science and Technology (IJEST)

ISSN : 0975-5462 Vol. 3 No.10 October 2011 7368

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2. Design of Journal Bearing

The following procedure may be adopted in designing journal bearings, when the bearing load, the

diameter and speed of the shafts are know:

1. Determine the bearing length by choosing ratio of l/d from table given below.

2. Check the bearing pressure, p=w/ld from the table for probable satisfactory value.

3. Assume a lubricant from table and its operating temperature (to). The temperature should be between 26.5oC

and 600 with 820C as a maximum for high temperature installation such as steam turbines.

4. Determine the operating value of ZN/p for the assumed bearing temperature and check this value with

corresponding values in table, to determine the possibility of maintaining fluid film operation.

The operating value of ZN/p is taken as 28.

5. Assume a clearance ratio c/d from table.

6. Determine the coefficient of friction (µ) by using the relation

33/108 x ZN/p x d/c + k

7. Determine the heat generated by using the relation,

Qg =µ.W.V N-m/s of J/s or watt.

8. Determine the heat at by using the above relation.

9. Determine the thermal equilibrium to see that the heat dissipated becomes at least to the heat generated. In

case the heat generated is more than the heat dissipated the either the bearing is redesigned or it is artificially

cooled by water.

In order to determine the coefficient of friction for well lubricated full journal bearings, the following

empirical relation established by McKee based on the experimental data, may be use.

3. Nomenclature

Coefficient of friction,

µ= 33/108 x ZN/p x d/c + k

Where,

Z is absolute viscocity of the lubricant in kg/m-s,

N is speed of the journal in rpm,

p is bearing pressure on the projected bearing area in N/mm2

= load on the journal + l x d

d= diameter of the journal,

c= diametral clearance and

k= factor to correct for end leakage. It depends upon the ratio of length to the diameter of the bearing (i.e. l/d)



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= 0.002 for l/d ratios of 0.75 to 0.8. The operating values of ZN/p should be compared with values given in the

table 1 to ensure safe margin between operating conditions and the point of film breakdown.

4. Design of Journal Bearing with CFD Approach

The journal in case of a submersible motor is the bearing surface of the rotor which consists of hard

chromed stainless steel material. The bearing consists of a Leaded bronze material which is the softer part out

these two. The failures of the bearing bush accounts for 90% of the failures in a submersible motor. In

manufacturing submersible pump sets suggests that the following factors are responsible for such failures :

1. Material of the bearing bush.

2. Poor Surface finish of the journal.

3. Wrong length and clearances maintained.

4. Machining defects like run-outs, etc.

5. Overall design of the Motor.

Figure 1 and 2 show a failed bearing bush and journal surface.

Fig.1. Worn out bearing bush (Courtesy VIRA PUMPS)

Fig. 2. Worn out bearing surface of the Rotor

The implication of this failure is the complete breakdown of the Motor i.e. the windings will getdamaged and expensive repairs would be required to be carried out. This clearly suggests that the design of such a



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journal should be properly investigated. A CFD approach would will assist in establishing the dimensions of the

bearing.

Table 1. Permissible bearing pressure (Source: P. Kannaiah, Machine Design, p.19.10)

5. CFD Analysis of Journal Bearing

Instead of taking the value directly from the above table, we will perform CFD Analysis on the bearing.

By this we will also be able to verify the value of bearing pressure ‘p’. We can then use the value obtained fromthe analysis and perform the design steps to calculate the length of bearing.

5.1 Modeling of the Journal Bearing for CFD Analysis Conducting the analysis on Flow simulation from Solidworks 2010 (Dassault Systems). The first task is

to model the bearing, journal and other related components to facilitate the CFD process.The bearing bush is

press fitted in the Housing which is of Cast Iron as shown figure 3Figures 3 and 4 show such various models.

Fig.3. Lower Housing model of a Submersible Motor



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Fig.4. Representation of the journal

Fig.5. Bearing bush of the Submersible Motor

Fig.6. Assembly for the CFD analysis



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Fig.7. General settings dialog box

Fig.8. Surface plot indicating Bearing pressure

Fig.9. Report showing the value of bearing pressure

5.2 Optimum Design:

The ratio d/c for journal bearing is 0.001.

Theoretically bearing pressure is calculated as,



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P = Bearing load/ d x l

= 288.82/ 25.98 x 27.79

= 0.4 N/mm2

Z is absolute viscosity of the lubricant

From Mckee eqn, coeff. of friction

µ= 33/108 x ZN/p x d/c + k

= 0.002

Then determine heat generated by using relation,

Qg =µ.W.V N-m/s

Where

V =π

d N

= π x 0.2598 x 2800

= 2285.32 m/min.

Therefore,

Qg = 1320.09 m/min

Fig. 9 shows value of the bearing pressure p = 0.38 or 0.4 N/mm 2. Use this value in the design of our

journal bearing as follows :

Consider the case for the design of the Journal bearing for a 1.5 hp or 1.1 kw submersible motor which

rotates with a constant speed of 2800 rpm or 293 rad/s.

We need to find the Radial load FN which is given by,FN = 9550 x kw/N x R --- (1)

Where R is the radius of the journal. In this case it is 0.01299 m

FN = 9550 x 1.1/2800 x 0.01299

= 288.82 N

Now, Area A = l x d

= l x 25.98

We know that,

p=w/ld --(2)

taking value of p= 0.4 N/mm2 and w= FN=288.82 N

so,

0.4 = 288.82/ l x 25.98 --(3)

Thus, l= 27.79 mm which is the bearing length. At present the bearing length used for 1.5 hp is 24 mm. The

recommendation made here is that the bearing length must be changed to 27.79 mm.

Let us check this by using a bearing pressure of 0.7 N/mm2 is used as per Table 1

From (3),



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0.7= 288.82/ l x 25.98

The length comes out to be 15.9 mm which is very less. Again if the value of bearing pressure is

increased then it is quite obvious that will get incorrect length of the bearing bush.

6. Verification and Validation

The results are implemented only in V4 (100 mm) type submersible pump sets with water cooled motor.

On the basis of work other problems which may occur in similar type of products like V3 (75 mm), V5 (125 mm),

V6 (150 mm) and V8 (200 mm) can be also implemented in order to optimization of design and enhance the life

of the product which again can be a different project altogether. V4 series pump sets are tested for 6 months

within industry for obtaining performance of the pump and the performance is good. Performance is often a

source of contention between customers and suppliers, particularly when deliverables are not adequately defined

within specifications. The performance of a product often influences profitability or reputation of the end-user. Assuch, many contracts or specifications include damages related to inadequate performance. Reliability may be

closely related to performance. For instance, a product specification may define parameters for up-time, or

acceptable failure rates. Reliability is a major contributor to brand or company image, and is considered a

fundamental dimension of quality by most end-users.

7. Results and Discussion

From the length of the bearing bush is getting 27.79 mm. At present the bearing length used for 1.5 hp

is 24 mm. The recommendation made here is that the bearing length must be changed to 27.79 mm. By using a

bearing pressure of 0.7 N/mm2 is used as per Table 1 By using relation 0.7 = 288.82/ l x 25.98 the length comes

out to be 15.9 mm which is very less. Again if the value of bearing pressure is increased then it is quite obviousthat will get incorrect length of the bearing bush.

8. Conclusion

Maximum bearing pressure is achieved from both theoretical as well as CFD calculation is

approximately 0.4 N/mm2. M/s Vira Pumps are ready to make V4 series pump sets for BIS approval of its

specific products. All facilities and pre-designed testing facilities are already available. This company is already

having ISO certification that is ISO 9001:2008. Up to 2005 organization had BIS certification/ ISI mark for a

some of its products which increased the face value of company & the customer faith in companies’ product.

Company increases its outsourcing strategies to gain profit and high customer satisfaction. Also increases the

durability of the product.

Acknowledgement

I am thankful to my Co-author Prof. J.S.Bagi, Production Engineering Dept., KIT Kolhapur, for their

encouragement and support to carry out this work.

References

[1] Val. S. Lobanoff and Robert Ross (1992), “Centrifugal Pump”, second edition, Gulf publication company, Huston,

Texas, USA.

[2] John Tuzson(2000), “Centrifugal Pump Design”, Wiley interscience, John Wiley And Sons.

[3] IS 9283:1995, Motors for Submersible PumpSets- Specification (First Revision).

[4] IS 8034:2002, Submersible PumpSets – Specification (Second Revision).

[5] G.K. Sahu (2000), “ Pumps” ,New Age International pvt. Ltd. Publishers.

[6] Solid works 2007 Manual and Tutorials.

[7] “Virajit Avinash Gundale,” A new design approach for water cooled submersible motor and radial flow type pump with emphasis on

both Electrical and Mechanical consideration “ Ph.D Thesis,UNEM Costarica, June 2010.[8] ProductCertificationSchemes.[Online]. Available:http://www.bis.org.in/cert/procert.htm

[9] Infrastructure.[Online].Available:http://www.virapump.org/submersiblepump/profile_submersible_pumps.aspx



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[10] Applicationofv4submersiblepump.[online].Available:http://virapumps.org/submersiblepump/submersible_pumps_v4.aspx

[11] RajivGandhiNationalQualityAward.[Online]. Available:http://www.bis.org.in/other/rgnqa_geninfo_10.pdf

[12] SolidModeling.[Online]. Available:http://en.wikipedia.org/wiki/Solid_modeling

[13] David Hoyle (2007), “Quality Management”.



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