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International eJournals International Journal of Mathematical Sciences, Technology and Humanities 4 (2011) 37 – 52

STRUCTURAL AND THERMAL ANALYSIS OF CONDENSER

BY USING FINITE ELEMENT ANALYSIS

Sk. Abdul Mateen1 and N. Amar Nageswara Rao2

Mechanical Engineering Department,

Nimra College of Engineering & Technology, Ibrahimpatnam, Vijayawada.

ABSTRACT:

In any power plant apart from the turbine, boiler and pump, the condenser is a vital component. Steam condenser is a device or an appliance in which steam condenses and heat released by steam is absorbed by water. The main considerations in the design of a condenser for a particular application are Thermal design and analysis, Mechanical design, Design for manufacture, physical size and cost.

The condenser is analyzed for static and thermal loading .The geometry of condenser is created in CATIA software as per the drawing .This model is imported to HyperMesh through IGES format and then for sheet metal components we will extract the mid surface, now for that mid surface we will create shell elements, solid elements were created for remaining part, and a converged mesh is developed in HyperMesh. The finite element model with various loading conditions are design pressure, hydro test pressure ,full vaccum, thermal loads and operating conditions (both mechanical and thermal loads) on the condenser .The supporting legs one is arrested in all the directions and the other one is arrested only in Z- direction and all rotations. All these are created by using HyperMesh and it is exported to ANSYS for solution. The deflections and stresses were obtained from analysis. Those values are correlated with material allowable values as per the ASME Section VIII Division 2.

Keywords: Condenser Analysis, Structural and Thermal Analysis, Finite Element Analysis

1. INTRODUCTION

A steam condenser is a device or an appliance in which steam condenses and heat released by steam is absorbed by water. Condenser are important heat and mass exchange apparatus in oil refining, chemical engineering, environmental protection, electric power generation, et al. Among different types of condenser, shell and tube condenser have been commonly used in

Sk. Abdul Mateen and N. Amar Nageswara Rao International Journal of Mathematical Sciences, Technology and Humanities 4 (2011) 37 – 52

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industries [1]. Master et al, [2] indicated that more than 35–40% of heat exchangers are of the shell and tube type, and this is primarily due to the robust construction geometry as well as easy maintenance and possible upgrades of shell and tube condenser. They are widely used as evaporators and condensers. The heat transfer effectiveness of shell and tube condenser can be improved by using baffles. Segmental baffles are most commonly used in conventional shell and tube condenser to support tubes and change fluid flow direction. Segmental baffles cause the shell-side fluid to flow in a tortuous, zigzag manner across the tube bundles, which can enhance the heat transfer on the shell side[3-6].

2. DESCRIPTION

In this work static and thermal analysis of the condenser made of carbon steel was carried out.

Table 1. Material properties of Carbon Steel- SA 516 Gr 70 Material Properties

Magnitudes

Density, tons/mm3 1.3738e-8

Young’s Modulus, N/mm2

1.9e5

Poisson’s Ratio 0.3 Thermal Expansion coefficient

7.1*e-6 / oc

3. MODELLING AND MESHING With the dimensional parameters the structure is modeled in CATIA modeling software as shown in Fig.1 The model is meshed for further analysis using a

Fig.1: The geometric model of the Condenser using CATIA.

meshing package HYPERMESH with free and mapped mesh. Meshing of the component plays an important role in analysis, as it is the basis for analyzing the component in any software package, which supports finite element techniques. The model consists of 74798 elements. Appropriate boundary conditions are incorporated in the analysis. Fig 2 shows shell 63 element and Fig3 shows solid 45 element considered for meshing. FE model of the condenser is shown in Fig 4.


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Shell 63 Elastic Shell It is defined by four nodes and six degrees of freedom i.e. UX, UY, UZ, ROTX, ROTY, ROTZ at each node. The element has stress stiffening, large deflection, and birth and death capabilities.

Fig.2: Shell63 Geometry Solid45 3d-Structural Solid It is defined by eight nodes and three degrees of freedom i.e. UX, UY, UZ at each node. The element has plasticity, elasticity, large deflection Capabilities.

Fig.3: Solid45 3d-Structural Solid

Fig.4: The Finite Element Model of the Condenser


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Table 2. Mesh is created in HyperMesh with the following quality parameters

4. CONDENSER 4.1 Structural Analysis Static analysis was carried out to know the strength of the condenser, which includes the parameters such as the design pressure, full vaccum and hydro test pressure. The Analysis has been carried out for these cases:

Case1). Design Pressure Pressure = 0.1078 MPa. Case2). Full Vaccum Pressure = 0.10135 MPa Case3). Hydro static Pressure Pressure =0.157 MPa

4.2 Thermal Analysis Thermal analysis was carried out to know the thermal stresses of the condenser, which includes the parameters such as thermal loading (stresses due to temperature) and Combined loading (both structural and thermal).The Analysis has been carried out for these cases:

Case4). Thermal loading (stresses due to temperature). ∆T = 99 o c Case5).Combined loading (both structural and thermal) Pressure=0.09316MPa and Temperature=44.450c

Max warpage 23 Aspect Ratio 3.95 Skew 60 Minangleof quad 35 Max angle of quad 152 Jacobian 0.55 Min angle of trias 21 Max angle of trias 110


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RESULTS Case 1. Design Pressure

Table 3. The induced displacements and stresses with Design Pressure of 0.1078 MPa

Name

Results as per Analysis

Allowable stress as per ASME SEC VIII DIV.2 (MPa)

Reference figure

Displacement in X-direction, mm

1.174 7 5

Displacement in Y-direction, mm

0.7962 7 6

Displacement in Z-direction, mm

1.267 7 7

Shear stress in XY-plane, MPa

19.409 157.2 8

Shear stress in YZ-plane, MPa

36.53 157.2 9

Shear stress in XZ-plane, MPa

94.738 157.2 10

Stress Intensity , Mpa

261.689 524 11

From the table 3 it is observed that the maximum stress induced is less than allowable stresses. Hence the design is safe as per the strength criteria. Fig 5 to Fig 7 shows the variation of max displacement in X, Y and Z-directions respectively 1.174, 0.7962 and 1.267 mm. The max. allowable displacement is 7mm. Hence the design is safe based on rigidity.

Fig.5: The Displacement in X-direction


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Fig.6:The Displacement in Y-direction

Fig.7: The Displacement in Z-direction

Fig.8: The variation of Shear Stress in XY-plane

Fig.9: The variation of Shear Stress in YZ-plane


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Fig.10: The variation of Shear Stress in XZ-plane

Fig.11:The variation of Stress Intensity

Fig 8 to Fig 11 shows the variations of normal and shear stresses. From the figure it is observed that the maximum stresses induced is 261.689 Mpa, which is less than allowable stress.

Case 2. Full Vaccum

Table 4. The induced displacements and stresses with Full Vaccum pressure of 0.01035 MPa

Name



Reference figure


1.104 7 12


0.7485 7 13


1.11 7 14


18.248 157.2 15


89.07 157.2 16


34.184 157.2 17

Stress Intensity , Mpa

245.94 524 18


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From the table 4 it is observed that the maximum stress induced is less than allowable stresses. Hence the design is safe as per the strength criteria. Fig 12 to Fig 14 shows the variation of max displacement in X, Y and Z-directions respectively 1.104, 0.7485 and 1.11 mm. The max. allowable displacement is 7mm. Hence the design is safe based on rigidity.

Fig.12:The Displacement in X-direction.


Fig.14:The Displacement in Z-direction

Fig.15:The variation of Shear Stress in XY-plane

Fig.16:The variation of Shear Stress in YZ-plane


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Fig.17:The variation of Shear Stress in XZ-plane



Case 3. Hydrotest Pressure Table 5. The induced displacements and stresses with Hydrotest pressure of 0.157 Mpa

Name



Reference figure


1.71 7 19


1.158 7 20


1.72 7 21


28.268 157.2 22


52.955 157.2 23


137.977 157.2 24

Stress Intensity , Mpa 381.125 524 25

From the table 5 it is observed that the maximum stress induced is less than allowable stresses. Hence the design is safe as per the strength criteria. Fig 19 to Fig 21 shows the variation of max displacement in X, Y and Z-directions respectively 1.71, 1.158 and 1.72 mm. The max.allowable displacement is 7mm. Hence the design is safe based on rigidity.


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Fig.19: The Displacement in X-direction

Fig.20: The Displacement in Y-direction



Fig.23:The variation of Shear Stress in YZ-plane


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Fig.24:The variation of Shear Stress in XZ-plane



Case4. Thermal Loading Table 6. The induced displacements and stresses with uniform Temperature loading of 990C

Name



Reference figure


0.6241 7 26


3.004 7 27


1.461 7 28


32.88 157.2 29


119.665 157.2 30


86.462 157.2 31


From the table 6 it is observed that the maximum stress induced is less than allowable stresses. Hence the design is safe as per the strength criteria. Fig 26 to Fig 28 shows the variation of max displacement in X, Y and Z-direction respectively 0.6241, 3.004 and 1.461 mm. The max. allowable displacement is 7mm. Hence the design is safe based on rigidity.


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Fig.26:The Displacement in X-direction




Fig30:The variation of Shear Stress in YZ-plane


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Fig31:The variation of Shear Stress in XZ-plane

Fig.32:The variation of Stress Intensity.


Case 5.Combined Loading. Table 7. The induced displacements and stresses with uniform Temperature loading of

44.450C and pressure 0.09316 MPa.

Name



Reference figure


1.194 7 33


1.658 7 34


0.8783 7 35


16.771 157.2 36


81.874 157.2 37


39.734 157.2 38


From the table 7 it is observed that the maximum stress induced is less than allowable stresses. Hence the design is safe as per the strength criteria. Fig 33 to Fig 35 shows the variation of max displacement in X, Y and Z-direction respectively 1.194, 1.658 and 0.8783 mm. The max. allowable displacement is 7mm. Hence the design is safe based on rigidity.


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Fig33:The Displacement in X-direction

Fig34:The Displacement in Y-direction

Fig35:The Displacement in Z-direction



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Fig37:The variation of Shear Stress in YZ-plane

Fig38:The variation of Shear Stress in XZ-plane

Fig39:The variation of Stress Intensity


For the material SA 516 Gr 70

KSm= 157.2 MPa

Minimum yield stress = 262 MPa

Minimum tensile stress = 481 MPa


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CONCLUSIONS The following conclusions are drawn from the present work.

1. The maximum deflection induced 1.267 mm under 0.1078 MPa loads which is with in the allowable limits i.e. < 7mm.

2. The maximum stress induced is 263 MPa which is less than allowable limits of 524 MPa. Hence the factor of safety is 1.992.





7. The maximum deflection induced 3.004 mm under uniform temperature of 990C load which is with in the allowable limits i.e. < 7mm.

8. The maximum stress induced is 361.782 MPa which is less than allowable limits of 524 MPa. Hence the factor of safety is 1.45.

9. The maximum deflection induced 1.658 mm under combined loading of 0.09316 MPa and uniform temperature of 990C load which is with in the allowable limits i.e. < 7mm.

10. The maximum stress induced is 226.085 MPa which is less than allowable limits of 524 MPa. Hence the factor of safety is 2.318.

REFERENCES 1 Gulyani, B. B., 2000, “Estimating Number of Shells in Shell and Tube Heat Exchangers: A

New Approach Based on Temperature Cross,” ASME J. Heat Transfer, 122, pp. 566–571.

2 Master, B. I., Chunangad,K. S., and Pushpanathan, V., 2003, “Fouling Mitigation Using Helixchanger Heat Exchangers,” Proceedings of the ECI Conference on Heat Exchanger Fouling and Cleaning: Fundamentals and Applica- tions, Santa Fe, NM, May 18–22, pp. 317–322.

3 Reppich, M., and Zagermann, S., 1995, “A New Design Method for Segmentally Baffled

Heat Exchangers,” Compute. Chem. Eng., 19, pp. 137–142.

4 Li, H. D., and Kottke, V., 1998, “Effect of the Leakage on Pressure Drop and Local Heat Transfer in Shell-and Tube Heat Exchangers for Staggered Tube Arrangement,” Int. J. Heat Mass Transfer, 41 2 , pp. 425–433.

5 Naim, A., and Bar-Cohen, A., 1996, New Developments in Heat Exchangers, Gordon and

Breach, Amsterdam, pp. 467–499.

6 Van der Ploeg, H. J., and Master, B. I., 1997, “A New Shell-and-Tube Option for Refineries,” PTQ Autumn, pp. 91–95.

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