Ijrtem 19615

Invention Journal of Research Technology in Engineering & Management (IJRTEM) www.ijrtem.com ǁ Volume 1 ǁ Issue 9 ǁ

ISSN: 2455-3689

Optimization of shell thickness of sub-baric Fryer for manufacture of fried food products using Finite Element Analysis (FEA) Mahesh kumar G1. Menon Rekha Ravindra2 1

Asst. Professor of Dairy Engineering, Dairy Science College, Hebbal, Bengaluru- 560024 2 Senior Scientist, SRS-NDRI Bengaluru -560030

Abstract: Sub-baric thermal fryer (SBTF) is vacuum frying equipment used for frying of food products like snack and sweets. It is cylindrical in geometry designed to work at different temperatures and vacuum levels. 160 ºC at 5 kPa pressure (vacuum). The cylindrical frying vessel is exposed to atmospheric pressure on the outside which leads to compressive forces acting on inside wall the fryer. The stresses developed will have direct bearing on shell thickness of the cylinder wall. There will be implosion of SBTF when Von Mises stress generated is greater than yield stress of the metal which is stainless steel (205MPa). Wall thickness of SBTF was optimized by Finite Element Analysis (FEA) by model development and simulation in Pro/ENGINNER. ANSYS-14 was used for Von Mises stress analysis, deformation and factor of safety. The wall thickness of shell was analyzed by hyper tetrahedron meshing. To validate the shell thickness, design software which uses ASME approved design equation was used for calculation. The model prediction was shown to be in good agreement with analytical calculation. The FEA resulted in Von Mises stress of 135.79 Mpa, a deformation of 1.55 mm and factor of safety of 1.5. With the results of the analysis, SBTF was fabricated as per FDA C-GMP standards from 4 mm thick AISI-316 SS. The fabricated equipment was subjected to various design and safety standard tests and found to work satisfactorily reconfirming validation of the design.

Keywords: Sub-baric thermal fryer, vacuum frying, ANSYS, PRO/ENGINEER, Gulabjamun frying

INTRODUCTION: Sub-baric thermal frying (SBTF) or vacuum frying is a novel and innovative technology used in many countries for manufacture of healthy and nutritious deep fried food products. The vacuum fried food products will have less oil uptake and without acrylamide (a compound which is reported to be carcinogenic and neurotoxin). The process has an added advantage of reuse of frying oil for many repeated cycles, with least Hydroxyl methyl furfural (HMF) production and without trans-fat formation. This process and technology is recent, novel and first of its kind that was tried in the dairy industry. Gulabjamun was the specific dairy product considered for processing in this study though the equipment developed could also be used for preparation of other similar deep fried food products.

SBTF is vacuum frying equipment used for frying of Gulabjamun under full vacuum. From functional requirements, SBTF was to be fabricated from AISI-316 as per FDA C-GMP standards. The fryer is in cylindrical in geometry designed to work at 160ºC at 5 kPa pressure (vacuum).

Fig. 1.1 Direction of Internal pressure SBTF is exposed to atmospheric pressure on outside which leads to compressive forces acting on inside leading to buckling (Fig. 1.1). The mechanical strength of the SBTF was determined by the thickness of the metal sheet (wall thickness) used in its fabrication which is the critical design parameter. There will be implosion when stress developed is more than yield stress of SS316, the material used in the design. The following design steps elaborate the procedures adopted for FEA and optimization of shell thickness of Sub-baric thermal fryer.

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Optimization of shell thickness of sub-baric Fryer for manufacture…

Materials and Methods.

SBTF is made of a cylindrical vessel with hemi spherical cover at the bottom side and flat circular plate on the top. SBTF was designed to work in full vacuum of as low as 5kPa. The outside operating pressure will be the ambient atmospheric pressure (101 kPa, NTP). Important design data (Hauviller, 1993). viz., composition of material, mechanical properties, dimensional drawing, and boundary conditions were required for FEA for stress analysis. Table 2.1 gives the composition of AISI 304 and AISI 316 SS. Tables 2.2 & 2.3 and Fig 2.1 depict dimensional drawings of SBTF. Table 2.1 Composition of stainless steel

Element

Unit

Carbon Manganese Phosphorus Sulphur Silicon Chromium Nickel Molybdenum

% max % max % max % max % max % max % max % max

AISI-304 AISISS 316 SS 0.08 0.08 2.00 2.00 0.045 0.045 0.030 0.030 1.00 1.00 18-20 18-20 8-10.5 10-14 2-3 Source: www.sail.co.in

Table 2.2 Mechanical Properties of AISI 304 and AISI-316 SS

Description Material of construction Inner diameter of chamber Length of vacuum changer Wall thickness Operating pressure ( inside) Operating pressure ( outside) Operating Temperature inside Operating Temperature outside Fixed support

Unit Value SS AISI-316 SS mm 400 mm 750 mm 4 kPa 5 kPa 101 ºC 160 ºC 25-30 SBTF was permanently mounted on SS frame and supporting skid.

Table 2.3 Design Data and boundary conditions

Description Material of construction Inner diameter of chamber Length of vacuum changer Wall thickness Operating pressure ( inside) Operating pressure ( outside) Operating Temperature inside Operating Temperature outside Fixed support

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Unit Value SS AISI-316 SS mm 400 mm 750 mm 4 kPa 5 kPa 101 ºC 160 ºC 25-30 SBTF was permanently mounted on SS frame and supporting skid.

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Fig.2.1 Dimensional drawing of Sub-baric Fryer (all dimension are in mm) D Model Generations (Modeling) : The 3-D modeling of the SBTF was developed using Pro/ENGINEER soft ware (Tickoo and maini (2009) and the FEA for stress using ANSYS-14. The 3-D modeling procedure, cycle and steps are explained in. Fig. 2.2 and 2.3 Thermal stress analysis cycle (FEA) : In order to optimize the wall thickness of SBTF cylinder the stress analysis was conducted using different design software (PRO-ENGINER and ANSYS) by following the procedures as detailed by Kraan et al., 2004; Gajjar et al., 2011; Chand et al., 2012.; Abdhul, 2013. The stress analysis cycle is shown in Fig 2.2

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Fig. 2.2 Stress analysis cycle D modeling for Stress analysis (FEA) : The 3-D model of the SBTF was developed using Pro/ENGINEER soft ware. The assembly 3-D model of equipment was saved in IGES-(Initial Graphics Exchange Specification) format to import to ANSYS-14 workbench for stress analysis (ANSYS, 2007). The operating parameters, material properties and boundary conditions were fed to Anysys-14 work bend for stress analysis. The stress (FEA) analysis procedure and steps are described in Fig 2.3. A vacuum of 5 kPa and frying temperature of 160C were set as process parameters which are the typical levels for preparation of Gulabjamoon.

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Optimization of shell thickness of sub-baric Fryer for manufacture‌ i. 3-D model Generation using –PRO-E

The 3-D modeling of the SBTF was developed in Pro/ENGINEER soft ware.

The assembly 3-D model of equipment was saved in IGES-(Initial Graphics Exchange Specification) format to import to Ansys-14 workbench for stress analysis.

Model of SBTF

ii. Dimensional Drawing of Equipment

Moc AISI-316 SS Diameter 400 mm Length750 mm Wall thickness 4 mm Dimensions of SBF & VIU iii Mesh Generation Meshing was done using tetrahedron mesh. In this tetrdedron meshing method the components was divided into small triangles which give no of nodes and elements of the component to be analyzed. The meshing was done by varying mesh sixe from 20,18,16,14, and 12mm. Due to change in density of the meshing it resulted in variation of no of nodes and element of meshed component Type: Hexahedron mesh Element size -12 mm No of nodes - 81157 No of Elements -30513 Tetrahedron Hyper meshing iv Defining FEA model Mechanical properties of AISI-316 SS

a. b.

Model was defined by feeding Mechanical properties of AISI-316 Stainless steel Wall thickness 4-6 mm

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Optimization of shell thickness of sub-baric Fryer for manufacture…

v. Defining Boundary conditions Inside temperature 160oC Outside temperature 30oC

Inside frying tempararue 160oC

Inside – Pressure (full vacuum 5kPa

Inside operating pressure 5kpa

Outside – Pressure 101kPa (NTP)

Outside pressure NTP

Fixed support by Pedestal to skid of equipment

vi. Run Finite Element Analysis determine

to

vii. Review Results viii. Rerun stress analysis, if yield stress of material is less then von-mises steel

a. b. c.

Model was mounted SS fixed structure Von mises stress - Kpa Deformation- mm Factory of safety

Compare with yield stress of Stainless steel (205MPa) Changes the wall thickness and meshing

Fig. 2.3 Modeling and Finite Element analysis using Pro-E and ANSYS-14

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Optimization of shell thickness of sub-baric Fryer for manufacture‌ Validation of Shell thickness : Theoretical calculations were performed to support the conceptual design and FEA structural analysis. To validate shell (wall) thickness obtained by ANSYS-14, shell thickness was once again recalculated by using ASME design equation 3.1 (ASME 2011). This recalculation was performed using the ASME design software programme with the same data as used earlier (Table 2.1, 2.2 2.3 and Fig 2.1)..

The calculation was to determine the wall thickness of the cylinder under vacuum without holes, nozzles etc. This calculation does not take into account the extra stress around holes for nozzles and is therefore a basic strength calculation. Calculation codes are as per ASME norms (ASME 2010).

Wall thickness was calculated by using: t=

Eq. 3.1

Where, t is the cylinder thickness in corroded condition (m), P is the design pressure (MPa), R is the cylinder inside radius in corroded conditioning (m), S is the maximum allowable stress at design temperature (MPa) and E is the joint efficiency in fraction.

Running of the ASME design software programme : The data was fed into programme for calculation of shell thickness. It requires the user to enter dimensions of model, pressure, operating temperature, yield stress value and density of stainless steel etc. (Table. 3.2).

Table 2.4 Data input for thickness calculation

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Optimization of shell thickness of sub-baric Fryer for manufacture‌ Results and Discussion Results of the FEA analysis for optimization of the cylinder shell thickness is shown in Fig 3.1 and Table 3.1. The results of the stress analysis are presented in terms of Von Mises (equivalent) stress and, deformation and factory of safety (Fig 3.1,3,2&3,3).

Further, to validate the FEA results, thickness was calculated by using ASME approved design software (Table 3.10).

Stress analysis of the Sub-Baric thermal fryer : The general picture of the stress analysis is shown in Figure 3.1. It depicts a magnified picture of the highest and lowest stress peak regions. The red circle and two yellow color circles at the bottom show the regions where the highest (peak) compressive stresses are generated which are much less than yield stress of SS-316 (Fig 3.1 and Fig 3.2). The peak stresses were seen only at bottom of the chamber (red & yellow color).

Fig 3.1 Max Van Mises Stress is 135.79 MPa Deformations from the stress analysis : The deformations generated from the stress analysis is presented in Fig. 3.2. The maximum total displacement was 1.5514 mm, noticed at the bottom of SBTF.

Fig 3.2 Total max deformation is 1.5514mm Factor of Safety: It is evident from the result of stress analysis (Fig 3.3) the minimum factor of safety obtained was 1.5096 which is indicated in yellow color at the bottom of the chamber. The highest factor of safety value (15) is shown in blue color. The vessel had experienced maximum stress at bottom only.

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Fig 3.3 Min Factor of safety is 1.5 Validation of stress analysis for calculation of shell thickness by using ASME approved design equation software.

To validate wall thickness of the shell, design data were fed to ASME design equation based soft ware. The results of thickness analysis results shown table 3.1 The wall thickness obtained was 2.82 mm.

Table 3.1 Result of Analysis of shell thickness

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Optimization of shell thickness of sub-baric Fryer for manufacture… 

Above calculation does not take into account the extra stress around holes for nozzles. SBTF is provided with fixtures like loading door, sight glass, flanges, pipe connections, etc. by weld joints. These joints create abrupt changes in cross section and lead to stress concentration and reduce the strength of material. To overcome this 4 mm wall thickness was considered for fabrication.

SUMMARY AND CONCLUSION The fabricated equipment was subjected to various safety standard tests like hydraulic pressure test, vacuum drop. The equipment successfully passed all the tests confirming to the safety standards. Besides, the equipment was also tested for actual frying of Gulabjamoon production and the results were excellent reconfirming the successful design of the equipment.

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