Introduction. Assessing & Optimising Heat Transfer, Structural Response and Fatigue in Mechanical Engineering Product Design

Transcription

1 Assessing & Optimising Heat Transfer, Structural Response and Fatigue in Mechanical Engineering Product Design Introduction Nigel Atkinson ANSYS UK Ltd 2010 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary

2 Invitation There are many challenges facing mechanical engineers as they strive to maximise the performance of heat exchanging equipment and to meet more demanding thermal management objectives. Typical requirements are to: Improve heat exchange Optimise cooling Reduce peak-temperatures Increase product efficiency Reduce power consumption Ensure structural integrity Minimise material costs Reduce equipment dimensions The seminar will introduce the unique capabilities of the ANSYS product suite to perform integrated flow, thermal, stress and fatigue analysis, giving mechanical engineers the simulation tools they need to deliver better performing designs, in shortened development times with reduced development costs. Many industrial situations 2010 ANSYS, Inc. All rights reserved. 2 ANSYS, Inc. Proprietary

3 Today s Agenda Introduction and Welcome Nigel Atkinson, ANSYS UK Overview of the ANSYS Engineering Simulation Software Suite: - ANSYS CFD to calculate flow distributions, pressure drops and conjugate heat transfer including convection, conduction and thermal radiation - ANSYS Mechanical to calculate both thermal stressing and structural fatigue - The Workbench environment to facilitate integrated multidisciplinary simulation Mark Leddin & Paul Everitt, ANSYS UK Improving CFD Predictions of Heat Transfer - Near-wall mesh refinement - Advanced turbulence modelling methods Paul Everitt, ANSYS UK, Case Studies - Heat exchangers and boilers - Cooling jacket - Radiators - Waste heat recovery unit - Thermal battery - Electronics thermal management - Other miscellaneous applications Mark Leddin & Paul Everitt, ANSYS UK Coffee Break Software Demonstration of Integrated Fluid Flow, Thermal Stressing and Fatigue Analysis on Heat Exchanging Device Mark Leddin & Paul Everitt, ANSYS UK Summary and Q&A 2010 ANSYS, Inc. All rights reserved. 3 ANSYS, Inc. Proprietary

4 ANSYS, The Company ANSYS are the world s largest CAE Company We design, develop, market and globally support a wide range of Engineering simulation software Over 1600 people worldwide, Over 150 in the UK A suite of multi-purpose software technologies for Structural Mechanics Fluid Dynamics Heat Transfer Electronics Electromagnetics Multiphysics 2010 ANSYS, Inc. All rights reserved. 4 ANSYS, Inc. Proprietary

5 Simulation Driven Product Development Instead of just using engineering simulation for verification or trouble-shooting, many companies are turning to Simulation Driven Product Development (SDPD) Design, simulate, optimize Physically test only the best candidates The benefits of SDPD Better performing products Shorter development times Reduced development costs 10X 100X Productivity Gain Customer needs Business drivers Technology trends 2010 ANSYS, Inc. All rights reserved. 5 ANSYS, Inc. Proprietary

6 ANSYS Portfolio ANSYS offer a full suite of single-physics applications They are integrated using the Workbench Environment The Workbench environment enables consistent model setup, direct geometry access, scripting, parametric design optimisation and automated updates 2010 ANSYS, Inc. All rights reserved. 6 ANSYS, Inc. Proprietary

8 Workbench Efficiencies Use one instance of the geometry Carry out analyses in parallel Chain Processes Geometry Update ripples through all Analysis instances No intermediate file transfers to manage Electric Steady-State Thermal Static Structural 2010 ANSYS, Inc. All rights reserved. 8 ANSYS, Inc. Proprietary

9 Parametric By Design Parameter definition in Mechanical Simulation (implicit, explicit, MBD) Input parameter created from an expression in ANSYS CFX Parameter definition based on linked Microsoft Excel cells Parameter definition based on ANSYS Mechanical APDL input files Output parameters created from an expression in ANSYS CFD-Post Input parameter created from an expression in ANSYS FLUENT 2010 ANSYS, Inc. All rights reserved. 9 ANSYS, Inc. Proprietary

10 Six-Sigma & Optimisation ANSYS DesignXplorer is a tool that provides all necessary tools for Design exploration: Response surfaces Six-Sigma analysis Optimization techniques ANSYS DesignXplorer is fully embedded in ANSYS Workbench and works from the parameter set definition, regardless of the complexity of the simulation 2010 ANSYS, Inc. All rights reserved. 10 ANSYS, Inc. Proprietary

12 Assessing and Optimising Heat Transfer, Structural Response and Fatigue in Mechanical Engineering Product Design 14 th June 2011 Paul Everitt Mark Leddin ANSYS UK Ltd 2010 ANSYS, Inc. All rights reserved. 12 ANSYS, Inc. Proprietary

13 Overview of the ANSYS Engineering Simulation Software Suite ANSYS Mechanical ANSYS CFD Conduction Yes Yes Thermal radiation Yes Yes Convective losses at surfaces Yes Yes Convection No Yes Simultaneous flow, conduction, radiation No Yes Thermal (and mechanical) stressing Yes No ANSYS Mechanical Convective heat flux or heat transfer coefficient Solid ANSYS CFD Fluid Solid Advantage is that CFD software calculates heat flux from fluid to solid No need to specify htc or heat flux from fluid to solid CFD also provides insight into fluid flow 2010 ANSYS, Inc. All rights reserved. 14 ANSYS, Inc. Proprietary

14 Heat Transfer Classification Three types of convection. Natural Convection Fluid moves due to buoyancy effects h T 1/ 4, h T 1/3 Thot Tcold Typical values of h (W/m 2 K) 4 4,000 Forced Convection Flow is induced by some external means. h f ( T) Boiling Convection Body is hot enough to cause fluid phase change h T Difficult to accurately specify valid htc or heat flux for complex geometry/flow So let CFD calculate the heat flux , , ANSYS, Inc. All rights reserved. 15 ANSYS, Inc. Proprietary T hot T cold T cold T hot

15 Improving CFD Predictions of Heat Transfer - Thermal Boundary Layer Flow Analogous to the viscous boundary layer that develops, there is also a thermal boundary layer. T, U Viscous Boundary Layer y Thermal Boundary Layer T (y) T U (y) In most industrial applications, free and forced convection occur simultaneously. The relative magnitude of these effects can be determined by using a modified Froude number, Fr. T w Fr Gr 2 Re g L T 2 U << 1 Forced convection dominates 1 Natural and Forced convection are important >> 1 Natural convection dominates 2010 ANSYS, Inc. All rights reserved. 16 ANSYS, Inc. Proprietary

16 Improving CFD Predictions of Heat Transfer - Thermal Boundary Layer Flow Require special approach to capture thermal as well as viscous boundary layers Meshing Automated Boundary Layer Inflation methods built-in to ANSYS Meshing Can control: Number of layers First cell height (y+ setting) Total Height Aspect ratio Smooth Transition Surface it inflates from Compatible with all methods and element shapes 2010 ANSYS, Inc. All rights reserved. 17 ANSYS, Inc. Proprietary

17 Improving CFD Predictions of Heat Transfer - Thermal Boundary Layer Flow Require special approach to capture thermal as well as viscous boundary layers Turbulent Models Omega based Low Reynolds number turbulence models suitable for near wall Can including turbulent transition effects Automatic Wall function Fine near wall mesh use k-omega Coarse near wall use wall functions Automatic switch Can model conduction through thin walls as well Includes films/coatings and thermal contact 2010 ANSYS, Inc. All rights reserved. 18 ANSYS, Inc. Proprietary

18 Feeding temperature (and pressure) results from ANSYS CFD as a load into ANSYS Mechanical In many situations, it is advantageous to use ANSYS CFD in tandem with ANSYS Mechanical Typically flow and conduction in ANSYS CFD followed by thermal and mechanical stressing in ANSYS Mechanical There are multiple options for exchanging results between ANSYS CFD and Mechanical software One-way transfer Unidirectional interaction between fields in fluids and solid domains Two-way transfer Bidirectional interaction between fields in fluids and solid domains 2010 ANSYS, Inc. All rights reserved. 19 ANSYS, Inc. Proprietary

19 Example 1: Hot and cold water T- junction ANSYS CFD is used to calculate the mixing of hot and cold water in a T-junction as well as to assess temperature in solid. The 3D temperatures in the solids are passed to ANSYS Mechanical ANSYS Mechanical is then used to assess structural stresses and deformation under thermal loads ANSYS, Inc. All rights reserved. 21 ANSYS, Inc. Proprietary

20 Hot and cold water T-junction Hot water from bottom and cold water from side pipe Conduction as well as flow included in CFD analysis 110 [bar] 10 [m/s] 20 [C] 10 [m/s] 80 [C] 2010 ANSYS, Inc. All rights reserved. 22 ANSYS, Inc. Proprietary

21 Hot and cold water T-junction Hot water from bottom and cold water from side pipe Conduction as well as flow included in CFD analysis Mixing of hot and cold water Streamlines Metal temperatures 2010 ANSYS, Inc. All rights reserved. 23 ANSYS, Inc. Proprietary

22 Hot and cold water T-junction Solid temperatures passed to ANSYS Mechanical and FE analysis performed to calculate deformation and stress Deformation Thermal stress 2010 ANSYS, Inc. All rights reserved. 24 ANSYS, Inc. Proprietary

23 Example 2: Air Brake Valve Another typical one-way transfer from ANSYS CFD to ANSYS Mechanical are pressure loadings Airbrake example where ANSYS CFD used to simulate flow through airbrake to calculate flow distribution and to assess pressure loading on valve. ANSYS Mechanical then used to assess structural deformation due to aerodynamic loading. Flow calculation performed in ANSYS CFD Pressure on valve passed to ANSYS Mechanical ANSYS Mechanical calculates valve deflection 2010 ANSYS, Inc. All rights reserved. 25 ANSYS, Inc. Proprietary

24 Case studies and software demonstration For the rest of the session, we d like to present Case-studies where ANSYS CFD has been used standalone or in tandem with ANSYS Mechanical to analyse heat transfer Waste heat recovery unit Water jacket Plate heat exchanger Electronics thermal management Exhaust system I-beam integrity Customer project yoomi, Intelligent Fluid Solutions Ltd Software demonstration of flow, heat transfer, thermal stressing and fatigue modelling in ANSYS ANSYS, Inc. All rights reserved. 26 ANSYS, Inc. Proprietary

26 yoomi - CFD Behind the Product yoomi is a rechargeable, BPA-free, selfwarming baby bottle that warms baby's feed to the natural temperature of breast milk at the touch of a button ( The yoomi bottle design was developed by Intelligent Fluid Solutions Ltd. between 2007 and Yoomi is being manufactured by Feed Me Bottles Ltd. in China, South Africa and UK. The yoomi bottle entered the UK market in Nov through John Lewis and is now also available in Mothercare & Boots. Yoomi is expanding internationally and is available in Scandinavia, Ireland and continental Europe ANSYS, Inc. All rights reserved. 28 ANSYS, Inc. Proprietary

27 yoomi - CFD Behind the Product The bottle exploits the subcooled nature of sodium acetate mixture, which remains liquid below its solidification temperature The mixture is contained inside a warming unit with channels for the milk flow When the solidification process is triggered, latent heat is released As the milk flows along the channels, it is heated to the correct temperature - above 32 o C The warmer is recharged by placing it in boiling water or a steam sterilizer ANSYS, Inc. All rights reserved. 29 ANSYS, Inc. Proprietary

28 yoomi - CFD Behind the Product Heat transfer and pressure drop in the warmer channels were studied in details: In order to improve the heat transfer from the warmer to the milk flow, the milk travelling time or the channel distance were maximized CFD was used to analyse a number of channel designs in order to obtain a heat transfer coefficient correlation h (x) and a friction factor correlation f (x) l 1 w These correlations (h and f) were then used to build a parametric model of the warmer channels 0.5l ANSYS, Inc. All rights reserved. 30 ANSYS, Inc. Proprietary

29 yoomi - CFD Behind the Product h h [mm] [mm] pressure drop h h [mm] [mm] temperature increase w [mm] w [mm] a) a) b) b) w [mm] w [mm] Parametric space of the warmer design was explored in terms of the channel width w and height h A number of contour maps of the pressure drop and the temperature increase were produced to help determine the optimum channel design 2010 ANSYS, Inc. All rights reserved. 31 ANSYS, Inc. Proprietary

30 yoomi - CFD Behind the Product Text The result of the design optimisation exercise was a zig-zag channel of the specific width w and height h 2010 ANSYS, Inc. All rights reserved. 32 ANSYS, Inc. Proprietary

31 Tmilk [C] yoomi - CFD Behind the Product Prototype 1 Prototype 3 Prototype 3, Al Prototype 3, enh. k. Prototype 3, Al and enh. k These initial CFD simulations did provide valuable information on the warmer thermal characteristics: time [s] milk temperature at steady drinking speed sensitivity to the material properties sensitivity to the milk flow rate and thermal boundary conditions but were significantly overpredicting the milk first drop temperature due to the singlephase flow representation 2010 ANSYS, Inc. All rights reserved. 33 ANSYS, Inc. Proprietary

32 yoomi - CFD Behind the Product An accurate prediction of the first drop temperature and the pressure variations inside the channel required multiphase CFD analysis modelling of conjugate heat transfer through solid parts solidification reaction of the mixture Using such multiphase CFD analysis, we were able to predict the first drop temperature with accuracy of 2-3 o C in comparison to the experimental measurements 2010 ANSYS, Inc. All rights reserved. 34 ANSYS, Inc. Proprietary

33 yoomi - CFD Behind the Product Use of CFD simulation techniques saved a large amount of time and development costs The product was developed in just 2.5 years and most of the time was spent on the problems related to production, marketing and distribution Four physical prototype were ever built, only 2 of them to test thermo-hydraulic performance of the bottle The simulation driven product development not only helped to meet the design objectives, but also enable us to better understand the physical processes and, therefore, to improve the performance of the product For more information on this work and Intelligent Fluid Solutions, please contact andrej.horvat@intelligentfluidsolutions.co.uk or visit ANSYS, Inc. All rights reserved. 35 ANSYS, Inc. Proprietary

34 Case Study Waste Heat Recovery This example shows the use of ANSYS CFD to simulate the flow of waste-heat exhaust gas to pre-heat water upstream of the water being passed over the primary heat. ANSYS CFD used to calculate flow/conduction analysis to calculate overall thermal performance and provide insight into fluid flow Set-Up Exhaust Gas - Air Flow Rate 630 l/s Exhaust Gas Temp 350 [C] Water Flow Rate 15 [l/s] Water Temp 15 [C] Tubes Copper All Outside Boundaries HTC = 10 [W m^-2 K^-1] Outside Temp = 15 [C] 2010 ANSYS, Inc. All rights reserved. 36 ANSYS, Inc. Proprietary

39 Case Study Water jacket Bearings can produce a considerable amount of heat during operation and requires cooling. This example shows an ANSYS CFD calculation on a water jacket to calculate the temperature distribution in the metal work as well as water flow. Concern about temperature distribution in metalwork Set-Up Fluid Water Flow Rate 135 l/h Temp In 5 [C] Solid - Aluminium Inside temperature 150 [C] (Heat generated by the bearing) Prescibed on inner wall of annulus Outside Boundary Fully insulated 2010 ANSYS, Inc. All rights reserved. 41 ANSYS, Inc. Proprietary

42 Case Study Water jacket Water streamlines coloured with temperature on journey through water passage Passage inside surface temperatures 2010 ANSYS, Inc. All rights reserved. 44 ANSYS, Inc. Proprietary

44 Case Study Plate Heat Exchanger Plate heat exchangers offer large surface areas for heat exchange. Using the latest CFD meshing methods, it is now possible to rapidly use ANSYS CFD to investigate the flow/conduction performance of plate heat exchangers Set-Up Fluid - Water Flow Rate 7.2 l/s Cold Temp In 15 [C] Hot Temp In 85 [C] Solid Copper All Outside Boundaries Fully Insulated 2010 ANSYS, Inc. All rights reserved. 46 ANSYS, Inc. Proprietary

46 Case Study Electronics Thermal Management Mechanical engineers are often tasked with ensuring that the electronic components within assemblies don t overheat. This example shows ANSYS CFD being used to calculate the flow of coolant air and conduction in a typical scenario where the peaktemperatures had to be kept below a certain temperature. Set-Up Cooling Fluid - Air Flow Rate 1 m/s at Inlet Temp In 20 [C] All Outside Boundaries Fully Insulated ICs heat source 1.5 Watts Watts ICs 2010 ANSYS, Inc. All rights reserved. 48 ANSYS, Inc. Proprietary

47 Case Study Electronics Thermal Management Geometry Air enclosure Single air inlet Two outlets Mesh Results Air and solid temperatures Component temperatures Structural displacement Temperatures transferred to ANSYS Mechanical for thermal stressing analysis 2010 ANSYS, Inc. All rights reserved. 49 ANSYS, Inc. Proprietary

48 Case Study Exhaust System An excellent example of ANSYS CFD and ANSYS Mechanical being used in tandem is in exhaust system design Fluid mechanics Thermal and structural loads Fatigue Time dependent one-way transfer of ANSYS CFD results to ANSYS Mechanical at multiple instances Assumption that the displacement of geometry due to thermal stressing doesn t have an impact on the flow One-way transfer of metalwork temperatures from CFD calculation to ANSYS Mechanical CFD geometry FE geometry 2010 ANSYS, Inc. All rights reserved. 50 ANSYS, Inc. Proprietary

51 Case study: Fire Simulation. We have a recently completed transient two-way coupled ANSYS CFD and ANSYS Mechanical example I-beam subjected to hot gases and thermal radiation from a fire Weaken under thermal load 2010 ANSYS, Inc. All rights reserved. 53 ANSYS, Inc. Proprietary

52 Temperature Dependent Properties Structural Properties defined in Engineering Materials Property tables entered as functions of temperature 2010 ANSYS, Inc. All rights reserved. 54 ANSYS, Inc. Proprietary

54 Software demonstration To showcase ANSYS CFD and ANSYS Mechanical, we ve prepared a software demonstration on a gas liquid heat exchanger Attendees will see these tools through the ANSYS Workbench environment ANSYS CFD used to simulate flow and conduction We ll show the workflow in performing an ANSYS CFD calculation Geometry (from CAD or ANSYS DesignModeler) CFD Meshing CFD Physics Set-up CFD Solving CFD Post-processing Then we ll transfer the data to ANSYS Mechanical and calculate Thermal stressing,deformation and fatigue 2010 ANSYS, Inc. All rights reserved. 56 ANSYS, Inc. Proprietary

55 Software demonstration Heat exchanger (gas/liquid) Confirm performance with CFD for 24 tube arrangement Assess performance with 16 tubes using ANSYS CFD software Need gas temperature change >250 K Fluid Set-Up Water enters at 10C, 9 m 3 per hour Hot gas enters at 933K, 0.4 kg/s, 10 bara Copper tubes Steel baffles and casing Flow results passed to structural analysis to obtain structural response under thermal load. Induced stress used to make fatigue prediction and calculate factor of safety Hot gas 2010 ANSYS, Inc. All rights reserved. 57 ANSYS, Inc. Proprietary

56 To software demonstration At the seminar, a live software demonstration was performed This pdf contains slides to summarise the demonstration 2010 ANSYS, Inc. All rights reserved. 58 ANSYS, Inc. Proprietary

62 Software demonstration Quantitative Results from CFD simulations 16 tube configuration yields acceptable gas temperature reduction 16 Tubes 24 Tubes Change in water temperature [K] Change in gas temperature [K] 6.3 K 7.7 K K K Change in water pressure [Pa] Change in gas pressure [Pa] 390 Pa 390 Pa 1492 Pa 2159 Pa 2010 ANSYS, Inc. All rights reserved. 64 ANSYS, Inc. Proprietary

63 Structural problem definition ANSYS Mechanical software used to assess structural integrity of 16 tube design under thermal loading Temperatures applied automatically from CFD model Boundary Conditions for a symmetrical model 2010 ANSYS, Inc. All rights reserved. 65 ANSYS, Inc. Proprietary

64 Response to thermal loadings Contours of deformation displayed on the Deformed shape (exaggerated) Equivalent Alternating Stress in the component due to thermal straining 2010 ANSYS, Inc. All rights reserved. 66 ANSYS, Inc. Proprietary

65 Fatigue Analysis An S-N curve is applied in the material properties. Hence the part s life (repeats to failure) can be calculated due to the stress cycling Contours of Factor Of Safety versus the specified required design life 2010 ANSYS, Inc. All rights reserved. 67 ANSYS, Inc. Proprietary

66 Submodel for detailed analysis To refine the results a submodel may be desireable with a locally refined mesh. This delivers more accurate stress results for the fatigue calculation ANSYS, Inc. All rights reserved. 68 ANSYS, Inc. Proprietary

67 Heat exchanger summary ANSYS CFD software used to assess thermal/flow performance of 24 and16 tube designs Acceptable performance achieved with 16 tube design ANSYS Mechanical software used to assess structural integrity of 16 tube design Life expectancy and safety factor quantified 2010 ANSYS, Inc. All rights reserved. 69 ANSYS, Inc. Proprietary

69 Invitation There are many challenges facing mechanical engineers as they strive to maximise the performance of heat exchanging equipment and to meet more demanding thermal management objectives. Typical requirements are to: Improve heat exchange Optimise cooling Reduce peak-temperatures Increase product efficiency Reduce power consumption Ensure structural integrity Minimise material costs Reduce equipment dimensions We hope that this seminar has introduced the unique capabilities of the ANSYS product suite to perform integrated flow, thermal, stress and fatigue analysis, giving mechanical engineers the simulation tools they need to deliver better performing designs, in shortened development times with reduced development costs ANSYS, Inc. All rights reserved. 71 ANSYS, Inc. Proprietary

70 Assessing & Optimising Heat Transfer, Structural Response and Fatigue in Mechanical Engineering Product Design Q&A Nigel Atkinson ANSYS UK Ltd 2010 ANSYS, Inc. All rights reserved. 72 ANSYS, Inc. Proprietary