Thermal Management of Electronics in Drilling and Completion. Gokul V Shankaran

Transcription

1 Thermal Management of Electronics in Drilling and Completion Gokul V Shankaran 1

2 Background Electronics circuitry in down hole tools to collect sensors data, drive actuators, multiplexing, data storage Present in both: Wireline tools Logging While Drilling (LWD/ MWD) tools Geothermal gradient ~ 25 to 30 o C/km in earth s crust Wells are getting deeper sink temperature keeps rising Formation temperature is about 100 to 120 o C at ~ 4 km IC packages rarely designed to withstand > 150 o C Narrow temperature band of operation Thermal management of Electronics is critical Focus on ANSYS ICEPAK in this study 2

3 Case Study: Problem Description I WIRELINE TOOLSTRING 7 long, 2.5 dia Houses 16 Electronic Section containing: PCB with ICs: Power = 11.1 W IGBT FETs x 3: Power = 11 W ea Actuator device: Power = 4 W Tool string studied in 8 dia well Natural convection in well fluid Natural convection and radiation within electronic section of tool 3

4 Problem Description II IGBT heat sink ELECTRONIC SECTION DETAILS Power components in red PCB components total 11.1 W Details in next slide IGBT x 3: 11 W ea Mounted on single heat sink Actuator: 4 W PCB (11.1 W) IGBT (11 W) x 3 Actuator (4 W) All parts mounted on the Core Core slides into housing Contact resistances between parts Core for mounting parts 4

5 Problem Description III PCB DETAILS All ICs modeled as 2 resistor network models: 1 resistor where only 1 is available Diodes modeled as lumped blocks (gen ceramic, k = 15 W/m.K) SOIC 32 SOIC 32 QFP 144 SO8 1 Name Q (W) jb (C/W) jc (C/W) QFP SO SO SOIC SOIC SOIC Diode 0.1 SOIC 14 SOIC 20 (x2) SO8 2 Diode (x6) 5

6 Problem Description IV 121 mm PCB LAYER DETAILS 6 layer PCB Layers 2 and 5 high coverage (VCC and GND) Layers 3 and 4 only vias 2 PCB models studied Uniform orthotropic conductivity Same planar and normal (k P, k N ) values used throughout the PCB Layer Thick (mil) % Cover PCB mm k P = 18.6 W/m.K; k N = 0.38 W/m.K Trace based local orthotropic conductivity Each cell in the PCB has a unique triad of k x, k y, k z Computed from pattern of Cu in each CFD cell 6

7 Modeling: Geometry I CAD to Icepak conversion in ANSYS Design Modeler (DM) 1. Import native CAD using ANSYS CAD interface 2. Use any DM tools to modify geometry as required 3. DM ELECTRONICS (DME): Main menu/ Tools/ Electronics convert into Icepak objects 7

8 Modeling: Geometry II DM Electronics/ SIMPLIFY tool 1. Geometry that already fits Icepak shape Transfers readily 2. Orthogonal/ cylindrical/ polygon shapes Use Simplify options Icepak Primitive shapes 3. Complex shapes Complex shapes (B splines, partial cylinders, etc) Transfer as Icepak CAD shape Combine DME tools with other DM tools like Slice, Fill, Extrude, Concept for efficient conversion 8 Icepak CAD shapes Icepak Primitive shapes

9 Modeling: Geometry III Import board layout and trace data directly into Icepak Board outline and components layout IDF import PCB traces ANSYS Ansoftlinks, Gerber, BRD formats IDF: Board Layout EDA (Cadence, Mentor, Altium, Zuken, etc) ANF, BRD, GBR: Traces 9

10 Modeling: System Level I Get the BIG PICTURE Larger dimensional scales Simpler model Less details PCB Simplified Model Board: Individual components NOT modeled PCB generates 11.1 W of component power Uniform orthotropic model of PCB compact PCB model Actuator lumped Fe block with 4 W IGBTs: Network resistor model with jb (C/W) Actuator: Actuator lumped Fe block with 4 W IGBT Actuator 10

11 Modeling: System Level II Model full tool string in well Big picture Capture overall heat flow from tool surface to well fluid Well fluid circulation patterns well (domain) sizing Consider all possible well conditions External to tool Well fluid properties, non Newtonian, etc Different formation temperature conditions Tool orientation gravity direction Do we have to model natural convection and radiation within the tool 11

12 Modeling: System Level III 4 Different cases considered: i. Top and Bottom Open; gravity: g 9.8 ˆj m/s 2 ii. Bottom at fixed 100 o C, Top open; g 9.8 ˆj m/s 2 iii. Same as ii, but g 9.8kˆ m/s 2 iv. Bottom at fixed 100 o C, Top adiabatic wall Well fluid is the cylindrical CFD domain Material: Liquid water Height: 20 in Cases i, ii, iii, 36 in Case iv Boundary Conditions Fixed Temp: 100 o Con Curved side of domain Domain top BC Well fluid Electronic section of Tool 12 Cases ito iii identify worst scenario Case iv proper well sizing Domain bottom BC

13 Mesh: System Level Sample Mesh ANSYS Icepak offers 3 types of mesh Hexa unstructured, Multilevel and Cartesian Combination of Hexa unstructured and Multilevel used Mesh within the tool Mesh in well fluid (b) 13 Vol mesh in Core Surface mesh on heat generating objects (a) Mesh (a) vertical section, (b) horizontal section at electronics, (c) away from electronics (c)

14 Results: System Level Flow Cases i, ii, iii Solved as laminar flow Should we expect well fluid to circulate or move upwards only Reasonable to expect annular circulation Low velocity vectors at bottom Case i unidirectional upward flow does not seem realistic Case iii Very different flow field as expected iii i ii 14

15 Results: System Level Thermal Cases i, ii, iii Temperatures compared for IGBTs and PCB Temperatures in cases i, ii are similar Case iii turns out to be cooler for the present tool Component Temperatures in o C; igbt refers to junction Component Case i Case ii Case iii igbt igbt igbt PCB Thus case ii may be considered as the worst case scenario Problems with case ii: Top opening too close to tool may numerically influence flow field Complete recirculation is not visible Capturing complete recirculation field may require well model to extend more above the tool work around in Case iv 15

16 Results: Case iv Well extended above tool total well height modeled = 30 Domain Top set to adiabatic wall: Enforces circulation Temperatures similar to case ii Component Temperatures in o C; igbt refers to junction Component Case i Case ii Case iv igbt igbt igbt PCB This solution has been used to create detailed zoom in models of the electronic section of the tool 16

17 Modeling: Detailed Zoom in Model I Focus: Electronic section of the tool string Case iv solution was chopped to create smaller model: To 1 from electronic housing at the top temperature within 1 o Crise from ambient To ~ 3 from electronic housing at the bottom Use plane contours to export profiles of P, UX, UY, UZ, T 17

18 Modeling: Detailed Zoom in Model II Zoom in Model Detailed Board model All components modeled as 2 resistor network blocks 2 Cases studies: (a) Lumped PCB, (b) Trace PCB Note the BCs in the domain T, UX, UY, UZ T= 100 o C T, P 18

19 Results: Zoom in Model I Type of PCB model important to temperature field Trace important for down hole tools conduction dominated Component Compact PCB T j ( o C) Trace PCB % diff U4-SO U8-SO U10-SO20_BW_A U9-SO20_BW_A U5-SOJ32_ U6-SOJ32_ U7-SQFP20X20_ U14-SO igbt igbt igbt

20 Results: Zoom in Model II Comparison of conductivities of the PCB Lumped PCB: Layer 1 all components are mounted Therefore most important to capture trace conductivity Layers 2, 5 almost fully copper (k ~ 385 W/m.K) Overdesign with lumped PCB k P = 18.6 W/m.K; k N = 0.38 W/m.K k P Conductivity of Lumped orthotropic PCB k N 20

21 Thermo Mechanical: Icepak Side Focus: Thermo mechanical with Icepak and Mechanical Here the components have all been modeled as solids Only hottest components or critical ones modified as shown Continues to use Trace PCB model Concentric solid and air contacts; solid corresponds to lead footprints SO8 IGBT 21

22 Thermo Mechanical: Work Bench Icepak is integrated into ANSYS Workbench from R13 Goal: CFD and thermal only Focus limited to modeling with Icepak Goal: Thermo Mechanical Detailed thermal field from Icepak 22

23 Thermo Mechanical: Icepak results Icepak Temperature field 23

24 Thermo Mechanical: Results Interpolated temperatures on PCB in Mechanical Ready for Mechanical analysis 24

25 Thank you Questions and Comments 25