ltcm Thermal Simulation of Microchannel Two-Phase Liquid Cooling of Cold Plates for Servers and Power Electronics Prof. John R. Thome and LTCM Staff

Transcription

1 Thermal Simulation of Microchannel Two-Phase Liquid Cooling of Cold Plates for Servers and Power Electronics Prof. John R. Thome ltcm Heat and Mass Transfer Laboratory and LTCM Staff Based partially on Project CMOSAIC funded by the Swiss National Science Foundation Nano-Tera RTD Denver Lecture, August 4,

2 List of Contents 3. Two-phase flow boiling and data (d) OUT INLET IN 2. CMOSAIC multimicrochannel & simulator Single-phase flow followed by two-phase flow without back flow, R1234ze(E) OUTLET 1. Applications for microscale two-phase cooling Flow direction (a) Photron Fastcam-Ultima APX Camera (e) Light Flow direction Micro-evaporator (b) ThermaCAM SC3000 IR Camera 4. Flow boiling heat transfer model (c) 5. Time-strip 2 Single-phase flow followed by twophase flow with back flow, R245fa 6. Micro-thermosyphons

3 Two-Phase Thermosyphon: Joint Project with ABB Cools 15 MVA Power Transformer! Multiport tubes to cool down a power electronics system such as IGBTs Multiport microchannel thermosyphon evaporator/ condenser cooling system with up to 107 kw thermal cooling duty.! 3

4 CERN High Energy Physics Pixel Detector for Particles: ALICE a large ion collider experiment! New generation of two-phase, microchannel cooled, ultralight weight pixel particle detectors.! 4

5 Modelling of Parallel Channel Flow Instabilities Saenen, T. and Thome, J.R. (2016). Dynamic Numerical Microchannel Evaporator Model to Investigate Parallel Channel Instabilities, ASME Journal of Electronics Packaging, in press. Dynamic numerical 1-D model to study and predict onset of two-phase parallel channel flow instabilites in multi-microchannel evaporators Saenen/Thome (2015). 5

6 Modelling of Parallel Channel Flow Instabilities R236fa for 67 parallel 100x100 micron channels with inlet orifice width of 50 microns Saenen/Thome (2015). 6

7 Effect of Channel Mass Flux on HTC & Minimum (a) R236fa, qw = 175 kw m -2, ein,rest = 2 (b) R236fa, qw = 171 kw m -2, ein,rest = 4 4 x x 104 αw α m 2 K 1 ] w [W m -2 K -1 ] CB AF transition of Costa Patry and Thome for G ch = 1481 kg m 2 s 1 Increasing G ch 1481 kg m 2 s kg m 2 s kg m 2 s kg m 2 s kg m 2 s 1 αw α [W m 2 K 1 ] w m -2 K -1 ] CB AF transition of Costa Patry and Thome for G ch = 911 kg m 2 s 1 Increasing G ch 911 kg m 2 s kg m 2 s kg m 2 s kg m 2 s kg m 2 s kg m 2 s kg m 2 s x [ ] x [-] CB: HTC is marginally influenced by channel mass flux x [ ] x [-] AF: HTC increases with increasing channel mass flux for a constant vapor quality Szczukiewicz, S., Borhani, N. and Thome, J.R. (2013). Two-Phase Flow Operational Maps for Multi-Microchannel Evaporators, Int. J. Heat and Fluid Flow, Vol. 34, pp

8 Mechanistic Models for Flow Pattern Approach x 104 R236fa, ein,rest = 4, qw = kw m -2, Gch = kg m -2 s -1 αw [W m -2 K -1 ] α w [W m 2 K 1 ] x [ ] x [-] experimental Costa Patry and Thome (2012) Bertsch et al. (2009) Method Total MAE [%] Bertsch et al. (2009) Costa-Patry and Thome (2012) Predict locations of CB-AF transition (minimum region is churn flow) and IB-CB transition (bubbly and bubbly/slug flow at maximum bubble frequency) using our flow pattern map while heat transfer predictions now part of flow patten-based method using mechanistic models for slug flow and annular flow. 8

9 3D Multilayer Pseudo-Chip Heat/Flow Spreading Simulations of simultaneous heat and twophase flow spreading in all channels of all layers Predicted flow distributions in a four layer CPU stack with two-phase multimicrochannel interlayer cooling for non-uniform heat fluxes in the layers. Mass flux by channel across each evaporator; mm 2 chip; Top: Heat Load Pattern 4 at 24 W/cm 2 ; TSAT = 60 C; Bottom: Heat Load Pattern 5 at 50 W/cm 2 ; TSAT = 60 C; Madhour, Y., d Entremont, B.P., Marcinichen, J.B., Michel, B. and Thome, J.R., Modeling of Two-Phase Evaporative Heat Transfer in 3-Dimensional Microcavity High Performance Microprocessor Chip Stacks, ASME Journal of Electronic Packaging, 136, pp to (2014) 2015 Best Paper Award. 9

10 Modelling/Validation of Thermosyphon Cooling Gravity-driven fluid Flow Rate is a function of Heat Input, plus Relative Height (Δh), Diameters, Fluid, etc. Passive thermosyphon two-phase cooling system for electronics with microchannel evaporator for high thermal duties (experience with up to 20 IGBT s in parallel). 10

11 Two-Phase vs. Water Cooling Pros/Cons Flow boiling with environmentally-friendly refrigerants in microchannel-evaporator elements is a convincing solution for cooling of electronics (and power supplies) because: It yields very large heat transfer coefficients, so low thermal resistance, It makes low temperature difference operation possible, It has high critical heat flux for high W/cm 2 operation (> 350 W/cm 2 ), It provides a near uniform temperature of cooled element, Hot spot cooling is self-compensated by boiling itself (cooling q 0.7 ), It has much lower pumping power vs. single-phase cooling, Refrigerant is a dielectric fluid and water is not, Evaporation temperature up to C possible so no refrigeration needed, Lower flow rate results in smaller piping so lighter in weight, Refrigerants do not freeze down to -40 C compared to water at 0 C; Consumes about 1/10 of energy to drive two-phase coolant w.r.t. water. Assembling a two-phase cooling system many can do, but controlling and understanding the system only a few are capable at present. 11

12 Choice of Working Fluid: Physical Properties 12

13 Micro-Evaporator Simulator Code 13

14 Micro-Evaporator Simulator Code Uniform Heat Flux with Heat Spreading Uniform Heat Flux without Heat Spreading 14

15 Multiple Evaporators in Parallel & Transient Codes Illustration of predicted flow distribution to four multimicrochannel evaporator cold plates operating in steady-state at 4 highly different imposed heat fluxes. Transient operation of a multi-microchannel evaporator cold plate in a transient test when changing imposed heat flux from 30 to 18 W/cm 2 while other cold plate in parallel remained at 30 W/cm 2, and compared versus LTCM s transient simulator code for multiple cooling elements. 15

16 Modelling/Validation of Thermosyphon Cooling + No driver thus more reliable + Passive mass flow rate modulation GOAL: Cool the two Intel Xeon E5620 processors of HP server ProLiant DL180 G6 CHARACTERISTICS:! Max Heat load per chip is 80W! Max heat flux of about 7W/cm2! Max system height is 8cm! Two parallel cooling branches! 1 common condenser at the back DESIGN CONSTRAINTS/CHOICES:! As few bends as possible! Same piping geometry on parallel branches! Shortest length as possible in main riser! Larger diameter in riser! Accumulator used to have a constant liquid height Passive thermosyphon two-phase cooling system for retrofit to HP servers in Yahoo! rack donated to LTCM lab: actual final system is much simpler than shown here! (presented at ITHERM2016). 16

17 Modelling/Validation of Thermosyphon Cooling GOAL: Investigate the influence of diameters, water flow rate and temperature, and FR! 3 layers package considered (silicon 0.35mm, indium heat spring of 0.1mm, copper 1.8mm! 1 reference case and 7 case studies! Diameters, coolant flow rate, working fluid, coolant temperature, FR and LA volume influences Cas e Fluid! #$ %&#! () *+, * - $+, *./ 0 1 2)34,& [-] [mm] [mm] [kg/h] [ C] [%] [cm3] GOAL: Cool the two Intel Xeon E5620 processors of HP server ProLiant DL180 G6 on turn off 3 fans and operate other 2 at halfspeed, so 95% less energy to drive fans 1 R134a R134a R134a R134a R134a R134a R1234ze R236fa R134a R134a Passive thermosyphon two-phase cooling system for retrofit to HP servers in Yahoo! rack donated to LTCM lab (presented at ITHERM2016). 17

18 Modelling/Validation of Thermosyphon Cooling GOAL: Investigate the influence of diameters, water flow rate and temperature, and FR! 3 layers package considered (silicon 0.35mm, indium heat spring of 0.1mm, copper 1.8mm! 1 reference case and 7 case studies! Diameters, coolant flow rate, working fluid, coolant temperature, FR and LA volume influences RESULTS:! Max vapor quality reached is 45%! Above that, friction is too high! Chip temperature always below 75 C RESULTS:! GDR and FDR observable! Higher safety factor is 1.3 or higher! Riser diameter decrease is critical Passive thermosyphon two-phase cooling system for retrofit to HP servers in Yahoo! rack donated to LTCM lab (presented at ITHERM2016). 18

19 Modelling/Validation of Thermosyphon Cooling GOAL: Investigate the influence of working fluid GOAL: Investigate the influence of LA size RESULTS:! Low heat flux: R236fa is better due to large liquid density! High heat flux: faster fall off for R236fa because of larger friction forces (high ρ l /ρ v ) RESULTS:! Lower liquid height in the downcomer when large Liquid Accumulator, thus lower flow rate in thermosyphon Passive thermosyphon two-phase cooling system for retrofit to HP servers in Yahoo! rack donated to LTCM lab (presented at ITHERM2016). 19

20 Modelling/Validation of Thermosyphon Cooling RESULTS for unbalanced heat load for 2 chips cooled in parallel:! Increase of flow rate in branch with highest heat flux " Desired behavior!!! Due to increase of driving potential, i.e. lower two-phase density in associated riser. Passive thermosyphon two-phase cooling system for retrofit to HP servers in Yahoo! rack donated to LTCM lab (presented at ITHERM2016). 20

21 Modelling/Validation of Thermosyphon Cooling GOAL: Evaluate dynamic responses to Heat load and Water coolant flow rate disturbances RESULTS:! Heat flux increase leads first to flow rate decrease due to extra friction in ME then to increase due to larger quality in riser! Water flow increase leads first to flow rate increase due to extra liquid height in LA then to decrease due to lower quality in riser RESULTS:! Local heat transfer coefficient profile obtained thanks to PDEs! HTC increases with higher heat flux and decreases with lower system pressure Passive thermosyphon two-phase cooling system for retrofit to HP servers in Yahoo! rack donated to LTCM lab (presented at ITHERM2016). 21

22 Conclusions and Modelling Experiences So Far Two-phase flow boiling: excellent cooling solution for CPUs, UPSs & IGBTs, controlling the flow with micro-orifices to prevent backflow, provide uniform flow distribution and create flash vapor to jump-start boiling. High-definition heat transfer measurements: simultaneous spatial and temporal views of two-phase flow and temperatures are very useful together with time-strip analysis tests for 4 different refrigerants. Flow patterns: play decisive role in accurate microchannel flow boiling heat transfer predictions and trends and for creation of mechanistic models for slug and annular flow all in our micro-evaporator code. Thermosyphon: our accurate modelling code for two-phase flow in entire system is imperative to accurate flow rate and design to avoid huge testing program for every change in server layout, cooling load, piping, etc. Micro-thermosyphon cooling systems: tested and validated versus our one-dimensional in-house code for entire system (steady and transients). Passive two-phase cooling technology: ready for simulation and design of cooling systems for servers, racks and datacenter! 22