1. Date of download: 6/3/2016 Copyright © ASME. All rights reserved. From: Two-Phase Convective Cooling for Ultrahigh Power Dissipation in Microprocessors J. Heat Transfer. 2015;138(1):011501-011501-6. doi:10.1115/1.4031111 System definition for thermodynamic analysis Figure Legend:

2. Date of download: 6/3/2016 Copyright © ASME. All rights reserved. From: Two-Phase Convective Cooling for Ultrahigh Power Dissipation in Microprocessors J. Heat Transfer. 2015;138(1):011501-011501-6. doi:10.1115/1.4031111 Pressure drop as a function of mass flux for R134a with inlet conditions saturated liquid at 358.15 K, and full vaporization of coolant (outlet condition saturated vapor) as determined by solving Eq. (3). Figure Legend:

3. Date of download: 6/3/2016 Copyright © ASME. All rights reserved. From: Two-Phase Convective Cooling for Ultrahigh Power Dissipation in Microprocessors J. Heat Transfer. 2015;138(1):011501-011501-6. doi:10.1115/1.4031111 Maximum ratio of thermal conductivity to microgap height (k/H), which serves as a proxy for heat transfer coefficient, plotted against the outlet pressure at which it occurs, for a variety of coolants. All fluids were investigated under the constraint of entering the microgap at 358.15 K as a saturated liquid, and leaving as a saturated vapor. Within each class of coolants (fluorinated electronic liquids: solid squares; HCFC/CFC/HFC refrigerants: solid circles; hydrocarbons: open triangles; alcohols: open squares; and water: open circle), a general trend is observed of increasing maximum k/H with P out. Figure Legend:

4. Date of download: 6/3/2016 Copyright © ASME. All rights reserved. From: Two-Phase Convective Cooling for Ultrahigh Power Dissipation in Microprocessors J. Heat Transfer. 2015;138(1):011501-011501-6. doi:10.1115/1.4031111 Maximum ratio of thermal conductivity to microgap height (k/H) as a function of maximum pressure for four coolants at decreasing inlet temperatures from 358.15 K, with each point taken at 10 K intervals of inlet temperature. The hollow symbols are from solution of the reduced-order model, which includes friction. The dotted arrows indicate the reduction in k/H due to friction. Figure Legend:

5. Date of download: 6/3/2016 Copyright © ASME. All rights reserved. From: Two-Phase Convective Cooling for Ultrahigh Power Dissipation in Microprocessors J. Heat Transfer. 2015;138(1):011501-011501-6. doi:10.1115/1.4031111 Depiction on P-h diagram of two possible cycles that can be considered when predicting impact of coolant, operating conditions, and microgap geometry on the system COP for two-phase cooling. Both process diagrams depict the same entrance pressure drop (1–2), microgap vaporization (2–3), and exit pressure drop (3–4). In the high COP process (a), heat is rejected at low temperature prior and the coolant is condensed (4–5) then pumped to elevated pressure (5–6) and preheated (6-1). COP comparisons in this work are performed using the low COP path depicted in (b), where vapor compression (4–5) and high temperature condensation (5-6) are associated with smaller expected condenser volumes, and the process does not require a low temperature heat reservoir. Figure Legend:

6. Date of download: 6/3/2016 Copyright © ASME. All rights reserved. From: Two-Phase Convective Cooling for Ultrahigh Power Dissipation in Microprocessors J. Heat Transfer. 2015;138(1):011501-011501-6. doi:10.1115/1.4031111 COP at the condition of maximum k/H, assuming vapor compression before condensing, i.e., path shown in Fig. 5(b), and accounting for all pressure drop constituents (inlet/exit manifolds, coolant acceleration due to liquid-to-vapor phase change, and friction), as a function of maximum pressure at inlet temperatures from 358.15 K to 308.15 K, with each point taken at 10 K intervals of inlet temperature. For each coolant, inlet temperatures are increasing from right to left. The hollow symbols are example results from solution of the reduced-order model, which include friction. For a given inlet condition and coolant, the maximum k/H will occur at a lower mass flux and larger gap height with friction than without, as indicated by the labels for the highest pressure case. The dotted arrows indicate the reduction in COP due to friction. Figure Legend:

7. Date of download: 6/3/2016 Copyright © ASME. All rights reserved. From: Two-Phase Convective Cooling for Ultrahigh Power Dissipation in Microprocessors J. Heat Transfer. 2015;138(1):011501-011501-6. doi:10.1115/1.4031111 Depiction of thermodynamic process on a P-h diagram for R-134 a with T in = 358.15 K, G = 7200 kg/m 2 s, and H = 150 μm both without friction (gray curve) and with friction (black curve). Without friction, the pressure drop (1) is entirely due to acceleration and is 248 kPa. With friction, the total pressure drop (2) + (3) is 1.53 MPa with 620 kPa attributable to accelerational pressure drop (2) and 910 kPa due to friction (3). Figure Legend: