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Research Papers: Evaporation, Boiling, and Condensation

Two-Phase Convective Cooling for Ultrahigh Power Dissipation in Microprocessors

[+] Author and Article Information
Peter A. Kottke

George W. Woodruff School
of Mechanical Engineering,
Georgia Institute of Technology,
771 Ferst Drive NW,
Atlanta, GA 30332-0405
e-mail: pk57@mail.gatech.edu

Thomas M. Yun

George W. Woodruff School
of Mechanical Engineering,
Georgia Institute of Technology,
771 Ferst Drive NW,
Atlanta, GA 30332-0405
e-mail: tyun@gatech.edu

Craig E. Green

George W. Woodruff School
of Mechanical Engineering,
Georgia Institute of Technology,
771 Ferst Drive NW,
Atlanta, GA 30332-0405
e-mail: cgreen8@gatech.edu

Yogendra K. Joshi

George W. Woodruff School
of Mechanical Engineering,
Georgia Institute of Technology,
771 Ferst Drive NW,
Atlanta, GA 30332-0405
e-mail: yogendra.joshi@me.gatech.edu
Fellow ASME

Andrei G. Fedorov

George W. Woodruff School
of Mechanical Engineering,
Georgia Institute of Technology,
771 Ferst Drive NW,
Atlanta, GA 30332-0405;
Parker H. Petit Institute of Bioengineering
and Bioscience,
Georgia Institute of Technology,
771 Ferst Drive NW,
Atlanta, GA 30332-0405
e-mail: agf@gatech.edu
Mem. ASME

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received February 9, 2015; final manuscript received July 14, 2015; published online August 11, 2015. Assoc. Editor: Gennady Ziskind.

J. Heat Transfer 138(1), 011501 (Aug 11, 2015) (6 pages) Paper No: HT-15-1103; doi: 10.1115/1.4031111 History: Received February 09, 2015

We present results of modeling for the design of microgaps for the removal of high heat fluxes via a strategy of high mass flux, high quality, and two-phase forced convection. Modeling includes (1) thermodynamic analysis to obtain performance trends across a wide range of candidate coolants, (2) evaluation of worst-case pressure drop due to contraction and expansion in inlet/outlet manifolds, and (3) 1D reduced-order simulations to obtain realistic estimates of different contributions to the pressure drops. The main result is the identification of a general trend of improved heat transfer performance at higher system pressure.

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References

Figures

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Fig. 1

System definition for thermodynamic analysis

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Fig. 2

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).

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Fig. 3

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 Pout.

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Fig. 4

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.

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Fig. 5

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.

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Fig. 6

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.

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Fig. 7

Depiction of thermodynamic process on a P-h diagram for R-134 a with Tin = 358.15 K, G = 7200 kg/m2 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).

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