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Research Papers: Evaporation, Boiling, and Condensation

# Evaporative Thermal Performance of Vapor Chambers Under Nonuniform Heating Conditions

[+] Author and Article Information
Je-Young Chang

Intel Corporation, 5000 W. Chandler Boulevard, CH5-157 Chandler, AZ 85226je-young.chang@intel.com

Ravi S. Prasher

Department of Mechanical and Aerospace Engineering, Arizona State University, Tempe, AZ 85287; and  Intel Corporation, 5000 W. Chandler Boulevard, CH5-157, Chandler, AZ 85226ravi.s.prasher@intel.com

Suzana Prstic

Intel Corporation, 5000 W. Chandler Boulevard, CH5-157 Chandler, AZ 85226

P. Cheng

Department of Mechanical and Aerospace Engineering, University of Missouri, Columbia, MO 65211

H. B. Ma

Department of Mechanical and Aerospace Engineering, University of Missouri, Columbia, MO 65211mah@missouri.edu

J. Heat Transfer 130(12), 121501 (Sep 23, 2008) (9 pages) doi:10.1115/1.2976786 History: Received October 10, 2007; Revised June 03, 2008; Published September 23, 2008

## Abstract

This paper reports the test results of vapor chambers using copper post heaters and silicon die heaters. Experiments were conducted to understand the effects of nonuniform heating conditions (hot spots) on the evaporative thermal performance of vapor chambers. In contrast to the copper post heater, which provides ideal heating, a silicon chip package was developed to replicate more realistic heat source boundary conditions of microprocessors. The vapor chambers were tested for hot spot heat fluxes as high as $746 W/cm2$. The experimental results show that evaporator thermal resistance is not sensitive to nonuniform heat conditions, i.e., it is the same as in the uniform heating case. In addition, a model was developed to predict the effective thickness of a sintered-wick layer saturated with water at the evaporator. The model assumes that the pore sizes in the sintered particle wick layer are distributed nonuniformly. With an increase of heat flux, liquid in the larger size pores are dried out first, followed by drying of smaller size pores. Statistical analysis of the pore size distribution is used to calculate the fraction of the pores that remain saturated with liquid at a given heat flux condition. The model successfully predicts the experimental results of evaporative thermal resistance of vapor chambers for both uniform and nonuniform heat fluxes.

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## Figures

Figure 1

Schematic of vapor chamber

Figure 2

Schematics of two heater test setups: (a) copper post heater setup and (b) silicon die heater setup

Figure 3

Schematic of package based heaters: (a) schematic of package with silicon die heaters and (b) locations of heaters at the back side of silicon die

Figure 4

Receding process of liquid in wick and possible particle structures

Figure 5

Schematic of wick structure and effective thickness

Figure 6

Comparisons of model predictions with experimental data of copper post heaters

Figure 7

Test results of vapor chambers with silicon die heaters under uniform die heating conditions

Figure 8

Test results of vapor chambers with silicon die heaters under nonuniform die heating conditions: (a) Only strip heater is powered; (b) both main heater and hot spot heater are powered

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