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research-article

Design of Thermal Ground Planes for Cooling Foldable Smartphones

[+] Author and Article Information
Ali Nematollahisarvestani

Department of Mechanical Engineering, University of Colorado at Boulder, 427 UCB, 1111 Engineering Dr, Boulder, CO 80309
alne8511@colorado.edu

Ryan Lewis

Department of Mechanical Engineering, University of Colorado at Boulder, 427 UCB, 1111 Engineering Dr, Boulder, CO 80309
ryan.j.lewis-1@colorado.edu

Y.C. Lee

Department of Mechanical Engineering, University of Colorado at Boulder, 427 UCB, 1111 Engineering Dr, Boulder, CO 80309
leeyc@colorado.edu

1Corresponding author.

ASME doi:10.1115/1.4042472 History: Received July 09, 2018; Revised January 01, 2019

Abstract

Foldable smartphones are expected to be widely commercialized in the near future. Thermal ground plane (TGP), known as vapor chamber or 2-D flat heat pipe, is a promising solution for the thermal management of foldable smartphones. There are two approaches to designing a TGP for foldable smartphones. One approach uses two TGPs connected by a graphite bridge and the other approach uses a single, large and foldable TGP. In this study, different thermal management solutions are simulated for a representative foldable smartphone with screen dimensions of 144?138.3 mm2 (twice the screen of iPhone 6s with a 10mm gap). In addition, the simulation includes two heat sources representing a main processor with dimensions of 14.45×14.41 mm2 and power of 3.3 Watts (A9 processor in iPhone 6S) and a broadband processor with dimensions of 8.26×9.02 mm2 and power of 2.5 Watts (Qualcomm broadband processor). For the simulation, a finite element method (FEM) model is calibrated and verified by steady state experiments of two different TGPs. The calibrated model is then used to study three different cases: a graphite heat spreader, two TGPs with a graphite hinge and a single, large, and foldable TGP. In the fully unfolded configuration, using a graphite heat spreader, the temperature difference across the spreader's surface is about 17 °C. For the design using two TGPs connected by a graphite bridge, the temperature difference is about 7.2 °C. Finally, for the design using a single large TGP with a joint region, the temperature difference is only 1-2 °C. These results suggest that a single foldable TGP or a configuration with two TGPs outperform the graphite sheet solution for the thermal management of foldable smartphones.

Copyright (c) 2019 by ASME
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