## 1 Introduction
The majority of these studies were experimental and numerical investigations on PCM combined with finned heat sinks [13; 14; 15; 16; 17; 18; 19; 20] or heat sinks with thermal conductivity enhancers, e.g., metallic foams [21; 22] or metallic particles [23; 24]. The investigated heat sinks' or devices' size were of magnitudes greater than the space available in modern portable electronic devices. Accordingly, those systems cannot be integrated in thin tablet computers or smartphones due to the lack of available space and will not be reviewed in any detail here since the overall approaches and geometries are vastly different. However, a small number of investigations with the aim of using PCM as part of the thermal management system of thin electronic devices (overall thickness in the range of 15 mm or smaller) have been published [10; 11; 12; 25; 26; 27; 28; 29; 30], and those are of great interest to the field of study and this work specifically. Numerical investigation on the thermal management of a modern computer tablet including thin PCM layers (0.5 mm) was performed by [PERSON] and [PERSON] [11]. In this work, a three-dimensional model of a modern tablet was presented. The model included all important heating sources: camera, battery, memory, SoC, and the power management-integrated circuit. The model was used to calculate the temperature history of the back and front surface of a tablet and of the SoC under a constant thermal power input of 7.5 W for different \"pseudo-PCM\", with melting temperatures ranging from 31.8 to 55.8 \({}^{\circ}\)C. The simulation showed that in the case of the lowest melting temperatures (below 40 \({}^{\circ}\)C), the PCM thermal storage was excellent at delaying the overheating of the SoC. The maximum SoC temperature, which was set at 80 \({}^{\circ}\)C, was reached 14 min later than if there was no PCM in the tablet. Moreover, it was observed that the duration before the back cover reaches 40 \({}^{\circ}\)C was reduced by 2 min when compared to the numerical study with no PCM. The first published experimental investigation (with a numerical component) using PCM in a setup similar to modern thin mobile devices was published by [PERSON] et al. [26]. A commercially available microencapsulated PCM with a melting point of 32 \({}^{\circ}\)C was inserted into a smartphone simulator. This device had a size of a typical smartphone (\(62\times 122\times 14\) mm). A ceramic heater was fixed inside the device producing 1.3 W. Two different PCM sheets were experimentally investigated (\(25\times 25\times 4\) mm and \(50\times 50\times 1\) mm). The results showed that the integration of the PCM clearly lead to a delay effect. The time until the maximum temperature of the heater was reached was delayed by 10 min for the thicker PCM sheet and 5 min for the thinner PCM sheet. [PERSON] and [PERSON] [27] studied gallium as a phase change material for passive cooling of a smartphone. Different experiments were carried out to quantify the variations in temperature and the holding time of a typical-sized hand-held device; however, it was made of stainless steel (\(40\times 40\times 3.5\) mm) so it was not entirely representative of a real device. A PCM layer with a thickness of 2.5 mm was mounted inside the containment between the heater and the ambient surface. The temperature holding time, which was defined as the duration until the outer surface of the containment reached 45 \({}^{\circ}\)C, was measured for different heat power input (1, 1.5, 2, 2.5, and 3 W). It was observed that the holding time of the gallium-filled containment was three times longer than that of an empty containment. [PERSON] et al.