# The Effect of Arachidic Acid Mixtures on the Cooling Performance of a Heat Sink
PCMs possess high latent heat storage capacity, which can be used to absorb the thermal energy of the surroundings as latent energy and change it from one phase to another [8]. Usually, solid-liquid phase change materials are used, but other types, such as solid-solid, solid-gas, and liquid-gas, also exist. PCMs have been used in many applications, such as thermal cooling of photovoltaic panels [9; 10], thermal comfort of buildings [11], water heating [12], thermal management in batteries [13], and cooling of electrical equipment [14; 15]. During the phase change, the PCM's temperature remains constant until all the material is completely melted; then, the temperature increases again, in theory to what it would have increased to without the PCM. When the heat source is turned off, the material re-solidifies and emits the absorbed heat. This is why PCMs are recommended for use in applications with non-continuous operation [16]. For example, when cooling portable devices such as palm pilots, cellular phones and personal digital assistants, these devices are not used for more than a few hours continuously at peak load. In addition, their 'idle' time is typically long enough to solidify the molten PCM for reuse. Studies on PCMs have focused on the thermal management of electronic devices at the system level. [PERSON] et al. [2] performed a numerical study of the distribution of temperature of a heat sink filled with two types of PCMs: salt-hydrate and wax. After performing multiple simulations, they concluded that an increase of heat flux leads to a reduction in the melting time of PCM. Moreover, they found that the salt-hydrate delayed the peak temperature more effectively than the wax. They also checked the significance of  
Figure 1: Lifetime degradation of AD8229 electronic device as a function of the operating temperature [6]. the density and thermal conductivity in delaying the steady state temperature. Experiments and numerical simulations of PCMs in cooling chips were performed by [17], where they discovered that this method decreases the resistance of thermal heat transfer from the chip to the ambient. Various configurations of heat sinks with two PCMs--namely paraffin wax and n-ecoisane--were studied in [18]. It was also found that circular pipes embedded with wax or n-ecoisane were more effective than a 2-mm-square pin fin heat sink. A numerical study of several configurations of a micro-channel heat sink with four PCMs (paraffin wax, n-eicosane, p116 and RT4) was performed by [19]. They concluded that PCM placed inside the base and channels of the heat sink grants a lower temperature. Another numerical and experimental study was conducted by [20] focusing on a PCM-based heat sink in the transient thermal management of plastic quad flat package electronic devices. The results showed that the presence of PCM in the cavities of the heat sinks increased the cooling performance more than the case without PCM. The usage of four heaters placed on the top of a heat storage unit filled with PCM (n-ecoisane) to cool a mobile electronic device was investigated by [21]. They concluded that using a larger amount of PCM could stabilize the mobile electronic device's temperature for a longer time. Previously, the heat was stored in the form of sensible heat, such as by heating water, oil, or rocks, but with developments in the energy domain, it was found that latent heat storage was one of the most efficient ways to store thermal energy [22], in addition to the various possible enhancements that could be applied to increase efficiency. Despite that latent heat storage techniques store a higher amount of heat compared to sensible heat storage ones, the charging and discharging processes of the former are slower. The hyper system takes advantage of the properties of both sensible and latent heat storage systems.