# Comparison of the Axial Fan and Synthetic Jet Cooling Systems
## 1 Introduction
[14]. The effect of the radiation of the heat sink acting simultaneously with natural convection was investigated by [PERSON] et al. [15]. The radiation turned out to account for as much as 27% of the total heat transfer. [PERSON] [16] optimized the thermosyphon heat sinks with rectangular radial fins dedicated to the LED lamp cooling, which was operated by natural convection. The measured radiation of the heat sink was negligible, and the numerical simulation was used to calculate the heat transfer parameters. The number and length of the fins varied, and the Pareto optimal solution was used to balance the heat sink mass and the thermal performance. [PERSON] and [PERSON] [17] investigated the heat sink with active cooling. The impinging jet and the duct flow were generated by the fan. The impinging jet exhibited higher thermal performance in comparison with the ducted flow. [PERSON] et al. [18] compared fan and impinging synthetic jet (SJ) active cooling methods. The synthetic jet actuator (SJA) achieved a higher heat transfer coefficient than the fan at the same or lower driving power. Additionally, the operation of the SJA caused less noise than the fan. [PERSON] et al. [19] proposed the heat sink with SJA contained within the volume not exceeding that of a regular heat sink. The use of the SJ increased the heat transfer by a factor of 2.2 compared to natural convection. The benefits of using SJ to cool electronics have been demonstrated many times over [20,21]. [PERSON] et al. [22] compared the SJ and continuous jet in impingement heat transfer. The SJ heat transfer parameters were better than in the case of the continuous jet but depended strongly on the Reynolds number of SJ. The SJ actuators are usually used to produce an impinging jet [22, 23, 24]; however, other configurations also exist, such as that proposed by [PERSON] [25] for the purpose of heat-sink cooling. In [25], the cylindrical SJA with orifices located at the curvilinear surface was used. The actuator was closed on one side by the loudspeaker, and on the other side, the heat sink was positioned in such a way that the fins were inside the actuator cavity. The heat sink was milled out of a single aluminum block. The amount of heat dissipated by the SJA reached values 3.7 times higher than those observed when the synthetic jet was turned off. This type of heat sink with an integrated SJA was also investigated in [26, 27, 28, 29]. [PERSON] et al. [27] investigated the SJA with different numbers and diameters of the orifices; there was a total of 11 cases. They showed that the heat performance of the device and the noise generated by the synthetic jet actuator depend on the ratio of the total cross-sectional area of the orifices and the effective area of the actuator diaphragm. These results may be seen as the more general form of the observations made by [PERSON] and [PERSON] [30], who had indicated that the ratio of an orifice to diaphragm diameter is related to the efficiency of the actuator. However, the investigation of [PERSON] and [PERSON] [30] was concerned with the SJ velocity and the efficiency of a single-orifice actuator, while the results of [PERSON] et al. [27] indicated this dependence on the heat performance and multi-orifice SJA. The flow parameters and the heat performance are directly related to each other in the case of the synthetic jet [8,24,31]. [PERSON] and [PERSON] [28] investigated the SJA with a heat sink inside a cavity for four different loudspeakers. The loudspeaker had a significant impact on the flow and heat transfer enhancement. The disparity of the thermal resistance between the different loudspeakers reached as much as 18%, while the sound pressure level was comparable for all investigated loudspeakers for the same electric power delivered to the SJA. The results from the literature survey are contradictory: in some conditions, the synthetic jet cooling outperforms the standard active cooling systems, such as continuous jets and fans, while in other conditions, it does not.