# Comparison of the Axial Fan and Synthetic Jet Cooling Systems
## 2 Materials and Methods  
The investigated synthetic jet actuator consisted of cylindrical housing, a heat sink inside the cavity and a loudspeaker (Figure 1). A radial heat sink with an outer diameter of 180 mm was used. The heat sink had 32 rectangular fins of 2 mm thickness and 25 mm height. Half of the fins were of a length of 57 mm, and the other half of a length of 42 mm. The fins were arranged alternately and axisymmetrically. The heat transfer area of the heat sink was \(S\) = 0.10 m\({}^{2}\). The heat sink was mounted on the round heater plate with a thin layer of thermal grease. The heater was insulated with a 100 mm thick layer of mineral wool (Figure 2). The heater plate was powered with a GW INSTEK PSB-1400 direct current power supply. A Keithley 2700 multimeter was used for the measurements of the voltage and current that supplied the heater. The accuracy of the DC voltage measurement was \(\pm\)0.05%, and the accuracy of the DC current measurement was \(\pm\)0.1%. The temperature was measured with nine K-type thermocouples with the reference junction temperature stabilized by the Kaye 170 Ice Point Reference. The signal of the thermocouples was recorded with a Keithley 2700 multimeter, which enabled the temperature measurement with a resolution of 0.001 K. Four of the thermocouples were used to measure the ambient temperature (\(T_{\infty}\)), another two thermocouples for the measurements of the insulation temperature (\(T_{\rm HD}\), \(T_{\rm D}\)) and the last three of them were fixed inside the grooves milled in the heat sink base at different radial distances in order to measure the average heat sink base temperature (\(T_{B}\)) (see Figure 2). Each thermocouple was calibrated, and the  
Figure 1: Model (**a**) and photo (**b**) of the SJA. Figure 2: Schematic diagram of the experimental setup: 1—loudspeaker, 2—heat sink with outer ring, 3—heater, 4—insulation. accuracy of the temperature measurement has been estimated to be better than \(\pm\)0.07 K in the considered temperature range. The air at atmospheric pressure was used as a working fluid. The ambient temperature in the laboratory was controlled with an air conditioning system. During the measurements, the ambient temperature was kept within 295 \(\pm\) 1.5 K.  
Three different cases of heat sink cooling were investigated: natural convection (passive method), active cooling with SJA when the heat sink was located inside the actuator cavity (Figure 3a) and active cooling with the fan (Figure 3b). Data on the heat transfer characteristics with the SJ at the resonant frequency was taken from [27; 28] for the actuator with 16 orifices of a diameter of 10 mm each. The results included data for two different loudspeakers: W.18.200.8.FGX [27] and W.18.180.8.FCX_v2 [28]. In the present work, these actuators are referred to as \"SJ ([PERSON] et al. [27])\" and \"SJ ([PERSON] and [PERSON] [28])\", respectively. For the case with an airflow forced by an axial fan, the AABCOOLING Black Jet Fan 12 V with a diameter of 120 mm was used. The fan's maximum flow rate is equal to 170 m\({}^{3}\)/h. The fan was mounted on a disk with a diameter of 180 mm and located directly over the heat sink (Figure 3b). The fan was powered with a Teledyne T3 PS3000 direct-current power supply. The measurements of the voltage and current supplying the heater were arranged in the way described above for the experiment with a synthetic jet actuator. The setup with an axial fan was investigated in two different configurations. In the first, the hot air was sucked from the heat sink; therefore, the direction of the hot airstream was consistent with the direction of the natural convection. This setup is referred to as \"upward flow\". In the second configuration, the impinging jet was created by the fan that blew cold air at the surface of the heat sink. This condition is referred to as \"downward flow\".