## 8 Results and Discussion
Figure 13 shows temperatures and pressure courses inside the enclosure at the heat load of 1000 W, working fluid amount of 80%, and with fans turned off inside the enclosure. This figure shows the part of the measurement during which the temperature inside the cabinet stabilized. It is seen that temperatures in some parts of the enclosure rose above 60 \({}^{\circ}\)C, but most temperatures were under 60 \({}^{\circ}\)C. This is a good sign that the cooling device is able to operate without the help of fans directing the airflow inside the enclosure. The pressure profile inside the device throughout the experiments corresponds to the changing temperature conditions inside the cabinet. Before starting the measurement, the  
Figure 12: Temperature courses at a heat load 1000 W, working fluid amount of 80% and with fans turned on inside the enclosure. Figure 13: Temperature courses at a heat load of 1000 W, working fluid amount of 80%, and with fans turned off inside the enclosure. air was sucked out of the device, and subsequently, the device was filled with the working medium so as to guarantee the conditions of heat transfer by changing the phase of the working medium. The device worked independently without connection to an external vacuum pump. During the whole experiment, no air was sucked in from the exterior into the device, which can also be seen from the course of the pressures in Figures 12 and 13. Figures 14 and 15 show a comparison of the results of the heating power transferred by cooling device obtained by measurement and by mathematical calculation at 1000 W and 500 W. Differences between the measured and calculated values of approximately about 25-30% can be seen. This demonstrates, therefore, that this simplified method considers idealized conditions. It often happens that the theoretical calculations differ from the real measured values, which are more decisive than the calculated ones. This calculation has shown the maximal theoretical heating power transferred by the cooling device at this setup and has additional indicative meaning for us. The entire loop thermosiphon system is controlled automatically, according to the heat flow with low operating noise and minimal electricity consumption. Another method of cooling is refrigeration units and air conditioners, which, unlike heat pipes, are directly dependent on an external energy source [42; 43]. The designed cooling system with a heat  
Figure 14: Comparison of measured and calculated results at a heat load of 1000 W.  
Figure 15: Comparison of measured and calculated results at a heat load of 500 W.  
pipe is a simple and highly efficient device that can be adapted to various operations in a wide range of parameters. The current market also offers several products to choose from in the field of active cooling [44]. The flow of the working substance in the heat pipe is ensured by gravity and the resulting buoyancy, which drives the flow of the two-phase refrigerant into the condenser. The height difference and density increase the potential of the driving force, which contributes to the increase in the flow and thus to the greater heat dissipation compared to the capillary heat pipe [27]. The big advantage is the unattended and simple operation of the entire system. From a functional point of view, it works without any problems while maintaining unchanged initial conditions during the entire period of operation inside the tube. In terms of heat transfer, the loop thermosiphon is a simple, commonly used heat exchanger. The difference is in the phase change that takes place in the heat pipe and does not take place in the water-air or air-air heat exchangers [7; 45]. On the other hand, the design of a heat pipe is more complex in terms of production in terms of material, time and finances. An important condition for the effective operation of the proposed system is to ensure the vacuum tightness of the heat pipe. The joints on the welds are very sensitive parts necessary to maintain pressure and are recommended to be inspected in detail.