## 2 Development of Experimental Apparatus: Prototype for a Mini Heat Exchanger
### Description of the Experimental Apparatus  
An experimental prototype was developed to assess the performance of a mini heat exchanger designed for cooling electronic components, such as computer processors. Figure 2 shows the configuration of the prototype, comprising (a) the experimental setup (left-one) and (b) the experimental scheme (right one). This setup simulates the thermal load that is typical of electronic components using an electrical resistance. The flow rate can be adjusted using a pump with variable power settings. A variable power supply allows for adjusting and monitoring the power of the electrical resistance, which simulates an electronic component. The mini heat exchanger, electrical resistance, and temperature sensors are thermally isolated. Data on physical quantities are collected via serial or Bluetooth communication using specialized hardware and software for data acquisition [30; 31; 32; 33]. The temperature sensors and pressure taps shown in Figure 2 were strategically positioned to calculate the average convective heat transfer coefficient (h) and the overall thermal resistance of the heat exchanger.  
Figure 1: Methodological flowchart.  
The mini heat exchanger used in the experiment, as shown in Figure 3, is a minichannel model, commonly known as a CPU water cooler block for AMD AM4 processors. It is also compatible with AM3 processors. This heat exchanger is specifically designed to support the AMD Ryzen AM4 processor family, which has a Thermal Design Power (TDP) ranging from 35 W to 65 W, according to the manufacturer's specifications [23]. Figure 3A,B depict the water cooler block designed to dissipate the heat generated at the CPU by the electrical resistance mounted on top. The components are separated by layers of Kapton tape, which prevents the flow of the electrical current. This mini heat exchanger features G1/4\" threads for connecting 3/8\" hoses that circulate fluid through its minichannels. This fluid circulation effectively removes heat, cooling both the CPU block and the electronic component, which in this case is an electrical resistance. It is composed of copper and acrylic, with a copper base measuring 0.05 m by 0.05 m.  
The electrical resistance installed above the mini heat exchanger was used to simulate the thermal load of an electronic component. This resistance tape measures 5.0 mm by 0.30 mm and has a resistivity of 0.50 ohms. Two thermocouples measured the average surface temperature.  
A Barrow-brand reservoir with a diameter of 50 mm and a height of 240 mm was installed in the prototype for deionized water circulation, alongside a 17 W SPB17 Plus pump. Both the reservoir and the pump feature G1/4\" threads. The pump is connected to a 12 V DC power source and includes speed control.  
The radiator used is a Freezemod TSRP45-BP360 model. It features 12 layers of copper tubes with a 4 mm spacing between the fins. The radiator's dimensions are 391 mm in length, 121 mm in height, and 45 mm in thickness, and it uses G1/4\" threaded connections.  
Figure 3: (**A**) Minichannel design. (**B**) Mini heat exchanger for the CPU block.  
Figure 2: (**a**) Experimental apparatus—prototype. (**b**) Experimental scheme.  
This type of radiator is commonly employed in conjunction with CPU block heat exchangers for heat dissipation. Three GS12 fans from the Freezemod brand were installed. Each fan operates at a rotational speed of 2000 \(\pm\) 10% RPM and has a flow rate of 116.76 m\({}^{3}\cdot\)h\({}^{-1}\), running continuously at 12 V. The dimensions of each fan are 120 \(\times\) 120 \(\times\) 25 mm.