Experimental Investigation of The Heat Transfer Characteristics of Hybrid Nanofluid Al₂O₃/CuO - Distilled Water with The Variation of Concentration Ratios

Excessive heat that occurs in the computer's CPU (Central Processing Unit) can cause a decrease in computer performance. Cooling fluid applied to the waterblock device can help reduce overheating temperatures. One of the cooling fluids used in waterblocks is the cooling fluid of the nanofluid type. Nanofluid is a working fluid that contains nanoparticles and base fluid to flow on the testing device. This


INTRODUCTION
CPU is an essential part of a computer device that functions as the main component of computer equipment.To maintain the state of temperature to remain stable, the CPU usually uses cooling media so that the temperature is maintained and does not run into overheating, which can damage the components.Cooling devices such as fans are less effective on laptops or computers in industries with high work performance.There are several methods to cooling the computer using a fan that is flowed by air-fluid, liquid cooling to the heatsink.Waterblock is one of the media that can use for cooling a laptop because the low price is also often found in the market.Waterblock is a heat control component of the cooling water system (Gupta et al., 2019).The element of the waterblock has two parts combined into one to form the heatsink block (Harun & Che Sidik, 2020).In the heatsink, there is a cavity where the liquid flows.The liquid is used to cool or maintain the stability of the temperature of the computer or laptop.
Thermal conductivity is the property of a fluid that describes the rate at which heat energy is transferred in response to a change in temperature (Zhang & Xu, 2020).In order for nanofluids to be used as working fluids in heat transfer devices, a nanometer-sized particle was initially mixed with a basic fluid in the form of pure metal particles and in the form of metal oxides to form suspensions with enhanced thermal capabilities In this study, researchers utilized essential fluid distillate water due to its availability and affordability.CuO and Al2O3 nanoparticles are subjected to ultrasound using an ultrasonic cleaner method to create nanofluids.CuO is one of the nanoparticles with the highest conductivity among other nanoparticles.CuO in a fluid can significantly increase fluid conductivity (Chaudhari et al., 2019).Al2O3 is a compound formed from aluminum and oxygen, so one of its properties is corrosion resistance.Nanofluid hybrids are a method of synthesizing a relatively new nanofluid (Benkhedda et al., 2020).The primary purpose of synthesizing nanofluid hybrids is to obtain the properties of the essential ingredients of their constituents.A mono nanofluid does not have all the characteristics needed for a particular purpose.One example has good thermal properties (Kazemi et al., 2020).Nanofluid hybrids are expected to produce better thermal conductivity compared to single nanofluids.In this study, the author carry out nanofluid hybrid synthesis with several composition ratios between nanoparticles Al2O3 and CuO by 25%: 75%, 50%: 50%, and 75%: 25% with a volume fraction of 0.3%.

MATERIALS AND METHODS
Mixing hybrid nanofluid is carried out by a two-stage method, which is carried out with nanoparticle preparation with a volume fraction of 0.3%and varying the mixture ratio between the two nanoparticles, namely Al2O3: CuO with a percentage ratio of 25%: 75%, 50%: 50%, 75%: 25%, and mixed into the primary fluid, namely distilled water.Before making hybrid nanofluids, first make mono nanofluids, which mix each nanoparticle with distilled water into a beaker, then each nanofluid is stirred using an ultrasonic cleaner for 3 hours.Where other ratios must separate the stirring results of each ratio, this is done so that the resulting nanofluid is more stable for each comparison of the concentration ratio.After the stirring process, the deposition process is carried out for approximately 24 hours.After the deposition process, each nanofluid is mixed according to the ratio used and stirred for 1 hour using an ultrasonic cleaner.Where other ratios must separate the stirring results of each ratio, this is done so that the resulting nanofluid is more stable for each comparison of the concentration ratio.This was done hoping that only a few nanoparticles settled in the bottle.
The number of nanoparticles and basic fluids used as constituents of hybrid nanofluids is obtained based on a set volume fraction of 0.3%.Based on the volume fraction brought, the number of nanoparticles and basic fluids can be seen in Table 1.Nanofluid hybrid testing is carried out on test design tools to determine the effect of nanofluid hybrids as cooling fluids.Figure 1 depicts the design of the nanofluid hybrid testing instrument.The power supply, the heater, the measuring cup, the waterblock, the thermocouple, the hose, the thermocouple monitor, the nylon plates, and the peristaltic pumps were the components that were utilized in this research.The hybrid nanofluids that have been created will be examined using the testing apparatuses built, and the testing procedure will be carried out in accordance with the scheme shown in Figure 2.

RESULT AND DISCUSSION
The manufacture of nanofluid hybrids is carried out using the ultrasonic cleaner for 3 hours.
After the stirring process, nanofluids are deposited for approximately 24 hours.The depositional process is carried out due to whether nanoparticles did not dissolve in the primary fluid.Therefore, nanoparticles that are not soluble are separated first to find out the mass of the precipitate, and from the mass of the sediment, it can be known how many nanoparticles dissolved in the basic fluid.Testing characteristics of nanofluid Al2O3-CuO/Distilled Water (Hybrid Nanofluids/Distilled Water) is carried out using a waterblock with a flow rate variation of 0.7-1.9liter per minute with an interval of 0.3 liter per minute.Following are the results obtained after testing.The temperature of the heater begins at 63.5 o C and falls to 60.8 o C, as shown in Figure 3(a), which depicts a temperature drop that happened in distilled water of 2.7 o C. Figure 3.a further explains that after 270 seconds, the temperature within the heater starts to stabilize.This information can be found in the figure.Figure 5. demonstrates that the more nanoparticles Al2O3, the higher the convection coefficient is directly proportional to the research conducted by (Wanatasanappan et al., 2020), which states that the greater the concentration of Al2O3 given, the greater the conduction coefficient value.Moreover, 75% Al2O3:25%CuO nanofluid hybrids have the highest thermal convection coefficient.According to (Hamid et al., 2017), the considerable increase in thermal conductivity is likely owing to the high kinetic energy of the nanoparticles, which results in the effect of Brownian motion.It shows that the highest pump power value occurs in nanofluid hybrids with a ratio of 75% Al2O3: 25% CuO with a value of 1.61 W, where the flow rate used is 1.9 liters/minute.Figure 6 also explains that the pump power increase is directly proportional to the flowrate and hybrid nanofluid used.Viscosity causes the increase in pump power to flowrate in a worling fluid.The viscosity value of distilled water is 0.000623 Ns/m 2 .In contrast, in nanofluid hybrids 25% Al2O3: 75% CuO viscosity value obtained is 0.000836 NS/m 2 and in nanofluid hybrids 50% Al2O3: 50% CuO viscosity value obtained is 0.000799 NS/m 2 and in nanofluid hybrids 75% Al2O3: 25% CuO viscosity value obtained is 0.000741316 NS/m 2 .A higher nanoparticle composition also influences the increase in pump power.Therefore, the viscosity value of a nanofluid hybrid is increasing.According to research conducted by (Alrashed et al., 2018), the higher the nanoparticles' composition, the higher the nanofluid hybrid's viscosity value will be higher and cause the power in the system to increase.In addition, research conducted by (Mukherjee et al., 2020), stated that the greater the flow rate used, the more pump power is needed.

CONCLUSION
The results of the Nanofluid Al2O3-CuO/Water hybrid experiment can be concluded as follows: 1.The use of hybrid nanofluids has a very significant effect on increasing the convection coefficient compared to only base fluids.2. Testing of hybrid nanofluids with varying ratios of Al2O3 and CuO (75%:25%, 50%:50%, and 25%:75%) applied to waterblocks is in the Reynolds number range of 41.9-217, while distilled water is in the Reynolds number range 130-353.3. The most significant value of the convection coefficient with the Reynolds number was obtained in the hybrid nanofluid 75% Al2O3 : 25% CuO with a value of 345.798W/m 2ᵒ C with a Reynolds Number of 59.88 at a flow of 1 L/minute, while distilled water was 80.734 W/m 2ᵒ C with a Reynolds Number of Reynold 353 at a flow of 1 L/min.The influence of nanofluid hybrid concentration ratio and flow rate causes differences in heat transfer characteristics.In addition, the greater the concentration of Al2O3 nanoparticles given, the greater the value of the convection coefficient.4. The highest pump power value occurs in hybrid nanofluids with a ratio of 75% Al2O3 : 25% CuO with a value of 1.61 W with a flow rate of 1.9 liters/minute.The increase in pump power is directly proportional to the rise in the flow rate of the working fluid.Hybrid nanofluid composition with the highest viscosity variations can affect the increase in pump power.
(Ali et al., 2015; Mukherjee et al., 2020).In the waterblock media employed in this research (Siricharoenpanich et al., 2020).Particles in the size of the nano that is dispersed in the primary fluid provide a very good brown motion effect to prevent agglomeration (Saghir & Rahman, 2021).One of the advantages of nanofluid is the ability to make heat transfer where several nanomaterials are suspended in heat transfer liquids such as water (Ahmad et al., 2021).Nanofluids can use many essential ingredients, such as water, ethylene glycol, and mineral oil (Askari et al., 2021).As a component of nanofluids, this type of nanoparticle, such as Al2O3, CuO, ZnO, TiO2, etc., has been extensively utilized (El-Behery et al., 2022).

Figure 1 .
Figure 1.A series of testing tools Figure 3.The Effect of Time on Temperature Reduction (a) 0.7 Liter/Minute of distilled water, (b) 0.7 Liter/Minute 75% Al2O3: 25%CuO Figure 3.(b) shows a decrease in the temperature in nanofluids 75% Al2O3: 25% CuO in 0.7 L/min of 24 o C where the heater temperature starts from 64.3 o C until it drops to 40.3 o C. Figure 3.(b) also shows a decrease in the temperature on the heater begins to stable at 240 seconds, which shows that at the second 240 data, the heater temperature decreases are ready to be taken and processed.Figure 3. (a) and Figure 3.(b) only display data Theater, Tin, Tout to show the difference in temperature with the variation of the hybrid nanofluid Al2O3/CuO-Distilled water in the variation of the flow rate and know the effect of time on the difference in temperature entrances and electronic temperature out temperature.The data obtained is stable for calculation or analysis based on data after 600 seconds.This is similar to research conducted by (Rafati et al., 2012)(Sharma et al., 2013) where the more prolonged the testing is carried out, nanofluids will be more stable to reduce the temperature (Shirzad et al., 2019).3.2 Differences between Heater Temperature with Working Fluid Temperature

Figure 4 .
Figure 4. Flowrate comparison to temperature differences

Figure 5 .
Figure 5.Comparison of Reynolds Numbers to Convection Coefficient

Figure 6 .
Figure 6.Flowrate comparison with pump power