Influence of Aluminum Silicate and Cerium (IV) Oxide Nanofluid on Pool Boiling Characteristics

Department of Mechanical Engineering, SRM Institute of Science and Technology, Ramapuram, Chennai 600089, India Department of Mechanical System Design Engineering, Seoul National University of Science & Technology, Seoul-01811, Republic of Korea Chemistry Department, College of Science, King Saud University, P.O. Box. 2455, Riyadh 11451, Saudi Arabia Department of Electromechanical Engineering, Faculty of Manufacturing, Institute of Technology, Hawassa University, Hawassa, Ethiopia


Introduction
Boiling heat transfer has always been a powerful energy extradition technology which persuades the way in achieving milestones in the advancement of the futuristic technologies. The ameliorations in the field of nanotechnology have gone hand-in-hand with almost all the fields, and the enhancement by implementing it in the boiling heat transfer has exhibited enormous increase in the efficiency of the process and has played a role in the elevation of the reliability of the process by increasing various factors that are need of the hour. Our experiments had us spectate that the PHF has inclined to a steep level upon addition of minimal quantity of nanoparticles. Nanofluids were prepared with the aid of dispersion of the nanoparticles of the order 10-50 nm which gave the increase of density of fluid and also high specific surface-area that paves the way to higher heat transfer between surface and fluids. It also grants acclimation of properties such as thermal conductivity and wettability by varying the concentrations. Our experiments were conducted based on pool boiling, and the results were focused mainly on uplifting of the PHF using nanofluids as the base fluid [1]. All these property enrichments are noticed because the high surface area of the nanoparticle and their enhanced thermal properties. Pool boiling is mode of the boiling phenomenon in which fluid is stationary with respect to heating surface in the beginning; vapor is spawned at a superheated wall that is tiny compared to the dimensions of the pool of ostensibly dormant liquid in which it is intent. In our experiments as cited in several papers, we use Ni-Chrome (80-20% composition) wire as the heating element through a set of platinum wire which has minimal resistance and anticorrosive in nature, and electricity is supplied. The bubbles formed by the cause are captured, and the certain parameters were calculated on the nucleation site, and the corresponding density with the diameter of the bubble that is formed when different nanofluid is applied [2,3]. The existence of a vermicular structure in CuO nanoparticles contributes to the particles' wear resistance and improved lubrication [4].
The literature demonstrated that a variety of parameters could affect the performance of pool boiling of nanofluids as represented by the pool boiling heat transfer coefficient including the amount of nanoparticle loading, the size of nanomaterials, the roughness of the heater, the thickness of the thermally insulating nanolayer, and the time of boiling. A number of parameters may directly affect the behavior of bubbles, including the density of nucleation sites, bubble diameter, bubble frequency, bubble waiting time, and growth time, considered as essential boiling parameters that might influence the boiling performance of pools.
It has been determined that cerium oxide nanoparticles can be considered as an attractive nanomaterial based on the data from all published experimental studies. They are inexpensive, have excellent chemical and physical properties, are nontoxic compared to other metal oxide powders, and are available as a readily available material. As acclaimed in various papers that the alumina [5] and silica nanoparticles [6] tend to increase the peak heat flux of the heating element, we have proposed to use a complex aluminum silicate which has the properties, and in addition to that, cerium was also employed for exhibiting high electron conductivity and also has an increased thermal conductivity due to its valence of electrons.

Materials and Methods
2.1. Chemical and Reagents. Aluminum silicate (Al 2 SiO 5 , 99.9% purity) and cerium (IV) oxide (CeO 2 , 99.9% purity), which was purchased from Platonic nanotech, were used to prepare nanofluids with DI water used as base fluid. All chemicals were of analytical grade. The average sizes were found to be 50 nm and 40 nm for aluminum silicate and cerium (IV) oxide, respectively. 2.1.2. Preparation of Nanofluids. Two methods are used for preparing nanofluids-one-step and two-step methods. Many researchers have reported that two-step method is most economical way to synthesize nanofluids. The advantage of two-step approach is it is cost-effective and able to produce large volumes of nanofluids. In this work, two-   International Journal of Photoenergy step method is adopted for preparing aluminum silicate (Al 2 SiO 5 ) and cerium oxide (CeO 2 ) nanofluids. In this process, nanoparticles are prepared and dispersed in the base fluid (distilled water) with or without the help of surfactants by mechanical stirring or ultrasonication methods. The twostep method is widely chosen because the nanoparticles have high surface area and surface energy interactions which tend to aggregate the nanoparticles which are available in dried form.
The following steps are involved in preparation of Al 2 SiO 5 and CeO 2 nanofluids: Determination of volume concentration (φ) for adding to base fluid was done by using the following equation [7]: The above equation can be simplified as By using the above formula, the quantities of nanoparticles to be added are determined as follows in Table 1.      International Journal of Photoenergy for experimenting peak heat flux enhancement in nanofluid. Through the lid of the beaker, voltage sensing wires are connected to two platinum wires which are suspended at ends of the beaker in which the Ni-Chrome wire is connected and current is passed through platinum wire to avoid contact resistance with test specimen. Hot plate is used to heat up to the saturation temperature T sat (100°C for water) of fluid, at 1 atm, while bulk temperature was being monitored with   Since thermocouples are placed too close to the surface, along with the minimal contact resistance of the tiny gap between the thermocouple tip and the wire surface, it is assumed that the measured temperature represents the boiling surface temperature.  International Journal of Photoenergy

Experimental Procedure.
Initially, the experiment is conducted in distilled water. The distilled water is heated on hot plate till its saturation temperature T sat is 100°C, and temperature was being monitored by thermocouple. Current is applied to Ni-Chrome wire through platinum wires by regulating the variac. Voltage and ammeter readings are noted during burnout [9] of Ni-Chrome wire for heat flux measurement and for comparing with various nanofluids. Similarly, the nanofluid is heated on a hot plate to saturation temperature T sat (100°C) of base fluid (distilled water) at atmospheric pressure 1 atm, while bulk temperature is monitored by thermocouples. Current is applied to Ni-Chrome wire that is regulated by variac for constant heat flux control, with increments of 0.5 A. The voltage measurements are noted at steady rate just after the current increase, and intervals are given after each increment to changes in system. Heat flux at any point is calculated by the following equation:   Figure 6 that pure Ni-Chrome wire has a smooth surface morphology as obtained while Figure 7(a) shows the SEM images of 0.1% of Al 2 SiO 5 -doped Ni-Chrome; Al 2 SiO 5 deposits are found on the Ni-Chrome wire, and with increasing concentration, there is a significant improvement observed. Figure 10 shows the elemental analysis of Ni-Chrome doped with Al 2 SiO 5 , in these compositions of Ni, Cr, Si, Al, and O that were present. SEM imaging of Ni-Chrome wire-untreated (uncoated) was taken initially to study surface morphology and provide for a base to compare with wires used in experimentation. Figure 6 showcases a plain Ni-Chrome wire and can be seen to have no coatings and a simple plain structured morphology.

Results and Discussion
As noticed in Figures 7-9, a certain layer of coating tends to form on the wire during experimentation which clearly enhances the heat flux of wire as the excess heat dissipation due to this nanocoating [10] is enhanced when compared to uncoated wire and also becomes more efficient with increase in volume concentration of nanofluids; this is also evident in the respective EDS data as shown in Figure 10, which generated that with increase in volume concentration, the amount deposited onto the wire also increases.
The aluminum silicate and cerium oxide nanofluids were tested with the base-fluid water, and enhancements were observed that varied with change in volume fraction. The varying bubble diameter at increasing heat flux is portrayed in Figures 11 and 12 which show that the bubble diameter increases as the heat flux applied to the wire increases.  International Journal of Photoenergy It is observed that starting at lower base temperature, a higher value for peak heat flux can be achieved, as illustrated by the graph above. Theoretically, bubble diameter was calculated using Haramura relation.
Bubble departure diameter, D b ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi σ g ρ l − ρ g v u u t = 2:77 mm for water: Experimentally, bubble diameter was calculated visually by using images captured during the experimentation process and using the Octave GNU software to attain exact values as shown in Figure 13.
Macrolayer thickness, δ, was calculated by the following formula, δðtÞ = ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi From the above formula, values where calculated using Octave GNU and it was inferred that the macrolayer thickness value decreases from the initial layer thickness as suggested by other literatures [11,12], while an increase in initial macrolayer thickness is observed with increase in base temperatures for fluids. Graph in Figure 14 shows the values of macrolayer thickness varying with increase in wall superheat of fluid.
Use preestablished models where comparative study was done to determine variations with these and our experimental model [13]. Table 2 shows clear comparison of existing models for pool boiling.
Hence, from experimental data as shown in Figures 15  and 16, it is observed that both Al 2 SiO 5 and CeO 2 show enhancements of about 120:5 ± 0:6% in PHF over water as base fluids for 0.3% volume concentration solutions. The reason for increase in PHF is also contributed by the macrolayer increase at higher temperatures [14]. Nucleation sites were determined using images captured from video taken during the experimentation process and were then fed into  Boiling has developed a great interest during the past few decades, as a method to increase the heat transfer rates with modest temperature differences. At high heat fluxes, heat transfer [15] by boiling is highly effective. Hence, find applications such coolants for nuclear reactors and also rocket engines where heat transfer rates are in high values (10 6 to 10 7 W/m 2 ). The probability to attain higher thermal energy conversion efficiency through boiling working fluid with heated surface is possible by these methodologies and has a large area of applications.
These coating of nanofluids over surface of wire or heater/heating surfaces tend to influence resistance which could be directly tracked to thermal conductance by inverse proportionality as shown in Figure 18 that when the coating increases, a decrease in resistance offered by wire is observed, and the values of resistance are for 60 mm of wire lengths as used in experimentation process for testing and generating direct relations. Nanofluids having high specific surface area serve to be better than other commercial fluids for heat transfer applications carrying more torridity between particles being the most important feature of nanofluids in heat carrying applications.
Using metallic fluids in heat carrying applications denotes significant difference when compared to commercial fluids for the same application. The hitch here being clogging of micrometer-sized particles in small passages and nanofluids being nanometer-sized can overcome this obstacle. Adding as low as 1-6 vol% of nanoparticle in a base fluid can enhance the heat carrying ability to a significant change of 20%. Usage of nanomaterials like Cu, Al, Si, Zn, Mg, and Se is advised on this prospect, and so a combination of aluminum and silicate forming aluminum silicate (Al 2 SiO 5 ) and cerium oxide is tested upon with 0.1%, 0.2%, and 0.3% of both the nanofluids. The stability of oxide-based nanofluids is higher, and therefore, both are chosen to be oxide-based nanofluids. Table 3 clearly depicts the improvement in peak heat flux (PHF) in comparison with other reported results.
Alumina particles have the tendency to decrease the pool boiling heat transfer but it has improved the CHF by 20% [20]. The CHF enhancement is due to the surface modifications that happen in the wire surface due to deposition of nanoparticles [21,22]. A main cost attributing factor for nanofluids is the use of stabilizers which increases the production cost of these nanofluids without which nanoparticles tent to settle over a period of time. So cheaper stabilizers or nanofluids which are more substantial without the use of stabilizers need to be invented. The stabilizers that are commercially used in nanofluids are proven to be unstable at high temperatures being a drawback for stability in heat carrying applications. Most nanofluids upon testing results have lower specific heat at their respective temperatures when compared to its base fluids. On production of nanofluids, the particles tend to agglomerate into larger particles resulting in limiting the main asset of nanoparticles' high surface area.