**2. Synthesis and modification of Field's alloy nanoparticles**

Nanoemulsification method is one of the most facile techniques to prepare nanosized Field's alloy particles. The illustrated nanoemulsification formation process is shown in **Figure 1**. Briefly, a certain amount of Field's alloy pellets was put into PAO

**109**

**Figure 1.**

silane solution of HFE7100.

*microscale droplets until nanoemulsion is formed.*

*Synthesis, Properties, and Characterization of Field's Alloy Nanoparticles and Its Slurry*

oil with or without certain amount of ethyl carbamate as surfactant. After that, the mixture was heated and kept at certain temperature (50, 70, 100, 150, and 180°C) in the help of silicone oil thermal bath and stirring for specific time under certain temperature under nitrogen protection to make the native or ethyl carbamate modified low melting temperature Field's alloy nanoparticles. As the time increases, the white color of PAO oil became gray and dark gradually. When the reaction finished, the nanoparticles were gathered by centrifuge and washed with acetone at least three times and then dried at 45°C overnight for ready to use. The native or modified Field's alloy slurry was made by dispersing certain amount of native or ethyl

*Illustrated scheme of the synthesis of molten Field's alloy nanoparticles using nanoemulsification method. (a) PAO and molten Field's alloys are in the reaction vessel. These two liquids are immiscible and phase separate; (b) polymer surfactant (ethyl carbamate) is soluble in PAO; (c) the mixture is heated up to certain temperature and the bulk molten alloy formed; (d) the microscale emulsion is stirred and breaks into* 

In order to make the as-prepared Field's alloy nanoparticles dispersed well in HFE7100 for long time, the nanoparticle surfaces were modified with a monolayer of 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane by mixing the nanoparticles in a

The size, morphologies, composition, and thermal properties of the synthesized Field's alloy nanoparticles were characterized by transmission electron microscopy (TEM), X-ray fluorescence spectrometry (XRF), and differential scanning calorim-

carbamate modified Field's nanoparticles into the desired base fluid.

**3. Characterization of as-prepared Field's alloy nanoparticles**

etry (DSC). The result and discussions were as the following.

*DOI: http://dx.doi.org/10.5772/intechopen.84224*

*Synthesis, Properties, and Characterization of Field's Alloy Nanoparticles and Its Slurry DOI: http://dx.doi.org/10.5772/intechopen.84224*

#### **Figure 1.**

*Nanoemulsions - Properties, Fabrications and Applications*

to the increased heat capacity of the carrier fluid.

changes from the solid to liquid phase.

of Field's alloy nanoparticles-HFE7100 slurry.

**2. Synthesis and modification of Field's alloy nanoparticles**

systems [30, 31].

inorganic PCMs, such as metal, alloy and salt hydrates, and organic PCMs, such as paraffins, polyethylene glycols, fatty acids, and esters [13–19]. Different types of nano-PCMs can be synthesized by using various synthetic methods [20–22]. By encapsulating or coating the nano-PCM with a suitable layer, the nano-PCMs can be dispersed in a base fluidic phase. However, nano-sized particles have a strong tendency to agglomerate and easily lead to precipitate in HTFs, which restricts their application as thermal energy storage media. Therefore, encapsulation or surface modification of nanoparticles to increase their dispersion ability in the carrier fluid is of primary importance. Various techniques such as interface polymerization [23] and coacervation [24] and emulsion polymerization [25, 26] were explored to make encapsulated nano-PCM. Meanwhile, some modified nanoparticles using certain way exhibit excellent dispersion stability in some HTFs [27–29]. As inexpensive and stable dielectric HTFs, PAO and HFE7100 are usually applied in cooling of avionic

Among those PCMs, the thermal conductivity of lots of low melting point metals, such as indium (In), bismuth (Bi), tin (Sn), and lead (Pb) and their eutectics, is at least two orders higher than that of inorganic PCMs. Meanwhile, their latent heat density and other thermal properties are comparable to inorganic PCMs, which makes low melting point metals or eutectic alloys highly attractive PCMs in practical applications. By taking advantages of nano-PCMs (such as their small size, large surface-to-volume ratio, good dispersion ability in base fluid, and large latent heat of fusion), these HTFs have some distinct merits such as high energy density thermal storage, large specific heat capacity, low flow drag, and enhanced thermal conductivity. Meanwhile, the fluids still keep the fluidic properties. All these aforementioned merits make these thermal fluids containing nano-PCM a promising HTF for electronic cooling equipment, thermal control, and those systems requiring high heat transfer rates [32–34]. The tight contact of nanoparticle and base fluid decreases the heat transfer resistance between nanoparticles and fluid, thus enabling fast exchange of heat transfer between phases [35]. Therefore, the slurry with nano-PCM could decrease the total pumping power in a heat transfer loop due

For a liquid, when the flow rate and thermal conductivity keep constant, the heat transfer capability is predominantly depending on its heat absorbing capacity [36]. Frequently, in high-flux heat removal case, dielectric fluids (such as HFE7100) are usually used to take the heat away through utilizing their latent heat of vaporization. As a low melting point alloy, Field's alloy is a eutectic alloy melt at approximately 62°C (144 F), in which composes with the weight percentage of 32.5% bismuth (Bi), 51% indium (In), and 16.5% tin (Sn). As a low melting point alloy, Field's alloy is selected due to its melting temperature a litter higher than the boiling point of HFE7100. Therefore, during liquid-vapor phase transition of HFE7100, the thermal fluid heat capacity can be increased significantly when the nano-PCM

This chapter mainly summarized our works in recently few years [37, 38], which include: (1) synthesis and modification of Field's alloy nanoparticles; (2) characterization of as-prepared Field's alloy nanoparticles; (3) jet impingement heat transfer

Nanoemulsification method is one of the most facile techniques to prepare nanosized Field's alloy particles. The illustrated nanoemulsification formation process is shown in **Figure 1**. Briefly, a certain amount of Field's alloy pellets was put into PAO

**108**

*Illustrated scheme of the synthesis of molten Field's alloy nanoparticles using nanoemulsification method. (a) PAO and molten Field's alloys are in the reaction vessel. These two liquids are immiscible and phase separate; (b) polymer surfactant (ethyl carbamate) is soluble in PAO; (c) the mixture is heated up to certain temperature and the bulk molten alloy formed; (d) the microscale emulsion is stirred and breaks into microscale droplets until nanoemulsion is formed.*

oil with or without certain amount of ethyl carbamate as surfactant. After that, the mixture was heated and kept at certain temperature (50, 70, 100, 150, and 180°C) in the help of silicone oil thermal bath and stirring for specific time under certain temperature under nitrogen protection to make the native or ethyl carbamate modified low melting temperature Field's alloy nanoparticles. As the time increases, the white color of PAO oil became gray and dark gradually. When the reaction finished, the nanoparticles were gathered by centrifuge and washed with acetone at least three times and then dried at 45°C overnight for ready to use. The native or modified Field's alloy slurry was made by dispersing certain amount of native or ethyl carbamate modified Field's nanoparticles into the desired base fluid.

In order to make the as-prepared Field's alloy nanoparticles dispersed well in HFE7100 for long time, the nanoparticle surfaces were modified with a monolayer of 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane by mixing the nanoparticles in a silane solution of HFE7100.
