**4.2 Test chamber and heaters**

*Nanoemulsions - Properties, Fabrications and Applications*

**4. Heat transfer loop test**

exothermic peak at 35.5°C was for their freezing. This observed melting-freezing temperature difference (about 27°C), called supercooling, had been well explained by the classical nucleation theory [39]. As shown in **Figure 4B**, no obvious changes of the slurry after running for 20 cycles, it suggested that slurry was very stable in ambient condition. It suggested that the nanoparticles are stable in ambient condition. As shown in **Figure 4C**, the nano-PCM slurry can undergo melting-freezing phase transition during heating and cooling scanning processes. The downward endothermic peak at 62.5°C was belonging to the melting of the Field's alloy nanoparticles, while the upward exothermic peak at 35.5°C was for their freezing. As shown in **Figure 4D**, no obvious changes of the nano-PCM slurry after running for 20 cycles, it suggested that

nano-PCM slurry is very stable in the temperature range under 100°C.

**4.1 Experimental setup for heat transfer loop test**

In order to investigate the Field's alloy nanoparticle slurry compared to the pure liquid of HFE7100, a jet impingement heat transfer test was carried out. This part will represent some experimental data and discuss the effect of mass fraction of Field's alloy nanoparticle in slurry on pressure drop and heat transfer performance.

It is noted that all of the heat transfer loop tests were carried out under 1 atmospheric pressure. After installation of the heater, the test vessel was evacuated and filled with the working fluid, HFE7100. Additional degassing process was carried out by boiling the liquid pool for 2 hours to remove the dissolved noncondensibles. **Figure 5** illustrated the flow loop utilized to conduct the experiments. A variable

**112**

**Figure 5.**

*Schematic diagram of the heat transfer loop test.*

**Figure 6A** illustrated the test chamber and **Figure 6B** showed our measured relationship between chamber pressure and saturation temperature of HFE7100.

**Figure 6.** *Illustrated scheme of test chamber (A) temperature vs. pressure of HFE7100 (B) and heater (C).*

The coolant within the reservoir was maintained at a constant temperature using a combination of an immersion heater and proper thermal insulation to ensure the test was under 1 atmosphere pressure. An acrylic cylinder with aluminum lids, which was 300 mm tall and 200 mm in diameter, was used as the test chamber. The test chamber contained approximately 500 ml of working slurry (pure HFE7100/ nano-PCM mixture). Heat was applied to the heater surface through a copper plate using a resistive heater controlled by a HP 6030A DC power supply system. The heater was built by soldering a 10×10×2-mm-copper block onto a matching size, 1-mm-thick resistive heater. **Figure 6C** showed the heater details. The resistive heater was made of a 5-ohm-thick film resistor with BeO substrate made by Barry Industries Inc. Soldering the thick film resistor to the copper plate minimizes the thermal contact resistance at the interface.

The temperature of slurry entering the test chamber was maintained at 56°C, 5°C below the liquid saturation temperature. Due to the large supercooling of nano-PCM particles (solidification temperature at 17.1°C), to ensure the PCM in solid phase, the slurry was chilled to 5°C by ice water. The nozzle inlet temperature (56°C) was controlled by an auxiliary heater powered by an AC regulator. The test heater surface was fastened at the bottom of the container using epoxy resin. The test vessel was insulated with a 25-mm-thick fiber glass blanket. A Bakelite layer (with a thermal conductivity less than 1 W/mK) underneath the heater was found to be a sufficient insulator. The uniformity of the Joule heating over the resistor surface was within 5%. The heat fluxes were also controlled at steady state for each set of testing. The jet impingement nozzle (a TG 0.7 full cone nozzle with the insert removed) was procured from Spraying Systems Co., and it had a passage with circular cross section, 0.76 mm in diameter. The coolant was allowed to enter the plenum of the nozzle where it flowed through a converging section as it existed to the chamber. Once the steady-state flow and temperature conditions were attained, the mean temperature of the heater and inlet and outlet temperatures of the slurry were calculated by the arithmetic mean of temperature readings. The heat transfer coefficient was then obtained by the following equation [40]:

$$\mathbf{h} = Q\mathcal{A}\{T\_w - T\_f\} \tag{1}$$

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**Figure 7.**

**4.4 Pressure drop**

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

**Specific heat (J kg<sup>−</sup><sup>1</sup> K<sup>−</sup><sup>1</sup> )**

**Thermal conductivity (W m<sup>−</sup><sup>1</sup>**

7880 170.5 70.1 40.2 –

7880 170.5 34.5 – –

1500 1180 0.07 – 0.60

 10% 1648 1079 0.075 4 0.69 23% 1883 948 0.084 9 0.75 30% 2036 877 0.091 11 0.79

 **K<sup>−</sup><sup>1</sup> )**

**Latent heat (kJ kg<sup>−</sup><sup>1</sup> )**

**Viscosity (mPa s) at 293 K**

A relation exists between the temperature of HFE7100 with Field's alloy nanoparticles slurry and its apparent viscosity. **Figure 7** shows the measured experimental data that exhibits the effect of temperature on apparent viscosity of pure HFE7100 and slurry with 30% (wt%) particle fraction. The results show that the ratio of the slurry viscosities keeps almost the same at 1.4 over the tested temperature range.

*Effect of temperature on apparent viscosity of pure HFE7100 and nano-PCM slurry.*

An important parameter was pressure drop between the inlet and the outlet of microchannel heat exchanger. In ideal case, the pressure drop should be as small

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

**Density (kg m<sup>−</sup><sup>3</sup> )**

**Slurry and its components**

Field's alloya (solid)

Field's alloy (liquid)

HFE7100 (298 K)b

Slurryc

*http://www.Matweb.com [42].*

*3M Data Book, HFE7100 for Heat Transfer, 2002 [43].*

*Bulk physical properties of slurries are calculated from those of solid PCM particles.*

*Physical properties of Field's alloy nano-PCM slurry and its components.*

*a*

*b*

*c*

**Table 1.**

where *Tw* is the average of the two surface temperatures extrapolated from the two embedded thermocouple readings. The pressure drop across the nozzle was measured at different mass fractions of slurry at a temperature of 20°C at the nozzle inlet (non-melting conditions).
