*3.2. Effect of Filling Quantity on Thermoelectric Performance of the Novel TEP*

As shown in Figure 6, the heat transfer coefficients of the novel TEP tended to increase as the polymeric nanofluid filling amount increased under the pressure of 400 torr in the tube. The thermal conductivity of the novel TEP is derived through the one-dimensional Fourier heat conduction equation and one-dimensional thermal resistance model. We controlled the experimental temperature of the heat source between 25 and 100 ◦C and let it operate at heating time until steady state. Between 50 and 60 ◦C, for the filling ratio in the tube of 100% and 80%, the difference in the thermal conductivity was a small increase of about 2%. However, the difference in the coefficient of thermal conductivity of the filling ratio of 100% and 80% in the tube is about 5% above 80 ◦C. Consequently, the phase change of the fluid increases as the temperature rises. At high temperature, the novel TEP with 80% filling ratio has more space for phase change and takes away more thermal energy, resulting in high thermal conductivity. The current and power of the novel TEP tended to increase as the temperature and filling ratio increased, as shown in Figure 7. When the solution was heated, the evaporation rate of liquid increased to take away more thermal energy, resulting in increasing the thermal conductivity of the novel TEP. Nevertheless, the distinction of the current and power of the novel TEP between 100% and 80% filling ratios was slight because of the novel TEP structural design factors, in which the difference in the electrode reaction area contacted by the filling ratios of 80% and 100% was not large. The electrode reaction surface area of the filling ratio of 100% was only 3.2 cm<sup>2</sup> larger than that of the filling ratio of 80%. The positive reaction was conducive to gas generation. The higher amount of space is conducive to the generation of redox reaction gas of the novel TEP for the filling ratio of 80%, so that the temperature of the polymeric nanofluid in the tube is higher and the electrical energy is increased.

**Figure 6.** Relationship between thermal conductivity and temperature of TEP.

**Figure 7.** Electric performances of TEP under different filling ratios. (**a**) Current, (**b**) power.
