**4. Conclusions**

The empirical formulae including both thermal conductivity and power density for the TEP of TiO2 nanofluid adopted the dimensional analysis method with thermoelectric experimentation and were applicable to temperatures between 25 and 100 ◦C and vacuum pressures between 400 and 760 torr in this paper, which were verified and not ordinary expressions. Their error values were separately less than 5.1% and 11.3%. The present empirical equations were not used to forecast the exact values, but instead of portending the thermodynamic activities of the novel TEP under various temperatures and vacuum pressures. For the thermal and electrical performance experiments with different filling volumes, the performances of the novel TEP tended to increase as the filling amount increased. The vacuum pressure inside the tube also affected the electrical and thermal performances of the novel TEP. The results indicated that the novel TEP with a filling ratio of 80% had better performance resulting from the space inside the tube required for the liquid– gas phase conversion to improve heat dissipation and power generation performances. The thermal performance of titanium dioxide nanofluid of the novel TEP and the electrical performance of the polymeric nanofluid of the novel TEP were respectively better among TiO2 nanofluid, TiO2 nanofluid with 0.2 wt.% NaOH, deionized water, and seawater. The temperature and vacuum pressure gradients of chemical and thermodynamic potentials were the driving forces, which had a significant role in the thermoelectric experiment. Finally, the formulas were suitable for an approximate estimation in the present study.

**Author Contributions:** Conceptualization, Q.G. and J.-C.W.; Data curation, R.-T.W. and J.-C.W.; Investigation, Q.G. and R.-T.W.; Methodology, R.-T.W. and J.-C.W.; Software, J.-C.W.; Supervision, R.-T.W. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** All data are offered by the authors for reasonable request and the novel TEP device is available from the authors.

**Conflicts of Interest:** The authors declare no conflict of interest.
