The Elusive Thomson Effect in Thermoelectric Devices. Experimental Investigation from 363 K to 213 K on Various Peltier Modules

Round 1

Reviewer 1 Report

The authors present a thorough study on the differences from what the commercial thermoelectric modules promis as far as cooling is concerned and how they actually perform, taking into account the Thomson effect. The materials, experimental methods, results and discussion are adequately described, although a little paragraph with the conclusions and take-home message arousing from all the research performed would be helpful for the reader. As it is now, it is hard to extract the final conclusions from the whole discussion section.

Author Response

As suggested, a paragraph has been added at the end of the paper containing the main conclusions on the research carried out. In this section, the main impact of the Thomson effect on the TE modules investigated has been highlighted with regard to the performances and the datasheets of the commercial devices. Opportunities related to the new class of TE materials are also mentioned.

Reviewer 2 Report

This paper deals with an experimental study to highlighting the contribution of the Thomson effect, in the temperature range from +90 °C to -60 °C on different Peltier modules commercially available.

The authors made experiments based on the Harman method to obtain parameters such as the Seebeck coefficient, electrical resistance , thermal conductace and the thermoelectric Figure of Merit. The authors described a simple setup consisting of a z-meter and a Compact DAQ board to acquire teperatures using K type thermocouples.

The authors contextualise their study in a coherent manner, with due regard to existing literature (using three self-citation on a total of sixteen references); however I suggest to futher expand the bibliography to include recent works on the thermoelectric modules characterization that can be found in MDPI journals.

This paper presents some interesting information, I have a slight concern about the use of thermocouples; some works can be find in recent literature, highlighting the greatest contribution to overall uncertainty on the estimation of thermal parameters given by temperatures measured with thermocouples suggesting that the measurement setup can be dramatically improved by employing more accurate temperature sensors instead of standard thermocouples, without making any adjustment to the core characterization technique. By doing so, also Thermo-Electric Modules designed for low temperature gradients can be reliably characterized. I think the authors should compare their setup with other proposal citing the proper works.

Some minor remarks:

Please use Kelvin for all temperature data; actually there is a mix of °C and K;

The cited cDAQ chassis model is probaly wrong (from the NI website I found cDAQ-9178); please check.

line 219 replace observed with observe.

Author Response

The bibliography has been expanded as suggested. In the Introduction section (lines 26-29), some general applications of thermoelectric devices for waste energy harvesting and refrigeration have been mentioned (lines 430-440 in the References section). Moreover, some recent works, found in MDPI journals, on the characterization of the thermoelectric modules have been considered and mentioned (lines 36-39 in the Introduction section, lines 445-448 in the References section). Unfortunately, the authors have not been able to make a comparison between the experimental methods due to the different theoretical approach adopted. In fact, the solution of the governing equation that includes the Thomson effect (equation 5 in the paper) requires the knowledge, a priori, of all temperature dependent thermoelectric properties involved. Therefore, the measures of both the dimensional figure of merit and the ohmic series resistance operated at different thermal levels using a z-meter are necessary.

As regards the measurement of the temperature, the minimum thermal level investigated (-60 °C) did not allow the authors to make alternative choices on the type of sensor. However, in the Materials and Experimental Methods section (lines 143-146), is reported a short remark about some preliminary measurements of the temperature uniformity on the ceramic plates, performed by the authors using an infrared camera.

All temperatures have been converted to Kelvin. The correct code of the cDAQ has been introduced. The typo in the line 219, now line 233, has been corrected.

Reviewer 3 Report

It is a great article dealing with the elusive Thomson effect in thermoelectric devices, with an experimental investigation from +90°C to -60°C on various Peltier modules.

I have several recommendations for gaining more interest to the paper by a broad range of researchers, dealing with the development of various classes of thermoelectric materials in which the effect can occur.

For those, I would recommend to include in the introduction, a sentence in the form of, many thermoelectric materials are being explored for power generation applications, such as silicides [1], PbTe [2], half-Heusler [3] and skutterudites [4] with the following references:

Yatir Sadia, Zeev Aminov, Dmitry Mogilyansky, Yaniv Gelbstein, Texture anisotropy of higher manganese silicide following arc-melting and hot-pressing, Intermetallics 68 71-77 (2016). Cohen, M. Kaller, G. Komisarchik, D. Fuks and Y. Gelbstein, Enhancement of the thermoelectric properties of n-type PbTe by Na and Cl co-doping, Journal of Materials Chemistry C 3, 9559 – 9564 (2015). Yunfei Xing et al., High-efficiency half-Heusler thermoelectric modules enabled by self-propagating synthesis and topologic structure optimization, Energy Environ. Sci. 12 3390 (2019). Rull-Bravo et al., Skutterudites as thermoelectric materials: revisited RSC Adv., 5, 41653 (2015).

Following taking into accounts the minor revisions specified above I will be glad to recommend on acceptance of the manuscript.

Author Response

As suggested, a sentence has been added in the Introduction section (lines 56-58) relating to ongoing research on new thermoelectric materials (References section, lines 464-471, and Conclusion section line 421).

Round 2

Reviewer 2 Report

The authors have addressed all the issues arisen from this reviewer. Therefore, no other doubts from my side