## 5 Conclusions  
In this work, a commercial instrument based on the transient hot-wire technique, the THW-L2, was implemented and validated to determine the thermal conductivity of fluids. A methodology to correct thermal conductivity values obtained with this commercial device was proposed and carefully analyzed to contribute to improve the reliability of the experimental data that it is usually obtained with such instrumentation. Nine different fluids were used to test the equipment, namely, water (W), ethylene glycol (EG), propylene glycol (PG), ethylene glycol:water 50:50 vol\(\%\) mixture, \(n\)-tetradecane (\(n\)-C\({}_{14}\)), \(n\)-hexadecane (\(n\)-C\({}_{16}\)), and MgO/\(n\)-C\({}_{14}\) 1, 5, and 10 wt\(\%\) nanofluids. The selection of the heating power of the wire was performed in such a way that kept the temperature rise between 2 and 3 K. Three independent series of experiments were carried out in the temperature range 283.15 to 333.15 K, recording six measurements per temperature every 10 K. Thermal conductivity was then obtained from the slope of the \(\Delta T_{\rm exp}\)-In(\(t\)) curve, and these computed data were used to analyze the deviation from the transient hot-wire model and the repeatability of the device. Additionally, a comparison with literature data was performed, with these results allowing one to obtain a relationship to correct the raw experimental data. The main results achieved in this work are summarized below:  
* The behavior of the device was checked by the ability to reproduce the theoretical THW curve and its linearization as \(\Delta T_{\rm exp}\)-In(\(t\)). Then, the deviation between the experimental data points and their linear fit emerging from the THW theory was found to be 1%. This departure of the experimental behavior from the THW model was discussed and analyzed to figure out which sources have some impact on it. * Equivalently, from the thermal conductivity data of independent identical tests, the repeatability of the device was found to be 0.58%. * Moreover, the experimental data here reported were compared to literature values, yielding the following mean deviations: 1.1% for W, 3.9% for EG, 4.6% for PG, 2.1% for EG:W 50:50, and 4.8% for \(n\)-C\({}_{14}\). * The obtained deviations show a systematic dependence on the thermal conductivity range of fluids, and an empirical correction factor has been proposed. This relationship is based on a linear regression of the deviation between experimental values and literature data, as a function of the mean thermal conductivity of the fluid. * When all these considerations summarized above are taken into account and the recommendations stated in this paper are followed, an expanded (\(k=2\)) uncertainty of 5% is estimated. * Finally, two different fluids--\(n\)-C\({}_{16}\) and MgO/\(n\)-C\({}_{14}\) nanofluids at 1, 5, and 10 wt\(\%\)--were also used to check the reliability of this proposal, and reductions in the thermal conductivity deviations from 7.5 to 2.3% for \(n\)-C\({}_{16}\), and from 9.1 to 4.3% from 8.6 to 3.7% and from 9.3 to 4.4% for MgO/\(n\)-C\({}_{14}\) at 1, 5, and 10 wt\(\%\), respectively, were obtained. Those new reported values are within the expanded uncertainty gathered in this work. Following the recommendations of this work, more reliable thermal conductivity values could be obtained when a commercial device is employed, especially in nanofluids research where the use of manufactured devices is quite popular. These proposed critical suggestions may be completed in wider temperature and thermal conductivity rangesto cover a broad variety of pure and complex materials besides fluids and nanofluids. Additionally, it would be interesting in future work to check this procedure with fluids other than water (or without water content) with high or moderate thermal conductivity. Conceptualization, J.I.P. and L.L. ; methodology, J.I.P. ; validation, L.L. ; formal analysis, J.I.P. and L.L. ; investigation, U.C. ; resources, L.L. ; data curation, J.I.P. and U.C. ; writing--original draft preparation, U.C.