A sensor for direct measurement of small convective heat fluxes: Validation and application to micro-structured surfaces

A sensor for measuring small convective heat flows (<0.2 W/cm^2) from micro-structured surfaces is designed and tested. This sensor {exploits the notion of thermal guard and is purposely designed} to deal with metal samples made by additive manufacturing, {such as} direct metal laser sintering (DMLS). For validation purposes, we utilize both experimental literature data and a computational fluid dynamic (CFD) model: Maximum and average deviations from CDF model in terms of the Nusselt number are on the order of +/- 13.7 % and +/- 6.3 %, respectively while deviations from literature data are even smaller. Similar works in the literature often have the necessity of maintaining one-directional heat flows along the main dimension of a conducting bar using insulating materials. Such an approach can be critical for small fluxes due to the curse of heat conduction losses along secondary directions. As a result, it is necessary to estimate those secondary fluxes (e.g. by numerical models), thus making the measurement difficult and indirect. On the other hand, depending on the manufacturing accuracy, the present sensor enables to practically reduce at will those losses, with direct measurement of the heat flux. To our knowledge, the adoption of thermal guard is not a common practice in convective heat transfer, especially when local measurements are of interest. We hope that this study may (i) shed light on the usefulness of the approach in this field; and (ii) provide an effective tool for future investigation on electronic cooling and convective heat transfer enhancement by micro-/nano-structured surfaces. Owing to a number of features of the proposed device, we suggest that it can be prospectively utilized in the near future (i) for industrial applications (due to simplicity and robustness of the design); (ii) for high temperature measurements (unlike foil sensors, no delamination issues can be experienced); (iii) in the context of micro-electromechanical systems (MEMS) (easy to miniaturize).