RESUMO
In this article, we present a cost-effective approach to the precision measurement of heat flux using commercial thermoelectric modules (TEMs). Two different methods of measuring heat flux with TEMs are investigated, namely, passive mode based on the Seebeck effect and active mode based on the Peltier effect. For both modes, a TEM as a heat flux meter is calibrated to show a linear relation between the voltage across the TEM and the heat flux from 0 to â¼450 W m-2. While both modes exhibit sufficiently high sensitivities suitable for low heat flux measurement, active mode is shown to be â¼7 times more sensitive than passive mode. From the speculation on the origin of the measurement uncertainty, we propose a dual TEM scheme by operating the top TEM in passive mode while its bottom temperature maintains constant by the feedback-controlled bottom TEM. The dual TEM scheme can suppress the sensitivity uncertainty up to 3 times when compared to the single-TEM passive mode by stabilizing the bottom temperature. The response time of a 15 × 15 mm2 TEM is measured to be 8.9 ± 1.0 s for heating and 10.8 ± 0.7 s for cooling, which is slower than commercial heat flux meters but still fast enough to measure heat flux with a time resolution on the order of 10 s. We believe that the obtained results can facilitate the use of a commercial TEM for heat flux measurement in various thermal experiments.
RESUMO
This article reports the active control of a local hotspot temperature for accurate nanoscale thermal transport measurement. To this end, we have fabricated resistive on-substrate nanoheater/thermometer (NH/T) devices that have a sensing area of â¼350 nm × 300 nm. Feedback-controlled temporal heating and cooling experiments of the NH/T device confirm that the feedback integral gain plays a dominant role in device's response time for various setpoint temperatures. To further verify the integration of the feedback controller with the NH/T devices, a local tip-induced cooling experiment is performed by scanning a silicon tip over the hotspot area in an atomic force microscope platform. By carefully optimizing the feedback gain and the tip scan speed, we can control the hotspot temperature with the accuracy of â¼±1 K for a broad range of setpoints from 325 K to 355 K. The obtained tip-substrate thermal conductance, including the effects of solid-solid conduction, water meniscus, air conduction, and near-field thermal radiation, is found to be a slightly increasing function of temperature in the range of 127 ± 25 to 179 ± 16 nW/K. Our work demonstrates the reliable controllability of a local hotspot temperature, which will allow the further improvement of various nanoscale thermal metrologies including scanning thermal microscopy and nanoscale thermometry.
