In-situ thermal transport measurement of flowing fluid using modulated photothermal radiometry

Recent Progress in Modulated Photothermal Radiometry

“…While these differing experimental designs produce similar results, some argue that the non-standardized apparatus design makes any comparisons inconclusive [ 45 ]. Other concerns, such as the lack of standard samples and uncertainty in the analysis, have started to be addressed [ 33 , 37 , 48 , 66 , 75 ]. Measurable sample parameters are mainly determined by modulation frequency bandwidth and resolution [ 66 , 75 ]; therefore, infrared photodetectors have become the main limiting factor as their low response time limits the usable upper-frequency range of MPTR [ 49 ].…”

“…Although cheap and simple, choppers limit the laser profile to a trapezoidal shape, whose sharpness varies throughout its frequency range [ 47 ]. Due to this, many researchers have increasingly opted for direct modulation of the laser drive current [ 33 , 37 , 48 , 49 , 50 ], as seen in Figure 5 a. Intensity profiles that are not sinusoidal will generate many harmonics in the temperature response; however, the signal processing of the response reduces the effect of higher-order generated harmonics, as covered in Section 4.3 .…”

“…For a two-layer sample, is simply the first layer’s thermal resistance . For samples of three layers and above, the value becomes increasingly complex [ 37 ]. While these simplified equations make the analysis simpler, they are reliant on 1 D transfer; therefore, an effort to understand Equation (18) is needed for cases with high penetration.…”

“…CSP plants also often feature fluidized thermal management and transport systems to move thermal energy from sources to storage and vice versa. Zeng et al [ 37 ] described a method of in situ monitoring of the thermal properties associated with a fluid using MPTR, citing CSP as a great application. MPTR has also gained traction in other fields that benefit from noninvasive monitoring.…”