Fig 1.
Schematic illustration of the transient hot-wire sensor setup for thermal conductivity measurements; the dashed line represents the direction of visualization by the scanning cryomacroscope [6].
Fig 2.
(a) Representative thermal histories, where H1 refers to the initial cooling rate between 12ºC and -100ºC, including experiments on DP6 + IONP (H1 = -1 to -7.5°C/min) and DP6+sIONP (H1 = -20°C/min), and where the reported temperature was measured at the inner surface of the cuvette. (b) A cryomacrograph of fractured DP6+sIONP (occurring at -123°C with H1 = -20°C/min). (c) A cryomacrograph of partially crystallized VS55 in the absence of nanoparticles. Both cryomacrographs are presented in regular color scheme and a negative color scheme, which may enhance physical events.
Fig 3.
Representative TEM image of sIONP.
Fig 4.
Thermal conductivity measurements of selected CPAs and nanofluids combinations; H1 refers to the initial cooling rate between 12ºC and -100ºC, where measurements were taken during passive warming to -100°C and at 3°C/min thereafter.
Fig 5.
Selected thermal conductivity measurements for DP6+IONP, where all other CPAs and nanofluids combinations were found within the yellow range; H1 refers to the initial cooling rate between 12ºC and -100ºC, where measurements were taken during passive warming to -100°C and at 3°C/min thereafter.
Pure DP6 was measured previously and is displayed here for reference [13, 18].
Table 1.
Best-fit polynomial approximation coefficients for thermal conductivity data displayed in Figs 4 and 5, where average values are listed in cases where the span of the polynomial approximation is smaller than two standard deviations of the experimental data over the relevant temperature range (denoted by †).
Fig 6.
Ratio of thermal conductivity of nanofluids to thermal conductivity of the pure CPA at -125°C (below glass transition temperature) for a cooling rate of H1 = -2.5°C/min; predictions are based on the Maxwell-Eucken model.