Fig. 10

Fluid temperature profiles from the TDTR hot-spot with subcooled cross-flow in a microchannel. Fluid temperature profiles (T(y)) normal to microchannel wall for two different hot-spot wall temperatures: T_HS ≈ 118 °C () and T_HS ≈ 143 °C (\({- \cdot}\)). The temperature profiles are based on both the similarity solution and the integrated BL energy equations for Pr > 1. The blue lines are the corresponding transient, nanometer length-scale temperature oscillations (\({\mathrm{\Delta }}T_{\omega _{\mathrm{p}}}^{{\mathrm{TDTR}}}\)) due to periodic heating by the TDTR pump laser at (ω_p/2π) = 976 kHz. As shown, the TDTR pump laser induces both DC and AC heating of the hotspot, where ΔT_DC = T_HS−T_bulk, \({\mathrm{\Delta }}T_{{\mathrm{AC}}} = {\mathrm{\Delta }}T_{\omega _{\mathrm{p}}}^{{\mathrm{TDTR}}}\), and \(\left. {{\mathrm{\Delta }}T_{\omega _{\mathrm{p}}}^{{\mathrm{TDTR}}}} \right|_{y = 0} \approx\)6.6 °C and ≈ 4.1 °C for T_HS ≈ 143°C (\({- \cdot}\)) and ≈ 118 °C (), respectively. The vertical lines correspond to the thermal BL thicknesses (δ_th) and thermal penetration depths (\(\ell _{{\mathrm{th}}}\)) for each experimental scenario—i.e., a vapor bubble after nucleation (, \(h_{\omega _{\mathrm{p}}}/h_0^{{\mathrm{scw}}} > \)1) or before release (\({- \cdot}\), \(h_{\omega _{\mathrm{p}}}/h_0^{{\mathrm{scw}}} \approx\)0.7)