Laboratory experiments on interfacial heat and gas exchange promoted by surface cooling: novel simultaneous thermal imaging and optical oxygen-concentration measurement

• Applicant: Dr.-Ing. Herlina Herlina
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
• Term: from 2017 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 327259972

• Final Report Year: 2025

Final Report Abstract

At present, most models used to estimate the gas transfer rate across the air- water interface mainly consider wind-shear and typically do not take buoyancy effects into account. At low to moderate wind speeds, however, buoyancy is a major contributor. To improve the accuracy of the predictions, a detailed study of buoyancydriven gas transfer in deep waters is necessary. As the interfacial mass transfer of low to moderate soluble gases (e.g. carbon dioxide, oxygen, methane) is characterized by an extremely thin gas concentration boundary layer, elucidating the physical mechanisms of the process is immensely difficult. In this work, a combined intensity-lifetime-based laser induced fluorescence system suitable for resolving the oxygen dynamics near the surface was developed and employed to generate experimental data in the form of gas concentration mappings in vertical planes under buoyant-convectively (and Marangoni forces) driven flow conditions in a relatively deep water body. Simultaneously, the distribution of the thermal structures at the surface were obtained using a high-precision infrared camera. Experiments were performed for bulk Rayleigh numbers ranging from 1.4 × 10^9 to 3.3 × 10^10 allowing the heat flux and gas transfer velocity to be related to the bulk Rayleigh number. Visualizations reveal the temporal and spatial variations of the concentration boundary layer as well as the structural developments of the deepsinking plumes and the small-scale plumes that tend to linger near the surface, which are typically found in evaporative-cooling induced gas transfer. Correlation between the surface thermal and gas-saturated plumes and their geometrical characteristics could also be explored and related to the heat and gas fluxes. In addition, fully-resolved numerical simulations of interfacial heat and gas transfer were performed to study the effect of surface-temperature-gradient induced Marangoni forces on the transfer process. The experimental and numerical data were found to complement one another, leading to a better understanding of the studied process.

Publications

• Imaging bioirrigation using a novel lifetime-based laser induced fluorescence (τ LIF) technique. In The 5th Nereis Park Conference ”Biological modification of the seabed: biogeochemical and ecological processes in a changing world, Southampton, NY, USA, 2017
  Murniati, E., Herlina, H. & Lorke, A.
  
• Measurements of surface-cooling induced gas-transfer using fluorescence-lifetime imaging (FLI) technique. In The 8th International Symposium on Gas Transfer at Water Surfaces, Plymouth, UK, 2022
  Murniati, E., Eiff, O. & Herlina, H.
  
• Simulation of high-intensity isotropic turbulence driven gas transfer. In The 8th International Symposium on Gas Transfer at Water Surfaces, Plymouth, UK, 2022
  Herlina, H. & Wissink, J. G.
  
• Surface-temperature-induced Marangoni effects on developing buoyancy-driven flow. Journal of Fluid Mechanics, 962.
  Wissink, Jan G. & Herlina, H.
  
• Unsteady flow and mass transfer induced by e Rayleigh-B´nard-Marangoni convection. In MathSEE Symposium, Karlsruhe, Germany, 2023
  Herlina, H. & Wissink, J. G.