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Laboratory study of unsteady energy transfer in surface layers of stratified water
Author(s) -
Viskanta R.,
Parkin J. R.
Publication year - 1976
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/wr012i006p01277
Subject(s) - thermal diffusivity , convection , boundary layer , mechanics , thermodynamics , molecular diffusion , heat transfer , turbulence , materials science , convective heat transfer , diffusion , buoyancy , physics , metric (unit) , operations management , economics
A Mach‐Zehnder interferometer was used to study the energy transfer in the surface layers of stratified water cooled from above. Laboratory measurements of the unsteady temperature distributions indicate that the thermal structure between the interface and the stable region is controlled by a buoyancy induced flow which is established a small distance below the surface. The thermal structure is quite complex and the column of water can be separated into several regions: (1) the surface skin layer, (2) the thermal boundary layer, (3) the convective layer, (4) the interfacial entrainment layer, and (5) the stable region. In the skin layer ( z < 0.2 mm) there exists a relatively sharp temperature gradient, and energy is transported by molecular diffusion. Turbulent diffusion contributes to the energy transport in the thermal boundary layer (0.2 < z < 3 mm), while in the convective layer, heat is transferred primarily by turbulent diffusion and free convection circulation. An unsteady energy transport model is developed by lumping the convective terms with the spatially dependent turbulent diffusivity. A simple expression for the diffusivity based on the kinetic energy equation is derived for the equilibrium layer. This expression is then used in a polynomial to obtain the vertical diffusivity profile. The theoretical model predicts behavior which is consistent with experimental results and in good agreement with measured vertical temperature profiles.