首页|An analytical theory for the forced convection condensation of shear-thinning fluids onto isothermal horizontal surfaces
An analytical theory for the forced convection condensation of shear-thinning fluids onto isothermal horizontal surfaces
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NSTL
Elsevier
We present an analytical theory for laminar forced convection condensation of saturated vapor on horizontal surfaces. The condensation produces shear-thinning film moving downstream due to the viscous-drag occurring at the vapor-liquid interface. The mathematical model is built based on a few input parameters, viz. power-law index (n), nondimensional film-thickness (eta(delta,l)), Prandtl number (Pr), and inertia number (Mc). A set of output parameters is used to analyze the distinct characteristics of the fluid-flow and condensation, viz. the condensate's nondimensional mass flow rate ((m) over cap), Nusselt number, specific enthalpy ratio (R-h), thermal retention coefficient (circle dot), and nondimensional wall-shear stress ((tau) over cap (w)). We have identified the subtlety of shear-thinning film flow when liquid's thermophysical properties vary according to the changes in wall-shear and the interfacial drag. Contextually, we illustrate that a rise in shear-thinning effect (obtained by decreasing n), keeping Mc and eta(delta,l) fixed, results in a decrease of (m) over cap, R-h, (tau) over cap (w), and (1/(sic)). We have demonstrated that for a fixed R h, a shear-thinning film, compared to the Newtonian film, would exhibit a greater.d, l but a smaller interfacial velocity (f'(i)). Furthermore, a greater film thickness is required for low Prliquids to attain the same degree of subcooling compared to high Prliquids. We perform systematic investigation over a wide range of eta(delta,l) We observe that for small.d, l values, the vapor boundary-layer moving onto the liquid-film exhibits similar flow-features as found in the well-known Blasius boundary-layer. Conversely, at large eta(delta,l), the present solution would remarkably differ from the Blasius solution. Finally, we establish an approximate theory for small.d, l motivated by the linearity in the cross-stream variations of velocity and temperature within the thin-film. This approximate theory gives rise to analytical correlations for R-h, (tau) over cap (w), and (m) over cap, which would be useful for engineers. (C) 2021 Elsevier Inc. All rights reserved.
NSTL
Elsevier
